Preparation of Modified Epoxy Resin-Based Chromium-Free Dacromet Coating and Evaluation of Its Corrosion Resistance

Epoxy resin modified by polyurethane was used to replace chromic anhydride for preparing Cr-free dacromet paint and coating. The corrosion resistance of as-obtained Cr-free dacromet coating on the surface of Q235 steel was evaluated and compared with that of conventional electroplated Zn coating, and its anticorrosion mechanism was discussed as well. Results indicate that as-obtained Cr-free dacromet coating possesses better thermal stability and corrosion resistance than conventional electroplated Zn coating. Besides, Cr-free dacromet coating mainly consists of Zn, Al, O, and C, and Zn is corroded before the corrosion of Al. Moreover, under the attack of corrosive medium, the Zn and Al powders in Cr-free dacromet coating are passivated to form the oxides of Zn and Al; and the main anticorrosion mechanism of the coating include shielding effect, electrochemical effect and passivation as well.