Effect of Mechanical Vibration and Grain Refiner on Microstructure and Mechanical Properties of AZ91Mg Alloy during Solidification

In the present work, microstructure and mechanical properties like hardness, tensile, and wear of AZ91 Mg alloy have been studied for four different samples of the same composition. The first sample was as-cast alloy; the second sample was given only mechanical vibration (15 Hz-2 mm), the third sample by adding 2 wt.% ZnO as a grain refiner, and the fourth sample with a collective effect of grain refiner and the imposition of mechanical vibration during solidification. The optimum results were obtained for the fourth sample, because both mechanical vibrations and grain refiner provide nucleating sites in the melt, resulting in grain growth restriction. Microstructural studies reveal that the combined effect results in fragmentation and uniform distribution of primary α-Mg and β-Mg17Al12 phases. It is witnessed that, among all samples, the fourth sample is showing superior density and mechanical properties when compared with the as-cast sample. Hardness at three different locations (top, middle, and bottom) is increased from 53-72, 55-79, to 58-92 BHN, respectively. Similarly, yield strength, UTS, and % elongation has increased from 90-121 MPa, 140-182 MPa, to 1.8-2.8, respectively. Likewise, the coefficient of friction and specific wear rate at 5 N was decreased from 0.59-0.13 to 1.07-0.43 mm3/Nm, respectively, whereas at 10 N load, these were 0.68-0.23 and 1.69-0.47 mm3/Nm respectively.