Adhesion properties, structure of surface and electrochemical behavior of conversion coatings obtained by phosphating and zirconium post-treating on steel

The Zinc-phosphated steels were post-treated with hexafluorozirconicacid solution in different conditions.Epoxy was applied on the samples and optimum condition was obtained using pull-off test. Structure of surface, electrochemical behavior of the samples were investigated using atomic force microscopic(AFM), open circuit potential (OCP).The results showed that zirconium post-treatment of the phosphated samplesformed the continuous coatings. Potential drop of post-treated samples decreased compared with single phosphated samples, during the first 30 minutes immersion in 3.5% NaCl solution at room temperature, showing a better performance of the coating.