Dynamic Electrochemical Impedance Spectroscopy for the Evaluation of Localised Corrosion on Aluminium Alloys

Abstract

Dynamic electrochemical impedance spectroscopy (dEIS), an extension of conventional EIS, was used for rapid measurements of initiation of localised corrosion on 3005 aluminium alloys with different Mn (1.08–1.39 wt. %) and Cu (0.15–0.22 wt. %) content by evaluating the onset and evolution of a Faradaic process observed in 0.5 M Na2SO4+0.1 M NaCl. Differences between samples were detected with highest sensitivity from the charge transfer resistance during chronoamperometry at ca. 120 mV above the corrosion potential. These differences were caused by differences in pitting initiation, and correlated well with filament density from a filiform corrosion (FFC) test of samples coated with a 20 μm epoxy topcoat. The observation can be explained by the role of pitting in FFC initiation and the similarity in FFC propagation with pit growth. The results suggest that dEIS is an efficient method for screening alloys for their FFC susceptibility.