Inhibition of AA5056 aluminum alloy surface in solutions based on rare-earth metal compounds

• O.A. Shloma, A.A. Didyk, A.A. Abrashov, N.S. Grigoryan, O.I. Bardina and T.A. Vagramyan

Mendeleev University of Chemical Technology, Russia, Moscow, Miusskaya sq., 9, 125047 Moscow, Russia

Abstract: The publication deals with chromate-free protective conversion coatings based on rare-earth metals (REM) for the AA5056 aluminum alloy. A technology has been developed for applying protective conversion coatings containing rare-earth metals (REMs) onto AA5056 aluminum alloy to replace the toxic chromating process in various industrial applications. The parameters for the deposition REM-based conversion coatings were optimized, and the physicochemical properties of the coatings were investigated to assess their potential for replacing chromate coatings. It was found that the addition of gallic acid to the working solution in an amount of 1.0–1.5 g/L enhances the protective ability, improves the strength of adhesion to paint coatings, and increases the growth of film thickness up to 141 nm. The results of corrosion tests in a salt spray chamber showed that the developed coatings are superior to chromate coatings in terms of protective ability. Lanthanum-containing layers under paint coatings are not only not inferior to chromate adhesion layers, but even surpass them in protective ability and in strength of adhesion to paint coatings. Cerium-containing coatings are a good alternative to toxic chromate films for protecting aluminum surfaces from pitting corrosion. The developed passivation processes are intended for the corrosion protection of aluminum items and structures, both as independent (final) protective coatings and as an adhesion-promoting layer under paint coatings.

Keywords: surface treatment, corrosion protection, rare-earth metals, conversion coatings, chromate-free passivation

Int. J. Corros. Scale Inhib., 2025, 14, no. 3, 1422-1433
doi: 10.17675/2305-6894-2025-14-3-20

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