Influence of trace Sr additions on the microstructures and the mechanical properties of Mg-Al-La-based alloy

The microstructure, tensile properties and creep behavior of the high-pressure die-cast Mg-4Al-4La-xSr (x=0, 0.12, 0.25, 0.50, wt%) alloys were thoroughly studied. First, the eutectic morphologies change drastically after trace Sr addition, with some Al11La3 particles becoming plate and their distributions being irregular to some extent. This is probably due to Al4Sr particles that act as the nucleation substrates for Al11La3 phase during solidification. Second, the tensile properties of ALa44 alloy are distinctly improved by trace Sr addition. For instance, the yield strength, ultimate tensile strength, and elongation at 150 °C are improved by 13%, 10%, and 16%, respectively, after 0.25 wt% Sr addition. Third, the influence of trace Sr addition on the creep behavior of ALa44 alloy is complicated that the creep resistance is slightly improved at 200 °C and 75 MPa, but it is deteriorated after trace Sr addition at 200 °C and 85 MPa. Finally, the underlying causes of the complicated creep behavior and the operative creep mechanisms for the studied alloys are analyzed and discussed based on TEM observations.