Effect of ball milling the hybrid reinforcements on the microstructure and mechanical properties of Mg–(Ti + n-Al2O3) composites

Abstract

In this study, composites containing pure magnesium and hybrid reinforcements (5.6wt.% titanium (Ti) particulates and 2.5wt.% nanoscale alumina (n-Al2O3) particles) were synthesized using the disintegrated melt deposition technique followed by hot extrusion. The hybrid reinforcement addition into the Mg matrix was carried out in two ways: (i) by direct addition of the reinforcements into the Mg–matrix, Mg–(5.6Ti+2.5n-Al2O3) and (ii) by pre-synthesizing the composite reinforcement by ball milling and its subsequent addition into the Mg–matrix, Mg–(5.6Ti+2.5n-Al2O3)BM. Microstructural characterization revealed significant grain refinement due to reinforcement addition. The evaluation of mechanical properties indicated a significant improvement in microhardness, tensile and compressive properties of the composites when compared to monolithic magnesium. For the Mg–(5.6Ti+2.5n-Al2O3) composite, wherein the reinforcements were directly added into the matrix, the improvement in strength properties occurred at the expense of ductility. For the Mg–(5.6Ti+2.5n-Al2O3)BM composites with pre-synthesized ball-milled reinforcements, the increase in strength properties was accompanied by an increase/retention of ductility. The observed difference in behaviour of the composites is primarily attributed to the morphology and distribution of the reinforcements obtained due to the ball-milling process, thereby resulting in composites with enhanced toughness.