A study of performance of corrosion prevention compounds on AA2024-T3 with electrochemical impedance spectroscopy

The performance of corrosion prevention compounds (CPC) on AA2024-T3 was assessed with electrochemical impedance spectroscopy (EIS). The good correlation between the protection performance of CPC and both the interfacial impedance and double layer capacitance allowed two assessment criteria to be defined; as found for AA7075-T6, excellent protection was exhibited by CPC-coated surfaces with interfacial impedances above 0.1 MΩ cm2 or double layer capacitances below 7.6 × 10−8 F/cm2. A correlation between double layer capacitance (Cdl) and corroded area was also obtained. This latter correlation offers an alternative to evaluation of CPC performance via the corroded area calculated from Cdl. In addition, a prediction method was demonstrated based on impedance parameters that showed the feasibility of using data from 30 days to predict the performance of CPC after 180 days exposure. It was found that the CPC failure can be greatly accelerated without changing the relative ranking among the CPC used by introducing intentional scratches on CPC-coated specimens. In particular, the minimum time needed to rank various CPC was reduced to 8 days for scratched specimens from several months for unscratched ones.