Influence of ultrasonication power on grain refinement, mechanical properties and wear behaviour of AZ91D/nano-Al2O3 composites

In this study, magnesium alloy (AZ91D) matrix composites reinforced with 1 wt% of nano alumina (n-Al2O3) were fabricated using novel Ultrasonic Treatment (UST) assisted squeeze casting method. UST was carried out at four different levels of ultrasonic power namely, 0 W (without UST), 1500 W, 2000 W and 2500 W at constant frequency and time. The composites were heat-treated at T6 condition under argon gas protected environment. Microstructural analysis was done using optical microscopy and high-resolution scanning electron microscopy. Physical, mechanical and tribological properties of the composites were evaluated. A significant refinement in grain structure and improvement in porosity was seen on an increase in UST power. Improvement was seen in micro-hardness, yield strength, ultimate tensile strength and % of elongation of the composite fabricated at 2500 W by 18%, 48%, 28%, and 10% respectively compared to an untreated composite. The composite fabricated at 2500 W showed less wear rate and coefficient of friction when compared to other composites at all sliding conditions. Scanning electron microscope images of the worn surface of the composite pins revealed that the wear mechanisms dominated were abrasion, adhesion, oxidation and delamination.