Studying the Anticorrosion, Morphological and Adhesion Properties of an Ambient Temperature Cobalt Induced-Phosphate Coating

Different properties of an ambient temperature phosphate coating containing cobalt ions were studied on a steel substrate. Surface treatment on the phosphate coating bath was conducted at T=25 ºC, pH=3.1 and t=30 min. Different analytical techniques including linear polarization, scanning electron microscope (SEM), EDX and Pull off test were employed in order to evaluate the phosphate coating properties. The results obtained from the polarization test revealed that corrosion resistance of the phosphate coating was enhanced in the presence of cobalt ions. SEM micrographs showed a better surface coverage for the cobalt induced phosphate coating. Results obtained from the pull off test also showed that the surface treatment of the steel substrate by phosphate coating reduced adhesion loss of the epoxy coating after 30 days immersion in 3.5 wt% NaCl solution. The decrease in the adhesion loss was more pronounced in the case of using cobalt ions in phosphate coating.