SBIR Phase I: Hydrotalcite-Based Conversion Coatings for High Copper-Content Aluminum Alloys

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9860554 This Small Business Innovation Research Phase I project is to develop chromate-free conversion coatings for high copper-content aluminum alloys, such as 2024-T3, based on the formation of hydrotalcite. Chemical conversion coatings have found widespread commercial and military applications in the protection of aluminum alloys, commonly used in automobile and aircraft manufacturing as structural materials. This is due to their excellent corrosion resistances and their abilities to serve as effective bases for paints. However, conventional chemical conversion baths contain hexavalent chromium and ferricyanide, which are highly toxic. The continued use of chromate conversion coatings has made the metal finishing industry one of the most significant contributors to environmental pollution. Thus, it is highly desirable to develop conversion-coating technologies utilizing non-chromate chemicals that can serve as alternative methods. The key to this project is the use of environmentally benign chemicals to form hydrotalcite-based coatings with excellent corrosion resistances. Conversion coatings will be performed with the aid of activators under optimal temperatures to accelerate the reaction rate. The formed coatings will be further treated with a simple organic compound to obtain hydrophobic and self-healing characteristics to enhance their corrosion resistances. The developed non-chromate, hydrotalcite-based conversion coating process could totally replace the polluting chromate conversion coating in metal finishing. This novel technology will be economically viable and be very beneficial with respect to environmental protection and human health.