Effects of Zn and Ca addition on microstructure and mechanical properties of as-extruded Mg-1.0Sn alloy sheet

The microstructure and mechanical properties of as-extruded Mg-1.0Sn, Mg-1.0Sn-0.5Zn, Mg-1.0Sn-0.7Ca and Mg-1.0Sn-0.5Zn-0.5Ca (all in wt%) alloy sheets were investigated and compared at room temperature. The results showed that the Mg-1.0Sn and Mg-1.0Sn-0.5Zn alloys exhibited relatively coarse grains and typical strong basal textures, whereas the Mg-1.0Sn-0.7Ca and Mg-1.0Sn-0.5Zn-0.5Ca alloys showed obvious grain refinement and weakened extrusion direction (ED)-split textures. The yield strength and ductility of the Mg-1.0Sn-0.5Zn alloy increased by approximately 20 MPa and 5%, respectively, than that of the Mg-1.0Sn alloy. Despite the similar ductilities of the Mg-1.0Sn-0.5Zn and Mg-1.0Sn-0.7Ca alloys, the yield strength improvement was more remarkable in the Mg-1.0Sn-0.7Ca alloy. In particular, the yield strength of the Mg-1.0Sn-0.7Ca alloy in tension along transverse direction was 209 MPa, which was about 73 MPa higher than that of the Mg-1.0Sn alloy. This was attributed mainly to the grain refinement from ~26 µm to ~9 µm and the precipitation strengthening induced by homogeneous distributed, spherical Mg2Ca nano-particles. Furthermore, ductility of the Mg-1.0Sn-0.5Zn-0.5Ca alloy in tension along the ED could reach up to 30.5%, which was almost twice that of the Mg-1.0Sn-0.7Ca alloy, because of increased activation of prismatic slip, enhanced grain boundary cohesion and improved intergranular strain propagation capacity. Therefore, individual addition of dilute Zn or Ca contributed to an improvement in the strength and ductility of the Mg-1.0Sn alloy, whereas combined addition of dilute Zn and Ca provided a new approach for achieving excellent ductility of the Mg-1.0Sn alloy.