Dissertations / Theses on the topic 'Alloy cast iron'

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.

Cast-iron (CI) based bulk amorphous alloy with compositions of Fe₇₅.₅₋ₓC₆.₀ Si₃.₃B₅.₅P₈.₇Cu₁.₀Alₓ (x = 0, 1 at.%) was synthesized by Cu mold casting. As indicated by increased critical diameters (dmax) for the amorphization, the substitution of Al enhanced the glass-forming ability of the alloy. However, the onset temperature of crystallization (Tₓ) and the range of supercooled liquid region (ΔTₓ) of the alloy decreased upon Al addition from 500 °C and 28 °C to 475 °C and 25 °C, respectively. It was revealed that the decreased thermal stability of the amorphous phase is related to the enhanced crystallization tendency to form primary α-Fe phase. Upon the nanocrystallization of primary α-Fe phase the Al-added alloy shows enlarged Ms of 176 emu g⁻¹, still keeping a reasonable small Hc value of 0.086 Oe. The present study revealed that the minor Al addition enhances not only the glass-forming ability, but also the nanocrystallization behavior of the CI based bulk amorphous alloy.

While using iron castings behind temperature of 500 oC namely at cyclic heat straining, degradation of structure and breaching iron castings. For this purpose introduce cast iron with content of Si and Mo. Focusing on improvement of SiMo51 for increased high-temmperature corrosion-and fatigue life in exhaust-gas temperatures up to 800 oC. Thesis set up survey types alloys, properties, and way of casting production.

Os discos de freio, durante a frenagem, são submetidos a tensões térmicas e mecânicas que podem ser relativamente altas quando muito bruscas (frações de segundo), situação em que a temperatura pode chegar a valores próximos de 600ºC. Esta variação de temperatura provoca choques térmicos que podem gerar trincas e/ou uma grande quantidade de deformação plástica no disco. A proposta deste trabalho foi a de investigar, através de experimentos, o comportamento mecânico e físico em quatro ligas de ferro fundido cinzento (A, B, C e E), utilizadas para produzir discos de freio de veículos automotivos. Para tanto, foram realizados ensaios termomecânicos de baixo ciclo em corpos de prova, entre 300ºC e 600ºC, nas condições em fase e fora de fase, adotando o critério de falha em 50% da tensão máxima (ASTM E-606) e em componentes (discos), além daqueles de difusividade térmica desde a temperatura ambiente até 600ºC. As curvas deformação em função da vida ( N) foram obtidas e analisadas segundo norma ASTM E 466/468. A análise microestrutural nos corpos de prova e peças, após os ensaios de fadiga, serviu para revelar a influência da morfologia e quantidade de grafita e da matriz sobre as propriedades mecânicas. A medição das difusividades térmicas teve como objetivo a verificação da influência do carbono equivalente e dos elementos de liga sobre esta propriedade física. Observou-se que, durante os ensaios de fadiga termomecânica em fase, em função da decomposição de parcela da cementita da perlita, houve, nos materiais, a chamada expansão grafítica, que teve influência na parte trativa do ciclo, diminuindo as tensões necessárias para se alcançar determinadas amplitudes de tensão mecânica. Pelos gráficos de amplitude de deformação mecânica em função do número de reversos para falhar, sob fadiga termomecânica em fase e fora de fase, observou-se que a melhor liga de ferro fundido cinzento foi a liga E. Esta constatação implicará em uma significativa redução dos custos de produção dos discos de freio, pois se poderá prescindir do elemento de liga Molibdênio, extremamente caro. Comparando-se os resultados de fadiga termomecânica com os de fadiga isotérmica a 25ºC, 300ºC e 600ºC, pôde-se verificar que os ensaios mais críticos foram os fora de fase, pois conduziram, comparativamente, a vidas menores.
Brake discs are submitted to thermal and mechanical stress that can be relatively high during abrupt braking action happens (fractions of seconds), causing the temperature to reach values as high as 600ºC. This temperature variation results in thermal shocks that can generate cracks and/or a large amount of plastic deformation in the disk. The main aim of this work was to investigate, through experiments, the mechanical and physical behavior of four alloys of gray cast iron (A, B, C and E), used to produce brake discs of automotives vehicles. Low cycle thermomechanical fatigue tests were carried out in components (discs) and in test specimens, between 300ºC and 600ºC, in the conditions in-phase and out-of-phase, adopting the failure criterion of 50% drop of the maximum tensile stress (ASTM E - 606). Thermal diffusivity values were measured from room temperature up to 600oC in order to analyze the effects of carbon content and alloying elements in physical properties. Curves -N were obtained and analyzed according to ASTM E 466/468 standard. Microstructural analysis was employed to reveal the influence of the matrix and morphology/amount of graphite on the mechanical properties. It was observed that, during in-phase thermomechanical fatigue tests, the volume expansion due to cementite decomposition into graphite and ferrite caused a decrease in the tensile stress necessary to achieve the mechanical strain imposed during tests. From M/2 x 2Nf graphs it was inferred that alloy E presented the best performance both in in-phase and out-of phase tests. The lack of Mo in this alloy implies in a significant reduction of cost production of the brake discs, due to the high cost of such alloying element. Out-of-phase thermomechanical fatigue tests resulted in shorter lives compared to isothermal fatigue tests carried out at 25ºC, 300ºC and 600ºC.

Solving of this diploma thesis is evaluation porosity in sequence on mechanical properties from different Al alloys. Castings were made by gravity casting to the iron-mould or gravity casting to the sand. Measurements (mechanical properties, porosity, DAS - dendrite arm spacing, shape factors and sphericity) were statistically analysed and dependencies which were detected were processed to the graphs.

Au cours des dernières décennies, des efforts importants ont été menés dans la modélisation des processus de rupture ductile entraînant des progrès substantiels. Cependant, la compréhension complète des mécanismes de rupture ductile dans des états de contraintes spécifiques demeure une question ouverte. Ceci est dû au manque de bases des données expérimentales et à la non validation des modèles pour ces conditions de chargement. Dans ce travail, les acquisitions de données sont principalement obtenues en utilisant la laminographie, ce qui rend possible l'imagerie de régions d'intérêt d'échantillons plats. L'utilisation d'éprouvettes larges (et minces) permet de générer différents états de contraintes et des conditions aux limites pertinentes pour l'ingénierie, qui ne pouvaient pas être évaluées jusqu'à présent en trois dimensions et en essais in-situ à des échelles micrométriques. La corrélation d'images volumiques (DVC) est utilisée pour mesurer les champs de déplacement à l'intérieur des échantillons en acquérant des images de laminographie 3D. Deux classes de matériaux représentatives de deux modes génériques de rupture ductile ont été examinées, à savoir les alliages d'aluminium (rupture par instabilité) et la fonte à graphite sphéroïdal (rupture par croissance de vide et coalescence).L'observation de la microstructure et les interactions déformations-endommagement pour différentes géométries d'échantillons et pour différents niveaux de triaxialité des contraintes associés ont été étudiées pour des alliages d'aluminium à une résolution micrométrique. De plus, un cadre combiné numérique-expérimental (DVC-FE) est introduit pour valider les simulations numériques à l'échelle microscopique pour la fonte à graphite sphéroïdal. Les simulations par éléments finis (FE), qui représentent la microstructure des matériaux étudiés, sont conduites avec des conditions aux limites de Dirichlet extraites des mesures DVC. Enfin, le cadre DVC-FE a été amélioré et utilisé comme une procédure d'identification intégrée pour l'étude du comportement élasto-plastique de la matrice ferritique de la fonte, non seulement en termes de champs cinématiques induits par la microstructure aléatoire, mais aussi avec les niveaux de charge globaux
In the last few decades significant efforts have been made in modeling ductile failure processes resulting in substantial progress. However, the full understanding of ductile failure mechanisms under specific stress states still remains an open question. This is partly due to missing experimental data and validation of models for such loading conditions.In this work, data acquisitions are mainly obtained by using laminography, which makes the imaging of regions of interest in flat samples possible. The use of large (and thin) specimens allows various stress states and engineering-relevant boundary conditions to be generated, which could not be assessed in three dimensions and in-situ at micrometer scales before. Digital Volume Correlation (DVC) is used for measuring displacement fields in the bulk of samples by registering 3D laminography images. Two material classes that are representative of two generic modes of ductile failure have been examined, namely, Al-alloys (failure by instability) and cast iron (failure by void growth and coalescence). The observation of microstructure and strain-damage interactions at micrometer resolution for various specimen geometries and associated levels of stress triaxiality are studied for Al-alloys. Additionally, a combined computational-experimental (DVC-FE) framework is introduced to validate numerical simulations at the microscopic scale for nodular graphite cast iron. Finite Element (FE) simulations, which account for the studied material microstructure, are driven by Dirichlet boundary conditions extracted from DVC measurements.Last, the DVC-FE framework is upgraded to an integrated identification procedure to probe elasto-plastic constitutive law of the cast iron ferritic matrix not only in terms of kinematic fields induced by the random microstructure but also by overall load levels

碩士
國立臺灣大學
機械工程學研究所
97
The primary purpose of this research is to study the effects of C and Si contents, method of post inoculation and the employment of chills on the (surface) microstructure and hardness of low-alloy ductile cast irons. The results show that, at a fixed CE, increasing Si content (from 1.15%Si to 1.68%Si) increases nodule count, but reduces carbide content. In addition, late inoculation exerts more effect on irons with higher Si than with lower Si. On the other hand, at a fixed Si content, irons with a higher C content and/or were late inoculated, have higher nodule count and less carbide content. In addition, late inoculation promotes bainite formation rather than pearlite, while no significant difference in matrix structure was obtained for irons without late inoculation. Regarding the hardness, casting AX has the highest hardness value HRC 50-54, among the four castings studied. Surface chilling significantly increases the nodule count, promotes uniform distribution of carbides and also refines carbide phase, and increases hardness. Finally, thermal analyses were performed to attain the cooling curves at different locations in the castings and correlated the cooling curves with the continuous cooling transformation diagram of similar compositions to predict the matrix structure formed.

Siu, King Sang = 網狀合金的白鑄鐵的退火處理 / 蕭健生.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2008.
Includes bibliographical references.
Abstracts in English and Chinese.
Siu, King Sang = Wang zhuang he jin de bai zhu tie de tui huo chu li / Xiao, Jiansheng.
Abstract --- p.i
摘要 --- p.iv
Acknowledgments --- p.v
Table of contents --- p.vi
List of table captions --- p.viii
List of figure captions --- p.ix
Chapter Chapter 1 --- Introduction
Chapter 1.1 --- Composite Materials --- p.1
Chapter 1.2 --- Nanostructured Material --- p.2
Chapter 1.3 --- Typical Methods of Fabrication of Nanostructure Material --- p.3
Chapter 1.4 --- Combination of the Ideas of Nanostructure and Composite --- p.4
Chapter 1.5 --- Phase Separation --- p.5
Chapter 1.6 --- Nucleation and Growth --- p.6
Chapter 1.7 --- Spinodal Decomposition --- p.8
Chapter 1.7.1 --- The Initiation of Spinodal Decomposition --- p.8
Chapter 1.7.2 --- Dynamics of Spinodal Decomposition --- p.9
Chapter 1.7.2.1 --- Classical Equation of Diffusion --- p.9
Chapter 1.7.2.2 --- Factors Deterring Spinodal Decomposition and Formation of Spinodal Network --- p.10
Chapter 1.7.3 --- Relationship between Wavelength of Spinodal Network and Undercooling --- p.11
Chapter 1.7.4 --- "Comparing Nucleation and Growth, and Spinodal Decomposition" --- p.11
Chapter 1.8 --- How to achieve large undercooling --- p.12
Chapter 1.9 --- Thermal annealing --- p.12
Chapter 1.9.1 --- Recovery --- p.13
Chapter 1.9.2 --- Recrystallization --- p.13
Chapter 1.9.3 --- Grain Growth --- p.14
Chapter 1.9.4 --- Equation of Ideal Grain Growth --- p.14
Chapter 1.9.5 --- Factor that slow down grain growth --- p.15
Chapter 1.10 --- Prospect of this Thesis Project --- p.16
References --- p.17
Figures --- p.19
Chapter Chapter 2 --- Experimental Method
Chapter 2.1 --- Introduction --- p.26
Chapter 2.2 --- Sample Fabrication --- p.26
Chapter 2.3 --- Procedures for Preparing Thermal Annealing --- p.26
Chapter 2.3.1 --- Preparation of Vacuum Environment --- p.26
Chapter 2.3.2 --- Sealing Silica Tube --- p.27
Chapter 2.4 --- Furnance --- p.27
Chapter 2.5 --- Samples Analysis --- p.27
Chapter 2.5.1 --- Optical Microscope --- p.27
Chapter 2.5.2 --- Scanning Electron Microscope (SEM) Analysis --- p.27
Chapter 2.5.3 --- Transmission Electron Microscope (TEM) Analysis --- p.28
Chapter 2.5.3.1 --- Sample Preparation --- p.28
Chapter 2.5.3.1.1 --- "Grinding, Polishing and Pouching" --- p.28
Chapter 2.5.3.1.2 --- Dimpling --- p.29
Chapter 2.5.3.1.3 --- I on Milling --- p.29
Chapter 2.5.3.2 --- Phase Identification --- p.30
References --- p.31
Figures --- p.31
Chapter Chapter 3 --- Grain Growth in Fe81C17Si5
Chapter 3.1 --- Abstract --- p.34
Chapter 3.2 --- Introduction --- p.35
Chapter 3.3 --- Experimental --- p.36
Chapter 3.4 --- Result --- p.37
Chapter 3.5 --- Discussion --- p.44
References --- p.48
Figures --- p.49
Chapter Chapter 4 --- High temperature thermal annealing of Fe81C14Si5 network alloys
Chapter 4.1 --- Abstract --- p.74
Chapter 4.2 --- Introduction --- p.75
Chapter 4.3 --- Experimental --- p.76
Chapter 4.4 --- Result --- p.77
Chapter 4.5 --- Discussion --- p.83
References --- p.86
Figures --- p.87

碩士
臺灣大學
機械工程學研究所
98
The primary purpose of this research is study the effects of C and Si contents, solidification cooling rate (with and without chilling), and late inoculation on microstructure, hardness and wear resistance of ductile cast irons under fixed alloy compositions of 2.5%Ni-1.0%Cr-0.5%Mo-0.4%Mn. The experimental results show that, at a fixed CE of about 4.13%, increasing Si content (from 1.15% to 1.68%) increases graphite nodule count, but reduces both carbide and bainite contents. In addition, the employment of late inoculation (0.1% Fe-Si inoculant) increases nodule count, while slightly reduces carbide content. On the other hand, at a fixed Si content of some 1.46%, increasing C content (from 3.44% to 3.81%) increases both graphite nodule count and bainite content, but reduces carbide content. Late inoculation promotes bainite formation. Furthermore, when the alloy solidification cooling rate was increased by chilling, the microstructure exhibits increased graphite nodular count and carbide content, and also the carbides formed are more refined. As a result, the hardness is higher with a higher solidification cooling rate. Regarding the pin-on-disc tests (Al2O3 as dics material), the results show that the chilled specimens exhibit higher wear loss compared with non-chilled specimens. By means of multiple linear regression analysis, wear loss is functions of nodule count and bainite content, with the nodule count being a positive effect, while the bainite content a negative effect. However, a reversed results on wear loss were obtained for pin-on-flat tests (S45C as stationary counter material). In summary, alloys with moderate nodule count and with a merely bainitic matrix can attain the best wear resistance. In addition, the wear resistance is affected more by varying Si content than by C content.

碩士
國立臺灣科技大學
機械工程研究所
83
The study was aimed to discuss that the effect of nodularity, matrix structure and alloy elements on the magnetic properties of ferritic nodular cast iron in as-cast and heat treated con- dition, and to promote the feasibly of ferritic nodular cast iron been applied as industry magnetic materials. The nodular cast iron bar which was cut into ring sample with outside dia- meter 30mm,inside diameter 18mm,and thickness 5.4mm.After wind- ing ,set up was used hysteresis loop measurement. The nodularity microstructure was analyzed with image analysis system to get the experiment data for analysis and discussion. The results of this experiment indicated that if the ferritic nodular cast iron with higher nodularity,it would have better soft magnetic properties. The addition of silicon element can promote the soft magnetic properties of ferritic nodular cast iron.Increasing the silicon content would lower the coercive force and hysteresis losses.But the addition of manganese elem- ent has adverse effect. Increasing the manganese content would cause segregation and lower the soft magnetic properties. Heat treatment with annealing would decrease the lattice defects and make the soft magnetic properties better,but in a longer anneal- ing time,graphite growing would affect the total magnetic prope- rties.The grain size would not show any specific influence on the magnetic properties of ferritic nodular cast iron.

Thesis (M.S.)--University of Wisconsin--Madison, 1988.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 280-284).

碩士
遠東科技大學
機械工程研究所在職專班
107
In this study, Stellite6 alloys were respectively overlaid on spheroidal graphite(SG) cast irons with 3.0 wt% carbon and 2.8 wt% silicon by plasma transferred arc (PTA) process in the fixed overlaying speed, travel speed and overlaying current by changing the additive content of NbC in the Stellite6 alloys. To explore its influence on the solidification structure of the overlayer and the interface region. In the study, we also used the overlayer with the NbC additve in cobalt-base superalloys for the cutting wear test to explore the effects of different the additive content of NbC in the Stellite6 alloys on the microhardness, the amount of carbides and the cutting wear characteristics of the overlayer. The results reveal that the Stellite6 overlayer melted on SG cast iron with 3.0 wt% carbon and 2.8 wt% silicon under overlaying current (I=100A) is a dendritic structure with M7C3 and M23C6 carbides and matrix structure is -Co. The micro-hardness (Hv) and bulk hardness (HRC) of the overlayer increases with the addition amount of NbC. The results of the cutting wear test show that the flank wear of the Stellite6 cobalt-based alloy overlayer does not increase with the addition of NbC, but it is found that when 30 wt% NbC carbide is added, that have better wear resistance. In the cutting wear test, the wear mechanisms of overlayers are mainly plastic groove, surface polish and adhesive wear as adhered to overlayers. Others minor mechanicsms include brittle crack and fracture. Among these, the case to plastic groove includes microcutting and plough. Keywords: plasma transferred arc, overlaying current, Stellite alloy, spheroidal graphite cast iron, wear .

碩士
遠東科技大學
機械工程研究所
103
This study used SCM440 Cr-Mo steel, a common element in wearable materials, as substrates, which were subjected to electrical discharge alloying (EDA) for steel surface modification. Two types of cast iron with lubricating graphite phase and different graphite patterns, i.e. flake graphite (FG) (FC250) and spheroidal graphite (SG) (FCD450), were selected as the electrodes in alloying. The approach with fixed discharge current and duty factor and varying pulse durations (100~1000ms) was used to find the machining parameters that lead to the optimal pulse durations for both the FG and SG cast iron electrodes in an attempt to obtain the alloy layers that contain graphite phase and have adequate hardness, corrosion resistance and surface roughness. On the other hand, assessment was made on whether it is feasible to increase the amounts of alloy elements diffused into the alloy layers, the number of eutectic graphite nodules and the thickness of these layers while maintaining better corrosion resistance and surface roughness. As such, two-stage variation of discharge current was considered. The discharge current was set at the high value of 50A for a machining duration of 5 minutes in the first stage and at the low value of 20 A for a machining duration of 25 minutes in the second stage. This was done to examine how variation of machining parameters (two-stage variation of discharge current) affects the microstructural characteristics, corrosion behavior and surface roughness on the alloy layers of the FG and SG cast iron electrodes. The experimental results show that the FC250 electrodes have produced thicker EDA alloy layers in the pulse durations of 500 ms and 1000 uns compared to the FCD450 electrodes and have produced alloy layers with maximum hardness up to Hv 1172 in the pulse duration of 100 ms. The alloy layers produced by the FC250 electrodes exhibit lower corrosion current (Icorr.=1.255 A • cm-2) compared to those produced by the FCD450 electrodes (Ecorr.=-0.4619 V). Both types of electrodes have produced alloy layers of which the surface roughness is directly proportional to the pulse duration. In addition, comparison of surface properties between EDA alloy layers produced respectively with one stage of discharge current, 20A, and two stages of discharge current, 50A and 20A, reveals that those in the latter case exhibit poorer thickness, hardness and surface roughness than those in the former case, with the exception that the FCD450 electrodes exhibit better corrosion resistance in the pulse duration of 1000ms. Moreover, X-ray diffraction analysis of the 20A-FC250, 20A-FCD450 and 50A+20A-FC250 specimens reveals that all the alloy layers have Cr3C2, Fe3C, C0.17Fe0.81Si0.02 and MoFe phases and only the 50A+20A-FCD450 specimens have all the phases except Fe3C. Keywords: Cr-Mo steel, electrical discharge alloying, cast iron, machining parameters

The Al-Cu 206 cast alloys have been widely used in automotive and aerospace industries due to the high strength and good elevated temperature properties. However, this family alloys have an extremely low upper limit for the iron content (usually less than 0.15 wt. %) because the presence of more Fe can cause a great loss of the mechanical properties, particularly the ductility. With the increasing use of the recycled aluminum alloys, the requirement for extremely low iron contents has become a main concern in terms of the manufacturing technique and cost. Therefore, manufacturing premium castings with higher iron contents has become a great challenge. In this study, the solidification behavior of the iron-rich intermetallics and the effect of alloy composition, cooling rate and solution heat treatment on the iron-rich intermetallics were systematically investigated in 206 cast alloys at 0.15, 0.3 and 0.5 wt. % Fe. The effect of the iron-rich intermetallics on the tensile properties was also evaluated. An optical microscope, a scanning electron microscope and a transmission electron microscope were used to observe the microstructures and analyze the volume fraction of the iron-rich intermetallics as well as the fracture surface. The solidification sequences of 206 cast alloys at 0.15-0.5 wt. % Fe were well established. The experimental results in the present thesis are divided into four parts. In the first part, the iron-rich intermetallics in 206 cast alloys at 0.15 wt. % Fe were studied. It was found that Chinese script a-Fe and platelet-like B-Fe can precipitate and coexist in the finally solidified alloy and the individual addition of either Mn or Si promotes the formation of a-Fe and hinders the occurrence of B-Fe. The critical cooling rate to effectively suppress the formation of B-Fe depends on the alloy composition. A casting process map is established to correlate the Mn and Si contents with cooling rate for the 206 cast alloys. In the second part, the iron-rich intermetallics in 206 cast alloys at 0.3 wt. % Fe were investigated. Platelet B-Fe and Chinese script a-Fe were observed in the solidified samples. Both the a-Fe and B-Fe phases can nucleate on the oxide films. In addition, a-Fe can also nucleate on Al6(FeMnCu) and Al3Ti particles while the earlier formed a-Fe phase can also nucleate the later formed B-Fe phase. In addition, Either Si or Mn favors the transformation of B-Fe into the a-Fe phase. At a combination of both high Mn and high Si, almost all B-Fe platelets can be converted into Chinese script a-Fe. For a cast Al-4.5Cu-0.3Fe alloy, 0.3% Mn and 0.3% Si are required to completely suppress the B-Fe phase. In the third part, the iron-rich intermetallics in 206 cast alloys at 0.5 wt. % Fe were studied. In addition to the two typical platelet B-Fe and Chinese script a-Fe phases, two extra phases, i.e. Chinese script Alm(FeMn) and platelet Al3(FeMn) were experimentally observed in the solidified alloys for the first time in the 206 cast alloys. Alm(FeMn), a-Fe and Al3(FeMn) are all possible as dominant iron-rich intermetallic phases. The individual addition of Si favors the formation of a-Fe but inhibits the precipitation of B-Fe while the individual addition of high Mn promotes the formation of Al3(FeMn). The combined addition of both Si and Mn enhances the formation of predominate a-Fe. Furthermore, the formation temperature of each iron-rich intermetallic phase decreases and the stable iron-rich intermetallic is gradually replaced by the metastable phase with increasing cooling rate. There exists a threshold cooling rate to obtain the predominant Chinese script Alm(FeMn) or a-Fe phases. Finally, the effect of iron-rich intermetallics on the tensile properties of the 206 cast alloys was performed. It was found that the tensile strengths linearly decrease with increasing iron content but higher strength are obtained for the alloys with dominant Chinese script iron-rich intermetallics than those with dominant platelet ones at similar iron levels. The 206 alloys above an iron level of 0.15% are hard to meet the minimum ductility (7%) in artificial overaging treatment (T7). However, the iron content limitation can be extended to 0.3%, or even to 0.5% to meet the 7% elongation in natural aging treatment (T4) condition under well controlled Mn and Si contents, providing the great potential to cast premium 206 alloys at high iron levels. - L'alliage Al-Cu 206 est largement utilisé dans les industries automobile et aéronautique en raison de sa grande résistance et de ses bonnes propriétés à température élevée. Toutefois, ce type d'alliage possède une faible teneur en fer (généralement une fraction massique inférieure à 0,15%), car la présence davantage de fer peut causer une diminution considérable des propriétés mécaniques. Avec l'utilisation de plus en plus croissante des alliages d'aluminium recyclé, l'exigence pour une teneur très basse en fer est devenue une préoccupation majeure en termes de technique de fabrication et de coût. Par conséquent, la fabrication de pièces de haute gamme avec une teneur élevée de fer est un très grand défi. Dans cette étude, le comportement des composés intermétalliques riches en fer au cours de la solidification et les effets de la composition de l'alliage, de la vitesse de refroidissement et de la mise en solution sur les phases intermétalliques riches en fer dans l'alliage 206 coulé à différentes teneurs massique de fer : 0,15, 0,3 et 0,5% a été étudié. L'effet des composés intermétalliques riches en fer sur les propriétés de traction a également été étudié. Un microscope optique, un microscope électronique à balayage et un microscope électronique à transmission ont été utilisés pour observer les microstructures et analyser la fraction volumique des composés intermétalliques riches en fer ainsi que la surface de rupture. Les séquences de solidification de l'alliage 206 coulé à teneur massique en fer comprise entre 0,15 ~ 0,5% ont été mis en place. Les résultats expérimentaux de la présente thèse sont divisés en quatre parties. Dans la première partie, les phases intermétalliques riches en fer dans l'alliage 206 coulé avec une teneur en fer de 0,15% ont été étudiées. Il a été constaté que la phase a-Fe à charactère chinois et B-Fe en forme de plaquettes coexistent et peuvent précipiter dans l'alliage solidifié et l'addition individuelle de Mn ou de Si favorise la formation de a-Fe et empêche l'apparition de B-Fe. La vitesse critique de refroidissement pour supprimer efficacement la formation de B-Fe dépend de la composition de l'alliage. Une carfographie du processes de coulée a été établie pour corréler entre la teneur du Mn et du Si avec un taux de refroidissement pour l'alliage 206 coulé. Dans la deuxième partie, les phases intermétalliques riches en fer dans l'alliage 206 coulé avec une teneur en fer de 0,3% ont été étudiées. Les phases à plaquettes B-Fe et celle à écriture chinoise a-Fe ont été observées dans les échantillons solidifiés. Les deux phases a-Fe et B-Fe peuvent germer sur des films d'oxyde. En outre, a-Fe peut aussi germer sur Al6(FeMnCu) et sur les particules Al3Ti, tandis que les phases a-Fe formées plus tôt peuvent également germer sur la phase B-Fe formée plus tard. En plus, ni Si ni Mn ne favorisent la transformation de la phase B-Fe en celle de a-Fe. À une combinaison du Mn et du Si élevés, presque toutes les plaquettes B-Fe peuvent être converties en phase à caractères chinois a-Fe. Pour une coulée de l'alliage Al-4,5Cu-0,3Fe, 0,3% Mn et 0,3% Si sont requis pour supprimer complètement la phase B-Fe. Dans la troisième partie, les phases intermétalliques riches en fer dans l'alliage 206 coulé avec une fraction de fer de 0,5% du poids ont été étudiées. En plus des deux phases, celle typiquement à plaquettes B-Fe et celle à écriture chinoise a-Fe, deux phases supplémentaires, c'est-à-dire, à écriture chinoise Alm(FeMn) et à plaquettes Al3(FeMn) ont été observés expérimentalement dans les alliages solidifiés pour la première fois dans l'alliage 206 coulé. Alm(FeMn), a-Fe et Al3(FeMn) sont toutes possibles comme phases intermétalliques riches en fer dominantes. L'addition individuelle de Si favorise la formation de a-Fe mais inhibe la précipitation de B-Fe, tandis que l'ajout individuel d'une grande fraction de Mn favorise la formation de Al3(FeMn). L'addition combinée de Si et de Mn améliore la formation prédominante de a-Fe. En outre, la température de formation de la phase intermétallique riche en fer diminue et la phase intermétallique riche en fer stable est progressivement remplacée par la phase métastable avec l'augmentation de la vitesse de refroidissement. Il existe un seuil de vitesse de refroidissement pour obtenir une prédominance de la phase à écriture chinoise Alm(FeMn) ou a-Fe. Enfin, l'effet des composés intermétalliques riches en fer sur les propriétés de traction de l'alliage 206 coulé a été étudié. Il a été constaté que la résistance ultime à la rupture diminue linéairement avec l'augmentation de la teneur en fer, mais une plus grande résistance à la traction est obtenue pour les alliages contenant des composés intermétalliques à écriture chinoise riches en fer que ceux à dominance de plaquettes à des teneurs similaires de fer. Les alliages 206 à teneur de fer suppérieur à 0,15% traités pas vieillissenent artificiel atteignent difficilement la ductilité minimale (7%) comparés à ceux ayant subi un traitment de type (T7). Cependant, la limitation de la teneur en fer peut être étendue à 0,3%, voire à 0,5% pour répondre à l'allongement de 7% dans le traitement de vieillissement naturel (T4) sous la condition de bien contrôler la teneur en Mn et celle en Si, ce qui fournit un grand potentiel de couler l'alliage 206 à des teneurs de fer élevées.

Thesis (M.S.)--University of Wisconsin--Madison, 1986.
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博士
國立成功大學
材料科學及工程學系碩博士班
91
The Electro Discharge Machining (EDM) features of the eutectic molding material with second phase were investigated in this study. Ferritic spheroidal graphite (SG) cast irons (2.1wt.%C~4.1wt.%C, 2.0wt.%Si~4.9wt.%Si) and Al-Si alloys (Al-1Si~29Si) were selected as testing materials. Effects of compositions, solidification rate, and EDM parameters were examined. 　　Experimental results indicated that the materials removal rate of the ferritic SG cast irons by EDM increased with a smaller graphite size and higher graphite nodule count. As for Al-Si alloys, the second phase, including primary and eutectic silicon particles, had remarkable effects on EDM characteristics. That is, higher primary silicon particles size and higher area fraction of silicon particles would accelerate the removal rate. The EDMed surfaces featured continuous ridges formed by overlapping discharge craters, and the ridge density also tended to increase with a finer graphite nodule size. Owing to the poor wettability between the cast iron melts and semi-molten graphite during solidification process, graphite particles were embedded in the cavities in-between the ridges. The Al-Si alloys EDMed surface feature was similar to that of SG cast irons, showing a wavy ridge pattern. The amount of silicon phase also affected the surface roughness. Notably, silicon particles were located in the ridge regions, not the troughs. 　　Finally, through this study that concerns the EDM characteristics of SG cast irons and Al-Si alloys, the effects of the heterogeneous second phase can be clearly clarified. This could serve as the practical reference for electro-discharge machining of mold materials with heterogeneous second phase and other engineering materials.