Corrosion resistance of Zn-Ni alloy coatings in industrial production

The corrosion behaviour of chromated zinc and chromated Zn-Ni alloy coatings, obtained from different industrial plants, was studied by means of salt spray tests and electrochemical tests in aerated 0.6 M NaCl solution. At almost neutral pH values, all the chromated Zn-Ni coatings show better corrosion resistance than conventional chromated zinc coatings. The acidity causes a decrease in the corrosion resistance of both chromated zinc and chromated Zn-Ni alloy; at low pH values the corrosion resistance of zinc coatings is better than that of alloy coatings because of depolarization of the cathodic reaction (hydrogen reduction), owing to the lower overvoltage of hydrogen reduction on nickel. The morphology of corrosion attack in both chloride environments is also reported.