Study on the passivation effect and corrosion mechanism of an environmentally protective insulating coating on non-oriented electrical steel

Abstract

In this study, we successfully developed three insulating coatings for non-oriented electrical steel. These coatings were composed of phosphate film-forming agents, passivating agents (vanadate, cerium nitrate, and zirconate), and polyurethane dispersants. The surface morphology, composition, electrochemical properties, and corrosion resistance of the three coatings were characterized using scanning electron microscopy (SEM), field-emission electron probe microanalyzer (EPMA), confocal Raman microscopy (CRM), scanning vibration electrode technology (SVET), electrochemical testing, and neutral salt spray experiments. The passivating agent substantially enhanced the compactness of the coating by forming a composite film with the phosphate film-forming agent, which prevented direct contact between the matrix and the corrosive medium and significantly improved the corrosion resistance of the coating. The zirconate passivator significantly increased the compactness of the coating, forming a composite film composed of continuous three-dimensional metals or metalloid oxides on the matrix surface, thereby providing a good shielding effect for the substrate. The incorporation of polyurethane increased fluidity and formed a cross-liked network structure with the composite coatings, enhancing corrosion resistance. The overall properties of the coating that had a zirconate passivator (TZB) demonstrated the best performance among the three systems, surpassing industrial standards, and fulfilling the application requirements for non-oriented electrical steel.