Electrochemical characterization of chromate coatings on galvanized steel

Chromate conversion coatings are still one of the most efficient intermediate surface treatments for galvanized steel. The performance of the complete system depends strongly on the composition and structure of the chromate layer, which is normally characterized by destructive methods. The main purpose of this paper is to develop an indirect non-destructive method, sensitive to changes in the chromate layer, that could be easily applied in industry quality control. Open circuit monitoring, polarization curves and electrochemical impedance are the techniques investigated. Chromate layers with different chromium contents and structures were tested in various electrolytes. It was verified that resistances and capacitances obtained by impedance measurements at low frequency range, can be very sensitive even to little changes in the chromate layer, depending on the composition of the electrolyte. (C) 1999 Elsevier Science Ltd. All rights reserved.