Improvement of corrosion protective performance of organic coating on low carbon steel by PEO pretreatment

•Carbon steel samples were pretreated by plasma electrolytic oxidation (PEO).•Samples with and without PEO pretreatment were coated by polyurethane (PU).•The cross-sections before and after corrosion test were observed by scanning electron microscope(SEM).•The anticorrosive performance of coatings were studied by ac/dc/ac electrochemical impedance spectroscopy. Employing pretreatment is a pressing need for preparing anticorrosive coatings on carbon steels. However, conventional pretreatments are usually based on Cr, P and some other toxic elements, which are harmful to human body. For this reason, green and environmental techniques attract more and more attention. In this paper, plasma electrolytic oxidation (PEO) process was used as a pretreatment to fabricate an underlayer for the organic coating on low carbon steel. The anticorrosive performance of the organic coated samples with and without PEO pretreatment was studied by potentiodynamic polarization, ac/dc/ac electrochemical impedance spectroscopy, salt spray and immersion tests, respectively. Results show that the PEO process produces an oxide layer with porous and rough surface structure on the low carbon steel substrate. The porous and rough PEO layer is beneficial for enhancing the adhesion strength and thickness of the organic topcoatings. The organic coated sample with PEO pretreatment exhibits improved corrosion resistance and longer service life in corrosive environment compared to that without PEO pretreatment.