Formation of conversion coatings on magnesium Mg90 in acidic tannin-containing solutions: influence of acid concentration and temperature

• V.A. Luchkina, A.Yu. Luchkin and A.A. Chirkunov

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

Abstract: The feasibility of producing a conversion coating (CC) on technical magnesium Mg90 in tannin-containing solutions was investigated, and the anticorrosion and adhesion properties of the resulting coatings were compared to a classic chromate coating. Parameters such as nitric acid concentration (C(HNO₃)) and solution temperature (t) were varied. Uniform decorative CCs were shown to form over a fairly wide range of acid concentrations and temperatures, but the optimal conditions were C(HNO₃)=75 g/L and t=60°C. According to the results of electrochemical and corrosion tests, tannin-containing CCs are inferior to a standard chromate coating in terms of anticorrosive effectiveness; however, they significantly improved the adhesion of AK-070 primer. This, in turn, positively affected the protective properties of the paint coating in a salt spray chamber.

Keywords: magnesium, conversion coatings, tannin, corrosion protection, paint and varnish coatings, adhesion

Int. J. Corros. Scale Inhib., 2026, 15, no. 2, 272-296
doi: 10.17675/2305-6894-2026-15-2-16

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