Sintered r-fe-b permanent magnet, method for producing the same, and use thereof

Abstract

The application discloses a sintered R-Fe-B permanent magnet and a preparation method and application thereof. The permanent magnet formula adopts specific proportions of R, Cu, Ti, Zr and B, controls the oxygen content of the product at different stages, adjusts the optimized distribution of the face-centered cubic structure and the close-packed hexagonal structure, and then carries out targeted intervention on the formation stages of the Ga-rich phase and the Ga-lean phase, so that the reasonable distribution of the Ga-rich phase and the Ga-lean phase is ensured, and the synchronous improvement of the resistivity and the magnetic performance is realized.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials and their preparation technology, and particularly relates to a sintered R-Fe-B permanent magnet, its preparation method and application. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets are widely used in permanent magnet motors due to their high remanence, high coercivity, and high energy product. In recent years, the rapid development of the high-end application market for rare-earth permanent magnet materials has also driven innovation in NdFeB magnet manufacturing technology, especially with increasingly stringent requirements for long-term service at high operating temperatures. Intrinsic coercivity (Hcj) is a crucial indicator of a NdFeB magnet's resistance to thermal demagnetization. Theoretically, NdFeB magnets should possess high coercivity to withstand demagnetization at high operating temperatures. Simultaneously, the requirements for the magnet's bending strength, resistivity, and other mechanical properties are also gradually increasing.

[0003] In recent years, optimizing the grain boundary phase structure has become a research hotspot for improving the magnetic properties of NdFeB magnets. By optimizing the grain boundary phase, non-ferromagnetic phases are formed at the grain boundaries, thereby weakening the exchange coupling between hard magnetic grains and enhancing the magnetic properties of NdFeB magnets. Patent document CN114255951A uses a main-auxiliary dual alloy method to control the formation of Ga-rich and Cu-rich phases at the grain boundaries, thereby improving the coercivity of the magnet. However, this method requires control of the formulation ratio of the dual alloy, the process operation is relatively complex, and there is no effective control over the Ga-rich phase, making it difficult to obtain high-performance products with specific ratio characteristics. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a sintered R-Fe-B permanent magnet, wherein the sintered R-Fe-B permanent magnet comprises a main phase grain and a grain boundary phase; the composition of the main phase grain includes R2T. 14 B; The grain boundary phase is located between the main phase grains, and the grain boundary phase includes Ga-rich phase and Ga-poor phase; wherein...

[0005] The Ga-rich phase includes R, Fe, Ga and M elements, wherein, by mass ratio, R accounts for 50-75 wt%, Fe accounts for 5-20 wt%, Ga accounts for 5-25 wt%, and M accounts for 1-6 wt%.

[0006] The Ga-depleted phase includes R, Fe, Ga and M elements, wherein, by mass ratio, R accounts for 30-60 wt%, Fe accounts for 15-35 wt%, Ga accounts for 0.01-1 wt%, and M accounts for 15-35 wt%.

[0007] R represents a rare earth element; M is selected from one or more of Al, Zr, Ti, Cu, Co, Mn, and Nb.

[0008] According to an embodiment of the present invention, R is a rare earth element, which includes at least Nd. Further, R may also include at least one rare earth element selected from the following: Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc.

[0009] According to an embodiment of the present invention, the Ga-rich phase is composed of R, Fe, Ga and M elements, wherein, by mass ratio, R accounts for 50-75 wt%, Fe accounts for 5-20 wt%, Ga accounts for 5-25 wt%, and M accounts for 1-6 wt%.

[0010] According to an embodiment of the present invention, the Ga-depleted phase is composed of R, Fe, Ga and M, wherein, by mass ratio, R accounts for 30-60 wt%, Fe accounts for 15-35 wt%, Ga accounts for 0.01-1 wt%, and M accounts for 15-35 wt%.

[0011] According to an embodiment of the present invention, in the Ga-rich phase, the proportion of R by mass ratio is 60 to 72 wt%, for example, 60 wt%, 62 wt%, 64 wt%, 66 wt%, 68 wt%, 70 wt%, 71 wt%, or 72 wt%.

[0012] According to an embodiment of the present invention, in the Ga-rich phase, the Fe content is 10 to 18 wt% by mass, for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, or 18 wt%.

[0013] According to an embodiment of the present invention, in the Ga-rich phase, the proportion of Ga by mass is 8 to 20 wt%, for example, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 17 wt%, 18 wt%, or 20 wt%.

[0014] According to an embodiment of the present invention, in the Ga-rich phase, the proportion of M by mass is 2 to 6 wt%; for example, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or 6 wt%.

[0015] According to an embodiment of the present invention, in the Ga-depleted phase, the proportion of R by mass ratio is 40 to 54 wt%, for example, 40 wt%, 42 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 53 wt%, or 54 wt%.

[0016] According to an embodiment of the present invention, in the Ga-depleted phase, the Fe content is 20-34 wt% by mass, for example, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 27 wt%, 28 wt%, 30 wt%, 32 wt%, or 34 wt%.

[0017] According to an embodiment of the present invention, in the Ga-depleted phase, the proportion of Ga by mass is 0.05 to 0.9 wt%, for example, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, or 0.9 wt%.

[0018] According to an embodiment of the present invention, in the Ga-depleted phase, the proportion of M by mass ratio is 15 to 32 wt%, for example, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 20 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, 32 wt%, or 34 wt%.

[0019] According to an embodiment of the present invention, the area ratio of the Ga-rich phase to all grain boundary phase regions is X1, and the area ratio of the Ga-poor phase to all grain boundary phase regions is X2, wherein...

[0020] 13% ≤ X1 ≤ 30%, preferably 18% ≤ X1 ≤ 28%, for example, X1 is 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27% or 28%;

[0021] 60% ≤ X2 ≤ 80%, preferably 64% ≤ X2 ≤ 79%, for example, X2 is 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78% or 79%;

[0022] And 0.20≤X1 / X2≤0.50, for example, X1 / X2 is 0.20, 0.25, 0.30, 0.35, 0.40, 0.45 or 0.50.

[0023] According to an embodiment of the present invention, the sintered R-Fe-B permanent magnet, based on a mass ratio of 100%, comprises the following components:

[0024] R: 27-33 wt%, R is a rare earth element, which includes at least Nd and at least one selected from the following rare earth elements: Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc;

[0025] B: 0.9–1.3 wt%;

[0026] Ga: 0.2–0.5 wt%;

[0027] M: 0.45–3 wt%; selected from one or more of Al, Zr, Ti, Cu, Co, Mn, and Nb.

[0028] The remainder consists of Fe and impurities. Preferably, the impurities are unavoidable impurities.

[0029] According to an embodiment of the present invention, M includes at least Cu, and may also be selected from at least one of Al, Ga, Zr, Ti, Nb, and Mn;

[0030] Furthermore, the Cu content in the permanent magnet is 0.35–1.1 wt%, preferably 0.35–1.0 wt%.

[0031] According to an embodiment of the present invention, M further includes at least one of Zr or Ti, and the content of Zr or Ti in the permanent magnet is 0.08 to 0.15 wt%, for example, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.14 wt%, or 0.15 wt%.

[0032] According to an embodiment of the present invention, in the permanent magnet, the mass percentage content of R, based on the mass of the permanent magnet, is 28.50 wt% or more and 32.50 wt% or less, for example, 29.0 wt%, 29.5 wt%, 30.0 wt%, 30.5 wt%, 31.0 wt%, 31.5 wt%, 32.0 wt%, or 32.5 wt%.

[0033] According to an embodiment of the present invention, in the permanent magnet, the mass percentage content of B, based on the mass of the permanent magnet, is 0.90 wt% or more and 1 wt% or less; for example, 0.90 wt%, 0.95 wt%, or 1 wt%.

[0034] According to an embodiment of the present invention, in the permanent magnet, the mass percentage content of Ga, based on the mass of the permanent magnet, is 0.25 to 0.35 wt%, for example, 0.25 wt%, 0.28 wt%, 0.3 wt%, 0.32 wt%, or 0.35 wt%.

[0035] According to an embodiment of the present invention, the content of M in the permanent magnet, based on the mass of the permanent magnet, is, for example, 0.45 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, or 3.0 wt%.

[0036] According to an embodiment of the present invention, the sintered R-Fe-B permanent magnet satisfies the following relations (1) and (2):

[0037] lg[R]+lg([Cu]+[Zr]+[Ti])-1.2*[B]≥0; (1)

[0038] 0.45≤[Cu]+[Zr]+[Ti]≤0.7; (2)

[0039] Where [R], [Cu], [Zr], [Ti] and [B] are the mass percentages of R, Cu, Zr, Ti and B, respectively.

[0040] According to an embodiment of the present invention, [Cu]+[Zr]+[Ti] is 0.45, 0.5, 0.55, 0.6, 0.65 or 0.7.

[0041] This invention also provides a method for preparing the above-mentioned sintered NdFeB permanent magnet, the method comprising:

[0042] The raw materials for preparing the sintered NdFeB permanent magnets are sequentially processed through a melting process, a powder preparation process, a molding process, and a heat treatment process to obtain the sintered NdFeB permanent magnets.

[0043] According to an embodiment of the present invention, in the smelting process, the rare earth raw material R (e.g., PrNd) has an oxygen content of a, the Fe has an oxygen content of b, and the BFe has an oxygen content of c.

[0044] a, b, and c satisfy the following conditions: a < 200 ppm, b < 250 ppm, and c < 450 ppm.

[0045] Preferably, a is 40 to 180 ppm, and for example, 50 to 150 ppm;

[0046] Preferably, b is 40–240 ppm, and for example, 70–220 ppm;

[0047] Preferably, c is 80 to 440 ppm, and for example, 120 to 300 ppm.

[0048] According to an embodiment of the present invention, the smelting process can be carried out using methods known in the art, such as the rapid solidification and spinning method to produce alloy flakes. Exemplarily, the specific steps of preparing alloy flakes in the smelting process are as follows: each raw material is heated to 1300–1600°C by electromagnetic induction to melt it, and then the molten alloy is poured onto a quenching roller (preferably a polished quenching roller), and after cooling, alloy flakes are obtained.

[0049] According to an embodiment of the present invention, the powder-making process includes hydrogen embrittlement, intermediate grinding, and / or air jet milling, and air jet milling powder is obtained after the powder-making process. In the present invention, the hydrogen embrittlement, intermediate grinding, and / or air jet milling can be performed using methods known in the art, as long as the air jet milling powder can be obtained.

[0050] According to an embodiment of the present invention, the oxygen content V during the air jet milling process is 25-150 ppm, preferably 40-140 ppm. Preferably, oxygenation can be introduced during the air jet milling process. The oxygenation method is not limited and can be oxygen-containing gas. Examples include the introduction of oxygen, air, or compressed air alone, a mixture of oxygen and argon, or a mixture of oxygen and nitrogen, etc., as long as the oxygen content in the air jet mill grinding chamber is maintained within the range of 25-150 ppm.

[0051] According to an embodiment of the present invention, the temperature during the air jet milling process is 30-40°C, for example, 30°C, 32°C, 34°C, 36°C, 38°C or 40°C.

[0052] Preferably, an antioxidant and / or lubricant may be added to the air-jet milled powder obtained after the milling process. The antioxidant and / or lubricant may be any antioxidant and / or lubricant known in the art, and no specific limitation is made in this invention. Alternatively, the antioxidant and / or lubricant may be selected, for example, from fatty acid esters. Further, the amount of the antioxidant and / or lubricant added is 0.1–1 wt% of the air-jet milled powder, for example, 0.1–0.5 wt%.

[0053] According to an embodiment of the present invention, the oxygen content of the alloy flakes prepared in the smelting process is x (wt%), the oxygen content of the air-jet milled powder after the air-jet milling process is y (wt%), and the particle size D50 of the air-jet milled powder is z (μm), and the three should satisfy the following relationships (3)-(6):

[0054] 0.12≥(y-2x)*z≥0.04; (3)

[0055] 0.025 ≥ x ≥ 0.003; (4)

[0056] 0.09≥y≥0.02; (5)

[0057] 4.5≥z≥2.3; (6).

[0058] If the present invention does not satisfy the range of the above relationships (3)-(6), then Ga-rich phase and Ga-poor phase cannot be formed or the proportion of Ga-rich phase and Ga-poor phase formed is not within the limit range, which will ultimately affect the magnetic properties and resistivity of the product.

[0059] According to an embodiment of the present invention, the molding process can dry-form the mixture (or air-jet mill): for example, filling the mixture into a mold disposed in a magnetic field and applying pressure to shape the mixture into a molded body. In this case, by applying a magnetic field while molding, the mixture can be molded with its crystallization axis oriented in a specific direction. Molding aids known in the art can be added as needed during the molding step. Preferably, the pressure applied can be 8 MPa or more and 300 MPa or less; the applied magnetic field can be a static magnetic field and / or a pulsed magnetic field, with a magnetic field strength of 2 to 5 T. Alternatively, wet molding can also be used: for example, molding a slurry in which the mixture is dispersed in a solvent such as oil to obtain a molded body.

[0060] Those skilled in the art will understand that there are no particular limitations on the specific shape of the molded body, and it can be adjusted according to the application conditions of the permanent magnet. For example, the molded body can be a cuboid, a flat plate, a column, a ring, or a C-shape.

[0061] According to an embodiment of the present invention, the conditions of the heat treatment process include: a sintering temperature of 900-1100°C (e.g., 1000°C) and a sintering time of 2-8 hours (e.g., 3 hours, 4 hours, 5 hours, 6 hours, 7 hours).

[0062] According to an embodiment of the present invention, a diffusion process may optionally be performed after the heat treatment process.

[0063] According to an embodiment of the present invention, in the diffusion process, a diffusion source is used to diffuse the product after the heat treatment process. Preferably, the diffusion source includes a heavy rare earth element RH, which is selected from at least one of gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium, and is preferably terbium.

[0064] Preferably, the mass content of heavy rare earth elements in the diffusion source is not less than 60%, and more preferably not less than 70%.

[0065] According to an embodiment of the present invention, in the diffusion process, a diffusion source is coated on the surface of the product from the heat treatment process for diffusion treatment.

[0066] Preferably, the diffusion process includes a first diffusion process and a second diffusion process;

[0067] The first diffusion treatment can be carried out at a holding temperature of 800℃ to 1000℃ for more than 2 hours and less than 40 hours; the rate of heating to the holding temperature can be more than 5℃ / min and less than 50℃ / min.

[0068] The second diffusion treatment can be carried out at a holding temperature of 450℃ to 650℃ for 2 hours to 20 hours; the rate of heating to the holding temperature can be 5℃ / min to 50℃ / min.

[0069] The present invention also provides the application of the above-mentioned permanent magnet in the fields of motors, loudspeakers, magnetic separators, computer disk drives, magnetic resonance imaging equipment, etc., preferably as the application of motor rotor magnets in motors.

[0070] Beneficial effects

[0071] The grain boundary phase of the present invention includes binary grain boundaries and triangular grain boundaries; wherein, the binary grain boundary is located between any two main phase grains, and the triangular grain boundary is located between any three or more main phase grains.

[0072] This invention prepares alloy flakes with different oxygen contents by controlling the oxygen content in the raw materials. It is speculated that alloy flakes with lower oxygen contents can provide a low-oxygen environment to promote the formation of face-centered cubic (FCC) structures within the grain boundary phase. Under conventional processes, a large proportion of the FCC structure within the grain boundary phase is located at two grain boundaries, with only a small portion existing at triangular grain boundaries. Simultaneously, due to the different lattice constants of the FCC and hexagonal close-packed (HPC) structures, Ga elements tend to concentrate in the FCC structure, resulting in a high Ga content at two grain boundaries. By introducing oxygen-containing gas into the air jet mill and controlling the oxygen content in the mill equipment within the range of 25–150 ppm, within the oxygen content range of this invention, the proportion of self-formed HPC structures in the triangular grain boundaries, or the proportion of HPC structures transformed from FCC structures, increases. This causes Ga elements in the triangular grain boundaries to transfer to the FCC structure at the two grain boundaries, promoting the formation of a Ga-depleted phase in the triangular grain boundaries. This invention combines particle size and formulation control to achieve different Ga content distributions in different regions of the product, forming distinct grain boundary phases with both Ga-rich and Ga-poor phase regions. It is important to note that while adding oxide powder can improve the distribution of the Ga-rich phase, oxide powder (e.g., metal oxide powder) cannot stably provide an oxygen-containing atmosphere, hindering the recombination of the close-packed hexagonal structure within the triangular grain boundaries. This is detrimental to the control of the Ga-poor phase and results in suboptimal mechanical properties (such as flexural strength). Therefore, adding oxide powder as an oxygenation process is not recommended.

[0073] Under the synergistic control of the raw material's R, Cu, Zr, Ti, and B satisfying the relationship lg[R]+lg([Cu]+[Zr]+[Ti])-1.2*[B]≥0, and the oxygen content of the raw material, the area ratio of Ga-rich phase to grain boundary phase is kept between 13% and X1≤30%, which significantly reduces the grain boundary energy with the main phase and thus improves the magnetic properties of the product. When the Ga-rich phase region at the grain boundary is too large (e.g., greater than 30%), the excess Ga element will enter the main phase, forming Nd2(Fe2+)2. 1-x Ga x ) 14 B. The molecular magnetic moment decreases, the magnetic properties decrease, and the lattice constant C increases, which in turn causes a change in the internal stress state of the crystal. Macroscopically, this manifests as a certain deterioration in the bending strength of the product.

[0074] This invention regulates the proportion of Ga-depleted phase within the range of 60%-80%, thereby improving the resistivity of the product by influencing interatomic interactions and electronic state distribution. During the air jet milling process, controlling the oxygen content in the milling equipment within the range of 25-150 ppm allows for the regulation of Ga-depleted phase formation at grain boundaries while reducing oxide formation. When the oxygen content of the air-jet milled powder is within the range of 0.02-0.09 wt%, the permanent magnet exhibits excellent mechanical properties (i.e., flexural strength). Excessive oxygen atmosphere during the air jet milling stage leads to the formation of a large amount of oxides at grain boundaries, reducing the bonding force between the grain boundary phase and the main phase, resulting in deterioration of the product's mechanical properties (flexural strength). By precisely controlling the area ratio of the Ga-depleted phase region to the grain boundary phase to 60% ≤ X2 ≤ 80%, and controlling the area ratio of the Ga-rich phase to the Ga-depleted phase to 0.20 ≤ X1 / X2 ≤ 0.50, it is possible to achieve both improved resistivity and enhanced magnet material properties.

[0075] The permanent magnet formulation of this invention uses a specific ratio of R, Cu, Ti, Zr, and B to control the oxygen content of the product at different stages, thereby adjusting the optimized distribution of face-centered cubic and close-packed hexagonal structures. This allows for targeted intervention in the formation stages of Ga-rich and Ga-poor phases, ensuring a reasonable distribution of Ga-rich and Ga-poor phases and achieving a simultaneous improvement in resistivity and magnetic properties. Attached Figure Description

[0076] Figure 1 This is a transmission electron microscope (TEM) image of the Ga-rich phase of the permanent magnet in Example 1;

[0077] Figure 2 This is a transmission electron microscope (TEM) image of the Ga-depleted phase of the permanent magnet in Example 1. Detailed Implementation

[0078] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0079] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0080] Test method:

[0081] The sintered NdFeB permanent magnets prepared in Examples 1-4 and Comparative Examples 1-6 of this invention were tested for magnetic properties, oxygen content, bending strength, and resistivity. The testing equipment and methods used are as follows:

[0082] Magnetic performance testing: NIM-62000 magnetic analyzer from the National Institute of Metrology, China, 7-5-5mm standard test;

[0083] Oxygen content: Analyzed using an oxygen, nitrogen, and hydrogen analyzer from Steel Research Institute Nake.

[0084] Bending strength: Universal mechanical testing machine, 35-5-5mm standard test;

[0085] Resistivity: Resistivity meter;

[0086] Area ratio calculation: The composition of the grain boundary phase was analyzed at high magnification using a JEOL-2010F scanning transmission microscope, followed by in-situ observation at low magnification. The proportion of the grain boundary phases at different contrasts was analyzed using Image-Pro Plus software.

[0087] Example 1

[0088] Sintered NdFeB magnets were prepared using the following method:

[0089] (1) The preparation method of alloy flakes is as follows: Prepare raw materials according to the composition table of neodymium iron boron material in Table 1 (all units are wt%). The oxygen content of the selected PrNd, Fe and BFe raw materials is detailed in Table 2. The raw materials are heated to 1400℃ by electromagnetic induction until they melt and then held for 10 min. Then they are poured onto the surface of the quenching roller and cooled to obtain Re-Fe-B alloy flakes. A small amount of alloy flakes are taken to test the oxygen content x.

[0090] (2) The alloy flakes obtained above are subjected to hydrogen absorption treatment, and then ground in an air jet mill with an oxygen content of 44ppm (oxygen is introduced in the way) (the temperature of the air jet mill is 31℃) to obtain air jet mill powder with D50 = 3.2μm. The air jet mill powder and antioxidant fatty acid ester are mixed evenly at a mass ratio of 99.95:0.05 to obtain a uniformly mixed alloy powder.

[0091] (3) The above alloy powder is filled into the molding die. The magnetic field orientation molding specifically includes: orientation molding in a magnetic field with a strength of 2T, followed by cold isostatic pressing at 170MPa*10s to obtain the green blank.

[0092] (4) Place the pressed green blank in a vacuum sintering furnace for sintering, and control the sintering temperature at 1070℃ for 4 hours.

[0093] (5) The sintered compact is sputtered with magnetron sputtering to arrange Tb onto the surface of the substrate and then subjected to diffusion heat treatment. The diffusion heat treatment process includes: a first-stage heat treatment at a diffusion temperature of 920°C for 30 hours; followed by a second-stage heat treatment at 510°C for 10 hours to obtain the rare earth permanent magnet of this embodiment.

[0094] Figure 1 These are images of grain boundary phases taken under high magnification using a transmission electron microscope. The composition of the Ga-rich phase is determined to be R. 65.9 Fe 15.2 Co 2.8 Cu 1.5 Ga 13.1 Zr 1.5 .

[0095] Figure 2 These are images of grain boundary phases taken under high magnification using a transmission electron microscope. The composition of the Ga-depleted phase is determined to be R. 51.5 Fe 32.1 Co 8.6 Cu 5.2 Ga 0.9 Zr 1.7 .

[0096] Example 2

[0097] The preparation process of Example 2 is the same as that of Example 1, except that:

[0098] In step (1), the composition table of the neodymium iron boron material in Example 2 is shown in Table 1, and the oxygen content of the selected PrNd, Fe, and BFe raw materials is shown in Table 2.

[0099] In step (2), the temperature of the air jet mill grinding chamber is 31°C, and the oxygen content of the air jet mill grinding chamber is 65ppm by introducing air.

[0100] Example 3

[0101] The preparation process of Example 3 is the same as that of Example 1, except that:

[0102] In step (1), the composition table of the neodymium iron boron material in Example 3 is shown in Table 1, and the oxygen content of the selected PrNd, Fe, and BFe raw materials is shown in Table 2.

[0103] In step (2), the temperature of the air jet mill grinding chamber is 33°C, and compressed air is introduced to make the oxygen content of the air jet mill grinding chamber 117ppm, so as to obtain air jet mill powder with D50 = 3.6μm.

[0104] Example 4

[0105] The preparation process of Example 4 is the same as that of Example 1, except that:

[0106] In step (1), the composition table of the neodymium iron boron material in Example 4 is shown in Table 1, and the oxygen content of the selected PrNd, Fe, and BFe raw materials is shown in Table 2.

[0107] In step (2), the temperature of the air jet mill grinding chamber is 36°C. A mixed gas with a volume ratio of air to nitrogen of 1:1 is introduced to make the oxygen content of the air jet mill grinding chamber 133ppm, so as to obtain air jet mill powder with D50 = 3.6μm.

[0108] Comparative Example 1

[0109] The preparation process of Comparative Example 1 is the same as that of Example 1, except that:

[0110] In step (1), the composition table of the neodymium iron boron material of Comparative Example 1 is shown in Table 1. The oxygen content of the selected PrNd, Fe, and BFe raw materials is shown in Table 2.

[0111] In step (2), the temperature of the air jet mill grinding chamber is 34°C, and oxygen is introduced to make the oxygen content of the air jet mill grinding chamber 38ppm.

[0112] Comparative Example 2

[0113] The preparation process of Comparative Example 2 is the same as that of Example 1, except that:

[0114] In step (1), the composition table of the neodymium iron boron material of Comparative Example 2 is shown in Table 1. The oxygen content of the selected PrNd, Fe, and BFe raw materials is shown in Table 2.

[0115] In step (2), the temperature of the air jet mill grinding chamber is 36°C, no oxygen-containing gas is introduced into the air jet mill grinding chamber, and the oxygen content in the air jet mill chamber is 15ppm.

[0116] Comparative Example 3

[0117] The preparation process of Comparative Example 3 is the same as that of Example 1, except that:

[0118] In step (1), the composition table of the neodymium iron boron material of Comparative Example 3 is shown in Table 1. The oxygen content of the selected PrNd, Fe, and BFe raw materials is shown in Table 2.

[0119] In step (2), the temperature of the air jet mill grinding chamber is 33°C, and oxygen is introduced to make the oxygen content of the air jet mill grinding chamber 176ppm, so as to obtain air jet mill powder with D50 = 4.2μm.

[0120] Comparative Example 4

[0121] The preparation process of Comparative Example 4 is the same as that of Example 1, except that:

[0122] In step (1), the composition table of the neodymium iron boron material of Comparative Example 4 is shown in Table 1. The oxygen content of the selected PrNd, Fe and BFe raw materials is shown in Table 2.

[0123] In step (2), the temperature of the air jet mill grinding chamber is 36°C, and oxygen is introduced to make the oxygen content of the air jet mill grinding chamber 107ppm.

[0124] Comparative Example 5

[0125] The preparation process of Comparative Example 4 is the same as that of Example 1, except that:

[0126] In step (1), the composition table of the neodymium iron boron material of Comparative Example 4 is shown in Table 1. The oxygen content of the selected PrNd, Fe and BFe raw materials is shown in Table 2.

[0127] In step (2), the temperature of the air jet mill grinding chamber is 31°C, and oxygen is introduced to make the oxygen content of the air jet mill grinding chamber 121ppm, so as to obtain air jet mill powder with D50 = 5.0μm.

[0128] Comparative Example 6

[0129] The preparation process of Comparative Example 4 is the same as that of Example 1, except that:

[0130] In step (1), the composition table of the neodymium iron boron material of Comparative Example 4 is shown in Table 1. The oxygen content of the selected PrNd, Fe and BFe raw materials is shown in Table 2.

[0131] In step (2), the temperature of the air jet mill grinding chamber is 32°C, and oxygen is introduced to make the oxygen content of the air jet mill grinding chamber 100ppm, so as to obtain air jet mill powder with D50 = 3.5μm.

[0132] Table 1. Raw materials and proportions (wt%) of permanent magnets in Examples 1-4 and Comparative Examples 1-6

[0133]

[0134]

[0135] Table 2 shows the oxygen content a in PrNd, the oxygen content b in Fe, the oxygen content c in BFe, the oxygen content V in the air jet mill grinding chamber, the oxygen content x in the alloy flakes, the oxygen content y in the air jet mill powder, and the air jet mill powder particle size D50z in Examples 1-4 and Comparative Examples 1-6.

[0136] Example 1 58 125 213 44 0.0047 0.0250 3.2 0.0498 Example 2 98 81 147 65 0.0035 0.0340 3.2 0.0864 Example 3 77 170 285 117 0.0103 0.0455 3.6 0.0898 Example 4 133 215 269 133 0.0168 0.0615 3.6 0.1004 Comparative Example 1 265 317 350 38 0.0287 0.0375 3.2 -0.0637 Comparative Example 2 122 118 150 15 0.0091 0.0160 3.2 -0.0070 Comparative Example 3 100 165 194 176 0.0113 0.1260 4.2 0.4345 Comparative Example 4 91 177 209 107 0.0109 0.0325 3.2 0.0342 Comparative Example 5 99 103 187 121 0.0098 0.0464 5.0 0.1340 Comparative Example 6 124 178 325 100 0.0186 0.048 3.5 0.0378

[0137] Table 3. Permanent magnet performance, resistivity, and bending strength in Examples 1-4 and Comparative Examples 1-6

[0138]

[0139]

[0140] Compared with Example 1, due to the selection of oxygen content in the raw material control, the alloy flakes of Comparative Example 1 have a higher oxygen content, which does not satisfy the relationship (3) 0.12≥(y-2x)*z≥0.04, resulting in a low proportion of Ga-rich phase in the product of Comparative Example 1. Consequently, the coercivity of Comparative Example 1 is significantly lower than that of Example 1.

[0141] In Comparative Example 2, no oxygen-containing gas was introduced during the air jet milling process, and the oxygen content in the air jet mill grinding chamber was 15 ppm. At this time, Ga element was still excessively concentrated in the two-grain boundary phase, and sufficient Ga-depleted phase could not be generated in the triangular grain boundary. As a result, the area ratio of the Ga-depleted phase region to the grain boundary phase in the product of Comparative Example 2 was 58%, and the resistivity of the product of Comparative Example 2 was significantly reduced.

[0142] In Comparative Example 3, an excessive amount of oxygen-containing gas was introduced into the air jet mill process, resulting in an oxygen content of 176 ppm in the mill grinding chamber and an oxygen content of 0.1260 wt% in the resulting air jet mill powder. The excessive oxygen content in the mill grinding chamber, while generating a high proportion of Ga-depleted phase, also caused the magnet to generate more oxides, leading to a significant deterioration in its bending strength.

[0143] In Comparative Example 4, the Cu content in the NdFeB material composition table is 0.3 wt%. The proportions of the raw materials do not satisfy the equation lg[R] + lg([Cu] + [Zr] + [Ti]) - 1.2*[B] ≥ 0. The reduction in Cu content decreases the competition between Cu and Ga at the grain boundaries, allowing excess Ga to enter the main phase. The area of ​​the Ga-rich phase region relative to the grain boundary phase is too high compared to X1, resulting in the appearance of Nd2(Fe) in the NdFeB main phase. 1-x Ga x ) 14 Phase B results in a decrease in magnetic properties and a significant deterioration in the bending strength of the magnet.

[0144] In Comparative Example 5, as the particle size of the air jet mill increases, the surface energy of the magnetic powder decreases. Even with the oxygen enrichment process, under the oxygen content atmosphere of 121 ppm in the air jet mill grinding chamber, the product of Comparative Example 5 is still insufficient to make the Ga element in the triangular grain boundary tend to move to the two grain boundary. It cannot obtain the diluted Ga-poor phase of the triangular grain boundary, so the area ratio of the Ga-poor phase region to the grain boundary phase in the product of Comparative Example 5 is 58%, and the resistivity of the product of Comparative Example 5 is significantly reduced.

[0145] In Comparative Example 6, the Zr content in the raw material of the neodymium iron boron material is 0.3 wt%, which increases the proportion of ZrB2 in the grain boundary phase. This results in a ratio of Ga-rich phase region to Ga-poor phase region in the grain boundary phase of 0.19, which does not meet the area ratio of Ga-rich phase to Ga-poor phase of this application (0.20≤X1 / X2≤0.50). Consequently, the coercivity Hcj of Comparative Example 6 is also significantly lower than that of Example 1.

[0146] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sintered R-Fe-B permanent magnet, characterized in that, The sintered R-Fe-B permanent magnet comprises a main phase grain and a grain boundary phase; the main phase grain comprises R2T. 14 B; The grain boundary phase is located between the main phase grains, and the grain boundary phase includes Ga-rich phase and Ga-poor phase; wherein... The Ga-rich phase comprises R, Fe, Ga, and M elements, wherein, by mass ratio, R accounts for 50–75 wt%, Fe accounts for 5–20 wt%, Ga accounts for 5–25 wt%, and M accounts for 1–6 wt%. The Ga-depleted phase comprises R, Fe, Ga, and M elements, wherein, by mass ratio, R accounts for 30–60 wt%, Fe accounts for 15–35 wt%, Ga accounts for 0.01–1 wt%, and M accounts for 15–35 wt%. R is a rare earth element; M is selected from one or more of Al, Zr, Ti, Cu, Co, Mn and Nb; M includes at least Cu, and also includes at least one of Zr and Ti; The area ratio of Ga-rich phase to grain boundary phase region is X1, and the area ratio of Ga-poor phase to grain boundary phase region is X2, where... 13%≤X1≤30%； 60%≤X2≤80%； And 0.20≤X1 / X2≤0.50; The sintered R-Fe-B permanent magnet satisfies the following relationships (1) and (2): lg[R]+lg([Cu]+[Zr]+[Ti])-1.2 [B]≥0;(1) 0.45≤[Cu]+[Zr]+[Ti]≤0.7; (2) Where [R], [Cu], [Zr], [Ti] and [B] are the mass percentages of R, Cu, Zr, Ti and B, respectively.

2. The permanent magnet according to claim 1, characterized in that, The sintered R-Fe-B permanent magnet, by mass ratio of 100%, comprises the following components: R: 27-33 wt%, R is a rare earth element, which includes at least Nd and at least one selected from the following rare earth elements: Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc; B: 0.9–1.3 wt%; Ga: 0.2–0.5 wt% M: 0.45–3 wt%; selected from one or more of Al, Zr, Ti, Cu, Co, Mn, and Nb. The remainder consists of Fe and impurities.

3. The permanent magnet according to claim 2, characterized in that, The permanent magnet contains 0.35 to 1.1 wt% Cu.

4. The permanent magnet according to claim 3, characterized in that, The Zr or Ti content in the permanent magnet is 0.08 to 0.15 wt%.

5. The method for preparing the permanent magnet according to any one of claims 1-4, characterized in that, The method includes: The raw materials for preparing the sintered R-Fe-B permanent magnets are sequentially processed through a melting process, a powder preparation process, a molding process, and a heat treatment process to obtain the sintered R-Fe-B permanent magnets.

6. The method according to claim 5, characterized in that, In the smelting process, the rare earth raw material R used has an oxygen content of a, Fe has an oxygen content of b, and BFe has an oxygen content of c. a, b, and c satisfy the following conditions: a < 200 ppm, b < 250 ppm, and c < 450 ppm.

7. The method according to claim 5, characterized in that, The powder preparation process includes hydrogen embrittlement, medium grinding and / or air jet milling, and air jet milled powder is obtained after the powder preparation process.

8. The method according to claim 7, characterized in that, The oxygen content V during the air jet milling process is 25–150 ppm.

9. The method according to claim 7, characterized in that, The temperature during the air jet milling process is 30-40℃.

10. The method according to claim 7, characterized in that, The oxygen content of the alloy flakes prepared in the smelting process is x (wt%), the oxygen content of the air-jet milled powder after the air-jet milling process is y (wt%), and the particle size D50 of the air-jet milled powder is z (μm). The three should satisfy the following relationships (3)-(6): 0.12≥(y-2x) z≥0.04;(3) 0.025≥x≥0.003；（4） 0.09≥y≥0.02；（5） 4.5≥z≥2.3；（6）。 11. The method according to claim 5, characterized in that, The conditions for the heat treatment process include: a sintering temperature of 900–1100℃ and a sintering time of 2–8 hours.

12. The method according to claim 5, characterized in that, After the heat treatment process, a diffusion process can be optionally carried out.

13. The use of the permanent magnet according to any one of claims 1-4 in the fields of motors, loudspeakers, magnetic separators, computer disk drives, or magnetic resonance imaging equipment.

14. The application according to claim 13, characterized in that, Applications of motor rotor magnets in electric motors.

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