Effect of rare earth elements addition on the tribological behavior of AZ91D magnesium alloy at elevated temperatures

The effect of 1, 2, and 3 wt% of lanthanum-base rare earth (RE) element additions on the wear behavior of AZ91 alloy was investigated under a normal load of 20 N at the wear temperatures of 25–250 °C. The wear tests were carried out using a pin-on-disk tribometer at a sliding speed of 0.4 ms−1 for a sliding distance of 1000 m. The results showed that there was no change in the wear rate of the alloys at the wear temperature of 25 °C. By increasing the wear temperature to 100 °C, the wear rates of AZ91 and the RE-containing alloys decreased by about 58% and 40%, respectively. At higher wear temperatures, the wear of AZ91 alloy increased as a result of softening of β-Mg17Al12 intermetallics resulting in severe plastic deformation and adhesion on the wear surface. However, the wear of the RE containing alloys decreased as the wear temperature increased to 200 °C due to the formation of stable oxide layers on the worn surfaces. The alloy containing 3 wt% RE exhibited the highest wear resistance at the wear temperatures of 150 and 200 °C. Further increase in the wear temperature to 250 °C led to severe plastic deformation and high adhesion of the alloys.