Improving the Mechanical Properties of Mg-5.6Ti-3Al Composite through Nano-Al2O3 Addition with Recrystallisation Heat Treatment

In the current study, the role of nano-Al2O3 addition to Mg-5.6Ti-3Al composite and subsequent recrystallisation heat treatment in improving the mechanical properties are investigated. The following Mg composites: (i) Mg-5.6Ti-3Al (with 3 wt% Al and 5.6 wt% Ti) and (ii) Mg-5.6Ti-3Al-2.5Al2O3 (with 3 wt% Al, 5.6 wt% Ti and 2.5 wt% Al2O3) were synthesised through the disintegrated melt deposition (DMD) technique followed by hot extrusion. Mg-5.6Ti-3Al-2.5Al2O3 composite was then subjected to recrystallisation heat treatment at 200ºC for 5 h. Mechanical property evaluation of the developed Mg composites indicated a significant improvement in microhardness and tensile properties when compared to pure Mg and Mg-5.6Ti-3Al. Microstructural characterisation revealed a significant grain refinement and uniform distribution of reinforcements/second phases in the developed Mg composites due to hybrid reinforcement additions and heat treatment. In case of as-extruded Mg-5.6Ti-3Al-2.5Al2O3 composite, the strength improvement occurred at the expense of ductility while for heat-treated composite, the increase in strength properties was accompanied by an increase in ductility. Based on the processing-structure-property correlation, it was identified that the presence of hard reinforcements/intermetallics in Mg matrix contributes to the improvement in strength properties while the stress relaxation during heat treatment contribute to the ductility enhancement.