Enhancement of the Epoxy Coating Corrosion/Cathodic Delamination Resistances on Steel by a Samarium Based Conversion Coating

Abstract

Samarium (III) (Sm)-based conversion layer was developed on carbon steel for improvement of the epoxy coating adhesion properties, corrosion protection performance, and cathodic delamination resistance. The post-heating and pre-heating actions impact on the Sm (III) film properties was studied. The morphology and chemistry of the Sm (III) film were examined by scanning electron microscopy, atomic force microscopy, contact angle, and X-ray photoelectron spectroscopy. The outcomes from these analyses proved that both pre-heating and post-heating actions altered the morphology and chemistry of the Sm (III) film. The pull-off test indicated that Sm (III) film could enhance the adhesion between the epoxy/steel through increasing the surface roughness and enhancing the surface free energy. The improvement in adhesion strength led to a decrease in the cathodic delamination rate up to 78%. Although both pre-heating and post-heating actions improved the corrosion protection performance of the epoxy film, the pre-heating method had a much higher impact on the epoxy film corrosion resistance enhancement. An excellent corrosion protective performance was observed in the samples preheated at 65°C after 1000 h exposure to salt spray test.