Influence of density-mismatch reinforcements and three-step T6 aging on Al7075 matrix composites

In this work, a hybrid Al7075 matrix composite was fabricated using reinforcements with a significant density mismatch. Granite powder (GrP) was fixed at 2 wt% while silicon nitride (Si3N4) varied at 3, 6, and 9 wt% and dispersed using a double-step stir casting technique. Microstructural analysis revealed that increasing reinforcement content led to higher porosity and agglomeration. Optimal aging time and its hardness were identified during peak-aged condition of alloy and composites, followed by homogenization and three-step aging based on optimized conditions. Results showed that hardness increased with total reinforcement content, achieving the highest values in heavily reinforced composites. However, specific strength varied among compositions. The composite containing 6 wt% Si₃N₄ exhibited superior wear resistance under both low and high load conditions. Microstructural observations corroborate the mechanical and wear behavior.