Effect of phosphate coatings on the performance of epoxy polyamide red oxide primer on galvanized steel

Conversion coatings on metals enhance paint or lacquer adhesion and promote corrosion resistance. Present study characterizes three different phosphate baths of zinc phosphate, calcium modified and manganese-modified formulations. It has been observed that manganese modified baths have shown better performance than the other two. The phosphated substrates were coated with epoxy coatings. The coated panels were examined for adhesion by pull off methods and corrosion resistant properties were evaluated by salt spray exposure studies. The electrochemical impedance behaviour of these specimens were also carried out and found that the coatings over phosphate surface performed well compared to these with base metal alone. SEM studies were also conducted to see the surface morphology of the phosphated surface.