Enhanced mechanical properties of as-cast rare earth bearing magnesium alloy via elevated-temperature homogenization

Abstract

The effects of elevated-temperature homogenization on the microstructure and mechanical properties of a magnesium alloy containing mischmetal rare earth (RE) were investigated. It was revealed that the homogenization treatment leads to spheroidization and partial dissolution of the Mg12RE phase in the eutectic constituent. For the optimum homogenized alloy (20 h at 535 ºC), the elimination of the deleterious eutectics and the solid solution strengthening effect of RE elements were the main contributing factors for improving the ultimate tensile strength and ductility. Accordingly, a 157 % increase in tensile toughness compared to the as-cast condition was recorded. Moreover, as a direct consequence of eliminating the eutectic constituent, homogenization led to a change in the fracture mechanism from a brittle intergranular mode to an intragranular cleavage with the incorporation of some ductile dimples. Accordingly, homogenization heat treatment was found to be an alternative enhancing route of strength-ductility trade off, besides thermomechanical processing (by hot deformation and dynamic recrystallization) and severe plastic deformation.