Effect of zinc and mischmetal on microstructure and mechanical properties of Mg-Al-Mn alloy

Mg-2Al-0.5Mn alloys with 0–0.5% Zn and 0.5%-1.0% La-Ce misch metal (MM) were prepared by metal mould casting method. Effect of alloying elements Zn and MM on microstructures were investigated by X-ray diffraction, optical microstructure and scanning electron microscope. The results showed that Zn and MM additions led to an obvious grain refinement. Addition of 0.5% Zn resulted in about 30% reduction in grain size for Mg-2Al-0.5Mn alloys, while 0.5% MM addition caused about 40% reduction in grain size. The tensile properties of the as-cast alloys were tested at room temperature. Mg-2Al-0.5Mn-0.5Zn-1MM alloy exhibited the best mechanical properties. Improvement of mechanical properties was attributed to the grain-refining effect and the formation of Al11MM3 phase which could inhibit dislocation movement and grain-boundary sliding during deformation.