Investigation by electrochemical impedance spectroscopy of filiform corrosion of electrocoated steel substrates

• The filiform corrosion of steel covered by a cataphoretic coating is studied by EIS.
• The steel is a very complex substrate.
• Many parameters must be optimized in order to remove the corrosion products.
• A short cathodic polarization is necessary to evacuate corrosion products.
• The procedure can be used to study different grades of steel.

This work aims at studying by electrochemical impedance spectroscopy (EIS) the susceptibility to filiform corrosion of low carbon steel covered by cataphoretic coating. The determination of the exposed metallic area variations of scratched samples during ageing test is an estimation of the disbonding of the coating and/or the filiform corrosion. This area can be evaluated by electrochemical impedance spectroscopy (EIS). A simplified electrical equivalent model used to estimate the exposed metallic area is valid if the corrosion products are correctly dissolved before characterization. Furthermore the steel is a very complex substrate and thus many parameters must be optimized in order to remove the corrosion products before EIS measurements.