A Study of Development and Sliding Wear Behavior of AZ91D/Al2O3 Composites Fabricated by Ultrasonic-Assisted Stir Casting

The current research work presents a detailed study of the development and wear performance of Al2O3 reinforced AZ91 Magnesium metal matrix composites. The fabrication of composites was performed using the ultrasonic-assisted stir casting process with optimized parameters. The Al2O3 reinforcement powder was varied in wt% of 0.75, 1.5, and 2.25, respectively. Different parametric combinations of stirrer speed, ultrasonic power, and reinforcement concentration were used to fabricate the composites as per the Taguchi L9 design matrix. These parameters were found to influence the distribution of the reinforcement particulates, resulting in the varying microstructure and wear resistance of the composites. The wear behaviour of composites was examined against the rotating EN-32 counterface steel disc of a pin-on-disc tribometer. The SEM, XRD, and EDX analyses were performed to analyze their surface morphologies, microstructures, phases, and elemental compositions. The enhancement in wear resistance was attributed to the uniform dispersion of particulates owing to the ultrasonic agitations. The microstructural images of the worn-out specimens elucidated the formation of wear tracks on the composite surface, which were caused by adhesion, micro-cutting of the soft matrix, oxidation, and delamination during sliding wear testing. The material removal has also occurred due to the pull-out of Al2O3 reinforcement particles and eruption of soft AZ91 Mg matrix. The composite developed at higher reinforcement concentration has shown a relatively smoother surface with light wear tracks and small agglomerations.