Comparison of Sb and Sr on modification and refinement of Mg2Si phase in AZ61-0.7Si magnesium alloy

The effects of Sb and Sr on the modification and refinement of Mg2Si phase in an AZ61-0.7Si magnesium alloy were investigated and compared. The results indicate that the difference of Sb and Sr in the modification and refinement of Mg2Si phase is significant. Addition of 0.4%Sb (mass fraction) to AZ61-0.7Si alloy can refine but not modify Mg2Si phase. Oppositely, by addition of 0.12%Sr to AZ61-0.7Si alloy, the Mg2Si phase changes from initial coarse Chinese script shape to fine granule and/or irregular polygonal shape. Accordingly, the Sr-modified AZ61-0.7Si alloy exhibits higher tensile and creep properties than the Sb-modified one. The difference of Sb and Sr in the modification and refinement of Mg2Si phase is possibly related to the following two aspects: 1) the disregistry at (100)Al4Sr//(100)Mg2Si is lower than that at (0001)Mg3Sb2//(111)Mg2Si (0.69% vs 1.72%) and 2) the onset crystallizing temperature of the Sr-modified AZ61-0.7Si alloy is lower than that of the Sb-modified one (603.1 °C vs 606.9 °C).