Neodymium iron boron magnet and its preparation method

Abstract

The present invention discloses a neodymium iron boron magnet and a preparation method thereof. The neodymium iron boron magnet of the present invention has the following composition: a Ce b Fe 100‑a‑b‑c‑d‑e M c B d Ti e (I); wherein RE is selected from one or more of La, Pr, Nd, Y, Ho, Dy, Gd, Tb, and Er, and M is Co, Al, Cu, Zr, and Ga; wherein 4≤b≤18, 0.3≤c≤5, 0.8≤d≤0.98, 0.07≤e≤0.2, and 27.5≤a+b≤32.5; wherein a to e represent the weight fractions of each element. The NdFeB magnet of the present invention has a high cerium content, good magnetic properties, and low hardness.

Description

Technical Field

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

[0002] Rare earth permanent magnet neodymium iron boron (Nd-Fe-B) has a high magnetic energy product and is widely used in fields such as machinery, transportation, and medical treatment. The types of rare earth elements in the Nd-Fe-B magnet are mainly Pr, Nd, and Dy, and the content of rare earth elements in the Nd-Fe-B magnet is about 30 wt%, which results in a large amount of Pr, Nd, and Dy being utilized. Due to the symbiotic characteristics of rare earth elements, the production of Nd-Fe-B magnets causes an unbalanced utilization of rare earth resources. The reserves of rare earth element cerium in the earth's crust are much higher than the contents of Pr, Nd, and Dy, and the price is much lower than that of Pr, Nd, and Dy. By partially replacing rare earth elements such as Pr, Nd, and Dy with Ce, not only can the cost be effectively reduced, but also the comprehensive and balanced utilization of rare earth resources can be promoted. However, an increase in the content of Ce in the magnet will reduce the magnetic properties of the magnet and affect the popularization of the Ce-containing neodymium iron boron magnet.

[0003] CN119230231A discloses a high-strength and high-thermal R-T-B rare earth permanent magnet, where R: 28.5 - 34.0 wt%, R is one or more of Nd, Pr, Dy, and Tb, B: 0.85 - 1.1 wt%, Ti: 0.1 - 0.4 wt%, Nb: 0.05 - 0.5 wt%, M: 0.01 - 8.0 wt%, and M is at least one of Al, Cu, Ga, Ni, Zn, Sn, Mn, and Zr. This rare earth permanent magnet does not contain Ce and has a high cost.

[0004] CN119560253A discloses a sintered neodymium iron boron magnet, including: R, the mass content of R is 28 - 33 wt%, R includes Nd and Ce, and optionally includes or does not include at least one of Pr, Dy, Tb, Ho, and Gd; M, the mass content of M is 1.5 - 2.5 wt%, M is selected from at least one of Co, Cu, Ga, Al, Mn, Nb, W, Hf, and Cr; B, the mass content of B is 0.95 - 1.05 wt%; Ti, the mass content of Ti is 0.1 - 0.25 wt%; Fe is the balance; the content of Ce is 0.3 - 5 wt%. This magnet has a low cerium content and high hardness. Summary of the Invention

[0005] In view of this, an object of the present invention is to provide a neodymium iron boron magnet with a high cerium content, good magnetic properties, and low hardness. Another object of the present invention is to provide a preparation method of a neodymium iron boron magnet, which can improve the magnetic properties of the neodymium iron boron magnet with a high cerium content and reduce the hardness.

[0006] The present invention achieves the above object through the following technical solutions.

[0007] On the one hand, the present invention provides a neodymium-iron-boron magnet, characterized in that the neodymium-iron-boron magnet has the following composition:

[0008] RE a Ce b Fe 100-a-b-c-d-e M c B d Ti e (I);

[0009] Wherein, RE is selected from one or more of La, Pr, Nd, Y, Ho, Dy, Gd, Tb, Er, and M is Co, Al, Cu, Zr, and Ga;

[0010] Wherein, 4 ≤ b ≤ 18, 0.3 ≤ c ≤ 5, 0.8 ≤ d ≤ 0.98, 0.07 ≤ e ≤ 0.2, 27.5 ≤ a + b ≤ 32.5;

[0011] Wherein, a to e respectively represent the weight parts of each element.

[0012] For the neodymium-iron-boron magnet according to the present invention, preferably, the grain boundary phase of the neodymium-iron-boron magnet contains REFe2 phase.

[0013] For the neodymium-iron-boron magnet according to the present invention, preferably, the content of RE in the REFe2 phase is 17 - 33 at%, and the content of Fe is 57 - 74 at%.

[0014] For the neodymium-iron-boron magnet according to the present invention, preferably, RE includes Gd, Pr, and Nd; the content of Gd is 0.25 - 0.4 weight parts, the content of Pr is 5.5 - 6.5 weight parts, and the content of Nd is 16 - 19 weight parts.

[0015] For the neodymium-iron-boron magnet according to the present invention, preferably, 6 ≤ b ≤ 15, 0.5 ≤ c ≤ 4, 0.85 ≤ d ≤ 0.95, 0.09 ≤ e ≤ 0.15.

[0016] For the neodymium-iron-boron magnet according to the present invention, preferably, the hardness of the neodymium-iron-boron magnet ≤ 660 HV.

[0017] On the other hand, the present invention provides a preparation method of the above neodymium-iron-boron magnet, comprising the following steps:

[0018] (1) Orient and press the alloy fine powder, and then perform isostatic pressing to obtain a green body;

[0019] (2) Sinter the green body at 1000 - 1100 °C to obtain a sintered body; subject the sintered body to primary tempering at 800 - 980 °C and then secondary tempering at 580 - 700 °C to obtain a neodymium iron boron magnet.

[0020] According to the preparation method of the present invention, preferably, the alloy fine powder is formed by mixing a first alloy fine powder and a second alloy fine powder;

[0021] The first alloy fine powder has a composition as shown in formula (II), and the second alloy fine powder has a composition as shown in formula (III):

[0022] RE a Ce b Fe 100-a-b-c-α-e M c B α Ti e (II)

[0023] RE a Ce b Fe 100-a-b-c-β-e M c B β Ti e (III)

[0024] Wherein, 0.8 ≤ α ≤ 0.9, 0.9 ≤ β ≤ 0.98, and α ≠ β.

[0025] According to the preparation method of the present invention, preferably, the average particle size of the alloy fine powder is 2.5 - 4 μm, the orientation pressing is carried out under the condition that the magnetic field strength is greater than 1.8 T, and the isostatic pressing pressure is 170 - 250 MPa.

[0026] According to the preparation method of the present invention, preferably, it further includes the following steps: melting the raw materials to obtain an alloy liquid; spinning the alloy liquid into flakes to obtain alloy flakes with a thickness of 0.2 - 0.4 mm;

[0027] Hydrogenating the alloy flakes to obtain alloy coarse powder; air-milling the alloy coarse powder to obtain alloy fine powder.

[0028] By regulating the element composition and microstructure of the magnet, the neodymium iron boron magnet with a high cerium content prepared by the present invention has a high coercivity and a low hardness. The magnet of the present invention has a low rare earth content and a low cost. The preparation method of the present invention can effectively improve the microstructure of the magnet, increase the coercivity of the magnet, and reduce the hardness. Description of the Drawings

[0029] Figure 1 It is a scanning electron microscope image of the neodymium iron boron magnet of Example 1.

[0030] Figure 2 It is a scanning electron microscope image of the neodymium iron boron magnet of Example 2.

[0031] Figure 3 SEM image of the neodymium-based boron magnet of Example 3.

[0032] Figure 4 SEM image of the neodymium-iron-boron magnet of Example 4.

[0033] Figure 5 SEM image of the neodymium-iron-boron magnet of Example 5.

[0034] Figure 6 SEM image of the neodymium-iron-boron magnet of Example 6.

[0035] Figure 7 SEM image of the neodymium-iron-boron magnet of Example 7.

[0036] Figure 8 SEM image of the neodymium-iron-boron magnet of Example 8.

[0037] Figure 9 SEM image of the neodymium-iron-boron magnet of Example 9. Detailed implementation manners

[0038] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0039] Neodymium-iron-boron magnet

[0040] The neodymium-iron-boron magnet of the present invention has the following composition:

[0041] RE a Ce b Fe 100-a-b-c-d-e M c B d Ti e (I).

[0042] RE is Gd, Pr and Nd. a is the weight part of RE. 4 ≤ a ≤ 27; preferably, 23.3 ≤ a ≤ 24.5. In some embodiments, 23.8 ≤ a ≤ 24.3.

[0043] The content of Gd is 0.25 - 0.4 weight part; preferably 0.3 - 0.35 weight part; more preferably 0.33 - 0.34 weight part. The content of heavy rare earth elements in the magnet of the present invention is less.

[0044] The content of Pr is 5.5 - 6.5 weight part; preferably 5.74 - 6 weight part; more preferably 5.87 - 5.99 weight part.

[0045] The content of Nd is 16 to 19 parts by weight; preferably 17.23 to 18.5 parts by weight; more preferably 17.6 to 17.97 parts by weight.

[0046] b represents the parts by weight of Ce. 4 ≤ b ≤ 18; preferably, 6.5 ≤ b ≤ 10; more preferably, 7.5 ≤ b ≤ 8.

[0047] 27.5 ≤ a + b ≤ 32.5; preferably, 29 ≤ a + b ≤ 32; more preferably, 30 ≤ a + b ≤ 31.5.

[0048] M is Co, Al, Cu, Zr and Ga. c represents the parts by weight of M. 0.3 ≤ c ≤ 5; preferably, 1 ≤ c ≤ 2; more preferably, 1.5 ≤ c ≤ 1.8.

[0049] The content of Co can be 0.1 to 1.5 parts by weight; preferably 0.3 to 1 part by weight; more preferably 0.6 to 0.8 part by weight.

[0050] The content of Al can be 0.1 to 1.5 parts by weight; preferably 0.3 to 1 part by weight; more preferably 0.5 to 0.7 part by weight.

[0051] The content of Cu can be 0.05 to 0.5 parts by weight; preferably 0.1 to 0.3 part by weight; more preferably 0.2 to 0.25 part by weight.

[0052] The content of Zr can be 0.05 to 0.5 parts by weight; preferably 0.1 to 0.3 part by weight; more preferably 0.2 to 0.25 part by weight.

[0053] The content of Ga can be 0.03 to 0.5 parts by weight; preferably 0.05 to 0.3 part by weight; more preferably 0.1 to 0.2 part by weight.

[0054] d is the parts by weight of B. 0.8 ≤ d ≤ 0.98; preferably, 0.85 ≤ d ≤ 0.95; more preferably, 0.88 ≤ d ≤ 0.91.

[0055] e is the parts by weight of Ti. 0.07 ≤ e ≤ 0.25; preferably, 0.09 ≤ e ≤ 0.15; more preferably, 0.09 ≤ e ≤ 0.1.

[0056] 100 - a - b - c - d - e is the parts by weight of Fe. 65 ≤ 100 - a - b - c - d - e ≤ 67.5; preferably, 66 ≤ 100 - a - b - c - d - e ≤ 67. In some embodiments, 100 - a - b - c - d - e = 66.09. In some other embodiments, 100 - a - b - c - d - e = 66.12.

[0057] The grain boundary phase of the Nd-Fe-B magnet of the present invention contains REFe₂ phase. In some embodiments, the grain boundary phase further contains RE-rich phase.

[0058] In the REFe₂ phase, the content of RE can be 17-33 at%; preferably 25-32 at%.

[0059] In the REFe₂ phase, the content of Fe can be 57-74 at%; preferably 57-63 at%.

[0060] The coercivity of the Nd-Fe-B magnet of the present invention can be ≥10 kOe; it can also be that the coercivity ≥16 kOe; it can also be that the coercivity ≥16.5 kOe. In some embodiments, the coercivity ≥17 kOe.

[0061] The hardness of the Nd-Fe-B magnet of the present invention is ≤660 HV; preferably, the hardness is ≤600 HV; more preferably, the hardness is ≤615 HV. The hardness of the Nd-Fe-B magnet can be ≥580 HV; it can also be ≥570 HV.

[0062] Preparation method of Nd-Fe-B magnet

[0063] The preparation method of the Nd-Fe-B magnet of the present invention includes the following steps: (1) the step of preparing a green body; (2) the step of sintering and tempering. In some embodiments, it also includes the steps of melting and preparing alloy sheets and powder making. Each step is introduced in detail below.

[0064] Step of preparing a green body

[0065] In the present invention, alloy fine powder is orientationally pressed and then isostatically pressed to obtain a green body. The composition of the alloy fine powder is determined according to the composition of the Nd-Fe-B magnet.

[0066] The average particle size of the alloy fine powder can be 2.5-4 μm.

[0067] The orientation pressing can be carried out under the condition that the magnetic field strength is greater than 1.8 T.

[0068] The isostatic pressing pressure can be 170-250 MPa; preferably 190-220 MPa.

[0069] In some embodiments, the alloy fine powder is formed by mixing a first alloy fine powder and a second alloy fine powder.

[0070] The first alloy fine powder has a composition as shown in formula (II): RE a Ce b Fe 100-a-b-c-α-e M c B α Ti e (II)

[0071] The second alloy fine powder has a composition as shown in formula (III): RE a Ce b Fe 100-a-b-c-β-e M c B β Ti e (III)

[0072] In formulas (II) and (III), the meanings and values of a, b, c, and e are as described above and will not be elaborated here. In formulas (II) and (III), α≠β.

[0073] 0.9≤β≤0.98; preferably, 0.9≤β≤0.96; more preferably, 0.92≤β≤0.94.

[0074] 0.8≤α≤0.9; preferably, 0.81≤α≤0.85; more preferably, 0.82≤α≤0.83.

[0075] The mass ratio of the first alloy fine powder to the second alloy fine powder can be 1:(0.5 - 2); preferably 1:(0.8 - 1.5); more preferably 1:(1 - 1.2).

[0076] Steps of sintering and tempering

[0077] In the present invention, the green body is sintered at 1000 - 1100 °C to obtain a sintered body; the sintered body is subjected to primary tempering at 800 - 980 °C and then secondary tempering at 580 - 700 °C to obtain a neodymium iron boron magnet.

[0078] The sintering temperature is 1000 - 1100 °C; preferably 1020 - 1070 °C.

[0079] The sintering time can be 1 - 8 h; preferably 4 - 6 h; more preferably 4 - 5 h.

[0080] Preferably, the primary tempering temperature is 850 - 950 °C; more preferably 880 - 910 °C.

[0081] The primary tempering time can be 1 - 8 h; preferably 2 - 6 h; more preferably 2.5 - 3 h.

[0082] Preferably, the secondary tempering temperature is 600 - 680 °C; more preferably 640 - 650 °C.

[0083] The secondary tempering time can be 1 - 8 h; preferably 3 - 7 h; more preferably 4 - 5 h.

[0084] This helps to form an appropriate microstructure, improve the magnetic properties of the magnet, and reduce the hardness.

[0085] Steps of melting and preparing alloy sheets

[0086] The present invention melts raw materials to obtain an alloy liquid; the alloy liquid is spun into flakes to obtain alloy flakes.

[0087] The thickness of the alloy flakes is 0.2 - 0.4 mm.

[0088] The melting temperature can be 1000 - 1800 °C; preferably, the melting temperature is 1200 - 1500 °C.

[0089] The melting can be carried out under vacuum conditions. Vacuum can refer to a pressure less than or equal to 0.05 MPa; it can also refer to a pressure less than or equal to 0.01 MPa.

[0090] Steps of powder making

[0091] The present invention hydrides the alloy flakes to obtain alloy coarse powder; the alloy coarse powder is milled by a jet mill to obtain alloy fine powder.

[0092] The hydriding includes steps of hydrogen absorption and dehydrogenation.

[0093] The hydrogen absorption can be carried out at 0.08 - 0.11 MPa; preferably, the hydrogen absorption is carried out at 0.09 - 0.1 MPa; more preferably, the hydrogen absorption is carried out at 0.095 - 0.1 MPa.

[0094] The hydrogen absorption time can be 1 - 5 h; preferably, the hydrogen absorption time is 2 - 4 h; more preferably, the hydrogen absorption time is 2 - 3 h.

[0095] The dehydrogenation temperature can be 500 - 650 °C; preferably, the dehydrogenation temperature is 550 - 600 °C; more preferably, the dehydrogenation temperature is 580 - 590 °C.

[0096] The dehydrogenation time can be 5 - 10 h; preferably, the dehydrogenation time is 6 - 9 h; more preferably, the dehydrogenation time is 7 - 8 h.

[0097] The average particle size of the alloy coarse powder can be 0.1 - 3 mm; preferably 0.5 - 2 mm; more preferably 0.5 - 1.5 mm.

[0098] The hydrogen content of the alloy coarse powder can be 800 - 1200 ppm.

[0099] The average particle size of the alloy fine powder can be 2.5 - 4 μm.

[0100] The following introduces the testing method:

[0101] Magnetic properties: Cylindrical specimens are prepared by wire cutting, centerless grinding and surface grinding. At 20 °C, the demagnetization curve of the specimens is tested by a NIM - 62000 permanent magnetic material magnetic property measurement system to obtain magnetic properties such as remanence, coercivity, magnetic energy product, squareness, etc.

[0102] Hardness: The sample has a specification of 15 mm × 15 mm × 4 mm. On its 15 mm × 15 mm surface, a Vickers hardness tester is used with a loading pressure of 0.5 kg and a holding time of 15 s. Ten points are measured for each sample, and the average value is taken.

[0103] Backscattered scanning electron microscope image: Tested using a Quanta 250 FEG scanning electron microscope.

[0104] Examples 1 - 9

[0105] Raw materials are provided according to the composition of the NdFeB magnet. The raw materials are melted in an intermediate frequency induction melting furnace under vacuum (pressure < 0.05 MPa) at a temperature of 1200 - 1500 °C to obtain an alloy liquid. The alloy liquid is spun into flakes to obtain alloy flakes with a thickness of 0.2 - 0.4 mm.

[0106] The alloy flakes are placed in a hydrogen pulverization furnace. The hydrogen pulverization furnace is evacuated and then hydrogen is introduced to 0.098 MPa to allow the alloy flakes to absorb hydrogen for 3 h to obtain hydrogen-absorbed alloy flakes. The hydrogen-absorbed alloy flakes are dehydrogenated at 580 °C for 8 h to obtain alloy coarse powder with an average particle size (SMD) of 0.1 - 3 mm. The alloy coarse powder is milled by a jet mill to obtain alloy fine powder with an average particle size (SMD) of 2.5 - 4 μm.

[0107] The alloy fine powder is oriented and pressed in a magnetic field molding press with an orientation magnetic field greater than 1.8 T, and then isostatically pressed under a pressure of 200 MPa to obtain a green body.

[0108] The green body is sintered at 1060 °C for 5 h to obtain a sintered body. The sintered body is subjected to primary tempering at 910 °C for 3 h and then secondary tempering at 640 °C for 5 h to obtain the NdFeB magnet.

[0109] The hydrogen content in the alloy coarse powder is shown in Table 1. The element composition, magnetic properties, and hardness of the NdFeB magnets in each example are shown in Table 2.

[0110] Three points are randomly selected in the REFe2 phase in the scanning electron microscope image of Example 3, denoted as S1, S2, and S3 respectively. Four points are randomly selected in the REFe2 phase in the scanning electron microscope image of Example 9, denoted as M1, M2, M3, and M4 respectively. The contents of RE and Fe in the above points are shown in Table 3.

[0111]

[0112]

[0113] As can be seen from Examples 1 - 6, when the B content is reduced to a certain value, the coercivity gradually increases, but when the B content further increases, the coercivity will gradually decrease. FromFigures 1-6 It can be seen that the content of the REF2 phase in the grain boundaries of the magnets in Examples 1-6 gradually increases, the coercivity shows a trend of first increasing and then decreasing, and the hardness shows a trend of gradually decreasing. Thus, it can be seen that the content of the REF2 phase has an important influence on the magnetic properties and hardness of the magnets. This may be because as the content of the REF2 phase increases, the isolation effect between grains is enhanced, which effectively weakens the exchange coupling effect between adjacent grains. However, too much REF2 phase will become nucleation points during the demagnetization process of the magnet, resulting in a decrease in coercivity.

[0114] Comparing Example 3 and Example 9, it can be seen that the Ti content and the contents of RE and Fe in REFe2 have an important influence on the magnetic properties and hardness of the magnet. This may be because as the Fe content in REFe2 increases, the exchange coupling effect between the main phase grains is enhanced, resulting in a decrease in coercivity.

[0115] Example 10

[0116] Raw materials are provided according to the composition of the first alloy sheet. The raw materials for forming the first alloy sheet are melted in a medium-frequency induction melting furnace under vacuum (pressure < 0.05 MPa) and at a temperature of 1200-1500 °C to obtain the first alloy liquid. The first alloy liquid is spun into flakes to obtain a first alloy sheet with a thickness of 0.2-0.4 mm.

[0117] Raw materials are provided according to the composition of the second alloy sheet. The raw materials for forming the second alloy sheet are melted in a medium-frequency induction melting furnace under vacuum (pressure < 0.05 MPa) and at a temperature of 1200-1500 °C to obtain the second alloy liquid. The second alloy liquid is spun into flakes to obtain a second alloy sheet with a thickness of 0.2-0.4 mm.

[0118] The first alloy sheet and the second alloy sheet are respectively subjected to hydrogen crushing to obtain a first alloy coarse powder with an average particle size (SMD) of 0.1-3 mm and a second alloy coarse powder with an average particle size (SMD) of 0.1-3 mm. The steps of hydrogen crushing are as follows:

[0119] The alloy sheet is placed in a hydrogen crushing furnace. The hydrogen crushing furnace is evacuated, and then hydrogen is introduced to 0.098 MPa to allow the alloy sheet to absorb hydrogen for 3 h to obtain the hydrogen-absorbed alloy sheet. The hydrogen-absorbed alloy sheet is dehydrogenated at 580 °C for 8 h.

[0120] The first alloy coarse powder and the second alloy coarse powder are respectively subjected to jet milling to obtain a first alloy fine powder with an average particle size (SMD) of 2.5-4 μm and a second alloy fine powder with an average particle size (SMD) of 2.5-4 μm.

[0121] The first alloy fine powder and the second alloy fine powder are mixed in a mass ratio of 1:1 to obtain a mixed alloy fine powder. The mixed alloy fine powder is oriented and pressed in a magnetic field forming press with an orientation magnetic field greater than 1.8 T, and then isostatically pressed at a pressure of 200 MPa to obtain a green body.

[0122] The green body was sintered at 1060°C for 5 hours to obtain a sintered body, and the sintered body was tempered at 910°C for 3 hours and then tempered at 650°C for 5 hours to obtain a NdFeB magnet.

[0123] The element composition, phase content of the first alloy sheet, the second alloy sheet and the NdFeB magnet, and the properties of the NdFeB magnet are shown in Table 4.

[0124]

[0125] It can be seen from Example 4 and Example 10 that the coercive force of the magnet prepared by the dual alloy process is higher than that by the single alloy process, and the hardness is lower than that by the single alloy process.

[0126] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A method for preparing a neodymium iron boron magnet, characterized in that, It includes the following steps: (1) Oriented pressing of the alloy fine powder, and then isostatic pressing to obtain a green body; The alloy fine powder is formed by mixing a first alloy fine powder and a second alloy fine powder; The first alloy fine powder has the composition shown in formula (II), and the second alloy fine powder has the composition shown in formula (III): Wherein, the mass ratio of the first alloy fine powder to the second alloy fine powder is 1:(0.8 - 1.5); (2) Sintering the green body at 1000 - 1100 °C to obtain a sintered body; performing primary tempering on the sintered body at 880 - 910 °C for 2.5 - 3 h, and then performing secondary tempering at 640 - 650 °C for 4 - 5 h to obtain a NdFeB magnet; The NdFeB magnet has the following composition: RE a Ce b Fe 100-a-b-c-d-e M c B d Ti e (I); Wherein, RE is Gd, Pr and Nd, and M is Co, Al, Cu, Zr and Ga; Wherein, 7.5 ≤ b ≤ 10, 1.5 ≤ c ≤ 1.8, 0.88 ≤ d ≤ 0.91, 0.09 ≤ e ≤ 0.15, 30 ≤ a + b ≤ 32; Wherein, a - e respectively represent the weight parts of each element; Wherein, Co is 0.6 - 0.8 weight parts, Al is 0.5 - 0.7 weight parts, Cu is 0.2 - 0.25 weight parts, Zr is 0.2 - 0.25 weight parts, and Ga is 0.1 - 0.2 weight parts; Wherein, the content of Gd is 0.3 - 0.35 weight parts, the content of Pr is 5.74 - 6 weight parts, and the content of Nd is 17.23 - 18.5 weight parts; Wherein, 0.81 ≤ α ≤ 0.85, 0.9 ≤ β ≤ 0.

96.

2. The preparation method according to claim 1, wherein The grain boundary phase of the NdFeB magnet contains REFe₂ phase.

3. The preparation method according to claim 2, characterized in that, The content of RE in the REFe₂ phase is 17 - 33 at%, and the content of Fe is 57 - 74 at%.

4. The preparation method according to claim 1, characterized in that, The hardness of the NdFeB magnet ≤ 660 HV.

5. The preparation method according to claim 1, characterized in that, The average particle size of the alloy fine powder is 2.5 - 4 μm, the oriented pressing is carried out under the condition that the magnetic field strength is greater than 1.8 T, and the isostatic pressing pressure is 170 - 250 MPa.

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