Effect of nanoparticle Al2O3 addition on microstructure and mechanical properties of 7075 alloy

Aluminium alloy matrix composites reinforced with 0.5, 1.0, 1.5 and 2.5 wt-% nanoparticle Al2O3 were fabricated by low frequency mechanical vibration combined with multi-frequency ultrasonic treatment. A microstructural study was carried out by optical, scanning electron and transmission electron microscopy and X-ray diffraction. The effect of reinforcements on the microstructural feature of the composites was investigated. Tensile and compression tests were carried out in order to identify the mechanical properties. The results of the microstructural study revealed a uniform distribution of nanoparticles in the matrix and dendrite refinement of the matrix alloy. It was also found that adding reinforcement content beyond 1.5 wt-% led to an increase in dendrite size values. Compared to the 7075 alloy, the yield strength, ultimate tensile strength and 0.2 compressive yield strength of 1.5 wt-% nano-Al2O3/7075 composite were increased by 74%, 57% and 100% respectively. The improved mechanical properties were due to particle pushing dendrite refinement and particle strengthening.