Optimization of Mn content for high strengths in high-speed extruded Mg-0.3Al-0.3Ca (wt%) dilute alloy

The effect of Mn content on mechanical properties and microstructure of Mg-0.3Al-0.3Ca-xMn (wt%, x=0, 0.2, 0.4, 0.8) dilute alloys extruded at a high die-exit speed of 60 m/min has been investigated. The strengths of the as-extruded samples increased with increasing Mn content, and Mg-0.3Al-0.3Ca-0.8Mn (AXM030308) alloy exhibited the highest 0.2% proof stress of 190 MPa. This is due to the formation of fine and strongly textured grain structure as well as the dispersion of high number density of Al-Mn particles. Subsequent solution treatment and peak aging resulted in further increase in strength. High number density of Guinier Preston zones (G.P. zones) were dispersed within fine grains with their [0001] axis normal to the extrusion direction in the peak aged Mg-0.3Al-0.3Ca-0.4Mn (AXM030304) alloy, exhibiting the highest 0.2% proof stress of 220 MPa with reasonable tensile ductility of 22%, which are superior to those of a peak aged 6063 aluminum alloy.