ELECTROCHEMICAL MODELING OF EXFOLIATION CORROSION BEHAVIOR OF 8090-ALLOY

The susceptibility of alloy 8090 T8171 to exfoliation corrosion has be en analysed using the electrochemical impedance spectroscopy technique (EIS). Corrosion susceptibility was determined in a standard medium ( EXCO tests). This acid solution creates a very severe attack in a shor t period of time and makes it possible to distinguish the different st ages of the corrosion process. The EIS technique enables collection im pedance spectra which show a variation with increasing exposure time i ind so is appropriate for recording these stages. The Nyquist diagram is initially described by a well defined capacitive semicircle, which suggests a corrosion process under activation control. This response i s linked to the existence of small pits on the surface of the working electrode. However, when the immersion time increases, the attack caus es the appearance of large pits on the electrode, leading to an impeda nce response comprised by two overlapping semicircles; the high-freque ncy semicircle related with the flat part of the working electrode and the low frequency are associated with the part covered by pitting. (C ) 1997 Elsevier Science Ltd. All rights reserved.