He Bolin

Experimental Research on Microhardness and Wear Resistance of MB8 Magnesium Alloy Treated by Ultrasonic Impact

Abstract The surface of MB8 wrought magnesium alloy was treated by HJ-III type ultrasonic impact treating (UIT) machine. The microstructures of the treated surface were analyzed by an optical microscope, and the grain refining mechanism of UIT was investigated by High Resolution Transmission Electron Microscopy (HRTEM). The wear resistance of MB8 wrought magnesium alloy was experimentally researched both with the treated and untreated specimens. The effect of UIT process on the microstructure and microhardness were also investigated using scanning electron microscope (SEM) and microhardness tester. The results indicate that the grains on the top surfaces of MB8 are highly refined. The severe plastic deformation is formed by UIT, and the thickness of the plastic deformation layer is approximately 180 µm. The microhardness and wear resistance of the treated surface layer of MB8 can be enhanced significantly compared to that of the untreated specimens. The longer the UIT time, the greater of the microhardness and wear resistance the treated surface layer of MB8 will be. When the impact current is 1.2 A and impact time is 6 min, the microhardness and wear resistance of the treated sample is about 102.8% and 51.83% higher than that of the untreated specimen, respectively.

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

Abstract 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.

Mechanism of semisolid microstructure evolution during stirring

The grain spheroidizing and fining mechanism during stirring was analyzed and discussed. The research indicates that stirring can restrict dendritic growth. According to the force analysis of dendrite arms, it found that stirring can reduce the length of free crystal and promote wall crystal to be free. According to M-S theory, it shows that it is favorable to make the grains global by stirring.