Influence of reinforcement on the fracture surface characteristics of multistage solutionized and precipitation-hardened ternary Al-Mg-Si hybrid composites

This study investigates the effect of SiC, B₄C, and hybrid (SiC + B₄C) reinforcements on the fracture surface characteristics of multistage solutionized and precipitation-hardened Al-Mg-Si (Al 6061) alloy. Composites are fabricated using two-stage stir casting with SiC (1–3 wt%), B₄C (1–3 wt%), and hybrid reinforcements (1–2 wt% each). As-cast (AC) samples are subjected to single-stage solutionizing (SSS) and multistage solutionizing (MSS), followed by artificial aging at 100 and 200 °C. Results show that MSS-aged samples exhibit a peak hardness of 222 VHN, a 177% improvement over AC (80 VHN). Similarly, UTS increases from 128 MPa (AC) to 287 MPa in hybrid composites, marking a 124% enhancement. Fractography shows that unreinforced Al 6061 failed mainly in a ductile mode with coarse dimples, while monolithic composites exhibit mixed ductile–brittle features. Hybrid composites exhibit refined dimples and strong interfacial bonding, thereby enhancing crack resistance. AAHT-treated samples show a shift toward brittle-dominant failure. The combined effect of dual reinforcements and MSS treatment enhances both strength and fracture resistance, demonstrating the potential of Al 6061 hybrid composites for lightweight structural applications.