Effect of Microstructure on the Thermal Expansion Behaviour and Mechanical Properties of a Hypereutectic Al-Si Alloy

초록

The effects of changes in microstructure of the Si phase on the thermal expasion coefficients (CTEs) and tensile properties of the hypereutectic Al-Si foundry alloy(A390) were investigated experimentally. Specimens were prepared by various fabrication processes such as permanent aold casting squeeze casting and spray casting and subsequently hot-extruded. CTEs of the spray-cast specimen were found to be about 10% lower than those of the permanent mold-cast specimen and the CTEs of hypereutectic Al-Si alloy(A390) were changed proportionally with the size of the Si phase. UTS of the spray-cast and hot-extruded specimen was drmatically improved by about 100% with improved elongation, compared to that of permanent mold-cast specimen. These improvement are mainly attributed to the reduction in size and aspect ratio of the brittle Si phase, and the elimination of microvoids/porosities formed during casting.