Enhancement of the corrosion protection performance, cathodic disbanding resistance and adhesion properties of epoxy coating through treatment of steel substrate by Nano structured vanadium-based conversion coating In the presence of Ni ions

Corrosion resistance of the mild steel must be improved before any outdoor applications by various techniques such as cathodic/anodic protection, coatings, surface treatments, inhibitors and application of anti-corrosion pigments. It is known that chemical conversion coatings are one of the most cost-effective methods of surface modification. They facilitate bond formation between the substrate and the organic coating together with improving corrosion resistance. Hence, in this study nanostructured vanadium conversion coatings were deposited on the surface of mild steel(st 37) on the basis of vanadium (VCC) and vanadium-Nickel (VNiCC) based conversion coating solutions. An epoxy/polyamine coating was then applied on the VCC and VNiCC substrates. The surface characterization was performed by field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM) measuring device. The adhesion strengths of the epoxy coatings applied on the surface treated samples were measured before and after 30 days of immersion in 3.5 wt.% NaCl solution by a pull-off test. In addition, The effect of VCC and VNiCC treatment on the epoxy coating performance was studied by electrochemical impedance spectroscopy (EIS) and cathodic disbonding (CD) tests. FE-SEM and AFM study show that the VNiCC is denser, More continuous and more surface roughness than VCC. The dry and recovery (adhesion strength after 30 days immersion in the 3.5 wt% NaCl solution) adhesion strengths of 2 - Masters student, Amirkabir University of Technology, Corrosion Engineering and Material Protection Departement, Hormozgan Campus 2- Professor, Polymer Eng. and Color Tech., Amirkabir University of Technology, Tehran 251 the coatings applied on the VNiCC samples were greater than VCC sample. In addition, the adhesion loss of the coating applied on the VNiCC substrate was lower than other samples. Also, the results obtained from EIS and cathodic disbonding test clearly revealed that the VNiCC could enhance the corrosion protective performance and reduced cathodic disbonding of the epoxy coating than other samples.