Corrosion Stability of Oxide Coatings Formed by Plasma Electrolytic Oxidation of Aluminum: Optimization of Process Time

Abstract

Electrochemical properties of oxide coatings formed by plasma electrolytic oxidation (PEO) on aluminum in sodium tungstate (Na2WO4 center dot 2H(2)O) with respect to process time were investigated using electrochemical impedance spectroscopy (EIS). Presence of tungsten was beneficial for the corrosion stability of obtained oxide coatings. However, neither the amount of tungsten in the oxide coating nor the coatings thickness were identified as important factors in corrosion stability of PEO coatings, i.e., morphology and porosity solely govern the corrosion stability of PEO coatings. The evolution of EIS spectra with immersion time for coatings anodized for 5 min and 7.5 min point to more efficient corrosion protection of aluminum substrate, compared to other tested samples.