Influence of pH and modifying additives on the protective properties of ultrathin conversion coatings for AMg3 aluminum alloy

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

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: Aluminum alloys have low corrosion resistance due to the presence of intermetallic particles in the composition. The natural oxide layer on the metal surface adversely affects the adhesion of subsequent layers of a painting system. In this regard, special anti-corrosion primers surface are created on aluminum alloys, including by the method of chemical oxidation. In the present work, ultrathin conversion primers (coatings) were obtained in a converting composition containing environmentally friendly molybdates and phosphates. The protective properties of such coatings were studied depending on the pH of the converting composition and with addition of modifying additives in the composition. It has been shown that a decrease in pH has a positive effect on the protective properties of primers due to an increase in the oxide film thickness. Among the modifying additives studied, 1,2,3-benzotriazole (BTA) showed the best result. The coatings obtained in solution with addition of BTA effectively adsorb the corrosion inhibitor at the stage of filling the coating. The investigated coatings show good protective properties in corrosion tests in a moisture chamber and high adhesion of the painting system.

Keywords: aluminum alloys, conversion coating, pitting corrosion, corrosion inhibitors

Int. J. Corros. Scale Inhib., 2023, 12, no. 1, 170-179
doi: 10.17675/2305-6894-2023-12-1-10

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