Structure-property optimization in natural fiber-reinforced aluminum composites for enhanced mechanical performance: Effect of coconut husk ash and Al2O3 particulates

The growing interest in agro-waste-reinforced aluminum composites is driven by sustainability goals. However, their engineering adoption remains limited. This is due to unreliable structure–property relationships, especially when biomass-derived particulates are combined with hard ceramics. Many existing studies rely on qualitative microstructural interpretation. This study, however, addresses this gap by establishing a dispersion structure–property framework for monolithic and hybrid coconut-husk-reinforced (CHA)/Al 2 O 3 -AA6063 composites. AA6063-based composites containing varying proportions of CHA and Al 2 O 3 were fabricated using additive double-stir friction processing. Microstructural features were examined using SEM, while particle dispersion was quantified using Lorenz curves and Gini coefficients. Mechanical performance was determined through hardness testing and tensile characterization, including elastic modulus, strength, ductility, and toughness. Loren-Gini analysis revealed increasing dispersion heterogeneity with reinforcement content, with Gini coefficients ranging from ∼ 0.48 (CHA-0) to ∼ 0.71 (CHA-4). Experimental density decreased from 2.74-2.59 g/cm 3 ; porosity was below 2.3% across all composites; hardness increased from 54.5 to 96.83 BHN; strength ranged from 135.09 to 221.20 MPa. Elastic modulus varied from 9.65 to 15.63 GPa, ductility declined from 12.28% (AA6063) to ∼ 6.22–7.81% in the reinforced system, and toughness decreased from 17.57 MJ/m 3 to 4.34–9.54 MJ/m 3 . The results show that hybrid compositions offer the most balanced combination of strength, stiffness, and damage tolerance for engineering applications.