Neodymium-iron-boron magnet and preparation method and application thereof

Abstract

The invention discloses a neodymium-iron-boron magnet and a preparation method and application thereof. The neodymium-iron-boron magnet comprises an R1-O-F enrichment area, the R1-O-F enrichment area is located in the area from the position with the vertical distance being 100 micrometers from the surface of the neodymium-iron-boron magnet to the center of the neodymium-iron-boron magnet, and R1 is one or more of Pr, Nd, Gd and Ho; the volume fraction of the R1-O-F enrichment area is 1%-5%, and the meaning of the volume fraction is the percentage of the volume of the R1-O-F enrichment area in the total volume of the neodymium-iron-boron magnet. The neodymium-iron-boron magnet disclosed by the invention has excellent residual magnetism, coercive force, Hd5 and high-temperature squareness.

Description

Neodymium iron boron magnet and its preparation method and application Technical Field

[0001] The invention relates to a neodymium iron boron magnet and a preparation method and application thereof. Background Art

[0002] RTB rare earth permanent magnet materials use grain boundary diffusion technology to introduce heavy rare earth elements Dy or Tb to increase the coercive force Hcj of the magnet while keeping the remanence Br basically unchanged. During the grain boundary diffusion process, the content of heavy rare earth diffused to the center of the magnet is limited. In order to improve the diffusion efficiency, the existing technology reduces the grain boundary melting point by grain boundary regulation. For example, CN115020057A mentions: the diffusion matrix is ​​composed of NdFeB main phase alloy and light rare earth alloy RL x M 1-x The NdFeB material is prepared to consist of a main phase, a Nd-rich phase, and a low-melting-point shell layer rich in M ​​located between the main phase and the Nd-rich phase. The Nd-rich phase is formed by RL and its oxides, and the low-melting-point shell layer is formed by non-rare earth elements M. However, this method will simultaneously accelerate the diffusion of the surface layer, making it very easy for the surface heavy rare earth to enter the main phase of the grain, resulting in limited improvement in magnetic properties, decreased overall consistency of the magnet, and worsened squareness. Summary of the invention

[0003] In order to solve the defects of poor uniformity and poor squareness of NdFeB magnets in the prior art, the present invention provides a NdFeB magnet and a preparation method and application thereof. The NdFeB magnet of the present invention has excellent remanence, coercive force, Hd5 and high temperature squareness.

[0004] The present invention provides a NdFeB magnet, comprising an R1-OF enriched zone, wherein the R1-OF enriched zone is located in a region from a vertical distance of 100 μm from the surface of the NdFeB magnet to the center of the NdFeB magnet, wherein R1 is one or more of Pr, Nd, Gd and Ho; and the volume fraction of the R1-OF enriched zone is 1%-5%, wherein the volume fraction means the percentage of the volume of the R1-OF enriched zone to the total volume of the NdFeB magnet.

[0005] In the present invention, the center of the NdFeB magnet refers to the geometric center of the NdFeB magnet.

[0006] In the present invention, the definition of "NdFeB" may be conventional in the art, that is, it refers to a type of permanent magnetic material including at least neodymium, iron and boron elements and inevitable impurities.

[0007] In the present invention, the NdFeB magnet may include a main phase grain and a grain boundary phase, wherein the main phase grain includes a main phase grain surface layer, a main phase grain epitaxial layer and a main phase grain core from the outside to the inside; the main phase grain includes R2Fe14 B phase, wherein R is at least one rare earth element including Nd. The grain boundary phase is located between the main phase grains; the region whose vertical distance from the geometric center of the main phase grain is 0.3-0.4 times the equivalent diameter of the main phase grain is the main phase grain epitaxial layer.

[0008] In the present invention, the test method for the volume fraction of the R1-OF enriched area can be: randomly testing 5 different areas of the NdFeB magnet, and obtaining the surface distribution diagrams of the R1, F, and O elements in the 5 different areas, and then calculating the volume fraction through commercial image processing software (such as Image Pro).

[0009] In the present invention, "O" in the R1-OF enriched region is oxygen element, and "F" is fluorine element.

[0010] In the present invention, preferably, the volume fraction of the R1-OF enriched zone is 2%, 2.2%, 3%, 2.5% or 2.8%.

[0011] In the present invention, preferably, the mass concentration of F in the NdFeB magnet presents a gradient increasing trend from a point at a vertical distance of 100 μm from the surface of the NdFeB magnet to the center of the NdFeB magnet.

[0012] In the present invention, preferably, the mass concentration of F in the NdFeB magnet is 0.02%-0.2%, more preferably 0.02%-0.15%, for example 0.026%, 0.052%, 0.1%, 0.124% or 0.130%, wherein % means the mass percentage of F in the NdFeB magnet.

[0013] In the present invention, preferably, the R1-OF-rich region is distributed in the grain boundary phase.

[0014] In the present invention, preferably, the main phase crystal grain epitaxial layer, the main phase crystal grain core and the main phase crystal grain surface layer do not contain the R1-OF rich region.

[0015] In the present invention, preferably, the NdFeB magnet includes Dy, and the concentration distribution of Dy satisfies: grain boundary phase>main phase crystal grain epitaxial layer>main phase crystal grain core≥main phase crystal grain surface layer.

[0016] In certain embodiments of the present invention, the concentration ratio of Dy in the grain boundary phase, the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface layer satisfies: grain boundary phase: main phase grain epitaxial layer: main phase grain core: main phase grain surface layer = (8-11): (4.5-6.5): (2-4): (1-4).

[0017] In a specific embodiment of the present invention, the concentration ratio of Dy in the grain boundary phase, the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface satisfies: grain boundary phase: main phase grain epitaxial layer: main phase grain core: main phase grain surface = 8.2:5.3:3.7:3.6.

[0018] In a specific embodiment of the present invention, the concentration ratio of Dy in the grain boundary phase, the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface satisfies: grain boundary phase: main phase grain epitaxial layer: main phase grain core: main phase grain surface = 9.1:5.7:2.8:2.8.

[0019] In a specific embodiment of the present invention, the concentration ratio of Dy in the grain boundary phase, the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface satisfies: grain boundary phase: main phase grain epitaxial layer: main phase grain core: main phase grain surface = 10.3:5.5:3.1:2.9.

[0020] In a specific embodiment of the present invention, the concentration ratio of Dy in the grain boundary phase, the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface satisfies: grain boundary phase: main phase grain epitaxial layer: main phase grain core: main phase grain surface = 8.9:6.1:2.9:2.8.

[0021] In a specific embodiment of the present invention, the concentration ratio of Dy in the grain boundary phase, the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface layer satisfies: grain boundary phase: main phase grain epitaxial layer: main phase grain core: main phase grain surface layer = 9.6: 4.9: 2.0: 1.9. Preferably, the relative concentration value of Dy in the main phase grain core is 2-4, for example, 2.8, 2.9, 3.1 or 3.7. The test method for the relative concentration value of Dy can be: respectively obtain the characteristic X-ray signals of Dy in the main phase grain core, the main phase grain surface, the main phase grain epitaxial layer and the grain boundary phase, and the device converts the signal value of each area into a mass concentration value according to its own standard sample database, and the mass concentration value is the relative concentration value of Dy in each area. The stronger the signal, the higher the concentration, and relative comparison can be made within the same field of view test area. For example, the relative value of the Dy concentration in the core of the main phase grain is a mass concentration value converted from a characteristic X-ray signal of Dy obtained by a field emission electron probe microanalyzer (EPMA) according to a built-in standard sample database.

[0022] Preferably, the relative value of the Dy concentration in the surface layer of the main phase grains is 1-4, for example, 1.9, 2.8, 2.9 or 3.6.

[0023] Preferably, the relative value of Dy concentration in the main phase grain epitaxial layer is 4.5-6.5, for example, 4.9, 5.3, 5.5, 5.7 or 6.1.

[0024] Preferably, the relative value of the Dy concentration in the grain boundary phase is 8-11, for example, 8.2, 8.9, 9.1, 9.6 or 10.3.

[0025] Preferably, in the region from the surface of the NdFeB magnet to a vertical distance of 800 μm from the surface of the NdFeB magnet, the concentration distribution of Dy satisfies: grain boundary phase>main phase grain epitaxial layer>main phase grain core≥main phase grain surface layer.

[0026] In the present invention, preferably, the thickness of the NdFeB magnet is 5-20 mm, wherein the thickness refers to the length of the NdFeB magnet along the orientation direction.

[0027] The present invention also provides a method for preparing the above-mentioned NdFeB magnet, which comprises the following steps:

[0028] The mixture including the main alloy and the F-containing additive is sequentially subjected to magnetic field forming and sintering to obtain a NdFeB matrix; the NdFeB matrix is ​​subjected to grain boundary diffusion treatment;

[0029] The main alloy includes one or more elements of Pr, Nd, Gd and Ho.

[0030] In the present invention, preferably, the mass content of the F-containing additive in the mixture is 0.1%-0.5%, for example, 0.2%, wherein % means the mass percentage of the F-containing additive to the mass of the mixture.

[0031] In the present invention, the F-containing additive is preferably a metal fluoride, and the metal fluoride is, for example, DyF3, TiF4, CeF3, MgF2 or CaF2.

[0032] In the present invention, preferably, the mass content of the main alloy in the mixture is 94%-98%, for example, 93.9%, 94.8%, 95.8%, 96.8% or 97.5%, wherein % means the mass percentage of the main alloy to the mass percentage of the mixture.

[0033] In the present invention, preferably, the mixture further comprises a Dy-containing additive.

[0034] The mass content of Dy in the Dy-containing additive is preferably 1%-30%, for example 15%, 18%, 19%, 20% or 23%, wherein % means the mass of Dy as a percentage of the mass of the Dy-containing additive.

[0035] The mass content of the Dy-containing additive in the mixture is preferably 2%-6%, for example 3%, 4% or 5%, wherein % means the mass percentage of the Dy-containing additive to the mass of the mixture.

[0036] Wherein, the Dy-containing additive is preferably a Dy-containing alloy.

[0037] The Dy-containing alloy may further include one or more of Pr, Nd, Fe, Cu, Ga and B.

[0038] Wherein, the mass content of Pr and Nd in the Dy-containing alloy is preferably 10%-20%.

[0039] Wherein, the mass content of Cu in the Dy-containing alloy is preferably 0.1%-0.4%.

[0040] Wherein, the mass content of Ga in the Dy-containing alloy is preferably 0-0.3%.

[0041] Wherein, the mass content of B in the Dy-containing alloy is preferably 0.88%-0.96%.

[0042] Wherein, the mass content of Fe in the Dy-containing alloy is preferably 60%-70%.

[0043] In the present invention, the main alloy preferably includes Pr and Nd.

[0044] The mass content of Pr and Nd in the main alloy is preferably 28%-31%, for example 29.8%.

[0045] Wherein, the main alloy preferably also includes one or more of Fe, Co, Cu, Ga, Ti and B.

[0046] Wherein, the mass content of Fe in the main alloy is preferably 60%-70%.

[0047] The mass content of Co in the main alloy is preferably 0.5%-1.5%, for example 1%.

[0048] The mass content of Cu in the main alloy is preferably 0.1%-0.2%, for example 0.15%.

[0049] The mass content of Ga in the main alloy is preferably 0.1%-0.2%, for example 0.15%.

[0050] The mass content of B in the main alloy is preferably 0.88%-0.96%, for example 0.94%.

[0051] The mass content of Ti in the main alloy is preferably 0.1%-0.3%, for example 0.2%.

[0052] In certain specific embodiments of the present invention, Dy is not included in the main alloy.

[0053] In the present invention, the preparation method of the main alloy may be conventional in the art, for example, comprising the following steps:

[0054] S1. Melting: Put the raw materials into the crucible for vacuum melting according to the formula;

[0055] S2, casting: casting the product of S1 in an Ar atmosphere and then cooling to obtain a quenched alloy;

[0056] S3, hydrogen crushing: the above-mentioned quenched alloy is subjected to hydrogen absorption in a hydrogen atmosphere, and then dehydrogenation is performed while vacuuming and heating is increased, and after dehydrogenation, the alloy is cooled to obtain powder;

[0057] S4. Airflow milling: The above powders are subjected to airflow milling in a nitrogen atmosphere with an oxidizing gas content of less than 100 ppm to obtain a main alloy.

[0058] The vacuum degree of the vacuum melting is, for example, 5×10 -2 Pa.

[0059] Wherein, the temperature of the vacuum melting is preferably below 1500°C.

[0060] The casting pressure is, for example, 55000Pa.

[0061] Wherein, the cooling speed is preferably 100°C / s-10000°C / s.

[0062] The temperature at which the hydrogen is broken is, for example, room temperature.

[0063] The purity of the hydrogen is, for example, 99.99%.

[0064] The hydrogen absorption pressure is, for example, 0.15 MPa.

[0065] The oxidizing gas is, for example, oxygen or water.

[0066] The pressure of the jet mill is, for example, 0.38 MPa.

[0067] In certain specific embodiments of the present invention, a Dy-containing additive may be added in the hydrogen fragmentation step, and the Dy-containing additive is as described above.

[0068] In certain specific embodiments of the present invention, a Dy-containing additive may be added during the jet milling step, and the Dy-containing additive is as described above.

[0069] In the present invention, preferably, the mixture is mixed with zinc stearate before the magnetic field forming.

[0070] The percentage of the mass of the zinc stearate to the total mass of the mixture and the zinc stearate is, for example, 0.12%.

[0071] In certain specific embodiments of the present invention, the mixture is prepared by adding the main alloy, the Dy-containing additive and the F-containing additive into a V-type mixer for mixing.

[0072] In the present invention, preferably, the magnetic field forming includes the following steps: performing primary forming and secondary forming on the mixture in sequence; wherein the primary forming includes a magnetizing stage and a demagnetizing stage, the magnetic field intensity of the magnetizing stage is 1.6T, and the pressure of the magnetizing stage is 0.35t / cm 2 The magnetic field intensity in the demagnetization stage is 0.2T; wherein the secondary forming pressure is 1.3t / cm 2 The secondary molding can further seal the molded body after the primary molding so that it does not come into contact with the air.

[0073] The one-step forming device is, for example, a right-angle oriented magnetic field forming machine.

[0074] The secondary forming device is, for example, an isostatic pressing machine.

[0075] In the present invention, preferably, the vacuum degree of the sintering is 5×10 -3 Pa.

[0076] In the present invention, preferably, the sintering includes a first stage, a second stage and a third stage in sequence, the temperature of the first stage is 200-400°C, the temperature of the second stage is 500-700°C, and the temperature of the third stage is 1000-1200°C.

[0077] Preferably, the temperature of the first stage is 300°C.

[0078] Preferably, the duration of the first stage is 0.5-2 hours, for example, 1 hour.

[0079] Preferably, the temperature of the second stage is 600°C.

[0080] Preferably, the duration of the second stage is 0.5-2 hours, for example, 1 hour.

[0081] Preferably, the temperature of the third stage is 1040°C.

[0082] Preferably, the duration of the third stage is 1-3 hours, for example, 2 hours.

[0083] In some embodiments of the present invention, a cooling step is further included after the sintering, and the cooling is performed, for example, in an Ar atmosphere, and the cooling pressure is, for example, 0.1 MPa. The cooling time is not particularly limited, and cooling to room temperature is sufficient.

[0084] In the present invention, preferably, the diffusion source of the grain boundary diffusion treatment includes Tb.

[0085] In the present invention, preferably, the diffusion source is single substance Tb or a compound containing Tb.

[0086] The Tb-containing compound is, for example, one or more of a Tb-containing hydride, a Tb-containing fluoride, a Tb-containing oxide, and a Tb-containing alloy.

[0087] The Tb-containing hydride is, for example, TbH 3 .

[0088] In the present invention, preferably, the mass percentage of Tb in the diffusion source to the mass percentage of the NdFeB matrix is ​​0.2%-0.5%, for example, 0.3%, 0.32%, 0.38% or 0.45%.

[0089] In the present invention, preferably, the temperature of the grain boundary diffusion treatment is 800-900°C, for example, 850°C.

[0090] In the present invention, preferably, the temperature time of the grain boundary diffusion treatment is 20-30 hours, for example, 24 hours.

[0091] In certain specific embodiments of the present invention, the grain boundary diffusion process is performed under an argon atmosphere.

[0092] In certain specific embodiments of the present invention, the grain boundary diffusion process is to diffuse along the orientation direction.

[0093] In the present invention, preferably, heat treatment is further included after the grain boundary diffusion treatment.

[0094] Wherein, the heat treatment is preferably performed in an Ar atmosphere.

[0095] The temperature of the heat treatment is preferably 400-600°C, for example 500°C.

[0096] The heat treatment time is preferably 2-4 hours, for example 3 hours.

[0097] The present invention also provides an application of the above-mentioned NdFeB magnet in magnetic steel.

[0098] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0099] The reagents and raw materials used in the present invention are commercially available.

[0100] The positive and progressive effects of the present invention are:

[0101] The NdFeB magnet provided by the present invention can promote the diffusion depth and diffusion uniformity of heavy rare earth, and has excellent high-temperature squareness and Hd5 after grain boundary diffusion treatment, and also has excellent coercive force and remanence. BRIEF DESCRIPTION OF THE DRAWINGS

[0102] FIG. 1 is a distribution diagram of F of the NdFeB magnet of Example 1 from the surface of the NdFeB magnet to a point at a vertical distance of 800 μm from the surface of the NdFeB magnet.

[0103] FIG. 2 is a distribution diagram of F of the NdFeB magnet of Comparative Example 1 from the surface of the NdFeB magnet to a point at a vertical distance of 800 μm from the surface of the NdFeB magnet.

[0104] FIG3 is a relationship diagram of the F element and the vertical distance from the surface of the NdFeB magnet in Example 1 and Comparative Example 1.

[0105] FIG. 4 is a distribution diagram of Nd, F, and O in the NdFeB magnet of Example 1.

[0106] FIG. 5 is a Dy distribution diagram of the NdFeB magnet of Example 1 at a vertical distance of 400 μm from the surface of the NdFeB magnet. DETAILED DESCRIPTION

[0107] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0108] Preparation Examples 1-7

[0109] The preparation steps of the main alloy or the Dy-containing alloy are as follows:

[0110] S1. Melting: According to the formula shown in Table 1, where the formula is the mass content of each element in all elements, the prepared raw materials are placed in an alumina crucible and melted in a high-frequency vacuum induction melting furnace at 5×10 -2 Vacuum melting is performed at a temperature below 1500°C in a vacuum of 1.5 Pa;

[0111] S2, casting: casting the product of S1 under Ar atmosphere and a pressure of 55000 Pa, and cooling at a rate of 100°C / s-10000°C / s to obtain a quenched alloy;

[0112] S3, hydrogen crushing: at room temperature, the above-mentioned quenched alloy is subjected to hydrogen absorption in a 99.99% hydrogen atmosphere and a pressure of 0.15 MPa, and then dehydrogenated while vacuuming and heating, and then cooled to obtain powder after dehydrogenation;

[0113] S4. Airflow milling: The above powders are subjected to airflow milling in a nitrogen atmosphere with an oxidizing gas content of less than 100 ppm and a pressure of 0.38 MPa to obtain a main alloy or a Dy-containing alloy.

[0114] Table 1

[0115]

[0116] Examples 1-5 and Comparative Examples 1-5

[0117] The preparation steps of NdFeB matrix are as follows:

[0118] S1. Add the main alloy, Dy-containing additive, F-containing additive and zinc stearate into a V-type mixer according to the types and contents in Table 2 and mix to obtain a mixture.

[0119] S2. After mixing the mixture with zinc stearate, primary forming and secondary forming are performed in sequence; wherein the primary forming includes a magnetizing stage and a demagnetizing stage, the magnetic field intensity in the magnetizing stage is 1.6T, and the pressure in the magnetizing stage is 0.35t / cm 2 The magnetic field intensity in the demagnetization stage is 0.2T; the pressure of the secondary forming is 1.3t / cm 2 The primary forming device is a right-angle oriented magnetic field forming machine, and the secondary forming device is an isostatic pressing machine; wherein the mass of zinc stearate accounts for 0.12% of the total mass of the mixture and zinc stearate.

[0120] S3, after secondary forming, at 5×10 -3 The sintering is carried out at 300°C and 600°C for 1 hour respectively, and then at 1040°C for 2 hours. After that, Ar gas is introduced to make the gas pressure reach 0.1MPa, and then cooled to room temperature to obtain a NdFeB matrix.

[0121] The preparation steps of NdFeB magnets are as follows:

[0122] S1. After the NdFeB substrates prepared in the above-mentioned Examples 1-5 and Comparative Examples 1-5 are processed into a length of 20 mm and a thickness of 5 mm and cleaned, TbH3 is sputtered and attached to the surface of the NdFeB substrate in a high-purity Ar gas atmosphere, and the grain boundaries are diffused at a temperature of 850° C. for 24 hours and cooled to room temperature; wherein the amount of the diffusion source (i.e., the mass percentage of Tb in the diffusion source to the mass percentage of the NdFeB substrate) is listed in Table 2, and the amount of the diffusion source is the mass percentage of Tb in the diffusion source to the mass percentage of the NdFeB substrate;

[0123] S2. The product obtained in S1 is heat treated in high-purity Ar gas at 500° C. for 3 hours, and then cooled to room temperature to obtain a NdFeB magnet.

[0124] Table 2

[0125]

[0126]

[0127] Effect Example 1

[0128] The following tests were performed on the NdFeB magnets obtained in Examples 1-5 and Comparative Examples 1-5:

[0129] 1. Surface scanning analysis using field emission electron probe microanalyzer (EPMA)

[0130] (1) The characteristic X-ray signals of Dy in the core of the main phase grain, the surface of the main phase grain, the epitaxial layer of the main phase grain and the grain boundary phase are obtained respectively. The equipment converts the signal value of each area into a mass concentration value according to its own standard sample database. The mass concentration value is the relative value of the Dy concentration in each area. The stronger the signal, the higher the concentration. Relative comparison can be made within the same field of view test area.

[0131] (2) The F distribution diagrams at different depths of the NdFeB magnet are obtained respectively, wherein the depth is the orientation direction of the NdFeB magnet.

[0132] The F distribution diagram of the NdFeB magnet of Example 1 from the surface of the NdFeB magnet to a point at a vertical distance of 800 μm from the surface of the NdFeB magnet is shown in FIG1 .

[0133] The F distribution diagram of the NdFeB magnet of Comparative Example 1 from the surface of the NdFeB magnet to a point at a vertical distance of 800 μm from the surface of the NdFeB magnet is shown in FIG2 .

[0134] The relationship diagram between the F element and the vertical distance from the surface of the NdFeB magnet in Example 1 and Comparative Example 1 is shown in FIG3 , which is obtained from FIG1 and FIG2 .

[0135] (3) Five different regions of the NdFeB magnet are randomly tested, and the surface distribution maps of the R1, F, and O elements in the five different regions are obtained. The volume fractions are then calculated using commercial image processing software (such as Image Pro).

[0136] The distribution diagram of Nd, F and O of the NdFeB magnet of Example 1 is shown in FIG4 .

[0137] (4) Obtain a Dy distribution diagram in the NdFeB magnet at a vertical distance of 400 μm from the surface of the NdFeB magnet.

[0138] The Dy distribution diagram of the NdFeB magnet of Example 1 is shown in FIG5 , wherein the center of the main phase grain in FIG5 is the core of the main phase grain. As can be seen from FIG5 , the NdFeB magnet of Example 1 includes the main phase grain epitaxial layer, the grain boundary phase, the main phase grain surface layer and the main phase grain core; and the Dy concentration distribution satisfies: grain boundary phase>main phase grain epitaxial layer>main phase grain core ≥main phase grain surface layer.

[0139] 2. The NIM-62000 permanent magnet material precision measurement system of China National Institute of Metrology was used to measure the remanence (Br), coercive force (Hcj), squareness (SQ) and Hd5 at test temperatures of 20°C and 150°C.

[0140] 3. Test of mass concentration of F: Tested using ion chromatography equipment.

[0141] The above test results are listed in Table 3:

[0142] Table 3

[0143]

[0144] Among them, the NdFeB magnets prepared in Examples 1-5 and Comparative Examples 3-5 include an R1-OF enriched region, and the F in the NdFeB magnet is located in a region from a vertical distance of 100 μm from the surface of the NdFeB magnet to the center of the NdFeB magnet, and the mass concentration of F in the NdFeB magnets of Examples 1-5 and Comparative Examples 3-5 shows a gradient rising trend from to the center of the NdFeB magnet, wherein, according to FIG. 3 , it can be seen that the mass concentration of F in the NdFeB magnet of Example 1 shows a gradient rising trend from to the center of the NdFeB magnet. The mass concentration of F in the NdFeB magnets of Comparative Examples 1 and Comparative Examples 2 does not have a gradient rising trend.

[0145] From the results in Table 3, it can be seen that the remanence of the NdFeB magnets of Examples 1-5 at 20°C is above 13.98 kGs, the coercive force at 20°C is above 29.5 kOe, the coercive force at 150°C is above 12.8 kOe, the squareness at 150°C is above 0.978, and the Hd5 at 150°C is above 12.54 kOe.

[0146] The volume fraction of the R1-OF enriched region in Comparative Examples 1-5 is not within the range of 1%-5%. Too high or too low a volume fraction will result in a decrease in the remanence, coercive force and Hd5 of the NdFeB magnet at low and high temperatures.

Claims

1. A neodymium iron boron magnet, characterized in that: The NdFeB magnet includes an R1-OF enriched zone, which is located in a region from a vertical distance of 100 μm from the surface of the NdFeB magnet to the center of the NdFeB magnet, wherein R1 is one or more of Pr, Nd, Gd and Ho; the volume fraction of the R1-OF enriched zone is 1%-5%, wherein the volume fraction means the percentage of the volume of the R1-OF enriched zone to the total volume of the NdFeB magnet.

2. The NdFeB magnet according to claim 1, wherein: The NdFeB magnet satisfies one or more of the following conditions: (a) the mass concentration of F in the NdFeB magnet presents a gradient upward trend from a vertical distance of 100 μm from the surface of the NdFeB magnet to the center of the NdFeB magnet; (b) the mass concentration of F in the NdFeB magnet is 0.02%-0.2%, preferably 0.02%-0.15%, for example, 0.026%, 0.052%, 0.1%, 0.124% or 0.13%; (c) the volume fraction of the R1-OF enriched zone is 2%, 2.2%, 3%, 2.5% or 2.8%.

3. The NdFeB magnet according to claim 1, wherein: The NdFeB magnet comprises main phase grains and grain boundary phases, wherein the main phase grains comprise, from outside to inside, a main phase grain surface layer, a main phase grain epitaxial layer and a main phase grain core, and the NdFeB magnet satisfies one or more of the following conditions: (a) the R1-OF enriched region is distributed in the grain boundary phase; (b) the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface layer do not contain the R1-OF enriched region; (c) the NdFeB magnet comprises Dy, and the concentration distribution of Dy satisfies: grain boundary phase>main phase grain epitaxial layer layer>main phase grain core≥main phase grain surface; wherein, preferably, the concentration ratio of Dy in the grain boundary phase, the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface satisfies: grain boundary phase: main phase grain epitaxial layer: main phase grain core: main phase grain surface = (8-11): (4.5-6.5): (2-4): (1-4); wherein, the concentration ratio of Dy in the grain boundary phase, the main phase grain epitaxial layer, the main phase grain core and the main phase grain surface satisfies, for example: 8.2: 5.3: 3.7 : 3.6, 9.1: 5.7: 2.8: 2.8, 10.3: 5.5: 3.1: 2.9, 8.9: 6.1: 2.9: 2.8 or 9.6: 4.9: 2.0: 1.9; wherein, preferably, the relative value of the Dy concentration in the core of the main phase grain is 2-4, for example, 2.8, 2.9, 3.1 or 3.7; wherein, preferably, the relative value of the Dy concentration in the surface layer of the main phase grain is 1-4, for example, 1.9, 2.8, 2.9 or 3.6; wherein, preferably, the main phase grain The relative value of Dy concentration in the epitaxial layer is 4.5-6.5, for example, 4.9, 5.3, 5.5, 5.7 or 6.1; wherein, preferably, the relative value of Dy concentration in the grain boundary phase is 8-11, for example, 8.2, 8.9, 9.1, 9.6 or 10.3; wherein, preferably, in the area from the surface of the NdFeB magnet to a vertical distance of 800 μm from the surface of the NdFeB magnet, the concentration distribution of Dy satisfies: grain boundary phase> epitaxial layer of main phase grain> core of main phase grain≥ surface of main phase grain.

4. The method for preparing a NdFeB magnet according to any one of claims 1 to 3, characterized in that: It includes the following steps: A mixture including a main alloy and a F-containing additive is sequentially formed and sintered by a magnetic field to obtain a NdFeB matrix; the NdFeB matrix is ​​then subjected to a grain boundary diffusion treatment; the main alloy includes one or more elements of Pr, Nd, Gd and Ho.

5. The method for preparing a NdFeB magnet according to claim 4, wherein: The preparation method of the NdFeB magnet satisfies one or more of the following conditions: (a) the mass content of the F-containing additive in the mixture is 0.1%-0.5%, for example, 0.2%; (b) the F-containing additive is a metal fluoride, and the metal fluoride is, for example, DyF3, TiF4, CeF3, MgF2 or CaF2; (c) the mass content of the main alloy in the mixture is 94%-98%, for example, 93.9%, 94.8%, 95.8%, 96.8% or 97.5%; (d) the mixture also includes a Dy-containing additive; wherein the mass content of Dy in the Dy-containing additive is preferably 1%-30%, for example, 15%, 18%, 19%, 20% or 23%; Wherein, the mass content of the Dy-containing additive in the mixture is preferably 2%-6%. For example, 3%, 4% or 5%; wherein the Dy-containing additive is preferably a Dy-containing alloy; wherein the Dy-containing alloy, for example, further includes one or more of Pr, Nd, Fe, Cu, Ga and B; wherein the mass content of Pr and Nd in the Dy-containing alloy is preferably 10%-20%; wherein the mass content of Cu in the Dy-containing alloy is preferably 0.1%-0.4%; wherein the mass content of Ga in the Dy-containing alloy is preferably 0-0.3%; wherein the Dy-containing The mass content of B in the Dy alloy is preferably 0.88%-0.96%; wherein the mass content of Fe in the Dy-containing alloy is preferably 60%-70%; (e) before the magnetic field forming, the mixture is also mixed with zinc stearate; wherein the mass of the zinc stearate accounts for a percentage of the total mass of the mixture and the zinc stearate, for example, 0.12%; (f) the preparation method of the mixture is: add the main alloy, the Dy-containing additive and the F-containing additive into a V-type mixer for mixing.

6. The method for preparing a NdFeB magnet according to claim 4, wherein: The main alloy comprises Pr and Nd; wherein the mass content of Pr and Nd in the main alloy is preferably 28%-31%, for example, 29.8%; wherein the main alloy preferably also comprises one or more of Fe, Co, Cu, Ga, Ti and B; wherein the mass content of Fe in the main alloy is preferably 60%-70%; wherein the mass content of Co in the main alloy is preferably 0.5%-1.5%, for example, 1%; wherein the mass content of Cu in the main alloy is preferably 0.1%-0.2%, for example, 0.15%; wherein the mass content of Ga in the main alloy is preferably 0.1%-0.2%, for example, 0.15%; wherein the mass content of B in the main alloy is preferably 0.88%-0.96%, for example, 0.94%; wherein the mass content of Ti in the main alloy is preferably 0.1%-0.3%, for example, 0.2%.

7. The method for preparing a NdFeB magnet according to claim 4, characterized in that: The preparation method of the main alloy comprises the following steps: S1, smelting: placing the raw materials into a crucible for vacuum smelting according to the formula; S2, casting: casting the product of S1 in an Ar atmosphere and then cooling to obtain a quenched alloy; S3, hydrogen crushing: after the quenched alloy absorbs hydrogen in a hydrogen atmosphere, the quenched alloy is dehydrogenated while vacuuming, and then cooled to obtain a powder after dehydrogenation; S4, air flow milling: air flow milling the powder in a nitrogen atmosphere with an oxidizing gas content of less than 100 ppm to obtain the main alloy; wherein the vacuum degree of the vacuum smelting is, for example, 5×10 -2 Pa; wherein the temperature of the vacuum melting is preferably below 1500°C; wherein the casting pressure is, for example, 55000Pa; wherein the cooling rate is preferably 100°C / s-10000°C / s; wherein the temperature of the hydrogen crushing is, for example, room temperature; wherein the purity of the hydrogen is, for example, 99.99%; wherein the pressure of the hydrogen absorption is, for example, 0.15MPa; wherein the oxidizing gas is, for example, oxygen or water; wherein the pressure of the air flow grinding is, for example, 0.38MPa.

8. The method for preparing a NdFeB magnet according to claim 4, characterized in that: The preparation method of the NdFeB magnet meets one or more of the following conditions: (a) the magnetic field forming comprises the following steps: the mixture is subjected to primary forming and secondary forming in sequence; wherein the primary forming comprises a magnetizing stage and a demagnetizing stage, the magnetic field intensity of the magnetizing stage is 1.6T, and the pressure of the magnetizing stage is 0.35t / cm 2 The magnetic field intensity in the demagnetization stage is 0.2T; wherein the secondary forming pressure is 1.3t / cm 2 ; wherein the primary forming device is, for example, a right-angle oriented magnetic field forming machine; wherein the secondary forming device is, for example, an isostatic pressing machine; (b) the vacuum degree of the sintering is 5×10 -3 Pa; (c) the sintering includes a first stage, a second stage and a third stage in sequence, the temperature of the first stage is 200-400°C, the temperature of the second stage is 500-700°C, and the temperature of the third stage is 1000-1200°C; wherein, preferably, the temperature of the first stage is 300°C; wherein, preferably, the time of the first stage is 0.5-2h, for example, 1h; wherein, preferably, the temperature of the second stage is 600°C; wherein, preferably, the time of the second stage is 0.5-2h, for example, 1h; wherein, preferably, the temperature of the third stage is 1040°C; wherein, preferably, the time of the third stage is 1-3h, for example, 2h; wherein, preferably, a cooling step is also included after the sintering, and the cooling is, for example, under an Ar atmosphere, and the cooling pressure is, for example, 0.1MPa.

9. The method for preparing a NdFeB magnet according to claim 4, wherein: The preparation method of the NdFeB magnet satisfies one or more of the following conditions: (a) the diffusion source of the grain boundary diffusion treatment includes Tb; (b) the diffusion source is single substance Tb or a compound containing Tb; wherein the compound containing Tb is, for example, one or more of a hydride containing Tb, a fluoride containing Tb, an oxide containing Tb and an alloy containing Tb; (c) the temperature of the grain boundary diffusion treatment is 800-900°C, for example, 850°C; (d) the temperature time of the grain boundary diffusion treatment is 20-30h, for example, 24h; (e) the grain boundary diffusion treatment is carried out in an argon atmosphere; (f) a heat treatment is further included after the grain boundary diffusion treatment; wherein the heat treatment is preferably carried out in an Ar atmosphere; wherein the temperature of the heat treatment is preferably 400-600°C, for example, 500°C; wherein the time of the heat treatment is preferably 2-4h, for example, 3h.

10. Use of the NdFeB magnet according to any one of claims 1 to 3 in magnetic steel.

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