Microstructural, Mechanical, and Tribological Behaviour of Stir-Cast LM13 Hybrid Metal Matrix Composites Reinforced with Silicon Carbide and Fly Ash

The present study focuses on the fabrication and characterization of LM13-based hybrid metal matrix composites reinforced with silicon carbide (SiC) and fly ash. Three hybrid compositions containing a constant 5 wt.% fly ash and varying SiC contents of 3, 6 and 9 wt.% were developed using the stir casting method. Microstructural observations revealed significant refinement of dendrite arm spacing and homogeneous dispersion of reinforcement particles within the matrix, indicating enhanced interfacial bonding. Mechanical characterization demonstrated notable improvement in hardness and tensile strength with increasing SiC content; the as-cast matrix alloy exhibited the lowest properties whereas Composite-3 (9 wt.% SiC + 5 wt.% fly ash) achieved the highest hardness (74.23 HV) and tensile strength (252.58 MPa), albeit at the expense of ductility. Tribological studies conducted under dry sliding conditions indicated that all hybrid composites possessed lower wear rates compared to the unreinforced alloy, with wear resistance improving progressively with SiC addition. Enhanced performance was attributed to the load-bearing capability of SiC, the formation of a mechanically mixed tribo-layer, and the abrasive resistance imparted by fly ash. Overall, the synergistic reinforcement strategy effectively upgraded the microstructure, mechanical properties and wear resistance of LM13 alloy, making Composite-3 the most suitable for high-performance automotive applications such as pistons and sliding components.