Synergistic Effect of Reinforcement (10 wt.% SiC) in Al-7Si LM25 Alloy-Based Metal Matrix Composites and Heat Treatment-Driven Mechanical and Tribological Stability
摘要
As-received Al–7Si LM25 alloy and its 10 wt.% SiC-reinforced composite was fabricated using ultrasonic-assisted stir casting. The combined influence of reinforcement and heat treatment (100–400 °C) on microstructural evolution, tensile behavior, and dry sliding wear performance was investigated. Ultrasonic processing facilitated uniform dispersion of SiC particles and refinement of eutectic Si morphology. Subsequent heat treatment promoted silicon spheroidization and Mg2Si precipitation, leading to improved matrix–reinforcement interaction. The composite exhibited a maximum tensile strength of ~166 MPa at 200 °C. Heat treatment at 400 °C resulted in enhanced ductility (~8.8%) and improved strain-hardening behavior, attributed to matrix recovery and improved interfacial compatibility. Tribological tests conducted under a 20 N load showed a systematic reduction in wear rate with increasing temperature. The wear rate decreased from 0.0026 to 0.0017 mm3/m for the base alloy and from 0.0021 to 0.0008 mm3/m for the composite. Correspondingly, mass loss decreased by approximately 45%, indicating improved wear resistance. The coefficient of friction exhibited a moderate increase with temperature, associated with oxide-layer effects and matrix softening. However, the composite consistently demonstrated lower friction compared to the unreinforced alloy. SEM analysis and schematic interpretation revealed a transition in wear mechanism from severe abrasive wear to mixed abrasive–oxidative wear, and finally to oxidative wear with the formation of a protective glaze layer at elevated temperatures. The results demonstrate that the combined effect of SiC reinforcement and heat treatment enhances tribological stability, indicating the potential of these composites for elevated-temperature, wear-critical applications.