EVALUATION OF ZN-CR III-ORGANIC COATING BY ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY

Abstract

Corrosion control of electrogalvanized steel employing Cr VI based treatments is widely known and studied. However, researchers have been trying to find out alternatives to replace these salts once they must be banned in accord to environmental and industrial guidelines. Cr III – based conversion coatings have shown performance compatible to Cr VI – based treatments. In this work, EIS measurements are performed in NaCl 0,05 mol/L and Na2 SO4 0,1 mol/L, during the immersion time, to evaluate the corrosion resistance of electrogalvanized steel passivated with Cr III – based conversion treatment and painted with three different organic coatings. The organic coatings are characterized by their adherence. The results show a similar behavior for the three coatings and, despite a second constant time has been pointed by the EIS fitting, the R2 values indicate a low corrosion rate. The system Zn – Cr III – organic coating is compatible to the system Zn – Cr VI – organic coating, for the immersion period considered.

Keywords

• Electrochemical impedance spectroscopy; Trivalent chromium; Electrogalvanized steel; Organic coating.