Corrosion behaviour of epoxy coatings electrodeposited on galvanized steel and steel modified by Zn-Ni alloys

The electrochemical and transport properties and thermal stability of epoxy coatings electrodeposited on hot-dip galvanized steel and steel modified by Zn-Ni alloys were investigated during exposure to 3% NaCl solution. Zn-Ni alloys were electrodeposited on steel by direct and pulse current. From the time dependence of pore resistance, coating capacitance and relative permittivity of epoxy coating, diffusion coefficient of water through epoxy coating, D(H2O) and thermal stability, it was shown that Zn-Ni sublayers significantly improve the corrosion stability of the protective system based on epoxy coating. Almost unchanged values of pore resistance were obtained over the long period of investigated time for epoxy coatings on steel modified by Zn-Ni alloys, indicating the great stability of these protective systems, due to the existence of the inner oxide phase layer and the outer layer consisting of basic salts. (C) 2000 Elsevier Science S.A. All rights reserved.