Multi-scale Simulation Of Microstructure Of Al-si Alloy During Near-liquidus Casting

Semi-solid metal(SSM) processing has caught attention widely because of its features of high quality, high yield and near net shape in recent years.Near-liquidus casting is simple and efficient for gaining metal slurry which is the key of semi-solid metal processing.In this paper the thermal field model,concentration field model,nucleation and growth model of liquid-solid phase transformation were established, which based on the features of Al-Si alloys during Near-liquidus casting.The change of solid fraction was used to couple macroscale calculation with mesoscale calculation.In this paper, we obtained how composition (5%,7% and 10%),pouring temperature (930.OK and 891.OK) and casting velocity speed (0.003m/s-0.0015m/s) influence the microstructure of alloy. Furthermore,the optimal composition and technical conditions suited to semi-solid metal processing were obtained.Simulation results show that:the microstructure of alloy during near-liquidus casting is much better than the one of normal casting.Grains of near-liquidus casting are uniform, fine and equiaxed.During near-liquidus casting, the grains of Al-5%Si,Al-7%Si and Al-10%Si are all fine and equiaxed, but the ones of Al-7%Si are the best symmetrical and equiaxed. Grains of near-liquidus casting are coarse, elongated and non-equiaxed when the casting velocity is larger, for example 0.003m/s. Microstructure of alloy is well when casting velocity decreased properly. The primary silicon in grains is uniform,fine and dispersive during near-liquidus casting, which can improve the mechanical properties and machinability of hypereutectic Al-Si alloy.In the research, we found Al-7%Si is the best composition suited to near-liquidus casting.Its optimal technical conditions are:pouring temperature is 891.OK, casting velocity is 0.002m/s;cooling coefficient is 1000J/(m2·K).