Microstructure and corrosion resistance of sintered NdFeB magnet modified by intergranular additions of MgO and ZnO
来源期刊：JOURNAL OF RARE EARTHS2008年第2期
论文作者：SHEN Liping SHAN Aidang LIU Qiongzhen MO Wenjian ZHANG Lanting WU Jiansheng Komuro Matahiro
Key words：NdFeB magnets; intergranular addition; magnetic properties; corrosion resistance; microstructure; rare earths;
Abstract: Microstructure and corrosion resistance of sintered Nd15Dy1.2Fe77Al0.8B6 and Nd22Fe71B7 magnets modified by intergranular addition of MgO and ZnO were investigated. Both the remanence and sintering density of the magnets increased slightly with intergranular additions of MgO and ZnO. There was a remarkable increase in coercivity of Nd22Fe71B7 after addition. Besides, the effects on magnetic properties and an improved corrosion resistance were observed. Compared with the native magnets without addition, corrosion potential of the magnets with MgO and ZnO additives was more positive and the current density in the anodic branch of the polarization curve was reduced. Corrosion resistance resulting from autoclave testing (2×105 Pa of steam pressure, 120 °C) showed that the corrosion rate of NdFeB magnets reduced with the increase of additive amount. Microstructure observation revealed that MgO and ZnO additives were incorporated into the intergranular phases in the magnets. With the introduction of MgO and ZnO, more intergranular phase with high oxygen content was formed while keeping the volume fraction of all the intergranular phases almost unchanged, which may contribute to improved corrosion resistance. Furthermore, addition of MgO and ZnO refined the grain size of Nd22Fe71B7.
SHEN Liping1，SHAN Aidang2，LIU Qiongzhen2，MO Wenjian2，ZHANG Lanting2，WU Jiansheng2，Komuro Matahiro3
(1.Hitachi China Research & Development Corporation Shanghai Branch, Shanghai 200020, China;
2.School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;
3.Advanced Research Laboratory, Hitachi Ltd., Hitachi-shi, Ibaraki-ken 319-1292, Japan)
Abstract:Microstructure and corrosion resistance of sintered Nd15Dy1.2Fe77Al0.8B6 and Nd22Fe71B7 magnets modified by intergranular addition of MgO and ZnO were investigated. Both the remanence and sintering density of the magnets increased slightly with intergranular additions of MgO and ZnO. There was a remarkable increase in coercivity of Nd22Fe71B7 after addition. Besides, the effects on magnetic properties and an improved corrosion resistance were observed. Compared with the native magnets without addition, corrosion potential of the magnets with MgO and ZnO additives was more positive and the current density in the anodic branch of the polarization curve was reduced. Corrosion resistance resulting from autoclave testing (2×105 Pa of steam pressure, 120 °C) showed that the corrosion rate of NdFeB magnets reduced with the increase of additive amount. Microstructure observation revealed that MgO and ZnO additives were incorporated into the intergranular phases in the magnets. With the introduction of MgO and ZnO, more intergranular phase with high oxygen content was formed while keeping the volume fraction of all the intergranular phases almost unchanged, which may contribute to improved corrosion resistance. Furthermore, addition of MgO and ZnO refined the grain size of Nd22Fe71B7.
Key words:NdFeB magnets; intergranular addition; magnetic properties; corrosion resistance; microstructure; rare earths;
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