Combined 3-Components Phosphate and Organic Coatings on Zinc Surfaces

In recent years, the production of galvanized sheet steels with organic coatings applied to its surfaces has considerably expanded. Phosphating of the zinc surfaces raises its roughness and surface tension, providing high adhesion of subsequent organic coatings and respectively, significant increasing of their protective properties. The paper presents the results obtained in the investigation of combined anti-corrosion coatings, including formation of phosphate films on galvanized steel surfaces followed by the application of three types of paint and varnish coatings. The indicators characterizing the phosphating preparation (density, pH, conductivity, acid capacity) as well as the thickness of the coatings were measured. The chemical composition of the phosphate films, their morphology and topography were determined by means of EDX and SEM, respectively. The adhesion, elasticity and impact toughness of the organic coatings, with and without phosphating treatment of the zinc surfaces were measured. The corrosion resistance of the combined coatings in a model sodium chloride solution was also determined.