Microstructure and mechanical properties of as-cast Mg-Sn-Zn-Y alloys

The effects of yttrium(Y) addition on the microstructure and mechanical properties of the as-cast Mg-5Sn-3Zn have been investigated. Results indicate that the addition of Y to Mg-5Sn-3Zn not only refines the grains but also promotes the precipitation of MgSnY phase with high stability. An increase addition of Y form 0.2-0.8 wt% increases the amount and size of MgSnY which would influence the mechanical properties of the as-cast alloys. The precipitation behavior of Mg2Sn and MgZn2 was also discussed. It was found that the MgZn2 phase is tend to precipitates attach to the Mg2Sn phase because the mismatch degree between them is relatively low, which have some guiding role in increase the amount of MgZn2 by Sn addition to enhance the performance of Mg-Sn-Zn alloys. In addition, Y to the Mg-5Sn-3Zn alloy general improves the mechanical properties but over does of Y would make it decrease, especially the elongation, which is affected by the grains and precipitates, improved significantly. The addition of 0.5 wt% Y gives the alloy favorable properties that the ultimate tensile strength reaches to 229 MPa and the elongation peaks at 19.2% at room temperature.