Improvement of mechanical properties and reduction of yield asymmetry of extruded Mg-Sn-Zn alloy through Ca addition

Effects of Ca content (0.0, 0.5, 1.0, 2.0 wt%) on the microstructure, texture and mechanical properties of Mg-1.0Sn-0.5Zn-based alloys were investigated. The results stated that secondary phase of Mg-Sn-Zn alloy was transformed from Mg2Sn to CaMgSn and Mg2Ca with an increase in the Ca content. Ca addition also seriously affected the dynamic recrystallization and texture formation during the extrusion process. As for the as-extruded alloys, as Ca content increased from 0.0 to 2.0 wt%, the grain size was significantly decreased from ∼25 μm to 4–6 μm, whereas the texture type was converted from strong basal texture into weakened extrusion direction (ED)-split texture. Under tension, the elongation to fracture of the as-extruded Mg-Sn-Zn alloy was increased initially with the addition of Ca (0.0–1.0 wt%), and then decreased after 2.0 wt% Ca addition, whereas the counterpart in compression was changeless regardless of Ca content. Both tensile and compressive yield strengths of Mg-Sn-Zn alloy were monotonously increased with increasing Ca content, whereas this increment of yield strength induced by Ca addition was more pronounced in compression than that in tension. Obviously improved tension-compression yield asymmetry of Mg-Sn-Zn alloy via Ca addition was ascribed to grain refinement, texture modification and newly formed CaMgSn and Mg2Ca phase precipitates.