Effect of changes in organo-silicon electrolyte concentration and composition on SiO2 ceramic coating prepared by plasma electrolytic oxidation on 6061 aluminum alloy

Abstract

An amorphous SiO2 ceramic coating with a thickness of ∼72 μm is prepared within 13 min in organo-silicon electrolyte, which is stable in strong acid solutions, reducing corrosion current density of 6061 aluminum alloy by 3 orders of magnitude. With the aim to reveal influence of the electrolyte concentration, NaOH content and additive (NaPO3)6 on microstructure and corrosion resistance of the coatings, SEM/EDS, XRD, electrochemical tests were used to characterize their thickness, surface and cross-sectional morphology and structure, and corrosion performance prepared by using different electrolytes under the same electric control parameters. The results show that they significantly affect the surface morphology, structure and corrosion resistance of the coatings. Dilution of the electrolyte results in a significant decrease in coating thickness and surface porosity, reduction of NaOH content leads to coating thinning, increased porosity but reduced pore size. Coatings with lower porosity or smaller pore sizes are more effective in resisting corrosive media penetration for long term immersion. Whereas, the additive (NaPO3)6 promotes coating thickening, widening of the transition layer, which helpfully improves the corrosion resistance of the coating.