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L'effet du taux de refroidissement, modification au strontium, traitement thermique du liquide et la mise en solution sur les caractéristiques des particules du silicium eutectique et les propriétés de traction de l'alliage A356
| Content Provider | Semantic Scholar |
|---|---|
| Author | Chen, Hu |
| Copyright Year | 2005 |
| Abstract | As one of the major families of aluminium alloys, Al-Si alloys offer excellent castability, good corrosion resistance, as well as a wide range of physical and mechanical properties. The commercially popular A356.2 alloy, belonging to the Al-Si-Mg system, has excellent casting characteristics, weldability, pressure tightness and corrosion resistance. The alloy is generally heat-treated (T6 treatment) to provide various combinations of tensile and physical properties that are attractive for several aircraft and automobile applications such as engine blocks, cylinderheads and wheels. Such critical components require that the casting parts exhibit consistent strength-ductility properties throughout the casting. It is well known that the morphology of the eutectic silicon particles in Al-Si alloys is a key factor which determines the mechanical properties of these alloys, hi the as-cast condition, the alloy microstructure contains brittle, acicular silicon particles in the form of plates with sharp sides and ends. From a mechanical point of view, the presence of such plate-like particles will degrade the mechanical properties because inherent stresses will be centralized on the sharp sides and ends and induce fracture more rapidly. On the other hand, if the eutectic silicon particles are obtained in a fine, fibrous form (fibrous silicon), such a morphology contributes to much better tensile properties with somewhat higher values of ultimate tensile strength and greatly increased values of ductility. In addition to the size and shape of the eutectic silicon particles, grain size and DAS (dendrite arm spacing) is also important for alloy properties. The DAS is determined by cooling rate. Higher cooling rates lead to a finer grain size and a smaller value of DAS which improve the properties. While a high cooling rate can also produce finer eutectic silicon particles, their morphology, however, remains the same (i.e. acicular). The 'modification' or change in the silicon particle morphology from acicular to fibrous is usually brought about by adding a 'modifier' to the alloy melt, for which strontium is commonly employed in the form of Al-10%Sr master alloy. The role of strontium is to primarily affect the nucleation and growth of the silicon phase by developing an effective impurity buildup in front of silicon growth fronts present in the solidifying alloy. Eventually, this impurity buildup produces the fine silicon particles which contain a high density of twins. |
| File Format | PDF HTM / HTML |
| DOI | 10.1522/24144617 |
| Alternate Webpage(s) | https://constellation.uqac.ca/565/1/24144617.pdf |
| Alternate Webpage(s) | https://doi.org/10.1522/24144617 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
