Investigation of the protective action of chromate coatings on hot-dip galvanized steel: role of wetting agents

Abstract Chromating is applied on hot-dip galvanized (HDG) steels in order to improve the protective action of metallic zinc coatings. In this study the influence of chromating on the corrosion resistance of zinc coating is investigated with the scanning Kelvin probe (SKP), XPS and AES surface analysis techniques. The combination of electrochemical local techniques and surface analysis is helpful to corrosion investigation of materials, for instance the paper focuses on the synergetic effect of three different constituents of the chromating product well known for their efficiency: phosphates, chromates and surfactants. For this purpose two types of products have been compared, an industrial formulation ( P Ind ) which is currently applied in the industrial lines and a reference product which has been formulated in the laboratory ( P Lab ) in order to sort out the effect of each constituent.