Study of Microstructure for Chromium-Free Passivating Coatings on Hot-Dipped Galvanized Steel

摘要

Conventionally, chromate conversion coatings with hexavalent chromium (Cr~(6+)) for galvanized steel sheets have been widely used as surface treatments such as passivations due to their excellent corrosion protection and low cost. However, such chromale coatings are toxic and regulated by global environmental legislation, such as Waste Electrical and Electronic Equipment (WEEE) [e.g., 1] and Restriction of Hazardous Substances (RoHS) [e.g., 2]. As a result, a great deal of interest in developing non-chromate passivating coatings that do not contain hexavalent chromium attracts much attention today [e.g., 3-5] Improving corrosion protection is one of the ideas for developing non-chromate passivating coatings in light of the inferior corrosion resistance of these coatings. Improvement methods include: (1) barrier protection for the sacrificial zinc layer against corrosive elements (e.g. oxygen, water, and chlorine ions);;and (2) inactivation of zinc surface or formation of hardly soluble compounds in the coating/zinc interface.