材料科学与技术 ›› 2020, Vol. 53 ›› Issue (0): 73-81.DOI: 10.1016/j.jmst.2020.04.018

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  • 收稿日期:2019-11-27 修回日期:2020-02-08 接受日期:2020-02-08 出版日期:2020-09-15 发布日期:2020-09-21

Role of primary Zr-rich particles on microstructure and magnetic properties of 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets

Tao Yuana,b, Xin Songa, Xianglong Zhoua, Wentao Jiaa, Munzali Musaa, Jingdong Wangb, Tianyu Maa,*()   

  1. a Frontier Institute of Science and Technology, State Key Laboratory for Mechanical Behavior of Materials, and MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi’an Jiaotong University, Xi’an, 710049, China
    b The Southwest Applied Magnetism Research Institute, Mianyang, 621000, China
  • Received:2019-11-27 Revised:2020-02-08 Accepted:2020-02-08 Online:2020-09-15 Published:2020-09-21
  • Contact: Tianyu Ma

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Abstract:

Trace Zr addition is essential for achieving desired cellular nanostructure and large coercivity in the pinning-controlled 2:17-type Sm-Co-Fe-Cu-Zr magnets that have served as the strongest high temperature permanent magnets for over 40 years. However, accompanying this is the formation of Zr-rich particles that may deteriorate the hard magnetic properties. Besides the formerly-reported 1:3R Zr-rich platelets, in this work, 1-2 μm sized Zr6(Co, Fe)23 (6:23) particles (Fm $\bar{3}$ m) and 100-200 nm sized 1:3R Zr-rich particles were also found based on combined structural identifications and element mapping analysis. Around such particles, the desired 1:5H cell wall precipitates that provide the strongest pinning force of magnetic domain wall motions are rare, forming the precipitate-free-zones (PFZs). The 1:5H-PFZs and the soft magnetism of both 6:23 and 1:3R Zr-rich particles act as local weak pinning points, which are unfavorable to retain the large magnetization in strong opposite fields and lead to poor squareness. As observed in a Sm25Co45.9Fe19.5Cu5.6Zr4.0 (wt.%) magnet, the co-existence of such Zr-rich particles and the associated 1:5H-PFZs leads to a pretty low squareness factor of only 52.89 % given the large coercivity of 29.04 kOe. Our findings suggest that careful controlling the Zr content and avoiding its aggregation to form harmful 6:23 and 1:3R Zr-rich particles are essential for achieving high squareness as well as large energy product in the Sm-Co-Fe-Cu-Zr permanent magnets.

Key words: Permanent magnets, Sm-Co alloys, Microstructure, Precipitates