Corrosion protection of aluminium by a cataphoretic epoxy coating

The corrosion behavior and thermal stability of epoxy coating electrodeposited on aluminium have been investigated during exposure to 3% NaCl. Electrochemical impedance spectroscopy (EIS), gravimetric liquid sorption experiments, thermogravimetric analysis (TGA) and polarization measurements were used. From the results obtained from EIS (pore resistance, coating capacitance, relative permittivity of coating, charge-transfer resistance, double-layer capacitance), gravimetric liquid sorption experiments (diffusion coefficient, energy of activation of water diffusion) and TGA (water content inside the coating and thermal stability), it can be concluded that the electrochemical, transport and thermal properties of an epoxy coating on aluminium are significantly improved with respect to the same epoxy coating on other substrates (steel, phosphatized steel, steel modified by Zn-Ni alloy). The better protective properties can be explained by less porous structure of the coating on aluminium, caused by lower rate of H-2 evolution, while the prolonged corrosion protection is due to the passive, mainly barrier film of Al2O3 on its surface. (C) 1999 Elsevier Science S.A. All rights reserved.