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

摘要

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 s tudied 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 - c orrosion 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 wi th electrochemical techniques.