E.I.S. characterization of protective coatings on aluminium alloys

Abstract

A traditional organic solvent coating and a water-borne coating associated or not with a chromate conversion treatment on aluminium alloys, were characterized by Electrochemical Impedance Spectroscopy in order to study their anti-corrosive properties. It was shown that the impedance diagrams are representative both of the coating and of the chromate treatment. From the results obtained for the organic coating alone, it was concluded that the surface treatment masks the response of the paint. Comparison of the results obtained for the two coatings revealed that the water-borne system confers better barrier properties than the traditional system. Whatever the coating thickness tested, the capacitive behaviour observed for all the systems in the low-frequency domain of the impedance diagrams was attributed to the action of the chromate pigments at the metal interface, which impedes the corrosion of the aluminium alloys. This result was corroborated by measurements carried out for a system in which the chromate pigments were replaced by neutral fillers.