Development of a New Electrodeposition Process for Plating of Zn-Ni-X (X = Cd, P) Alloys: I. Corrosion Characteristics of Zn-Ni-Cd Ternary Alloys

A new Zn‐Ni‐Cd plating process was developed which offers a unique way of controlling and optimizing the Ni and Cd contents in the final deposit. Zinc‐nickel‐cadmium alloy was deposited from a bath in the presence of and 1 g/L nonyl phenyl polyethylene oxide. Using this process a Zn‐Ni‐Cd ternary alloy, with a higher nickel content as compared to that obtained from conventional Zn‐Ni baths, was synthesized. The Zn‐Ni‐Cd alloy coatings deposited from an electrolyte containing has a Zn to Ni ratio of 2.5:1. The increase in nickel content accounts for the observed decrease in the corrosion potential to a value lower than that of Cd but higher than the corrosion potential of iron. The coatings have superior corrosion resistance and barrier properties than the typical Zn‐Ni and cadmium coatings. Polarization studies and electrochemical impedance spectroscopy analysis on Zn‐Ni‐Cd coatings show a barrier resistance that is ten times higher than that of a conventional Zn‐Ni coating. © 2000 The Electrochemical Society. All rights reserved.