The Effect of Immersion Time and Immersion Temperature on the Corrosion Behavior of Zinc Phosphate Conversion Coatings on Carbon Steel

The formation and corrosion performance of zinc phosphate coating on carbon steel at different temperatures and immersion times was studied. The corrosion performance of coatings was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. The characterization and composition of coatings were studied by SEM and EDS analysis. The corrosion resistance in 3.5% wt. NaCl solution was increased in the presence of zinc phospoate conversion coatings. The effect of immersion time and coating temperature were studied on anti-corrosion behavior of coatings. Coating temperature showed a significant effect in phosphate conversion coating and higher corrosion resistance was obtained with 45 degrees C operating temperature. Also the experimental results indicated that the corrosion resistance increased with increasing the immersion time. This behavior can be related to the increase of the phosphate coating continuity which formed on the surface. Surface analysis results indicated that the coating obtained from 20 min immersion time was more uniform and continuous.