Fabrication characteristics and mechanical behaviour of rice husk ash – Alumina reinforced Al‑Mg‑Si alloy matrix hybrid composites

Abstract

The fabrication characteristics and mechanical behaviour of Al‑Mg‑Si alloy matrix composites reinforced with alumina (Al2O3) and rice husk ash (RHA, an agro‑waste) was investigated. This was aimed at assessing the viability of developing high performance Al matrix composites at reduced cost. Al2O3 particulates added with 0, 2, 3, and 4 wt% RHA were utilized to prepare 10 wt% of the reinforcing phase with Al‑Mg‑Si alloy as matrix using two‑step stir casting method. Density measurement, estimated percent porosity, tensile testing, micro‑hardness measurement, optical microscopy, and SEM examination were used to characterize the composites produced. The results show that the less dense Al‑Mg‑Si/RHA/Al2O3 hybrid composites have estimated percent porosity levels as low as the single Al2O3 reinforced grade (< 2.3% porosity). The hardness of the hybrid composites decreases slightly with increase in RHA content with a maximum reduction of less than 11% observed for the Al‑4 wt% RHA‑6wt% Al2O3 composition (in comparison with the Al‑10 wt% Al2O3 single reinforced composition). Tensile strength reductions of 8% and 13%, and specific strengths which were 3.56% and 7.7% lower were respectively observed for the 3 wt% and 4 wt% RHA containing hybrid composites. The specific strength, percent elongation and fracture toughness of the 2 wt% RHA containing hybrid composite was however, higher than that of the single Al2O3 reinforced and other hybrid composite compositions worked on. RHA thus has great promise to serve as a complementing reinforcement for the development of low cost‑high performance aluminum hybrid composites.