The influence of Zn additions on the microstructure and creep resistance of high pressure die cast magnesium alloy AE44

Mg–4Al–4RE (AE44) alloys with 1 wt.%, 2 wt.% and 4 wt.% Zn additions were produced by high pressure die casting and their mechanical properties, especially creep properties at elevated temperatures, were evaluated. Although the tensile properties appear not be affected by the additions of Zn, there is a significant decrease in creep resistance with increasing Zn addition. To understand the influence of Zn additions on creep resistance, microstructures of the alloys before and after creep testing or long-term annealing at high temperatures were examined. It is revealed that, as a result of Zn additions, there is a transition in the predominant intermetallic phase form Al–RE to Al2REZn2. The Zn additions also lead to an increased level of Zn solute supersaturated in the α-Mg matrix and, as a result, dynamic precipitation occurred during creep. Based on the microstructural observations, the adverse effect of Zn additions on creep resistance of AE44 is discussed.