Development of a hybrid bamboo leaf ash/eggshell ash reinforced aluminum composite via stir casting for structural applications

Abstract

Aluminum metal matrix composites (AMMCs) reinforced with sustainable agro-waste particulates offer a promising route for developing cost-effective and eco-friendly structural materials. This study investigates the development of a first-of-its-kind hybrid AMMC using bamboo leaf ash (BLA) and eggshell ash (ESA) as dual agro-waste reinforcements within an AA6063 aluminum alloy matrix, fabricated via a two-step stir casting technique. The novelty lies in the synergistic combination of BLA (silica-rich) and ESA (calcium-rich) ashes, which has not been previously reported for AA6063 composites. Both BLA and ESA were processed from agricultural waste into fine particulates (< 125 μm). Composites with reinforcement compositions of 0 wt% (base alloy), 5 wt% BLA, 5 wt% ESA, 10 wt% hybrid (5% BLA + 5% ESA), and 15 wt% hybrid (7.5% BLA + 7.5% ESA) were synthesized. Comprehensive characterization was conducted to evaluate mechanical properties, density, and microstructure. The results demonstrate that the hybrid reinforcement produces a synergistic effect, with the 15 wt% hybrid composite yielding optimal properties: Rockwell hardness (HRB) of 80.4 and Charpy impact strength of 40.74 J, representing improvements of + 26% and + 85% over the unreinforced matrix, respectively. A concomitant reduction in density was also observed. Microstructural analysis confirmed uniform distribution of reinforcement particulates and good interfacial contact at the optical level. This research establishes, for the first time, the synergistic potential of hybrid BLA/ESA reinforcements, presenting a viable, sustainable composite material suitable for non-critical structural applications such as door and window frames, while promoting agricultural waste valorization and a circular economy.