Corrosion and wear properties of PEO coatings formed on AM60B alloy in NaAlO2 electrolytes

Coatings with a thickness of 22–32 μm were formed on an AM60B magnesium alloy by plasma electrolytic oxidation (PEO) in electrolytes containing 12.0–24.0 g/l NaAlO2 and other additives. SEM analyses of the coated samples showed that the coatings were compact with relatively low porosity. X-ray diffraction revealed that the coatings consisted of mainly MgAl2O4 and MgO phases. The relative amount of MgAl2O4 in the coating increased with increasing NaAlO2 concentration. The relatively compact and thick coatings provide good corrosion protection for magnesium, as indicated by the results of potentiodynamic polarization tests. In addition, the PEO treatment also significantly improved the wear resistance of the alloy. Pin-on-disk wear tests showed that the PEO treatment reduced the wear volume loss by a factor of 10.