Microstructure and magnetic properties of high coercivity die-upset Nd-Fe-B magnets prepared by Nd-Cu alloy addition

Die upsetting is an effective method to produce bulk anisotropic Nd-Fe-B magnets with nanostructure and full density [1]. A variety of experimental evidence suggests that the grain boundary a play key role in magnetic hardening [2]. Therefore, the grain boundary diffusion method is an effective way to improve the coercivity of die-upset magnet [3, 4]. However, the special role of the grain boundary after diffusion on both magnetic structure and microstructure of the die upsetting magnets is unclear and controversial. In order to obtain the excellent coercivity in the die-upset nanocrystal-line magnets, it is necessary to get better understanding on the mechanism of the enhanced coercivity. In this work, we have fabricated nanocrystalline Nd-Fe-B magnets by hot pressing and die upsetting methods with low melting point eutectic Nd-Cu alloy addition. The coercivity has been dramatically enhanced by Nd-Cu alloy addition. To investigate mechanism of the enhancement of the coercivity, we observed microstructure and the initial magnetization curve of the die upsetting magnets with different Nd-Cu addition.