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

摘要

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. Due to environmental concerns and worker safety issues, there is a pressing need to identify and adopt alternative eco-friendly coatings with equivalent performance. 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 polyani-line phosphate, is studied for its anticorrosive properties. Long-term performance evaluation studies of this eco-friendly coating scheme were carried out on 15CDV6 steel, an ultra-high- strength steel used in the aerospace industry. 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 spectro-scopic studies and salt fog exposure tests were carried out to evaluate the anticorrosive properties of the coat- ing schemes. Cadmium- and chro-mate-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.