Electrochemical properties and thermal stability of epoxy coatings electrodeposited on aluminium and modified aluminium surfaces

The corrosion behaviour of epoxy coatings electrodeposited on aluminium, as well as on electrochemically and chemically modified aluminium were investigated during exposure to 3 % NaCl. Electrochemical impedance spectroscopy (EIS) and thermogravimetric analysis (TGA) were used for the determination of the protective properties of epoxy coatings on aluminium, anodized aluminium, phosphatized and chromatized-phosphatized aluminium. The protective properties of epoxy coatings on anodized and chromatized-phosphatized aluminium are significantly improved with respect to the same epoxy coatings on aluminium and phosphatized aluminium: higher values of the pore resitance and charge-transfer resistance, lower values of the coating capacitance, double-layer capacitance and relative permittivity (from EIS) smaller amount of absorbed water inside the coating (From TGA). On the other hand, the lower values of the ipdt temperature indicate a lower thermal stability of the epoxy coatings on anodized and chromatized-phosphatized aluminium.