Improved Mechanical Properties of ZX21 Magnesium Alloy by Mischmetal Addition and Hot Deformation

Microstructural evolutions and improvement of mechanical properties of ZXE21y (Mg-2Zn-1Ca-yRE, wt%) alloys via mischmetal rare earth (RE) addition and applying thermomechanical processing by the hot extrusion process were investigated. It was revealed that the refinement of as-cast grain size effectively saturates at ~ 1 wt% RE with grain size reduction of 52.9% compared to the RE-free alloy; while higher additions just increase the amount of Mg₁₂RE-type eutectic constituents. Accordingly, adding 1 wt% RE improved the ductility with 50% improvement in the total elongation; while higher RE additions showed an adverse effect due to the increase in the amount of the intergranular eutectic constituents. Hot extrusion resulted in a remarkable grain refinement by dynamic recrystallization (DRX) with grain size reduction of 96% compared to the as-cast counterpart as well as fragmentation and dispersion of intermetallics, leading to a significant improvement of strength, ductility, and tensile toughness toward achieving a remarkable strength-ductility synergy. In this regard, the tensile toughness of the Mg-2Zn-1Ca-1RE alloy showed 42% improvement after applying the extrusion process.