[P1] RE-Fe-B Magnets

[P1-37] Coercivity enhancement of hot deformed NdFeB magnets by doping multicomponent Ce-Tb-Pr-Al-Zn alloys

*HUANG WEI CHANG¹, P.H. Lin¹, Y.J. Wong¹, W.J. Wong¹, W.C. Chang¹ (1. Department of Physics, National Chung Cheng University (Taiwan))

Keywords:

Hot deformed NdFeB magnets,coercivity enhancement,multicomponent Ce-Tb-Pr-Al-Zn alloys

How to enhance coercivity of NdFeB magnets with the reduced Tb or Dy usage has long been an important issue. NdFeB magnet prepared by hot deformation (HD) exhibits anisotropic nano-structure, and therefore higher coercivity than that of the traditional sintered magnet with micrometer-scale structure. Both grain boundary diffusion (GBD) and doping with heavy rare earth (HRE) containing alloys were reported to significantly increase _iH_c. Nevertheless, for GBD, there are some disadvantages, including the large reduction of B_r and (BH)_max, much complex process, and the limit of magnet size. In order to enhance coercivity, keep high (BH)_max and reduce HRE usage simultaneously, 2wt% (Ce_1-x-yPr_xTb_y)₇₀Al_30-zZn_z (x=0-0.1, y=0.3-0.5, z=5-15) alloy powders are doped into the commercial MQU-F powders, and subsequently the as-mixed powders were hot pressed and deformed into fully dense magnets in this work. Magnetic properties of the above hot deformed NdFeB magnets with reduction ratio of 70 % are reported. The experimental results show that all studied samples exhibit fine microstructure with well aligned platelet-shape grains and good (00L) texture, and therefore good squareness of demagnetization curve, high remanence and energy product ((BH)_max). By doping Tb₇₀Al₁₅Zn₁₅ powders, the coercivity is significantly increased from 15.0 kOe to 25 kOe, and the efficiency of coercivity enhancement per unit Tb usage (Δ_iH_c/wt% Tb) is 5.6 kOe/wt%Tb. Most interestingly, by doping (Ce_0.6Tb_0.4)₇₀Al₁₅Zn₁₅ and (Ce_0.6Tb_0.3Pr_0.1)₇₀Al₁₅Zn₁₅ powders, Δ_iH_c/wt% Tb could be further increased to 9.1 and 11.8 kOe/wt%Tb and high _iH_c of 22.0 and 21.9 kOe is persisted, respectively. (BH)_max is slightly decreased from 40.5 MGOe to 37.5-39.5 MGOe. Microstructure analysis shows that Ce, Zn, and Al prefer to distribute mostly at grain boundary, while Tb or Pr distributes over grain interior and boundary. The magnetic isolation effect due to R-rich phase containing Nd, Ce, Zn, Al at the grain boundary contributes to coercivity enhancement. In additional to magnetic isolation, the strengthened magnetocrystalline anisotropy field of 2:14:1 phase due to Tb or Pr substitution gives rise to the significant enhancement of coercivity. This study provides a useful way to significantly enhance coercivity of hot deformed NdFeB magnets and keep high energy product with the reduced Tb usage.