High-pressure die casting of semi-solid aluminium-silicon alloys is used in the automotive industry to manufacture components, like housings, brackets, and bars. It is commonly known that during high-pressure die casting, defect bands may be created that follow the contour of the component surface. These bands consist mainly of a eutectic phase. This phenomenon is also observed in semi-solid metal slurry high-pressure die casting. These bands could lead to premature failure of the component in service. The origin of these bands is not fully understood and so this research focuses on investigating these bands and their origins further. A series of casting trials were conducted with varying plunger velocity. Subsequent investigation using optical and scanning electron microscopy showed that a change of the plunger velocity alters the number of bands present in the samples. Energy dispersive X-ray spectroscopy revealed that a measurable difference in aluminium quantity across the band was noticed and it was postulated that aluminium migrates towards the component centre. Therefore, different mechanisms responsible for particle migrations found in literature were investigated and assessed quantitatively using experimental data and information from published literature. It was found that the Saffman lift force and the Mukai-Lin-Laplace effect were the mechanisms that were most likely to cause such a migration of aluminium. Further experimental investigation is recommended to identify which of the two mechanisms is ultimately responsible for the migration and to optimise the high-pressure die casting procedure to minimise defect band formation. / Produktion av högtrycksgjutning av halvfasta aluminium-kisellegeringar används i fordonsindustrin för att tillverka komponenter, som exempel till kåpor, konsoler och stag. Det är allmänt känt att defektband kan formas under högtrycksgjutning som följer konturen av komponentytan. Dessa band består huvudsakligen av eutektisk fas. Detta fenomen har också observerats vid högtrycksgjutning produktion av halvfast slurry. Potentiellt kan dessa band leda till en försämring av komponentens mekaniska egenskaper och resultera i ett förtida brott. Ursprunget av dessa band är inte helt kartlagda och det är därför viktigt att fokusera ytterligare på denna forskning och att undersöka dessa band och deras ursprung. En serie med gjutningsförsök genomfördes med varierande kolvhastighet. Efterföljande undersökning med optisk- och svepelektronmikroskopi visade att en förändring av kolvhastigheten förändrar antalet band som finns i proverna. Energidispersiv röntgenspektroskopi avslöjade en mätbar skillnad i aluminiumkvantitet över bandet, och det antogs att aluminium migrerar mot centrum av komponenten. Därför undersöktes och utvärderades olika mekanismer som ansvarar för partikelmigrationer som finns att finna i litteratur med hjälp av experimentella data och information från publicerad litteratur. Det visade sig att Saffman lyftkraft och Mukai-Lin-Laplace effekten var de mekanismer som mest troligen orsakade migration av aluminium. Ytterligare experimentella försök rekommenderas för att identifiera vilken av dessa två mekanismerna som i slutändan är ansvarig för migrationen. Detta för att optimera gjutningsprocessen och därmed minimera uppkomsten av defektband.

Aluminium castings with a large grain structure have poor mechanical properties which are primarily due to casting defects as opposed to fine grain structure. The grain refinement practice using chemical addition is well established for wrought alloys, however in the case of casting alloys, the practice of adding grain refiners and the impact on castability is not well established. The addition of well known Al-5Ti-B grain refiner to casting alloys with silicon (Si) content above 3 wt.% is not effective. This is believed to be due to the chemical reaction between Ti and Si. The current research aim is to find an alternative, but effective, chemical phase which can refine Al-Si alloy grains. Based on a crystallographic database search and intermetallic phases found in Aluminium–Niobium-Boron, there exists several iso-structural phases similar to those of Al3Ti and TiB2. We have selected a phase which exhibits chemical phase stability with Si (below 900 oC) and developed a potential novel grain refiner Nb-B for Al-Si cast alloys. Various Al-Si binary alloys and a commercial sourced LM6 (Al-10Si-Mg) cast alloys were cast after novel grain refiner addition to the melt. It is the first time that such fine grain structures were achieved for Al-Si alloys when Si >4wt.%. It is believed that Nb-B grain refiner enhances the heterogeneous nuclei in the melt. The effectiveness of this grain refiner under various cooling rate conditions is investigated to simulate various practical casting conditions. Due to increased heterogeneous nuclei density, a fine grain structure is also obtained at low cooling rates and the grain size is less sensitive to the cooling rate. The processing of high Si containing alloys for complex shaped castings with reduced defects, fine grain structure and improved mechanical properties are now possible.

Carcaças de transmissão estão geralmente sujeitas a tensões cíclicas geradas durante o funcionamento do motor, e estas tensões são mais críticas a temperaturas elevadas e em tempos prolongados. Os gradientes térmicos induzidos no interior de componentes sujeitos a variações de temperatura durante o período de funcionamento podem levar a tensões e deformações internas e a repetição destes ciclos térmicos pode causar a nucleação e a propagação de trincas por um processo denominado de fadiga termomecânica. Este trabalho apresenta um estudo sobre as diferenças das propriedades mecânicas de duas ligas de Al-Si fundidas sobre pressão em molde permanente (injetadas), uma identificada como sendo a Liga A, que contém o elemento de liga Mg, e a Liga B que não contém o Mg, para uso em carcaças de transmissão de veículos automotivos. Neste estudo foram realizados ensaios mecânicos de dureza, de tração e de fadiga isotérmica e anisotérmica e análises fratográficas e microestruturais por microscopia ótica e eletrônica de varredura. A Liga A apresentou resistência mecânica superior à Liga B em toda a faixa de temperatura analisada, apesar da maior quantidade de defeitos de fundição existentes nesta liga. Foi utilizada a metodologia S-N, cujos dados foram inferidos a partir dos ensaios de fadiga termomecânica. A Liga A apresenta desempenho ligeiramente superior à Liga B, especialmente para baixos níveis de tensão aplicados. Entretanto, para ensaios executados sob controle de deformação, não houve diferença significativa na resistência à fadiga entre as duas ligas. / Gear Box housings are usually subjected to cyclic stresses generated during engine operation. Such stresses are more critical at high temperatures and long times. Thermal gradients induced within the components submitted to variation of temperature during working may result in internal stresses and strains. Thermal cycling can result in crack nucleation and propagation by the process of thermomechanical fatigue (TMF). The main aim of this work was to evaluate the effects of Mg content on the mechanical properties of permanent mold cast Al-Si alloys. Two alloys, one containing Mg addition (\"A\" alloy) and another without Mg (\"B\" alloy) were tested under strain temperature TMF controlled conditions. In this study were performed mechanical tests of hardness, tensile strength, and anisotropic / isothermal fatigue and microstrutural / photographic analysis by scanning electronic microscopy (SEM). Using the S-N approach inferred from the TMF results, \"A\" alloy (Mg-added) presented a slightly better performance then \"B\" alloy especially at low stress amplitude levels. However, in the TMF testing conditions was not observed any significant difference in fatigue resistance for both alloys.

O objetivo deste trabalho é realizar um estudo comparativo das propriedades mecânicas e metalúrgicas em duas peças de ligas de Al-Si produzidas por injeção sob baixa pressão. As peças estudadas referem-se às placas acessórias utilizadas para fornecer sustentação durante a entrada e saída de vaus por carros de combate do Exército Brasileiro, sendo uma nacional e a outra importada. Para a caracterização metalúrgica foram realizados ensaios metalográficos (microscopia óptica e eletrônica). Para a obtenção das propriedades mecânicas foram realizados ensaios de tração, microdureza Vickers e impacto. Quanto aos resultados metalográficos observou-se: na peça nacional, a presença de uma estrutura predominantemente eutética com silício em forma acicular e a fase Al15 (Fe, Mn)3Si2 com morfologia tipo escrita chinesa; na peça importada, foi identificado silício disperso com formato arredondado. A análise da porosidade por gases realizada no canal de alimentação indicou baixos índices para as duas peças. De outro modo, foi observada a presença de porosidades por contração na peça nacional. Nos resultados mecânicos, a peça importada apresentou valores significativamente superiores para a tensão de escoamento e máxima, energia de impacto e deformação. A partir dos resultados obtidos nos ensaios mecânicos realizaram-se simulações no software Solidworks, módulo Simulation, para a determinação da ocorrência de falha quando utilizado por dois carros de combate: o Leopard 1A5, sobre lagartas, e o URUTU, sobre roda. As simulações indicaram falha da peça nacional pelo uso do carro sobre rodas. O resultado em peso da composição química da peça nacional revelou uma liga de alumínio com 12%Si e 0,88%Fe, enquanto a peça importada apresentou 10,38%Si, 0,294%Mg e somente 0,12%Fe. Com a análise dos resultados, conclui-se que os principais fatores da baixa durabilidade da peça nacional foram, preponderantemente, a composição química e a morfologia do silício. / The objective of this research is to perform a comparative study of the mechanical and metallurgical properties in two castings of Al-Si alloys produced by injection under low pressure. The pieces studied refer to soil reinforcing plates used as accessory plates used to provide support during the entry and exit of the Brazilian Army combat vehicles, one national and other imported. For the metallurgical characterization, metallographic analysis by electron and optical microscopy were performed and. To obtain the mechanical properties tensile tests, Vickers microhardness and impact were performed. Regarding the metallographic results, it was observed: In the national piece, the presence of a predominantly eutectic structure with needle-shaped silicon and the Al15(Fe,Mn)3Si2 phase with Chinese writing morphology; In the imported part, dispersed silicon with a rounded shape was identified. The gas porosity analysis performed on the feed channel indicated low indexes for the two pieces.Otherwise, the presence of porosities by contraction in the national piece was observed. In the mechanical results, the imported part presented values significantly higher for the yield stress and maximum, impact energy and deformation. From the results obtained in the mechanical tests it was able to perform simulations on the Solidworks software, Simulation mode, to determine the failures occurrence when used by two battle cars: Leopard 1A5, on caterpillars, and URUTU, on wheels. The simulations indicated failure of the national part by the use of the car on wheels. The weight result of the chemical composition of the domestic part revealed an aluminum alloy with 12% Si and 0.88% Fe, while the imported piece revealed 10.38% Si, 0.294% Mg and only 0.12% Fe. Analyzing the results, it is concluded that the main factors of the low durability of the national piece were, predominantly, the chemical composition and the morphology of the silicon.

Carcaças de transmissão estão geralmente sujeitas a tensões cíclicas geradas durante o funcionamento do motor, e estas tensões são mais críticas a temperaturas elevadas e em tempos prolongados. Os gradientes térmicos induzidos no interior de componentes sujeitos a variações de temperatura durante o período de funcionamento podem levar a tensões e deformações internas e a repetição destes ciclos térmicos pode causar a nucleação e a propagação de trincas por um processo denominado de fadiga termomecânica. Este trabalho apresenta um estudo sobre as diferenças das propriedades mecânicas de duas ligas de Al-Si fundidas sobre pressão em molde permanente (injetadas), uma identificada como sendo a Liga A, que contém o elemento de liga Mg, e a Liga B que não contém o Mg, para uso em carcaças de transmissão de veículos automotivos. Neste estudo foram realizados ensaios mecânicos de dureza, de tração e de fadiga isotérmica e anisotérmica e análises fratográficas e microestruturais por microscopia ótica e eletrônica de varredura. A Liga A apresentou resistência mecânica superior à Liga B em toda a faixa de temperatura analisada, apesar da maior quantidade de defeitos de fundição existentes nesta liga. Foi utilizada a metodologia S-N, cujos dados foram inferidos a partir dos ensaios de fadiga termomecânica. A Liga A apresenta desempenho ligeiramente superior à Liga B, especialmente para baixos níveis de tensão aplicados. Entretanto, para ensaios executados sob controle de deformação, não houve diferença significativa na resistência à fadiga entre as duas ligas. / Gear Box housings are usually subjected to cyclic stresses generated during engine operation. Such stresses are more critical at high temperatures and long times. Thermal gradients induced within the components submitted to variation of temperature during working may result in internal stresses and strains. Thermal cycling can result in crack nucleation and propagation by the process of thermomechanical fatigue (TMF). The main aim of this work was to evaluate the effects of Mg content on the mechanical properties of permanent mold cast Al-Si alloys. Two alloys, one containing Mg addition (\"A\" alloy) and another without Mg (\"B\" alloy) were tested under strain temperature TMF controlled conditions. In this study were performed mechanical tests of hardness, tensile strength, and anisotropic / isothermal fatigue and microstrutural / photographic analysis by scanning electronic microscopy (SEM). Using the S-N approach inferred from the TMF results, \"A\" alloy (Mg-added) presented a slightly better performance then \"B\" alloy especially at low stress amplitude levels. However, in the TMF testing conditions was not observed any significant difference in fatigue resistance for both alloys.

O objetivo deste trabalho é realizar um estudo comparativo das propriedades mecânicas e metalúrgicas em duas peças de ligas de Al-Si produzidas por injeção sob baixa pressão. As peças estudadas referem-se às placas acessórias utilizadas para fornecer sustentação durante a entrada e saída de vaus por carros de combate do Exército Brasileiro, sendo uma nacional e a outra importada. Para a caracterização metalúrgica foram realizados ensaios metalográficos (microscopia óptica e eletrônica). Para a obtenção das propriedades mecânicas foram realizados ensaios de tração, microdureza Vickers e impacto. Quanto aos resultados metalográficos observou-se: na peça nacional, a presença de uma estrutura predominantemente eutética com silício em forma acicular e a fase Al15 (Fe, Mn)3Si2 com morfologia tipo escrita chinesa; na peça importada, foi identificado silício disperso com formato arredondado. A análise da porosidade por gases realizada no canal de alimentação indicou baixos índices para as duas peças. De outro modo, foi observada a presença de porosidades por contração na peça nacional. Nos resultados mecânicos, a peça importada apresentou valores significativamente superiores para a tensão de escoamento e máxima, energia de impacto e deformação. A partir dos resultados obtidos nos ensaios mecânicos realizaram-se simulações no software Solidworks, módulo Simulation, para a determinação da ocorrência de falha quando utilizado por dois carros de combate: o Leopard 1A5, sobre lagartas, e o URUTU, sobre roda. As simulações indicaram falha da peça nacional pelo uso do carro sobre rodas. O resultado em peso da composição química da peça nacional revelou uma liga de alumínio com 12%Si e 0,88%Fe, enquanto a peça importada apresentou 10,38%Si, 0,294%Mg e somente 0,12%Fe. Com a análise dos resultados, conclui-se que os principais fatores da baixa durabilidade da peça nacional foram, preponderantemente, a composição química e a morfologia do silício. / The objective of this research is to perform a comparative study of the mechanical and metallurgical properties in two castings of Al-Si alloys produced by injection under low pressure. The pieces studied refer to soil reinforcing plates used as accessory plates used to provide support during the entry and exit of the Brazilian Army combat vehicles, one national and other imported. For the metallurgical characterization, metallographic analysis by electron and optical microscopy were performed and. To obtain the mechanical properties tensile tests, Vickers microhardness and impact were performed. Regarding the metallographic results, it was observed: In the national piece, the presence of a predominantly eutectic structure with needle-shaped silicon and the Al15(Fe,Mn)3Si2 phase with Chinese writing morphology; In the imported part, dispersed silicon with a rounded shape was identified. The gas porosity analysis performed on the feed channel indicated low indexes for the two pieces.Otherwise, the presence of porosities by contraction in the national piece was observed. In the mechanical results, the imported part presented values significantly higher for the yield stress and maximum, impact energy and deformation. From the results obtained in the mechanical tests it was able to perform simulations on the Solidworks software, Simulation mode, to determine the failures occurrence when used by two battle cars: Leopard 1A5, on caterpillars, and URUTU, on wheels. The simulations indicated failure of the national part by the use of the car on wheels. The weight result of the chemical composition of the domestic part revealed an aluminum alloy with 12% Si and 0.88% Fe, while the imported piece revealed 10.38% Si, 0.294% Mg and only 0.12% Fe. Analyzing the results, it is concluded that the main factors of the low durability of the national piece were, predominantly, the chemical composition and the morphology of the silicon.

O objetivo deste trabalho é realizar um estudo comparativo das propriedades mecânicas e metalúrgicas em duas peças de ligas de Al-Si produzidas por injeção sob baixa pressão. As peças estudadas referem-se às placas acessórias utilizadas para fornecer sustentação durante a entrada e saída de vaus por carros de combate do Exército Brasileiro, sendo uma nacional e a outra importada. Para a caracterização metalúrgica foram realizados ensaios metalográficos (microscopia óptica e eletrônica). Para a obtenção das propriedades mecânicas foram realizados ensaios de tração, microdureza Vickers e impacto. Quanto aos resultados metalográficos observou-se: na peça nacional, a presença de uma estrutura predominantemente eutética com silício em forma acicular e a fase Al15 (Fe, Mn)3Si2 com morfologia tipo escrita chinesa; na peça importada, foi identificado silício disperso com formato arredondado. A análise da porosidade por gases realizada no canal de alimentação indicou baixos índices para as duas peças. De outro modo, foi observada a presença de porosidades por contração na peça nacional. Nos resultados mecânicos, a peça importada apresentou valores significativamente superiores para a tensão de escoamento e máxima, energia de impacto e deformação. A partir dos resultados obtidos nos ensaios mecânicos realizaram-se simulações no software Solidworks, módulo Simulation, para a determinação da ocorrência de falha quando utilizado por dois carros de combate: o Leopard 1A5, sobre lagartas, e o URUTU, sobre roda. As simulações indicaram falha da peça nacional pelo uso do carro sobre rodas. O resultado em peso da composição química da peça nacional revelou uma liga de alumínio com 12%Si e 0,88%Fe, enquanto a peça importada apresentou 10,38%Si, 0,294%Mg e somente 0,12%Fe. Com a análise dos resultados, conclui-se que os principais fatores da baixa durabilidade da peça nacional foram, preponderantemente, a composição química e a morfologia do silício. / The objective of this research is to perform a comparative study of the mechanical and metallurgical properties in two castings of Al-Si alloys produced by injection under low pressure. The pieces studied refer to soil reinforcing plates used as accessory plates used to provide support during the entry and exit of the Brazilian Army combat vehicles, one national and other imported. For the metallurgical characterization, metallographic analysis by electron and optical microscopy were performed and. To obtain the mechanical properties tensile tests, Vickers microhardness and impact were performed. Regarding the metallographic results, it was observed: In the national piece, the presence of a predominantly eutectic structure with needle-shaped silicon and the Al15(Fe,Mn)3Si2 phase with Chinese writing morphology; In the imported part, dispersed silicon with a rounded shape was identified. The gas porosity analysis performed on the feed channel indicated low indexes for the two pieces.Otherwise, the presence of porosities by contraction in the national piece was observed. In the mechanical results, the imported part presented values significantly higher for the yield stress and maximum, impact energy and deformation. From the results obtained in the mechanical tests it was able to perform simulations on the Solidworks software, Simulation mode, to determine the failures occurrence when used by two battle cars: Leopard 1A5, on caterpillars, and URUTU, on wheels. The simulations indicated failure of the national part by the use of the car on wheels. The weight result of the chemical composition of the domestic part revealed an aluminum alloy with 12% Si and 0.88% Fe, while the imported piece revealed 10.38% Si, 0.294% Mg and only 0.12% Fe. Analyzing the results, it is concluded that the main factors of the low durability of the national piece were, predominantly, the chemical composition and the morphology of the silicon.

Submitted by Ronildo Prado (ronisp@ufscar.br) on 2017-08-21T19:43:10Z No. of bitstreams: 1 DissRAVR.pdf: 4897870 bytes, checksum: 357d31e652f80cf53a70451ae1ebc870 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-21T19:43:18Z (GMT) No. of bitstreams: 1 DissRAVR.pdf: 4897870 bytes, checksum: 357d31e652f80cf53a70451ae1ebc870 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-21T19:43:24Z (GMT) No. of bitstreams: 1 DissRAVR.pdf: 4897870 bytes, checksum: 357d31e652f80cf53a70451ae1ebc870 (MD5) / Made available in DSpace on 2017-08-21T19:43:30Z (GMT). No. of bitstreams: 1 DissRAVR.pdf: 4897870 bytes, checksum: 357d31e652f80cf53a70451ae1ebc870 (MD5) Previous issue date: 2017-01-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / The present research work deals with directional solidification (DS) of Al-15wt.% and 18wt.% Si alloys and further characterization of the related microstructures. Emphasis is given on the eutectic growth being affected not only by solidification kinetics (V-eutectic growth rate and G-thermal gradient) but also by melt superheat, which is varied in two degrees for each alloy, i.e., 6% and 23% above the liquidus temperature. The dependences of interphase spacing (X) on both solidification kinetics (fast, intermediate and slow cooling conditions) and on melt superheat during solidification of hypereutectic alloys are reported for the first time. Furthermore, functional experimental interrelations of tensile mechanical properties and interphase spacing between eutectic Si particles of both alloys evaluated are proposed. It is shown by these correlations that the tensile properties increase with the decrease in these spacings. More significant variations in properties are associated with a certain range of spacings (1.0^m < X < 2.3^m) in the case of the Al-15wt.%Si alloy. Tensile strength and elongation-to-fracture decrease with increasing alloy silicon content. The applicability of eutectic growth expressions such as X=f (V-1/2) and X=f (G-a x V-b) has been verified for the present tested alloys and experimental conditions. / O presente trabalho inclui a solidificação direcional das ligas Al-15%Si e Al-18%Si (% em peso), além da caracterização das microestruturas decorrentes. Foi dada ênfase ao crescimento eutético, sendo afetado não só pela cinética de solidificação (velocidade de avanço da frente eutética e gradiente térmico), mas também pelo superaquecimento, que foi variado em dois níveis para cada liga, isto é, 6% e 23% acima da temperatura liquidus. As dependências do espaçamento eutético, (Xe) tanto relacionadas à cinética de solidificação (condições de resfriamento rápido, intermediário e lento) quanto ao superaquecimento durante a solidificação de ligas hipereutéticas, são relatadas pela primeira vez na literatura especializada. Além disso, inter-relações experimentais funcionais de propriedades mecânicas de tração e espaçamentos interfásicos, entre as partículas de Si eutético, foram propostas para ambas as ligas. É mostrado por estas correlações que ductilidade e resistência mecânica aumentam com a diminuição destes espaçamentos microestruturais. Variações mais significativas nas propriedades estão associadas a um determinado intervalo de espaçamentos (1,0^m < X < 2,3^m) para o caso da liga Al-15%Si. O limite de resistência à tração (LRT) e o alongamento específico (5) diminuem com o aumento do teor de silício da liga. A aplicabilidade de expressões de crescimento eutético como X=f (V-1/2) e X=f (G-a x V-b) foi verificada para as ligas testadas nas presentes condições experimentais.

Les alliages Al-Si sont largement utilisés dans l’industrie automobile en fonderie sous pression, en particulier pour la fabrication des blocs moteurs, en raison de leurs bon rapport résistance/ poids et leurs excellentes propriétés mécaniques. Du fait de l’internationalisation de la production, la composition chimique de ces alliages et les paramètres du procédé HPDC peuvent varier d’un pays à l’autre, ils peuvent même varier d’un site de fabrication à l’autre dans le même pays. Or, les conceptions des pièces automobiles sont aujourd’hui de type déterministe et elles sont réalisées sur la base des matériaux et procédés européens, ce qui peut affecter les propriétés de ces pièces dans le cas d’une localisation hors Europe. Ainsi, il est important de pouvoir adapter les conceptions rapidement et à moindre coût en prenant en compte les contraintes matériau/ process locales. Dans cette thèse, nous avons proposé une approche méthodologique permettant de prédire les caractéristiques mécaniques en fonction de la variabilité matériaux/ process en s'appuyant sur une étude expérimentale/ statistique de l’effet de la variabilité des principaux éléments d’alliage (Si, Cu, Mg) et des paramètres procédé (température de la coulée et pression d’injection) sur les propriétés mécaniques des alliages d’Al-Si moulés sous pression. La microstructure et le taux de porosités ont également été évalués. Cette méthodologie a abouti à la construction d’un outil de conception produit permettant de prédire les caractéristiques mécaniques dans le cas du changement de l’un (ou des) paramètres Matériau/ Process. / Secondary Al-Si alloys are widely used in automotive industry for engine blocks because they offer a considerable weight reduction whilst maintaining good mechanical properties. The ever-expanding internationalisation of production, with same stages of production processes spread across a number of countries to produce locally, causes however high variability in the casting products. The chemical composition of the same alloys and the working variables of the unchanged high-pressure die casting process (HPDC) may change for the same casting parts from one country to another, they can even sometimes vary from one manufacturing site to another within the same country. Designing for aluminium automotive components does call today for new deterministic design methods that are often achieved from European material and casting process databases, which can affect the properties of these parts in the case of a location outside Europe. Thus, it is important to adapt the design of die casting parts quickly and inexpensively by taking into account the material and process local constraints. In this work, a methodological approach which permits to predict mechanical properties as a function of material and process variability based on an experimental/ statistical study on the effect of the variability of the primary factors of alloying elements contents (Si, Cu and Mg) and HPDC process parameters (casting temperature and injection pressure) on mechanical properties of die cast aluminium alloys has been proposed. The microstructural features and the porosity level were also investigated and assessed. This approach has resulted in statistical design tool that will allow designers to make changes to the design of their casting and to industrialize them outside Europe.

Les alliages aluminium-silicium sont les alliages d’aluminium de moulage les plus couramment employés en raison de leur faible poids, de leurs caractéristiques mécaniques et de leur fluidité. Leurs propriétés mécaniques, en particulier leur résistance, peuvent être améliorées par l’affinage des grains et la modification des précipités de silicium. Par contre, la précipitation de composés intermétalliques riches en fer, comme la phase dite beta, a un effet néfaste sur la tenue en traction et la ductilité de ces alliages. Bien que diverses méthodes aient été proposées pour atténuer les effets de la phase beta, la compréhension des mécanismes de sa croissance pourrait s’avérer utile pour réduire ses effets néfastes. L’objectif de cette étude est d’établir la relation entre la vitesse de refroidissement et les caractéristiques microstructurales des alliages Al-Si hypoeutectiques. Dans une pièce coulée réelle, la vitesse de refroidissement locale peut grandement changer d’un point à l’autre du fait de la géométrie de la pièce mais aussi du fait des paramètres de coulée. Les variations de vitesse de refroidissement affectent le processus de solidification, et ceci est rendu évident par les changements des températures caractéristiques des courbes de refroidissement enregistrées en différents endroits d’une pièce. Les relations entre ces températures caractéristiques et la taille des grains et la modification du silicium eutectique sont présentées. Cette étude a aussi porté sur l’effet de la vitesse de refroidissement sur la morphologie de la phase beta dans le cas d’un alliage ternaire Al-Fe-Si. La croissance de la phase beta a été caractérisée par tomographie post-mortem et in-situ. Enfin, certains écarts par rapport aux caractéristiques de solidification usuelles, telles que la précipitation en écriture chinoise de la phase beta et la formation de rosettes, ont été observés et sont discutés. / Aluminum-silicon alloys are the most common aluminum casting alloys produced due to their fluidity characteristic and mechanical and light weight properties. However, there are several issues concerning application of Al-Si hypoeutectic alloys such as strength, which may be improved by refining grain size of the alloy and modifying silicon precipitates. Furthermore, precipitation of Fe-bearing intermetallics such as the so-called beta phase has a detrimental effect on tensile and ductility properties of Al-Si hypoeutectic alloys. Although various methods have been proposed to mitigate the effect of beta phase, the understanding of the mechanism of growth may be useful to reduce its detrimental effects. The objective of this study is to establish the relationship between the cooling rate and morphology features in Al-Si hypoeutectic alloys. In real casting condition, cooling rate is one of the factors that is not easy to predict, because it is related to the geometry of the parts and to the casting process itself. Changes in cooling rate affect the solidification process, and this is made apparent by the changes in the characteristic temperatures of cooling curves recorded in different locations of a part. The relation between these characteristic temperatures and grain size and eutectic silicon modification are presented. Furthermore, the present study also includes the effect of cooling rate on the morphology of beta phase in the case of a ternary Al-Fe-Si alloy. An attempt to characterize the growth of beta phase was performed through post-mortem and in-situ tomography. In addition, some variations from usual solidification features such as script monoclinic phase and rosettes were observed and are discussed.