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 electrodeposition under various conditions were investigated. The influence of the deposition solution and deposition current density on the composition, phase structure, current efficiency and corrosion properties of Zn-Ni alloys were examined. It was shown that the chemical composition and phase structure affect the anticorrosive properties of Zn-Ni alloys. A Zn-Ni alloy electrodeposited from a chloride solution at 20 mA cm(-2) exhibited the best corrosion properties, so this alloy was chosen for further examination. Epoxy 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 the pore resistance, coating capacitance and relative permittivity of the epoxy coating, the diffusion coefficient of water through the epoxy coating, D(H2O), and its thermal stability, it was shown that the Zn-Ni sublayer significantly 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.