Modification of boundary structure and magnetic properties of Nd-Fe-B sintered magnets by diffusing Al/Cu co-added alloy ribbons

In this work, grain boundary diffusion (GBD) process with Pr80-xAlxCu20 (x=0, 10, 15, 20) low melt-point alloys was applied to the commercial 42M sintered Nd-Fe-B magnets. The best coercivity enhancement of diffused magnet is the Pr65Al15Cu20 GBD magnet, from 16.38 kOe to 22.38 kOe. Microstructural investigations indicated that increment of Al content in the diffusion source can form the continuous grain boundary (GB) phase clearly, optimizing the microstructure to enhance coercivity. The coercivity enhancement is mainly due to the formation of continuous GB phase to separate the main phase grains. The exchange decoupling between the adjacent main phase grains is enhanced after the GBD process. Meanwhile, the introduction of Al can promote Pr infiltrate into the magnet effectively which increases the diffusion rate of rare-earth elements within a certain range. This work provides a feasible method to enhance coercivity and reduce the usage of the rare-earth resource by replacing partial rare-earth element with non-rare-earth elements in the diffusion source.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Coercivity enhancement of sintered Nd-Fe-B magnets by grain boundary diffusion with Pr_80–xAl_xCu₂₀ alloys

Jin¹,

Jin²,

Ding³

et al. 2023

“…Al has been widely used in diffusion sources because it can effectively improve the wettability of GB phase. [6,16,17] In the preparation of Nd-Fe-B alloy, a small amount of Co is usually added to improve the magnetic properties. [18][19][20][21] Chen et al [22] reported that the coercivity and remanence at high temperatures can be increased simultaneously due to the formation of the Dy and Co enriched shell structure, when the commercial sintered Nd-Fe-B magnet diffused with Dy 60 Co 40 alloy.…”

Section: Introductionmentioning

confidence: 99%

Coercivity and microstructure of sintered Nd–Fe–B magnets diffused with Pr–Co, Pr–Al, and Pr–Co–Al alloys*

Jin¹,

Jin²,

Zhu³

et al. 2021

The commercial 42M Nd–Fe–B magnet was treated by grain boundary diffusion (GBD) with Pr70Co30 (PC), Pr70Al30 (PA) and Pr70Co15Al15 (PCA) alloys, respectively. The mechanism of coercivity enhancement in the GBD magnets was investigated. The coercivity was enhanced from 1.63 T to 2.15 T in the PCA GBD magnet, higher than the 1.81 T of the PC GBD magnet and the 2.01 T of the PA GBD magnet. This indicates that the joint addition of Co and Al in the diffusion source can further improve the coercivity. Microstructural investigations show that the coercivity enhancement is mainly attributed to the exchange-decoupling of the GB phases. In the PCA GBD magnet, the wider thin GB phases can be formed and the thin GB phases can still be observed at the diffusion depth of 1500 μm due to the combined action of Co and Al. At the same time, the formation of the Pr-rich shell can also be observed, which is helpful for the coercivity enhancement.

“…[15,16] By adjusting the distribution and composition of the GB phase, the RE-M (M = Al, Cu) is reported to be beneficial for high coercivity through addition or grain boundary diffusion process after annealing process. [17][18][19][20] Recently, the Nd-Fe-B magnets prepared from Nd-rich Ga-doped Nd-Fe-B strip cast flakes have become an important object of research. [21,22] In these Ga-doped magnets, continuous GB phases were formed which brings out the isolated intergrain exchange coupling.…”

Section: Introductionmentioning

confidence: 99%

Effects of post-sinter annealing on microstructure and magnetic properties of Nd–Fe–B sintered magnets with Nd–Ga intergranular addition*

Zhu¹,

Jin²,

Jin³

et al. 2021

We investigate the effects of post-sinter annealing on the microstructure and magnetic properties in B-lean Nd–Fe–B sintered magnets with different quantities of Nd–Ga intergranular additions. The magnet with fewer Nd–Ga additions can enhance 0.2 T in coercivity, with its remanences nearly unchanged after annealing. With the further increase of the Nd–Ga addition, the annealing process leads coercivity to increase 0.4 T, accompanied by a slight decrease of remanence. With the Nd–Ga addition further increasing and after annealing, however, the increase of coercivity is basically constant and the change of remanence is reduced. Microstructure observation indicates that the matrix grains are covered by continuous thin grain boundary phase in the magnets with an appropriate Nd–Ga concentration after the annealing process. However, the exceeding Nd–Ga addition brings out notable segregation of grain boundary phase, and prior formation of part RE 6Fe13Ga phase in the sintered magnet. This prior formation results in a weaker change of remanence after the annealing process. Therefore, the diverse changes of magnetic properties with different Nd–Ga concentrations are based on the respective evolution of grain boundary after the annealing process.