An investigation on the tribological behavior of AZ91 and AZ91+3wt% RE magnesium alloys at elevated temperatures

The wear behavior of AZ91 and AZ91+3wt% RE magnesium alloys was investigated under a normal load of 20N at the wear testing temperatures of 25-250°C and sliding speeds of 0.4 and 1ms-1. As the sliding speed increased from 0.4 to 1ms-1 at the wear temperature of 25°C, the wear rates of AZ91 and AZ91+3wt% RE alloys decreased by about 8% and 60%, respectively. With an increase in the wear temperature to 100°C, the wear rate of AZ91 alloy was reduced by 58% at a sliding speed of 0.4ms-1, while the wear rate was sharply increased at a sliding speed of 1ms-1. At higher wear temperatures, the wear of the AZ91 alloy at both sliding speeds soared as a result of the softening of β-Mg17Al12 phase. However, the wear rate of AZ91+3wt% RE alloy showed a minimum at the wear temperatures of 100 and 200°C at sliding speeds of 1 and 0.4ms-1, respectively. Superior wear behavior of AZ91+3wt% RE at the elevated temperatures could be attributed to its higher thermal stability and strength. Furthermore, a rise in sliding speed led to a 55% reduction in the wear rate of AZ91+3wt% RE alloy at the wear temperature of 100°C due to the formation of stable oxide layers on the wear surface.