“Experimental Study on the Mechanical and Microstructural Properties of Aluminium Hybrid Composites Reinforced with Graphite and Rice Husk Ash”

Abstract

This study investigates the mechanical properties of graphite powder (GP) and rice husk ash (RHA) reinforced aluminium matrix composites in comparison with pure aluminium. Tensile test specimens were fabricated with identical dimensions to ensure repeatability, having a total length of 170 mm, a gauge length of 90 mm, a gauge diameter of 12.5 mm, and a grip diameter of 20 mm. Hardness test samples were prepared with dimensions of 25 × 25 × 2 mm, while Charpy V-notch impact specimens measured 55 × 10 × 10 mm³.Pure aluminium exhibited an ultimate tensile strength of 90 MPa and a yield strength of 34.5 MPa. The incorporation of GP and RHA led to a gradual improvement in tensile properties, with the maximum values obtained for the composite containing 2.05% GP and 0.41% RHA. This composition achieved an ultimate tensile strength of 147.98 MPa and a yield strength of 55.85 MPa, corresponding to improvements of 64.42% and 61.88%, respectively. The improvement is attributed to effective load transfer and dispersion strengthening mechanisms.Rockwell hardness increased significantly from 20 HRB for pure aluminium to a maximum of 89 HRB for the highest reinforced composite due to the presence of hard silica-rich RHA particles and grain refinement. Impact test results showed a non-linear trend, with the highest impact energy of 15.3 J observed at the 1.23% GP–1.23% RHA composition due to crack-bridging and crack-deflection mechanisms, while higher reinforcement levels resulted in reduced toughness because of increased brittleness.Overall, the results demonstrate that GP–RHA hybrid reinforcement effectively enhances the mechanical performance of aluminium matrix composites, with an optimal balance of strength, hardness, and impact toughness achieved at intermediate reinforcement levels.