Corrosion behavior of a conversion coating based on zirconium and colorants on galvanized steel by electrodeposition

Corrosion performance of Zr-based coating on substrates obtained by zinc electrodeposition in an alkaline bath is compared to chromate coatings (Cr III and Cr VI). The 'nano Zr' is a conversion coating formed by immersion in a hexafluorozirconic acid solution. Since the 'nano Zr' coating is transparent, the addiction of a colorant provides color to the surface. In this case, the colorant, when applied after the conversion coating, conferred the yellow color to the surface. The coating produced improves the corrosion protection of the substrate. For this study the samples were analyzed by electrochemical impedance spectroscopy (EIS) and accelerated corrosion test in a humidity chamber. The results showed similar behaviors between the 'nano Zr', colorant and the chromate (Cr III) coating. Therefore this kind of conversion coating is a promising substitute for chromate coatings. (author)