Investigation of modifying additives to increase the protective properties of molybdate conversion coatings for AMg3 aluminum alloy

• A.S. Konovalov, Yu.A. Kuzenkov and O.Y. Grafov

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

Abstract: The presence of corrosive agents, such as chlorides, in the atmosphere or water can lead to active pitting corrosion of magnesium-containing aluminum alloys. One of the methods of protecting them is coatings obtained by chemical oxidation in molybdate compounds. To enhance the anticorrosive properties of such coatings, modifying additives are added to the conversion composition and then the coatings are filled with a corrosion inhibitor solution. In this research, ultrathin molybdate conversion coatings and their interaction with a number of modifying additives, which have different effects on oxide film formation, were investigated. It was shown that the best effect is achieved by adding sodium silicate and magnesium nitrate to the conversion composition, as well as their combinations with sodium tetraborate and sodium carbonate. According to X-ray photoelectron spectroscopy data, this may be due to an increase in the proportion of Mo(V) compounds in the coatings. Corrosion tests in a G-4 humidity chamber show that modified molybdate conversion coatings are not inferior to standard chromate coatings in terms of protection properties.

Keywords: aluminum alloys, conversion coatings, pitting corrosion, corrosion inhibitors, molybdates, chromate-free technologies

Int. J. Corros. Scale Inhib., 2026, 15, no. 1, 523-534
doi: 10.17675/2305-6894-2026-15-1-27

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