The present paper is aiming to examine the tribological properties of Mg-Al-Zn alloy, AZ91. Especially, effect of precipitate morphology on tribological properties, such as wear rate and coefficient of friction, was systematically investigated for cast material. Accelerated aging treatment was carried out at temperatures ranging from 150°C to 300°C for 100 hours after solution-treatment at 413°C for 48 hours. A pin-on-disc wear testing machine was used to evaluate tribological properties at room temperature under dry condition, in which an SUJ2 steel disc was used as the counterface. Vickers hardness after the accelerated aging treatment of AZ91 alloy was about HV80 to HV90. Since the hardness of AZ91 was approximately eight times smaller than that of SUJ2, the dominant wear mechanism was assumed to be abrasive wear. However, the composition of wear debris, rise in temperature during wear tests, change in hardness near the wear surface and macroscopic flow of specimens indicated that the adhesive wear also contributed to the wear properties when the size of precipitates were small or the spacing between precipitates were large. It was suggested that the contribution of adhesive wear increased the wear rate and the coefficient of friction. It was concluded that the wear resistance of AZ91 alloy under dry condition would be improved by densely dispersing the precipitates with sufficiently large size, e.g., precipitates with its length of about 1mm that were observed in materials aged at 200°C.
