Dissertationen zum Thema „Aluminum castings. Metals“

Dissertation (Ph.D.)--Worcester Polytechnic Institute.
Keywords: Time-Temperature-Property curve, Jominy End Quench, ANOVA analysis. Quench Factor Analysis, Taguchi design, Polymer quench, Cast Al-Si-Mg alloys, Quenching, Heat treatment. Includes bibliographical references (p.115-117).

Thesis (Ph. D.)--Worcester Polytechnic Institute.
Keywords: Microstructure; Elastic-Plastic Fracture Mechanics; Crack closure; A356; J-integral; Conventionally cast and SSM Al-Si-Mg alloys; Residual stress; Heat treatment; Fatigue crack growth mechanisms; Threshold stress intensity factor; Plastic zone; Paris law; Fracture toughness; Roughness. Includes bibliographical references.

Thesis (M.S.)--Worcester Polytechnic Institute.
Keywords: microstructure; casting; Fluid Bed; Quality Index; Aluminum; A356; heat treatment; SSM; Semi Solid Metal Includes bibliographical references. (p.105-106)

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

Properties of cast aluminum components can be improved by strategically placing ferrous inserts to locally improve properties such as wear resistance and stiffness. A cost-effective production method is to cast-in the insert using the solidification of the molten aluminum as a joining method. Metallurgically bonding between the metals could potentially improve both load and heat transfer across the interface. The metallurgical bond between the steel and the aluminum has to be strong enough to withstand stresses related to solidification, residual stresses, thermal expansion stresses, and all other stresses coupled with the use of the component. Formation of a continuous defect free bond is inhibited by the wetting behavior of aluminum and is governed by a diffusion process which requires both energy and time. Due to the diffusional nature of the bond growth in combination with post manufacturing heat treatments defects such as Kirkendall voids can form. The effect of aluminum alloying elements during liquid-solid bond formation in regards to microstructural changes and growth kinetics has been described. A timeframe for defect formation during heat treatments as well as microstructural changes has been established. The effect of low melting point coatings (zinc and tin) on the nucleation of the metallurgical bond has been studied as well the use of a titanium coating for microstructural modification. A set of guidelines for successful metallurgical bonding during multi- material metal casting has also been constructed.

The aim of this study was to produce partially reinforced aluminum metal matrix composite components by insertion casting technique and to determine the effects of silicon content, fiber vol% and infiltration temperature on the mechanical properties of inserts, which were the local reinforcement parts of the components. Silicon content of alloys was selected as 7 wt% and 10 wt%. The reinforcement material, i.e. Saffil fiber preforms, had three different fiber vol% of 20, 25 and 30 vol% respectively. The infiltration temperatures of composite specimens were fixed as 750 °
C and 800 °
C. In the first part of the thesis, physical and mechanical properties of composite specimens were determined according to the parameters of silicon content of the matrix alloy, infiltration temperature and vol% of the reinforcement phase. X-ray diffraction examination of fibers resulted as the fibers mainly composed of deltaalumina fibers and scanning electron microscopy analyses showed that fibers had planar isotropic condition for infiltration. Microstructural examination of composite specimens showed that appropriate fiber/matrix interface was created together with small amount of micro-porosities. Bending tests of the composites showed that as fiber vol% increases flexural strength of the composite increases. The highest strength obtained was 880.52 MPa from AlSi10Mg0.8 matrix alloy reinforced with 30 vol% Saffil fibers and infiltrated at 750 °
C. Hardness values were also increased by addition of Saffil fibers and the highest value was obtained as 191 HB from vertical to the fiber orientation of AlSi10Mg0.8 matrix alloy reinforced with 30 vol% Saffil fibers. Density measurement revealed that microporosities existed in the microstructure and the highest difference between the theoretical values and experimental values were observed in the composites of 30 vol% Saffil fiber reinforced ones for both AlSi7Mg0.8 and AlSi10Mg0.8 matrix alloys. In the second part of the experiments, insertion casting operation was performed. At casting temperature of 750 °
C, a good interface/component interface was obtained. Image analyses were also showed that there had been no significant fiber damage between the insert and the component.

The aim of the present study was to investigate the effects of different levels of Saffil alumina fiber addition, magnesium content in aluminum alloy matrix and casting temperature on the mechanical behavior, microstructure and physical properties of short fiber reinforced aluminum matrix composites. The main alloying element silicon was kept constant at 10 wt%. Magnesium contents were selected as 0.3 wt% and 1 wt%. Saffil alumina fiber preforms varied from 10 to 30 vol%. The casting temperatures were fixed at 750 °
C and 800 °
C. Micro porosity was present at the fiber-fiber interactions. Closed porosity of the composites increased when fiber vol% increased, however, variation in casting temperature and magnesium content in matrix did not have influence on porosity. Hardness of the composites was enhanced with increasing fiber vol%, magnesium content in matrix and decreasing casting temperature. Alignment of fibers within the composite had an influence on hardness
when fibers were aligned perpendicular to the surface, composites exhibited higher hardness. The highest hardness values obtained from surfaces parallel and vertical to fiber orientation were 155.6 Brinell hardness and 180.2 Brinell hardness for AlSi10Mg1 matrix 30 vol% alumina fiber reinforced composite cast at 800 °
C and at 750 °
C, respectively. 30 vol% Saffil alumina fiber reinforced AlSi10Mg0.3 matrix composite cast at 750 °
C showed the highest flexural strength which is 548 MPa. Critical fiber content was found as 20 vol% for all composites.

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.

This study is on the production and testing of an aluminum metal matrix composite. Metal Matrix Composites can be produced in several different ways. In this study, an aluminum matrix composite is produced by direct addition of the reinforcement ceramic into the liquid metal. The ceramic reinforcement for this process was a mixture of TiB2 and Al2O3 which was produced by means of a thermite reaction of reactants Al, B2O3 and TiO2 all in powder form with their respective stoichiometric amounts. This ceramic mixture was ground to fine powder size and then added to liquid aluminum in small percentages. After casting and taking samples of unreinforced alloy and reinforced alloys, their tensile strength and hardness as material properties were measured and compared. Another issue is the wetting of ceramic particles by molten Aluminum. The aim of the experiments in general is to find a better way to produce a composite material with desired mechanical properties.

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 iii 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.

Orientador: Maria Helena Robert
Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-18T15:19:59Z (GMT). No. of bitstreams: 1 Pinheiro_FrancioniGomes_M.pdf: 4724053 bytes, checksum: 96f025d7f0e3e288c1b9b2379de497e9 (MD5) Previous issue date: 2011
Resumo: Este trabalho tem por objetivo avaliar a viabilidade técnica da fabricação e utilização do componente de motor (espaçador do ventilador) empregando tecnologia de materiais celulares. Foi empregado processo de tixoinfiltração em pré-formas pós-removíveis de NaCl em estado livre, tendo como matéria prima a mesma liga A356.0 da peça atual (fabricada por fundição convencional). Foi projetada e construída uma nova matriz metálica para se adaptar ao novo tipo de processo. Foram analisados parâmetros de processo como a granulometria do agente bloqueador (NaCl), a proporção da liga e do agente bloqueador e a distribuição de massa do alumínio disposto na matriz. Análises da qualidade dos componentes porosos e dos benefícios na manufatura demonstraram que o processo de tixoinfiltração é tecnicamente viável, com a obtenção de produtos com peso da ordem de 50% do peso do produto convencional, e dimensões finais adequadas, eliminando processos de usinagem e reduzindo tempo de fabricação do componente. Testes de montagem e funcional demonstraram bom desempenho quando submetido às condições de compressão exercidas na montagem e em teste preliminar em motor em funcionamento. Conclui-se que o processo é viável, que produtos mais leves podem ser obtidos em menor tempo de fabricação, mas ajustes visando maior resistência à compressão são necessários e servem como sugestão para futuros estudos
Abstract: This study aims to evaluate the feasibility of the manufacturing and utilization of an engine component (spacer fan) produced by cellular materials technology. The process used was thixoinfiltration of the alloy A356.0 into pre-forms of loose NaCl particles. This alloy is currently used for the production of the conventional cast parts. It was design and built a new metallic tooling to fit the new process. Process parameters were analyzed as the particle size of the space holder (NaCl), the ratio of metal/space holder weight content and the alloy mass distribution inside the metallic tooling. Analysis of the quality of porous parts produced and the benefits in the new process for their manufacture showed that the thixoinfiltration process is technically feasible, resulting products with 50% lowest weight if compared with current cast part and with near net shape, eliminating machining operations and reducing the manufacturing time. Assembly and functional tests showed good performance of the porous part when submitted to conditions of compression, due to assembly and preliminary engine running test. It is possible to conclude that the thixoinfiltration process is feasible, lighter products with reduced manufactuing time can be obtained, but further process adjustments to aim compression resistance are necessary and it is left here as a suggestion for future studies
Mestrado
Manufatura
Mestre em Engenharia Automobilistica

Composites have been developed with great success by the use of fiber reinforcements in metallic materials. Fiber reinforced metal matrices possess great potential to be the next generation of advanced composites offering many advantages compared to fiber reinforced polymers. Specific advantages include high temperature capability, superior environmental stability, better transverse modulus, shear and fatigue properties. Although many Metal Matrix Composites (MMCs) are attractive for use in different industrial applications, Aluminium Matrix Composites (AMCs) are the most used in advanced applications because they combine acceptable strength, low density, durability, machinability, availability, effectiveness and cost. The present study focuses on the fabrication of aluminium matrix composite plates by squeeze casting using plain weave carbon fiber preform (AS4 Hexcel) as reinforcement and a matrix of wrought aluminium alloy 1235-H19. The objective is to investigate the process feasibility and resulting materials properties such as hardness at macro- and micro-scale, impact and bend strength. The properties obtained are compared with those of 6061/1235-H19 aluminium plates that were manufactured under the same fabrication conditions. The effect of fiber volume fraction on the properties is also investigated. Furthermore, the characterization of the microstructure is done using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) in order to establish relationships between the quality of the fiber/aluminium interface bond and mechanical properties of the composites. In conclusion, aluminium matrix composite laminate plates were successfully produced. The composites show a good chemical bond between the fiber and the aluminium matrix. This bond resulted from heterogeneous precipitation of aluminium carbides (Al4C3) at the interface between aluminium matrix and carbon fiber. The hardness at macro- and micro-scale of the composites increases by over 50% and the flexural modulus increases by about 55%. The toughness of the composite decreases due to the presence of brittle phases which can be improved by better oxidation prevention. Also, an optimal carbon volume fraction was observed that provides optimal properties including peak hardness, peak stiffness and peak toughness.

Foundry aluminum alloys play a fundamental role in several industrial fields, as they are employed in the production of several components in a wide range of applications. Moreover, these alloys can be employed as matrix for the development of Metal Matrix Composites (MMC), whose reinforcing phases may have different composition, shape and dimension. Ceramic particle reinforced MMCs are particular interesting due to their isotropic properties and their high temperature resistance. For this kind of composites, usually, decreasing the size of the reinforcing phase leads to the increase of mechanical properties. For this reason, in the last 30 years, the research has developed micro-reinforced composites at first, characterized by low ductility, and more recently nano-reinforced ones (the so called metal matrix nanocomposite, MMNCs). The nanocomposites can be obtained through several production routes: they can be divided in in-situ techniques, where the reinforcing phase is generated during the composite production through appropriate chemical reactions, and ex situ techniques, where ceramic dispersoids are added to the matrix once already formed. The enhancement in mechanical properties of MMNCs is proved by several studies; nevertheless, it is necessary to address some issues related to each processing route, as the control of process parameters and the effort to obtain an effective dispersion of the nanoparticles in the matrix, which sometimes actually restrict the use of these materials at industrial level. In this work of thesis, a feasibility study and implementation of production processes for Aluminum and AlSi7Mg based-MMNCs was conducted. The attention was focused on the in-situ process of gas bubbling, with the aim to obtain an aluminum oxide reinforcing phase, generated by the chemical reaction between the molten matrix and industrial dry air injected in the melt. Moreover, for what concerns the ex-situ techniques, stir casting process was studied and applied to introduce alumina nanoparticles in the same matrix alloys. The obtained samples were characterized through optical and electronic microscopy, then by micro-hardness tests, in order to evaluate possible improvements in mechanical properties of the materials.

High Pressure Die Casting (HPDC) is low-cost technique for the mass production of complex, non-ferrous parts. Despite its benefits such as dimensional accuracy, surface quality and high production rate
some mechanical drawbacks limit use of HPDC in production of critical parts especially under dynamical loads. This study aims to improve impact resistance and surface hardness of die cast parts by means of tool steel inserts. These inserts act as a barrier between the impactor and die casting alloy, in order to avoid surface deformation and reduce stress localization which leads crack formation. Except the impact surface, whole insert is embedded into the die casting alloy by placing them on specially machined die casting molds prior to the metal injection. The mentioned method was evaluated by mechanical test and micro-examinations which were applied on AISI D2 tool steel inserted A518.0, A413.2 and Zamak5 alloy samples. To see the effect of inserts on energy absorbance under single destructive loads, both monolithic (conventional) and inserted (produced by mentioned technique) samples were subjected to Charpy impact test. In order to observe its behavior under non-destructive, cyclic, low velocity impacts
a dedicated real rifle part was produced by this method and tested in the real service loads. Explicit Finite Elemental Analysis was also carried out to understand how the inserts increases the energy absorbance and protect the die cast body by simulating both destructive and non-destructive impact loads. In addition to these, micro-examinations were also conducted especially on insert-die casting alloy interface for chemical and physical interactions, defects and stability. In regards of experimental findings, mechanical feasibility of the method was achieved. It was proved that steel inserts improve energy absorbance, stress distribution and impact-surface hardness of die cast products.

Manufacturers of cast metal parts are interested in the development of a feedback control system for use with the Precision Sand-Casting (PSC) process. As industry demands the ability to cast more complex geometries, there are a variety of challenges that engineers have to address. Certain characteristics of the mold, such as thick-to-thin transitions, extensive horizontal or flat surfaces, and sharp corners increase the likelihood of generating defective casts due to the turbulent metal-flow during fills. Consequently, it is critical that turbulent flow behavior within the mold be minimized as much as possible. One way to enhance the quality of the fill process is to adjust the flow rate of the molten metal as it fills these critical regions of the mold. Existing systems attempt to predict the position of the metal level based on elapsed time from the beginning of the fill stage. Unfortunately, variability in several aspects of the fill process makes it very difficult to consistently predict the position of the metal front. A better approach would be to embed a sensor that can detect the melt through a lift-off distance and determine the position of the metal-front. The information from this sensor can then be used to adjust the flow rate of the aluminum as the mold is filled. This thesis presents the design of a novel non-invasive sensor monitoring system. When deployed on the factory floor, the sensing system will provide all necessary information to allow process engineers to adjust the metal flow-rate within the mold and thereby reduce the amount of scrap being produced. Moreover, the system will exhibit additional value in the research and development of future mold designs.

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.

Published Article
This paper is based on tests performed on die component specimens manufactured by EOS-DMLS (direct metal laser sintering) and LENS (laser engineered net shape) RP (rapid prototyping) technology platforms, as well as manufactured specimens machined out of preferred standard hot work steel DIN 1.2344. These specimens resemble typical components used in metal high pressure die casting tool sets. The specimens were subjected to a programme of cyclic immersion in molten aluminium alloy and cooling in water-based die release medium. The heat checking and soldering phenomena were analyzed through periodic inspections, monitoring crack formation and evidence of surface washout. At the end of the thermal tests, mechanical strength and hardness tests were performed to assess toughness and core resistance variations in relation to the initial conditions. Finally metallographic investigations were performed through optical microscopy on all the specimens considered. The outcomes of this research will be presented and used by the CSIR for further development and application of the assessed EOS-DMLS and LENS rapid prototyping technologies in rapid die manufacturing techniques and die design principles, including time and economic feasibility criteria to be applied when considering rapid die manufacture.

The aim of this study is to investigate the mechanical behavior and its relation with processing and microstructure of the silicon carbide particulate (SiCp) reinforced aluminum matrix composite. Aluminum 7075 alloy is chosen as matrix alloy, in which zinc is the main alloying element. Four different additions of SiCp were used and the weight fractions were 10%, 15%, 20% and 30%. Composites were processed by with squeeze casting and the applied pressure during casting was 80 MPa. The mould is specially designed to produce both specimens ready for tensile and three point bending tests. Both as-cast and heat treated aluminum composites were examined and T6 heat treatment was applied. Three point bending tests were performed to reveal the fracture strength of aluminum composites. 10wt% SiCp aluminum composites showed the maximum flexural strength in both as-cast and heat treated composites. The mechanical test results revealed that precipitated phases in heat treated composites, behaved like fine silicon carbide particulates and they acted as barriers to dislocation motion. Maximum flexural strength increased about 40 MPa (10%) in as-cast and 180 MPa (44%) in heat treated composites. Tensile testing was also conducted to verify the results of the three point bending tests. Hardness tests were done to find the effect of silicon carbide addition and to find the peak hardness in heat treatment. For as-cast specimens hardness values increased from 133 to 188 Vickers hardness (10 kg.) with increase in SiCp content from 0 to 30wt% and for heat treatment specimens hardness values increased from 171 to 221 Vickers hardness (10 kg.). The peak hardness values were obtained at 24 hours precipitation heat treatment. SEM studies were carried out to examine the heat treated composites, to take SEM photographs and to obtain a general elemental analysis. Theoretical volume percentage addition of SiCp was checked with Clemex Image Analyzer program. Distribution of SiCp was determined by mettalographic examination. Second phases that were formed during heat treatment was searched by x-ray analysis.

During World War I, Otto Meyer invented the alloy Fritzi metal, and the composition died with him. However,  there  are  descriptions  of  the  alloy's properties.  Previously,  an  attempt  to  identify  the composition  was  made, resulting  in  simulated  properties  that  did not match those described. In this project, Thermo-Calc simulations concerning solidus and liquidus temperatures were conducted, and combined  with  previous  research  on  the  Al-Zn-Cu system. These  suggested  that  the  composition 75Al20Zn5Cu  wt%  (weight percent) would  be  a  closer  match  for  the  description,  especially  if considering  that the stated melting temperature may have been the pouring temperature. In addition, density  tests  and  calculations  found  the  alloy significantly  lighter than  described.  However,  the description  was  possibly not  literal.  With  a selected  composition,  casting  trials,  hardness  and weldability  tests  followed. The  alloy  was  found  easy  to  cast  with  and sufficiently  hard  for  its application.  Welding  the  material  proved  to  be possible if the correct method, pulsed direct current, was  used.  In  the  end,  the  proposed  alloy  was  similar to  the  description,  and  potential explanations were made for the remaining differences.
Under  första  världskriget  uppfann  Otto  Meyer  legeringen  Fritzimetall,  och sammansättningen  dog med  honom.  Däremot  finns  beskrivningar  av legeringens egenskaper. Tidigare gjordes ett försök att identifiera sammansättningen,  vilket  resulterade  i  simulerade  egenskaper  som  inte matchade  de beskrivna.   I   detta   projekt   gjordes   simuleringar   i   Thermo-Calc   av   solidustemperatur   och liquidustemperatur,  vilka kombinerades med tidigare forskning på Al-Zn-Cu-systemet. Sammantaget såg   det   ut   som   sammansättningen   75Al20Zn5Cu   wt%   (viktprocent)   skulle   vara   närmare beskrivningarna,   särskilt   om   man   överväger   att   den   beskrivna   smälttemperaturen   kan   vara gjuttemperaturen.  Dessutom  fann  test  och beräkningar  kring  densiteten  att  legeringen  var  avsevärt lättare  än  den beskrevs som. Det är dock möjligt att beskrivningen inte var bokstavlig. Med en vald sammansättning följde av gjutförsök, hårdhetstest och svetsbarhetstest. Legeringen fanns vara lätt att gjuta  med  och  hård nog för tillämpningen. Att svetsa materialet visade sig vara möjligt med korrekt metod, pulserad likström. I slutändan liknade den föreslagna legeringen beskrivningarna, och möjliga förklaringar gjordes för de kvarvarande skillnaderna.

Aluminum alloys are having more attention due to their high specific stiffness and processing advantages. 7075 aluminum alloy is a wrought composition aluminum alloy in the Al-Zn-Mg-Cu series. Due to the significant addition of these alloying elements, 7075 has higher strength compared to all other aluminum alloys and effective precipitation hardenability characteristic. On the other hand, aluminum alloys have some drawbacks, which hinder the widespread application of them. One of the most commonly encountered defects in aluminum alloys is the hydrogen porosity. Additionally, in case of 7075, another problem is the lack of fluidity. Magnesium addition is thought to be effective in compensating this deficiency. Accordingly, in this study, die cast 7075 aluminum alloy samples with hydrogen porosity and additional magnesium content were investigated. The aim was to determine the relationship between hydrogen content and hydrogen porosity, and the effects of hydrogen porosity, additional magnesium and T6 heat treatment on ultimate tensile and flexural strength properties of pressure die cast 7075 aluminum alloy. 7075 aluminum alloy returns were supplied from a local pressure die casting company. After spectral analysis, pressure die casting was conducted at two stages. In the first stage, 7075 aluminum alloy with an increase in magnesium concentration was melted and secondly 7075 aluminum alloy was cast directly without any alloying addition. While making those castings, hydrogen content was measured continuously before each casting operation. As a final operation T6 heat treatment is carried out for certain samples. Finally, in order to accomplish our aim, mechanical and microstructural examination tests were conducted.

The Master’s thesis was conducted under the project FR-TI1/070 “Optimalization of heavy steel casting manufacture” in cooperation with ŽĎAS a. s. foundry. It evaluates rate of conchoidal fracture in samples extracted from experimental castings. The testing bar for the static tensile test were extracted from thermal axis of casting. The research part describes ways of deoxidating the liquid metal and usage of separate deoxidating chemical parts, followed by summary of research knowledge on conchoidal fractures. In the practical part, the process of sample evaluation is described. The conchoidal fracture, the surface of which was evaluated on the fracture surfaces, influences mechanical qualities of cast steel. Simultaneously, impacts of metallurgical factors on rate of conchoidal fracture were examined

L'objectif de cette thèse était de développer et de caractériser la microstructure et les propriétés mécaniques des céramiques bio-inspirées. L'alumine inspirée par la nacre fabriquée par texturation à la glace (freeze-casting), précédemment développée dans le cadre de la thèse de F. Bouville, a été choisie comme matériau de référence. La simplification et le changement d’échelle du procédé d’élaboration des matériaux ont été étudiés. Le procédé sophistiqué de freeze-casting a été remplacé par le pressage uniaxial à cru. Les mesures de diffraction des électrons rétrodiffusés ont confirmé le bon alignement après frittage des plaquettes d'alumine utilisées pour préparation du matériau. Le cycle de frittage assisté par effet de champs a été adapté à de plus grandes quantités de poudre céramique et d'additifs organiques. La deuxième partie du projet a été consacrée à la modification de l'interphase entre les plaquettes d'alumine, afin d’améliorer les propriétés mécaniques du matériau. Diverses possibilités ont été explorées: ajout de poudre de zircone, dépôt de zircone sur les plaquettes par réaction sol-gel ou substitution de la phase vitreuse par du graphène. Tous les matériaux obtenus ont été caractérisés par flexion quatre points sur des barrettes entaillées. La troisième partie de cette étude a porté sur le développement de composites multicouches métal/céramique, par frittage simultané d'alumine et de titane. L'épaisseur et la composition de la feuille de titane ont été modifiées pour étudier leur influence sur les phénomènes de diffusion lors du frittage. Les composites ont été caractérisés par MEB, EBSD, spectroscopie à rayons X à dispersion d'énergie et tomographie à rayons X au synchrotron. La fabrication simplifiée des matériaux permet de préparer des échantillons de plus grandes dimensions de céramiques inspirées par la nacre, sans passer par une étape de freeze-casting. Cependant, la croissance des grains doit être limitée pour maintenir de bonnes propriétés mécaniques. La modification de l'interphase entre les plaquettes d'alumine n'a pas amélioré les propriétés mécaniques des matériaux par rapport au matériau de référence. D'autre part, le dépôt de nano-zircone sur la surface des plaquettes semble prometteur et devrait faire l'objet d'études plus poussées. Dans le cas des composites alumine/titane, les composites architecturées multiéchelles ont été fabriqués de manière assez simple. Cependant, il est crucial d'éviter la fissuration des feuilles de métal afin d’améliorer les propriétés mécaniques
The goal of this thesis was to develop and characterize the microstructure and the mechanical properties of bioinspired ceramic composites. Nacre-like alumina fabricated by freeze-casting previously developed in Bouville thesis was chosen as a reference material. Simplifying and up-scaling material fabrication was intended. Architectural levels were added to the microstructure to further improve mechanical properties of the material. Sophisticated processing by freeze-casting was substituted by uniaxial pressing. Electron backscatter diffraction observations confirmed the good alignment of alumina platelets used to prepare the material. The field assisted sintering cycle was adapted to greater quantities of ceramic powder and organic additives. The second part of the project was dedicated to the modification of the interphase between alumina platelets. Various possibilities were explored: adding fine zirconia powder, depositing zirconia on the platelets by sol-gel reaction, or substituting the glassy phase by graphene. All obtained materials were characterized by four point bending on notched bars. The third part of this study was focused on the development of multilayered metal/ceramic composites, by simultaneous sintering of alumina and titanium. The titanium foil thickness and composition were varied. The composites were characterized by SEM, EBSD, energy dispersive X-ray spectroscopy and synchrotron X-ray tomography. Detailed microstructural and chemical characterization was performed to understand mechanisms of titanium diffusion into ceramic matrix. Simplified material fabrication allows to prepare larger samples of nacre-like ceramics. However grain growth should be limited to maintain good mechanical properties. Modification of the interphase between alumina platelets did not improve mechanical properties of the materials as compared to the reference material. On the other hand, depositing nano-zirconia on platelets surface seems promising and should be further investigated. In case of alumina/titanium composites, a multiscale architecture composites were process in a rather simple way. However, avoiding metal foil cracking is crucial to improve mechanical properties

Indiana University-Purdue University Indianapolis (IUPUI)
Aluminum extrusion is a metal forming process used for the production of a large variety of solid, semi-solid and complex hollow products. During extrusion, the hot aluminum billet goes under severe plastic deformation as it is forced to flow through a smaller die cavity that defines the final shape of the extruding product. Surface finish and dimensional accuracy are the two most important criteria that specify the productivity and feasibility of the extrusion process which is highly influenced by the flow of aluminum through the deforming die. Therefore, die design is considered as one of the most important characteristics of the extrusion process that influences aluminum flow, quality of the extruding product and its dimensional accuracy. Currently, development of extrusion dies is primarily based upon the empirical knowledge of the die designer gained through trial and error, which inevitability is an expensive, time consuming and ineffective method. However, owing to the technological advancements of this century in the field of finite element modeling, this decade old trial and error method can now be replaced by numerical simulations that not only save time and money but also, can accurately predict the flow of aluminum through a die as well as predict die deformation occurring during the extrusion process The motivation of this research project came from a private extrusion die manufactures need for improving their pioneered modular die based on good analytical and scientific understanding of the dies performance during the extrusion process. In this thesis, a commercial simulation package Deform 3D is used to simulate the thermo-mechanical interactions of aluminum flow through the deforming modular die for the production of Micro Multi-Port (MMP) tubes.

Manufacturing of light-weight materials is associated with several types of casting defects during solidification. Porosity defects are common, especially in aluminum and its alloys, which initiate crack propagation and thereby cause drastic deterioration in the mechanical properties. These defects, classified as micro and macro defects (based on their sizes), are mainly governed by release of hydrogen into the liquid at the solid-liquid interface, which triggers the nucleation and growth of hydrogen bubbles in the melt. Subsequently, these bubbles interact with solidifying interfaces such as dendritic arms and eutectic fronts, leading to the formation of pores. Macroscopic defects in the form of voids are created due to solidification shrinkage. The primary focus of the present work is to develop phenomenological models for the evolution of microporosity and microstructures during solidification. The issues outlined above typically occur in multi-phase environments comprising of solid, liquid and gaseous phases, and over a range of length and time scales. Any phenomenological prediction would, therefore, require a multi-phase-scale approach. Principles of volume averaging are applied to equations of conservation to obtain single-field formulations. These are then solved with appropriate interface tracking techniques such as Enthalpy, Level-set, Volume-of-fluid and Immersed-boundary methods. The framework is built up on a standard pressure based incompressible fluid flow solver (SIMPLER algorithm) and coupled modeling strategies are proposed to address the interfacial dynamics. A two-dimensional framework is considered with a fixed-grid Cartesian co-ordinate system. Scaling analyses are performed to bring out the relative effects of various competing parameters in order to obtain further insights into this complex phenomenon. The numerical results and scaling predictions are validated against experimental observations published in literature. In literature, numerical predictions of microporosity mainly include criteria based models based on empirical relations and deterministic/stochastic models based on diffusion driven growth assuming spherical bubbles. The dynamic evolution of non-spherical bubble-metal interface in a three-phase system is yet to be captured. Moreover, several in-situ experiments have shown elongated bubble shapes during the engulfment phase, therefore a criterion to define the dependence on cooling rates and the resulting bubble morphology can possibly deliver further practical insights. We propose a numerical model for hydrogen bubble growth, its movement and subsequent engulfment by a solidifying front, combining the features of level-set and enthalpy methods for tracking bubble-metal and solid-liquid interfaces, respectively. The influx of hydrogen into heterogeneously nucleated bubbles results in growth of bubbles to sizes up to a few hundreds of microns. In the first part of this numerical study, a methodology based on the level-set approach is developed to simultaneously capture hydrogen bubble growth and movement in liquid aluminum. The solidification is first assumed to occur outside the micro-domain providing a specified hydrogen influx to the bubble-in-liquid system. The level-set equation is formulated in such a way as to account for simultaneous growth and movement of the bubble. The growth of a bubble with continuous and fixed hydrogen levels in the melt is studied. The rates of growth of bubble-liquid and solidifying interfaces are compared using an order of magnitude analysis. This scaling analysis explains the thought experiment proposed in the literature, where difference in bubble shapes was attributed to the cooling rate. Moreover, it shows explicit dependence on bubble radius and cooling rate leading to a new criterion for bubble elongation proposed in this thesis. This also highlights the comparison between solidification and hydrogen diffusion time-scales which primarily govern the competitive growth behavior. The bubble-in-liquid model is coupled with microscopic enthalpy method to incorporate effects of solidification and study the interaction of solid-liquid and bubble-liquid interfaces. The phenomena of bubble engulfment and elongation are successfully captured by the proposed model. A parametric study is carried out to estimate the bubble elongation based on different initial bubble sizes and varying cooling rates encountered in typical sand, permanent mold and die casting processes. Although simulation of microstructures has been extensively studied in the literature, very few models address the phenomena of simultaneous growth and movement of equiaxed dendrites. The presence of different flow environments and multiple dendrites are known to alter the position and shape of the dendrites. The proposed model combines the features of the following methods, namely, the Enthalpy method for modeling growth; the Immersed Boundary Method (IBM) for handling the rigid solid-liquid interfaces; and the Volume of Fluid (VOF) method for tracking the advection of the dendrite. The algorithm also performs explicit-implicit coupling between the techniques used. Validation with available literature is performed and dendrite growth in presence of rotational and buoyancy driven flow fields is studied. The expected transformation into globular microstructure in presence of stirring induced flows is successfully simulated. A simple order estimate for time required for stirring is performed which agrees with numerical predictions. In buoyancy driven environment of a settling dendrite, the arm tip speeds show expected higher velocity of the upstream tip compared to its counterpart. The model is extended to study thermal and hydrodynamic interactions between multiple dendrites with appropriate considerations for different orientations and velocities of the dendritic solid entities. The present model can be used for the prediction of grain sizes and shapes and to simulate morphological transformations due to different melt flow scenarios. In the final part, the methodology presented for growth and engulfment of hydrogen bubbles is extended to study the phenomenon of diffusion driven bubble growth occurring in direct foaming of metals. The source of hydrogen is determined by the rate of decomposition of the blowing agent. This is accounted for by a source term in the hydrogen species conservation equation, and growth rate of hydrogen bubbles is calculated on the basis of diffusive flux at the interface. The level-set method is used for tracking the bubble-liquid interface growth, and the macroscopic enthalpy model is used for obtaining heat transfer and solid front position. The model is validated with analytical solution by comparing the front position and the solidification time. The variation of foam density with a transient hydrogen generation source is studied and qualitatively compared with results reported in literature. The modeling strategies proposed in this work are generic and therefore have potential in simulating a variety of complex multi-phase problems.

A hot chamber die casting machine designed for zinc was donated to Purdue University. This machine was slated for retrofit of components necessary for aluminum hot chamber die casting. Existing components designed for zinc, mainly H-13 and cast iron, do not have the necessary service life to economically produce castings due to chemical attack on machine components from molten aluminum. Multiple systems were redesigned, including the pot, plunger, gooseneck, furnace, and cooling lines. All components were upgraded to allow for the higher service temperatures needed for molten aluminum, along with a niobium gooseneck and anviloy nozzle to resist chemical attack of injection components. Once design and retrofitting were complete aluminum alloy A380 was used in conjunction with a niobium gooseneck design to create tensile bars. These tensile bars were subsequently tested and mechanical properties evaluated.

Aluminum-Silicon (Al-Si) alloys are often preferred in the die casting industry due to excellent castability, high strength, corrosion resistance and low cost. Commonly, iron (Fe) is alloyed with the alloys to prevent die soldering. However, the addition of Fe in most of Al-Si alloys leads to formation of the intermetallic β-AlFeSi. The β-AlFeSi is harmful to the alloy structural integrity due to its needle-like morphology that creates stress concentration at the microscopic level. The phase presence is unfavorable to the mechanical properties and significantly reduces the elongation of the alloys. This research attempted to find viable way to control the morphology and formation of the β-AlFeSi phase.

Thermodynamic simulations were done to investigate the sequence of intermetallic formation and other phases at different alloy compositions. The analysis of solidification paths of different alloys provided the correlation between the phase formation sequence and the fraction of the β-AlFeSi phase. The analysis also identified the feasible region of alloy design for minimizing the β-AlFeSi formation. Based on the thermodynamics simulation analysis, five alloys of different compositions were designed to validate the finding of the simulation.

The tensile test results of the alloys indicated that lowering the Fe content increases the elongation of the alloy. The results also showed that elongation was reduced with the increase of Si level due to the formation of eutectic Silicon. The change of both Fe and Mn did not significantly affect the mechanical property of the alloy when the ratio of Fe to Mn was constant. Microscopic analysis showed that lowering the Fe level had effectively altered the morphology of the β-AlFeSi needle like structure. The β-AlFeSi was found to be smaller in terms of size when Fe is lower, subsequently reducing the probability of β-AlFeSi phase to be stress riser and crack initiation.

The influence of heat treatment to the mechanical property of the alloys was also studied. The mechanical result on the heat-treated samples indicated that heat treatment is a viable method to improve the elongation property of the alloy. Microscopic observations showed that the β-AlFeSi phase was broken into shorter structures over the solution heat treatment process, resulting in better elongation.

碩士
遠東科技大學
電機工程研究所
101
Owing to the development of the global high-tech and computer industry, not only traditional industry also labor intensive instead of technical management. Fast and accurate automation equipment reduces risk and save the cost. The servo control technology is the main of part in the automation industry . It could be widely used in industry, science, medical and military. Because of that, the design focus on the accuracy and speed. The research is used for servo control system by YASKAWA. There are five servo motor and driver in the system and testing best in the hood of the motor by deburring machine for aluminum alloy metal die casting sample.

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.

Additive manufacturing can bring several advantages in tooling applications especially hot working tooling as high pressure die casting. Printing of conformal cooling channels can lead to improved cooling and faster solidification, which, in turn, can possibly result in better quality of the cast part. However, few studies on advantages of additive manufactured tools in high pressure die casting are published.The aim of this study was to investigate and quantify the effect of conformal cooling on microstructure and mechanical properties of high pressure die cast aluminum alloy. Two tools each consisting of two die inserts were produced with and without conformal channels using additive manufacturing. Both tools were used in die casting of aluminum alloy. Aluminum specimens were then characterized microstructurally in light optical microscope for secondary arm spacing measurements and subjected to tensile and hardness testing. Cooling behavior of different inserts was studied with a thermal camera and by monitoring the temperature change of cooling oil during casting. Surface roughness of die inserts was measured with profilometer before and after casting.Thermal imaging of temperature as a function of time and temperature change of oil during casting cycle indicated that conformal insert had faster cooling and lower temperature compared to conventional insert. However, thermal imaging of temperature after each shot in a certain point of time showed higher maximum and minimum temperature on conformal die surface but no significant difference in normalized temperature gradient compared to the conventional insert.The average secondary dendrite arm spacing values were fairly similar for samples from conventional and conformal inserts, while more specimens from conventional insert demonstrated coarser structure. Slower cooling in conventional insert could result in the coarser secondary dendrite arm spacing.Tensile strength and hardness testing revealed no significant difference in mechanical properties of the specimens cast in conventional and conformal die inserts. However, reduced deviations in hardness was observed for samples cast with conformal insert. This is in agreement with secondary dendrite arm spacing measurements indicating improved cooling with conformal insert.Surface roughness measurement showed small wear of the inserts. More castings are needed to observe a possible difference in wear between the conventional and conformal inserts.Small observed differences in cooling rate and secondary arm spacing did not result in evident difference in mechanical properties of the aluminum alloy but the variation in properties were reduced for samples cast with conformal cooling. Future work may include more accurate measurement of cooling behavior with a thermocouple printed into the die insert, casting of thicker specimen for porosity evaluation and fatigue testing and longer casting series to evaluate the influence of conformal cooling on tool wear.

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.