Study Of Silicon Phase Refining In Hypereutectic Al-Si Alloy

Hypereutectic Al-Si alloy is good piston material with good wear resistance and low linear expansion coefficient and widely used in cylinders and pistons.However,coarse primary silicon and acicular eutectic silicon in hypereutectic Al-Si alloy adversely affect mechanical properties,so it is necessary to refine silicon phase effectively.Setting GM-390 alloy as baseline alloy,microstructure and heredity of GM-390 alloy were studied and optimized alloy with high strength and wear resistance was developed.Orthogonal experimental method was used to study influence of four orthogonal variables including stirring temperature,stirring time,stirring speed and return charge on microstructure.DoE orthogonal matrix for 4 elements factors and 3 levels was designed for microstructure optimization and results of orthogonal experiment were analyzed by Minitab.The optimized parameters as followed: stirring temperature is 800 °C,stirring time is 0.5 h,stirring speed is 60 rpm and return charge is 25%.It is proved that microstructure of optimized alloy has great retention and heredity in remelted alloys by remelting experiment.Compared with reference material GM-390,microstructure of remelting alloys is better than reference material and microstructure of specimen remelted for 2 hours is better than other three groups.Statistic data of primary silicon in the specimen remelted for 2 hours as followed: average diameter is 27 ?m,area ratio is 7.1% and max length is 111 ?m.Die-casting parameters in die-casting experiments of GM-390 alloy were researched,which will provide reference for optimized alloy diecasting experiments.The optimal die-casting parameters of GM-390 alloy as followed: die-casting pressure is 85 MPa,die-casting temperature is 700 °C and injection speed is 2 m/s.