Corrosion behaviour of epoxy coatings on modified aluminium surfaces

The electrochemical and transport properties and thermal stability of epoxy coatings electrodeposited on aluminium and modified aluminium surfaces (anodized phosphatized and chromatized-phosphatized aluminium) have been investigated in 3% NaCl solution by electrochemical impedance spectroscopy (EIS) gravimetric liquid sorption experiment and thermogravimetric analysis (TGA). Higher values of pore resistance and charge-transfer resistance and lower values of coating capacitance and double layer capacitance were observed for epoxy coatings on anodized and chromatized and phosphatized aluminium. Smaller values of diffusion coefficient of water through epoxy coating from sorption measurements and smaller amount of absorbed water inside the coatings from TGA were obtained for coatings on anodized and chromatized-phosphatized aluminium. On the other hand the somewhat lower thermal stability of these coatings was obtained.