Abstract:The effect of T6 heat treatment (solution temperature and holding time) on the microstructure and mechanical properties of the Al-7Si-0.3Mg-0.3Y alloy was investigated by means of metallographic observation, mechanical properties test and fracture observation. The results indicate that T6 heat treatment can efficiently refine the microstructure and increase the mechanical properties. After by treated for 535℃×4.5h 180℃×8h, the morphology of eutectic Si changes from fibrous and nubbly to granular shape, the corners more rounded and passivated, and the tensile strength and elongation and hardness of the alloy reach to 271MPa , 6.5% and 73HB respectively. In contrast to the as-cast condition, the fracture surfaces of the alloy treated with T6 heat treatment are covered larges number of dimples and the dimples distribute more uniformly, and the fracture mechanism shows mixed-rupture characteristics of quasi-cleavage and dimples fracture.