The effect of Zr-conversion coating on adhesion and anti-corrosion properties of epoxy with and without Zinc Aluminium Plolyphosphate (ZAPP) pigment coated mild steel

Organic coatings are considered an effective way to prevent corrosion of steel substrate.Using conversion coating as a thin film layer also helps to improve adhesion of the subsequent layer to the surface and provides a long-term corrosion resistance. In this study,anti-corrosive properties and adhesion of the coating to the surface was investigated for an epoxy organic coating containing ZAPP pigments with and without a Zirconium based conversion coatingtreatment on the St37 substrate. The interaction of organic and conversion coating was studied usingElectrochemical Impedance Spectroscopy(EIS) and Pull-off adhesion tests.Results indicated that using conversion coating as a thin film before applying organic coating,improves adhesion of the coating to the substrate and also gives a better protection against corrosive elements in long periods of immersion times. Field emission scanning electron microscopy and energy dispersive x-ray spectroscopy(FE-SEM/EDX) also proved the presence of Zirconium at the substrate/coating interface after 4 weeks of immersion in 3.5 wt.% NaCl.