Morphology and corrosion resistance of Cr(III)-based conversion treatments for electrogalvanized steel

The effectiveness of Cr(VI)-based passivation treatments is well accepted but there are many problems with regard to their environmental suitability. Because these compounds are carcinogenic and toxic, eco-friendly systems capable of replacing them are being evaluated. In this work, the corrosion behavior in 0.5 M NaCl solution of zinc coatings deposited from a free-cyanide alkaline bath and treated with Cr³⁺ based passivation coatings were characterized through DC and EIS techniques. The salt spray test as well as studies of the surface structure and chemical composition were also performed. From these analyses it was inferred that (1) the green-colored Cr³⁺ passivated coatings provide better corrosion resistance than the yellow- and blue-colored coatings, and (2) together with an adequate painting system, they could be a less polluting and less toxic alternative to traditional chromate coatings.