Electrodeposition and characterization of Zn-Ni alloys as sublayers for epoxy coating deposition

The chemical composition and phase structure of Zn-Ni alloys obtained by el ectrodeposition under various conditions were investigated. The influence o f the deposition solution and deposition current density on the composition , phase structure, current efficiency and corrosion properties of Zn-Ni all oys were examined. It was shown that the chemical composition and phase str ucture affect the anticorrosive properties of Zn-Ni alloys. A Zn-Ni alloy e lectrodeposited from a chloride solution at 20 mA cm(-2) exhibited the best corrosion properties, so this alloy was chosen for further examination. Ep oxy coatings were formed by cathodic electrodeposition of an epoxy resin on steel and steel modified with a Zn-Ni alloy. From the time dependence of t he pore resistance, coating capacitance and relative permittivity of the ep oxy coating, the diffusion coefficient of water through the epoxy coating, D(H2O), and its thermal stability, it was shown that the Zn-Ni sublayer sig nificantly affects the electrochemical and transport properties, as well as the thermal stability of epoxy coatings. On the basis of the experimental results it can be concluded that modification of a steel surface by a Zn-Ni alloy improves the corrosion protection of epoxy coatings.