Influence of corrosion inhibitors on the protective properties of chromate-free conversion coatings on D16 aluminum alloy

• D.O. Chugunov, Yu.A. Kuzenkov and S.Y. Rybakov

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: Aluminum alloys of the Al-Mg-Cu system, which includes the D16 alloy, exhibit reduced corrosion resistance in atmospheric and neutral chloride-containing environments. In this work, chromate-free conversion coatings obtained by chemical oxidation were investigated for the anticorrosion protection of this alloy. To enhance the protective properties of the coating, 1,2,3 benzotriazole (BTA) and EDTA-Na2 modifying additives were added to the conversion solution. The properties of the obtained oxide films were evaluated using a complex of methods: corrosion tests in a humidity chamber, anodic polarization, electrochemical impedance spectroscopy (EIS), and energy dispersive X-ray microanalysis (EDS). It was shown that the addition of EDTA-Na2 to the conversion solution provides a greater anticorrosion effect due to the homogenization of the oxide composition of the resulting coatings. This same coating variant demonstrates the best protective properties after sealing in a sodium oleate solution with BTA. EIS data confirm an increase in coating resistance and charge transfer resistance, indicating the formation of a two-layer coating. Corrosion tests in a G-4 humidity chamber show a twofold increase in the time to the appearance of the first corrosion defects (pits) for such coatings compared to unmodified coatings. The developed approach represents an environmentally friendly alternative to traditional chemical oxidation in chromate formulations.

Keywords: aluminum alloys, conversion coatings, chemical oxidation, pitting corrosion, corrosion inhibitors, oxidation temperature, chromate-free technologies

Int. J. Corros. Scale Inhib., 2026, 15, no. 4, 361-370
doi: 10.17675/2305-6894-2026-15-4-15

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