Corrosion performance of electrogalvanizes steel treatment with Cr (III)-based products

Abstract

The corrosion resistance of pure zinc coatings can be improved through the application of suitable chemical passivation treatments. Hexavalent chromium compounds have widely been used to formulated conversion layers providing better anticorrosive protection as well as anchorage properties to painting systems. However, taking into account that they are produced using hazardous chemical ingredients, the development of alternative and “green” thechnologies with equivalent protective performance is a paramount purpose of many R & D laboratories working around the world. In this work, the corrosion behavior of zinc coatings obtained from free-cyanide alkaline baths and latterly subjected to a Cr(III) based passivation treatment, with and without a sealing treatment, was studied. The experimental work involved electrochemical impedance spectroscopy measurements on 0.5 M Na2SO4 solution, surface microestructural and morphological characterization by electronic microscopy as well as chemical analysis by EDXS. The analysis and interpretation of all the data coming from these batteries of tests allowed inferring that both the Cr(III) based conversion treatment + adequate sealer provide a good corrosion resistance and, therefore, together with an adequate painting system, they could be a less pollution and less toxic alternative to the traditional chromate coatings.