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DE-102025131728-A1 - ND-FE-B MAGNET WITH HIGH REMAIN AND HIGH COERCITIVE FIELD STRENGTH AND METHOD FOR ITS MANUFACTURING

DE102025131728A1DE 102025131728 A1DE102025131728 A1DE 102025131728A1DE-102025131728-A1

Abstract

The present disclosure relates to a high-remanence, high-coercive Nd-Fe-B magnet. The Nd-Fe-B magnet comprises main-phase crystal grains of phase R 2 T 14 B and a grain boundary phase A. The Nd-Fe-B magnet contains the elements R, M, B, and Fe, where R comprises the rare-earth elements RL and RH. RL represents at least one of the elements Pr, Nd, La, Ce, and Y, and RH represents at least one of the elements Dy, Tb, Gd, and Ho. The element M comprises Co and Cu, and optionally M', where M' comprises one or more of the elements Cr, Ni, Ga, Al, Zr, Nb, and Ti. In the grain boundary phase A, the R content is 29 to 55 at%, the Co content is 3 to 7 at%, and the Cu content is 7 to 20 at%. The Nd-Fe-B magnet provided by the invention has a low content of impurity elements as well as an effectively increased diffusion depth of the heavy rare earth elements and is characterized by a high coercive field strength and high remanence.

Inventors

  • Zhixue Li
  • Shaofang LI
  • Yi Cheng
  • Lijun CAO
  • Fei Du
  • Zhan Wang

Assignees

  • Beijing Zhong Ke San Huan High-Tech Co. Ltd.
  • Tianjin Sanhuan Lucky New Material Co., Ltd.

Dates

Publication Date
20260513
Application Date
20250811
Priority Date
20241113

Claims (10)

  1. A high-remanence, high-coercive Nd-Fe-B magnet characterized in that the Nd-Fe-B magnet comprises main-phase crystal grains of phase R 2 T 14 B and a grain boundary phase A; the Nd-Fe-B magnet contains the elements R, M, B and Fe, wherein R comprises the rare-earth elements RL and RH, where RL comprises at least one of the elements Pr, Nd, La, Ce and Y, and RH comprises at least one of the elements Dy, Tb, Gd and Ho, Fe is iron, B is boron, and M comprises Co, Cu and M', where M' comprises one or more of the elements Cr, Ni, Ga, Al, Zr, Nb and Ti; the R content in the grain boundary phase A is 29 to 55 at%, the Co content is 3 to 7 at% and the Cu content is 7 to 20 at%; where the diffusion depth of the heavy rare earth elements RH in the Nd-Fe-B magnet is 500µm or more.
  2. Nd-Fe-B magnet according to Claim 1 , characterized in that M comprises Ga and the Ga content in the grain boundary phase A is 2 to 11 at%.
  3. Nd-Fe-B magnet according to Claim 1 , characterized in that the Nd-Fe-B magnet fulfills one or more of the following conditions: A. The Nd-Fe-B magnet contains one or more of the elements C, N and O as impurities; the content of impurity elements in the Nd-Fe-B magnet is ≤ 1500 ppm; B. The content of N in the Nd-Fe-B magnet is ≤ 200 ppm.
  4. Nd-Fe-B magnet according to Claim 1 , characterized in that the R content in the Nd-Fe-B magnet is 28.5 to 31 wt.%, the M content is 0.8 to 3 wt.%, the B content is 0.94 to 1.02 wt.%, the remainder being iron and unavoidable impurities; and/or that the Co content in the Nd-Fe-B magnet is 1 to 1.5 wt.%, the Cu content is 0.15 to 0.3 wt.%, the Ga content is 0.2 to 0.4 wt.% and the Zr and/or Ti content is 0.05 to 0.35 wt.%.
  5. Nd-Fe-B magnet according to Claim 1 , characterized in that the D50 particle size of the main phase crystal grains is 2.5 to 4µm.
  6. Method for producing an Nd-Fe-B magnet with high remanence and high coercivity according to Claim 1 , comprising the following steps: S1. Applying a diffusion source to the surface of an Nd-Fe-B substrate to form a layer; S2: Performing a first and a second diffusion treatment on the Nd-Fe-B substrate coated with the layer to obtain a diffusion-treated magnet; S3. Performing a tempering treatment on the diffusion-treated magnet to produce the Nd-Fe-B magnet; wherein the Nd-Fe-B substrate comprises R1, M1, B and Fe; R1 comprises at least one of the rare-earth elements Dy, Tb, Pr, Nd, Ce, La, Y, Ho and Gd; M1 comprises Co, Cu and M1', wherein M1' comprises one or more of the elements Cr, Ni, Ga, Al, Zr, Nb and Ti; The content of R1 in the Nd-Fe-B substrate is 28.5 to 31 wt%, the content of M1 is 0.6 to 2.5 wt%, the content of B is 0.94 to 1.02 wt%, the content of Co is 0.5 to 2.5 wt%, the remainder consists of Fe and impurity elements, wherein the impurity elements include one or more of the elements C, O and N, and the impurity content is ≤ 1500 ppm, wherein the N content is ≤ 200 ppm; the diffusion source comprises RH1, M2 and R2, wherein RH1 comprises at least one of the elements Dy, Tb and Ho, R2 comprises at least one of the elements Pr and Nd, M2 comprises Co and M2', wherein M2' comprises one or more of the elements Ga, Al and Cu; The RH1 content in the diffusion source is 30 to 70 wt%, the M2 content is 5 to 30 wt%, the R2 content is 20 to 50 wt%, and the Co content is 1 to 15 wt%; the temperature of the second diffusion treatment is 840 to 880 °C, with a holding time of 4 to 20 hours; the ratio of the temperature of the first diffusion treatment to the temperature of the second diffusion treatment is 1.01 to 1.08; the ratio of the holding time of the first diffusion treatment to the holding time of the second diffusion treatment is 0.1 to 0.3.
  7. Procedure according to Claim 6 , characterized in that the process fulfills one or more of the following conditions: The R1 content in the Nd-Fe-B substrate is 29.5 to 30.5 wt.%, the M1 content is 0.6 to 1.5 wt.%, the B content is 0.96 to 1.0 wt.%, the remainder consists of Fe and impurities menten; The Dy content in the Nd-Fe-B substrate is 2 to 4 wt.%; The Co content in the Nd-Fe-B substrate is 1 to 1.5 wt.%, the Cu content is 0.1 to 0.3 wt.%, the Ga content is 0.1 to 0.5 wt.%, and the Zr and/or Ti content is 0.05 to 0.35 wt.%.
  8. Procedure according to Claim 6 , characterized in that the method satisfies one or more of the following conditions: Step S2 is repeated before step S3 to obtain the diffusion-treated magnet; The total number of repetitions of step S2 is 2 to 8.
  9. Procedure according to Claim 6 , characterized in that the process further comprises the following steps: The Nd-Fe-B raw material in the form of alloy powder is subjected to a shaping treatment and subsequently a sintering treatment to obtain the Nd-Fe-B substrate; The D50 particle size of the Nd-Fe-B crude alloy powder is 2 to 5 µm; The shaping treatment is a directional press forming, which is carried out at an orientation flux density of 1.8 to 2.3 T; The sintering treatment comprises a first sintering stage and a second sintering stage, wherein the temperature of the first sintering stage is 750 to 980 °C for a sintering time of 8 to 10 hours, and the temperature of the second sintering stage is 1000 to 1080 °C for a sintering time of 8 to 12 hours; The degree of vacuum during the sintering treatment is in the range of 10⁻⁵ to 10⁻² Pa; The density of the Nd-Fe-B substrate obtained by sintering is 7.5 to 7.8 g/ cm³ .
  10. Procedure according to Claim 6 , characterized in that in step S1 the weight increase of the Nd-Fe-B substrate with the applied diffusion layer is 0.5 to 1.5%; the content of RH1 in the diffusion source is 45 to 65 wt.%, the content of M2 is 10 to 20 wt.%, the content of R2 is 30 to 40 wt.% and the content of Co is 5 to 10 wt.%; in step S3 the temperature of the tempering treatment is 450 to 690 °C, with a holding time of 0.5 to 4 hours.

Description

Field of invention The present disclosure relates to the field of Nd-Fe-B magnets, in particular to an Nd-Fe-B magnet with high remanence and high coercivity, and to a method for its manufacture. State of the art Sintered Nd-Fe-B magnets are characterized by excellent magnetic properties and are therefore widely used in numerous fields such as the automotive industry, medical technology, electronic information processing, and aerospace. In recent years, the performance of sintered Nd-Fe-B magnets has been continuously improved, steadily expanding their range of applications and increasing the demands placed on their magnetic properties (e.g., magnetic performance and high-temperature stability). One of the most common methods for producing Nd-Fe-B magnets with high coercivity is the so-called grain boundary diffusion process, in which heavy rare-earth elements such as Dy, Tb, or Ho are introduced onto the magnet surface. The concentration difference between the magnet surface and the interior acts as the driving force for the diffusion of these heavy rare-earth elements. This process allows for the production of Nd-Fe-B magnets with excellent overall magnetic properties while simultaneously requiring minimal consumption of heavy rare-earth elements. However, the diffusion depth of heavy rare-earth elements in magnets produced using grain boundary diffusion is currently limited. As the magnet's thickness increases, ensuring diffusion to the interior becomes increasingly difficult, resulting in low diffusion efficiency. Consequently, increasing the coercive field strength is only possible to a limited extent, which negatively impacts the magnetic properties. Furthermore, existing techniques for improving high-temperature stability often involve incorporating the element cobalt into the Nd-Fe-B magnet. In the CN115346746A A method is disclosed in which a diffusion source containing cobalt (Co) and other components such as light and/or heavy rare-earth elements is used to perform a combined grain boundary diffusion treatment. However, since light and/or heavy rare-earth elements accumulate in the grain boundary phase, further diffusion of Co into the grain boundary phase is hindered. As a result, the Co element penetrates the grain boundary phase only to a very limited extent or almost not at all, so that the magnetic properties and temperature stability of the magnet cannot be effectively improved. For this reason, the patent specification proposes to apply an M1-Co metal powder to the magnet surface to increase the Co content in the grain boundary phase by diffusion and thus improve both the magnetic properties and the temperature stability. However, since the diffusion source used does not contain any heavy rare-earth elements, the increase in the coercive field strength of the magnet is limited, which means that the requirements for high-performance magnets cannot be met. Object of the invention The object of the present invention is to provide an Nd-Fe-B magnet with high remanence and high coercivity, as well as a method for its production. The Nd-Fe-B magnet produced by the method according to the invention has a low content of impurities, the diffusion depth of the heavy rare-earth elements is effectively increased, the remanence decrease is minimal, and the magnet exhibits high coercivity and high rectangularity. To achieve the aforementioned objective, a first aspect of the invention provides an Nd-Fe-B magnet, wherein the Nd-Fe-B magnet comprises main phase crystal grains of phase R 2 T 14 B as well as a grain boundary phase A; The Nd-Fe-B magnet contains the elements R, M, B and Fe, where R comprises the rare earth elements RL and RH, RL comprises at least one of the elements Pr, Nd, La, Ce and Y, RH comprises at least one of the elements Dy, Tb, Gd and Ho, Fe is iron, B is boron, and M comprises Co, Cu and M', where M' comprises one or more of the elements Cr, Ni, Ga, Al, Zr, Nb and Ti; The content of R in the grain boundary phase A is 29 to 55 at%, the content of Co is 3 to 7 at%, and the content of Cu is 7 to 20 at%. Optionally, M includes Ga, where the Ga content in the grain boundary phase A is 2 to 11 at%. Optionally, the Nd-Fe-B magnet fulfills one or more of the following conditions: A. The impurities mentioned include one or more of the elements C, N and O; the content of impurity elements in the Nd-Fe-B magnet is ≤ 1500 ppm; B. The N content in the Nd-Fe-B magnet is ≤ 200 ppm. Optionally, the R content in the Nd-Fe-B magnet is 28.5 to 31 wt.%, the M content is 0.8 to 3 wt.%, the B content is 0.94 to 1.02 wt.%, the remainder consists of iron and unavoidable impurities; and/or, The Co content is 1 to 1.5 wt.%, the Cu content is 0.15 to 0.3 wt.%, the Ga content is 0.2 to 0.4 wt.%, and the Zr and/or Ti content is 0.05 to 0.35 wt.%. Optionally, the D50 particle size of the main phase crystal grains is 2.5 to 4 µm. A second aspect of the invention relates to a method for producing an Nd-Fe-B magn