Microstructural evolution of die-cast and homogenized AZ91 Mg-alloys during dry sliding condition

Microstructural evolution of die-cast and homogenized AZ91 Mg-alloys was investigated during dry sliding wear condition. Tribological tests were performed using a pin-on-disc (EN8 steel) configuration with a normal load of 50 N at a constant sliding speed of 2.5 ms(-1) under ambient environment. Delamination was recognized as a predominant wear mechanism in both of these materials. The die-cast AZ91 Mg-alloy exhibits lower coefficient of friction and higher wear rate. This can be ascribed to increase in the intensity of load bearing capacity of hard beta-Mg17Al12 phase, and crack formation/de-cohesion at the interface between primary alpha-Mg and discontinuous beta-Mg17Al12 phases. On the contrary, the homogenized AZ91 Mg-alloy experiences higher coefficient of friction and lower wear rate. The friction-induced microstructural evolution (supersaturated beta-Mg to eutectic (alpha + beta-Mg17Al12)) tending to minimize the wear rate by providing barrier to material removal in the near surface region of homogenized AZ91 Mg-alloy. Therefore, experimental observation revealed that an inverse relationship exists between wear rate and coefficient of friction for the investigated materials. The analysis of worn surfaces and subsurfaces by electron microscopy provided evidence to delamination wear and microstructural evolution. (C) 2017 Production and hosting by Elsevier B.V. on behalf of Chongqing University. This is an open access article under the CC BY-NC-ND license.