Cadmium- and Chromate-Free Coating Schemes for Corrosion Protection of 15CDV6 Steel

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Electrodeposits of cadmium- and chromate-based inorganic inhibitor pigments in paint formulations are extensively used in the aerospace industry to provide long-term corrosion protection for high-strength steel hardware. In this work, an eco-friendly cadmium- and chromate-free coating scheme comprised of zinc nickel alloy plating, trivalent chromium- based passivation, followed by a primer based on polyaniline phosphate, is studied for its anticorrosive properties.

For comparative purposes, two extensively used cadmium- and chromate-based schemes complying to aerospace and military specifications comprised of cadmium plating, hexavalent chromium-based passivation followed by two different chromate-based primers were studied on 15CDV6 steel substrate.

Electrochemical impedance spectroscopic studies and salt fog exposure tests were carried out to evaluate the anticorrosive properties of the coating schemes. Cadmium- and chromate-free scheme exhibited excellent performance in the long-term corrosion evaluation studies. The results obtained in accelerated tests show the possibility of replacement of cadmium- and chromate-based schemes for corrosion protection of steels with an eco-friendly option.

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