Microstructures and mechanical properties of extruded and heat treated Mg–6Zn–1Si–0.5Mn alloys

Si-rich intermetallic particles stabilize the fine grained microstructure in extruded Mg–6Zn–1Si–0.5Mn alloy, resulting in a yield strength (YS) of ∼200 MPa, ultimate tensile strength (UTS) of ∼310 MPa with an elongation of ∼20%. Ca additions further refine the grain size leading to an increase in UTS by 30 MPa with no decrease in YS and elongation. The extruded Mg–6Zn–1Si–0.5Mn alloy can be age-hardened with the precipitation of fine [0 0 0 1]Mg rod-like β1′ (Mg4Zn7) particles and YS ∼ 290 MPa and UTS ∼ 320 MPa were achieved in the peak aged condition. The mechanical properties were further enhanced by pre-aging the alloy at 70 °C due to the refinement of the precipitate microstructure with YS ∼ 350 MPa and UTS ∼ 360 MPa.