Microstructural evolution and mechanical properties of Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr alloy prepared via pre-ageing and hot extrusion

The Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr (wt%) alloy was pre-aged prior to hot extrusion. Pre-ageing treatment introduced uniform distribution of plate-like Mg5RE precipitates, which transformed into nano-scale globular Mg5RE particles by split and spheroidization during hot extrusion. These globular Mg5RE particles contributed to continuous dynamic recrystallization by promoting the evolution of low misorientation sub-grain boundaries to high misorientation grain boundaries and caused grain refinement through grain boundary pinning. The improved mechanical properties were ascribed to the grain refinement, globular Mg5RE and LPSO precipitates. The ratio of compressive to tensile yield strength is 1.2. The yield strength asymmetry was attributed to the deformation asymmetry of LPSO phase and non-isotropic deformation behaviors of Mg matrix in tension and compression.