Effect of Trace B2O3 and Ultrasonic Treatment on Microstructures of In-situ Mg2Si/AM60 Composites

Effects of trace B2O3 and ultrasonic treatment on microstructures of in-situ Mg2Si/AM60 composites were investigated. The results show that microstructures of in-situ Mg2Si/AM60 composites become fine firstly, and then grow with increasing the content of B2O3 to 0.60% (mass fraction). Meanwhile, impurity Fe is removed from melt by FeB. Semi-continuous reticular Mg17Al12 phase transforms into granular, and coarser Chinese script type Mg2Si phase transforms into fibrous and granular when adding 0.40% B2O3, whose average grain size decreases from 140 mu m to 50 mu m, and the refined effort is closely related to heterogeneous nucleation of AlB2 phase. The morphology of Mg17Al12 phase and Mg2Si phase become finer and more uniform with ultrasonic treatment of 600 W power for 60 s.