Electrochemical behavior of epoxy coating on phosphated mild steel

Conversion coatings on mild steel enhance its adhesion and corrosion resistance. In this study, effect of phosphate surface pretreatment of mild steel on the corrosion resistive and adhesive properties of epoxy coating was investigated. First mild steel surface was prepared. Then zinc and iron phosphate conversion coatings were applied by immersing them in phosphate bath. After that, epoxy coating was sprayed with a spray gun. The influence of phosphating on protection performance of epoxy coating was studied in 3.5% NaCl solution by electrochemical testing for 15 days. Open circuit potential and electrochemical impedance spectroscopy results were obtained. Nyquist and bode plots were used to explain the impedance results. The adhesion strength of the epoxy coating was studied by pull off adhesion test and cathodic disbondment test. As a result, it was observed that the epoxy coating on phosphate pretreated surface performed well as compared to the epoxy coating with base metal alone. The corrosion resistance and adhesive strength of epoxy coating on pretreated mild steel was increased significantly.