An Electrochemical Evaluation of Possible Non-Chromate Conversion Coating Treatments for Electrodeposited Zinc-Nickel Alloys

Abstract

SUMMARYA number of possible non-chromate conversion coating formulations have been studied to examine their efficacy as replacements for chromate-based coating treatments on electrodeposited zinc-nickel alloys. Data have been collected from both electrochemical and conventional salt fog corrosion tests. In the latter tests all the alternative non-chromate systems studied delayed the onset of the corrosion of the zinc-nickel coating itself but only the simple molybdate and the permanganatelmolybdate dual treatment brought about improvements in times to red rusting of the steel substrate. The electrochemical evaluations suggested that simple molybdate-treated surfaces act as only moderate barriers to the chloride environments. Of the two dual treatments, permanganatel molybdate behaved similarly to the simple molybdate treated surfaces in the electrochemical tests, but the molybdatel permanganate was more protective, although this was not exhibited in the salt fog corrosion tests.