Low-boron high-coercivity neodymium iron boron permanent magnet

Abstract

The invention discloses a low-boron high-coercivity neodymium-iron-boron permanent magnet and a preparation method thereof, and belongs to the technical field of permanent magnets, the preparation method of the permanent magnet comprises the following steps: taking Pr, Fe, Cu and Ga as raw materials, smelting the raw materials through a vacuum melt-spinning furnace to obtain a Pr65Cu25 melt-spinning sheet and a Pr65Fe30Ga5 melt-spinning sheet, grinding the melt-spinning sheet through a three-head grinder to obtain Pr65Cu25 alloy powder and Pr65Fe30Ga5 alloy powder, and sintering the Pr65Cu25 alloy powder and the Pr65Fe30Ga5 alloy powder to obtain the low-boron high-coercivity neodymium-iron-boron permanent magnet. Under the protection of argon or nitrogen, mixing the two to obtain additive phase powder; the low-boron neodymium-iron-boron magnet raw materials are adopted to prepare the main phase alloy powder, and the Pr, Fe, A < l >, Cu and Ga raw materials are adopted to prepare the additive phase powder, the additive phase powder is added into the main phase alloy powder, a lubricating agent is added, and mixing, grinding, compression molding, isostatic pressing treatment, sintering and tempering treatment are conducted to obtain the low-boron neodymium-iron-boron magnet. And the obtained neodymium iron boron permanent magnet has relatively high coercive force and magnetic performance.

Description

Technical Field

[0001] The invention belongs to the technical field of permanent magnets, and in particular relates to a low-boron and high-coercivity neodymium iron boron permanent magnet. Background Art

[0002] With its excellent magnetic properties, sintered NdFeB permanent magnets are widely used in the automotive industry, household appliances, wind power generation, electronic communications and other fields. At present, the remanence Br and maximum magnetic energy product (BH)max of sintered NdFeB permanent magnets are very close to the theoretical values, but their coercive force Hcj can only reach one-third of the theoretical value, which is far from the theoretical value.

[0003] The traditional method to improve the coercivity of NdFeB permanent magnets is to replace part of Nd with heavy rare earth elements (HRE) such as Dy and Tb to form (HRE, Nd)2Fe with higher magnetocrystalline anisotropy field. 14 B phase (HRE = Dy, Tb), but because the heavy metals Dy and Tb are antiferromagnetically coupled with iron atoms, adding heavy rare earths will lead to a decrease in their remanence and magnetic energy product. Moreover, as a non-renewable resource, heavy rare earths are very expensive. If heavy rare earths are continuously added using traditional methods, not only will the cost be greatly increased, but it will also cause a sharp consumption of heavy rare earth resources, which is not conducive to the comprehensive balanced utilization and sustainable development of rare earth resources.

[0004] In this regard, existing technologies mostly use the grain boundary diffusion process to prepare high coercive force NdFeB permanent magnets with low or no heavy rare earths, but the coercive force improvement is not significant enough, and there is still much room for optimization. Summary of the invention

[0005] The object of the present invention is to provide a low-boron and high-coercivity NdFeB permanent magnet, so as to solve the problem that the coercivity of the NdFeB permanent magnet prepared by the existing grain boundary diffusion process still needs to be improved.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A low-boron high-coercivity NdFeB permanent magnet comprises a main phase alloy powder and an additional phase powder, wherein the amount of the additional phase powder is 2%-5% of the mass of the main phase alloy powder.

[0008] The main phase alloy powder is made of low-boron neodymium iron boron magnet raw material.

[0009] The added phase powder is made of Pr, Fe, Cu and Ga raw materials.

[0010] Furthermore, the low-boron NdFeB magnet raw material includes the following components in mass percentage: Pr-Nd or Nd: 30.5%-32.5%, B: 0.85%-0.95%, Al: 0.5%-1.2%, Cu: 0.1%-0.5%, Co: 0.6%-2.0%, Ga: 0.1%-0.6%, Zr: 0.1%-0.3%, and the balance is Fe.

[0011] Furthermore, the added phase powder is composed of Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 The Ga5 alloy powder is composed according to a mass ratio of 1:1-5.

[0012] The method for preparing the above-mentioned low-boron and high-coercivity NdFeB permanent magnet comprises the following steps:

[0013] S1, subjecting the low-boron NdFeB magnet raw material to rapid solidification and spinning to obtain a NdFeB spinning strip with an average thickness of 3±0.5 mm, and subjecting the NdFeB spinning strip to hydrogen crushing treatment to obtain a main phase alloy powder;

[0014] S2, using Pr, Fe, Cu, and Ga as raw materials, Pr is obtained by smelting in a vacuum belt furnace. 65 Cu 25 Belt and Pr 65 Fe 30 The stripped sheet of Ga5 was ground by a three-head grinder to obtain Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 Ga5 alloy powder, and then the two are mixed under argon or nitrogen protection to obtain added phase powder;

[0015] S3, adding the additional phase powder to the main phase alloy powder, adding a lubricant, and mixing in a mixer under argon or nitrogen protection for 90 minutes to obtain a coarse powder, adding the coarse powder to a jet mill, and grinding for 15-20 minutes under a nitrogen atmosphere to obtain a fine powder;

[0016] S4, the fine powder is pressed into a shape under the condition of oxygen content ≤ 500ppm on a press with a magnetic field strength of 1800kA / m and 40-80MPa, and then isostatically pressed to obtain a NdFeB compact;

[0017] S5. The NdFeB compact is subjected to sintering and tempering treatments in sequence to obtain a low-boron and high-coercivity NdFeB permanent magnet.

[0018] Furthermore, in the hydrogen crushing treatment in step S1, the hydrogen absorption pressure is 0.08MPa-0.15MPa, the dehydrogenation temperature is 540°C-590°C, and the average particle size of the main phase alloy powder is 1.5μm-3.5μm.

[0019] Furthermore, the average particle size of the added phase powder in step S2 is 0.06 μm-0.3 μm.

[0020] Furthermore, in step S3, the grinding gas pressure of the jet mill is 0.5MPa-0.7MPa; the classifying wheel speed of the jet mill is 3500rpm-5000rpm, and the amount of lubricant is 0.1%-1% of the total mass of the added phase powder and the phase alloy powder.

[0021] Furthermore, in step S3, the lubricant is zinc stearate and / or calcium stearate.

[0022] Furthermore, in step S4, the pressure of the medium static pressure treatment is 150-200 MPa, and the time is 20 minutes.

[0023] Furthermore, in step S5, the sintering temperature is 850-950° C., and the sintering time is 8-10 h.

[0024] Furthermore, the tempering treatment in step S5 includes: primary tempering and secondary tempering, wherein the primary tempering temperature is 750-900° C., the tempering time is 2-5 hours, and the secondary tempering temperature is 440-550° C., the tempering time is 5-8 hours.

[0025] Beneficial effects of the present invention:

[0026] The present invention provides a low-boron and high-coercivity NdFeB permanent magnet, wherein the main alloy powder is prepared from low-boron NdFeB magnet raw materials, and the additive phase powder is prepared from Pr, Fe, Al, Cu, and Ga raw materials. The obtained NdFeB permanent magnet has high coercivity and magnetic properties;

[0027] Specifically, the main phase alloy powder uses low-boron NdFeB magnet raw material, which can precipitate rare earth iron-rich grain boundary phase with a low melting point during the sintering process, which is beneficial to lowering the sintering temperature and inhibiting the formation of non-ferromagnetic boron-rich phase, and effectively ensures that the magnetic properties of the obtained magnet, such as remanence and maximum magnetic energy product, are excellent;

[0028] The main phase alloy powder does not contain heavy rare earth elements such as terbium and dysprosium, but the added phase powder without heavy rare earth elements is prepared by using Pr, Fe, Al, Cu, and Ga as raw materials. 65 Cu 25 Alloy powder and Pr 65 Fe 30The Ga5 alloy powder works synergistically, reducing the consumption of heavy rare earth while reducing the influence of heavy rare earth on the magnetic properties of the magnet, such as the remanence Br and the maximum magnetic energy product (BH) max. The introduction of more Pr elements in the added phase powder makes the distribution of Pr and Nd elements more uniform. Some Pr elements exchange elements with the main phase grains, so that the main phase crystals form a shell structure, which improves the anisotropy of the main phase grains and the coercive force of the magnet. The introduction of non-magnetic Cu elements reduces the magnetization intensity of the grain boundary phase and enhances the magnetic isolation effect between the grains. , and can also form low-melting-point Nd-Cu and Nd-Fe-Cu eutectic phases with Nd and Fe in the grain boundary phase, promote the formation of thin-layer continuous grain boundary phases between grains, and further improve the coercive force of the magnet; the addition of Ga element promotes the formation of thin-layer grain boundary phases in the microstructure of sintered NdFeB magnets, resulting in an increase in coercive force; Since the composition of Fe element is similar to that of rare earth iron phase in the grain boundary phase, during heat treatment, the magnet does not need to decompose a large amount of main phase to form rare earth iron grain boundary phase, which reduces the consumption of iron element in the main phase grains and maintains a higher remanence and magnetic energy product of the magnet. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] A low-boron high-coercivity NdFeB permanent magnet comprises a main phase alloy powder and an additional phase powder, wherein the amount of the additional phase powder is 2% of the mass of the main phase alloy powder.

[0032] The main phase alloy powder is made of low-boron NdFeB magnet raw material, which includes the following components in mass percentage: Pr-Nd: 31%, B: 0.9%, Al: 0.85%, Cu: 0.25%, Co: 1.2%, Ga: 0.55%, Zr: 0.18%, and the balance is Fe.

[0033] The added phase powder is composed of Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 The Ga5 alloy powder is composed in a mass ratio of 1:1.

[0034] The method for preparing the above-mentioned low-boron and high-coercivity NdFeB permanent magnet comprises the following steps:

[0035] S1. Rapidly solidify the low-boron NdFeB magnet raw material to obtain a NdFeB spinning strip with an average thickness of 3 mm, and subject the NdFeB spinning strip to hydrogen crushing treatment, wherein the hydrogen absorption pressure is 0.08 MPa and the dehydrogenation temperature is 540°C to obtain a main phase alloy powder with an average particle size of 1.5 μm-3.5 μm;

[0036] S2, using Pr, Fe, Cu, and Ga as raw materials, Pr is obtained by smelting in a vacuum belt furnace. 65 Cu 25 Belt and Pr 65 Fe 30 The stripped sheet of Ga5 was ground by a three-head grinder to obtain Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 Ga5 alloy powder, and then mixed the two under nitrogen protection to obtain an added phase powder with an average particle size of 0.06μm-0.3μm;

[0037] S3, adding the additional phase powder to the main phase alloy powder, adding zinc stearate, the amount of zinc stearate is 0.1% of the total mass of the additional phase powder and the phase alloy powder, mixing in a mixer under argon protection for 90 minutes to obtain a coarse powder, adding the coarse powder to a jet mill, the grinding gas pressure of the jet mill is 0.5MPa; the classifying wheel speed of the jet mill is 3500rpm, grinding for 15 minutes under a nitrogen atmosphere to obtain a fine powder;

[0038] S4, the fine powder is pressed into a shape at 40 MPa on a press with a magnetic field strength of 1800 kA / m under the condition of an oxygen content of ≤500 ppm, and then isostatically pressed at a pressure of 150 MPa for 20 min to obtain a NdFeB compact;

[0039] S5. After sintering the NdFeB compact at a temperature of 850°C for 8 hours, perform primary and secondary tempering, wherein the primary tempering temperature is 750°C for 2 hours, and the secondary tempering temperature is 440°C for 5 hours, to obtain a low-boron and high-coercivity NdFeB permanent magnet.

[0040] Example 2

[0041] A low-boron high-coercivity NdFeB permanent magnet comprises a main phase alloy powder and an additional phase powder, wherein the amount of the additional phase powder is 3.5% of the mass of the main phase alloy powder.

[0042] The main phase alloy powder is made of low-boron NdFeB magnet raw material, which includes the following components in mass percentage: Pr-Nd: 32.5%, B: 0.90%, Al: 0.5%, Cu: 0.1%, Co: 0.6%, Ga: 0.1%, Zr: 0.1%, and the balance is Fe.

[0043] The added phase powder is composed of Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 The Ga5 alloy powder is composed in a mass ratio of 1:3.

[0044] The method for preparing the above-mentioned low-boron and high-coercivity NdFeB permanent magnet comprises the following steps:

[0045] S1. Rapidly solidify the low-boron NdFeB magnet raw material to obtain a NdFeB spinning strip with an average thickness of 3 mm. The NdFeB spinning strip is subjected to hydrogen crushing treatment, wherein the hydrogen absorption pressure is 0.12 MPa and the dehydrogenation temperature is 570°C to obtain a main phase alloy powder with an average particle size of 1.5 μm-3.5 μm.

[0046] S2, using Pr, Fe, Cu, and Ga as raw materials, Pr is obtained by smelting in a vacuum belt furnace. 65 Cu 25 Belt and Pr 65 Fe 30 The stripped sheet of Ga5 was ground by a three-head grinder to obtain Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 Ga5 alloy powder, and then mixed the two under argon protection to obtain an added phase powder with an average particle size of 0.06μm-0.3μm;

[0047] S3, adding the additional phase powder to the main phase alloy powder, adding calcium stearate, the amount of calcium stearate is 0.5% of the total mass of the additional phase powder and the phase alloy powder, mixing in a mixer under argon protection for 90 minutes to obtain a coarse powder, adding the coarse powder to a jet mill, the grinding gas pressure of the jet mill is 0.6MPa; the classifying wheel speed of the jet mill is 4000rpm, grinding for 18 minutes under a nitrogen atmosphere to obtain a fine powder;

[0048] S4, the fine powder is pressed into a shape at 60 MPa on a press with a magnetic field strength of 1800 kA / m under the condition of an oxygen content of ≤500 ppm, and then isostatically pressed at a pressure of 180 MPa for 20 min to obtain a NdFeB compact;

[0049] S5. After sintering the NdFeB compact at a temperature of 900°C for 9 hours, perform primary and secondary tempering, wherein the primary tempering temperature is 800°C for 4 hours, and the secondary tempering temperature is 500°C for 6 hours, to obtain a NdFeB permanent magnet with low boron and high coercivity.

[0050] Example 3

[0051] A low-boron high-coercivity NdFeB permanent magnet comprises a main phase alloy powder and an additional phase powder, wherein the amount of the additional phase powder is 5% of the mass of the main phase alloy powder.

[0052] The main phase alloy powder is made of low-boron NdFeB magnet raw material, which includes the following components in mass percentage: Nd: 30.5%, B: 0.85%, Al: 0.5%, Cu: 0.5%, Co: 1.0%, Ga: 0.3%, Zr: 0.2%, and the balance is Fe.

[0053] The added phase powder is composed of Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 The Ga5 alloy powder is composed in a mass ratio of 1:5.

[0054] The method for preparing the above-mentioned low-boron and high-coercivity NdFeB permanent magnet comprises the following steps:

[0055] S1. Rapidly solidify the low-boron NdFeB magnet raw material to obtain a NdFeB spinning strip with an average thickness of 3.5 mm. The NdFeB spinning strip is subjected to hydrogen crushing treatment, wherein the hydrogen absorption pressure is 0.15 MPa and the dehydrogenation temperature is 590° C. to obtain a main phase alloy powder with an average particle size of 1.5 μm-3.5 μm.

[0056] S2, using Pr, Fe, Cu, and Ga as raw materials, Pr is obtained by smelting in a vacuum belt furnace. 65 Cu 25 Belt and Pr 65 Fe 30 The stripped sheet of Ga5 was ground by a three-head grinder to obtain Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 Ga5 alloy powder, and then mixed the two under nitrogen protection to obtain an added phase powder with an average particle size of 0.06μm-0.3μm;

[0057] S3, adding the additional phase powder to the main phase alloy powder, adding calcium stearate, the amount of calcium stearate is 1% of the total mass of the additional phase powder and the phase alloy powder, under argon or nitrogen protection, mixing in a mixer for 90 minutes to obtain a coarse powder, adding the coarse powder to a jet mill, the grinding gas pressure of the jet mill is 0.7MPa; the classifying wheel speed of the jet mill is 5000rpm, grinding for 20 minutes under a nitrogen atmosphere to obtain a fine powder;

[0058] S4, the fine powder is pressed into shape at 80 MPa on a press with a magnetic field strength of 1800 kA / m under the condition of an oxygen content of ≤500 ppm, and then isostatically pressed at a pressure of 200 MPa for 20 min to obtain a NdFeB compact;

[0059] S5. After sintering the NdFeB compact at a temperature of 950°C for 10 hours, perform primary and secondary tempering, wherein the primary tempering temperature is 900°C for 5 hours, and the secondary tempering temperature is 550°C for 8 hours, to obtain a low-boron and high-coercivity NdFeB permanent magnet.

[0060] Comparative Example 1

[0061] A low-boron high-coercivity NdFeB permanent magnet comprises a main phase alloy powder and an additional phase powder, wherein the amount of the additional phase powder is 2% of the mass of the main phase alloy powder.

[0062] The main phase alloy powder is made of low-boron NdFeB magnet raw material, and the low-boron NdFeB magnet raw material is the same as that in Example 1.

[0063] The added phase powder is Pr 65 Cu 25 alloy powder.

[0064] The method for preparing the low-boron and high-coercivity NdFeB permanent magnet is different from that in Example 1 only in the preparation process of the added phase powder. The specific preparation process of the added phase powder is as follows:

[0065] Pr and Cu are used as raw materials and Pr is obtained by smelting in a vacuum belt furnace. 65 Cu 25 The strips were then ground with a three-head grinder to obtain Pr with an average particle size of 0.06 μm-0.3 μm. 65 Cu 25 Alloy powder, that is, added phase powder;

[0066] The remaining raw materials and preparation process are the same as in Example 1.

[0067] Comparative Example 2

[0068] A low-boron high-coercivity NdFeB permanent magnet comprises a main phase alloy powder and an additional phase powder, wherein the amount of the additional phase powder is 2% of the mass of the main phase alloy powder.

[0069] The main phase alloy powder is made of low-boron NdFeB magnet raw material, and the low-boron NdFeB magnet raw material is the same as that in Example 1.

[0070] The added phase powder is Pr 65 Cu 25 alloy powder.

[0071] The method for preparing the low-boron and high-coercivity NdFeB permanent magnet is different from that in Example 1 only in the preparation process of the added phase powder. The specific preparation process of the added phase powder is as follows:

[0072] Pr and Cu are used as raw materials and Pr is obtained by smelting in a vacuum belt furnace. 65 Cu 25 The strips were then ground with a three-head grinder to obtain Pr with an average particle size of 0.06 μm-0.3 μm. 65 Cu 25 Alloy powder, that is, added phase powder;

[0073] The remaining raw materials and preparation process are the same as in Example 1.

[0074] The NdFeB permanent magnets obtained in Examples 4 to 6 and Comparative Examples 1 to 2 were processed into cylinders, respectively, and the residual magnetic induction intensity Br, the intrinsic coercive force Hcj and the maximum magnetic energy product (BH)max(MGOe) were tested according to the method specified in GB / T 3217-2013;

[0075] The results are shown in Table 1:

[0076] Table 1

[0077]

[0078]

[0079] It can be seen from the data recorded in Table 1 that compared with the NdFeB permanent magnets obtained in Comparative Examples 1 and 2, the intrinsic coercive force of the NdFeB permanent magnets obtained in Examples 4, 5 and 6 is significantly improved, while the remanence and maximum magnetic energy product do not change much.

[0080] It should be noted that, in this article, relational terms such as first and second, etc. 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.

[0081] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low-boron and high-coercivity NdFeB permanent magnet, characterized in that: It comprises a main phase alloy powder and an additional phase powder, wherein the amount of the additional phase powder is 2%-5% of the mass of the main phase alloy powder; The main phase alloy powder is made of low-boron NdFeB magnet raw material; The added phase powder is made of Pr, Fe, Cu and Ga raw materials.

2. The low-boron and high-coercivity NdFeB permanent magnet according to claim 1, characterized in that: The low-boron NdFeB magnet raw material includes the following components in mass percentage: Pr-Nd or Nd: 30.5%-32.5%, B: 0.85%-0.95%, Al: 0.5%-1.2%, Cu: 0.1%-0.5%, Co: 0.6%-2.0%, Ga: 0.1%-0.6%, Zr: 0.1%-0.3%, and the balance is Fe.

3. The low-boron and high-coercivity NdFeB permanent magnet according to claim 1, characterized in that: The added phase powder is composed of Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 The Ga5 alloy powder is composed according to a mass ratio of 1:1-5.

4. A method for preparing a low-boron and high-coercivity NdFeB permanent magnet according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, subjecting the low-boron NdFeB magnet raw material to rapid solidification and spinning to obtain a NdFeB spinning strip with an average thickness of 3±0.5 mm, and subjecting the NdFeB spinning strip to hydrogen crushing treatment to obtain a main phase alloy powder; S2, using Pr, Fe, Cu, and Ga as raw materials, Pr is obtained by smelting in a vacuum belt furnace 65 Cu 25 Belt and Pr 65 Fe 30 The stripped piece of Ga5 was ground by a three-head grinder to obtain Pr 65 Cu 25 Alloy powder and Pr 65 Fe 30 Ga5 alloy powder, and then the two are mixed under argon or nitrogen protection to obtain an added phase powder; S3, adding the additional phase powder to the main phase alloy powder, adding a lubricant, and mixing in a mixer under argon or nitrogen protection for 90 minutes to obtain a coarse powder, adding the coarse powder to a jet mill, and grinding for 15-20 minutes under a nitrogen atmosphere to obtain a fine powder; S4, the fine powder is pressed into a shape under the condition of oxygen content ≤ 500ppm on a press with a magnetic field strength of 1800kA / m and 40-80MPa, and then isostatically pressed to obtain a NdFeB compact; S5. The NdFeB compact is subjected to sintering and tempering treatments in sequence to obtain a low-boron and high-coercivity NdFeB permanent magnet.

5. The method for preparing a low-boron and high-coercivity NdFeB permanent magnet according to claim 4, characterized in that: In the hydrogen crushing treatment in step S1, the hydrogen absorption pressure is 0.08MPa-0.15MPa, the dehydrogenation temperature is 540°C-590°C, and the average particle size of the main phase alloy powder is 1.5μm-3.5μm.

6. The method for preparing a low-boron and high-coercivity NdFeB permanent magnet according to claim 4, characterized in that: The average particle size of the added phase powder in step S2 is 0.06 μm-0.3 μm.

7. The method for preparing a low-boron and high-coercivity NdFeB permanent magnet according to claim 4, characterized in that: In step S3, the grinding gas pressure of the jet mill is 0.5MPa-0.7MPa; the classifying wheel speed of the jet mill is 3500rpm-5000rpm, and the amount of lubricant is 0.1%-1% of the total mass of the added phase powder and the phase alloy powder.

8. The method for preparing a low-boron and high-coercivity NdFeB permanent magnet according to claim 4, characterized in that: The medium pressure treatment in step S4 is performed at a pressure of 150-200 MPa for 20 minutes.

9. The method for preparing a low-boron and high-coercivity NdFeB permanent magnet according to claim 4, characterized in that: In step S5, the sintering temperature is 850-950° C. and the sintering time is 8-10 hours.

10. The method for preparing a low-boron and high-coercivity NdFeB permanent magnet according to claim 4, characterized in that: The tempering treatment in step S5 includes: primary tempering and secondary tempering, wherein the primary tempering temperature is 750-900° C., the tempering time is 2-5 hours, and the secondary tempering temperature is 440-550° C., the tempering time is 5-8 hours.

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