Electrochemical Characteristics of PEO Treated Electric Arc Coatings on Lightweight Alloys

Abstract

The complex technology of the surface treatment of Al, Mg, Ti alloys for size reconstruction and strengthening is presented herein. This consists of electric arc spraying of aluminum alloys or powder wire in an aluminum shell and then treatment with plasma electrolytic oxidation (PEO). Once treated, oxide-ceramic coatings maintain extreme hardness, durability and resistance to wear. At the same time their corrosion-resistant properties are also significant. Dynamic potential dependences were studied for electric arc Al coatings and PEO treatments on Al, Mg, Ti alloys and corrosion currents were analyzed for exposure to a corrosive environment for a period of from 1 hour to 30 days. It was established that PEO treated coatings on Al alloys have a higher corrosion resistance than untreated sprayed coatings. In Mg alloys, an intermediate layer of aluminum electric arc coating between the substrate and PEO-treated coating is necessary in order to ensure high corrosion resistance. This is due to the specifics of the formation of the MgO and Al2O3 oxide phases in the plasma discharge channels. At the same time Al coatings on Ti alloys, including those of post-PEO treatment, were characterized as having lower corrosion resistance within the range of electrode potential from corrosion potential up to repassivation potential, than were untreated Ti-alloys. Yet it was found that the corrosion resistance of PEO treated coatings increases at higher anode potentials. Under cathode polarization the hydrogen discharge is less likely to occur on PEO-coatings than on untreated Ti alloys which more effectively prevents hydrogenation.