Advanced Microstructural and Tribo-Mechanical Characterization of Al6061-Sic-Gr Hybrid Composites Fabricated Via Two-Stage Stir Casting

Abstract

The development of lightweight metal matrix composites (MMCs) with superior mechanical and tribological performance is of critical importance for aerospace, automotive, and structural applications. This study investigates the fabrication, microstructural evolution, and property evaluation of Al6061 alloy-based composites reinforced with varying weight fractions of silicon carbide (SiC) and graphite (Gr), both as mono-reinforcements and in hybrid form, using a two-stage stir casting process. The process ensured improved wettability and homogeneous dispersion of reinforcements by introducing preheated particles at the semi-solid state. Comprehensive microstructural analysis using SEM and EDS confirmed uniform distribution of reinforcements and minimal porosity in hybrid compositions. Mechanical testing revealed that the incorporation of 6 wt.% SiC enhanced hardness and tensile strength, whereas graphite additions (up to 6 wt.%) improved wear resistance and ductility. The optimal balance was observed in hybrid composites containing 6 wt.% SiC and 4–6 wt.% Gr, which exhibited significant improvements in wear rate (70% reduction) and strength (UTS ~128 MPa) while maintaining acceptable ductility. Wear behavior assessed via pin-on-disc tests showed that the hybrid composites outperformed mono-reinforced and base alloy in frictional stability and surface integrity. These results confirm the effectiveness of hybrid reinforcement strategy and two-stage stir casting in producing multifunctional MMCs. The study provides a robust framework for tailoring aluminium-based composites for industrial-scale manufacturing with high-performance metrics suitable for tribo-mechanical applications.