Neodymium-iron-boron grain boundary diffusion method and applications

Abstract

This invention provides a method and application for NdFeB grain boundary diffusion. The method includes: magnetizing diffusion source alloy powder to impart different magnetic properties; spontaneously and uniformly adsorbing the different magnetic properties of the diffusion source alloy powder onto the surface of a NdFeB magnet, forming a multi-layered diffusion source alloy layer; and then subjecting it to diffusion treatment, allowing the multi-layered diffusion source alloy powder to work synergistically and diffuse into the interior of the NdFeB magnet. The diffusion source alloy forms a shell structure on the surface of the NdFeB grains, resulting in a high-performance NdFeB magnet. This invention forms a multi-layered diffusion source alloy layer on the magnet surface through spontaneous adsorption. Thermal diffusion allows the alloy powder to fully penetrate into the magnet and bond with the surface of the NdFeB grains, thereby increasing the penetration depth of the diffusion source alloy and resulting in a significant diffusion effect, further improving the magnetic properties of the magnet. The preparation method is simple and suitable for large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet material preparation technology, specifically relating to a neodymium iron boron grain boundary diffusion method and its application. Background Technology

[0002] Sintered NdFeB magnets are widely used in high-tech fields such as new energy vehicles, rail transportation, and wind power generation. Their low coercivity severely restricts their service stability and reliability, making the improvement of magnet coercivity a key research focus both domestically and internationally. Grain boundary diffusion technology can effectively improve the coercivity of NdFeB magnets, promoting the iterative upgrades and rapid development of sintered NdFeB magnets. The principle involves preparing a diffusion source containing modifying elements and attaching it to the magnet surface. Under a certain heat treatment temperature, the modifying elements in the diffusion source diffuse along the magnet grain boundaries into the magnet interior, repairing surface defects and optimizing the magnet's microstructure, ultimately achieving the goal of improving the magnet's coercivity. After years of development, diffusion technology has evolved, with diffusion source attachment methods including vapor deposition, magnetron sputtering, electrophoretic deposition, slurry impregnation, and powder coating. Among these, slurry impregnation and powder coating are favored by the industry due to their lower cost, simpler process, and applicability to multi-component alloy diffusion sources. In the above method, in order for the diffusion source powder to be adsorbed on the magnet surface for subsequent processing, it is necessary to fully mix the specific solvent or colloid with the diffusion source powder. However, carbon and oxygen in the solvent or colloid will also penetrate into the magnet during the diffusion heat treatment process, which will increase the fluctuation range of the magnet's coercivity and damage the magnet's remanence and magnetic energy product to a certain extent. This will make it difficult to control the batch uniformity and consistency of the diffusion magnet products. When the original magnet has an anisotropic structure, the magnetic properties of the obtained diffusion magnet products are less stable. Chinese invention patent CN116544022A discloses a method for improving the performance of NdFeB magnets, comprising: depositing ferromagnetic alloy diffusion source powder onto the surface of a magnetized or magnetized NdFeB magnet under magnetic adsorption to obtain a magnet to be diffused; and subjecting the magnet to diffusion heat treatment. This invention fundamentally avoids the adverse effects of impurities introduced by conventional powder coating deposition diffusion methods on magnet performance. While achieving high-quality utilization of rare earth elements, it significantly improves the service stability of the magnet. The overall process is simple, the diffusion effect is stable, and it has a wide range of applications, suitable for mass production of high-performance magnets. However, the ferromagnetic alloy diffusion source powder used in this invention has a particle size between 1 and 100 μm, and only after magnetization can it obtain a suitable magnetic particle size. Only then will the magnet surface have a suitable amount of powder, resulting in a magnet with a coercivity H. cj ~20kOe, diffusion depth ~320μm; moreover, it cannot improve the batch uniformity and consistency of diffusion magnet products with anisotropic structures in the existing technology.

[0003] In view of this, the present invention provides a grain boundary diffusion method for neodymium iron boron magnets based on the prior art, which further improves the magnetic properties of the magnets by increasing the diffusion depth of the alloy. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method and application for NdFeB grain boundary diffusion, which significantly improves the coercivity of the original magnet while also ensuring the consistency of magnet performance in batch production.

[0005] To achieve the above-mentioned technical effects, the technical solution provided in this application includes:

[0006] This application first provides a method for NdFeB grain boundary diffusion, characterized by: magnetizing diffusion source alloy powder to give the powder different magnetic properties; adsorbing the diffusion source alloy powders of different magnetic properties to spontaneously and uniformly adsorb onto the surface of the NdFeB magnet to form a multi-layer diffusion source alloy layer; and then subjecting it to diffusion treatment to allow the multi-layer structure of the diffusion source alloy layer to exert a synergistic effect and diffuse into the interior of the NdFeB magnet. The diffusion source alloy forms a shell structure on the surface of the NdFeB grains, resulting in a high-performance NdFeB magnet.

[0007] In a preferred embodiment, the chemical formula of the diffusion source alloy is R. a M1 b M2 c Where R is one or more of Dy, Tb, Pr, Nd, Ho, La, Ce, and Y; M1 is one or more of Fe, Co, Ni, and Gd; M2 is one or more of Al, Cu, Ga, Zr, Ti, Nb, Zn, Mg, Mn, V, Cr, and B, where a, b, and c are the atomic percentages of the diffusion source alloy, 10≤a≤90, 15≤b≤70, 0≤c≤50, and satisfy a+b+c=100.

[0008] In a preferred embodiment, the multilayer structure has at least a first alloy powder layer and a second heavy rare earth diffusion source powder layer.

[0009] In a preferred embodiment, the first alloy powder layer acts as an "open circuit", the atomic percentage of R is a≥30%, and M2 contains at least one of low melting point metals such as Al, Cu, and Ga, with an atomic percentage c≥5%.

[0010] In a preferred embodiment, the first alloy powder layer contains at least M1 and R, wherein the atomic percentage of R is a≥30%, and M2 contains at least one of low-melting-point metals such as Al, Cu, and Ga, with an atomic percentage c≥5%, and the remainder is b, where a+b+c=100 and b≠0.

[0011] In a preferred embodiment, the second heavy rare earth diffusion source powder layer plays a "reinforcing" role. R contains at least one heavy rare earth element selected from Dy, Tb, and Ho, and the heavy rare earth element accounts for ≥20% of the total atomic percentage of rare earth R. At the same time, the atomic percentage a of R satisfies 15%≤a≤90%, with the remainder being b, a+b+c=100, and b≠0.

[0012] Furthermore, the method for preparing the diffusion source alloy includes weighing raw materials according to the chemical formula and smelting them to obtain the diffusion source alloy.

[0013] As a preferred embodiment, the NdFeB grain boundary diffusion method provided by the present invention includes the following steps:

[0014] S1. Prepare the diffusion source alloy powder;

[0015] S2. The diffusion source alloy powder is magnetized to give the powder different magnetic properties;

[0016] S3. Different magnetic diffusion source metal powders, after being magnetized as described in S2, spontaneously and uniformly adsorb onto the surface of the NdFeB magnet to obtain a diffusion source alloy with a multilayer structure;

[0017] S4. The neodymium iron boron magnet described in S3 is subjected to diffusion treatment.

[0018] Further, S1 includes weighing raw materials according to the chemical formula, melting them in a protective gas atmosphere to obtain a diffusion source alloy, and then crushing the diffusion source alloy to a particle size of 0.5~800μm to obtain the diffusion source alloy powder.

[0019] Further, S2 includes magnetizing the diffusion source alloy powder to give the powder different degrees of magnetism, wherein the magnetic strength is 20~150 emu / g.

[0020] Furthermore, in S3, the mass of the adsorbed magnetization diffusion source alloy powder is 0.1~10wt% of the mass of the NdFeB magnet.

[0021] Furthermore, in S4, the diffusion process includes heat treatment under vacuum conditions. The first alloy powder layer acts as an "open circuit," and the second powder layer containing heavy rare earth diffusion source acts as a "reinforcing" layer. The two powder layers work synergistically in subsequent diffusion to form a superior microstructure.

[0022] Furthermore, after the diffusion treatment, the diffusion depth of the diffusion source alloy powder is ≥800μm.

[0023] Preferably, the diffusion depth is ≥1100μm.

[0024] More preferably, the diffusion depth is ≥1200μm.

[0025] Furthermore, the diffusion process includes a vacuum degree better than 10. -3 Pa, keep at 800-1000℃ for 4-20 hours, and then keep at 450-650℃ for 1.5-6 hours.

[0026] The above diffusion method can significantly improve the diffusion depth of the diffusion source alloy powder, and the coercivity of the prepared magnet is significantly improved, far exceeding that of the original magnet.

[0027] As a second objective of the invention, the present invention provides a high-performance neodymium iron boron magnet, which is prepared by the neodymium iron boron grain boundary diffusion method described above.

[0028] Preferably, the coercivity H of the high-performance neodymium iron boron magnet is... cj ≥20kOe.

[0029] More preferably, coercivity H cj ≥22kOe.

[0030] Most preferably, the coercivity H cj ≥33kOe.

[0031] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0032] 1. The NdFeB grain boundary diffusion method provided in this invention uses magnetized diffusion source alloy powder (chemical composition R) a M1 b M2 c Multiphase ferromagnetic and / or paramagnetic powders are used to achieve spontaneous and uniform adsorption of diffusion source alloy powders on the surface of NdFeB magnets, without the need to introduce solvents or colloids in traditional diffusion processes, thus avoiding their adverse effects on magnet performance. In particular, it can significantly improve the coercivity (H) of the magnet. cj ≥20kOe).

[0033] 2. The multi-layer diffusion source alloy provided by this invention has a first alloy powder layer that acts as an "open circuit" and a second heavy rare earth-containing diffusion source powder layer that acts as a "reinforcing" layer. The two powder layers work synergistically in the subsequent diffusion process to form a superior microstructure. After diffusion, the diffusion source alloy elements penetrate deep into the grains of the magnet (diffusion depth greater than 800 μm) rather than simply being physically attached, thereby significantly improving the bonding force between the diffusion source alloy and the magnet. This results in the formation of a homogeneous diffusion source alloy surface layer on the original magnet surface, making the magnet surface layer denser and forming a continuous and homogeneous surface structure, which in turn enhances the magnetic properties of the rubidium iron boron magnet.

[0034] 3. The NdFeB grain boundary diffusion method provided by this invention has a simple overall process flow and stable diffusion effect, making it more suitable for the stable mass production of irregularly shaped high-performance NdFeB magnets.

[0035] 4. The NdFeB grain boundary diffusion method provided by this invention realizes the high-quality and intensive utilization of rare earth elements. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A flowchart illustrating the fabrication process of the high-performance magnet provided by this invention.

[0038] Figure 2 This is a backscattering scan of the high-performance magnet prepared in Example 1 of the present invention.

[0039] Figure 3 The images show actual neodymium iron boron magnets with different irregular structures obtained by using the technical solution of Embodiment 1 of the present invention. Detailed Implementation

[0040] The detailed embodiments of the invention disclosed herein should be understood as exemplary only, and the invention may be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as a representative basis for teaching those skilled in the art to employ the invention in different ways in any suitable detailed embodiment.

[0041] This invention provides a method for fabricating high-performance magnets based on NdFeB grain boundary diffusion. (See reference...) Figure 1The preparation steps mainly include: providing diffusion source alloy powder; magnetizing the diffusion source alloy powder to give it different magnetic properties; adsorption, whereby the magnetized diffusion source alloys with different magnetic properties are spontaneously and uniformly adsorbed onto the magnet surface to obtain a diffusion source alloy with a multi-layer structure; and finally, through diffusion treatment, leveraging the synergistic effect of the multi-layer powders to obtain a high-performance neodymium iron boron magnet. Specifically, the blocky alloy is prepared into diffusion source alloy powder by means of melting and crushing. Then, the diffusion source alloy powder is magnetized by a magnetizer to give the powder different magnetic properties. The magnetized diffusion source alloy powder spontaneously and uniformly adsorbs onto the magnet surface by its own magnetic properties, with the stronger magnetic powder preferentially adsorbed in the first layer and the weaker magnetic powder adsorbed in the second layer. Finally, through diffusion treatment, a high-performance magnet is obtained.

[0042] The technical solution of this application will be described in detail below through specific embodiments.

[0043] Example 1

[0044] This embodiment provides a multilayer structure diffusion source alloy and a NdFeB grain boundary diffusion method, specifically,

[0045] 1. Prepare the raw materials for each alloy: according to the chemical formula Pr 55 Fe 30 Al 15 Dy 80 Fe5Al 10 The atomic ratio shown in Ga5 is used to configure the raw materials for each alloy;

[0046] 2. Provide alloy diffusion source powder: The above alloy raw materials are placed in a rapid solidification furnace for melting under an Ar protective atmosphere to obtain alloy rapid solidification flakes of the corresponding composition. The alloy raw materials are crushed in a hydrogen crushing furnace and then subjected to final fine crushing in an air jet mill to obtain the corresponding alloy diffusion source powder. The average particle size of the two alloy diffusion source powders is 3.2 μm.

[0047] 3. Magnetization Treatment: The alloy diffusion source powder was placed in a sealed container and magnetized using a magnetizer under a protective atmosphere. The magnetizer parameters were kept constant. Due to different Fe content, the alloy diffusion source powder acquired different levels of magnetism. The magnetic properties of the powder were measured using a vibrating sample magnetometer (VSM). The measured Pr... 55 Fe 30 Al 15 The magnetic properties of the alloy powder are 100 emu / g, Dy 80 Fe5Al 10 The Ga5 alloy powder has a magnetic field strength of 25 emu / g, ensuring that the strongly magnetic Pr... 55 Fe 30 Al15 Powder preferentially adsorbs to form an inner layer, while the magnetically weaker powder Dy 80 Fe5Al 10 Ga5 was subsequently adsorbed to form the outer layer;

[0048] 4. Diffusion Treatment: Under a protective atmosphere, the magnetized diffusion source alloy powder is spontaneously and uniformly adsorbed onto the surface of a N55 neodymium iron boron magnet (original magnet 1) via adsorption. Excess agglomerated diffusion source alloy powder is removed using a non-magnetic tool, resulting in a magnet to be diffused with multi-layered alloy powder uniformly adsorbed on the surface of the neodymium iron boron magnet. The first layer is an alloy powder Pr that acts as an "open circuit". 55 Fe 30 Al 15 The weight gain is 0.4 wt%, and the second layer contains a heavy rare earth diffusion source Dy. 80 Fe5Al 10 Ga5, with a weight gain of 0.6 wt%, and an alloy diffusion source adsorbed on the surface of the NdFeB magnet with a mass of 1.0 wt% of the NdFeB magnet mass, underwent diffusion treatment in a vacuum heat treatment furnace at a vacuum degree of 6 × 10⁻⁶. -3 The high-performance magnet is obtained by treating the magnet at 900℃ for 10 hours, followed by tempering at 500℃ for 2 hours.

[0049] Using the above technical solution, different batches of high-performance magnet products were obtained by repeating the operation under the same conditions. See Table 1 for 1-3, which are three batches of products obtained by repeating the operation.

[0050] See Figure 2 Figure 1 shows the backscattered scanning image of the high-performance magnet prepared in this embodiment. As can be seen from the figure, using the diffusion method provided by this invention, the surface residue visible in the cross-section from the surface to the interior of the magnet after diffusion is the remaining alloy diffusion source on the outer surface of the magnet after diffusion. That is, the magnetic diffusion source alloy powder is uniformly distributed on the surface of the magnet, and an excellent microstructure can be formed after diffusion treatment. The high magnification image (enlarged image in the dashed box) in the figure shows the near-surface structure of the magnet after diffusion. This region has a thin and continuous grain boundary structure, and the shell structure formed by heavy rare earth is obvious, which can significantly improve the magnetic properties of the magnet. The magnet after diffusion has an excellent microstructure.

[0051] Example 2

[0052] This embodiment provides a multilayer structure diffusion source alloy and a NdFeB grain boundary diffusion method, including the following steps:

[0053] 1. Prepare the raw materials for each alloy: according to the chemical formula Pr 26 Nd 30 Co 25 Al6Cu5Ga8, Pr 10 Tb65 Fe 10 The atomic ratio shown in Al8Cu7 is used to configure the raw materials for each alloy;

[0054] 2. Provide alloy diffusion source powder: Melt in a rapid solidification furnace under Ar protective atmosphere to obtain alloy rapid solidification flakes of the corresponding composition. Use a medium crushing furnace to perform medium crushing treatment on the corresponding alloy, and then perform fine crushing treatment on a ball mill to obtain alloy diffusion source powder with an average powder particle size of 2.9μm.

[0055] 3. Magnetization Treatment: The alloy diffusion source powder is placed in a sealed container and magnetized using a magnetizer under a protective atmosphere. The magnetizer parameters are kept constant. Due to the different Fe and Co element contents, the alloy diffusion source powder acquires different degrees of magnetic properties. The magnetic properties of the powder are measured using a vibrating sample magnetometer (VSM). 26 Nd 30 Co 25 The magnetic properties of Al6Cu5Ga8 alloy powder are 90 emu / g, Pr 10 Tb 65 Fe 10 The Al8Cu7 alloy powder has a magnetic field strength of 30 emu / g, ensuring that the strongly magnetic Pr... 26 Nd 30 Co 25 Al6Cu5Ga8 powder preferentially and spontaneously adsorbs to form an inner layer, while Pr powder with weaker magnetic properties... 10 Tb 65 Fe 10 Al8Cu7 was subsequently adsorbed to form the outer layer;

[0056] 4. Diffusion Treatment: Taking the cerium-containing 38MT grade as an example, under a protective atmosphere, the diffusion source alloy powder with corresponding magnetic properties is adsorbed onto the surface of a 38M NdFeB magnet (original magnet 2). Excess agglomerated diffusion source alloy powder is removed using a non-magnetic tool, resulting in a magnet to be diffused with multi-layered alloy powder uniformly adsorbed on the surface of the NdFeB magnet. The first layer is a low-melting-point alloy powder, Pr. 26 Nd 30 Co 25 Al6Cu5Ga8, with a weight gain of 6wt%, the second layer is a heavy rare earth diffusion source Pr 10 Tb 65 Fe 10 Al8Cu7, with a weight gain of 4 wt%, and an alloy diffusion source adsorbed on the surface of the NdFeB magnet with a mass of 10 wt% of the NdFeB magnet, underwent diffusion treatment in a vacuum heat treatment furnace at a vacuum degree of 4 × 10⁻⁶. -3 The high-performance magnet is obtained by treating the magnet at 880℃ for 15 hours, followed by tempering at 480℃ for 2 hours.

[0057] Referring to Table 2, Examples 2-3 are multiple batches of products obtained using the same alloy ratio and the same method.

[0058] Example 3

[0059] This embodiment provides a high-performance magnet obtained by NdFeB grain boundary diffusion, including the following steps:

[0060] 1. Prepare the raw materials for each alloy: according to the chemical formula Pr 50 Co 35 Al5Cu5Ga5, Dy 30 Tb 50 Fe 20 The atomic ratios shown are used to prepare the raw materials for each alloy.

[0061] 2. Provide alloy diffusion source powder: Melt in a rapid solidification furnace under Ar protective atmosphere to obtain alloy rapid solidification flakes of the corresponding composition. Use a hydrogen crushing furnace to perform medium crushing treatment on the corresponding alloy rapid solidification flakes, and perform final fine crushing treatment on an air jet mill to obtain alloy diffusion source powder with an average powder particle size of 2.1μm.

[0062] 3. Magnetization Treatment: The alloy diffusion source powder is placed in a sealed container and magnetized using a magnetizer under a protective atmosphere. This process imparts different degrees of magnetic properties to the powder. The magnetic properties of the powder are measured using a vibrating sample magnetometer (VSM). 50 Co 35 The magnetic properties of Al5Cu5Ga5 alloy powder are 115 emu / g, Dy 30 Tb 50 Fe 20 The alloy powder has a magnetic strength of 50 emu / g, ensuring that the strongly magnetic Pr... 50 Co 35 Al5Cu5Ga5 powder preferentially and spontaneously adsorbs to form an inner layer, while the weaker magnetic powder Dy 30 Tb 50 Fe 20 Subsequently, it is adsorbed to form the outer layer;

[0063] 4. Diffusion Treatment: Taking a 48UH grade tile-shaped magnet as an example, under a protective atmosphere, the magnetized diffusion source alloy powder is spontaneously and uniformly adsorbed onto the surface of the 48UH neodymium iron boron magnet (original magnet 3) through adsorption. Excess agglomerated diffusion source alloy powder is removed using a non-magnetic tool, resulting in a magnet to be diffused with multi-layered alloy powder uniformly adsorbed on the surface of the neodymium iron boron magnet. The first layer is the alloy powder Pr that acts as an "open circuit". 50 Co 35Al5Cu5Ga5, with a weight gain of 0.1wt%, the second layer is a heavy rare earth diffusion source Dy. 30 Tb 50 Fe 20 The weight gain was 0.1 wt%, and the mass of the alloy diffusion source adsorbed on the surface of the NdFeB magnet was 0.2 wt% of the NdFeB magnet mass. Diffusion treatment was carried out in a vacuum heat treatment furnace with a vacuum degree of 3 × 10⁻⁶. -3 The high-performance magnet is obtained by treating the magnet at 930℃ for 8 hours, followed by tempering at 650℃ for 6 hours.

[0064] See Table 3, 1-3 for multiple batches of products obtained using the same alloy ratio and method as in this embodiment.

[0065] Comparative Example 1-1

[0066] The difference between Comparative Example 1-1 and Example 1 is that Comparative Example 1 uses an impregnation method to prepare the slurry, according to the chemical formula Pr 55 Fe 30 Al 15 Dy 80 Fe5Al 10 The atomic ratio of Ga5 was used to prepare corresponding alloy diffusion source powders. A series of diffusion source slurries were prepared using a slurry impregnation method. Multilayer alloy powders were obtained by impregnating N55 neodymium iron boron magnets into the slurry. The first layer was an alloy powder Pr. 55 Fe 30 Al 15 The weight gain was 0.4 wt%, and the second layer contained heavy rare earth diffusion source powder Dy. 80 Fe5Al 10 Ga5, with a weight gain of 0.6 wt% and a total weight gain of 1.0 wt%, with all other conditions remaining the same as in Example 1.

[0067] See Table 1. Comparative Example 1-1, 1-2, represents multiple batches of products obtained using the same method.

[0068] Comparative Examples 1-2

[0069] The difference between Comparative Examples 1-2 and Example 1 is that a near-monolayer hybrid structure is formed on the surface, and the two alloy powders Pr are prepared. 55 Fe 30 Al 15 and Dy 80 Fe5Al 10 Ga5 was pre-mixed physically to a uniform consistency and then magnetized. When it was adsorbed onto the surface of the magnet, it formed a near-monolayer homogeneous mixed layer, rather than a spontaneously layered multilayer structure. Two sets of experiments were conducted in Comparative Examples 1-2, namely 1 and 2, with the remaining conditions consistent with Example 1.

[0070] Comparative Examples 1-3

[0071] The difference between Comparative Examples 1-3 and Example 1 is that the magnetic differences between the two alloy powders were too small, resulting in disordered adsorption on the surface. By adjusting the magnetization parameters, the magnetic properties of the two powders were made almost identical. The magnetic properties of the powders were measured using a vibrating sample magnetometer (VSM). 55 Fe 30 Al 15 The magnetic properties of the alloy powder are 50 emu / g, Dy 80 Fe5Al 10 The Ga5 alloy powder has a magnetic strength of 40 emu / g. Due to the small difference in magnetic properties between the fine powders, after adsorption, the two powders randomly and disorderly adsorb onto the magnet surface. All other conditions remain consistent with Example 1. See Comparative Examples 1-3 in Table 1; 1-2 represent multiple batches of products from this comparative example.

[0072] Comparative Examples 1-4

[0073] The difference between Comparative Examples 1-4 and Example 1 is that the two alloy powders have too large a difference in magnetic properties to spontaneously form a two-layer structure. By adjusting the magnetization parameters, the two powders were made to have significantly different magnetic properties. The magnetic properties of the powders were measured using a vibrating sample magnetometer (VSM). 55 Fe 30 Al 15 The magnetic properties of the alloy powder are 170 emu / g, Dy 80 Fe5Al 10 The magnetic properties of Ga5 alloy powder are 5 emu / g. During adsorption, the strongly magnetic Pr... 55 Fe 30 Al 15 The powder rapidly adsorbs and occupies almost all surface positions; weakly magnetic powder Dy 80 Fe5Al 10 Ga5 was almost unable to adsorb, ultimately forming a near-monolayer structure, with all other conditions remaining consistent with Example 1. See Comparative Examples 1-4 in Table 1; 1-2 represent multiple batches of products from this comparative example.

[0074] Comparative Examples 1-5

[0075] The difference between Comparative Examples 1-5 and Example 1 is that the adsorption order of the two fine powders is exchanged, and the magnetization parameters are adjusted to make Pr 55 Fe 30 Al 15 The magnetic properties of the alloy powder are 25 emu / g, Dy 80 Fe5Al 10The Ga5 alloy powder has a magnetic strength of 85 emu / g. The alloy powder containing heavy rare earth elements, which acts as a "strengthening" agent, is adsorbed in the first layer, while the alloy powder acting as an "opening" agent is adsorbed in the second layer. All other conditions remain the same as in Example 1. See Comparative Examples 1-5 in Table 1; 1-2 represent multiple batches of products from this comparative example.

[0076] Comparative Examples 1-6

[0077] The difference between Comparative Examples 1-6 and Example 1 is that only one alloy component was subjected to monolayer adsorption, resulting in Pr with a magnetic strength of 100 emu / g. 55 Fe 30 Al 15 The alloy powder is adsorbed onto the magnet surface, forming a single layer of "open-circuit" alloy powder, without utilizing the "reinforcing" effect of the second layer. All other conditions remain consistent with Example 1. See Comparative Examples 1-6 in Table 1; 1-2 represent multiple batches of products from this comparative example.

[0078] Comparative Examples 1-7

[0079] The difference between Comparative Examples 1-7 and Example 1 is that only a single-layer adsorption of one alloy component is performed, allowing Dy80Fe5Al10Ga5 alloy powder with a magnetic strength of 25 emu / g to be adsorbed onto the magnet surface, forming a single layer of "reinforcing" alloy powder. The "open circuit" effect of the first layer is not utilized. All other conditions remain the same as in Example 1. See Table 1 for Comparative Examples 1-7, where 1-2 represent multiple batches of products from this comparative example.

[0080] Comparative Example 2-1

[0081] The difference between Comparative Example 2-1 and Example 2 is that Comparative Examples 1-8 use the impregnation method commonly used in industry to prepare the slurry, according to the chemical formula Pr 26 Nd 30 Co 25 Al6Cu5Ga8, Pr 10 Tb 65 Fe 10 The corresponding alloy diffusion source powder was prepared using the atomic ratio shown in Al8Cu7. A series of diffusion source slurries were prepared using a slurry impregnation method. Multilayer alloy powders were obtained by impregnating 38MT NdFeB magnets into the slurry. The first layer was an alloy powder Pr. 26 Nd 30 Co 25 Al6Cu5Ga8, with a weight gain of 6wt%, the second layer contains heavy rare earth diffusion source powder Pr 10 Tb 65 Fe 10 Al8Cu7, with a weight gain of 4 wt%, and a total weight gain of 10 wt%, with other conditions remaining consistent with Example 2. See Comparative Example 2-1 in Table 1, where 1-2 represent multiple batches of products from this comparative example.

[0082] Comparative Example 2-2

[0083] The difference between Comparative Example 2-2 and Example 2 is that the adsorption order of the two fine powders is exchanged, and the magnetization parameters are adjusted to make Pr 26 Nd 30 Co 25 The magnetic properties of Al6Cu5Ga8 alloy powder are 35 emu / g, Pr 10 Tb 65 Fe 10 The Al8Cu7 alloy powder has a magnetic strength of 80 emu / g. The alloy powder containing heavy rare earth elements, which acts as a "strengthening" agent, is adsorbed in the first layer, while the alloy powder acting as an "opening" agent is adsorbed in the second layer. All other conditions remain the same as in Example 2. See Comparative Example 2-2 in Table 2, where 1-2 represent multiple batches of products from this comparative example.

[0084] Performance characterization:

[0085] Magnetic properties were tested on each embodiment and comparative example, including remanence (B). r ), coercivity (H) cj Squareness (H) k / H cj Meanwhile, the diffusion depth of the diffusion source was statistically analyzed by observing the backscattered scanning pattern. Refer to Table 1 for a comparison table of the magnetic properties and diffusion depth of the magnets prepared in Example 1 and Comparative Examples 1-1 to 1-7.

[0086] Table 1. Comparison of magnetic properties and diffusion depth of magnets prepared in Example 1 and Comparative Examples 1-1 to 1-7

[0087] As can be seen from the data in Table 1, the NdFeB grain boundary diffusion method provided in Example 1 of this invention significantly improves the coercivity H of the magnet sample compared to the original magnet. cj The diffusion depth of the diffusion source reached 1100 μm, and the magnet performance of the mass-produced products was basically consistent. However, when the corresponding alloy diffusion source powder slurry was prepared by the commonly used impregnation method in existing technology (Comparative Example 1-1), the carbon and oxygen in the slurry would diffuse into the magnet during the diffusion process, resulting in a decrease in the magnet's coercivity H. cj While the fluctuation amplitude increases, it also damages the remanence Br and squareness H of the magnet to some extent. k / H cj The magnetic properties of the magnet prepared by diffusion are far inferior to those of the magnet prepared in Example 1, and the diffusion depth is reduced to 850 μm.

[0088] In Comparative Examples 1-2, the two powders were physically mixed uniformly before magnetization, and a near-monolayer mixed structure was formed on the surface of the magnet. The synergistic effect of the first and second layers could not be exerted, and the magnetic properties of the magnet obtained by diffusion were also reduced. At the same time, the diffusion depth was 630 μm.

[0089] In Comparative Examples 1-3 and 1-4, if the magnetic difference between the two alloy powders is too large or too small after magnetization treatment, the magnetic properties of the magnet obtained by diffusion and the diffusion depth of the diffusion source will also decrease. If the magnetic difference is too small, the two powders will randomly and randomly adsorb on the magnet surface, and cannot form an ordered multilayer structure. This will lead to uneven diffusion and large performance fluctuations. If the magnetic difference is too large, the strong magnetic powder will be quickly adsorbed and occupy almost all surface positions, while the weak magnetic powder can hardly be adsorbed, and finally a near-single-layer structure will be formed, which cannot play the "reinforcing" role of the second layer, and the effect is not as good as in Example 1.

[0090] In Comparative Examples 1-5, the adsorption order of the two powder layers was swapped, allowing the Dy layer containing heavy rare earth elements to "enhance" the adsorption process. 80 Fe5Al 10 Ga5 alloy powder is adsorbed in the first layer, allowing Pr, which acts as an "open circuit," to... 55 Fe 30 Al 15 The alloy powder is adsorbed in the second layer. After diffusion treatment, the heavy rare earth elements directly contact the magnet surface, but lack the "open circuit" effect. The magnetic properties of the magnet prepared by diffusion are not as good as those of the magnet prepared in Example 1, and the diffusion depth is reduced.

[0091] In Comparative Examples 1-6, the monolayer adsorption of the alloy component with only one "open circuit" effect resulted in limited improvement in coercivity Hcj and reduced diffusion depth.

[0092] In Comparative Examples 1-7, monolayer adsorption of only one type of "strengthening" alloy component resulted in an increase in coercivity Hcj, but due to the lack of grain boundary cleaning in the "open-circuit" alloy, its remanence B was reduced. r The losses are greater, and the diffusion effect is not as good as in Example 1.

[0093] Further, see Figure 3 To implement the technical solution of Embodiment 1 of this invention, after diffusion treatment of original magnets with different irregular structures, the resulting neodymium iron boron magnets are shown in the physical image. The alloy diffusion depth of the magnets can reach approximately 1100 μm, and the alloy distribution is uniform. The magnetic properties are consistent with the remanence (B) shown in Table 1. r ), coercivity (H) cj Squareness (H) k / H cjThe results are similar, indicating that the technical solution of the present invention can effectively overcome the problem of batch uniformity and consistency of diffusion magnet products with irregular structures in the prior art. Therefore, the NdFeB grain boundary diffusion method provided by the present invention has a simple overall process flow and stable diffusion effect, and is more suitable for the stable batch production of irregularly shaped high-performance NdFeB magnets.

[0094] Refer to Table 2, which is a comparison table of the magnetic properties of the magnets prepared in Example 2 of the present invention and Comparative Examples 2-1 and 2-2.

[0095] Table 2 Comparison of magnetic properties and diffusion depth of magnets prepared in Example 2 and Comparative Examples 2-1 to 2-2

[0096] Referring to Table 2, compared with the original magnet, the magnet prepared by the diffusion method provided by the present invention has significantly improved its coercivity and magnetic properties, and the magnet diffusion depth is deeper, reaching 1200μm. At the same time, the performance of the magnets produced in batches is basically consistent.

[0097] Comparative Example 2-1 uses a common impregnation method to prepare a corresponding alloy diffusion source powder slurry. The carbon and oxygen in the slurry will diffuse into the magnet during the diffusion process, leading to an increase in the magnet's coercivity H. cj While the fluctuation amplitude increases, it also damages the remanence B of the magnet to some extent. r With squareness H k / H cj The magnetic properties of the magnet obtained by diffusion are far inferior to those of the magnet prepared in Example 2.

[0098] In Comparative Example 2-2, the adsorption order of the two layers of powder was exchanged, allowing the alloy powder containing heavy rare earth elements, which plays a "strengthening" role, to be adsorbed in the first layer, and the alloy powder that plays a "circuit-opening" role to be adsorbed in the second layer. During diffusion, the heavy rare earth elements directly contact the magnet surface, but lack the "circuit-opening" effect. The magnetic properties of the magnet obtained by diffusion are not as good as those of the magnet prepared in Example 2, and the diffusion depth is reduced.

[0099] Refer to Table 3, which is a comparison table of the magnetic properties and diffusion depth test results of the magnets prepared in Example 3 of the present invention.

[0100] Table 3. Comparison of magnetic properties and diffusion depth test results of magnets prepared in Example 3

[0101] As can be seen from the data in Table 3, the NdFeB grain boundary diffusion method provided by the present invention in Example 3 can significantly improve the coercivity of the original magnet while ensuring the consistency of the performance of the mass-produced magnets.

[0102] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

Claims

1. A method for NdFeB grain boundary diffusion, characterized in that: include: After magnetization, the diffusion source alloy powder is made to have different magnetic properties. Through adsorption, the diffusion source alloy powders with different magnetic properties are spontaneously and uniformly adsorbed on the surface of the NdFeB magnet to form a multi-layer diffusion source alloy layer. After diffusion treatment, the multi-layer structure of the diffusion source alloy layer powders exerts a synergistic effect and diffuses into the interior of the NdFeB magnet. The diffusion source alloy forms a shell structure on the surface of the NdFeB grains, resulting in a high-performance NdFeB magnet.

2. The NdFeB grain boundary diffusion method according to claim 1, characterized in that: The chemical formula of the multilayer diffusion source alloy is R. a M1 b M2 c Wherein, R is one or more of the rare earth metals Dy, Tb, Pr, Nd, Ho, La, Ce, and Y; M1 is a combination of one or more of Fe, Co, Ni, and Gd; M2 is one or more of Al, Cu, Ga, Zr, Ti, Nb, Zn, Mg, Mn, V, Cr, and B, where a, b, and c are the atomic percentages of the diffusion source alloy, 10≤a≤90, 15≤b≤70, 0≤c≤50, and satisfy a+b+c=100.

3. The NdFeB grain boundary diffusion method according to claim 1, characterized in that: The multilayer structure has at least a first alloy powder layer and a second heavy rare earth diffusion source powder layer. And / or, the first alloy powder layer contains at least M1 and R, wherein the atomic percentage of R is a≥30%, M2 is at least one of low melting point metals Al, Cu, and Ga, with an atomic percentage of c≥5%, and the remainder is b, a+b+c=100, b≠0; And / or, in the second heavy rare earth diffusion source powder layer, R contains at least one of the heavy rare earth elements Dy, Tb, and Ho, and the atomic percentage of the heavy rare earth element in the total amount of R is ≥20%, while the atomic percentage a of R satisfies 15%≤a≤90%, the remainder is b, a+b+c=100, and b≠0.

4. The NdFeB grain boundary diffusion method according to claim 1, characterized in that: Includes the following steps: S1. Preparation of diffusion source alloy powder; S2. The diffusion source alloy powder is magnetized to give the powder different degrees of magnetism; S3. The different magnetic diffusion source metal powders after magnetization treatment described in S2 are spontaneously and uniformly adsorbed onto the surface of the neodymium iron boron magnet to obtain a diffusion source alloy with a multilayer structure; S4. The neodymium iron boron magnet described in S3 is subjected to diffusion treatment.

5. The NdFeB grain boundary diffusion method according to claim 4, characterized in that: S1 includes weighing raw materials according to the chemical formula, melting them in a protective gas atmosphere to obtain a diffusion source alloy, and then crushing the diffusion source alloy to a particle size of 0.5~800μm to obtain the diffusion source alloy powder.

6. The NdFeB grain boundary diffusion method according to claim 4, characterized in that: S2 includes magnetizing the diffusion source alloy powder to give the powder different magnetic properties, wherein the magnetic strength is 20~150 emu / g.

7. The NdFeB grain boundary diffusion method according to claim 4, characterized in that: In S3, the mass of the adsorbed magnetization diffusion source alloy powder is 0.1~10wt% of the mass of the NdFeB magnet.

8. The NdFeB grain boundary diffusion method according to claim 4, characterized in that: In S4, the diffusion process includes heat treatment under vacuum conditions. The first alloy powder layer acts as an open circuit, and the second layer containing heavy rare earth diffusion source powder acts as a strengthening function. The two powder layers play a synergistic role in subsequent diffusion. After the diffusion treatment, the diffusion depth of the diffusion source alloy powder is ≥800μm; preferably, the diffusion depth is ≥1100μm; more preferably, the diffusion depth is ≥1200μm.

9. The NdFeB grain boundary diffusion method according to any one of claims 4-8, characterized in that: The diffusion process includes a vacuum degree better than 10. -3 Pa, keep at 800~1000℃ for 4~20h, and then keep at 450~650℃ for 1.5~6h.

10. A high-performance neodymium iron boron magnet, prepared by the neodymium iron boron grain boundary diffusion method as described in any one of claims 4-9; Coercivity H cj ≥20kOe; preferably, coercivity H cj ≥22kOe; more preferably, coercivity H cj ≥33kOe.

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