Dry Sliding Wear Behavior of Mg-Zn-Gd Alloy before and after Cryogenic Treatment

The dry sliding wear behavior of Mg-1.5Zn-0.15Gd alloy before and after cryogenic treatment was studied by wear tests using a ball-on-disk configuration at room temperature. The wear tests were performed at speeds ranging from 0.05 to 0.7m/s under three different applied loads (5, 7, and 10N). The worn surfaces and wear debris were analyzed using a scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer (EDS). The results show that the wear rate of alloy decreases with increasing sliding speed. Two different wear mechanisms were identified under different sliding speeds. During low-speed sliding at 0.05m/s, abrasive wear occurs with a high wear rate. When the sliding speed increases to 0.5m/s, the wear mechanism transforms into oxidative wear with a low friction coefficient and wear rate. The wear resistance of the alloy is improved after cryogenic treatment. Such improvement is minor at high sliding speeds due to the formation of an oxidation layer on the wear surfaces, which weakens the hard-phase support effect during wearing. A wear map of each mechanism as a function of load and sliding speed is provided.