<![CDATA[Aluminum matrix composites often suffer from low mechanical performance due to poor reinforcement distribution and manufacturing defects during the stir casting process. This study aims to evaluate the effect of stirring duration on the mechanical properties, microstructural distribution, and fracture behaviour of Al-Si-Cu matrix composites reinforced with Al2O3 particles. Composites were fabricated using varying mechanical stirring durations of 5, 10, 15, and 20 minutes, with three replicates evaluated for each experimental condition (n=3). Material performance evaluation was conducted through Ultimate Tensile Strength (UTS), elongation at break, and Brinell hardness (HBW) testing, accompanied by Scanning Electron Microscopy (SEM) for microstructural and fracture morphology analysis. The results indicate that mechanical properties followed a parabolic trend with increasing stirring duration. A 10-minute stirring duration was optimal, achieving peak UTS (163.33 MPa), maximum elongation, and highest hardness (87.32 HBW). Microstructural SEM observation revealed uniform Al2O3 particle dispersion and solid interfacial bonding at 10-minute, yielding a ductile fracture with fine dimples. Conversely, prolonged stirring for 20 minutes significantly reduced UTS to 56.78 MPa and deteriorated elongation, suspected to be due to gas entrapment porosity and particle pull-out voids, which triggered a cleavage-dominated brittle fracture mode. In conclusion, controlling stirring duration is critical to optimizing microstructural homogeneity, enhancing ductility, and preventing premature failure in cast composites.]]>
