The Substitution of Cobalt for Nickel in Bright Nickel Plating Solutions

Abstract

SummaryThe paper describes an investigation of the full and partial substitution of cobalt for nickel in decorative nickel chromium plating systems. As the result of laboratory experiments on the effect of cobalt additions to a proprietary high chloride base bright nickel solution, two automatic plating plants were converted to cobalt-nickel alloy deposition by the introduction of cobalt anode material. One plant was operated with microcracked chromium and the other with crackfree chromium. Experience with the production plant is described. Accelerated (CASS) and static exposure corrosion tests carried out to compare the corrosion resistance of cobalt, cobalt-nickel and nickel deposits under crackfree, microcracked and microporous chromium on steel and zinc substrates are reported, together with mobile tests to compare the performance of cobalt-nickel with nickel under crackfree chromium on zinc alloy diecast headlamp rims. It is shown that the corrosion resistance of some plating systems containing cobalt is at least as good as the equivalent nickel system. Other systems suffer from staining by cobalt corrosion products. The corrosion resistance of copper/cobalt/crackfree chromium was found to be significantly better than that of copper/nickel/crackfree chromium on steel substrates.