Study on forming mechanism of sphere-like α phase in microstructure of semisolid hypereutectic Al-Si alloy

A large number of sphere-like α phases have firstly been found in microstructure of semisolid hypereutectic Al-Si alloy prepared by electromagnetic stirring. The results of the experiments indicated that this kind of sphere-like α phases appeared above eutectic temperature 575°C, and it remained in the microstructure of semisolid hypereutectic Al-Si alloy reheated above eutectic temperature. Based on the experiment results and theoretical analysis, this kind of α phase nucleates through the mergence of similar solid aluminum atom clusters in hyper eutectic Al-Si alloy melt under the electromagnetic force and high pressure in some mini-zone of the semisolid melt caused by electromagnetic stirring.