Ultrathin Conversion Coatings on AMg3 Aluminum Alloy. Part 1. Optimization of the Coating-Fabrication Process

Abstract—The decrease of the corrosion resistance of aluminum alloys of different doping systems results from their phase and surface heterogeneity. Operation in environments of various aggressiveness contributes to the emergence of local types of corrosion damage on aluminum alloys. This results in premature failure of metal structures. A rather wide range of coatings are used to protect aluminum alloys, among which conversion coatings occupy a significant share due to their production effectiveness and compatibility with many paint systems. In this regard, the possibility of fabrication of submicron protective conversion coatings on AMg3 aluminum alloy in molybdenum converting media has been studied in this work. Electrochemical studies have shown that the addition of ammonium nitrate to the molybdenum-converting compound does not affect subsequent treatment (filling) of the resulting coatings in a corrosion-inhibitor solution. The optimal time for fabrication of coatings and its subsequent filling has been revealed. It has been shown that the studied molybdenum-conversion coatings are similar in protective properties to the traditional chromate coating.