Organic-inorganic composite passivation and corrosion resistance of zinc coated NdFeB magnets

An organic-inorganic composite passivation of Zn coated NdFeB magnets was carried out using Ce-containing compound and organosilane as source materials. Effects of organosilane content on the microstructure of composite passivation layer were analyzed, and the corrosion resistance and corrosion mechanism of the passivated Zn/NdFeB specimens were deeply studied. Composition, elemental distribution, phase structure and morphology of the specimens were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. The corrosion resistance of the specimens was studied by polarization curves, electrochemical impedance spectroscopy, neutral salt spray text and mass gain test. Results show that adding an appropriate amount of organosilane during the passivating process can form a passivation layer composed of Ce, Si, and O. The optimized Zn(CS-1)/NdFeB achieves the longest NSS time of 840 h, which is twice that of Zn(Ce-5)/NdFeB specimens. Organosilane can build a framework for the passivation layer and make the passivation layer more compact. During the corrosion process, the corrosion medium invasion path is long due to the support of the organosilane frame on the surface, so the corrosion resistance of Zn(CS)/NdFeB is greatly enhanced.