The study of corrosion stability of organic epoxy protective coatings on aluminium and modified aluminium surfaces

Epoxy coatings were formed by cathodic electrodeposition of an epoxy resin on aluminium and modified aluminium surfaces (phosphatized, chromatized-phosphatized and anodized aluminium) using a constant voltage method (resin concentration 10 wt.%, temperature 27 degrees C, applied voltage 250 V). The corrosion behavior of these coatings was investigated during exposure to 3% NaCl using electrochemical impedance spectroscopy (EIS) and polarization measurements. From the dependence of resistance, capacitance and relative permittivity of the coating, obtained from EIS, on the rate of hydrogen evolution reaction in the electrodeposition bath, obtained from polarization curves, it can be observed that the epoxy coating on aluminium and modified aluminium surfaces is a good barrier against the transport of corrosive agents. The time corresponding to contact between electrolyte and aluminium surface under the coating is greater in the case of surface modification by chromato-phosphatized and anodized aluminium than in the case of phosphatize one.