Chromate conversion coatings are still one of the most efficient intermedia
te surface treatments for galvanized steel. The performance of the complete
system depends strongly on the composition and structure of the chromate l
ayer, which is normally characterized by destructive methods. The main purp
ose of this paper is to develop an indirect non-destructive method, sensiti
ve to changes in the chromate layer, that could be easily applied in indust
ry quality control. Open circuit monitoring, polarization curves and electr
ochemical impedance are the techniques investigated. Chromate layers with d
ifferent chromium contents and structures were tested in various electrolyt
es. 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 electrol
yte. (C) 1999 Elsevier Science Ltd. All rights reserved.