Effects of lead addition on the microstructure and mechanical properties of as-cast Mg–4Zn alloys

► Significant improvements on ductility by adding only 1wt% Pb into the Mg–4Zn alloy. ► Pb additions suppress the formation of the intermetallic compounds, and affect the morphology of intermetallic particles. ► Pb distributes in α-Mg matrix at solid solution state. The effects of 1.0 and 3.0wt% lead (Pb) additions on the microstructure and mechanical properties of as-cast Mg–4wt%Zn alloys were studied. Tensile and nanoindentation tests were conducted to evaluate the mechanical properties of the as-cast alloys and the nanomechanical properties of primary α-Mg phase, respectively. Significant improvements of mechanical properties were achieved including the ultimate tensile strength (UTS) from 213MPa to 225MPa and elongation (E) from 14% to 20% by adding only 1.0wt% Pb into the Mg–4Zn alloy. It was found that the additions of Pb change the morphology of intermetallic phases in cast Mg–4%Zn alloy. In addition, Pb suppressed the formation of the intermetallic compounds and slightly decreased the grain size of Mg–4%Zn alloy. The nanohardness of primary α-Mg increases steady with addition of Pb.