MODELS FOR THE IMPEDANCE BEHAVIOR OF PROTECTIVE COATINGS AND CASES OF LOCALIZED CORROSION

Simple equivalent circuits (EC) for the impedance behavior of polymer coated steel and anodized Al alloys and Al-based metal matrix composites are discussed. The use of these ECs for the determination of protective surface properties and their degradation with exposure time to corrosive environments is illustrated. It is demonstrated that the pitting model for Al alloys can be used to determine pit growth rates from EIS data obtained at the corrosion potential. For very short exposure times an inductive loop is observed which is due to polarization during the anodic cycle of the applied ac signal.