Ultra-thin inhibited molybdate conversion coatings for the protection of AMg3 aluminum alloy

In order to prevent corrosion of aluminum alloys inhibitors and coatings, for example the ones that can be obtained by chemical oxidation, can be used. The combination of these two protection methods allows one to obtain coatings with high protective properties. In this work, ultra-thin inhibited conversion coatings obtained in molybdate converting compositions and their modifications, including known inhibitors of aluminum alloy corrosion, were investigated. It was shown that subsequent treatment of the coatings in a corrosion inhibitor solution has a greater effect on the coatings obtained in a solution based on phosphatomolybdic acid than on the coatings obtained in a solution based on sodium molybdate. This difference is apparently associated with the structure and composition of the coatings under study. Among inorganic modifying additives, sodium silicate and sodium tetraborate demonstrate the best effect of increasing protective properties, and tannin and 5-methyl benzotriazole (5-methyl BTA) among organic ones. According to corrosion tests in a humidity chamber, the highest corrosion resistance is demonstrated by coatings obtained in converting compositions with addition of sodium silicate.