Influence of solution treatment on microstructure and properties of in-situ Mg2Si/AZ91D composites

The influence of solution treatment on the microstructure and properties of Mg2Si/AZ91D composites fabricated from Mg-SiO2 system via in-situ processing method was investigated. The results show that coarse Chinese script shape Mg2Si phases can be formed by adding SiO2 into AZ91D magnesium alloy with Si content up to 1.5% of the alloy melt. During solution treatment, the morphology and distribution of the coarse Chinese script shape Mg2Si phases are modified. Meanwhile, the β-Mg17Al12 phase is dissolved into the magnesium matrix. With increasing holding time, the coarse Mg2Si phases tend to dissolve, break and spheroidize. After solution treatment at 420 °C for 16 h, Mg2Si phases become the finest and relatively well-distributed phase. The tensile strength and elongation are increased by 14.9% and 38.9%, respectively. It is believed that the Mg2Si phases continuously dissolve and break, and finally the spheroidized Mg2Si particles are obtained due to the interface tension of Mg2Si/Mg interface.