Improving mechanical properties and yield asymmetry in high-speed extrudable Mg-1.1Al-0.24Ca (wt%) alloy by high Mn addition

The chemical composition of a Mg-1.1Al-0.33Ca-0.44Mn (wt%) alloy, AXM10304, has been optimized for high speed extrusion. The extrudability is substantially improved from 24 m/min to 60 m/min by slightly reducing the Ca content from 0.33 wt% to 0.24 wt%. Then, the effect of Mn content on the mechanical properties and microstructures of extruded Mg-1.1Al-0.24Ca based alloys were investigated. In a solution-treated condition, tensile yield stress is enhanced to 200 MPa with increasing Mn content up to 0.68 wt% and the compressive yield stress is also improved to 164 MPa with increasing Mn content up to 1.0 wt% due to grain size refinement. After an artificial aging, Guinier Preston zones were dispersed within the Mg matrix, and the tensile and compressive yield stresses are increased by 70 MPa and 30 MPa regardless of the Mn content. Consequently, the peak-aged 1.1Al-0.24Ca-1.0Mn alloy, AXM1021, exhibits high tensile and compressive yield stresses of 263 MPa and 197 MPa with a good yield asymmetry of 0.74 (a ratio of compressive yield stress to tensile one).