Uniform alumina coatings on the inner surfaces of aluminum alloy tubes by plasma electrolytic oxidation for enhanced mechanical and corrosion resistance
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Uniform alumina coatings on the inner surfaces of aluminum alloy tubes by plasma electrolytic oxidation for enhanced mechanical and corrosion resistance
Uniform alumina coatings on the inner surfaces of aluminum alloy tubes by plasma electrolytic oxidation for enhanced mechanical and corrosion resistance
Ng, Y., Tan, X. Y., Meng, T. L., Yong, A. M., & Liu, H. (2026). Uniform alumina coatings on the inner surfaces of aluminum alloy tubes by plasma electrolytic oxidation for enhanced mechanical and corrosion resistance. Surface and Coatings Technology, 524, 133289. https://doi.org/10.1016/j.surfcoat.2026.133289
Abstract:
Protective coatings on the inner surfaces of metallic tubes are critical for aerospace, automotive, marine, and energy applications, yet remain a significant challenge due to difficult access. Here, we demonstrate the successful fabrication of dense, uniform alumina coatings on the inner walls of Al-6061 alloy tubes (20 mm diameter, 200 mm length) using plasma electrolytic oxidation (PEO). The conformal coatings (∼10 μm) exhibit predominantly γ-Al2O3 phase with minor α-Al2O3 inclusions, confirmed by X-ray diffraction. Cross-sectional nanoindentation revealed a hardness of ∼8.0 GPa, five times higher than the substrate. Dielectric breakdown strength exceeded 60 kV/mm. Electrochemical testing in 3.5 wt% NaCl showed a reduction in the corrosion current from 0.77 to 0.04 μA and nearly doubled pitting potential induced by the PEO coating. Microstructural investigations further revealed that while uncoated tubes suffered from pitting corrosion, intergranular corrosion, and stress corrosion cracking, the PEO coatings suppressed these degradation modes by mitigating electrolyte penetration and alleviating residual stress. These findings establish PEO as a viable strategy for producing robust inner-surface ceramic coatings, enabling improved reliability of tubular aluminum components in demanding environments.
License type:
Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Funding Info:
There was no specific funding for the research done