Improving the wear properties of AZ31 magnesium alloy under vacuum low-temperature condition by plasma electrolytic oxidation coating

• Al-doped coating on AZ31 Mg alloy was prepared by plasma electrolytic oxidation.
• PEO coating by Al doping improved the hardness and wear resistance of Mg alloy.
• Wear mechanism of PEO coating at vacuum low-temperature is adhesion and abrasion.

In this paper, Al-doped ceramic coatings with a thickness of 22–27 µm were prepared on AZ31 magnesium alloy by plasma electrolytic oxidation (PEO) in electrolytes that contain varied concentrations of NaAlO2, aiming to improve its wear resistance under vacuum low-temperature (−50 °C) condition. These obtained ceramic coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the ceramic coatings with typical porous structure were mainly consisted of MgO and MgAl2O4 phases, indicating that the Al elements were participated into the coating during the PEO process. We found that at the concentrations 5 g/L NaAlO2, the coating has its highest surface hardness (6.2 GPa) and lowest friction coefficients (0.21) under vacuum low-temperature condition. Our results demonstrate that such PEO coatings are very promising to improve the wear properties under vacuum low-temperature condition.