Investigations into Corrosion Resistance of Decorative Nickel and Chromium Electrodeposits

The results of accelerated corrosion tests, outdoor exposure tests and more fundamental electro-chemical studies have been critically compared as a means of predicting corrosion resistance of nickel+chromium electrodeposits in service. The aim was to compare the relative merits in British atmospheres of some of the various alternative nickel and chromium systems available and to ascertain which of the commonly used accelerated tests placed these systems in the same order of merit as did outdoor exposure. All tests were performed with plated steel panels, some of which were deformed before exposure. The coating systems which gave the best corrosion protection in all outdoor trials were found always to include the thicker chromium deposits, but while crack-free chromium was best on static exposure, micro-cracked chromium was good in both static and mobile conditions. Duplex nickel gave much better protection during mobile tests than on static exposure. The Corrodkote test was the most generally applicable rapid accelerated corrosion test for assessing plated steel. The acetic acid salt spray test gave results which correlated most closely with those obtained on outdoor exposure but takes longer to perform.