Microstructural and Mechanical Analysis of Sustainable Bottom Ash Reinforced LM13 Metal Matrix Composites

Aluminium matrix composites (AMCs) reinforced with waste-derived fillers have gained significant attention as sustainable and cost-effective alternatives to conventional ceramic-reinforced systems for automotive structural applications. This study addresses the critical knowledge gap concerning LM13 aluminium alloy reinforced exclusively with bottom ash (BA), a thermal power plant by-product whose microstructure–property relationships and composition-dependent behaviour in this alloy system remain poorly understood. LM13–BA composites were fabricated via stir casting with reinforcement contents of 0, 2, 4, 6, and 8 wt.%, and systematically characterized for phase constitution, microstructure, density, and mechanical behaviour. SEM confirmed uniform nano-scale particle dispersion up to 6 wt.%, while XRD identified strengthening phases including Mg 2 Si, Al 2 O 3 , periclase, and perryite, collectively contributing to grain refinement and improved interfacial bonding. Mechanical evaluation revealed that 6 wt.% BA yielded peak shear strength of 208.605 MPa representing a 113% improvement over the unreinforced alloy, alongside hardness gains of 29.5% in BHN and 25.5% in VHN, and a 57% enhancement in impact strength reaching 21.2 kJ/m 2 . Beyond this threshold, agglomeration and porosity at 8 wt.% caused measurable property deterioration, confirming the existence of an optimal reinforcement window. These findings establish 6 wt.% bottom ash as the optimal loading for LM13-based composites, demonstrating its viability as a standalone, environmentally responsible reinforcement for automotive and structural applications.