Microstructure Control and Improvement in Magnetic Properties of Rare-Earth Magnet Powders by Absorption Treatment

NdFeB磁体是一种典型的由Nd2Fe_(14)&Gt；B相组成的稀土磁体，具有较高的烧结功率。但也存在耐蚀性低、磁学性能随时间呈下降趋势(老化效应)等问题。我们提出了一种新的方法。(吸锌)，赋予高耐腐蚀性。研究发现，锌吸收处理也改善了磁性能随时间的变化关系。利用透射电子显微镜、场发射扫描电子显微镜和X射线衍射仪对HDDR-NdFeB磁粉及其粘结磁体的微观结构进行了表征。实验结果表明：1.经吸锌处理后，粉末表面和晶界上形成了Fe_1t；11&Gt；Zn_&lt；40&gt；和NdZn_5相；3.未经锌吸附处理的NdFeB的时效效应归因于α-Fe磁畴的存在。4.经锌吸附处理的HDDR-NdFeB中没有形成α-Fe磁畴。5.由于经锌吸附处理的HDDR-FeNdB中没有a-Fe磁畴，所以经再磁化处理后具有与原始磁化一样高的磁强值。6.锌吸附处理可以提高材料的耐蚀性和老化的磁性能。本研究阐明了这种改善的机制。

NdFeB magnet is a typical rare-earth magnet made of Nd_2Fe_<14>B phase that has a high coersive power. However, it has some problems that it has a low corrosion resistance and a tendency of decreasing in magnetics with time (seasoning effect). We have proposed a new method. (Zn-absorption) to give a high corrosion resistance. It has been found that the Zn-absorption treatment also give an improvement in time-dependence in magnetic properties. In this research project, the microstructures in HDDR-NdFeB magnet powder and bond magnets, made from the powders were characterized by means of transmission electron microscopy (TEM), scanning electron microscopy with a field emission gun (FE-SEM) and x-ray diffraction experiments (XRD). From the experimental results, we drew the conclusions as follows :1.After the Zn-absorption treatment, phases of Fe_<11>Zn_<40> and NdZn_5 are formed on the surface of the powders and on the grain boundaries of Nd_2Fe_<14>B.2.In HDDR-NdFeB without the Zn absorption treatment, α-Fe domains are formed in addition to h-Nd_2O_3 on the surface of the powders and on the grain boundaries of Nd_2Fe_<14>B after corrosion treatment.3.The seasoning effect in magnetic properties of NdFeB without Zn absorption treatment is attributable to the presence of α-Fe domains.4.In HDDR-NdFeB with the Zn-absorption treatment, α-Fe domains are NOT formed.5.Since there are not domains of a-Fe in HDDR-FeNdB with the Zn absorption treatment, it can have the value for coersive power as high as the original one by re-magnetization.6.The Zn absorption treatment can improves the corrosion resistance and the seasoning in magnetic properties. The present study has clarified the mechanism of the improvement.