Evaluation of environmentally friendly coatings for electrogalvanized steel

C.R. TOMACHUK; C.I. ELSNER; A.R. DI SARLI; C.A.C. CHAVES; D.J.C. SPINELLI; O.B. FERRAZ

Fortaleza

Congreso; Congresso Latino Americano de Corrosão LATIN CORR 2006; 2006

ABRACO

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 pure zinc coatings can be improved by means of suitable chemical passivation treatments. Hexavalent chromium compounds have been used to create conversion layers providing better anticorrosive protection as well as anchorage properties to the painting systems. However, as it is well known, 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, zinc coatings obtained from free-cyanide alkaline bath and submitted to a Cr3+ based passivation treatment, with and without a sealer, were studied. The corrosion behavior was investigated through polarization curves and electrochemical impedance spectroscopy in NaCl 3.5%wt solution at room temperature. Morphological observations on the coatings surface were also performed. The experimental results allow inferring that the Cr3+ based conversion treatment + adequate sealer presents a good corrosion resistance, suggesting that they could be a non polluting alternative to the traditional chromated coatings.