In this research, AA7068/Si3N4 composites were fabricated through stir casting with the attachment of ultrasonic treatment. The quenching medium and aging duration significantly influenced the hardness of Al alloy samples. Peak hardness was achieved after 12 h of artificial aging at the temperature of 140°C. The addition of nano Si3N4 significantly refined the microstructure of unreinforced AA7068. The dispersion of intermetallic compounds (MgZn2) and grain boundary discontinuation were noticed after the T-6 heat treatment. Ultimate tensile strength, yield strength, and hardness were improved by 70.95%, 76.19%, and 44.33%, respectively, with the addition of 1.5 weight % Si3N4 compared to as-cast alloy due to the combined effect of heat treatment, hall-Petch, Orowan, thermal miss match, load-bearing strengthening mechanisms and uniform dispersion of reinforcement. A reduction in percentage elongation was noticed due to composites’ brittle nature by the effect of ceramic Si3N4 particles’ inclusion. The fracture surfaces reveal ductile failure for alloy and mixed-mode failure in the case of composites.

The present work comprises the development of Al6061/nano Al2O3 composites with 0 to 4 weight percent in steps of 0.5 wt. % of nano alumina particles by using ultrasonic assisted stir casting. Casted samples were subjected to heat treatment and hot forging. Further forged and heat-treated gear blanks of nano Al2O3 (0 to 3.0 weight %) reinforced nanocomposites were machined to make spur gears for the wear test. The results have shown that nano Al2O3 reinforcement in the Al6061 matrix with heat treatment and forging improves the hardness and compressive strength up to 3.5 wt. %, after that, it starts decreasing because of the agglomeration of nano alumina particles. SEM results reveal grain refinement of the pure alloy after reinforcement. Removal of porosity and voids observed after forging operation. Wear resistance increasing with incorporation of Al2O3 nanoparticles in base alloy, reinforcement wt. %, precipitation hardening and hot forging also improves wear resistance and mechanical properties. These composites have widespread applications in gear, brake discs, crankshaft, clutch plates, pistons, and other components of automobiles and aircraft structures.