Comparison of the corrosion resistances of chromium-passivated and cerium-passivated Zn/NdFeB magnets

作者：Zhang, Pengjie; Chen, Jing; Yang, Hongyi; Xu, Guangqing^*; Lv, Jun; Cui, Jiewu; Sun, Wei; Li, Bingshan; Wang, Dongmei; Wu, Yucheng^*

来源：CORROSION REVIEWS, 2023, 41(2): 171-182.

DOI：10.1515/corrrev-2022-0014

• cerium passivation
• corrosion resistance
• trivalent chromium passivation
• Zn
• NdFeB magnet

Chromium-free passivation of Zn coating on NdFeB magnets becomes a research hotspot due to the serious harm of chromium ions to the human body. Chromium-based and cerium-based passivation technologies are conducted on electroplating Zn/NdFeB respectively. Morphologies, elemental compositions and phase structures of the two passivated coatings are characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The corrosion resistances of the two passivated specimens are compared by neutral salt spray test, accelerated aging test and electrochemical measurements. A complete and smooth passivation film can be obtained on the surface of Zn/NdFeB, filling the gaps and pores in Zn coating. Compared with un-passivated Zn/NdFeB, Zn(Ce)/NdFeB and Zn(Cr)/NdFeB possess excellent corrosion resistance. In comparison, Zn(Ce)/NdFeB possesses excellent anti-corrosion performance, increasing the red-rust appearing time from 288 to 432 h, which is still lower than that of Zn(Cr)/NdFeB (528 h). Therefore, the self-repair effect of cerium passivation technology during the corrosion process should be further studied to achieve the purpose of replacing chromium passivation technology.