Fabrication, Mechanical Characterisation and Tribological Behaviour of Aluminium 6061 Hybrid Metal Matrix Composites Reinforced with Silicon Carbide and Graphite Particulates

Aluminium-based metal matrix composites (AMMCs) have gained significant attention in the aerospace, automotive and defence sectors owing to their superior specific strength, stiffness and wear resistance compared with unreinforced aluminium alloys. The present study investigates the fabrication, mechanical behaviour and tribological performance of Al 6061 hybrid composites reinforced with varying weight percentages of silicon carbide (SiC) particulates (5 wt% and 10 wt%) and a hybrid combination of SiC (5 wt%) with graphite (Gr, 3 wt%). Composites were fabricated using liquid-state stir casting followed by permanent mould casting. Microstructural characterisation was carried out using optical microscopy and scanning electron microscopy (SEM) to assess particle distribution, porosity and interfacial bonding. Mechanical properties evaluated include density, Brinell and Rockwell hardness, ultimate tensile strength (UTS), yield strength, percentage elongation, and Charpy impact energy. Tribological behaviour was assessed on a pin-on-disc tribometer under dry sliding conditions at varying normal loads (10–30 N) and sliding speeds (1.0–2.0 m/s) over a sliding distance of 500–1000 m. Results indicate that incorporation of 10 wt% SiC increases UTS by 26.1% and reduces wear rate by 49.7% relative to the unreinforced Al 6061 matrix. The hybrid Al-SiC-Gr composite demonstrates improved machinability and a balanced tribological performance, suggesting suitability for applications demanding combined wear resistance and lubricity. Statistical analysis using Analysis of Variance (ANOVA) confirms that normal load exerts the most significant influence on wear rate, followed by sliding speed and sliding distance.