Electrochemical studies on corrosion resistance of phosphate chemical conversion coatings on low carbon steel API 5L grade B

Zinc phosphate chemical conversion coatings was formed on low carbon steel (API 5L grade B) from nitrate bath andthe corrosion performance of coatings was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy studies. The characterization and composition of coatings were studied by SEM and EDSanalysis in different immersion times. The corrosion resistance in 3.5 %wt. NaCl solution increased in the presence of zinc phosphate conversion coatings. The effect of immersion time and coating temperature were investigated on anti-corrosion behavior of coatings. Coating temperature indicated a significant effect in phosphate conversion coating and higher corrosion resistance was obtained with 70 ºC operating temperature. Also the experimental results showed the increase in corrosion resistance with increasing the immersion time. This behavior can be due to the increase of the phosphate coating continuity and which formed on the surface. Surface analysis results indicated that uniform and continuous coating was obtained in agreement with electrochemical techniques.