Corrosion behaviour of epoxy coatings electrodeposited on galvanized steeland 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 b y Zn-Ni alloys were investigated during exposure to 3% NaCl solution. Zn-Ni alloys were electrodeposited on steel by direct and pulse current. From th e time dependence of pore resistance, coating capacitance and relative perm ittivity of epoxy coating, diffusion coefficient of water through epoxy coa ting, D(H2O) and thermal stability, it was shown that Zn-Ni sublayers signi ficantly improve the corrosion stability of the protective system based on epoxy coating. Almost unchanged values of pore resistance were obtained ove r the long period of investigated time for epoxy coatings on steel modified by Zn-Ni alloys, indicating the great stability of these protective system s, 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 reserv ed.