Effect of surface modification by Fe-P alloys on corrosion behaviour of epoxy coatings electrodeposited on steel

Abstract

Corrosion behaviour of electrodeposited epoxy coatings on electrochemically modified steel surface by Fe-P alloys of different chemical and phase structures has been investigated by exposure to 3% NaCl. The electrochemical impedance spectroscopy (EIS), polarisation measurements and corrosion potential time measurements have been used. The steel surface was modified by electrochemical deposition of thin films of Fe-P alloys from sulfate acid solution at various cut-rent densities, with the aim of improving the corrosion resistance of organic film. Epoxy topcoat was formed by cathodic electrodeposition of an epoxy resin on previously modified steel surface using constant voltage method (resin concentration 10 wt%, temperature 299 K, applied voltage 250 V). From the time dependence of pore resistance, coating capacitance and relative Permittivity of coating, obtained from EIS and corrosion potential time measurements it can be observed that the Fe-P alloys improve the corrosion stability of the protective system based on epoxy coating. The electrodeposition current densities, which cause different chemical and phase structures of Fe-P sublayers, exhibit the great influence on the formation and characteristics of epoxy coating.