Preparation and Corrosion Resistance of Zn-Al Coating on Sintered NdFeB Permanent Magnet

doi:10.11902/1005.4537.2022.003

Journal of Chinese Society for Corrosion and protection

2023, Vol. 43

Issue (1): 104-110 DOI: 10.11902/1005.4537.2022.003

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Preparation and Corrosion Resistance of Zn-Al Coating on Sintered NdFeB Permanent Magnet

JIANG Jie¹^,², JIANG Jianjun², YANG Lijing², LEI Bufang¹, ZHAO Yu³, LIN Jianqiang⁴, SONG Zhenlun²(

)

^1.School of Materials Science and Engineering, Taiyuan University of science and Technology, Taiyuan 030024, China
^2.Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Key Laboratory of Marine Materials and Related Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
^3.Hangzhou Permanent Magnet Group Co. Ltd., Ningbo 311231, China
^4.Ningbo Zhaobao Magnetic Industry Co. Ltd., Ningbo 315299, China

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Abstract

A Cr-free Zn-Al coating was prepared via a two-step process, namely spraying Zn-Al paste and subsequently baking, on the surface of sintered Nd-Fe-B permanent magnet, and which was further examined by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, and differential thermal comprehensive thermal analyzer (TG-DTA) in terms of its morphology, composition, and formation mechanism of the coating. The corrosion behavior of the coated Nd-Fe-B magnet was studied via immersion testing in 3.5%NaCl solution, and neutral salt spray testing. The results show that Zn-Al coating is uniformly coated on the surface of the NdFeB magnet, the coating thickness is about 27 µm, while, its corrosion resistance to neutral salt spray testing is higher than 1000 h; In other word, the Cr-free Zn-Al coating can provide excellent cathodic protection and physical barrier for NdFeB permanent magnet.

Key words: chromium-free Zn-Al coating micromorphology silane corrosion resistance rare earth

Received: 01 January 2022 32134.14.1005.4537.2022.003

ZTFLH:

TG174

Fund: National Key Research and Development Program of China(2021YFB3502902);Key Research and Development Program of Ningbo(2021Z024)

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	Jie JIANG
	Jianjun JIANG
	Lijing YANG
	Bufang LEI
	Yu ZHAO
	Jianqiang LIN
	Zhenlun SONG

Cite this article:

JIANG Jie, JIANG Jianjun, YANG Lijing, LEI Bufang, ZHAO Yu, LIN Jianqiang, SONG Zhenlun. Preparation and Corrosion Resistance of Zn-Al Coating on Sintered NdFeB Permanent Magnet. Journal of Chinese Society for Corrosion and protection, 2023, 43(1): 104-110.

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https://www.jcscp.org/EN/10.11902/1005.4537.2022.003 OR https://www.jcscp.org/EN/Y2023/V43/I1/104

Fig.1 Surface morphology (a, b) and elemental distribution mapping analysis (c, d)

Fig.2 Cross-sectional morphology (a), EDS results (b) and XRD pattern (c) of Zn-Al coating, of the cross-section

Fig.3 FTIR spectrum of KH-560 silane hydrolysate

Fig.4 Thermogravimetric analysis and differential thermal analysis curves of Zn-Al coating: (a) TG-DTG, (b) TG-DTA

Fig.5 Photo-digital images of Zn-Al coating samples after NSS corrosion test at different time

Fig.6 Photo-digital images of Zn-Al coating samples after different time corrosion tests with 20%NH₄NO₃

Fig.7 XRD spectra of Zn-Al coating at different corrosion time in 20%NH₄NO₃

Fig.8 Polarization curve of the sample in 3.5%NaCl solution after soaking in 20% NH₄NO₃ for different time

Table 1 Electrochemical test results of samples immersed in 20%NH₄NO₃ for different times in 3.5%NaCl solution

Fig.9 Nyquist (a) and Bode (b, c) diagram of the sample in 3.5%NaCl solution after soaking in 20%NH₄NO₃ for different time

Fig.10 Magnetic properties of original samples, 300 ℃ heat treated samples and Zn-Al coating samples: (a) demagnetization curve at room temperature, (b) magnetic property data analysis

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