[O2] RE-Fe-B Magnets II

11:35 AM - 11:50 AM JST(2:35 AM - 2:50 AM UTC)

[O2-3] Synthesis and Magnetic Properties of Plate-Type Nd-Fe-B Magnets by Electrically Heated Powder Rolling

*Jungryang KIM¹, Yusuke HIRAYAMA¹, Kenta TAKAGI¹, Ayako S. SUZUKI², Mayuka NOZAKI² (1. National Institute of Advanced Industrial Science and Technology (AIST) (Japan), 2. S. S. Alloy Co., Ltd. (Japan))

Keywords:

Electrically heated powder rolling,Nd-Fe-B magnet

To improve the performance of electric appliances, eco-friendly power generation, and electric vehicles, enhancing the efficiency of motors is essential. A key factor in this improvement is the magnetic properties of permanent magnets, which play a critical role in motors. Currently, Nd-Fe-B permanent magnets are primarily used due to their high magnetic properties [1]. However, one challenge to motor efficiency is the eddy current loss in Nd-Fe-B magnets. Eddy currents, induced by a changing magnetic flux, flow perpendicular to the direction of the magnetic flux and cause an increase in the temperature of the magnet. As the temperature increases, the magnetic properties of the Nd-Fe-B magnets decrease [2]. To minimize eddy current losses, the conductor can be produced thinner, and plate-type Nd-Fe-B magnets can be laminated with a nonconductive adhesive to create electrically isolated layers. Zheng An et al. reported that a 1mm-thick laminated permanent magnet can reduce eddy current loss by up to 90% compared to conventional sintered Nd-Fe-B magnets [3]. Recent methods for producing plate-type Nd-Fe-B magnets include the PLP (press-less process) [4] and the hot rolling method [5]. We have introduced the electrically heated powder rolling (EPR) method. In this method, electricity is directly transmitted to the rolling target through the roll itself, generating Joule heat due to the electrical resistance of the target material. This technique allows for simultaneous heating and rolling, in contrast to the traditional hot rolling, where the material is preheated. Therefore, it can simplify the process by forming powder into a sheet in a single step, eliminating the multiple processes required in conventional methods.The sintering behavior and magnetic properties of Nd-Fe-B magnets were investigated. Nd-Fe-B powder was prepared via hydrogen decrepitation of an ingot produced by casting. After dehydrogenation, green compacts were prepared and sealed in SUS sheaths with BN powder to prevent sticking. The sheathed samples were then subjected to the EPR using an SKD roll. After rolling, plate-type magnets were extracted.When the rolling conditions of 0.3 mm/s rolling speed and a load of 0.06 t at 900 A, the Nd-Fe-B plate magnet achieved a density of approximately 7.2 g/cm³, reaching 95% of full densification. The magnetic properties at the center of the plate magnet were measured as M_90kOe = 142.6 A·m²/kg and H_c = 80.5 kA/m, which are lower than typical sintered magnets [1]. The thicknesses of the plate magnet are 1.15~1.32 mm.

[1] M. Sagawa et al., IEEE Trans. Magn., 20 (1984) 1584-1589.
[2] N. J. Yu et al., J. Magn., 18(3) (2013) 235-239.
[3] Z. An et al., IEEE Trans. Power Electron., 37(10) (2022) 12391-12405.
[4] M. Sagawa, The Micromeritics, 66 (2023) 43-50.
[5] Q. Li et al., J. Mater. Res. Technol., 26 (2023) 4506-4515.