Improved performance of cerium conversion coatings on steel with zinc phosphate post-treatment

The steel samples were pre-treated by cerium conversion layer. Then, zinc phosphate conversion coating was used as sealing agent for the cerium conversion layer to enhance its corrosion resistance. The corrosion performance and surface characteristics of the samples were characterized by electrochemical impedance spectroscopy, scanning electron microscope and X-ray photoelectron spectroscopy. Results revealed that the post-treatment of the cerium conversion coating by phosphate coating significantly increased its corrosion resistance. A denser conversion layer with less cracks were precipitated on the steel surface after post-treatment by zinc phosphate. The surface free energy was significantly increased after post-treatment by zinc phosphate.