Investigations on the microstructural evolution and mechanical properties of novel Al 6061/7075–granite–SiC metal matrix composites fabricated through two-stage stir casting

This study aims to explore the untapped potential of scrap granite particles as reinforcement to enhance the performance of monolithic Al alloy. Through a two-stage stir casting process, the aluminium alloy matrix (AA6061/AA7075) is reinforced with waste granite particles (GP) (5 wt.% and 2 wt.%) and silicon carbide (SiC) (2 wt.%). The microstructural, mechanical and tribological properties of aluminium-based single and hybrid reinforced composites are investigated using ASTM standards. Microstructural characterisation, including optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD), confirms the presence of grain refinement and microstructural strain in the composites. The tensile, hardness, impact energy and wear resistance properties of M2 (AA6061, 2 wt.% GP) and Z1 (AA7075, 2 wt.% SiC) composites surpassed those of M1 (AA6061, 5 wt.% GP) and Z2 (AA7075, 2 wt.% SiC, 2 wt.% GP) composites, underscoring their enhanced performance. M2 composite demonstrates a significant 14.97% increase in hardness and a precise 0.82% increase in tensile strength compared to M1. Similarly, the Z1 composite showcases a remarkable 50.1% improvement in hardness and 22.2% enhancement in tensile strength compared to their respective counterpart (Z2). SEM-based fractography analysis of tensile and impact test specimens revealed the presence of dimples, cleavage facets, river lines, intergranular cracks and disbonding, offering valuable insights into the failure mode. Furthermore, the worn surfaces exhibited wear mechanisms involving abrasion and adhesion-delamination. The utilisation of granite particles as reinforcement in these composites resulted in significantly improved properties, positioning them as a promising alternative for future sustainable materials.