Experimental Investigation of the Influence of Particle Size and Surface Treatment on the Mechanical Properties of Palm Kernel Shell Ash-Reinforced Aluminium Matrix Composites

Agricultural waste-derived ceramic reinforcements for aluminium matrix composites offer a promising route to developing low-cost, lightweight structural materials from Nigeria's abundant agro-industrial by-products, with palm kernel shell ash representing a widely available, silica-rich reinforcement candidate across the South South and South East agricultural zones. This study experimentally investigates the influence of palm kernel shell ash particle size and surface treatment on the mechanical properties of composites produced by stir casting. Palm kernel shell ash was sieved to particle size fractions of 75, 150, and 250 micrometres, and chemically treated with 10 percent hydrofluoric acid to improve wettability and interfacial bonding with the aluminium matrix. Composite specimens at reinforcement weight fractions of 5, 10, and 15 percent were produced by two-stage stir casting using recycled AA6063 alloy as the matrix material. Tensile strength, yield strength, elongation, hardness, and impact energy were determined following standard ASTM procedures. Results showed that composites reinforced with 75-micrometre acid-treated particles at 10 percent weight fraction achieved the highest ultimate tensile strength of 194 MPa, representing a 38 percent improvement over the unreinforced alloy, and a hardness of 72 HRB. Scanning electron microscopy of fracture surfaces revealed improved particle-matrix interfacial bonding in acid-treated specimens relative to untreated controls, with evidence of matrix-dominated fracture rather than interfacial debonding. Keywords: aluminium matrix composite, palm kernel shell ash, particle reinforcement, stir casting, mechanical properties.