A novel die-casting Mg alloy with superior performance: Study of microstructure and mechanical behavior

Abstract

In this work, a novel Mg–6Y–3Zn–1Al (WZA631, wt.%) alloy with great performance is successfully prepared through high pressure die-casting method, and microstructure characteristics and mechanical behavior are systematically investigated. Results show that the WZA631 alloy is primarily composed of equiaxed α-Mg grain, block and irregular (Al,Zn)2Y phases, as well as honeycomb-shaped 18R long period stacking ordered (LPSO) phase. The α-Mg grain has finer average grain size than other die-casting Mg alloys and (Al,Zn)2Y phase with cubic structure (a = 0.76 nm) is firstly reported. Mechanical tests demonstrate that yield strength, ultimate tensile strength, and elongation of the studied alloy at room temperature are 175 MPa, 281 MPa and 9.8%, respectively, which is better compared with existing commercial or some newly die-casting alloys. For the yield strength, grain boundary strengthening, solid solution strengthening and second phase strengthening are dominant contribution mechanisms. Superior ultimate tensile strength and elongation is attributed to the abnormal work-hardening effect in stage III due to joint action of solute atoms (Y and Zn) as well as coherent LPSO phases. Underlying principles of grain refinement, strengthening effect and work-hardening are well discussed.