Neodymium-iron-boron magnet with heavy rare earth segregation distribution, preparation method therefor, and use thereof

Abstract

The present application discloses a neodymium-iron-boron magnet with heavy rare earth segregation distribution, a preparation method therefor, and a use thereof. The preparation method comprises: mixing a first alloy, a second alloy, and an auxiliary phase alloy, and then performing orientation compression, sintering and tempering treatment to prepare the neodymium-iron-boron magnet with heavy rare earth segregation distribution, wherein magnet main-phase crystal grains of the neodymium-iron-boron magnet have a core-shell structure, and heavy rare earth on the surface of the main-phase crystal grain core structure is distributed in a segregation mode. According to the present application, an auxiliary phase and a boron-rich phase in a grain boundary are introduced into a multi-alloy method to perform metallurgical reaction, a concentration difference is used and a heavy rare earth segregation region capable of constructing roadblock type distribution is formed, thereby preparing a neodymium-iron-boron magnet with ultrahigh comprehensive performance and heavy rare earth segregation distribution. The method involves an easily-controlled process and is suitable for batch production.

Description

A neodymium iron boron magnet with concentrated distribution of heavy rare earth and its preparation method and application

[0001] This application is based on and claims priority from a Chinese patent application with application number 202311817107.0 filed on December 26, 2023, entitled “A neodymium iron boron magnet with concentrated distribution of heavy rare earths, its preparation method and application”. Technical Field

[0002] The present application specifically relates to a neodymium iron boron magnet with a concentrated distribution of heavy rare earths, a preparation method thereof, and an application thereof, and belongs to the technical field of rare earth permanent magnet materials. Background Art

[0003] At present, NdFeB magnets have become an indispensable key core component in the fields of wind power generation, new energy vehicles, rail transportation, etc., and with the demand for technological iteration and upgrading in these fields, magnets are urgently required to have high stability, high performance, miniaturization and other characteristics. The magnetic parameters for judging the quality of NdFeB magnets mainly include three, among which the coercive force H cj Residual magnetism B reflects the ability of the magnet to resist changes in the external environment without demagnetization, which determines the stability of the magnet during service. r It reflects the magnitude of the magnetic force that a magnet can generate externally. It is an important parameter in the design of magnetic circuits for magnetic functional devices and a key indicator for evaluating magnet performance. The maximum magnetic energy product (BH) m Reflects the energy density that can be stored in the magnet, (BH) m The larger the value, the smaller the magnetic device can be designed under the same external magnetic force output requirement. It is related to the residual magnetism B r is proportional to the square of, that is (BH) m ∝B r 2 In practical applications, as the coercive force H cj and maximum magnetic energy product (BH) m As the sum of the increases, it is gradually applied to scenes with higher service requirements, so the industry usually uses H cj +(BH) m At present, the magnet is prepared by introducing heavy rare earth Dy / Tb into the alloy smelting (alloying) process to form Dy2Fe with a higher magnetocrystalline anisotropy field. 14 B or Tb2Fe 14 B phase is the most direct and effective means to improve the coercivity of NdFeB magnets. However, a large amount of Dy / Tb replacing Nd in the main phase will lead to remanent magnetization B r and (BH) m This means that there is a certain contradiction between improving the coercive force and maintaining a high maximum magnetic energy product. In other words, the comprehensive performance of the magnet is greatly improved. cj +(BH)m There are considerable challenges.

[0004] The process of introducing heavy rare earth into NdFeB magnets by alloying is simple, and the performance uniformity and consistency of the prepared magnet products are good. Correspondingly, the heavy rare earth is evenly distributed inside the magnet grains. The analysis of magnetic domain evolution during the demagnetization process of the magnet shows that heavy rare earth has a pinning effect on the nucleation and movement of the reverse magnetization domain. The higher the concentration of heavy rare earth in the microscopic area, the stronger the pinning effect and the coercive force H cj Obviously, comprehensively increasing the heavy rare earth content of magnet grains in order to further improve the coercivity will not only significantly deteriorate the maximum magnetic energy product of the magnet, making it difficult to prepare high-comprehensive-performance NdFeB magnets, but will also increase the use of expensive heavy rare earth resources and significantly increase production costs.

[0005] Summary of the Invention

[0006] The main purpose of this application is to provide a heavy rare earth segregated distribution NdFeB magnet and its preparation method and application. The heavy rare earth segregated distribution NdFeB magnet provided in this application has the comprehensive performance of high coercivity and high remanence. The comprehensive performance of the magnet H cj +(BH) m >70.

[0007] To achieve the aforementioned invention objectives, the technical solutions adopted in this application include:

[0008] The present invention provides a method for preparing a neodymium iron boron magnet having a segregated distribution of heavy rare earths, which comprises:

[0009] The first alloy, the second alloy and the auxiliary phase alloy are mixed and then subjected to orientation pressing, sintering and tempering treatment to obtain a neodymium iron boron magnet with a concentrated distribution of heavy rare earth;

[0010] The main phase crystal grains of the NdFeB magnet have a core-shell structure, and the heavy rare earth elements on the surface of the core structure of the main phase crystal grains are segregated and distributed.

[0011] The embodiments of the present application also provide a neodymium iron boron magnet with a segregated distribution of heavy rare earths obtained by the aforementioned preparation method.

[0012] The embodiments of the present application also provide applications of the aforementioned heavy rare earth segregated distribution neodymium iron boron magnet in the fields of wind power generation, new energy vehicles or rail transportation.

[0013] Compared with the existing technology, the beneficial effects of the present application are: the present application uses a multi-alloy method to introduce a metallurgical reaction between the auxiliary phase and the boron-rich phase in the grain boundary, and utilizes the concentration difference and the formation to construct a heavy rare earth segregation zone with a "roadblock" distribution. The "roadblock" distribution of the heavy rare earth regional segregation can still effectively curb the reversal and movement of the reverse magnetization domain during the demagnetization process, while effectively improving the coercive force of the magnet, while minimizing the damage of the heavy rare earth to the remanence and magnetic energy product, and can prepare NdFeB magnets with ultra-high comprehensive performance and heavy rare earth segregation distribution. The method is easy to control and suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] FIG1 is a schematic diagram of the microstructure of a neodymium iron boron magnet with a concentrated distribution of heavy rare earths in a typical embodiment of the present application and a neodymium iron boron magnet with a uniform distribution of heavy rare earths in the prior art;

[0016] FIG2 is a schematic diagram of the formation mechanism of a neodymium iron boron magnet with a segregated distribution of heavy rare earths prepared in a typical embodiment of the present application;

[0017] Figures 3a-3c are backscattered photos of the magnet in Comparative Example 1 of the present application and distribution diagrams of Tb and Nd elements;

[0018] 4a-4g are backscattered photos of the magnet in Example 1 of the present application and distribution diagrams of Tb, Nd, and Pr elements. DETAILED DESCRIPTION

[0019] In view of the shortcomings of the prior art, the applicant of this case, after long-term research and extensive practice, was able to propose the technical solution of this application. The technical solution of this application will be clearly and completely described below. Obviously, the embodiments described are part of the embodiments of this application, but not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of this application.

[0020] Specifically, as one aspect of the technical solution of the present application, a method for preparing a neodymium iron boron magnet with a heavy rare earth segregated distribution includes:

[0021] The first alloy, the second alloy and the auxiliary phase alloy are mixed and then subjected to orientation pressing, sintering and tempering treatment to obtain a neodymium iron boron magnet with a concentrated distribution of heavy rare earth;

[0022] The main phase crystal grains of the NdFeB magnet have a core-shell structure, and the heavy rare earth elements on the surface of the core structure of the main phase crystal grains are segregated and distributed.

[0023] In some preferred embodiments, the particle size of the main phase grains is 3-8 μm, and the shell thickness is related to the amount of auxiliary alloy added.

[0024] In some preferred embodiments, the chemical formula of the first alloy is as shown in Formula (I):

[0025] Re x B y M z Fe 100-x-y-z Formula (I)

[0026] Among them, Re is selected from at least one of Tb, Dy, Gd, Pr, Nd, La, Ce, Y, and Ho, M is selected from at least one of Cu, Zr, Co, Ga, Si, Sn, Ge, Ti, Zn, and Al, B is boron, and Fe is iron; x, y, and z are the mass percentage contents of the corresponding elements, and satisfy 29≤x≤34, 1.0<y≤2.0, and 0≤z≤3.

[0027] Furthermore, in the formula (I), x is preferably 29 to 32, more preferably 29 to 31, and most preferably 29.5; y is preferably 1.0 to 1.6, more preferably 1.0 to 1.4, and most preferably 1.1; and z is preferably 1.5 to 2.5, more preferably 1.5 to 2.

[0028] In some preferred embodiments, the chemical formula of the second alloy is as shown in Formula (II):

[0029] Re x B y M z Fe 100-x-y-z Formula (II)

[0030] Among them, Re is selected from at least one of Tb, Dy, Gd, Pr, Nd, La, Ce, Y, and Ho, M is selected from at least one of Cu, Zr, Co, Ga, Si, Sn, Ge, Ti, Zn, and Al, B is boron, and Fe is iron; x, y, and z are the mass percentage contents of the corresponding elements, and satisfy 29≤x≤34, 0.8<y≤0.99, and 0≤z≤3.

[0031] Furthermore, in the formula (II), x is preferably 29 to 32, more preferably 29 to 31, and most preferably 30; y is preferably 0.9 to 0.98, more preferably 0.92 to 0.96, and most preferably 0.94; and z is preferably 1.5 to 2.5, more preferably 1.5 to 2.

[0032] In some preferred embodiments, the general chemical formula of the auxiliary phase alloy is as shown in formula (III):

[0033] Re a M b Fe 100-a-b Formula (III)

[0034] Among them, Re is selected from at least one of Tb, Dy, Gd, Pr, Nd, La, Ce, Y, and Ho, M is selected from at least one of Cu, Zr, Co, Ga, Si, Sn, Ge, Ti, Zn, and Al, and Fe is iron; a and b are the mass percentage contents of the corresponding elements, respectively, and satisfy 50≤a≤70 and 0≤b≤30.

[0035] Furthermore, in the formula (III), a is preferably 55 to 70, more preferably 60 to 70, and most preferably 63; b is preferably 0 to 20, more preferably 0 to 15, and most preferably 10.

[0036] In some preferred embodiments, the mass ratio of the first alloy to the second alloy is 1:(3-10).

[0037] In some preferred embodiments, the mass ratio of the auxiliary phase alloy to the sum of the first alloy, the second alloy and the auxiliary phase alloy is 0.5 to 10:100.

[0038] In some preferred embodiments, the powder particle sizes of the first alloy, the second alloy, and the auxiliary phase alloy are independently 2 to 5 μm.

[0039] In some preferred embodiments, the magnetic field strength used in the orientation pressing process is 1.5-2.0T.

[0040] In some preferred embodiments, the sintering temperature is 900-1100°C.

[0041] In some preferred embodiments, the sintering treatment time is 1 to 6 hours.

[0042] In some preferred embodiments, the tempering heat treatment includes primary tempering treatment, secondary tempering treatment and tertiary tempering treatment.

[0043] Furthermore, the temperature of the first-stage tempering treatment is 850-900° C., and the time is 1-4 hours.

[0044] Furthermore, the temperature of the secondary tempering treatment is 700-800° C., and the time is 1-4 hours.

[0045] Furthermore, the temperature of the third-stage tempering treatment is 450-600° C., and the time is 1-4 hours.

[0046] In some preferred embodiments, the preparation method includes: preparing a first alloy casting sheet, a second alloy casting sheet, and an auxiliary phase alloy casting sheet by smelting according to the ratio of each element, and then performing hydrogen crushing and air flow grinding treatment respectively to obtain a first alloy powder, a second alloy powder, and an auxiliary phase alloy powder.

[0047] Furthermore, the hydrogen pressure in the hydrogen crushing process is 0.1-0.4 MPa, the hydrogen absorption time is 2-5 hours, the dehydrogenation temperature is 320-500° C., and the dehydrogenation time is 4-10 hours.

[0048] Furthermore, the hydrogen content in the powders obtained after hydrogen crushing of the first alloy flakes, the second alloy flakes, and the auxiliary phase alloy flakes is lower than 1500 ppm; and the average particle size of the obtained powders is 100-250 μm.

[0049] FIG1 is a schematic diagram of the microstructure of the NdFeB magnet with concentrated distribution of heavy rare earth in the present application and the NdFeB magnet with uniform distribution of heavy rare earth in the prior art.

[0050] The schematic diagram of the formation mechanism of the NdFeB magnet with concentrated distribution of heavy rare earth prepared in this application is shown in FIG2 . The magnet contains a main phase, a boron-rich phase dispersed around the main phase, and an auxiliary phase alloy containing heavy rare earth. The auxiliary phase alloy makes the concentration of heavy rare earth (HRE) in the grain boundary higher than that in the grain. Due to the existence of the concentration gradient, the heavy rare earth in the auxiliary phase alloy has a tendency to migrate toward the original main phase grains. In addition, HRE2Fe 14 B compared to Pr / Nd2Fe 14 Because the boron formation energy is lower, the heavy rare earth elements in the original grains will also migrate to the periphery of the grains and react with the boron-rich phase, thus forming a heavy rare earth segregation region around the original main phase grains. The rare earth elements in the original main phase, the rare earth elements in the auxiliary phase, iron, and the boron-rich phase react through metallurgical reactions to form a new main phase shell around the original grains. This "roadblock" distribution of heavy rare earth segregation regions effectively prevents the reversal and movement of magnetized domains during demagnetization, not only improving the utilization of heavy rare earths but also minimizing the loss of remanence while enhancing the magnet's coercivity, resulting in the production of NdFeB magnets with ultra-high overall performance.

[0051] Another aspect of the embodiments of the present application further provides a neodymium iron boron magnet with a segregated distribution of heavy rare earths prepared by the aforementioned preparation method.

[0052] Furthermore, the H of the NdFeB magnet cj +(BH) m >70.

[0053] Another aspect of the embodiments of the present application further provides the application of the aforementioned heavy rare earth segregated distribution neodymium iron boron magnet in the fields of wind power generation, new energy vehicles or rail transportation.

[0054] The technical solution of the present application is further described in detail below in conjunction with several preferred embodiments and drawings. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific operation process are given, but the scope of protection of the present application is not limited to the following embodiments.

[0055] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0056] Example 1

[0057] The first alloy, the second alloy quick-setting alloy sheet and the auxiliary phase quick-setting alloy sheet were prepared according to the ratio of each element. The vacuum degree during the preparation of the main phase quick-setting alloy sheet was 3x10 -2 Pa, the rotation speed is 2.0 m / s, the pouring temperature is 1350 °C, and the vacuum degree during the preparation of the auxiliary phase rapid solidification alloy casting is 3x10 -2 Pa, the rotation speed is 2.0m / s, the pouring temperature is 1000℃, and the mass percentage of the first alloy chemical formula is Nd 24 Tb 5.5 B 1.1 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 68.9 , the second alloy chemical formula mass percentage is Nd 30 B 0.92 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 68.58 , the auxiliary phase chemical formula mass percentage is Pr 10 Tb 45 Fe 45 The first alloy, the second alloy rapid solidification alloy sheet and the auxiliary phase alloy sheet were powdered separately. The alloy rapid solidification alloy sheet was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then vacuum dehydrogenated at 450°C for 9 hours to obtain hydrogen-fragmented powder. Thereafter, the hydrogen-fragmented powder was further crushed using a jet mill to obtain the first alloy powder, the second alloy powder and the auxiliary phase alloy powder, respectively.

[0058] The main phase alloy powder and the auxiliary phase alloy powder are mixed, with the ratio of the first alloy to the second alloy being 1:4, and the auxiliary phase alloy powder accounting for 2.5% of the total weight (main phase alloy powder + auxiliary phase alloy powder). The mixed powder is then subjected to orientation pressing in a 1.8T magnetic field and isostatic pressing at a pressure of 160MPa to obtain a magnet. The magnet is then sintered in a vacuum sintering furnace, isolated from the atmosphere, at a sintering temperature of 1040°C for 4 hours. Finally, it is heat treated at 900°C, 750°C, and 500°C for 2 hours each to obtain a NdFeB permanent magnet.

[0059] Comparative Example 1

[0060] According to the method of Example 1, an iron neodymium boron permanent magnet was prepared. The difference from Example 1 is that it was prepared by direct melting. The chemical formula mass percentage is the same as the nominal composition of Example 1, which is Pr 0.25 Nd 24.86 Tb 5.42 B 0.93 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 68.04 .

[0061] The remanence and coercivity of the products prepared in Example 1 and Comparative Example 1 of the present application were tested using an ultra-high coercivity permanent magnet measuring instrument, model PFM14.CN, provided by HIRST. The test results are as follows:

[0062] The distribution of rare earth elements in the grains of the iron-neodymium-boron permanent magnets prepared in Example 1 and Comparative Example 1 of the present application was analyzed using electron probe surface scanning. The test results are shown in Figures 3a-3c and 4a-4g. Figures 3a-3c are for Comparative Example 1, and Figures 4a-4g are for Example 1. The Tb element in the iron-neodymium-boron permanent magnet prepared in Example 1 exhibits a segregated distribution (indicated by the red arrow), while the Tb element in the comparative example exhibits a uniform distribution.

[0063] Example 2

[0064] The first alloy, the second alloy quick-setting alloy sheet and the auxiliary phase quick-setting alloy sheet were prepared by melting according to the ratio of each element. The vacuum degree during the preparation of the main phase quick-setting alloy sheet was 3x10 -2 Pa, the rotation speed was 2.0 m / s, the pouring temperature was 1350 °C, and the vacuum degree during the preparation of the auxiliary phase rapid solidification alloy casting was 3x10 -2 Pa, the rotation speed is 2.0m / s, the pouring temperature is 1000℃, and the mass percentage of the first alloy chemical formula is Nd 29.5 B 1.2 Al 0.1 Cu 0.2Ga 0.1 Zr 0.1 Fe 68.8 , the second alloy chemical formula mass percentage is Nd 24.5 Tb 4.5 Dy 0.5 B 0.90 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 69.10 , the auxiliary phase chemical formula mass percentage is Pr 35 Tb 25 Fe 40 The first alloy, the second alloy rapid solidification alloy sheet and the auxiliary phase alloy sheet were powdered separately. The alloy rapid solidification alloy sheet was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then vacuum dehydrogenated at 450°C for 10 hours to obtain hydrogen-fragmented powder. Thereafter, the hydrogen-fragmented powder was further crushed using a jet mill to obtain the first alloy powder, the second alloy powder and the auxiliary phase alloy powder, respectively.

[0065] The main phase alloy powder and the auxiliary phase alloy powder are mixed, with the ratio of the first alloy to the second alloy being 1:5, and the auxiliary phase alloy powder accounting for 3% of the total weight (main phase alloy powder + auxiliary phase alloy powder). The mixed powder is then subjected to orientation pressing in a 1.8T magnetic field and isostatic pressing at a pressure of 160MPa to obtain a magnet. The magnet is then sintered in a vacuum sintering furnace, isolated from the atmosphere, at a sintering temperature of 1060°C for 4 hours. Finally, it is heat treated at 900°C, 700°C, and 500°C for 2 hours each to obtain a NdFeB permanent magnet.

[0066] Comparative Example 2

[0067] According to the method of Example 2, an iron-neodymium-boron permanent magnet is prepared. The difference from Example 2 is that the B content in the first alloy is equal to that in the second alloy, and the chemical formula mass percentage is Nd 29.5 B 0.90 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 69.10 .

[0068] The remanence, coercive force and magnetic energy product of the magnets prepared in Example 2 and Comparative Example 2 of the present application were measured using an ultra-high coercive force permanent magnet measuring instrument, model PFM14.CN, provided by HIRST. The test results are as follows:

[0069] Example 3

[0070] The first alloy, the second alloy quick-setting alloy sheet and the auxiliary phase quick-setting alloy sheet were prepared according to the ratio of each element. The vacuum degree during the preparation of the main phase quick-setting alloy sheet was 3x10 -2 Pa, the rotation speed was 2.0 m / s, the pouring temperature was 1380 °C, and the vacuum degree during the preparation of the auxiliary phase rapid solidification alloy casting was 3x10 -2 Pa, the rotation speed is 2.0m / s, the pouring temperature is 1100℃, and the mass percentage of the first alloy chemical formula is Nd 29.5 Tb 0.5 B 1.2 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 68.3 , the second alloy chemical formula mass percentage is Nd 23 Dy 5.5 Tb 1.5 B 0.88 Al 0.1 Cu 0.2 Ga 0.1 Zr 0.1 Fe 68.62 , the auxiliary phase chemical formula mass percentage is Nd 15 Dy 30 Tb 10 Fe 45 The first alloy, the second alloy rapid solidification alloy sheet and the auxiliary phase alloy sheet were powdered separately. The alloy rapid solidification alloy sheet was subjected to hydrogen absorption at room temperature and a hydrogen pressure of 0.2 MPa for 3 hours, and then vacuum dehydrogenated at 450°C for 10 hours to obtain hydrogen-fragmented powder. Thereafter, the hydrogen-fragmented powder was further crushed using a jet mill to obtain the first alloy powder, the second alloy powder and the auxiliary phase alloy powder, respectively.

[0071] The main phase alloy powder and the auxiliary phase alloy powder are mixed, with the ratio of the first alloy to the second alloy being 1:3, and the auxiliary phase alloy powder accounting for 2% of the total weight (main phase alloy powder + auxiliary phase alloy powder). The mixed powder is then subjected to orientation pressing in a 1.8T magnetic field and isostatic pressing at a pressure of 160MPa to obtain a magnet. The magnet is then sintered in a vacuum sintering furnace, isolated from the atmosphere, at a sintering temperature of 1070°C for 4 hours. Finally, it is heat treated at 900°C, 780°C, and 500°C for 2 hours each to obtain a NdFeB permanent magnet.

[0072] Comparative Example 3

[0073] According to the method of Example 3, a NdFeB permanent magnet was prepared. The difference from Example 3 is that the NdFeB permanent magnet was heat treated at 900°C and 500°C for 2 hours respectively (tempering heat treatment was performed only twice) to obtain a NdFeB permanent magnet.

[0074] The remanence and coercivity of the products prepared in Example 3 and Comparative Example 3 of the present application were tested using an ultra-high coercivity permanent magnet measuring instrument, model PFM14.CN, provided by HIRST. The test results are as follows:

[0075] Comparative Example 4

[0076] The method is the same as Example 1, except that the second alloy powder is absent;

[0077] The remanence and coercivity of the products prepared in Example 1 and Comparative Example 4 of the present application were tested using an ultra-high coercivity permanent magnet measuring instrument, model PFM14.CN, provided by HIRST. The test results are as follows:

[0078] Comparative Example 5

[0079] The method is the same as in Example 1, except that the auxiliary phase alloy powder is absent;

[0080] The remanence and coercivity of the products prepared in Example 1 and Comparative Example 5 of the present application were tested using an ultra-high coercivity permanent magnet measuring instrument, model PFM14.CN, provided by HIRST. The test results are as follows:

[0081] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0082] It should be understood that the technical solution of the present application is not limited to the above-mentioned specific implementation cases. Any technical variations made according to the technical solution of the present application without departing from the scope of protection of the purpose of the present application and the claims shall fall within the scope of protection of the present application.

Claims

1. A method for preparing a Nd-Fe-B magnet with heavy rare earth segregation distribution, characterized in that, Including: Mixing a first alloy, a second alloy and a secondary phase alloy, followed by orientation pressing, sintering and tempering treatments to obtain a neodymium iron boron magnet with a heavy rare earth segregation distribution; Wherein, the magnet main phase grains of the neodymium iron boron magnet have a core-shell structure, and the heavy rare earth segregation is distributed on the surface of the main phase grain core structure.

2. The preparation method according to claim 1, characterized in that: The chemical general formula of the first alloy is shown in Formula (I): Re x B y M z Fe 100-x-y-z Formula (I) Wherein, Re is selected from at least one of Tb, Dy, Gd, Pr, Nd, La, Ce, Y, Ho, M is selected from at least one of Cu, Zr, Co, Ga, Si, Sn, Ge, Ti, Zn, Al, B is boron, and Fe is iron; x, y, z are the mass percentage contents of the corresponding elements respectively, and satisfy 29 ≤ x ≤ 34, 1.0 < y ≤ 2.0, 0 ≤ z ≤ 3.

3. The preparation method according to claim 1, characterized in that: The chemical general formula of the second alloy is shown in Formula (II): Re x B y M z Fe 100-x-y-z Formula (II) Wherein, Re is selected from at least one of Tb, Dy, Gd, Pr, Nd, La, Ce, Y, Ho, M is selected from at least one of Cu, Zr, Co, Ga, Si, Sn, Ge, Ti, Zn, Al, B is boron, and Fe is iron; x, y, z are the mass percentage contents of the corresponding elements respectively, and satisfy 29 ≤ x ≤ 34, 0.8 < y ≤ 0.99, 0 ≤ z ≤ 3.

4. The preparation method according to claim 1, characterized in that: The chemical general formula of the auxiliary phase alloy is shown in Formula (III): Re a M b Fe 100-a-b Formula (III) Wherein, Re is selected from at least one of Tb, Dy, Gd, Pr, Nd, La, Ce, Y, Ho, M is selected from at least one of Cu, Zr, Co, Ga, Si, Sn, Ge, Ti, Zn, Al, and Fe is iron; a, b are the mass percentage contents of the corresponding elements respectively, and satisfy 50 ≤ a ≤ 70, 0 ≤ b ≤ 30.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the first alloy to the second alloy is 1:(3 - 10).

6. The preparation method according to claim 1, characterized in that: The mass ratio of the secondary phase alloy to the sum of the first alloy, the second alloy and the secondary phase alloy is 0.5 - 10:

100.

7. The preparation method according to claim 1, characterized in that: The powder particle sizes of the first alloy, the second alloy and the secondary phase alloy are all independently 2 - 5 μm.

8. The preparation method according to claim 1, characterized in that: The magnetic field strength used in the orientation pressing process is 1.5 - 2.0 T.

9. The preparation method according to claim 1, characterized in that: The temperature of the sintering treatment is 900 - 1100 °C; and / or, the time of the sintering treatment is 1 - 6 h.

10. The preparation method according to claim 1, characterized in that: The tempering heat treatment includes a primary tempering treatment, a secondary tempering treatment and a tertiary tempering treatment.

11. The preparation method according to claim 10, wherein: The temperature of the primary tempering treatment is 850 - 900 °C, and the time is 1 - 4 h; and / or, the temperature of the secondary tempering treatment is 700 - 800 °C, and the time is 1 - 4 h; and / or, the temperature of the tertiary tempering treatment is 450 - 600 °C, and the time is 1 - 4 h.

12. The preparation method according to claim 1, characterized in that, Including: Melting and preparing a first alloy ingot, a second alloy ingot and a secondary phase alloy ingot according to the element ratios, and then respectively performing hydrogenation crushing and jet milling treatments to obtain a first alloy powder, a second alloy powder and a secondary phase alloy powder.

13. The preparation method according to claim 12, characterized in that: The hydrogen pressure in the hydrogenation crushing process is 0.1 - 0.4 MPa, the hydrogen absorption time is 2 - 5 h, the dehydrogenation temperature is 320 - 500 °C, and the dehydrogenation time is 4 - 10 h; And / or, the hydrogen content in the powders obtained after hydrogenation crushing of the first alloy ingot, the second alloy ingot and the secondary phase alloy ingot is all lower than 1500 ppm; the average particle sizes of the obtained powders are all 100 - 250 μm.

14. A neodymium iron boron magnet with a heavy rare earth segregation distribution prepared by the preparation method according to any one of claims 1-13; preferably, the H of the neodymium iron boron magnet cj +(BH) m > 70.

15. Application of the neodymium iron boron magnet with heavy rare earth segregation distribution according to claim 14 in the fields of wind power generation, new energy vehicles or rail transit.

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