Effect of Ultrasonic Impact Treating on Wear Resistance and Microhardness of AZ91D Magnesium Alloy

The surface of AZ91D magnesium alloy was treated using a HJ-III type ultrasonic impact treating (UIT) machine and the microstructures on the treated surface was investigated by an optical microscope and a High Resolution Transmission Electron Microscope. The wear resistance of AZ91D magnesium alloy was experimentally studied both for the treated and un-treated samples. The effects of UIT on the worn surfaces and microhardness were also investigated using SEM and microhardness tester. The results indicate that the severe plastic deformation in the surface of AZ91D is formed by UIT, and the thickness of the plastic deformation layer is approximately 120 μm. The grains on the top surfaces of AZ91D are highly refined. The wear resistance and microhardness of the treated surface layer of AZ91D alloy could be enhanced significantly compared to that of the un-treated sample. The longer the impact time and the higher the impact current, the greater the wear resistance and the microhardness of the treated surface layer of AZ91D would be. When the UIT time is 9 min and the current is 1.5 A, the microhardness and wear resistance of the treated specimen is about 112.5% and 57.39% higher than those of the untreated specimen, respectively.