Microstructure characteristic and excellent corrosion protection properties of sealed Zn–TiO2 composite coating for sintered NdFeB magnet

In this paper, a protective sealed Zn–TiO2 composite coating (SCC) was prepared on sintered NdFeB magnet by electrodeposition and sol–gel combined technique. For a comparison, unsealed Zn–TiO2 composite coating (UCC) was also studied. The surface morphologies of composite coating were studied using scanning electron microscope (SEM). The microstructure of composite coatings and structure of sealing layer were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectrum, respectively. The anticorrosive properties of composite coatings in neutral 3.5 wt.% NaCl solutions were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) technique. The results of corrosion tests showed that due to the blocking effect of sealing layer, SCC could suppress the corrosion process by holding back the transfer or diffusion of corrosive medium, and therefore showed the excellent corrosion protection properties for sintered NdFeB magnet.