烧结型NdFeB永磁体锌铬膜处理工艺及性能研究

Property and Technology of Zn-Cr Coating on Sintered NdFeB Permanent Magnet

在烧结型NdFeB永磁体表面制备了锌铬转化膜,确定了成膜的工艺条件。利用盐水全浸试验评定了膜层的耐腐蚀性能,并与电镀锌、电镀镍进行了比较。利用电化学方法测试了成膜处理前后NdFeB永磁体的稳定电位和自腐蚀电流。利用SEM,XPS,EDS和XRD研究了锌铬膜的微观形态和组成,测试了处理前后NdFeB永磁体的磁性能。结果表明,锌铬膜相对于NdFeB永磁体属于阳极型涂层,有电化学保护作用、机械阻挡作用和钝化作用。NdFeB永磁体经锌铬膜处理后耐蚀性能显著提高,磁性能变化不大。

Zn-Cr coating was of sintered NdFeB permanent obtained on the surface magnet by special solution immersion, removing excess solution, baking at 80±5℃ for 20 min and sintering at 290-310℃ for 30 min. The suitable conditions of the technology were established. The corrosion-resistant property of the coating was studied by 3.5 % salt solutions immersion test and compared with plating zinc and plating nickel on the surface of NdFeB permanent magnet. The corrosion-resistant property of Zn-Cr coating is significantly superior to that of Zn and Ni coating. The φorr and jcorr, of the bare sample and Zn-Cr coating sample were examined by electrochemical method in 3.5% salt solutions respectively. The result shows that the value of φcorr, of Zn-Cr coating is less than that of bare NdFeB substrate, and Zn-Cr coating makes sacrifice to protect NdFeB substrate as anode in corrosion medium. The microphotography of surface and cross section of the coating were observed by SEM. The results show that Zn-Cr coating is covered even on the surface of the substrate and Zn flakes lay nearly parallel to matrix, which discourage tacking the substrate. The corrosive medium from atcomposition of coating was investigated by means of XRD, XPS and EDS. The test results indicate that the coating consists of Zn（O）, Zn（Ⅱ）, Cr（Ⅲ） and a litde Cr（Ⅵ）, and the Cr（Ⅵ） possesses passivation function to Zn flake and NdFeB substrate. Therefore, the NdFeB after Zn-Cr coating treatment processes get high corrosion-resistant property. And the coating has no negative effects on magnetic properties.