Sintered neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention relates to a sintered neodymium-iron-boron magnet and a preparation method thereof, and the preparation method comprises the following steps: carrying out diffusion heat treatment and annealing heat treatment on a neodymium-iron-boron magnet deposited with a heavy rare earth element film under vacuum to obtain the sintered neodymium-iron-boron magnet, wherein the temperature of the diffusion heat treatment is lower than that of the annealing heat treatment. According to the preparation method, the use amount of the heavy rare earth can be saved, and the magnetic performance of the magnet can be improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of permanent magnetic materials, and in particular to a sintered NdFeB magnet and a preparation method thereof, in particular to a grain boundary diffused Ce-based sintered NdFeB magnet and a preparation method thereof. Background Art

[0002] Neodymium iron boron (Nd-Fe-B) magnets are increasingly used for their excellent magnetic properties, and are widely used in medical MRI, computer hard disk drives, audio, mobile phones, etc.; with the requirements of energy conservation and low-carbon economy, Nd-Fe-B magnets have begun to be used in automotive parts, household appliances, energy-saving and control motors, hybrid vehicles, wind power generation and other fields. With the rapid development of new energy vehicles and wind power generation, heavy rare earth (HER) grain boundary diffusion technology (GBD technology) has gradually become the most commonly used method to improve sintered Nd-Fe-B magnets.

[0003] However, with the widespread application of grain boundary diffusion sintered Nd-Fe-B magnets, the demand for rare earths has also seen a rapid and unbalanced growth. On the one hand, the rare earth elements praseodymium (Pr), neodymium (Nd), terbium (Tb), and dysprosium (Dy) with low crustal abundance used in existing rare earth permanent magnet materials have led to rapid consumption and soaring prices of the above rare earths. On the other hand, rare earths such as cerium (Ce, which is only 5% of Pr / Nd in price) with high crustal abundance are in large backlogs, resulting in a huge imbalance in the use of resources, and the separation of rare earths will cause environmental pollution.

[0004] In order to solve the above problems, grain boundary diffusion Ce-based sintered Nd-Fe-B magnets came into being and became one of the important directions of rare earth permanent magnet research, with important application and research value. However, most of the current research still uses the traditional grain boundary diffusion process, resulting in low magnetic properties of grain boundary diffusion Ce-based sintered Nd-Fe-B magnets.

[0005] Therefore, it is necessary to provide a new method for preparing grain boundary diffused Ce-based sintered Nd—Fe—B magnets. Summary of the invention

[0006] In order to solve the above technical problems, the present disclosure provides a sintered NdFeB magnet and a preparation method thereof.

[0007] In a first aspect, the present disclosure provides a method for preparing a sintered NdFeB magnet, the method comprising the following steps:

[0008] Under vacuum, performing diffusion heat treatment and annealing heat treatment on the NdFeB magnet deposited with the heavy rare earth element film to obtain the sintered NdFeB magnet;

[0009] Wherein, the temperature of the diffusion heat treatment is lower than the temperature of the annealing heat treatment.

[0010] As a preferred technical solution of the present disclosure, the temperature of the diffusion heat treatment is 650-800° C. and the time is 10-30 hours.

[0011] As a preferred technical solution of the present disclosure, the temperature of the annealing heat treatment is 850-950° C. and the time is 4-30 hours.

[0012] As a preferred technical solution of the present disclosure, the NdFeB magnet is a Ce-based sintered NdFeB magnet, and the general structural formula is (Ce 0.3+x R 0.7-x ) y Fe z T m B n ,in:

[0013] R is any combination of Pr and Nd;

[0014] T is any combination of transition metals Co, Al, Mn, Cu, Ga and Si;

[0015] 0≤x≤0.3, 28≤y≤32, 65≤z≤72, 0≤m≤2, 0.8≤n≤1.1.

[0016] As a preferred technical solution of the present disclosure, the method for preparing the NdFeB magnet deposited with a heavy rare earth film comprises:

[0017] S1: pre-treating the NdFeB magnet;

[0018] S2: forming a heavy rare earth element film on the surface of the pretreated NdFeB magnet.

[0019] As a preferred technical solution of the present disclosure, the pretreatment method includes polishing or polishing after removing the surface oxide layer.

[0020] As a preferred technical solution of the present disclosure, the method for forming the heavy rare earth element film includes a coating method commonly used for rare earth permanent magnet grain boundary diffusion, such as spraying, magnetron sputtering, electrophoretic deposition or screen printing;

[0021] The heavy rare earth element contained in the heavy rare earth element film is Dy and / or Tb.

[0022] As a preferred technical solution of the present disclosure, the preparation method comprises:

[0023] (1) polishing the Ce-based sintered NdFeB magnet or polishing it after removing the surface oxide layer;

[0024] (2) sputtering and depositing heavy rare earth elements on the surface of the pretreated Ce-based sintered NdFeB magnet to form a heavy rare earth element film;

[0025] (3) Under vacuum, the Ce-based sintered NdFeB magnet deposited with a heavy rare earth element film is subjected to thermal diffusion treatment at 650-800° C. for 10-30 h, and then the temperature is raised to 850-950° C. for annealing treatment for 4-30 h to obtain the sintered NdFeB magnet.

[0026] In a second aspect, the present disclosure provides a sintered NdFeB magnet prepared using the preparation method described in the first aspect.

[0027] In a third aspect, the present disclosure provides a use of the sintered NdFeB magnet described in the second aspect in preparing energy exchange materials.

[0028] Compared with the prior art, the technical solution provided by the embodiments of the present disclosure has the following advantages:

[0029] (1) The preparation method disclosed in the present invention can not only save the amount of heavy rare earth but also improve the magnetic properties of the magnet;

[0030] (2) The heat treatment time of the present invention is short, which can greatly shorten the preparation time and has a higher cost performance;

[0031] (3) The sintered NdFeB magnet obtained by the preparation method provided by the present disclosure has more excellent magnetic properties and can be better applied to the preparation of energy exchange materials. DETAILED DESCRIPTION

[0032] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0033] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0034] In the current prior art, in order to solve the imbalance of rare earth element consumption and optimize the performance of NdFeB magnets, Ce elements are introduced into NdFeB magnets to form Ce-based NdFeB magnets, and at the same time, diffusion technology can be used to further improve the performance of NdFeB magnets. However, the magnetic properties of the existing grain boundary diffused Ce-based NdFeB magnets are still not high and cannot meet the application requirements. To this end, the present disclosure provides a new method for preparing sintered NdFeB magnets.

[0035] In a first aspect, the present disclosure provides a method for preparing a sintered NdFeB magnet, the method comprising the following steps:

[0036] Under vacuum, performing diffusion heat treatment and annealing heat treatment on the NdFeB magnet deposited with the heavy rare earth element film to obtain the sintered NdFeB magnet;

[0037] Wherein, the temperature of the diffusion heat treatment is lower than the temperature of the annealing heat treatment.

[0038] The present invention limits the temperature of diffusion heat treatment to be lower than the temperature of annealing heat treatment, and first uses a lower temperature for diffusion, so that when the heavy rare earth enters the interior of the magnet, it diffuses only along the grain boundary without undergoing a substitution reaction with the grain, so that the heavy rare earth can enter effectively and slow down the growth of the magnet grains, thereby reducing the amount of heavy rare earth used; after the heavy rare earth enters the magnet along the grain boundary, it is treated at a higher temperature, so that the heavy rare earth can undergo a substitution reaction with the grains to form a hard (Nd, HRE)2·Fe 14 B hard magnetic shell further improves the magnetic properties of the magnet; therefore, the preparation method defined in the present disclosure can not only save the amount of heavy rare earth but also improve the magnetic properties of the magnet.

[0039] As a preferred technical solution of the present invention, the temperature of the diffusion heat treatment is 650-800°C, for example, 660°C, 680°C, 700°C, 720°C, 730°C, 750°C, 760°C, 780°C, etc., and the time is 10-30h, for example, 12h, 15h, 18h, 20h, 22h, 25h, 28h, etc.

[0040] As a preferred technical solution of the present invention, the temperature of the annealing heat treatment is 850-950°C, for example, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, etc., and the time is 4-30h, for example, 5h, 10h, 15h, 20h, 25h, etc.

[0041] Compared with the sintered NdFeB magnet obtained by first diffusing at high temperature and then annealing at low temperature in the current prior art, the sintered NdFeB magnet obtained by the preparation method provided by the present invention saves a large amount of heavy rare earth while maintaining the same magnet performance. At the same time, the performance of the magnet is greatly improved. In addition, the heat treatment time of the present invention is short, which can greatly shorten the preparation time and has a higher cost-effectiveness.

[0042] As a preferred technical solution of the present disclosure, the NdFeB magnet is a Ce-based sintered NdFeB magnet, and the general structural formula is (Ce 0.3+x R 0.7-x ) y Fe z T m B n ,in:

[0043] R is any combination of Pr and Nd;

[0044] T is any combination of transition metals Co, Al, Mn, Cu, Ga and Si;

[0045] 0≤x≤0.3, 28≤y≤32, 65≤z≤72, 0≤m≤2, 0.8≤n≤1.1.

[0046] The "R" and "T" described in the present disclosure do not only represent one element, but can also represent one element or a combination of multiple elements. When it is a combination of multiple elements, the relative molar amount of all elements added together satisfies 0.7-x, and the same applies to T. For example:

[0047] Ce-based sintered NdFeB magnets are (Ce 0.3 Pr 0.05 Nd 0.65 ) 30 Fe 67.7 Co1Ga 0.1 Al 0.2 B1. In the above structure, R is a combination of Pr and Nd, the sum of which is 0.7 (x=0), and T is a combination of Co, Ga, and Al, the sum of which is 1.3.

[0048] Another example:

[0049] Ce-based sintered NdFeB magnets are (Ce 0.5 Pr 0.1 Nd 0.4 ) 32 Fe 66.4 Ga 0.5 Al 0.2 B 0.9 In the above structure, R is a combination of Pr and Nd, the sum of which is 0.5 (x=0.2), and T is a combination of Ga and Al, the sum of which is 0.7.

[0050] As a preferred technical solution of the present disclosure, the method for preparing the NdFeB magnet deposited with a heavy rare earth film comprises:

[0051] S1: pre-treating the NdFeB magnet;

[0052] S2: forming a heavy rare earth element film on the surface of the pretreated NdFeB magnet.

[0053] A pure and smooth magnet surface is beneficial to the subsequent deposition of heavy rare earth elements. Therefore, as a preferred technical solution of the present disclosure, the pretreatment method includes polishing or polishing after removing the surface oxide layer.

[0054] The present disclosure does not limit the polishing method too much, as long as the purpose of achieving a pure and smooth surface of the magnet can be achieved. As a specific embodiment of the present disclosure, the polishing or polishing after removing the surface oxide layer includes:

[0055] The NdFeB magnet is grinded with 800, 1500, and 2000 grit sandpaper in turn to polish the surface, or the oxide layer on the surface of the magnet is removed by cleaning with dilute acid and then polishing the surface, etc., as long as the surface of the magnet is pure and smooth, which is conducive to the dense deposition of heavy rare earth.

[0056] As a preferred technical solution of the present disclosure, the method for forming the heavy rare earth element film includes common coating methods for rare earth permanent magnet grain boundary diffusion such as spraying, magnetron sputtering, electrophoretic deposition or screen printing, preferably magnetron sputtering.

[0057] As a preferred technical solution of the present disclosure, the heavy rare earth element contained in the heavy rare earth element film is Dy and / or Tb.

[0058] As a preferred technical solution of the present disclosure, when the method for forming the heavy rare earth element film is the magnetron sputtering, the sputtering step includes:

[0059] The pretreated NdFeB magnets were sputtered with high-purity Tb (99.9 wt%), Dy (99.9 wt%) or TbDy alloy (99.9 wt%), wherein the vacuum was evacuated to 5 × 10 -4 Pa, filled with high-purity argon, the working gas pressure is 0.5-2Pa, and the sputtering power is 70-100W.

[0060] As a specific embodiment of the present disclosure, the sputtering step includes: placing a polished NdFeB magnet into a magnetron sputtering sample stage, placing high-purity Tb (99.9 wt%), Dy (99.9 wt%) or TbDy alloy (99.9 wt%) at a corresponding strong magnetic target position, and evacuating the vacuum to 5×10 -4 Pa, high-purity argon gas is filled in, the working gas pressure is 0.5-2Pa, the sputtering power is 70-100W, and the sputtering time is controlled to obtain heavy rare earth element films of different thicknesses.

[0061] As a preferred technical solution of the present disclosure, the thickness of the heavy rare earth element film is 0.1-0.4% of the thickness of the pretreated NdFeB magnet, for example, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, etc.

[0062] In the present disclosure, 0.1-0.4% of the thickness of the NdFeB magnet is understood as follows:

[0063] For NdFeB magnets, the number of heavy rare earth element films required is N, and the thickness of a single-sided heavy rare earth element film is (0.1-0.4%) / N, for example:

[0064] When the NdFeB magnet only needs to be coated on one side, the thickness of the heavy rare earth element film on the single side is (0.1-0.4%) / 1, which is 0.1-0.4% of the thickness of the NdFeB magnet;

[0065] When the NdFeB magnet needs to be coated on both sides, the thickness of the heavy rare earth element film on each side is (0.1-0.4%) / 2, which is 0.05-0.2% of the thickness of the NdFeB magnet;

[0066] When the NdFeB magnet needs to be coated on six sides, the thickness of the heavy rare earth element film on each side is (0.1-0.4%) / 6, which is 0.016-0.06% of the thickness of the NdFeB magnet.

[0067] That is, since the volume or weight of the sputtering material and the raw material are used in a certain proportion, and since the density remains basically unchanged, the total amount of heavy rare earth elements used is certain regardless of whether it is single-sided or multi-sided.

[0068] As a preferred technical solution of the present disclosure, the preparation method comprises:

[0069] (1) polishing the Ce-based sintered NdFeB magnet or polishing it after removing the surface oxide layer;

[0070] (2) sputtering and depositing heavy rare earth elements on the surface of the pretreated Ce-based sintered NdFeB magnet to form a heavy rare earth element film;

[0071] (3) Under vacuum, the Ce-based sintered NdFeB magnet deposited with a heavy rare earth element film is subjected to thermal diffusion treatment at 650-800° C. for 10-30 h, and then the temperature is raised to 850-950° C. for annealing treatment for 4-30 h to obtain the sintered NdFeB magnet.

[0072] In a second aspect, the present disclosure provides a sintered NdFeB magnet prepared using the preparation method described in the first aspect.

[0073] In a third aspect, the present disclosure provides a use of the sintered NdFeB magnet described in the second aspect in preparing energy exchange materials.

[0074] The sintered NdFeB magnet obtained by the preparation method provided by the present disclosure has more excellent magnet properties and can be better applied to the preparation of energy exchange materials.

[0075] The following is described by way of specific examples:

[0076] Example 1

[0077] This embodiment provides a method for preparing a sintered NdFeB magnet, as follows:

[0078] (1) Initial magnet pretreatment

[0079] The structural formula is (Ce 0.3 Pr 0.05 Nd 0.65 ) 30 Fe 67.7 Co1Ga 0.1 Al 0.2 The Ce-based sintered NdFeB magnet of B1 was cut into 50×30×3mm square samples, where the sample size along the c-axis direction was 3mm;

[0080] The cut samples were polished with 800, 1500, and 2000 grit sandpapers in turn;

[0081] (2) Heavy rare earth element film deposition

[0082] The polished NdFeB magnet was placed on the magnetron sputtering sample stage, high-purity Dy (99.9wt%) was placed on the corresponding strong magnetic target position, and the vacuum was evacuated to 5×10 -4 Pa, fill with high-purity argon, adjust the gas flow to adjust the working gas pressure to 1Pa, sputtering power to 100W, control the sputtering time to obtain a Dy layer with a thickness of 2μm on both sides (a total of 4μm, which is 0.13% of the thickness of the NdFeB magnet) (the sputtering layer is perpendicular to the c-axis of the magnet);

[0083] (3) Vacuum heat treatment

[0084] The magnet with the heavy rare earth element film deposited on it was placed in a vacuum heat treatment furnace and evacuated to 5×10 -4 Pa, set the following heat treatment program:

[0085] First, a thermal diffusion treatment was performed at 650°C for 30 h, and then an annealing heat treatment was performed at 900°C for 4 h;

[0086] After the heat treatment is completed, the furnace chamber is cooled naturally to room temperature and then taken out to obtain a sintered NdFeB magnet (a sintered NdFeB magnet after grain boundary diffusion).

[0087] Example 2

[0088] This embodiment provides a method for preparing a sintered NdFeB magnet.

[0089] The difference from Example 1 is that in this example, the initial Ce-based sintered NdFeB magnet is (Ce 0.5 Pr 0.1 Nd 0.4 ) 32 Fe 66.4 Ga 0.5Al 0.2 B 0.9 , the heat treatment procedure is:

[0090] First, a thermal diffusion treatment is performed at 700°C for 20 hours, and then an annealing heat treatment is performed at 900°C for 16 hours.

[0091] Example 3

[0092] This embodiment provides a method for preparing a sintered NdFeB magnet, as follows:

[0093] (1) Initial magnet pretreatment

[0094] The structural formula is (Ce 0.35 Nd 0.65 ) 29 Fe 69.81 Ga 0.3 B 0.89 The Ce-based sintered NdFeB magnets were cut into 50×10×7mm square samples, where the sample size along the c-axis direction was 7mm;

[0095] The cut samples were polished with 800, 1500, and 2000 grit sandpapers in turn;

[0096] (2) Heavy rare earth element film deposition

[0097] The polished NdFeB magnet was placed on the magnetron sputtering sample stage, high-purity Tb (99.9wt%) was placed on the corresponding strong magnetic target position, and the vacuum was evacuated to 5×10 -4 Pa, fill with 99.999% high-purity argon, adjust the gas flow to adjust the working gas pressure to 2Pa, sputtering power to 70W, control the sputtering time to obtain a Tb layer with a thickness of 6μm on both sides (a total of 12μm, which is 0.17% of the thickness of the NdFeB magnet) (the sputtering layer is perpendicular to the c-axis of the magnet);

[0098] (3) Vacuum heat treatment

[0099] The magnet with the heavy rare earth element film deposited on it was placed in a vacuum heat treatment furnace and evacuated to 5×10 -4 Pa, set the following heat treatment program:

[0100] First, a thermal diffusion treatment is performed at 750°C for 30 hours, and then an annealing heat treatment is performed at 890°C for 30 hours;

[0101] After the heat treatment is completed, the furnace chamber is cooled naturally to room temperature and then taken out to obtain a sintered NdFeB magnet (a sintered NdFeB magnet after grain boundary diffusion).

[0102] Example 4

[0103] This embodiment provides a method for preparing a sintered NdFeB magnet.

[0104] The difference from Example 1 is that in this example, the initial Ce-based sintered NdFeB magnet is (Ce 0.5 Pr 0.2 Nd 0.3 ) 32 Fe 66.6 Cu 0.2 Al 0.2 B1, heat treatment procedure is:

[0105] First, a thermal diffusion treatment is performed at 800°C for 10 hours, and then an annealing heat treatment is performed at 900°C for 8 hours.

[0106] Example 5

[0107] This embodiment provides a method for preparing a sintered NdFeB magnet.

[0108] The difference from Example 1 is that in this example, the initial Ce-based sintered NdFeB magnet is (Ce 0.6 Pr 0.4 ) 28 Fe 69.7 Co 0.8 Cu 0.2 Al 0.2 B 1.1 , the heat treatment procedure is:

[0109] First, a thermal diffusion treatment is performed at 800°C for 15 hours, and then an annealing heat treatment is performed at 950°C for 4 hours.

[0110] Example 6

[0111] This embodiment provides a method for preparing a sintered NdFeB magnet.

[0112] The difference from Example 1 is that in this embodiment, the Dy and Tb layers with a thickness of 6 μm on both sides (a total of 12 μm, which is 0.4% of the thickness of the NdFeB magnet) are obtained by controlling the sputtering time of deposition (the ratio of the two is 1:1, and the sputtering layer is perpendicular to the c-axis of the magnet)

[0113] The heat treatment procedure is:

[0114] First, a thermal diffusion treatment is performed at 750°C for 20 hours, and then an annealing heat treatment is performed at 850°C for 30 hours.

[0115] Comparative Example 1

[0116] This comparative example provides a method for preparing a sintered NdFeB magnet.

[0117] The only difference from Example 1 is that the heat treatment procedure is different. In this comparative example, the heat treatment procedure is:

[0118] First, a thermal diffusion treatment is performed at 900°C for 4 hours, and then an annealing heat treatment is performed at 600°C for 5 hours.

[0119] Comparative Example 2

[0120] This comparative example provides a method for preparing a sintered NdFeB magnet.

[0121] The only difference from Example 2 is that the heat treatment procedure is different. In this comparative example, the heat treatment procedure is:

[0122] First, a thermal diffusion treatment is performed at 900°C for 16 hours, and then an annealing heat treatment is performed at 500°C for 5 hours.

[0123] Comparative Example 3

[0124] This comparative example provides a method for preparing a sintered NdFeB magnet.

[0125] The only difference from Example 1 is that the heat treatment procedure is different. In this comparative example, the heat treatment procedure is:

[0126] First, heat treatment was performed at 900°C for 4 h, and then heat treatment was performed at 650°C for 30 h.

[0127] Comparative Example 4

[0128] This comparative example provides a method for preparing a sintered NdFeB magnet.

[0129] The only difference from Example 1 is that the heat treatment procedure is different. In this comparative example, the heat treatment procedure is:

[0130] First, heat treatment was performed at 900°C for 30 h, and then heat treatment was performed at 650°C for 4 h.

[0131] Comparative Example 5

[0132] This comparative example provides a sintered NdFeB magnet, which is the initial (Ce 0.3 Pr 0.05 Nd 0.65 ) 30 Fe 67.7 Co1Ga 0.1 Al 0.2 B1 Ce based sintered NdFeB magnets.

[0133] Performance Testing

[0134] The performance test of the sintered NdFeB magnets provided in Examples 1-6 and Comparative Examples 1-5 was performed as follows:

[0135] The permanent magnetic properties of the samples were measured using a hysteresis loop instrument. The results are shown in Table 1:

[0136] Table 1

[0137]

[0138] It can be seen from the examples and performance tests that the sintered NdFeB magnet prepared by the preparation method provided in the present disclosure has a higher coercive force and a higher magnetic property, thereby realizing the preparation of Ce-based sintered NdFeB magnet.

[0139] From the comparison between Example 1 and Comparative Example 5, it can be seen that compared with the initial NdFeB magnet, the coercive force of the sintered NdFeB magnet obtained in Example 1 is improved by more than 4kOe, which is a significant improvement; from the comparison between Example 1 and Comparative Examples 1, 3-4, and from the comparison between Example 2 and Comparative Example 2, it can be seen that compared with the sintered NdFeB magnet prepared by the traditional grain boundary diffusion method, the heat treatment procedure defined in the present invention can maximize the improvement of the magnetic properties of the magnet.

[0140] In Example 2, the initial coercive force of the NdFeB magnet is 7.12 kOe, and the coercive force of the sintered NdFeB magnet obtained in Example 2 is increased by more than 2 kOe.

[0141] In Example 3, the initial coercive force of the NdFeB magnet is 9.87 kOe, and the coercive force of the sintered NdFeB magnet obtained in Example 3 is increased by more than 6 kOe.

[0142] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0143] The above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a sintered NdFeB magnet, characterized in that: The preparation method comprises the following steps: Under vacuum, performing diffusion heat treatment and annealing heat treatment on the NdFeB magnet deposited with the heavy rare earth element film to obtain the sintered NdFeB magnet; Wherein, the temperature of the diffusion heat treatment is lower than the temperature of the annealing heat treatment.

2. The preparation method according to claim 1, characterized in that: The temperature of the diffusion heat treatment is 650-800° C. and the time is 10-30 hours.

3. The preparation method according to claim 1, characterized in that: The annealing heat treatment is performed at a temperature of 850-950° C. and for a time of 4-30 hours.

4. The preparation method according to claim 1, characterized in that: The NdFeB magnet is a Ce-based sintered NdFeB magnet, and its general structural formula is (Ce 0.3+x R 0.7-x ) y Fe z T m B n ,in: R is any combination of Pr and Nd; T is any combination of transition metals Co, Al, Mn, Cu, Ga and Si; 0≤x≤0.3, 28≤y≤32, 65≤z≤72, 0≤m≤2, 0.8≤n≤1.

1.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The method for preparing the NdFeB magnet deposited with a heavy rare earth film comprises: S1: pre-treating the NdFeB magnet; S2: forming a heavy rare earth element film on the surface of the pretreated NdFeB magnet.

6. The preparation method according to claim 5, characterized in that: The pretreatment method includes polishing or polishing after removing the surface oxide layer.

7. The preparation method according to claim 6, characterized in that: The method for forming the heavy rare earth element film includes spraying, magnetron sputtering, electrophoretic deposition or screen printing; The heavy rare earth element contained in the heavy rare earth element film is Dy and / or Tb.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The preparation method comprises: (1) polishing the Ce-based sintered NdFeB magnet or polishing it after removing the surface oxide layer; (2) sputtering and depositing heavy rare earth elements on the surface of the pretreated Ce-based sintered NdFeB magnet to form a heavy rare earth element film; (3) Under vacuum, the Ce-based sintered NdFeB magnet deposited with a heavy rare earth element film is subjected to thermal diffusion treatment at 650-800° C. for 10-30 h, and then the temperature is raised to 850-950° C. for annealing treatment for 4-30 h to obtain the sintered NdFeB magnet.

9. A sintered NdFeB magnet prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the sintered NdFeB magnet according to claim 9 in preparing energy exchange materials.

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