Development and Wear Analysis of Al6061 Hybrid Composites Dual-Reinforced with SiC and Graphite Particles

Aluminium Metal Matrix Composites (AMMCs) have gained considerable attention across aerospace, automotive, and defence sectors owing to their superior specific strength, stiffness, and wear resistance compared with unreinforced aluminium alloys. Their ability to be tailored through the selection of reinforcement type, size, and volume fraction makes them particularly attractive for structural and tribologically demanding applications, including armour panels, engine components, brake systems, and lightweight load-bearing structures. 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, a cost-effective and scalable manufacturing route suited to near-net-shape production. Microstructural characterisation was carried out using optical microscopy and scanning electron microscopy (SEM) to assess particle distribution, porosity, and interfacial bonding quality between the matrix and reinforcement phases. 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 sliding distances of 500–1000 m, simulating operational contact conditions experienced in engineering assemblies. 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, demonstrating the pronounced effect of hard ceramic reinforcement on load-bearing and wear-resisting capacity. The hybrid Al–SiC–Gr composite demonstrates improved machinability and a balanced tribological performance, suggesting suitability for applications demanding combined wear resistance and intrinsic lubricity, such as bearing housings, piston liners, and sliding contact components in defence platforms. 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, thereby providing a quantitative basis for the optimisation of composite performance under service-relevant conditions.