Corrosion-resistant plasma electrolytic oxidation coating modified by Zinc phosphate and self-healing mechanism in the salt-spray environment

Aluminum alloys are widely used in many industrial applications. However, they are susceptible to corrosion especially in aggressive media such as high salinity which can expedite the corrosion reactions. In this work, zinc phosphate modified plasma electrolytic oxidation (PEO) coatings are fabricated and demonstrated to have excellent corrosion resistance for a much longer duration (> 11,000 h) than conventional PEO coatings (< 1,000 h). Insoluble zinc phosphate is distributed in the pores of the coating serving as a barrier against the high-salinity medium. A self-healing mechanism is discovered as zinc phosphate migrates from the surface to pores continuously wetting the corrosion droplets on the super-hydrophilic coating until all the zinc phosphate is consumed.