Study On A357 Alloy Semi-solid Rheo-squeeze Casting Characteristics

Through the research of this paper, the optimum technological parameters of SSRTM rheo-casting have been obtained. When the stirring initial temperature of the melt was 640~650℃, the stirring rate was 600r/min, the stirring end temperature of the melt was 605~610℃, the semi-solid globular structure of A357 alloy could be obtained. Finaly, the average grain size of the primary α(Al) could reach 74μm, the shape factor was 0.86. Compared with the pure liquid squeeze casting, the less shrinkage cavity and porosity defects of A357 Alloy U-shaped specimen was produced by semisolid rheo-squeeze casting. While, the microstructure of A357 alloy samples was nearly spherical morphology, the mechanical properties of alloy specimen body anatomy can reach, tensile strength was 335 Mpa, yield strength was 271 mpa, elongation was 7.5%, hardness was 108 HBW. Under the conditions of sirring time 0.5~3min and stirring temperature 606~610℃, semi solid slurry of A357 alloy was prepared by isothermal stirring process, which was stable, controllable and efficient. Simultaneously, the intinal crystallization precipitation of non-dendrite αA-(Al) grains and latter crystallization precipitation of fine αB-(Al) grains was found in this study. The grain size of αA-(Al) and αB-(Al) grains increased gradually with the increase of isothermal stirring time, but the shape factor had no obvious change. At different stirring temperature, the temperature of semi-solid slurry was more low, the grain size of αA-(Al) was more large. However, the grain size of αB-(Al) was minimum under isothermal stirring at 601-603℃, and the minimum grain size could reach 53μm.