Behaviour of micro- and   nano-alumina-reinforced Mg–3Zn–0.7Zr–1Cu alloy composites processed at different sintering temperatures

This study aims to develop a magnesium-based hybrid composite via a powder metallurgy (PM) technique by simultaneously reinforcing the matrix (Mg–3Zn–0.7Zr–1Cu) alloy with micro-alumina (3.0 wt%) and nano-alumina (0.5 wt% and 1.0 wt%) particulates. The extensive processing involved two different sintering temperatures (400 and 450 °C) followed by hot extrusion and a heat treatment process. The study aimed to add to our understanding of the effects of sintering temperature and alumina content on the physical characteristics of Mg-based composites. It was revealed that increasing sintering temperature improves the density of composites by increasing their diffusion rates. In addition, significant improvements in the hardness, tensile properties and compressive properties of the composites were observed at higher sintering temperatures. It was also discovered that composites with higher alumina concentrations experienced agglomeration and were more porous than other composites. A micro-structural examination showed that composites with higher concentrations of nano-alumina had a finer grain structure than other composites and underwent a marginal reduction in grain size. However, the tensile and compressive properties of composites decreased when the nano-alumina content was increased to 1.0 wt%. The magnesium hybrid composite containing 3.0 wt% micro-alumina and 0.5 wt% nano-alumina sintered at 450 °C displayed the greatest tensile strength properties in all composites studied. A transformation from brittle to mixed-mode failure, with sufficient evidence of increased plastic deformation, was also noted in the hybrid composites. The present study suggests that adding up to 0.5 wt% nano-alumina and employing a higher sintering temperature enhances the overall characteristics of magnesium/alumina micro-composites.