In the present work, alumina (Al₂O₃)-filled cast aluminium alloy (A356) composites were fabricated using stir casting technique by varying Al₂O₃ contents (0, 5, 10, 15, 20 and 25 wt.%). The fabricated composites were studied for their physical, mechanical and fracture toughness behaviour experimentally, theoretically and compared with finite element analysis method to validate the experimental and theoretical results. The physical and mechanical results showed that the addition of alumina to A356 alloy led to the improvement in tensile strength, flexural strength, hardness and impact strength. The void content of A356 alloy composites increased from 1.01% to 3.30% from 0 to 25 wt.% Al₂O₃. Young’s modulus value varied from 80 GPa to 111.27 GPa at 0 to 25 wt.% Al₂O₃ filled A356 alloy composite. The maximum value of flexural strength as calculated experimentally is found to be 389 MPa at 25 wt.% Al₂O₃. A 3D simulation of the composite using the unit cell model was developed in ANSYS using appropriate boundary conditions for tensile and flexural strength. Stress intensity factor for the crack propagation is determined using 2D simulation of the single side edge cracked plate in compact tension. The mechanical properties determined in papers I and II are used for the optimization purpose. Technique for order preference by similarity to ideal solution was applied to rank the composites using criteria based on mechanical properties like tensile strength, Young’s modulus, flexural strength and stress intensity factor. As per the results obtained from the optimization, the composite with 25 wt.% SiC exhibits the optimal properties.