Effect of Al addition on microstructure and mechanical properties of Mg-Zn-Sn-Mn alloy

The microstructure and properties of the as-cast, as-homogenized and as-extruded Mg-6Zn-4Sn-1Mn (ZTM641) alloy with various Al contents (0, 0.5, 1, 2, 3 and 4 wt.%) were investigated by OM, XRD, DSC, SEM, TEM and uniaxial tensile tests. The results show that when the Al content is not higher than 0.5%, the alloys are mainly composed of alpha-Mg, Mg2Sn, Al8Mn5 and Mg7Zn3 phases. When the Al content is higher than 0.5%, the alloys mainly consist of alpha-Mg, Mg2Sn, MgZn, Mg-32(Al,Zn)(49), Al2Mg5Zn2, Al11Mn4 and Al8Mn5 phases. A small amount of Al (<= 1%) can increase the proportion of fine dynamic recrystallized (DRXed) grains during hot-extrusion process. The room-temperature tensile test results show that the ZTM641-1Al alloy has the best comprehensive mechanical properties, in which the ultimate tensile strength is 332 MPa, yield strength is 221 MPa and the elongation is 15%. Elevated-temperature tensile test results at 150 and 200 degrees C show that ZTM641-2Al alloy has the best comprehensive mechanical properties.