The Impact of Solution Treatment Time (T6) and Deep Cryogenic Treatment on the Microstructure and Wear Performance of Magnesium Alloy AZ91

In this study, the AZ91 magnesium alloy was subjected to solution and ageing heat treatment (T6) and deep cryogenic (DC) treatment to enhance the wear performance. For this purpose, the solution treatment process was performed at 400 °C for 4 h, 5 h, and 6 h, followed by ageing at 200 °C for 10 h to complete T6 treatment. Then, the DC treatment was carried out at − 196 °C for 48 h. The pin-on-disc method was employed to measure the wear resistance of the samples. The results show that the solution treatment period altered the microstructure of AZ91; the eutectic phase was more dissolved in the matrix after 4 h of solution treatment time. Regarding the DC-treated AZ91, new double twins frame-like β phases were observed on the surface. Moreover, cryogenic treatment improved the hardness from 63 to 75 HV, but the wear rate was slightly higher than untreated AZ91 in dry medium. On the other hand, lower wear rate was obtained when applying 4 h of solution treatment time with DC treatment. In contrast, 6 h of solution treatment time with DC treatment exhibited higher wear rate, probably due to greater amounts of double twins.