Improvement of wear and corrosion protection of PEO on AA2024 via sol-gel sealing

Abstract : Plasma electrolytic oxidation (PEO) is a versatile and cost-effective technique to obtain protective oxide coatings in light metals, although its intrinsic porosity is a drawback for long-term corrosion resistance. Sol-gel layers are pointed as a useful tool to seal PEO porosity and increase its corrosion resistance, although little is known about its influence on the wear performance of PEO coatings. In this study, a PEO coating obtained on AA2024 was sealed with a hybrid sol-gel via dip-coating. Two withdrawal speeds were set in order to investigate the influence of the sol-gel filling in its sealing ability. Both sol-gel application conditions were able to fill the PEO pores and microcracks and change its wettability. EIS results showed samples sealed with sol-gel maintained the protective behavior upon 28 days and increased the resistance of the system by several orders of magnitude in comparison to unsealed PEO coatings. Pin-on-disk tests indicate the sol-gel decrease the shear stresses of the coating, decreasing its wear rate in 40% compared to the unsealed PEO.