Investigating the impact of heat treatment on the tribological behaviour of AZ80 magnesium alloy at high temperatures

Abstract

The purpose of this research is to investigate the effect of heat treatment on the high-temperature wear characteristics of stir-cast AZ80 magnesium alloy. Dry sliding wear tests were performed on as-cast, T4, and T6 AZ80 using ASTM G99 - 17 at 25 °C, 150 °C, and 250 °C with a constant normal load of 10 N, a sliding speed of 1 m/s, and a sliding distance of 1000 m. Microstructures were analyzed with a Field-Emission Scanning Electron Microscope (FESEM) and an Electron Microprobe Analyzer (EMPA). X-ray diffraction (XRD) was used to examine the phases before and after the wear tests. In addition to α-Mg, the intermetallic phases Mg17Al12 and Mg2Al3 are also identified in AZ80. Compared to as-cast AZ80, T6 heat-treated alloy shows a maximum grain size of 72.64 ± 25 μm, with grain coarsening of 38.83 %. All test specimens, including T6 AZ80, exhibit indication of the Al-rich zone in the EPMA analysis, while T6 AZ80 shows evidence of the Mn-rich zone. Except for T4 AZ80 at 250 °C and T6 AZ80 at 150 °C and 250 °C, where the alloy experiences adhesive wear and oxidation, the abrasive wear and oxidation are common mechanisms observed in all test settings. At 150 °C, adhesive wear is responsible for 9.5 mg of the total wear in T6 AZ80. The alloy's wear behaviour is unaffected by presence of Zn. Intermetallic oxides (MgAl2O4) play a vital role in deciding the wear characteristics of the alloy.