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Cockfield, Tracey J. "Twin-roll casting of aluminium eutectic alloys." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270607.
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Musson, Nicholas John. "The squeeze casting of aluminium alloys and composites." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293609.
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Moffat, Andrew James. "Micromechanistic analysis of fatigue in aluminium silicon casting alloys." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/52400/.
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Due to increasingly stringent environmental legislation, there is a requirement for lower emissions and greater overall efficiency of light vehicle diesel (LVD) engines. This continues to be achieved through the optimisation of design and careful selection of the materials used in key LVD engine components, for example pistons, so that they are lighter and can operate at higher temperatures. Pistons are non-serviceable parts and so must be able to withstand the fatigue and high temperature environment of the car engine. It is therefore important to understand the mechanisms of fatigue in these alloys to help inform alloy development for the next generation of pistons. Pistons are typically produced from multi-component Al-Si casting alloys. These alloys exhibit a complex, multiphase microstructure comprising α-aluminium as the matrix with silicon particles and several intermetallic phases. Previous research on Al-Si casting alloys has demonstrated that porosity is detrimental to fatigue life as cracks initiate freely at pores. However, with improved casting techniques porosity can be greatly reduced and other microstructural features influence fatigue life. In particular, Si particles have been shown to play an important role in the initiation and subsequent propagation of fatigue cracks. This study assesses the role of Si content and other microstructural features on fatigue behaviour by testing a set of well-characterised multi-component, Al-Si casting alloys with varying Si content. Fatigue initiation behaviour was investigated at room temperature using S-N and short fatigue crack growth experiments. Pores, Si particles and intermetallic phases were shown to cause fatigue crack initiation. In a 0.67wt% Si containing alloy, large-scale porosity was observed and was the foremost reason for fatigue initiation. In two alloys the Al9FeNi phase was observed to be the most detrimental hard particle causing fatigue crack initiation. Nanoindentation results showed that Al9FeNi had a lower hardness and higher modulus than Si and so Al9FeNi may be expected to fracture preferentially, consistent with the fatigue results. X-ray computed tomography demonstrated that all the alloys investigated contained a complex, interconnected, intermetallic sub-structure. As a result, the micromechanisms of fatigue are different to those in conventional particulate Al-Si alloys because particle fracture is required to ensure a level of crack continuity. At room temperature and 350˚C, and at low and high crack growth rates, the crack tip may be described as a diffuse region of micro-damage and intact ligaments. It is the extent of this damage in the alloys that controls the crack growth rates exhibited and simple trends between the Si content and roughness, reported for particulate systems, do not hold true in the alloys investigated in this study. The balance of the micromechanisms of fatigue was shown to be dependent on temperature. This highlights the importance of fatigue studies at temperatures that are characteristic of those experienced in service.
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Graziani, Alessandro. "Chemical composition modification of casting aluminium alloys for engine applications." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10018/.
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The research activities were focused on evaluating the effect of Mo addition to mechanical properties and microstructure of A354 aluminium casting alloy. Samples, with increasing amount of Mo, were produced and heat treated. After heat treatment and exposition to high temperatures samples underwent microstructural and chemical analyses, hardness and tensile tests. The collected data led to the optimization of both casting parameters, for obtaining a homogeneous Mo distribution in the alloy, and heat treatment parameters, allowing the formation of Mo based strengthening precipitates stable at high temperature.
Microstructural and chemical analyses highlighted how Mo addition in percentage superior to 0.1% wt. can modify the silicon eutectic morphology and hinder the formation of iron based β intermetallics. High temperature exposure curves, instead, showed that after long exposition hardness is slightly influenced by heat treatment while the effect of Mo addition superior to 0,3% is negligible. Tensile tests confirmed that the addition of 0.3%wt Mo induces an increase of about 10% of ultimate tensile strength after high temperature exposition (250°C for 100h) while heat
treatments have slight influence on mechanical behaviour.
These results could be exploited for developing innovative heat treatment sequence able to reduce residual stresses in castings produced with A354 modified with Mo.
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Gelder, Andrew. "Lithium-aluminium casting alloys and their associated metal-mould reactions." Thesis, Aston University, 1992. http://publications.aston.ac.uk/9775/.
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Aluminium - lithium alloys are specialist alloys used exclusively by the aerospace industry. They have properties that are favourable to the production of modern military aircraft. The addition of approximately 2.5 percent lithium to aluminium increases the strength characteristics of the new alloys by 10 percent. The same addition has the added advantage of decreasing the density of the resulting alloy by a similar percentage. The disadvantages associated with this alloy are primarily price and castability. The addition of 2.5 weight percent lithium to aluminium results in a price increase of 100% explaining the aerospace exclusivity. The processability of the alloys is restricted to ingot casting and wrought treatment but for complex components precision casting is required. Casting the alloys into sand and investment moulds creates a metal - mould reaction, the consequences of which are intolerable in the production of military hardware. The primary object of this project was to investigate and characterise the reactions occurring between the newly poured metal and surface of the mould and to propose a method of counteracting the metal - mould reaction. The constituents of standard sand and investment moulds were pyrolised with lithium metal in order to simplify the complex in-mould reaction and the products were studied by the solid state techniques of powder X-Ray diffraction and magic angle spinning nuclear magnetic resonance spectroscopy. The results of this study showed that the order of reaction was: Organic reagents> > Silicate reagents> Non silicate reagents Alphaset and Betaset were the two organic binders used to prepare the sand moulds throughout this project. Studies were carried out to characterise these resins in order to determine the factors involved in their reaction with lithium. Analysis revealed that during the curing process the phenolic hydroxide groups are not reacted out and that a redox reaction takes place between these hydroxides and the lithium in the molten alloys. Casting experiments carried out to assess the protection afforded by various hydroxide protecting agents showed that modern effective, protecting chemicals such as bis-trimethyl silyl acetamide and hexamethyldisilazane did not inhibit the metal - mould reaction to a sufficiently high standard and that tri-methylchlorosilane was consistently the best performer. Tri-methyl chlorosilane has a simple functionalizing mechanism compared to other hydroxide protecting reagents and this factor is responsible for its superior inhibiting qualities. Comparative studies of 6Li and 7Li N.M.R. spectra (M.A.S. and `off angle') establish that, for solid state (and even solution) analytical purposes 6Li is the preferred nucleus. 6Li M.A.S.N.M.R. spectra were obtained for thermally treated laponite clay. At temperatures below 800oC both dehydrated and rehydrated samples were considered. The data are consistent with mobility of lithium ions from the trioctahedral clay sites at 600oC. The superior resolution achievable in 6Li M.A.S.N.M.R. is demonstrated in the analysis of a microwave prepared lithium exchanged clay where 6Li spectroscopy revelaed two lithium sites in comparison to 7Li M.A.S.N.M.R. which gave only a single lithium resonance.
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Ammar, Hany. "Effet des imperfections de la coulée sur les propriétés en fatigue des alliages de fonderie aluminium silicium = Effect of casting imperfections on the fatigue properties of aluminum-silicon casting alloys /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2006. http://theses.uqac.ca.
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Begg, John. "Process optimisation in the squeeze casting of zinc-aluminium alloys and composites." Thesis, Loughborough University, 1992. https://dspace.lboro.ac.uk/2134/27495.
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Squeeze casting is a process which has the potential to produce castings with exceptional mechanical properties. It also appears to be the most suitable route to produce sound cast metal matrix composites. An investigation was carried out into the squeeze casting of four zinc–aluminium alloys: commercial ZAS (simple eutectic alloy); commercial ZA12 (simple eutectic alloy); commercial ZA27 (peritectic alloy); binary Zn-37Al (solid solution alloy). Although the three commercial alloys can be cast by a variety of conventional gravity and pressure processes it was considered that squeeze casting would produce castings with more homogeneous microstructures and enhanced room temperature properties. The binary Zn-37Al was considered to be a suitable alloy for squeeze casting.
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Yakoub, M. M. "Squeeze casting of zinc-aluminium (ZA) alloys and ZA-27/SiC composites." Thesis, Loughborough University, 1987. https://dspace.lboro.ac.uk/2134/25378.
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Engineering applications of the recently developed zinc-aluminium casting alloys have been restricted due to certain inherent disadvantages such as segregation. However, segregation can be overcome by thorough mh:!ng of the melt and close temperature control or by rapid solidification of the melt, which can be achieved by squeeze casting. A more serious problem exists in service if components are subjected to a modest temperature increase to about 80°C, when there is a drastic loss of strength. It was therefore thought that the incorporation of ceramic fibres in the matrix could improve the properties of the material at modestly elevated temperatures. In the majority of engineering applications, stresses exist in more than one direction, so castings with isotropic properties are preferred and consequently reinforcement of composite in three dimensions would be necessary to maintain isotropic properties. An investigation was conducted to establish the influence of squeeze casting on the mechanical properties and structure of ZA-8, ZA-12 and ZA-27 alloys. The relationship between these factors and controlled process variables such as die temperature and applied squeeze pressure was established. The mechanical properties of the castings at room temperature and the effect of ageing at 95°C on tensile strength and dimensional changes were established. The results showed a substantial improvement in the tensile strength of the 'as-cast' squeeze cast alloys when compared with the 'as-cast' gravity die cast alloys. In the case of ZA-27 alloy, squeeze casting significantly improved ductility, which is a feature of benefit for all composite systems. The results also showed that pressure and die temperature substantially affect dimensional changes of the alloys when aged at 95°C. A major aspect of the research was the evaluation of the mechanical properties of the fibre reinforced ZA-27 alloy at elevated temperatures. Short silicon carbide fibres were randomly oriented in the matrix to obtain isotropic properties by a technique involving squeeze infiltration, followed by remelting and dispersal in the melt using specially designed equipments. Squeeze casting was used in the final stage of the composite fabrication. Castings of squeeze cast composite (with up to 10% volume fibre) and squeeze infiltrated composite (with up to 18-20% volume fibre) were produced with a sound structure and with fibres that were uniformly distributed and randomly oriented in three dimensions. It was found that the reaction between the fibres and molten alloy must be closely controlled for optimum properties of the composite. In this respect, the optimum time of contact between the fibre and the molten alloy was experimentally determined. It was found that the fibre supplied was of inferior tensile strength, which resulted in poor tensile strength of the tested composite up to a temperature of 100°C. However, the fibre brought substantial Improvement ln the tensile strength of the composite when tested at temperatures of 150 to 250°C. The modulus of elasticity of the composite was substantially improved at room temperature as well as at elevated temperature. The fatigue life of the squeeze cast composite was improved compared with squeeze cast matrix alloy (fibre-free). Squeeze cast composites with 3% volume fibre showed an Improvement in tribological properties compared with squeeze cast matrix alloy and squeeze cast and squeeze infiltrated composites with higher volume percentage of fibre. Wear of cutting tools was adversely affected by the presence of fibre.
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Fiorese, Elena. "Process parameters affecting quality of high-pressure die cast aluminium alloys." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3426773.
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High pressure die casting (HPDC) is a widely used process for manufacturing components with high production rate and complex geometries. However, high pressure die casting is still considered a “defect generating process”, since an amount of 5-10% of scrap is usually detected in castings. For this reason, the availability of new standards and tools for optimizing the process is one of the prominent needs of foundry field.
Both these issues are tackled in this Thesis. First, a new classification of defects and reference dies for estimating the static mechanical properties of aluminium alloys have been developed and then published as CEN Technical Reports, satisfying the need for new standards. Then, a novel and comprehensive methodology has been developed for optimizing HPDC process through the definition of meaningful behavioural models. Some newly defined process parameters have been hence introduced, by representing the most important physical phenomena affecting casting quality and the integral nature of HPDC, and an original approach is outlined. In particular, in order to provide an effective representation of the different process stages, the following parameters have been found to be more influential and effective in representing transmitted forces, mechanical energy exchange and heat removal: the root mean square acceleration in the second stage, the energy associated to the flow forces in the whole cycle, the work of the pressure forces in the third stage and the normalized thermal gradient. The first two parameters embody the plunger motion time-history, the third parameter represents the hydraulic pressure time-history, while the last one concentrates on some thermal aspects. These parameters take advantage from signal processing techniques of the measured position and pressure profiles. Four experimental campaigns (in the whole 210 castings) using different injection machines, different alloys and different geometries of the die have been carried out to validate the novel process parameters and to prove the general validity of the approach.
The statistical correlation with the measured static mechanical properties, density and percentage of porosity, as well as the metallographic analysis (percentage of oxides on fracture surfaces, analysis of different kinds of internal defect) prove the soundness of the developed method.
Given the significance of the plunger motion profile in explaining the casting quality, analytical models for computing the root mean square acceleration and the energy associated to the flow forces have been developed. These analytical models permit selecting in advance the best plunger motion profile, which guarantees reliability and soundness of castings, thus satisfying the need expressed by foundries for effective optimization tools.La pressocolata è un processo ampiamente utilizzato per produrre componenti con elevata produttività e geometria complessa. Comunque, la pressocolata è ancora considerata un “processo generatore di difetti”, dal momento che una percentuale del 5-10% di scarto è rilevata di solito nei getti. Per questa ragione, la disponibilità di nuovi standard e strumenti per l’ottimizzazione di processo è uno dei bisogni più importanti del settore della fonderia. Entrambe queste criticità sono affrontate in questa Tesi. Per prima cosa, è stata sviluppata e successivamente pubblicata come Report Tecnici riconosciuti dal CEN una nuova classificazione dei difetti e degli stampi di riferimento per stimare le proprietà meccaniche statiche delle leghe di alluminio, rispondendo al bisogno di nuovi standard. Poi, è stata sviluppata una metodologia nuova e completa per ottimizzare il processo di pressocolata attraverso la definizione di metamodelli significativi. Quindi, sono stati introdotti dei nuovi parametri di processo, che rappresentano i più importanti fenomeni fisici che influenzano la qualità dei getti e la natura integrale del processo di pressocolata, ed è stato delineato un approccio originale. In particolare, allo scopo di fornire una rappresentazione efficace delle diverse fasi del processo, si è dimostrato che i seguenti parametri sono i più influenti ed efficaci nel rappresentare le forze trasmesse, il flusso di energia meccanica e l’asportazione del calore: il valore quadratico medio dell’accelerazione in seconda fase, l’energia associata alle forze di flusso nell’intero ciclo, il lavoro delle forze di pressione nella terza fase e il gradiente termico normalizzato. I primi due parametri descrivono l’effetto del profilo di moto del pistone; il secondo è invece legato anche alla pressione esercitata dal pistone stesso, mentre l’ultimo rappresenta esclusivamente fenomeni di natura termica. Lo sviluppo ed il calcolo di questi parametri sfrutta le tecniche di elaborazione numerica dei segnali, al fine di estrarre le informazioni dai profili misurati di posizione e di pressione del pistone. La validazione del metodo proposto è stata condotta attraverso quattro diverse campagne sperimentali, con un totale di 210 getti analizzati, nelle quali sono state utilizzate diverse macchine di iniezione, diversi stampi e diverse leghe, al fine di ottenere risultati generali ed estendibili. La correttezza del metodo proposto è confermata dalla correlazione statistica dei parametri proposti con la resistenza meccanica statica, con la densità, la porosità, e da alcune significative analisi metallografiche (percentuale di ossidi sulle superfici di frattura, analisi dei difetti interni). Data l’efficacia dimostrata dei parametri proposti, ed in particolare di quelli legati al profilo di moto del pistone, l’approccio è stato esteso tramite lo sviluppo di alcune relazioni analitiche per calcolare i due parametri cinematici. Ciò rappresenta uno strumento efficace per sintetizzare a priori il profilo di moto ottimale del pistone che, nel rispetto dei vincoli di macchina, consenta di ottimizzare la qualità dei getti.
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Yang, Xinliang. "Particle dispersion in aluminium and magnesium alloys." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/14437.
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High shear mixing offers a promising solution for particle dispersion in a liquid with intensive turbulence and high shear rate, and has been widely used in the chemical, food and pharmaceutical industries. However, a practical high shear mixing process has not yet been adapted to solve the particle agglomeration in metallurgy due to the high service temperature and reactive environment of liquid metal. In this study, the effect of high shear mixing using the newly designed rotor-stator high shear device have been investigated with both Al and Mg matrix composites reinforced with SiC particles through casting. The microstructural observation of high shear treated Al and Mg composites show improved particle distribution uniformity in the as-cast state. Increased mechanical properties and reduced volume fraction of porosity are also obtained in the composite samples processed with high shear. With the melt conditioning procedure developed for twin roll casting process, two distinct solutions has been provided for thin gauge Mg strip casting with advanced microstructure and defect control. The melt conditioning treatment activates the MgO as heterogeneous nuclei of α-Mg through dispersion from continuous films to discrete particles. Thus enhanced heterogeneous nucleation in the twin roll casting process not only refines the α-Mg grain size but also eliminates the centre line segregation through equiaxed grain growth and localized solute distribution. The grain refinement of the α-Mg through SiC addition has also been studied through EBSD and crystallographic approaches. Two reproducible and distinct crystallographic orientation relationships between α-SiC (6H) and α-Mg have been determined: [1010]SiC//[2113]Mg, (0006)SiC//(1011)Mg, (1216)SiC//(2202)Mg and [0110]SiC//[1100]Mg, (0006)SiC// (0002)Mg, (2110)SiC//(1120)Mg.
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Payandeh, Mostafa. "Rheocasting of Aluminium Alloys : Slurry Formation, Microstructure, and Properties." Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Material och tillverkning – Gjutning, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-26297.
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Innovative materials with novel properties are in great demand for use in the criticalcomponents of emerging technologies, which promise to be more cost-effective and energyefficient.A controversial issue with regard to manufacturing complex industrial products isto develop advanced materials with optimised manufacturability in addition to the requiredmechanical and physical properties. The objective of this research study was to develop andoffer new solutions in material-processing-related issues in the field of mechanical andelectrical engineering. This was achieved by investigating the new opportunities affordedby a recently developed rheocasting method, RheoMetalTM process, with the goal of comingto an understanding of the critical factors for effective manufacturing process. A study of the evolution of microstructure at different stages of the rheocasting process,demonstrated the influence of multistage solidification on the microstructural characteristicsof the rheocast components. The microstructural investigation onquench slurry showed itconsists of the solute-lean coarse globular α-Al particles with uniform distribution ofalloying elements, suspended in the solute-rich liquid matrix. Such inhomogeneous slurryin the sleeve seems to play a critical role in the inhomogeneity of final microstructure. Inthe rheocast component, the separation of the liquid and solid parts of slurry during fillinginfluenced on the microstructural inhomogeneity. The relationship between the microstructural characteristics and properties of the rheocastcomponents was investigated. The study on the fracture surfaces of the tensile-testedspecimens showed that the mechanical properties strongly affected by microstructuralinhomogeneity, in particular macrosegregation in the form of near surface liquid segregationbands and subsurface porosity. The thermal conductivity measurement showed variation ofthis property throughout the rheocast component due to variations in the ratio of solute-leanglobular α-Al particles and fine solute α-Al particles. The result showed silicon in solidsolution have a strong influence (negative) on thermal conductivity and precipitation ofsilicon by heat treatment process increase the thermal conductivity.RheoCom
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Zhou, Yipeng. "Solidification behaviour of Fe-rich intermetallic compounds in aluminium alloys." Thesis, Brunel University, 2018. http://bura.brunel.ac.uk/handle/2438/15965.
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The industrial use of recycled aluminium is greatly limited by the degraded mechanical properties due to the increased impurities. Fe, one of the common impurity content in Al alloys, is difficult to eliminate once introduced into aluminium during primary production or recycling processes. Due to the low solid solubility of Fe in Al, the formation of Fe-rich intermetallic compounds (Fe-IMCs) is inevitable, which is one of the main causes for the deterioration of mechanical properties in various cast Al alloys. In order to obtain desirable mechanical properties of recycled Al alloys, modification and refinement of the Fe-IMCs are urgently required as the compact and refined morphologies of such intermetallics are generally non detrimental to Al alloy's performance. However, manipulating the solidification behaviour of the Fe-IMCs phases, including nucleation and growth, is very challenging because of the inherently more difficult heterogeneous nucleation of the Fe-IMCs compared with that of a pure metal or a solid solution; and the strong growth anisotropy. Limited understanding on mechanisms of nucleation and growth of the multicomponent Fe-IMCs is available in the literature. The aim of this study is to gain a deeper understanding on the heterogeneous nucleation and growth behaviour of Fe-IMCs in various Al alloys. The nucleation and growth of both primary and eutectic Fe-IMCs have been investigated during various solidification conditions including a number of different cooling rates and casting temperatures. Based on the experimental results of the solidification of several ternary and quaternary alloys, effect of Mg on the solidification behaviour of Fe-IMCs was investigated. Further the surface modified TiB2 particles were used to enhance the heterogeneous nucleation of Fe-IMCs in order to refine the Fe-IMCs particles. The dominant Fe-IMC in Al-5Mg-2Si-1.2Fe-0.7Mn alloy is identified, using transmission electron microscopy (TEM), as α-AlFeMnSi with a body centred cubic (BCC) lattice structure and lattice parameter of 1.256nm. In the current alloy system, the nucleation of primary α-AlFeMnSi occur at lower cooling rate (≤0.8K/s) when required nucleation undercooling is reached, as the slower cooling rate allows longer diffusion time for the solute to form a stable nucleation embryo. When casting with 20K superheat, the size of primary α-AlFeMnSi increases gradually from 24.5±3.1μm (870K/s) to 251.3±75.3μm (0.02K/s) and the size of α-AlFeMnSi eutectic increased gradually from 102.0μm (870K/s) to 623.3μm (0.02K/s). The Fe and Mn concentration in α-AlFeMnSi appears to reduce with the increased cooling rate due to the relatively insufficient solute supply when solute concentration is low (1.2wt.% Fe and 0.7wt.% Mn). Microstructure observation reveals that the {011} plane, especially on <111> orientation, is the preferred growth orientation of BCC primary α-AlFeMnSi, resulting in rhombic dodecahedral in 3D. The eutectic α-AlFeMnSi, prefers to initiate on the primary α-AlFeMnSi. In addition to the substantial nucleation undercooling, the research revealed that the nucleation of primary α-AlFeMnSi also rely on the local solute concentration and the solute diffusion. Compared with α-Al, the growth of α-AlFeMnSi is less sensitive to the cooling rate changes due to the complexities in multi-components interaction and different diffusion efficiency of different elements. The addition of Mg to Al-1.2Fe-0.7Mn and Al-2Si-1.2Fe-0.7Mn alloys was found to lead to a morphology change of Fe-IMCs. Al6(Fe,Mn), the predominant Fe-IMC in the Al-1.2Fe-0.7Mn-xMg alloy, changed from needle morphology to interconnected lamellar morphology when Mg composition increased from 0.004wt.% to 6.04wt%. A Mg-rich layer at about 5-20nm in thickness was commonly observed on the Fe-IMC/α-Al interface in the alloys with Mg content. The eutectic lamellar spacing for Al6(Fe,Mn) increases from 1.8±0.3μm to 4.5±0.8μm when Mg content increased from 0.004wt.% to 6.04wt.%. In the case of α-Al12(Fe,Mn)3Si, the predominant Fe-IMC in Al-2Si-1.2Fe-0.7Mn-yMg alloys, its lamellar spacing of the eutectic increased from 1.4±0.3μm to 3.25±0.8μm when Mg increased from 0.04wt.% to 5.41wt.%. Owing to the strong anisotropy of the Fe-IMC crystals, the segregation of solute Mg on preferred growth orientation is higher, causing greater growth restriction on this orientation. Consequently, the growth velocity on other orientations becomes relatively more significant. To optimise the morphology of Fe-IMCs in Al alloys, a novel Αl-Ti-B(Fe) grain refiner for Fe-IMCs has been developed to enhance the heterogeneous nucleation of Fe-IMCs. The addition of the novel grain refiner to an Al-5Mg-2Si-1.2Fe-0.7Mn alloy under controlled solidification condition results in a considerable refinement of the primary Fe-IMCs from 251.3±75.3μm to 110.9±45.5μm and from 127.3±36.2μm to 76.5±18.2μm at cooling rates of 0.02K/s and 0.15K/s, respectively. TEM investigations on the refiner reveal a Fe-rich adsorption monolayer in a zigzag fashion on the prismatic planes on the boride particles. This surface modification is beneficial for the heterogeneous nucleation of the Fe-IMCs. Further investigation of the Al alloy with this grain refiner addition revealed that there existed specific orientation relationships (ORs) between TiB2 and Fe-IMCs: (001)[020]Al13Fe4 // (11-20)[10-10]TiB2, and (001)[120]Al13Fe4 ∠6.05˚ (11-20)[10-11]TiB2; (0-11)[100]α-AlFeMnSi // (0001)[-2110]TiB2, and (0-11)[111]α-AlFeMnSi ∠4.5˚ (0001)[10-10]TiB2. The Fe adsorption on substrate particle, the observed ORs between TiB2 and Fe-IMCs, and the refinement of primary α-AlFeMnSi with the addition of modified TiB2 provide evidence of structure templating and composition templating required by heterogeneous nucleation of Fe-IMCs. This research has delivered contribution to the understanding and new approach for optimizing the morphology of Fe-IMCs in the Fe-containing Al alloys. Using the slow cooling rates (≤0.15K/s), the formation compact primary α-AlFeMnSi can be considerably encouraged. With a lower casting temperature, the size and volume fraction of large Chinese-script α-AlFeMnSi can be significantly reduced. With addition of reasonable Mg content the morphology of Fe-IMC can be modified. Particularly, with the addition of the Al-Ti-B(Fe) grain refiner in well-controlled condition, the primary α-AlFeMnSi can be significantly refined. Thus, by implementing these approaches, the optimized Fe-IMC morphology in the microstructure of Fe-containing Al alloy is able to offer promising mechanical performance.
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Kotadia, Hirenkumar R. "Solidification behaviour of Al-Sn-Cu immiscible alloys and Al-Si cast alloys processed under intensive shearing." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/4517.
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Alloy castings are usually solidified with a coarse columnar grain structure under normal casting conditions unless the mode of the solidification is carefully controlled. It is desirable for the grain structure to be fine and equiaxed to improve their mechanical performance as finished castings. It is possible to develop a fine and equiaxed grain structure either by increasing the number of nucleation sites or by grain multiplication. Immiscible alloys with a microstructure in which a soft phase is dispersed homogeneously in a hard matrix have significant potential applications in advanced bearing systems, especially for the automotive industry. Despite considerable efforts made worldwide, including extensive space experiments, no casting techniques so far can produce the desired immiscible microstructure of alloys. Experimental results on Al-Sn-Cu immiscible alloys have confirmed that intensive shearing using melt conditioning by an advanced shearing technology (MCAST) unit, is an effective way to achieve a fine and uniform dispersion of the soft phase without macro-demixing, and that such a dispersed microstructure can be further refined in alloys with precipitation of the primary Al phase prior to the demixing reaction. In addition, it was found that melt shearing at 200 rpm for 60 s will be adequate to produce a fine and uniform dispersion of the Sn phase, and that a higher shearing speed and prolonged shearing time can only achieve further minor refinement. A study of Al-Si hypoeutectic and hypereutectic alloys presents the effects of the processing temperature and intensive shearing on the microstructural and mechanical properties which have been investigated systematically. Attempts have been made to explain the solidification mechanism with intensive melt shearing. The sheared melt was cast into tensile test samples by high pressure die caster (HPDC) to examine the microstructures and mechanical properties. The experimental results reveal that significant grain refinement and uniformity of grains was achieved by the intensive shearing and also a considerable increase in mechanical properties with pouring temperature by changing intermetallic particles morphology, the position of defect band and reduced microscopic defects.
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Drezet, Jean-Marie. "Direct chill and electromagnetic casting of aluminium alloys: thermomechanical effects and solidification aspects." Lausanne, 2000. http://library.epfl.ch/theses/?display=detail&nr=1509.
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Sjölander, Emma. "Heat treatment of Al-Si-Cu-Mg casting alloys." Doctoral thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Material och tillverkning – Gjutning, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-15695.
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Environmental savings can be made by increasing the use of aluminium alloys in the automotive industry as the vehicles can be made lighter. Increasing the knowledge about the heat treatment process is one task in the direction towards this goal. The aim of this work is to investigate and model the heat treatment process for Al-Si casting alloys. Three alloys containing Mg and/or Cu were cast using the gradient solidification technique to achieve three different coarsenesses of the microstructure and a low amount of defects. Solution treatment was studied by measuring the concentration of Mg, Cu and Si in the α-Al matrix using wavelength dispersive spectroscopy (WDS) after various times at a solution treatment temperature. A diffusion based model was developed which estimates the time needed to obtain a high and homogenous concentration of alloying elements for different alloys, temperatures and coarsenesses of the microstructure. It was shown that the yield strength after artificial ageing is weakly dependent on the coarseness of the microstructure when the solution treatment time is adjusted to achieve complete dissolution and homogenisation. The shape and position of ageing curves (yield strength versus ageing time) was investigated empirically in this work and by studying the literature in order to differentiate the mechanisms involved. A diffusion based model for prediction of the yield strength after different ageing times was developed for Al-Si-Mg alloys. The model was validated using data available in the literature. For Al-Si-Cu-Mg alloys further studies regarding the mechanisms involved need to be performed. Changes in the microstructure during a heat treatment process influence the plastic deformation behaviour. The Hollomon equation describes the plastic deformation of alloys containing shearable precipitates well, while the Ludwigson equation is needed when a supersaturated solid solution is present. When non-coherent precipitates are present, none of the equations describe the plastic deformation well. The evolution of the storage rate and recovery rate of dislocations was studied and coupled to the evolution of the microstructure using the Kocks-Mecking strain hardening theory.
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Siavashi, Kiavash. "The effect of casting parameters on the fluidity and porosity of aluminium alloys in the aost foam casting process." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3525/.
Full textAbstract:
The Lost Foam Casting process has been firmly established for Aluminium and ferrous alloys. This process offers many advantages over conventional casting processes but its full potential has yet to be reached due to the many defects introduced to the casting associated with decomposition of the foam pattern during mould filling. The foam pattern commonly used in this process is Expanded Polystyrene (EPS) which degrades to liquid and vapour byproducts. The liquid decomposition byproducts travel to the metal/mould interface, where the globules of liquid foam can become trapped against the coating and their molecular weight is reduced due to the heat from the molten metal. At the same time, they release bubbles of gas into the castings. These globules can wick into the refractory coating only if their molecular weight is sufficiently reduced to below a critical molecular weight. In this study, to improve the quality of Aluminium alloys made by Lost Foam Casting, easier removal of the decomposition byproducts was obtained by using low molecular weight foam patterns. The molecular weight of expanded Polystyrene was not reduced when it was exposed to γ-rays because of cross-linking while the molecular weight of Poly Methyl Methacrylate (PMMA) was significantly due to chain session. Therefore, plates of Probead-70™ (a copolymer of Polystyrene 30 wt %-Poly Methyl Methacrylate 70 wt %) were exposed to γ-rays and reduced their molecular weight by up to about 85% below the critical molecular weight value. With low molecular weight foam patterns the decomposition byproducts require less reduction to reach the critical molecular weight to become absorbed by the coating, and consequently less defects are introduced into the casting. γ-radiation was employed to reduce the molecular weight of the foam. The porosity content of the castings was significantly reduced leading to an improvement of their mechanical properties such as their fatigue life which was increased by 100%. Lost Foam Casting has also been reported to experience complexities with fluidity. Misrun is likely to occur in Lost Foam Casting due to the formation of a large amount of gas at the metal/foam interface, increasing the back pressure, compared to the conventional castings. This reduces the velocity of the molten metal which might lead to solidification of the molten metal before filling the mould entirely. In the current work, a reproducible fluidity test was designed and the effects of different casting parameters on fluidity were examined. In some of the castings inserted thermocouples were employed to study the filling behaviour to determine the velocity of molten metal, thickness of the metal/foam interface and the time of freezing. It was concluded that it is not recommended to alter the coating thickness in order to improve fluidity, because the effect of coating thickness depends on the pouring temperature of the castings and permeability of the coating. The metallostatic pressure was found to affect the fluidity insignificantly (within the values in the current work, 2600-2700 Pa). Instead, increasing coating permeability, decreasing the density of the foam pattern and increasing the pouring temperature were found to increase the fluidity in Lost Foam Casting. However the effect of increasing pouring temperature and decreasing foam density may be detrimental to the quality of castings. The molecular weight of the foam pattern and the use of brominated foam patterns did not have a considerable effect on fluidity in Lost Foam Casting. It was also found that solidification in the Lost Foam Casting occurs at the metal/foam interface. A heat balance between the molten metal and the mould, and the foam pattern, was developed to give a fluidity equation to aid interpretation of the fluidity results. In summary, this research has provided a better understanding of the effect of casting parameters on the fluidity of Lost Foam Casting and the heat transfer from the molten metal to the foam pattern and to the mould. In addition, the quality of AL alloys castings was improved by reducing the molecular weight of the foam pattern used in the Lost Foam Casting process.
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Laukli, Hans Ivar. "High Pressure Die Casting of Aluminium and Magnesium Alloys : Grain Structure and Segregation Characteristics." Doctoral thesis, Norwegian University of Science and Technology, Department of Materials Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-379.
Full textAbstract:
Cold chamber high pressure die casting, (HPDC), is an important commercial process for the production of complex near net shape aluminium and magnesium alloy castings. The work presented in the thesis was aimed at investigating the microstructure formation in this type of casting. The solidification characteristics related to the process and the alloys control the formation of grains and defects. This again has a significant impact on the mechanical properties of the castings.
The investigations were carried out mainly using the AM60 magnesium alloy and the A356 aluminium alloy. Two different casting arrangements were used: the cold chamber HPDC and the gravity die casting methods, which allowed for different flow and solidification conditions. The microstructures in the castings were investigated using optical microscopy, image analysis, scanning electron microscopy, electron back scatter diffraction measurements and electron probe microanalysis.
In the HPDC experiments, the shot sleeve solidification conditions were investigated primarily by changing the melt superheat on pouring. This significantly affected the microstructures in the castings. The fraction of externally solidified crystals (ESCs) was consistently found to be largest near the gate in both the AM60 and the A356 die castings. This was attributed to the inherent shot sleeve solidification conditions and the flow set up by the plunger movement. When the superheat was increased, a lower fraction of ESCs was found in the castings. Furthermore, a high superheat gave ESCs with branched dendritic/elongated trunk morphology whilst a low superheat generated coarser and more globular ESCs, both in the AM60 and the A356 castings. The ESCs typically segregated towards the central region of the cross sections at further distances from the gate in the die castings.
When a thin layer of thermal insulating coating was applied on the shot sleeve wall in the production of AM60 die castings, it nearly removed all ESCs in the castings. Using an A356 alloy, (and no shot sleeve coating), with no Ti in solution gave a significantly lower fraction of ESCs, whereas AlTi5B1 grain refiner additions induced an increase in the fraction of ESCs and a significantly finer grain size in the castings. The formation of globular ESCs was enhanced when AlTi5B1 grain refiner was added to the A356 alloy.
In controlled laboratory gravity die casting experiments, typical HPDC microstructures were created by pouring semi-solid metal into a steel die: The ESCs were found to segregate/migrate to the central region during flow, until a maximum packing, (fraction of ESCs of ~35-40%), was reached. The extent of segregation is determined by the fraction of ESCs, and the die temperature affects the position of the ESCs. The segregation of ESCs was explained to occur during flow as a result of lift forces.
The formation of banded defects has also been studied: the position of the bands was affected by the die temperature and the fraction of ESCs. Based on the nature of the bands and their occurrence, a new theory on the formation of defect bands was proposed: During flow the solid distribution from the die wall consists of three regions: 1) a solid fraction gradient at the wall; 2) a low solid fraction region which carries (3) a network of ESCs. A critical fraction solid exists where the deformation rate exceeds the interdendritic flow rate. When the induced stress exceeds the network strength, deformation can occur by slip, followed by liquid flow. The liquid flow is caused by solidification shrinkage, hydrostatic pressure on the interior ESC network, and gaps forming which draw in liquid.
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Smillie, Matthew John. "Casting and Analysis of Squeeze Cast Aluminium Silicon Eutectic Alloy." Thesis, University of Canterbury. Mechanical Engineering, 2006. http://hdl.handle.net/10092/1086.
Full textAbstract:
Squeeze casting is the practise of solidifying metals under mechanically applied pressure via a slow displacement of a die volume. It has been shown that squeeze casting enhances the mechanical properties of cast metals. Research into other high integrity casting processes has shown that using techniques that enhance melt quality can further increase the mechanical properties. Therefore a bottom-tapped, bottom-fed squeeze casting machine was designed and built around a pre-existing squeeze casting die designed for uniaxial pressure application. This was used to obtain quantitative metallurgical and microstructural information on the squeeze castings produced, including the effects of common micro-alloying additions of strontium modifier and titanium modifier on the microstructure and hardness of a commercial aluminium silicon eutectic alloy. These were examined using a Taguchi design of experiments approach. It was found that squeeze casting reduced porosity and secondary dendrite arm spacing and increased hardness, and reduced or eliminated increases in porosity and secondary dendrite arm spacing associated with micro-alloying addition. The size of possibly deleterious iron-rich precipitates was reduced, and the morphology of such precipitates changed to a possibly less deleterious form without further alloy additions of manganese. It was also found that melt control and handling is essential for consistent quality of castings in the production of small volume squeeze castings, such as the ones produced in this experimental work.
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Cisternas, Fernández Martín Matías. "Modeling of solidification of TiAl alloys in centrifugal casting." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0218.
Full textAbstract:
Les alliages TiAl sont un groupe de matériaux important pour les industries automobile et aérospatiale, de par leur faible densité et bonne tenue mécanique à haute température. Cependant, à cause de leur forte réactivité à l’état liquide, au moment de couler ces alliages, il faut utiliser une faible surchauffe pour limiter la contamination. La coulée centrifuge est une option pour améliorer le remplissage du moule à faible surchauffe. En coulée centrifuge, l’effet de la poussée d’Archimède sur le mouvement du liquide est renforcé, ce qui modifie l’écoulement par l’effet combiné de la force centrifuge et de force de Coriolis qui apparaissent dans le système en rotation. Ceci fait que des motifs particuliers de macroségrégation et de distribution de microstructures se forment dans la pièce solidifiée, et l’origine de ces motifs n’est pas très bien comprise. L’objectif de cette thèse est d’expliquer l’écoulement du liquide ainsi que le transport des grains solides et des espèces chimiques pendant la solidification d’alliages TiAl en coulée centrifuge. Un modèle 3D volume finis de solidification multi-échelle a d’abord été développé dans le cadre de cette thèse. Un tel modèle était nécessaire à cause de la nature tridimensionnelle des écoulements. Le modèle a ensuite été utilisé pour simuler des essais expérimentaux de solidification dirigée d’échantillons cylindriques en alliage TiAl GE (Ti-47Al-2Cr-2Nb), précédemment réalisés dans le cadre du projet ESA GRADECET. Ces essais ont été réalisés dans la “Large Diameter Centrifuge” de l’ESA, à des intensités de centrifugation entre 5g et 20g, où g est l’accélération standard de la gravité terrestre. Les résultats des simulations montrent que la force de Coriolis modifie complètement l’écoulement du liquide pendant la solidification, résultant en une unique boucle de convection dans le bain liquide. Inversement, la force de Coriolis n’a qu’un faible effet sur le mouvement des grains équiaxes. A forte centrifugation, le mouvement des grains est surtout gouverné par l’équilibre entre la gravité apparente et la force de trainée. Les résultats montrent aussi que la macroségrégation finale de l’aluminium n’est pas symétrique et présente un fort enrichissement le long du bord d’attaque de l’échantillon. Ceci est dû à l’asymétrie de l’écoulement induite par la force de CoriolisTiAl alloys are an important material for automotive and aerospace industries due to their low density and high strength at high temperatures. However, due to their high reactivity in liquid state, low superheat must be used in casting in order to limit contamination. Centrifugal casting is an option to enhance mold filling at low superheat. In centrifugal casting the buoyancy driven flow is intensified and the flow structure is modified by the combined effect of the non-inertial accelerations – centrifugal and Coriolis – which appear in the rotating system. The consequence are particular patterns of macrosegregation and of distribution of microstructures in the solidified part. These patterns are not well understood. The objective of this thesis is to explain the flow structure, as well as the transport of solid grains and of chemical species during solidification of TiAl alloys in centrifuged systems. In the framework of this thesis a 3D finite-volume implementation of a multiscale solidification model was developed, which was required due to the inherently three-dimensional nature of the flow. The model was then used to simulate dedicated experiments of directional solidification of cylindrical samples of the TiAl GE alloy (Ti-47Al-2Cr-2Nb) that were previously conducted in the frame of the ESA GRADECET project. These experiments were carried out in the ESA “Large Diameter Centrifuge” at centrifugation levels between 5g and 20g, where g is the normal terrestrial gravity acceleration. The results of the simulations show that the Coriolis acceleration entirely modifies the liquid flow structure during solidification and lead to a one-vortex fluid flow pattern in the domain. On the contrary, it is shown that the Coriolis acceleration has only a weak impact on the motion of equiaxed grains. At high gravity level the grain motion is mainly controlled by the balance between the apparent gravity and the drag force. It is also shown that the final aluminum macrosegregation pattern show a strong enrichment on the flight velocity side of the sample due to the asymmetry of the liquid flow induced by the Coriolis force
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Watson, Douglas. "Microstructure and mechanical properties of ductile die-cast Al-Mg-Si-Mn alloys." Thesis, Brunel University, 2015. http://bura.brunel.ac.uk/handle/2438/12874.
Full textAbstract:
Aluminium alloys have been seen a dramatic increase in transport manufacturing in past two decades. This is primarily driven by the achievement of effective weight-savings, increased vehicle fuel efficiency and reduced CO2 emissions in transport. One of the significant progresses in most recent years has been in the application of aluminium-intensive car body structure, in which the manufacturing of thin wall castings with improved ductility is one of the critical issues. High pressure die casting (HPDC) is a fast and economical near-net shape manufacturing method to produce thin wall components. Therefore the application of HPDC process to make thin wall structural components for aluminium-intensive car body structure is one of the most challenges in recent development. However, the currently available die cast aluminium alloys are unable to fulfil this requirement because of the insufficient ductility, which is essential for joining castings with sheets and extruded parts. This has become critical in further development and extensive acceptance in car manufacturing industry. Generally, the mechanical properties of die castings are determined by alloy composition, defect levels and microstructure in the castings. In the present study, the significant achievement is the development of Al-Mg-Si-Mn alloy for HPDC process to provide improved ductility in die castings in order to satisfy the requirement of mechanical properties, in particular ductility for the application in automotive body structure. Starting from the thermodynamic analysis and CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) modelling of Al-Mg-Si system for solidification and phase formation, the alloy composition was optimised using international standard tensile samples to review the effect of various alloying elements on the mechanical properties. Another achievement is the understanding of the solidification and microstructural evolution, the relationship between the microstructure and mechanical properties, and the strengthening mechanisms in the developed alloy. The solidification behaviour in the shot sleeve and in the die cavity was examined for the formation of the primary α-Al phase, eutectic Al-Mg2Si phases in the alloy. The morphology, size and size distribution of the primary α-Al phase were characterised under different solidification conditions. The growth morphology of the primary α-Al phase formed in the shot sleeve and in the die cavity was analysed using the Mullins-Sekerka instability theory and the growth rate of eutectic Al-Mg2Si phases during solidification was calculated using Jackson-Hunt theory. Still another achievement is the study of the effect of Mn and Fe on the morphology, size and distribution of various Fe-rich compounds in the Al-Mg-Si alloy produced by HPDC process. The assessment was associated with the mechanical properties of yield strength, ultimate tensile strength and elongation with different Fe and Mn contents. CALPHAD modelling of multi-component Al-Mg-Si-Mn-Fe and Al-Mg-Si-Fe systems was studied to find out the effect of Fe impurity in the Al-Mg-Si alloy. The precise accumulation of iron during HPDC using fully recycled materials was examined to predict the maximum cycles to produce castings with required mechanical properties. The strengthening mechanism and the relationship between the microstructure and mechanical properties are explored in the alloy made by secondary materials. Furthermore, the effect of nickel on the microstructure and mechanical properties of the die-cast Al-Mg-Si-Mn alloy was also studied in association with the formation of Ni-rich intermetallics during solidification in the die-cast Al-Mg-Si-Mn alloy containing different Ni contents. The final achievement is the understanding of the repeatability of die castings made by the new alloy with industrial scale components. The tensile properties of standard samples that were obtained directly from HPDC process and made by the machined die castings at different locations were further assessed for the reproducibility of casting components made by the Al-Mg-Si-Mn alloy. The distributions of yield strength, ultimate tensile strength and elongation of the tensile samples were analysed by the average values with standard deviations and by the Weibull statistical model with three parameters. The correlations between the mechanical properties and the microstructural features, porosity levels and fracture morphology were investigated for the different types of samples. It was found that three-parameter Weibull analysis was capable of analysing the reproducibility of die cast components and the scattering of tensile properties was mainly due to the presence of porosity and non-uniform microstructure in the die-castings.
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Tu, Zhiqiang. "Fabrication and Mechanical Properties of Carbon Fiber Reinforced Aluminum Matrix Composites by Squeeze Casting." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40523.
Full textAbstract:
Rapid modern technological changes and improvements bring great motivations in advanced material designs and fabrications. In this context, metal matrix composites, as an emerging material category, have undergone great developments over the past 50 years. Their primary applications, such as automotive, aerospace and military industries, require materials with increasingly strict specifications, especially high stiffness, lightweight and superior strength. For these advanced applications, carbon fiber reinforced aluminum matrix composites have proven their enormous potential where outstanding machinability, engineering reliability and economy efficiency are vital priorities.
To contribute in the understanding and development of carbon fiber reinforced aluminum matrix composites, this study focuses on composite fabrication, mechanical testing and physical property modelling. The composites are fabricated by squeeze casting. Plain weave carbon fiber (AS4 Hexcel) is used as reinforcement, while aluminum alloy 6061 is used as matrix. The improvement of the squeeze casting fabrication process is focused on reducing leakage while combining thermal expansion pressure with post-processing pressing. Three different fiber volume fractions are investigated to achieve optimum mechanical properties. Piston-on-ring (POR) bend tests are used to measure the biaxial flexural stiffness and fracture strength on disc samples. The stress-strain curves and fracture surfaces reveal the effect of fiber-matrix interface bonding on composite bend behaviour. The composites achieved up to 11.6%, 248.3% and 90.1% increase in flexural modulus, strain hardening modulus and yield strength as compared with the unreinforced aluminum alloy control group, respectively. Analytical modelling and finite element modelling are used to comparatively characterise and verify the composite effective flexural modulus and strength. Specifically, they allowed
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evaluating how far the experimental results deviate from idealized assumptions of the models, which provides an insight into the composite sample quality, particularly at fiber-matrix interfaces. Overall, the models agree well with experimental results in identifying an improvement in flexural modulus up to a carbon fiber volume fraction of 4.81vol%. However, beyond a fiber content of 3.74vol%, there is risk of deterioration of mechanical properties, particularly the strength. This is because higher carbon fiber volume fractions restrict the infiltration and wetting of carbon fibre by the liquid, potentially leading to poor fiber-matrix interface bonding. It is shown that higher thermal expansion pressures and subsequent post-processing pressing can overcome this challenge at higher carbon fiber volume contents by reducing fiber-aluminum contact angle, improving infiltration, reducing defects such as porosity, and overall improving fiber-matrix bonding.
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Ferraro, Stefano. "Influence of trace elements on secondary die-cast aluminium alloys." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423822.
Full textAbstract:
Recycling play a key role on saving of natural resources and on reducing pollution. The recycling of aluminium alloys is also cost-effective, since it reduce the material cost and creates a considerable energy-saving. The use of recycled Al alloys (usually called secondary) has improved in recent years also because of their comparable mechanical properties with primary aluminium alloys.
During the production of secondary aluminium alloys, the scrap are mixed regardless of their specific chemical composition, and then master alloys or pure elements are added to the molten metal. Furthermore, certain impurity elements are either difficult or expensive to remove, and their role in mechanical properties can be important. Due to the presence of these additional trace elements, a number of complex intermetallic phases can therefore form in multi-component Al-Si alloys. Mechanical and physical properties of alloys and castings are strongly related to sizes, morphologies and distribution of these intermetallic phases, which are in turn a function of alloy composition and cooling rate.
The Al–Si based alloys are transversally used in different foundry processes. Among all the technologies, high-pressure die-casting (HPDC) represents the most common process to produce automotive components by secondary Al–Si alloys because it allows one to increase the production by lowering the cycle time and to obtain economically components with complex geometries and high quality surface.
The effects of trace elements and intermetallics phases on features of aluminium castings are still not fully understood, especially when components are made by means of HPDC process. The motivation of the research presented in this doctoral thesis was, therefore, to fill this gap in knowledge. The study has aimed at understanding the influence of various trace elements on the microstructure and mechanical properties of secondary die-cast aluminium alloys and, in particular, on secondary AlSi9Cu3(Fe) die-cast alloys.
A literature review and a sufficient background of previously reported results on the influence of trace elements on the features of aluminium alloys as well as the formation of intermetallic phases were carried out. It was found that the mechanical and microstructural analysis generally referred to primary cast Al alloys with low concentration of trace elements outside of those studied. Furthermore the samples were usually produced on gravity die-cast, while some intermetallics phases were frequently observed in high-pressure die-casting, where higher cooling rates and different feeding conditions exist.
Special attention has been given to:
The effects of Bismuth addition on secondary die-cast aluminium alloys: Bismuth substitute the lead in free-cutting wrought Al alloys, and this is leading to a steady increase of Bi content in secondary Al alloys due to the recycling process.
The nucleation temperature of primary Fe-rich intermetallic compounds, as function of Fe, Mn and Cr content and cooling rate: Fe-rich phases have a high specific gravity and tend to segregate to the bottom of aluminium melts and holding furnaces. These phases form primary solid particles, generally called sludge, thus reduce the effective capacity of the furnace.
The influence of Fe, Mn and Cr addition, separately or in combination, on the microstructural and mechanical characteristics of secondary die-cast aluminium alloys: sludge crystals are hard and brittle compact inclusions which can compromise the machining operations, with a considerable effects on the cutting tool life, and even more degrade the mechanical and physical properties of the component. As recycling of aluminium alloys becomes more common, sludge will be a problem of increasing importance due to the concentration of Fe, Mn and Cr in the scrap cycle.Il riciclaggio gioca un ruolo chiave sul risparmio delle risorse naturali e sulla riduzione dell'inquinamento. Il riciclo dell'alluminio è oltretutto economicamente conveniente, in quanto riduce il costo del materiale a fronte di un considerevole risparmio energetico. L'utilizzo di leghe di alluminio riciclate (comunemente chiamate leghe secondarie) è aumentato negli ultimi anni anche grazie alle loro proprietà meccaniche, le quali sono in alcuni casi comparabili con le leghe di alluminio primarie. Durante il processo di produzione dell'alluminio secondario i rottami vengono mescolati assieme indipendentemente dalla loro composizione chimica specifica. Al termine del processo fusorio la composizione viene regolata tramite l'aggiunta di leghe madri o di metalli puri. Tuttavia alcune impurezze presenti nel rottame rimangono all'interno della lega in quanto il loro processo di rimozione è complicato o non economicamente conveniente. A causa della presenza di questi elementi in traccia, un certo numero di fasi intermetalliche complesse si può formare nei getti. Di conseguenza le proprietà meccaniche e fisiche dei componenti in lega di alluminio sono fortemente correlate alla dimensione, alla morfologia e alla distribuzione di tali fasi intermetalliche, le quali sono a loro volta funzione della composizione della lega e della velocità di raffreddamento del metallo. Grazie alle loro elevata colabilità, le leghe Al-Si sono molto utilizzate in tutti i processi di fonderia. Tra le diverse tecnologie, la pressocolata (HPDC - high-pressure die-casting) rappresenta il processo più comune per la produzione di getti di alluminio nel settore automotive. Questa tecnologia permette di ottenere componenti con geometrie complesse e un'ottima finitura superficiale con una riduzione dei costi grazie alla elevata produttività e al basso tempo ciclo. Gli effetti degli elementi in traccia e delle fasi intermetalliche sulle proprietà dei getti in alluminio non sono ancora del tutto noti, soprattutto quando i componenti sono prodotti tramite pressocolata. Obiettivo di questo lavoro di dottorato di ricerca era perciò quello di supplire a queste lacune. Lo scopo del presente lavoro è studiare l'influenza di diversi elementi in traccia sulla microstruttura e sulle proprietà meccaniche di getti in lega secondaria di alluminio prodotti mediante pressocolata, ed in particolare nella lega AlSi9Cu3(Fe). In prima analisi, è stata condotta una recensione della letteratura sull'influenza degli elementi in traccia sulle proprietà delle leghe di alluminio e sulla formazione delle fasi intermetalliche. Questo ha permesso di constatare che le caratteristiche meccaniche e microstrutturali legate alla presenza di fasi indesiderate sono normalmente valutate in getti prodotti con leghe primarie di alluminio, in cui è presente una bassa concentrazione di impurezze al di fuori di quelle studiate. Inoltre i campioni studiati sono generalmente prodotti mediante colata in gravità, mentre alcune fasi intermetalliche sono tipiche della pressocolata, in cui la velocità di raffreddamento è molto più elevata e sono presenti diverse condizioni di alimentazione e di riempimento dello stampo. Nel presente lavoro è stata posta particolare attenzione a: Gli effetti dell'aggiunta di Bismuto nelle leghe di alluminio secondarie pressocolate: il Bismuto ha sostituito il Piombo nelle leghe di alluminio da deformazione plastica ad alta lavorabilità alle macchine utensile. Questo ha comportato un aumento del contenuto di Bismuto nelle leghe secondarie di alluminio a causa del processo di riciclaggio degli sfridi di lavorazione. La temperatura di nucleazione dei precipitati intermetallici ricchi in Ferro in funzione della velocità di raffreddamento e della concentrazione in lega di Ferro, Cromo e Manganese: le fasi ricche in ferro hanno un elevata densità e tendono a segregare sul fondo del fondo del forno di mantenimento. L'insieme di queste fasi primarie forma una fanghiglia, chiamata sludge, che riduce l'effettiva capacità del forno. L'effetto dell'aggiunta di Ferro, Cromo e Manganese, singolarmente o in combinazione tra di loro, sulle caratteristiche microstrutturali e meccaniche delle leghe di alluminio secondarie pressocolate: le particelle di sludge sono inclusioni compatte dure e fragili, le quali possono compromettere le operazioni di lavorazione meccanica, con una conseguente riduzione della durata degli utensili, ed una marcata riduzione delle proprietà meccaniche e fisiche del componente. Il problema delle particelle di sludge nelle leghe secondarie di alluminio assume un'importanza sempre maggiore a causa dell'aumento del riciclo dell'alluminio e della presenza di Fe, Mn e Cr nel ciclo del rottame.
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Bates, William. "Casting repair and Surface Modification of Aluminum Alloys using Friction Stir Processing (FSP)." Thesis, Högskolan Väst, Avdelningen för Industriell ekonomi, Elektro- och Maskinteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-16675.
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This thesis investigates using friction stir welding to repair common surface defects found in aluminum-silicon sand castings. Wherein, the effect of welding parameters: weld RPM, weld speed, and number of weld passes, were evaluated using hardness, porosity density, welding temperature, microstructure refinement as metrics. Therefrom, the results strongly suggest friction stir welding: reduces porosity size, reduces porosity density in a specific area, increases average hardness, improves hardness uniformity, increases surface roughness, redistributes microstructure features in a manner that theoretically improves strength, and maintains a welding temperature less than 660 degrees Celsius.
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Zhu, Baiwei. "On the influence of Si on anodising and mechanical properties of cast aluminium alloys." Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Material och tillverkning, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-35096.
Full textAbstract:
The combination of two cost-effective processes, i.e. casting and anodising, would be an interest for the aluminium component applications. However, there are some obstacles in the application of anodising on cast Al alloys. The challenges mostly relate to the alloying elements especially Si and the surface quality. With the development of casting process, cast aluminium alloys with low Si content can be casted, and a complex geometry component with reasonably good surface finish can be achieved. This study aims to identify the influence of Si on anodising and mechanical properties of Al-Si alloys. In this study, six Al-Si alloys with three different Si level and two different Sr level were investigated. Sr acts as a modifier to change the morphology of Si particles. The directional solidification technology was used to vary the microstructure coarseness by controlling the cooling rate to study the influence of Si level, Si particle morphology and cooling rate on mechanical properties, oxide layer formation and corrosion protection performance in cast Al-Si alloys. This study has observed that Si has a significant influence on anodising. During anodising, Si particles are anodised at a lower rate than the Al phase. The presence of Si particles in eutectic phase make the oxide layer locally thinner and more defected due to the low oxide growth rate in eutectic phase. This study observed the presence of residual metallic Al phase beneath or between Si particles. Due to their presence and their geometry, Al can be shielded by Si particles and prevented from oxidation. Si particles also act as a key role in the corrosion protection of oxide layer in Al-Si alloys. The corrosion attack propagates along Si particles as well as oxide defects to the Al substrate. It is found that the morphology of Si particles has a significant influence on the oxide layer formation and corrosion protection performance of the oxide layer on cast Al-Si alloys. A substantially improvement the corrosion resistance of anodised layer on Al-Si alloys is attributed to the morphology change from interconnected flakes to disconnected Si fibres when Sr is added, with less oxide defects and better oxide distribution. The Si level governs the mechanical properties of Al-Si based alloys. An increase of Si content in Al alloys improves the mechanical properties such as ultimate tensile and yield strength as well as hardness of the materials, but decreases the ductility. However, an increase of Si level in Al alloys decreases the thickness of oxide layer, and thereby, the corrosion protection of the oxide layer is deteriorated.Kombinationen av två kostnadseffektiva processer, gjutning och anodisering, är av intresse för tillämpning på aluminiumkomponenter. Det finns dock hinder för tillämpning av anodisering på gjutna aluminiumlegeringar. Utmaningarna relaterar till effekten av legeringselement, i synnerhet Si, och komponentens ytkvalité. Med utvecklingen av gjutprocesser kan aluminiumlegeringar med lågt Si-innehåll gjutas, och komponenter med komplex geometri med förbättrad ytkvalité kan uppnås. Denna studie syftar till att identifiera påverkan av Si på anodisering och mekaniska egenskaper hos Al-Si-baserade legeringar. I denna studie undersöktes sex Al-Si-legeringar med tre nivåer av Si och två nivåer av Sr. Tillsatser av Sr leder till modifikation av morfologin hos Si-partiklar. Med hjälp av tekniken ”riktad stelning” varierades stelningshastigheten för att studera sambanden mellan halten och morfologin av Si, mikrostrukturens grovlek och dess inverkan på mekaniska egenskaper, samt oxidskiktets bildning och korrosionsbeständighet hos gjutna Al-Si-legeringar. Denna studie visar att Si har ett betydande inflytande på anodisering r. Under anodisering, anodiseras Si-partiklar i en lägre takt än Al-fasen. Närvaron av Si-partiklar i eutektisk fas bidrar till ett lokalt förtunnat oxidskikt med fler defekter på grund av den låga oxidtillväxthastigheten i eutektisk fas. Denna studie observerade förekomsten av kvarvarande metalliska Al fasen under eller mellan Si-partiklar. På grund av Si-partiklarnas närvaro och geometri, kan Al skärmas från oxidation. Si-partiklar har även en nyckelroll i korrosionsskydd av oxidskiktet i Al-Si-legeringar. Korrosionsangreppet propagerar längs Si-partiklar samt oxiddefekter till Al-substrat. Morfologin av Si-partiklar har funnits ha en betydande inverkan på oxidskiktets bildning och korrosionsskydd hos gjutna Al-Si-legeringar. En väsentlig förbättring av korrosionsbeständigheten i anodiserat skikt hos Al-Si-legeringar tillskrivs förändring av kiselns morfologi från sammankopplade flingor till osammanhängande fibrer när Sr tillsätts, med mindre oxiddefekter och bättre fördelning av oxid. Si halten påverkar de mekaniska egenskaperna hos Al-Si-baserade legeringar. En ökning av Si innehålleti Al-legeringar förbättrar de mekaniska egenskaperna såsom brott och sträckgräns samt hårdhet hos materialen, men minskar duktiliteten. En ökning med Si halt i Al-legeringar minskar dessvärre tjockleken hos oxidskiktet, och därigenom, försämrar oxidskiktets korrosionsskydd.
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Shilvock, W. D. "The effect of alloy and impurity variation on the treatment, casting and physical properties of aluminium-silicon eutectic alloys." Thesis, University of Canterbury. Engineering, 1995. http://hdl.handle.net/10092/8133.
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The aluminium-silicon eutectic alloy finds widespread use in commercial light alloy foundries world-wide. The intrinsic characteristics which ensure that this traditional alloy continues in use are excellent fluidity, moderate strength, good ductility, low shrinkage, no requirement for post casting heat treatment and exceptional corrosion resistance. The latter two are particularly noteworthy as they assure the eutectic alloy finds favour in numerous roles for which the higher strength Al-7%Si-Mg alloy is less well suited.
The research reported in this thesis aimed to quantify the changes in physical and structural properties of sand-cast Al-Si eutectic alloy due to compositional variations within the specified range provided by British Standard 1490-LM6. The eutectic alloy was selected for investigation primarily due to members of the local (NZ) aluminium industry expressing concerns regarding consistent production of castings capable of surpassing the physical requirements of the BS1490-LM6 standard.
To achieve the desired aim approximately 500 standard test bars (as used in industry and specified by BS1490) were produced using conditions replicating those encountered in a small, commercial foundry. Each specimen cast was of varying composition with the major variables being Na, Sr, Ti, B, Si, Mg, Mn and Fe. Physical and structural properties including: hardness, tensile strength, ductility, 0.2% proof strength, porosity, grain size and eutectic silicon morphology were monitored for each specimen produced. The combined composition and physical/structural data were then subjected to extensive statistical analysis via multi-linear-regression. The results of the statistical analysis are presented as a series of expressions relating the measured properties to the relevant compositional variables. The sometimes complex and inter-related effects of the elements responsible for significant property variation are illustrated in both numerical and graphical forms.
The full analysis results and associated findings are too numerous to be summarised here. An example of a significant finding is that, with the exception of grain refinement, boron is detrimental to every property monitored. Almost without exception the unwanted effects of boron are already manifest at boron levels as low as 0.01%. Another finding of interest is that within the confines of the given compositional range, the controversial practice of adding manganese to counteract iron-induced embrittlement has little effect on ductility while being highly deleterious to tensile strength. Indeed the embrittling effects of iron were found to be far smaller in magnitude than anticipated given the concern which surrounds this element. This led to the conclusion that further investigation into the effects of iron on parameters such as fatigue endurance warrant investigation.
Two compromises were unavoidable in this research firstly, an inability to assess the level and hence effects of phosphorus variations, and secondly the boron additive used was not of the desired type. Surprisingly, the effects of boron mentioned above were not found to be discernibly influenced by the latter compromise.
Two less significant areas of experimentation were also touched upon in the course of this research, namely the suitability of various materials for use in conditions requiring contact with molten aluminium, and the contamination and compositional variations which occur during degassing by conventional lance and tablet methods.
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Forté, Martin. "Modélisation de l'écoulement de l'aluminium semi-solide dans le moulage sous pression /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2006. http://theses.uqac.ca.
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Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2006.La p. de t. porte en outre: Mémoire présenté à l'Université du Québec à Chicoutimi comme exigence partielle de la maîtrise en génie. CaQCU Bibliogr.: f. [142-145]. Document électronique également accessible en format PDF. CaQCU
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MALAVAZI, JEFFERSON. "Caracterização microestrutural dos compostos intermetálicos e seu efeito no comportamento mecânico nas ligas de Al-9%Si com adições de Fe e Mn." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10554.
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Jaradeh, Majed. "The Effect of Processing Parameters and Alloy Composition on the Microstructure Formation and Quality of DC Cast Aluminium Alloys." Doctoral thesis, KTH, Materialvetenskap, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4205.
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The objective of this research is to increase the understanding of the solidification behaviour of some industrially important wrought aluminium alloys. The investigation methods range from direct investigations of as-cast ingots to laboratory-scale techniques in which ingot casting is simulated. The methods span from directional solidification at different cooling rates to more fundamental and controlled techniques such as DTA and DSC. The microstructure characteristics of the castings have been investigated by optical and Scanning Electron microscopy. Hardness tests were used to evaluate the mechanical properties. The effects of adding alloying elements to 3XXX and 6XXX aluminium alloys have been studied with special focus on the effects of Zn, Cu, Si and Ti. These elements influence the strength and corrosion properties, which are important for the performance of final components of these alloys. Solidification studies of 0-5wt% Zn additions to 3003 alloys showed that the most important effect on the microstructure was noticed at 2.5 wt% Zn, where the structure was fine, and the hardness had a maximum. Si addition to a level of about 2% gave a finer structure, having a relatively large fraction of eutectic structure, however, it also gave a long solidification interval. The addition of small amounts of Cu, 0.35 and 1.0 wt%, showed a beneficial effect on the hardness. Differences have been observed in the ingot surface microstructures of 6xxx billets with different Mg and Si ratios. Excess Si compositions showed a coarser grain structure and more precipitations with possible negative implications for surface defect formation during DC casting. The comparison of alloys of different Ti content showed that the addition of titanium to a level of about 0.15 wt% gave a coarser grain structure than alloys with a normal Ti content for grain refinement, i.e. < 0.02 wt%, although a better corrosion resistance can be obtained at higher Ti contents. The larger grain size results in crack sensitivity during DC casting. A macroscopic etching technique was developed, based on a NaOH solution, and used in inclusion assessment along DC cast billets. Good quantitative data with respect to the size and spatial distribution of inclusions were obtained. The results from studied billets reveal a decreasing number of inclusions going from bottom to top, and the presence of a ring-shaped distribution of a large number of small defects in the beginning of the casting. The present study shows how composition modifications, i.e. additions of certain amounts of alloying elements to the 3xxx and 6xxx Al alloys, significantly change the microstructures of the materials, its castability, and consequently its mechanical propertiesQC 20100901
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Wang, Yun. "Solidification microstructure selection and coupled eutectic growth in Al-Fe and Al-Fe-Mn alloys." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324449.
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Míšek, Jakub. "Vliv odplynění na kvalitu odlitků vyrobených technologií vysokotlakého lití." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318844.
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This thesis examines the influence of the degassing process on hydrogen contend and on the quality of part casted by high pressure casting technologies. The type of defects occurring in the casting is analyzed based on macrostructure and microstructure observations. For the overall assessment is used the statistical observation of the evolution trend of scrapping during the experiment. The results show that shortening of the degassing time may affect the incidence of porosity defect.
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Mardan, Milad. "Hot tearing study of aluminium alloys above the solidus temperature with the aid of a direct chill casting surface simulator (DCSS) = : Étude sur la fissuration à chaud d'alliages d'aluminium au-dessus du solidus à l'aide d'un simulateur de surface de la coulée semi-continue." Thesis, Université Laval, 2011. http://www.theses.ulaval.ca/2011/27824/27824.pdf.
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La déchirure à chaud est un défaut important observé lors de la coulée de certains alliages d'aluminium. Elle se produit au cours de la solidification lorsqu’une petite quantité de phase liquide reste emprisonnée dans la phase solide, affaiblissant la résistance en tension et conduisant à la fissuration de l’alliage. Dans le cas de la coulée semi-continue d’alliages d'aluminium (coulée avec refroidissement intensif et continue), la fissuration à chaud s’initie à la surface des lingots de laminage, là où la microstructure est particulièrement vulnérable, c’est-à-dire juste après la zone du refroidissement primaire. Afin d'étudier le comportement thermomécanique de ces alliages lors de la fissuration à chaud et l'impact de l’utilisation d’affineurs de grains, des essais de traction ont été effectués à de faibles taux de déformation sur des échantillons solidifiés dans un état semi-solide (fraction solide ~90-95% vol.) avec l'aide d'un appareil appelé DCSS (Direct Chill Surface Simulator). Cet appareil est constitué d’un banc d’essai reproduisant les conditions existantes pendant le refroidissement primaire du procédé de coulée semi-continue d’alliages d’aluminium.
Le comportement thermomécanique des échantillons partiellement solidifiés sous l’application de charges en tension a été analysé et la formation de fissures à chaud a été observée. La température à différents endroits dans les échantillons, la charge appliquée et la déformation en surface ont été mesurées lors d’essais de traction effectués sur les alliages d'aluminium AA5182, AA6111 et AA3104. La microstructure de chaque spécimen a été examinée et analysée à l'aide d’un microscope optique afin d’évaluer l’aspect colonnaire ou équiaxe des grains et de son effet sur le comportement thermomécanique de l'alliage. Une importance particulière a été portée sur l'évaluation de la fraction solide présente dans chaque échantillon coulé au début des essais de traction, tenant compte de la température locale, du gradient thermique et des taux de refroidissement appliqués.
Il a été observé que des concentrations excessives d’affineur de grains diminuaient la résistance mécanique en tension des coquilles solidifiées en raison d’une porosité plus élevée induite par une nucléation plus facile des nouvelles phases (gaz inclus). On a aussi constaté que les taux de refroidissement de l’alliage augmentaient avec la quantité d’affineur de grains, relié à un phénomène associé au nombre plus élevé des points de contact avec la surface du moule causés par les nombreux petits grains équiaxes. Finalement, la conception d’un critère basé sur la contrainte thermomécanique pour expliquer la fissuration à chaud a été renforcée par l’observation d’une meilleure résistance mécanique en tension obtenue sur des coquilles avec des microstructures non affinées pour les alliages AA5182 et AA6111 ayant des fractions solides similaires, mais avec des tailles de grain significativement différentes.Hot tearing is a severe defect in aluminum castings which is produced during solidification when a certain amount of liquid phase remains and weakens the tensile resistance of the alloy. In direct chill casting of aluminum alloys, hot tears initiate at the surface of sheet ingots just after the primary cooling zone, where the microstructure is particularly vulnerable. In order to study the thermomechanical properties of these alloys and the effect of grain refiners on their thermo-mechanical behaviour, tensile tests were carried out on specimens in the semi-solid state (~90-95% solid fraction) and at low strain rates using an apparatus called Direct Chill Surface Simulator (DCSS). This apparatus is an instrumented rig test reproducing the conditions prevailing during the primary cooling stage of the DC casting process. The thermomechanical behavior of solidifying shells and the hot tear formation under applied tensile loads was analyzed and the occurrence of hot tearing was observed. The temperature in different locations of the casting, applied load and surface strain were monitored during the tensile tests conducted on aluminum alloys AA5182, AA6111 and AA3104. The microstructure of the tested specimens was examined using the optical microscope to evaluate the columnar or equiaxed aspect of grains and their effect on the thermomechanical response of the alloy. A special emphasis has been given to the evaluation of the solid fraction existing in the castings at the start of the tensile tests, taking into account the local temperature, thermal gradient and cooling rates experienced. It was found that excessive grain refiner additions decreased the strength of solidifying shells because of the increased level of porosity induced by easier nucleation of new phases (gas included). It was also observed that cooling rates increased with the level of grain refiner, a phenomenon that was associated to the higher number of contact points with the mould obtained with numerous small equiaxed grains. Finally, the concept of a stress based criterion for hot tearing was reinforced by the strengths obtained on not grain refined AA5182 and AA6111 alloys showing similar solid fraction near the surface, but with significantly different grain sizes.
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Proni, Cecilia Tereza Weishaupt 1959. "Avaliação da tixoconformabilidade das ligas AA 2011 e AA 2014." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264031.
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Orientador: Eugênio José ZoquiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: A tixoconformação é uma técnica de processamento de materiais no estado semi-sólido que permite a produção de peças com geometrias near net shape com melhores propriedades mecânicas e com razoável redução no custo final de produção, se comparados aos métodos de fundição e conformação plástica tradicionais. Dentro das várias possibilidades de materiais passíveis de trabalho por esta via, as ligas de alumínio são as mais utilizadas, servindo a diversos segmentos industriais. Contudo, o fornecimento de matéria prima próprias ao tixo-processamento está restrito a alguns produtores, justificando a necessidade de aprofundamento e ampliação de conhecimento com respeito às ligas já produzidas por fundição convencional. Este trabalho apresenta um exame da viabilidade de tixoconformação de duas ligas comerciais: AA 2011 e AA 2014. Esta avaliação foi executada em três etapas distintas: 1) análise dos seus constituintes, das temperaturas de fusão e de solidificação, dos microprecipitados existentes e dos tipos de porosidade; 2) reaquecimento de amostras para observar a resposta à globularização em duas temperaturas distintas (duas frações sólidas) e em quatro tempos de espera diferentes, com a posterior análise quantitativa por meio da metalografia; 3) ensaios de viscosidade nas mesmas condições, com posterior análise microestrutural via MEV e EDS das amostras que apresentaram valores de viscosidade muito altos. Os resultados destas avaliações mostraram que estas duas ligas são tixoconformáveis até a temperatura de 610°C, pois apresentaram valores de viscosidade abaixo de 1x106 Pa.s e tensão máxima abaixo de conformação de 1,0 MPa, conforme escolhas adequadas entre tempos de espera e taxa de aquecimento. Porém, também foi constatada a formação de alumina nos poros de algumas amostras após o reaquecimento necessário à tixoconformação, fornecendo um valor mais alto de viscosidade para estas amostras, se em comparação aos valores encontrados em outros ensaios com pouca ou nenhuma formação de alumina. A eliminação de porosidade na matéria prima com a conseqüente minimização do surgimento de alumina viabilizará a tixoconformação de ambas as ligas
Abstract: Thixoforming is a technique for processing materials in the semi-solid state which allows the production of parts near-net-shape geometries, with better mechanical properties and reasonable reduction in the final production cost, compared to traditional casting and plastic forming. Among the various possibilities of materials that can work in this way, aluminium alloys are the most used. However, the world provision of raw material for thixoforming is restricted to few producers, justifying the need for deepening and widening of knowledge with respect to alloys already produced by the conventional casting industries. This dissertation presents an examination of the feasibility of thixoforming of two commercial alloys: AA 2011 and AA 2014. This evaluation was performed in three steps: 1) analysis of their constituents, analysis of melting and solidification temperatures, analysis of the existing micro precipitates and quantity and types of porosity, 2) reheating samples to observe the globularization response to two different temperatures (two solid fractions) and four holding times, with the subsequent quantitative analysis by metallography, 3) tests of the viscosity under the same conditions, with subsequent microstructural analysis by SEM and EDS of the samples that showed very high viscosity values. The results of these evaluations showed that these two alloys are thixoformable up to temperatures of 610°C, since their viscosity values were achieved below than 106 Pa.s, and consequently maximum conformation stress of 1.0 MPa, as appropriate choices between waiting times and heating rate were achieved. However, the formation of alumina in the pores of some samples after the necessary reheating to previous to thixoforming, provide a higher value of viscosity, when compared to values found in other trials with little or no alumina. The elimination of porosity in the raw material, with the consequent minimizing the appearance of alumina will make possible the thixoforming of both alloys
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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Kolařík, Martin. "Optimalizace výroby hliníkového odlitku s použitím numerické simulace." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-401577.
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The master’s thesis deals with the analysis of casting technology of the selected aluminium casting. It is a casting of a part of CNC milling machine and it is cast by gravity casting into a permanent mold. The defects which are the cause of a high percentage of nonconforming production were analyzed. Furthermore, the master’s thesis includes a complete analysis of filling and solidification of this casting in the ProCast simulation program. Numerical simulation results are verified and improved. Then the causes of problematic casting defects are proven on several calculated variants. Measures are proposed to minimize the tendency to produce castings with defects leading to nonconforming production.
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Jankes, Erik. "Využití řízeného naplyňování slitin Al-Si při tlakovém lití." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231052.
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This master thesis will cover the possibility of using directed gassing of Al-Si alloys in a high pressure die casting foundry. As a control gas, rotary degasser with gaseous 20 % H2 in N2 as a medium was used. Castings were casted via high pressure die casting machine. The aim of this research is to compare internal defect such as porosity or shrinkage of a casts made from degassed and control gassed melt.
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Hamasaiid, Anwar. "Transferts thermiques interfaciaux en fonderie en moules métalliques d'alliages légers." Toulouse 3, 2007. http://www.theses.fr/2007TOU30249.
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L'objectif de ce projet est d'étudier les transferts thermiques interfaciaux pendant la solidification des alliages légers dans les procédés de fonderie par gravité et sous pression. Pour cela, nous avons développé des méthodes expérimentales et des capteurs appropriés permettant d'effectuer les mesures de température dans le moule et en surface de la pièce pendant le remplissage et la solidification. Nous avons également enregistré les paramètres procédés sur une installation de fonderie sous pression particulièrement bien instrumentée. Pour la mesure de température de surface de la pièce coulée, nous avons adapté une technique pyrométrique utilisant un pyromètre et une fibre optique auxquels nous avons ajouté un crystal de saphir transparent dans la gamme de longueur d'onde du pyromètre. Ainsi, nous avons effectué plusieurs centaines de cycles pendant lesquels trois alliages ASG03, AS9U3 et AZ91D ont été coulés par ces deux procédés. Les mesures de température ont été exploitées par une méthode inverse pour évaluer le coefficient d'échange thermique et la densité de flux de chaleur à l'interface pièce/moule pour chaque cycle effectué. Les résultats obtenus ont été comparés entre les diverses conditions de coulée et avec les microstructures des pièces produites. Nous avons proposé deux modèles analytiques pour la Résistance Thermique de Contact (RTC) à l'interface liquide/solide pour les deux conditions de contact rencontrées dans les deux procédés étudiés. .The present investigation is about the interfacial heat transfer during the solidification of light alloys in Gravity (GDC) and High Pressure (HPDC) Die Casting processes. The study consists of three principle fields, experimental, analytical and modelling. The Experimental activity involves measuring the temperature around the casting-die interface, in the mould and at the surface of the castings and other process parameters during die filling and solidification. For this purpose, suitable experimental methods and sensors have been developed. Particularly a pyrometric measurement method has been adapted to measure the casting surface temperature during its solidification. Hundredths of trials were performed using Al-7Si-0. 3Mg, A-9Si-3Cu and AZ91 D alloys during the two investigated processes. From the temperature measurements, interfacial heat transfer coefficient and heat flux density have been evaluated using an inverse method. The obtained results have been analysed with regards to the various process parameters and to the microstructure of the castings. .
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Mašková, Lenka. "Řízená krystalizace odlitků z hliníkových slitin ve skořepinových formách." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-228994.
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The aim of this thesis is to verify a possibility of controlling the crystallisation of aluminium alloys poured in shell moulds in order to achieve directional solidification. For this purpose, new cooling plant has been designed and fabricated. Several sample castings were produced under different initial conditions. Based on the evaluation of measured temperatures, a numerical simulation of heat transfer was created using the ProCAST software. Finally, the sample castings were sectioned into specimens that were, subsequently, metallographically polished and the evaluation of their structure with respect to the amount and types of defects was performed.
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Santos, Jorge. "Al-7Si-Mg semi-solid castings – microstructure and mechanical properties." Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Material och tillverkning, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-38693.
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The vehicles industry is facing increasing demands for fuel efficiency and cost reduction due to environmental legislation, sustainability and customer demands. Therefore, there is a great need to develop and produce lightweight components by using materials and processes that offer higher specific strength and/or design optimization. Semi‐solid aluminium casting offers design freedom and castings with lower shrinkage and gas entrapment defects compared to high pressure die castings. The lack of understanding of microstructure and defect formation, and design data, for semi‐solid castings is a barrier for foundries and designers in the vehicles industry to use semi‐solid castings. In this study, the effect of two grain refiners on slurry formation and surface segregation of semi‐solid Al‐7Si‐0.3Mg castings produced by the Rheometal™ process was evaluated. The influence of grain refinement on primary α‐Al grain size, shape factor and solid fraction was analysed in addition to the solute content of the surface segregation layer. The influence of magnesium on the formation of intermetallic phases during solidification and the heat treatment response of Al‐7Si‐Mg semi‐solid castings was investigated. The magnesium content was varied from 0.3 to 0.6wt.% and the semi-solid castings were analysed in the T5 and T6 conditions. Energy dispersive spectroscopy was used to identify the intermetallic phases formed during solidification. Tensile testing was performed and the results were correlated to the magnesium and silicon concentration measured in the interior of the α‐Al globules formed during slurry preparation. The results suggest that the addition of grain refiner decreases the solid fraction obtained in the Rheometal™ process. However, no significant effect was observed on the α‐Al grain size and shape factor. A good correlation was obtained between the magnesium concentration in the interior of the α‐Al globules formed during slurry preparation and the offset yield strength for all alloys. The low magnesium solubility in α‐Al at temperatures in the solidification range of the Al‐7Si‐Mg alloys is suggested to be the reason for the low hardening response for the T5 heat treatment compared to the T6 condition.
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Carpentier, David. "Modélisation de la formation des microporosités lors de la solidification d'alliages à base d'aluminium." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL125N.
Full textAbstract:
En fonderie d'aluminium, la présence de microporosités au sein des pièces moulées nuit considérablement à leurs propriétés mécaniques. On comprend par conséquent que la modélisation et la prédiction de la formation des microporosités peuvent être d'un grand soutien pour le fondeur. Dans cette étude, nous avons observé tout d'abord expérimentalement la sensibilité à la formation des microporosités d'alliages binaires d'aluminium-silicium (Al-3%Si, Al-7%Si, Al-11%Si) dans des conditions de solidification unidirectionnelle ou uniforme. La caractérisation de nos essais nous a permis de retrouver certaines tendances déjà observées expérimentalement dans la littérature et notamment une augmentation de la fraction volumique de pores avec: la teneur initiale en hydrogène dissous, une microstructure plus grossière, une pression extérieure plus faible. Au vu de ces résultats, nous avons alors adopté une approche thermodynamique ou nous avons montré notamment que, dans l'intervalle de solidification des alliages d'aluminium, la diminution de la température et l'enrichissement en soluté du liquide résiduel peuvent diminuer considérablement la solubilité de l'hydrogène. Dans ces conditions, la formation des microporosités peut avoir lieu dans les premiers stades de la solidification ou les pertes de pression associées au retrait de solidification sont alors négligeables. Notre étude a abouti à la définition d'un modèle analytique de prédiction de la fraction volumique de pores se caractérisant par les deux étapes suivantes: 1) la détermination de la fraction solide critique à partir de laquelle la formation des microporosités devient thermodynamiquement possible, 2) le calcul de la fraction volumique de pores à partir de la résolution du bilan de masse pour l'hydrogène. Notre approche peut être utilisée pour d'autres alliages d'aluminium et/ou dans des conditions de solidification plus compliquées
39
Balde, Mamadou. "Optimisation microstructurale d'un alliage d'aluminium à hautes performances mécaniques par utilisation du procédé CobaPress™." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEM041.
Full textAbstract:
Le CobaPress™ est un procédé hybride de coulée et de forge permettant l’obtention de pièces automobiles du type liaison au sol. L’avantage principal réside dans le fait qu’il est possible de produire des pièces à géométrie complexe, le tout en réduisant la quantité de porosités dans la pièce et de leur conférer une meilleure durée de vie en fatigue.L’objectif principal vise à améliorer les propriétés mécaniques de ces pièces en réduisant la quantité de silicium initialement présente à 7% dans les alliages d’aluminium lors du CobaPress™. On souhaite dans le contexte de cette thèse adapter le procédé CobaPress™ pour développer un nouvel alliage d’aluminium à hautes propriétés mécaniques appelé alliage HMP. Le travail porte sur l’étude microstructurale du matériau au sens des équilibres thermodynamiques et des évolutions attendues pendant les étapes du procédé pour déterminer la composition chimique idéale de l’alliage HMP. L’utilisation du logiciel Thermocalc© nous permettra de tenir compte des températures de fusion et de brûlure, mais également de la formation des différentes phases. De plus, des essais de compression plane encastrée sont menés pour étudier la refermeture des porosités, mais également la sous-structuration de l’alliage au cours du traitement thermique à température fixée mais à différentes vitesses et niveaux de déformation. Des observations EBSD sont également effectuées afin de caractériser les phénomènes microstructuraux tels que la restauration et la recristallisation. Nous nous intéressons également l'influence des secondes phases sur l’amorçage des fissures au cours d’essais en fatigue sur l’alliage HMPCobaPress™ is a hybrid process of casting and forging leading to the manufacturing of high integrity/critical safety components and sub-assemblies for the automotive industry. The advantages to manufacture automotive parts using this process are multiple such as an important decreasing of the porosities amount, a better fatigue life cycle, the elaboration of complex geometries.Throughout this process, the main objective consists of the elaboration of chassis parts with higher mechanical properties by reducing the silicon content usually at 7% in the cast CobaPressed aluminum alloys. A new hybrid cast/wrought aluminum alloy called HMP alloy with lower silicon content is then developed. The objective is to improve the static and cyclic mechanical properties of the parts thanks to this alloy. The use of Thermocalc© simulations allowed us to set up with annealing temperatures and chemical composition of the HMP alloy. Channel die experiments have been carried out to study the reclosing of porosities, but also sub-structure evolution for a fixed temperature and various strain rates. Observations on EBSD have been made in order to characterize recovery and/or recrystallization phenomena.Because the secondary phases may have a detrimental effect on the cyclic properties, we are also interesting in the influence of these phases on crack initiation during fatigue tests on the HMP alloy
40
Kini, Anoop Raghunath. "Semisolid Die Casting of Wrought A6061 Aluminium Alloy." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/3317.
Full textAbstract:
The mechanical properties achieved with high performance wrought aluminium alloys are
superior to cast aluminum alloys. To obtain an intricate shaped component, wrought alloys are commonly subjected to forging followed by subsequent machining operation in the automobile industry. As machining of such high strength wrought aluminium alloys adds to cost, productivity gets affected.
Shortening the process by near net shaped casting would tremendously enhance productivity. However, casting of such alloys frequently encounter hot tear defect. Therefore, circumventing hot tear to
successfully die cast near net shaped wrought alloy components is industrially relevant. A recent advanced casting process, namely ‘Semisolid Die casting’, is proposed as a likely solution.
Hot tearing originates due to lack of liquid flow in the inter-dendritic region. To reduce hot tear susceptibility, fine and non-dendritic grain structure is targeted, amenable for processing by semisolid
route. For semisolid processing an adequate freezing range for processing is required. Accordingly A6061 wrought alloy whose composition is tuned with higher silicon and magnesium content within the grade limits, is chosen for the study.
With the objective of obtaining fine and non-dendritic microstructured billets, electromagnetic stirring (EMS) and cooling slope (CS) methods are employed. On conducting a parametric study with
EMS, a finest possible primary α-Al grain size of about 70 μm is obtained at low stirring time at stirring
current levels of 175 A and 350 A, with the addition of grain refiner. CS, on the other hand, rendered a grain of 60 μm at a slope length of 300 mm at a slope angle of 45° with grain refiner addition. Of the two methods, CS billets are chosen for subsequent induction heating. A 3-step induction heating cycle has been devised to attain a temperature of 641°C in the billet on the basis of factors including coherency
point, viscosity of the slurry and solid fraction sensitivity with temperature. The billet microstructure is found to be homogenous throughout after quenching in water. The characterization of phase along
primary α-Al grain boundary and its composition analysis is done by SEM and EPMA respectively, after billet casting as well as induction heating. In addition, the bulk hardness is determined in BHN.
The induction heated billets are semisolid die cast to produce an engine connecting rod used in automobiles. The microstructure is characterized at various locations, and is found to consist of smooth
α-Al grains in a background matrix of fine grains formed due to secondary solidification. The component
hardness is found to be 66 BHN comparable with A6061 alloy under T4 heat treated condition. X-ray radiography does not confirm presence of surface hot tear, which is the normal defect associated with casting of wrought aluminium alloys. No defects are observed along the constant cross-sectional area of the connecting rod, suggesting that the processing could be suitable for semisolid extrusion.
41
Kini, Anoop Raghunath. "Semisolid Die Casting of Wrought A6061 Aluminium Alloy." Thesis, 2013. http://etd.iisc.ernet.in/2005/3317.
Full textAbstract:
The mechanical properties achieved with high performance wrought aluminium alloys are
superior to cast aluminum alloys. To obtain an intricate shaped component, wrought alloys are commonly subjected to forging followed by subsequent machining operation in the automobile industry. As machining of such high strength wrought aluminium alloys adds to cost, productivity gets affected.
Shortening the process by near net shaped casting would tremendously enhance productivity. However, casting of such alloys frequently encounter hot tear defect. Therefore, circumventing hot tear to
successfully die cast near net shaped wrought alloy components is industrially relevant. A recent advanced casting process, namely ‘Semisolid Die casting’, is proposed as a likely solution.
Hot tearing originates due to lack of liquid flow in the inter-dendritic region. To reduce hot tear susceptibility, fine and non-dendritic grain structure is targeted, amenable for processing by semisolid
route. For semisolid processing an adequate freezing range for processing is required. Accordingly A6061 wrought alloy whose composition is tuned with higher silicon and magnesium content within the grade limits, is chosen for the study.
With the objective of obtaining fine and non-dendritic microstructured billets, electromagnetic stirring (EMS) and cooling slope (CS) methods are employed. On conducting a parametric study with
EMS, a finest possible primary α-Al grain size of about 70 μm is obtained at low stirring time at stirring
current levels of 175 A and 350 A, with the addition of grain refiner. CS, on the other hand, rendered a grain of 60 μm at a slope length of 300 mm at a slope angle of 45° with grain refiner addition. Of the two methods, CS billets are chosen for subsequent induction heating. A 3-step induction heating cycle has been devised to attain a temperature of 641°C in the billet on the basis of factors including coherency
point, viscosity of the slurry and solid fraction sensitivity with temperature. The billet microstructure is found to be homogenous throughout after quenching in water. The characterization of phase along
primary α-Al grain boundary and its composition analysis is done by SEM and EPMA respectively, after billet casting as well as induction heating. In addition, the bulk hardness is determined in BHN.
The induction heated billets are semisolid die cast to produce an engine connecting rod used in automobiles. The microstructure is characterized at various locations, and is found to consist of smooth
α-Al grains in a background matrix of fine grains formed due to secondary solidification. The component
hardness is found to be 66 BHN comparable with A6061 alloy under T4 heat treated condition. X-ray radiography does not confirm presence of surface hot tear, which is the normal defect associated with casting of wrought aluminium alloys. No defects are observed along the constant cross-sectional area of the connecting rod, suggesting that the processing could be suitable for semisolid extrusion.
42
Singh, Shailesh Kumar. "Experimental and Numerical Investigation on Friction Welding of Thixocast A356 Aluminium Alloy." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/2847.
Full textAbstract:
The challenges of weight reduction and good strength in automotive industry have drawn considerable interest in thixocasting technologies. Joining of such components with conventional fusion welding creates voids, hot cracking, distortion in shape, and more importantly evolution of dendritic microstructure that ultimately would lead to inferior mechanical properties of the weld region. Thus, the purpose of making thixocast component is lost. The friction welding which is a solid state joining process can avoid defects associated with melting and solidification in a typical fusion weld and can be a promising alternative. This process produces a weld under compressive force at the contact of workpieces rotating or moving relative to one another to produce heat and plastically displacing material from the faying surfaces. Research on semisolid processing has its origin in the early 1970s. However, from the literature survey on semisolid processing it is clear that, till date, not much work has been done in field of joining of semisolid processed components. In the area of solid state welding, in particular, it is not at all explored. In view of this, the present work is focused on exploration of joining of Thixocast A356 Aluminium alloy component by friction welding and comparison of its performance with friction weld of conventionally cast sample of the same alloy. The study is carried out experimentally as well as numerically. Moreover, the material behaviour of thixocast component at elevated temperature in solid state is also described with the help of processing maps and constitutive modelling.
The hot workability of thixocast and conventionally cast A356 alloy is evaluated with the help of processing maps developed on the basis of the dynamic materials model approach using the flow stress data obtained from the isothermal compression test in wide range of temperature (300-500℃) and strain rates (0.001s-1-10s-1). The domains of the processing map are interpreted in terms of the associated microstructural mechanism. On comparing the flow stress at elevated temperature of thixocast and conventionally cast A356 alloy samples, it is observed that the flow stress of the latter showed higher value at different strain level, temperature and strain rates. This indicates that the flow property of the thixocast alloy sample is better than
that of the conventionally cast one (i.e. response to plastic flow is better for the former); while at room temperature thixocast sample has higher strength. Moreover to investigate the general nature of the influence of strain, strain rate and temperature on the compressive deformation characteristics of thixocast A356 and conventionally cast A356 aluminium alloy, a comprehensive model describing the relationship of the flow stress, strain rate and temperature of the alloys at elevated temperatures is proposed by hyperbolic-sine Arrhenius-type equation and Johnson-Cook model. The validity of descriptive results based on the proposed constitutive equation is also investigated and a comparison between two constitutive models is also made. In order to numerically model the friction welding process of a thixocast A356 aluminium alloy and conventionally cast alloy of same material using a finite element method (FEM), temperature dependent physical properties, mechanical properties as well as viscoplastic constitutive equations were used in the model. A two- dimensional axisymmetric finite element model has been developed. The modelling is based on a coupled thermomechanical approach. First, a nonlinear, transient two-dimensional heat transfer model is developed to determine the temperature fields. Later, the temperature fields are used as input for a nonlinear, two-dimensional structural model in order to predict the distortions and von Mises stress. The finite element models are parametrically built using APDL (ANSYS Parametric Design Language) provided by ANSYS. The validation of the model is carried out by comparing with the experiment. Once validated, the thermomechanical model was used to perform parametric studies in order to investigate effects of various process parameters on temperature and stress distribution in the workpieces. This helps in deciding the range of parameters for friction welding experiments in order to get good weld. Both thixocast and conventionally cast samples exhibited similar temperature distribution during the friction welding process, because of identical thermophysical properties. The magnitude of von Mises stress distribution during friction welding of thixocast A356 sample is found to be lower than that of the conventionally cast sample. It is because of their different constitutive behaviour at elevated temperature. Moreover, the developed FEM model can be successfully used to predict the residual stress at various locations for different set of parameters and geometry for friction welding of thixocast and conventionally cast A356 alloy. This helps in reducing time consuming and expensive experiments on residual stress measurement.
The chosen experiments based on Taguchi L27 orthogonal array were conducted on the friction welding machine which works on the principles of continuous drive-mechanism. The experimental specimens were machined from thixocast A356 aluminium alloy connecting rods as well as conventionally cast A356 aluminium alloy ingot in the form of cylindrical bars of dimensions 85mm length and 20mm diameter. The parameters used for welding were friction pressure, rpm, forge pressure, burn-off, and upset pressure. The effects of welding parameters on performance characteristics (i.e. tensile strength and weld efficiency) were evaluated. Taguchi method was applied to investigate the influence of each parameter on strength of joints and evaluate the combination of parameters that leads to the highest weld strength. Accordingly optimum process parameters was identified which helps in achieving the tensile strength of more than parent material. The optimized process parameters for friction welding of thixocast A356 aluminium alloy are rpm = 500, friction pressure = 60, upset time = 5, upset pressure = 100 and burn off = 5. The empirical relationships were also developed to predict the tensile strength. The developed relationship can be effectively used to predict the tensile strength of welded joint with a correlation coefficient of 0.86, which indicates the strong positive relationship between predicted and experimental data. Friction welding of thixocast A356 aluminium alloy helps to achieve very fine eutectic silicon particles of the order of 0.4 at the interface due to severe plastic deformation taking place during welding. Obtaining such fine eutectic silicon particles is difficult to be achieved within few seconds of processing by any other method. The hardness variation of friction welded thixocast alloy shows higher value as compared to that of a conventionally cast sample in the heat affected zone, which indicates better weld strength of the former. This was also confirmed by the tensile strength studied and fatigue test. This indicates that weldability of cast alloys will get improved if the microstructure is modified to globular type.
43
Singh, Shailesh Kumar. "Experimental and Numerical Investigation on Friction Welding of Thixocast A356 Aluminium Alloy." Thesis, 2013. http://etd.iisc.ernet.in/handle/2005/2847.
Full textAbstract:
The challenges of weight reduction and good strength in automotive industry have drawn considerable interest in thixocasting technologies. Joining of such components with conventional fusion welding creates voids, hot cracking, distortion in shape, and more importantly evolution of dendritic microstructure that ultimately would lead to inferior mechanical properties of the weld region. Thus, the purpose of making thixocast component is lost. The friction welding which is a solid state joining process can avoid defects associated with melting and solidification in a typical fusion weld and can be a promising alternative. This process produces a weld under compressive force at the contact of workpieces rotating or moving relative to one another to produce heat and plastically displacing material from the faying surfaces. Research on semisolid processing has its origin in the early 1970s. However, from the literature survey on semisolid processing it is clear that, till date, not much work has been done in field of joining of semisolid processed components. In the area of solid state welding, in particular, it is not at all explored. In view of this, the present work is focused on exploration of joining of Thixocast A356 Aluminium alloy component by friction welding and comparison of its performance with friction weld of conventionally cast sample of the same alloy. The study is carried out experimentally as well as numerically. Moreover, the material behaviour of thixocast component at elevated temperature in solid state is also described with the help of processing maps and constitutive modelling.
The hot workability of thixocast and conventionally cast A356 alloy is evaluated with the help of processing maps developed on the basis of the dynamic materials model approach using the flow stress data obtained from the isothermal compression test in wide range of temperature (300-500℃) and strain rates (0.001s-1-10s-1). The domains of the processing map are interpreted in terms of the associated microstructural mechanism. On comparing the flow stress at elevated temperature of thixocast and conventionally cast A356 alloy samples, it is observed that the flow stress of the latter showed higher value at different strain level, temperature and strain rates. This indicates that the flow property of the thixocast alloy sample is better than
that of the conventionally cast one (i.e. response to plastic flow is better for the former); while at room temperature thixocast sample has higher strength. Moreover to investigate the general nature of the influence of strain, strain rate and temperature on the compressive deformation characteristics of thixocast A356 and conventionally cast A356 aluminium alloy, a comprehensive model describing the relationship of the flow stress, strain rate and temperature of the alloys at elevated temperatures is proposed by hyperbolic-sine Arrhenius-type equation and Johnson-Cook model. The validity of descriptive results based on the proposed constitutive equation is also investigated and a comparison between two constitutive models is also made. In order to numerically model the friction welding process of a thixocast A356 aluminium alloy and conventionally cast alloy of same material using a finite element method (FEM), temperature dependent physical properties, mechanical properties as well as viscoplastic constitutive equations were used in the model. A two- dimensional axisymmetric finite element model has been developed. The modelling is based on a coupled thermomechanical approach. First, a nonlinear, transient two-dimensional heat transfer model is developed to determine the temperature fields. Later, the temperature fields are used as input for a nonlinear, two-dimensional structural model in order to predict the distortions and von Mises stress. The finite element models are parametrically built using APDL (ANSYS Parametric Design Language) provided by ANSYS. The validation of the model is carried out by comparing with the experiment. Once validated, the thermomechanical model was used to perform parametric studies in order to investigate effects of various process parameters on temperature and stress distribution in the workpieces. This helps in deciding the range of parameters for friction welding experiments in order to get good weld. Both thixocast and conventionally cast samples exhibited similar temperature distribution during the friction welding process, because of identical thermophysical properties. The magnitude of von Mises stress distribution during friction welding of thixocast A356 sample is found to be lower than that of the conventionally cast sample. It is because of their different constitutive behaviour at elevated temperature. Moreover, the developed FEM model can be successfully used to predict the residual stress at various locations for different set of parameters and geometry for friction welding of thixocast and conventionally cast A356 alloy. This helps in reducing time consuming and expensive experiments on residual stress measurement.
The chosen experiments based on Taguchi L27 orthogonal array were conducted on the friction welding machine which works on the principles of continuous drive-mechanism. The experimental specimens were machined from thixocast A356 aluminium alloy connecting rods as well as conventionally cast A356 aluminium alloy ingot in the form of cylindrical bars of dimensions 85mm length and 20mm diameter. The parameters used for welding were friction pressure, rpm, forge pressure, burn-off, and upset pressure. The effects of welding parameters on performance characteristics (i.e. tensile strength and weld efficiency) were evaluated. Taguchi method was applied to investigate the influence of each parameter on strength of joints and evaluate the combination of parameters that leads to the highest weld strength. Accordingly optimum process parameters was identified which helps in achieving the tensile strength of more than parent material. The optimized process parameters for friction welding of thixocast A356 aluminium alloy are rpm = 500, friction pressure = 60, upset time = 5, upset pressure = 100 and burn off = 5. The empirical relationships were also developed to predict the tensile strength. The developed relationship can be effectively used to predict the tensile strength of welded joint with a correlation coefficient of 0.86, which indicates the strong positive relationship between predicted and experimental data. Friction welding of thixocast A356 aluminium alloy helps to achieve very fine eutectic silicon particles of the order of 0.4 at the interface due to severe plastic deformation taking place during welding. Obtaining such fine eutectic silicon particles is difficult to be achieved within few seconds of processing by any other method. The hardness variation of friction welded thixocast alloy shows higher value as compared to that of a conventionally cast sample in the heat affected zone, which indicates better weld strength of the former. This was also confirmed by the tensile strength studied and fatigue test. This indicates that weldability of cast alloys will get improved if the microstructure is modified to globular type.
44
Kund, Nirmala Kumar. "Study Of Solidification And Microstructure Produced By Cooling Slope Method." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2536.
Full textAbstract:
In most casting applications, dendritic microstructure morphology is not desired because it leads to poor mechanical properties. Forced convection causing sufficient shearing in the mushy zone of the partially solidified melt is one of the means to suppress this dendritic growth. The dendrites formed at the solid-liquid interface are detached and carried away due to strong fluid flow to form slurry. This slurry, consisting of rosette or globular particles, provides less resistance to flow even at a high solid fraction and can easily fill the die-cavity. The stated principle is the basis of a new manufacturing technology called “semi-solid forming” (SSF), in which metal alloys are cast in the semi-solid state. This technique has numerous advantages over other existing commercial casting processes, such as reduction of macrosegregation, reduction of porosity and low forming efforts. Among all currently available methods available for large scale production of semisolid slurry, the cooling slope is considered to be a simple but effective method because of its simple design and easy control of process parameters, low equipment and running costs, high production efficiency and reduced inhomogeneity. With this perspective, the primary objective of the present research is to investigate, both experimentally and numerically, convective heat transfer and solidification on a cooling slope, in addition to the study of final microstructure of the cast billets.
Some key process parameters are identified, namely pouring temperature, slope angle, slope length, and slope cooling rate. A systematic scaling analysis is performed in order to understand the relative importance of the parameters in influencing the final properties of the slurry and microstructure after solidification. A major part of the present work deals with the development of an experimental set up with careful consideration of the range of process parameters involved by treating the cooling slope as a heat exchanger. Subsequently, a comprehensive numerical model is developed to predict the flow, heat transfer, species concentration solid fraction distribution of aluminum alloy melt while flowing down the cooling slope. The model uses a variable viscosity relation for slurry. The metal-air interface at the top during the melt flow is tracked using a volume of fluid (VOF) method. Solidification is modeled using an enthalpy based approach and a volume averaged technique. The mushy region is modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed or fragmented grains. In addition, the solidification model also incorporates a fragmentation criterion and solid phase movement.
The effects of key process parameters on flow behavior involving velocity distribution, temperature distribution, solid fractions at the slope exit, and macrosegregation, are studied numerically and experimentally for aluminium alloy A356. The resulting microstructures of the cast billets obtained from the experiments are studied and characterized. Finally the experimental results are linked to the model predictions for establishing the relations involving interdependence of the stated key process parameters in determining the quality of the final cast products. This study is aimed towards providing the necessary guidelines for designing a cooling slope and optimizing the process parameters for desirable quality of the solidified product.
45
Kund, Nirmala Kumar. "Study Of Solidification And Microstructure Produced By Cooling Slope Method." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2536.
Full textAbstract:
In most casting applications, dendritic microstructure morphology is not desired because it leads to poor mechanical properties. Forced convection causing sufficient shearing in the mushy zone of the partially solidified melt is one of the means to suppress this dendritic growth. The dendrites formed at the solid-liquid interface are detached and carried away due to strong fluid flow to form slurry. This slurry, consisting of rosette or globular particles, provides less resistance to flow even at a high solid fraction and can easily fill the die-cavity. The stated principle is the basis of a new manufacturing technology called “semi-solid forming” (SSF), in which metal alloys are cast in the semi-solid state. This technique has numerous advantages over other existing commercial casting processes, such as reduction of macrosegregation, reduction of porosity and low forming efforts. Among all currently available methods available for large scale production of semisolid slurry, the cooling slope is considered to be a simple but effective method because of its simple design and easy control of process parameters, low equipment and running costs, high production efficiency and reduced inhomogeneity. With this perspective, the primary objective of the present research is to investigate, both experimentally and numerically, convective heat transfer and solidification on a cooling slope, in addition to the study of final microstructure of the cast billets.
Some key process parameters are identified, namely pouring temperature, slope angle, slope length, and slope cooling rate. A systematic scaling analysis is performed in order to understand the relative importance of the parameters in influencing the final properties of the slurry and microstructure after solidification. A major part of the present work deals with the development of an experimental set up with careful consideration of the range of process parameters involved by treating the cooling slope as a heat exchanger. Subsequently, a comprehensive numerical model is developed to predict the flow, heat transfer, species concentration solid fraction distribution of aluminum alloy melt while flowing down the cooling slope. The model uses a variable viscosity relation for slurry. The metal-air interface at the top during the melt flow is tracked using a volume of fluid (VOF) method. Solidification is modeled using an enthalpy based approach and a volume averaged technique. The mushy region is modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed or fragmented grains. In addition, the solidification model also incorporates a fragmentation criterion and solid phase movement.
The effects of key process parameters on flow behavior involving velocity distribution, temperature distribution, solid fractions at the slope exit, and macrosegregation, are studied numerically and experimentally for aluminium alloy A356. The resulting microstructures of the cast billets obtained from the experiments are studied and characterized. Finally the experimental results are linked to the model predictions for establishing the relations involving interdependence of the stated key process parameters in determining the quality of the final cast products. This study is aimed towards providing the necessary guidelines for designing a cooling slope and optimizing the process parameters for desirable quality of the solidified product.
46
Cho, Jae-Ik. "Microsegregation of copper in aluminium casting alloys." 2003. http://www.library.wisc.edu/databases/connect/dissertations.html.
Full text
47
Nguyen, Chuong Luu. "Surface properties and finishing of aluminium casting alloys." 2010. http://hdl.handle.net/2292/5633.
Full textAbstract:
Aluminium alloys are materials of huge practical importance. However their use is dependent on surface oxides and hydroxides which are critical in protecting the highly reactive underlying metal. The stability and integrity of the oxides and hydroxides are also crucial in finishing and bonding applications. Better understanding of these surfaces has significant implications in enhancing their application. LM6 and LM25 aluminium-silicon casting alloys were studied as these materials show a particularly inhomogeneous phase structure and complex surface behaviour. This complexity is of fundamental interest and leads to considerable practical difficulties, especially in surface finishing. The surfaces were characterised, subjected to thermal treatments and modified with Ion Assisted Deposition coatings of TiN. A characterisation method for these surfaces was also developed based around the layered structure of aluminium hydroxides. It was observed that the thermally induced surface segregation of minor elements, such as Mg and Na, is availability-limited. Surface concentrations of these elements are determined by the net effect of enriching via surface segregation and depleting through surface evaporation. The inhomogeneous phase structure of the alloys used in this study enables the observation of two migration processes driven by different forces. Below the oxide dominated surface layer, the migration of Mg is driven by chemical potential gradient and is primarily perpendicular to the surface. Closer to the surface, concentration driven horizontal diffusion of the element occurs. The deposition of a thin TiN layer has been used to probe the interface. While the deposition conditions of TiN coatings affect the chemistry of the coatings, substrate surface conditions determine how well bonding is achieved between the film and substrate. The height difference between silicon particles in the eutectic phase and the primary aluminium phase of the casting alloys provides surface roughening and optimal adhesion through mechanical interlocking with the coating. This height difference is achieved by preferentially removing the surface exposed primary aluminium phases with ion bombardment.
48
Chirita, Georgel. "Mechanical and fatigue properties of functionally graded aluminium silicon alloys." Doctoral thesis, 2011. http://hdl.handle.net/1822/19650.
Full textAbstract:
Tese de doutoramento em Engenharia Mecânica (ramo de conhecimento em Mecânica de Materiais)Many structural components encounter service conditions and, hence, required materials performance, which vary with location within the component. It is well known that abrupt transitions in materials composition and properties within a component often result in sharp local concentrations of stress, whether the stress is internal or applied externally. It is also known that these stress concentrations are greatly reduced if the transition from one material to the other is made gradual. By definition, functionally graded materials are used to produce components featuring engineered gradual transitions in microstructure and/or composition, the presence of which is motivated by functional performance requirements that vary with location within a part. With functionally graded materials, these requirements are met in a manner that optimizes the overall performance of the component. The research on functionally graded materials (FGMs) is encouraged by the need for properties that are unavailable in any single material and the need for graded properties to offset adverse effects of discontinuities for layered materials. Centrifugal casting is a very common method for obtaining functionally graded materials, mainly composite materials or metallic materials which has high differences of density and low solubility on different phases or different materials of the same alloy. The present work is emphasizing the fact that the centrifugal process could be successfully used for obtaining functionally graded materials also for metallic materials (alloys) with moderate solubility and small differences of density of the different phases, as is the case of most aluminum alloys. The first approach of the problem was to isolate the effects of the centrifugal casting technique (the centrifugal pressure effect, the fluid dynamics and the inherent vibration effects) in order to identify the reason of mechanical properties improving. To have a reference for comparison, castings obtained by both centrifugal casting technique and gravity casting technique were tested. To isolate the vibration effect, experimental equipment was designed and constructed in order to be able to cast within a certain level of vibration equivalent with the vibration level of the centrifugal casting equipment. The results are confirming that there is a correlation of improving mechanical properties with the vibration of the melt during solidification. The difference of the mechanical properties of castings obtained by gravity casting technique and by centrifugal casting technique could be explained by the fact that, the vibration due to the inherently vibration of the equipment, the fluid dynamics and the centrifugal pressure make the melt, during solidification, to initiate more nuclei of solidification. Then, the centrifugal pressure moves the nuclei of solidification to the furthest point of the mould (where the pressure is higher) fact that explains the obtained results which are higher on one side of the ingots which corresponds with the side of the mould where the pressure is higher and smaller on the other side where the pressure is smaller. This causes several differences in microstructures in both sides of the ingot. The mechanical and fatigue properties are largely influenced by microstructure and the presence of material inhomogeneities. Pores, inclusions or secondary phase particles are common sites for fatigue crack nucleation in aluminium alloys. The constituent particle’s size and shape are also important characteristics that influence crack nucleation. This study intends to assess also the problem of fatigue life prediction by establishing a relation within some of the characteristics of the micro structural features of studied aluminium silicon alloys such as: micropores, secondary dendrites arm spacing (SDAS), volume fractions of phases (α-Al phase, eutectic and intermetallic phases), the size of silicon lamellas in interdendritic eutectic regions and the size and shape of silicon particles. This evaluation was performed along the ingots gradients for different aluminum alloys.
Muitos componentes estruturais, nas suas condições de serviço, requerem desempenhos que variam com a localização dentro do componente. É sabido que transições bruscas de composição química dos materiais no componente muitas vezes resultam em acentuadas concentrações de tensão locais. É também sabido que estas concentrações de tensões são muito reduzidas/atenuadas se a transição de um material para outro é feita gradualmente. Por definição, materiais com gradiente funcional de propriedades são usados para produzir componentes de engenharia com transições graduais na microestrutura e / ou composição química, cuja presença é motivada por exigências de desempenho funcional, que variam com a localização de cada parte do componente. Com materiais com gradiente funcional, estes requisitos são cumpridos de uma forma que otimiza o desempenho geral do componente. A pesquisa sobre materiais com gradiente funcional (FGMs) é incentivada pela necessidade de propriedades que não estão disponíveis em qualquer material único ou em componentes obtidos pelas junção de partes diferentes materiais onde existe o efeito negativo da sua junção. A fundição centrífuga é um método muito comum para a obtenção de materiais com gradiente funcional, principalmente materiais compósitos ou materiais metálicos, que tem grandes diferenças de densidade e baixa solubilidade em diferentes fases ou em diferentes materiais da mesma liga. O presente trabalho visa enfatizar o fato de que o processo de fundição centrifuga pode ser utilizada com sucesso para a obtenção de materiais com gradiente funcional também para materiais metálicos (ligas) com solubilidade moderada e pequenas diferenças de densidade das diferentes fases, como é o caso da maioria das ligas de alumínio. A primeira abordagem do problema foi isolar os efeitos da técnica de fundição centrífuga (o efeito das pressões centrífugas, a dinâmica dos fluidos e os efeitos da vibração inerente), a fim de identificar o motivo da melhoria das propriedades mecânicas. Para ter uma referência para comparação, foram obtidos e testados provetes de vazamentos por ambas as técnicas, quer de fundição centrífuga quer de fundição por gravidade. Para isolar o efeito da vibração, um equipamento experimental foi projetado e construído de modo a ser capaz de reproduzir um determinado nível de vibração equivalente ao nível de vibração do equipamento de fundição centrífuga. Os resultados confirmam que há uma correlação entre a melhoria das propriedades mecânicas com a vibração da liga durante a solidificação. A diferença das propriedades mecânicas de peças fundidas obtidas pela técnica da gravidade e pela técnica de fundição centrífuga poderia ser explicada pela vibração inerente do sitema, pela dinâmica dos fluidos e pel pressão centrífuga, que originam, durante a solidificação, mais núcleos/germens de solidificação. A pressão centrífuga move os núcleos de solidificação para o ponto mais afastado do eixo de rotação (onde a pressão é maior) que explica que os resultados obtidos são mais elevados nessa zona do que do lado mais próximo do eixo de rotação, que corresponde ao lado do molde em que a pressão é menor. Isto causa substanciais diferenças de microestrutura e mambos os lados dos lingotes. As propriedades mecânicas e de fadiga são grandemente influenciadas pela microestrutura assim como pela presença de inomogeneidades no material. Poros, inclusões ou partículas de fases secundárias são responsáveis pela nucleação de fendas de fadiga em ligas de alumínio. O tamanho das partículas e a sua forma são também características importantes que influenciam a nucleação da fenda. Este estudo pretende avaliar a previsão da vida à fadiga através de correlações com características microestruturais das ligas de alumínio-silício estudadas tais como: microporos, espaçamento entre braços das dendrites (SDAS), frações volumicas de fases ou constituintes( α primária, eutético e intermetálicos), a espessura das lamelas do silicio eutéctico e dimensões de partículas de silicio eutéctico. Esta avaliação é feita para diferentes diferentes zonas ao longo do gradiente de propriedades dos lingotes das diferentes ligas de alumínio.
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Apoorva, *. "Microstructure Evolution In Semisolid Processing." Thesis, 2011. https://etd.iisc.ac.in/handle/2005/2382.
Full textAbstract:
In this thesis, we present an experimental and numerical study of globularization during reheating of thixocast billet having non-dendritic microstructure. The process of reheating is an important step in the semisolid processing and is essential to control its microstructure and hence its mechanical properties. Material chosen for this study is Aluminum alloy, A356. The primary focus of this study is the heat treatment below eutectic temperature i.e. transformation in solid phase. It is found that during short duration heat treatment, globularization of primary α grains and spheroidization of eutectic Si flakes take place which improves the mechanical properties of semisolid cast products significantly. A prolonged heat treatment is found to degrade the properties of castings since it enhances the porosity and coarsening of Si. The study suggests that a precise heat treatment practice can be designed to improve the semisolid microstructure. A computational model based on Phase field approach has been proposed to study this phenomena. Predictions based on this model are qualitatively compared with corresponding experimental observations. Since eutectics form an important step in multiphase solidification, an attempt has been made to develop an enthalpy based explicit micro-scale model for eutectic solidification. In this preliminary study, growth of adjacent α and β phases in a two dimensional Eulerian framework has been simulated. The model is qualitatively validated with Jackson Hunt theory. Results show expected eutectic growth. This methodology promises significant saving in computational time compared to existing numerical models.
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Apoorva, *. "Microstructure Evolution In Semisolid Processing." Thesis, 2011. http://etd.iisc.ernet.in/handle/2005/2382.
Full textAbstract:
In this thesis, we present an experimental and numerical study of globularization during reheating of thixocast billet having non-dendritic microstructure. The process of reheating is an important step in the semisolid processing and is essential to control its microstructure and hence its mechanical properties. Material chosen for this study is Aluminum alloy, A356. The primary focus of this study is the heat treatment below eutectic temperature i.e. transformation in solid phase. It is found that during short duration heat treatment, globularization of primary α grains and spheroidization of eutectic Si flakes take place which improves the mechanical properties of semisolid cast products significantly. A prolonged heat treatment is found to degrade the properties of castings since it enhances the porosity and coarsening of Si. The study suggests that a precise heat treatment practice can be designed to improve the semisolid microstructure. A computational model based on Phase field approach has been proposed to study this phenomena. Predictions based on this model are qualitatively compared with corresponding experimental observations. Since eutectics form an important step in multiphase solidification, an attempt has been made to develop an enthalpy based explicit micro-scale model for eutectic solidification. In this preliminary study, growth of adjacent α and β phases in a two dimensional Eulerian framework has been simulated. The model is qualitatively validated with Jackson Hunt theory. Results show expected eutectic growth. This methodology promises significant saving in computational time compared to existing numerical models.