Morphology and Anti-Corrosive Performance of Cr(III) Passivated Zn–Fe Alloy Coating on NdFeB Substrate |
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Authors: | Ba Li Xiaoshun Zhou Xiaoping Chen Song Fu Xiangdong Wang Dongliang Zhao |
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Affiliation: | 1.College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China;2.Central Iron and Steel Research Institute Co., Ltd., Beijing 100081, China;3.Zhejiang Innuovo Magnetics Co., Ltd., Dongyang 322118, China |
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Abstract: | In this study, low-iron Zn–Fe alloy coatings and pure Zn coatings, with or without trivalent chromium passivation treatment, were electrodeposited onto a sintered NdFeB magnet from a weak acid chloride bath. The surface morphology and structure of the coatings were then examined using the X-ray diffraction, a scanning electron microscope and 3D white-light interfering surface analysis. Meanwhile, the electrodeposition behavior and anti-corrosive properties of the coatings were investigated using cyclic voltammetry, potentiodynamic polarization, electrochemical impedance spectroscopy, and natural salt spray tests. The results indicate that a passivated Zn–Fe alloy coating with a 0.9 wt.% Fe content provided much better corrosion resistance than a pure Zn coating and could provide both anodic protection and physical barrier function in the NdFeB substrates. The Fe element in Zn–Fe alloy coating was predominantly in solid solution in η-phase and small amounts in elemental form, which was beneficial to acquire a compact coating and passivation film. Finally, the passivated Zn–Fe alloy coating withstood 210 h against a neutral 3.5 wt.% NaCl salt spray without any white rust, which was 3–4 times longer than the pure Zn coating. |
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Keywords: | Nd-Fe-B, pure Zn coatings, Zn– Fe alloy coatings, trivalent chromium passivation, corrosion resistance |
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