Corrosion behavior of the composite ceramic coating containing zirconium oxides on AM30 magnesium alloy by plasma electrolytic oxidation

The deterioration process of a plasma electrolytic oxidation (PEO) coating containing zirconium oxides on AM30 magnesium alloy in 3.5 wt.% NaCl solution have been investigated. The coating consists of an outer porous layer and an inner dense layer. The content of MgF2 is high in the pores and an MgO-rich layer is evident in the inner layer. The corrosion resistance of the outer layer gradually decreases in the initial immersion stage (96 h) due to the decomposition of MgO, and the deterioration of the inner layer is delayed by the blocking effect of the outer layer.

► Zirconium oxides (Mg2Zr5O12 and t-ZrO2) are deposited on the surface of AM30 alloy.
► Deterioration of the coating initiates from the hydration of MgO to form Mg(OH)2.
► Deposition of zirconium oxides improves the corrosion resistance of the coating.
► Deterioration of the inner layer is delayed with the effect of the outer layer.