Galvanized steel protection evaluation by electrochemical methds

C.R. TOMACHUK; A.R. DI SARLI; C.I. ELSNER; O.B. FERRAZ

Recife - Pernambuco

Congreso; 2nd International Corrosion Meeting - INTERCORR 2008; 2008

Asociación Brasilera de Corrosión

In the last 30 years, zinc plating had remarkable development due to the increasing demand for coatings with better corrosion resistance from the automotive industry. The corrosion resistance of these coatings can be improved by means of suitable chemical passivation treatments. Hexavalent chromium compounds have been used to create conversion layers on Zn providing better anticorrosive protection as well as anchorage properties to painting systems. However, new and more severe environmental regulations impose elimination of hexavalent chromium compounds on passivation baths and its replacement by environmentally friendly chemicals. In this work, the electrochemical behaviour of electrogalvanized steel with Cr3+ based passivation layer and of zinc with organic fillers coatings were studied, and their corrosion response compared with that exhibited by electrogalvanized steel protected with traditional Cr6+ conversion treatment. The corrosion behaviour was investigated through polarization curves and electrochemical impedance spectroscopy in NaCl 3.5% wt solution at room temperature. Morphological observations on the coatings surfaces were also performed. The experimental results allow inferring that the zinc+polymer coating system investigated in this study shows a corrosion resistance superior to that presented by the Cr3+ protected coating and comparable to that exhibited by the coating protected by the Cr6+ conversion treatment, suggesting that it can be a non-polluting alternative to replace this latter system.