EIS characterization of protective coatings on aluminium alloys

A traditional organic solvent coating and a water-borne coating associated or not with a chromate conversion treatment on aluminium alloys, were chara cterized by Electrochemical Impedance Spectroscopy in order to study their anti-corrosive properties. It was shown that the impedance diagrams are representative both of the coa ting and of the chromate treatment. From the results obtained for the organ ic coating alone, it was concluded that the surface treatment masks the res ponse of the paint. Comparison of the results obtained for the two coatings revealed that the w ater-borne system confers better barrier properties than the traditional sy stem. Whatever the coating thickness tested, the capacitive behaviour obser ved for all the systems in the low-frequency domain of the impedance diagra ms was attributed to the action of the chromate pigments at the metal inter face, 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. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.