Influence of cryogenic treatment on the microstructure and mechanical behaviour of Aluminium-Silicon Carbide-Graphite composites

The advancement of modern engineering applications demands lightweight materials with superior mechanical and tribological performance. In this context, aluminum-based hybrid metal matrix composites reinforced with ceramic and solid lubricant phases have gained significant attention. The present study investigates the influence of cryogenic treatment on the microstructure and mechanical behavior of Aluminum-Silicon Carbide-Graphite (Al-SiC-Gr) hybrid composites fabricated using the stir casting technique. Initially, Al6061 composites reinforced with varying SiC contents (11–15 wt%) were evaluated to determine the optimum reinforcement level based on tensile strength, hardness, and wear performance. An optimum SiC content of 13 wt% was identified, beyond which porosity and particle agglomeration adversely affected mechanical properties. Subsequently, hybrid composites containing 13 wt% SiC with 1–3 wt% graphite were produced and subjected to deep cryogenic treatment at -196 °C with a soaking duration of 24 h, followed by controlled warming to room temperature. The effects of cryogenic treatment on microstructure were examined using optical microscopy, scanning electron microscopy, and energy-dispersive X-ray analysis. Cryogenically treated specimens exhibited grain refinement, enhanced interfacial bonding, and increased precipitation density, leading to notable improvements in mechanical performance. Compared to untreated specimens, cryo-treated hybrid composites showed enhancements of 6–8% in ultimate tensile strength, 15–20% in yield strength, and 3–8% in hardness, accompanied by a reduction in ductility. The findings demonstrate that cryogenic treatment acts as an effective post-processing technique to further enhance the mechanical performance of Al-SiC-Gr hybrid composites, making them suitable for advanced structural and tribological applications.