Characterization of Nickel Oxide Layers on the AZ91 Mg Alloys by Plasma Electrolytic Oxidation

Characterization of nickel oxide layers on the AZ91 Mg alloys by plasma electrolytic oxidation (PEO) was investigated. For this purpose, PEO coating was carried out on the present sample in the alkaline electrolyte with nickel ion at three different voltage responses, i.e., 150, 250, 350 V. The amount of nickel oxide increased by increasing process time, and changed the color of sample from light grey to moderate olive brown. It was observed from potentio-dynamic polarization analysis that polarization resistance of oxide layer was increased with increasing nickel ions. Also microhardness of the sample processed at 350 V was higher than those of the samples.