Sintered neodymium-iron-boron magnetic matrix with high grain size consistency and preparation method and application of sintered neodymium-iron-boron magnetic matrix

Abstract

The invention discloses a sintered neodymium-iron-boron magnetic matrix with high grain size consistency and a preparation method and application of the sintered neodymium-iron-boron magnetic matrix. The size standard deviation SD of main phase crystal grains of the sintered neodymium-iron-boron magnetic matrix is less than or equal to 2; the calculation formula of SD is SD =, and the SD refers to the size of the ith main phase grain in the matrix; the mean value refers to the mean value of the sizes of all main-phase grains; the number refers to the number of all main phase grains. The neodymium-iron-boron magnetic matrix obtained by the method is high in grain boundary size consistency, and the coercive force of a diffused magnet is improved compared with that of a traditional magnet; the coercive force temperature coefficient beta is improved, the coercive force standard deviation SHcj of the magnet is smaller than 22KA / m, and the magnetic performance stability is enhanced to a certain extent.

Description

Technical Field

[0001] This invention relates to the field of neodymium iron boron (NdFeB) magnet technology. Specifically, it relates to a sintered NdFeB magnetic matrix with high grain size uniformity, its preparation method, and its applications. Background Technology

[0002] With the increasing demand for high-performance NdFeB magnets, sintered NdFeB, as a leading rare-earth permanent magnet material, is increasingly in high demand in rapidly developing fields such as electronics, automobiles, new energy, and rail transportation. For example, high-performance NdFeB magnets are needed in drive motors and air conditioning compressors of new energy vehicles to improve motor efficiency and power density; high-performance NdFeB magnets are also required in micro-motors in the electronics field to achieve miniaturization and high performance. The addition of heavy rare-earth elements (such as dysprosium and terbium) can significantly improve the demagnetization resistance and high-temperature resistance of NdFeB materials. However, this also brings some problems: first, the maximum energy product will decrease sharply, affecting the overall performance of the material; second, heavy rare-earth elements are scarce and expensive, resulting in high magnet production costs.

[0003] Grain boundary diffusion technology was proposed by Nakamura et al. in Japan in 2005. This technology uses elemental or compound Tb and Dy as diffusing agents, and through diffusion heat treatment, heavy rare earth elements are diffused from the surface of the magnet along the grain boundaries into the interior of the magnet, replacing Nd2Fe. 14 Nd in the β phase is distributed at grain boundaries and on grain surfaces to improve the coercivity of NdFeB magnets, while rarely penetrating into the grains. This not only improves coercivity but also reduces the adverse effects of heavy rare earth elements on remanence. Furthermore, it increases the thickness of the thin grain boundary phase, making it more continuous and smooth, weakening the exchange coupling between grains, and further enhancing the magnet's coercivity. In recent years, grain boundary diffusion has made significant progress both theoretically and technically, with various diffusion techniques and diffusion processes tailored to sintered magnets of different compositions being continuously developed.

[0004] Existing grain size control technologies have limitations in controlling the grain size distribution of sintered rare earth iron boron (Re-Fe-B) permanent magnets. For example, while adjusting the sintering process or adding specific additives can control grain size distribution, precise control is often difficult to achieve, leading to unstable magnetic properties of the magnet. Some methods may introduce impurities, affecting the magnetic properties of the magnet. Furthermore, some grains may become excessively refined, resulting in longer diffusion channels for heavy rare earth elements. To achieve the same diffusion depth, a longer diffusion time is required, increasing the amount of heavy rare earth elements used and production costs. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides the following technical solution: A sintered NdFeB magnetic matrix, wherein the standard deviation S of the main phase grain size of the sintered NdFeB magnetic matrix is... D ≤2; S D The calculation formula is: S D = , in, This refers to the size of the i-th principal phase grain in the matrix; This refers to the average size of all principal phase grains; This refers to the number of all principal phase grains.

[0006] Preferably, the size fluctuations of the main phase grains in the central region and the surface region of the sintered NdFeB magnetic matrix are small, and the size standard deviation S of the main phase grains in the central region and the surface region is small. D ≤2, S D In the calculation formula, This refers to the size of the i-th principal phase grain in the central region and the surface region; This refers to the average size of all principal phase grains in the central and surface regions; This refers to the number of all principal phase grains in the central and surface regions.

[0007] According to an embodiment of the present invention, the surface region refers to the region between the surface of the magnetic substrate and a distance of 1 mm from the surface of the magnetic substrate, and the central region refers to the region between the geometric central axis of the magnetic substrate and a distance of 60 μm from the geometric central axis.

[0008] According to an embodiment of the present invention, the sintered NdFeB magnetic matrix has a cubic structure, wherein the easy magnetization direction of the magnetic matrix is ​​c, the length direction of the magnetic matrix is ​​a, and the width direction of the magnetic matrix is ​​b; on any cross section perpendicular to the easy magnetization direction c, the average number of principal phase grains at the four corners and the center point is denoted as Z. c On any cross section perpendicular to direction a, the average number of principal phase grains at the four corners and the center is denoted as Z. a On any cross section perpendicular to direction b, the average number of principal phase grains at the four corners and the center is denoted as Z. b Z a Z b and Z c Satisfies: 0.49 ≤ (Z) a +Z b ) / (5*Z c )≤0.51.

[0009] In this invention, the corners and center positions are located on any cross-section perpendicular to the easy magnetization direction c, the length direction a, or the width direction b. The corners refer to the vertex of this arbitrary cross-section, located within a range from the edge of the magnetic substrate surface to 1 mm from the surface of the magnetic substrate. When the magnetic substrate has a cubic structure, the cross-section is square, and there are four corners. The center position refers to the region between the geometric central axis of this arbitrary cross-section and a distance of 60 μm from the geometric central axis. See [link to relevant documentation] for the corner and center positions. Figure 1 As shown.

[0010] According to an embodiment of the present invention, the sintered NdFeB magnetic matrix, by mass ratio of 100%, comprises the following components: R: 26~32wt%, 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; M: 0.5~3wt%, M is at least one of Al, Cu, Ga, Zr, Ti, Nb, and Mn; B: 0.8~1.1wt% The balance consists of T and impurities, where T is at least one of Fe and Co.

[0011] The impurities mentioned are unavoidable.

[0012] The present invention also provides a method for preparing the above-mentioned sintered NdFeB magnetic matrix, the method comprising: taking alloy flakes obtained by a smelting process from the raw materials, and obtaining magnetic powder by a powdering process; taking the magnetic powder by a molding process to obtain a molded body, and then taking a heat treatment process to prepare the sintered NdFeB magnet.

[0013] According to an embodiment of the present invention, the raw materials for preparation, by mass percentage, comprise: R: 26~32wt%; R is a rare earth element, which includes at least Nd, or Nd and at least one of the following elements: Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc; M: 0.5~3wt%; M is selected from at least one of Al, Cu, Ga, Zr, Ti, Nb, and Mn; B: 0.8–1.1 wt% The balance is T and unavoidable impurities; T is selected from Fe and / or Co.

[0014] According to an embodiment of the present invention, the smelting process can be carried out using any method known in the art that can obtain the alloy flakes, such as using a rapid solidification strip casting method to produce alloy flakes. Exemplarily, the smelting process for preparing alloy flakes specifically includes: mixing the raw materials and heating them to 1300-1600°C using electromagnetic induction to obtain an alloy melt, which is then poured onto a quenching roller (preferably a polished quenching roller), and cooled to obtain alloy flakes.

[0015] According to an embodiment of the present invention, the thickness of the alloy flakes is 0.15-0.45 mm, for example, 0.2 mm, 0.3 mm, 0.4 mm or any two of the above values.

[0016] According to an embodiment of the present invention, the powder preparation process includes sequentially subjecting alloy flakes to hydrogen crushing, air jet milling and ball milling to obtain magnetic powder.

[0017] According to an embodiment of the present invention, the hydrogen crushing is HD hydrogen crushing. In this invention, the HD hydrogen crushing can be performed using methods known in the art. Preferably, the HD hydrogen crushing is carried out in equipment known in the art, such as a single HD furnace.

[0018] For example, the hydrogen crushing includes: absorbing hydrogen from the alloy flakes at 150-320°C and dehydrogenating them at 400-520°C to obtain coarse alloy powder, denoted as HD powder.

[0019] According to an embodiment of the present invention, the particle size of the coarse alloy powder obtained by hydrogen crushing is 10-100 μm, for example, 50 μm.

[0020] According to an embodiment of the present invention, the air jet mill is performed in an inert gas atmosphere. Preferably, the inert gas is selected from at least one of nitrogen, argon, helium, etc.

[0021] According to an embodiment of the present invention, the air jet mill specifically includes: controlling the feed rate V of the alloy coarse powder (HD powder) and grinding it under the grinding pressure P to obtain air jet mill powder, wherein 0.10MPa≤P≤0.50MPa, 1kg / min≤V≤5kg / min.

[0022] According to an embodiment of the present invention, the unit output q of the air jet mill and the feed rate V satisfy the relationship I: 0.9≤q / V≤1.1.

[0023] The inventors discovered that when the discharge velocity V is too high and does not satisfy 0.9≤q / V≤1.1, less coarse alloy powder is used for grinding; when the discharge velocity V is too low and does not satisfy 0.9≤q / V≤1.1, more coarse alloy powder is used for grinding, which easily accumulates. Only when the unit output q of the air jet mill and the feed velocity V satisfy 0.9≤q / V≤1.1 can the air jet mill achieve sufficient grinding.

[0024] According to an embodiment of the present invention, the average particle size of the air jet mill powder is 2.6~3.6μm.

[0025] According to an embodiment of the present invention, after air jet milling, the air jet milled powder is further subjected to ball milling. Preferably, the ball milling includes: mixing the air jet milled powder with metal balls, optionally adding or not adding an antioxidant, to obtain ball-milled magnetic powder, wherein the mixing time T is 60~120 min.

[0026] According to an embodiment of the present invention, the ratio of the particle size distribution X90 to X10 of the ball milled magnetic powder is u, and the unit yield q of the air jet mill and the particle size distribution of the ball milled magnetic powder satisfy the relationship II: 1≤Ln(q*60) / u≤1.25.

[0027] According to an embodiment of the present invention, the average diameter of the metal sphere is 1~3mm.

[0028] According to an embodiment of the present invention, the metal ball is selected from steel balls.

[0029] According to an embodiment of the present invention, the mixing is carried out in a mixer known in the art. Exemplarily, the mixer is a three-dimensional mixer.

[0030] According to an embodiment of the present invention, the amount of antioxidant used is 0.01 to 1 wt% of the magnetic powder mass, for example, 0.1 wt% or 0.5 wt%.

[0031] According to an embodiment of the present invention, the antioxidant is selected from substances known in the art, such as fatty acid esters. Adding an antioxidant ensures thorough mixing of the magnetic powder and facilitates molding. By adding an antioxidant, the flowability of the magnetic powder can be improved, thereby enhancing the mixing effect and efficiency, which is beneficial for subsequent molding processes.

[0032] According to an embodiment of the present invention, by controlling the powder-making process to meet the following conditions: 0.10MPa≤P≤0.50MPa, 1kg / min≤V≤5kg / min and 0.9≤q / V≤1.1, the particle size distribution of the ball-milled magnetic powder with the ratio u of X90 and X10 satisfies the above-mentioned relationship II, thereby preparing a sintered NdFeB magnetic matrix with good grain size uniformity, whose main phase grain size standard deviation S D≤2, diffusion of the magnetic matrix through grain boundaries can improve the overall performance of NdFeB magnets.

[0033] According to an embodiment of the present invention, the molding process includes: dry molding or wet molding of magnetic powder in a magnetic field to obtain a molded body.

[0034] Preferably, the dry molding process includes: filling magnetic powder into a mold and pressing it to obtain a molded body. Further, in the dry molding process, molding aids known in the art can be added to the magnetic powder as needed; this invention does not impose specific limitations. Further, the pressure during dry molding can be adjusted according to the needs of the molded body, for example, above 8 MPa and below 300 MPa.

[0035] Preferably, the wet molding process includes: dispersing magnetic powder in a solvent to obtain a magnetic powder slurry, followed by compression molding. Further, the solvent can be a solvent known in the art, such as oil. Further, during wet molding, the compression molding pressure can be adjusted according to the needs of the molded body, for example, above 8 MPa and below 300 MPa.

[0036] Preferably, during pressure molding, the magnetic powder can be oriented in a specific direction by applying a magnetic field. The applied magnetic field can be a static magnetic field and / or a pulsed magnetic field, and its magnetic field strength can be, for example, 1~5T.

[0037] According to embodiments of the present invention, those skilled in the art should understand that the present invention does not particularly limit the shape of the molded body, which can be adjusted according to the application conditions of the permanent magnet. For example, the molded body can be selected from at least one of the following shapes: cuboid, flat, columnar, ring-shaped, or C-shaped.

[0038] According to an embodiment of the present invention, the heat treatment process includes: sintering the obtained molded body under vacuum conditions or an inert atmosphere.

[0039] According to an embodiment of the present invention, the temperature of the heat treatment process is 950~1150℃, preferably 1000~1100℃.

[0040] According to an embodiment of the present invention, the heat treatment process takes 1-20 hours, for example, 5 hours, 10 hours, or 15 hours.

[0041] The present invention also provides the application of the above-mentioned sintered NdFeB magnetic matrix in the preparation of permanent magnets.

[0042] The present invention also provides a permanent magnet, wherein the raw material of the permanent magnet is selected from the above-mentioned sintered NdFeB magnetic matrix.

[0043] The present invention also provides a method for preparing the above-mentioned permanent magnet, the method comprising a diffusion process of the above-mentioned sintered NdFeB magnetic matrix.

[0044] According to an embodiment of the present invention, the diffusion process specifically includes: applying a diffusion source to the surface of a sintered NdFeB magnetic substrate for diffusion treatment.

[0045] Preferably, the diffusion source includes a rare earth element R, which is selected from at least one of praseodymium, neodymium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium, and is preferably terbium.

[0046] Preferably, the mass content of rare earth element R in the diffusion source is not less than 60%, preferably not less than 70%, for example, 80% or 90%.

[0047] According to an embodiment of the present invention, the diffusion process includes a first diffusion process, cooling, and a second diffusion process; The first diffusion treatment specifically includes: a first diffusion temperature of 800℃-1000℃ and a first diffusion time of 2h-40h; after the first diffusion treatment, cooling to room temperature, the cooling rate can be carried out using methods known in the art.

[0048] The second diffusion treatment specifically includes: a second diffusion temperature of 450℃-650℃ and a second diffusion time of 2h-20h. Preferably, after the second diffusion treatment, the sample is cooled to room temperature, and the cooling rate can be achieved using methods known in the art.

[0049] In this invention, the heating rate to the first diffusion temperature or the second diffusion temperature can be the same or different, and can be independently selected from 5℃ / min to 50℃ / min.

[0050] 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.

[0051] Beneficial effects: This invention controls the grinding pressure and the feed rate of HD powder during the powder preparation process, and obtains ball-milled magnetic powder with high particle size uniformity after ball milling. The magnetic matrix prepared by this ball-milled magnetic powder has high grain size uniformity, and the grain size distribution is closer to a normal distribution with a low standard deviation S of grain size. D ≤2, the obtained magnetic matrix has continuous grain boundaries, which improves the saturation of heavy rare earth elements in the diffused grain boundaries. The diffused grain boundaries are more uniform and continuous, reducing the presence of triangular grain boundaries. The uniform, continuous and highly consistent grain boundaries provide efficient diffusion channels, improve the saturation and utilization of heavy rare earth elements in the grain boundaries, and increase the utilization rate of heavy rare earth elements in the magnetic matrix under the same amount of heavy rare earth elements.

[0052] The NdFeB magnetic matrix obtained by this invention exhibits high grain boundary size uniformity, and its coercivity after diffusion is improved compared to traditional magnets; the coercivity temperature coefficient β is improved, and the standard deviation S of the magnet's coercivity is reduced. Hcj With a value less than 22 kA / m, the stability of magnetic properties has been enhanced to some extent.

[0053] This invention effectively improves the stability of magnetic property fluctuations while reducing the cost of using heavy rare earth elements, effectively expanding their application temperature range, and significantly improving the magnetic property stability of magnets in high-temperature environments. The manufacturing process employed is easily implemented on existing industrial production equipment, demonstrating promising prospects for industrial application. Attached Figure Description

[0054] Figure 1 This is a schematic diagram showing the sampling locations of the grains in the magnetic substrate M11 of Example 1; Figure 2 Metallographic structure of the blank for magnetic substrate M11 in Example 1; Figure 3 This is the gain size distribution of the magnetic substrate M11 in Example 1. In the figure, the horizontal axis "gain size" refers to the size of the grains, in micrometers (μm); the horizontal axis "count" represents the quantity. Figure 4 The image shows the EPMA diagram of the permanent magnet M12 after diffusion in Example 1. Figure 5 Metallographic structure of the N11 magnetic matrix blank in Comparative Example 1; Figure 6 The grain size distribution of the magnetic matrix N11 in Comparative Example 1 is shown. Figure 7 The image shows the EPMA diagram of the permanent magnet N12 after diffusion in Comparative Example 1. Detailed Implementation

[0055] 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.

[0056] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0057] Example 1 The preparation method of neodymium iron boron sintered magnets is as follows: (1) Preparation of RFeBM substrate by melting method: The raw materials are melted in an argon atmosphere. The alloy formula consists of R, M, B, with the balance being Fe and unavoidable impurities. Among them, R contains 7% Pr, 21% Nd, and 3% Gd, M contains 0.17% Al, 0.21% Ti, 0.5% Co, 0.3% Cu, 0.2% Ga, and 0.98% B, with the remaining elements being Fe and unavoidable impurities. The raw materials are prepared according to the formula ratio and added to the melting furnace. After the alloy melts, the temperature is raised to 1430℃ and held for 10 minutes. Then it is cooled to 1400℃ for casting. A fast-solidifying sheet with an average thickness of 0.28 mm is obtained by the strip casting process. (2) Powdering: The obtained flakes are placed in a hydrogen crushing furnace for hydrogen absorption at 310°C. After the reaction is complete, they are dehydrogenated at 505°C to obtain HD powder. During the air jet milling process, the grinding pressure was set to P, the feed rate of HD powder was V, and the unit output q of the air jet mill powder is shown in Table 1. Steel balls with an average particle size of 2.0 micrometers and fatty acid esters with a mass ratio of 0.10 wt% were added to the mixing tank of the three-dimensional mixer. The mixing time was 90 min, and magnetic powder with D90=3.1 μm was obtained.

[0058] The particle size distribution of the ball-milled powder after mixing is denoted as u for X90 / X10, as shown in Table 1.

[0059] (3) Molding: The mixed powder obtained in step (2) after adding the molding formulation is pressed into a compact under a magnetic field (specifically 2T); after isostatic pressing, a compact of approximately 4.6 g / cm³ is formed. 3 The pressed blank.

[0060] (4) Sintering: First, hold at 350℃ for 3 hours, then raise the temperature to 850℃ and hold for 1 hour to degas, then hold at 1060℃ for 120 minutes to sinter, and after cooling to room temperature, age at 520℃ for 300 minutes to form a sintered NdFeB magnetic matrix. The magnets obtained in step (4) are processed to obtain products with dimensions of 45*30*8mm (8mm is in the c direction). Then, surface chemical pretreatment is carried out by degreasing, cleaning and pickling to obtain a magnetic substrate M11 with no oxide skin on the surface. (5) A dispersant is prepared by using heavy rare earth element powder dysprosium hydride or metallic dysprosium, organic solid pine modified alkyd resin powder, and ethanol, with a weight percentage of 60%, 5%, and 35%, respectively. After stirring the above dispersant for 120 min, the magnet pretreated in step (5) is dipped in the dispersant for 5 seconds and then taken out and placed in an oven at 90°C for 20 min to dry. After drying, a magnet to be diffused is obtained with a coating layer weight increase of 1.2 wt% of the total weight of the magnet.

[0061] (6) Diffusion process: The NdFeB substrate coated with diffusing agent in step (5) is placed into a diffusion furnace for diffusion treatment. The specific diffusion treatment includes: the first diffusion treatment temperature is 850℃, the time is 15h, the heating rate is 20℃ / min, and then it is cooled to room temperature; the second diffusion treatment temperature is 500℃, the aging time is 5h, and the heating rate is 15℃ / min; after the second diffusion, it is cooled to room temperature to obtain the diffused permanent magnet M12, which is used to test the magnetic properties.

[0062] Examples 2-7 The manufacturing methods of Examples 2-7 are basically the same as those of Example 1, except that: Step (2) used different grinding pressures, feed rates, and different unit outputs of air jet mills as shown in Table 1.

[0063] Comparative Example 1 The manufacturing method of Comparative Example 1 is basically the same as that of Example 1, except that: Step (2) used different grinding pressures and feed rates as shown in Table 1, as well as different unit outputs of air jet mills. The remaining steps were the same as in Example 1, to obtain magnetic matrix N11 and diffused permanent magnet N12.

[0064] Comparative Examples 2-9 The manufacturing methods of Comparative Examples 2-11 are basically the same as those of Example 1, except that: Step (2) used different grinding pressures and feed rates as shown in Table 1, as well as different unit outputs of air jet mills. The remaining steps were the same as in Example 1.

[0065] Table 1. Powdering parameters of Examples 1-7 and Comparative Examples 1-9

[0066] Test Example 1 The instrument for testing the number and size of the following grains is based on Python programming and uses a driven segmentation model (Segment Anything Model, SAM) for image segmentation. It utilizes the zero-shot segmentation capability to quickly obtain the target grain mask through simple interaction (points, boxes, masks) and obtain the grain size and number of grains.

[0067] EPMA testing instrument: Field Emission Electron Probe Microscope (FE) EPMA (JEOL Ltd., 8530F).

[0068] Magnetic property testing instrument: NIM-62000 magnetic measuring instrument from the National Institute of Metrology, China.

[0069] The specific testing method is as follows: 1. Number of grains: Take the magnetic substrates prepared in the above examples and comparative examples, such as... Figure 1 As shown, the magnetic substrate has three directions a*b*c, where c is the easy magnetization direction. On any cross-section perpendicular to the easy magnetization direction c, five unit areas of 60μm*60μm each are taken at the four corners (1mm from the edge of the magnet) and the center (at the center of the magnet's surface). The average number of grains within these five unit areas is denoted as Z. c ; Define an arbitrary cross-section perpendicular to direction a, and take five unit areas of 60μm x 60μm each at the four corners and the center. Define the average number of grains within these five unit areas as Z. a ; Define an arbitrary cross-section perpendicular to direction b, and take five unit areas of 60μm x 60μm each at the four corners and the center. Define the average number of grains within these five unit areas as Z. b .

[0070] 2. Standard deviation of grain size: Record the grain size of all grains within the above 15 unit areas and calculate the standard deviation S of the grain size. D S D = ,in: This refers to the size of a single grain; This refers to the average value of all grain sizes; It refers to the number of all grains within 15 unit areas.

[0071] 3. Magnetic Performance Testing: In each of the above embodiments and comparative examples, 15 test samples were taken from the following locations within the diffusion furnace, with a loading capacity of ≥1 ton: 8 vertices, 1 body center, and 6 face centers of a cuboid. After uniformly removing the surface material from the test samples, 7mm*7mm*4mm square pieces were machined from each sample along the magnetization direction. Each group of square pieces was saturated with magnetization, and the coercivity Hcj and Br value of each square piece were accurately measured using a BH magnetometer. The test conditions were 20℃ and 150℃. The coercivity at T0=20℃ was recorded as Hcj(T0), and the coercivity at T1=150℃ was recorded as Hcj(T1); the Br value at 20℃ was also recorded. The test results for each group were the average of the 15 square pieces.

[0072] 4. Temperature coefficient β of magnet coercivity: The temperature coefficient β of coercivity is obtained by referring to the following formula, based on the coercivity of the diffused magnet measured in test method 3 above. It is the relative rate of change of magnetic coercivity Hcj with temperature: .

[0073] 5. The standard deviation S of Hcj for magnetic propertiesHcj Calculate the standard deviation S of Hcj for each group of 15 squares at 20℃ obtained from test method 3 above. Hcj = , in, This refers to the Hcj of a single square in each group; This refers to the mean Hcj of each group of 15 squares; This refers to a sample size of 15 for each group.

[0074] The test results are recorded in Tables 2-1 and 2-2.

[0075] Table 2-1 Test results of Examples 1-7 and Comparative Examples 1-9 (I)

[0076] Table 2-2 Test results of Examples 1-7 and Comparative Examples 1-9 (II)

[0077] The test results above show that: In Examples 1-7, by controlling the pressure P and the feed rate V of HD powder in the powder preparation process, powder with high particle size uniformity from air jet milling is obtained. This precisely controls the degree of grain breakage, avoiding excessive grain refinement or coarsening and ensuring grain boundary integrity. Grain and grain boundary optimization is achieved, resulting in a normal distribution and strong uniformity of the magnetic matrix grain size (i.e., satisfying relation II), with a standard deviation S of the main phase grain size. D ≤2, the grain boundaries are continuous and uniform, the triangular grain boundaries are reduced, the resistance to the movement of magnetic domain walls is reduced, the nucleation centers of reverse magnetic domains are reduced, and the diffusion channels of heavy rare earths are optimized, thus improving the diffusion saturation of heavy rare earths. Therefore, the coercivity after diffusion is significantly improved.

[0078] In contrast, the grinding pressure in Comparative Example 1 was too high, resulting in excessive fragmentation of the grains in the air-jet mill and the appearance of cracks at the grain boundaries. In Comparative Example 2, the grinding pressure was too low, resulting in insufficient grain refinement and uneven size. Neither of these conditions could form continuous grain boundaries, thus failing to achieve the desired optimization effect between grains and grain boundaries, and thus limiting the improvement in magnet performance.

[0079] The HD powder in Comparative Examples 3 and 5 was fed at too high a rate, resulting in severe powder agglomeration and blockage of diffusion channels. Simultaneously, insufficient grinding led to a high proportion of coarse particles, increased microstructural defects, poor particle size distribution, and poor grain distribution, resulting in (Za+Zb) / (5 Zc) is out of range, so S D If the value is greater than 2, the overall quality of the magnet will also be poor.

[0080] The HD powder in Comparative Example 4 was fed too slowly, resulting in loose powder distribution; excessive grinding led to uneven density in subsequent molding, with a high proportion of fine powder and poor grain distribution, resulting in (Za+Zb) / (5 Zc) is out of range, so S D If the value is greater than 2, the overall quality of the magnet will also be poor.

[0081] Comparative Examples 6 and 7 used conventional grinding pressure. Different feeding speeds also resulted in magnetic powder distribution that was either too loose or too agglomerated, neither of which could achieve a high-quality powder particle size distribution (not satisfying Relationship II). This could not provide a basis for subsequent molding and sintering, and could not guarantee the uniformity of the overall grain of the magnet, thus failing to obtain a better microstructure. Therefore, the effect of improving magnet performance through diffusion was limited.

[0082] Similarly, Comparative Example 8 had too low grinding pressure and too fast feeding speed, and Comparative Example 9 did not undergo ball milling. Neither of these conditions could achieve a high-quality powder particle size distribution (not satisfying Relationship II), resulting in poor uniformity of the overall grain size of the magnet and an inability to improve the magnet performance through diffusion.

[0083] In summary, compared to Comparative Examples 1-9, the coercivity of the diffused magnets in Examples 1-7 can be increased by more than 10%, and the standard deviation S of the coercivity of the same batch of magnets is... Hcj The strength is controlled within 22 KA / m. Furthermore, the magnet obtained under the powder-making process conditions of this invention exhibits good operating temperature stability, with a coercivity temperature coefficient β less than -0.47%, significantly enhancing the stability of the magnet under different operating temperature environments.

[0084] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application 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 NdFeB magnetic matrix, characterized in that, The standard deviation of the main phase grain size S of the sintered NdFeB magnetic matrix D ≤2; S D The calculation formula is: S D = , in, This refers to the size of the i-th principal phase grain in the matrix; This refers to the average size of all principal phase grains; This refers to the number of all principal phase grains.

2. The sintered NdFeB magnetic matrix according to claim 1, characterized in that, The sintered NdFeB magnetic matrix has a cubic structure, wherein the easy magnetization direction of the magnetic matrix is ​​c, the length direction of the magnetic matrix is ​​a, and the width direction of the magnetic matrix is ​​b; on any cross-section perpendicular to the easy magnetization direction c, the average number of principal phase grains at the four corners and the center point is denoted as Z. c On any cross section perpendicular to direction a, the average number of principal phase grains at the four corners and the center is denoted as Z. a On any cross section perpendicular to direction b, the average number of principal phase grains at the four corners and the center is denoted as Z. b Z a Z b and Z c Satisfies: 0.49 ≤ (Z) a +Z b ) / (5*Z c )≤0.

51.

3. The sintered NdFeB magnetic matrix according to claim 1 or 2, characterized in that, The sintered NdFeB magnetic matrix, by mass ratio of 100%, comprises the following components: R: 26~32wt%, 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; M: 0.5~3wt%, M is at least one of Al, Cu, Ga, Zr, Ti, Nb, and Mn; B: 0.8~1.1wt% The balance consists of T and impurities, where T is at least one of Fe and Co.

4. The method for preparing the sintered NdFeB magnetic matrix according to any one of claims 1-3, characterized in that, The preparation method includes: obtaining alloy flakes from the raw materials through a smelting process, obtaining magnetic powder through a powder-making process; obtaining a molded body from the magnetic powder through a molding process, and then preparing the sintered NdFeB magnet through a heat treatment process.

5. The preparation method according to claim 4, characterized in that, The raw materials for preparation, by mass percentage, include: R: 26~32wt%; R is a rare earth element, which includes at least Nd, or Nd and at least one of the following elements: Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc; M: 0.5~3wt%; M is selected from at least one of Al, Cu, Ga, Zr, Ti, Nb, and Mn; B: 0.8–1.1 wt% The balance is T and unavoidable impurities; T is selected from Fe and / or Co.

6. The preparation method according to claim 4 or 5, characterized in that, The thickness of the alloy flakes is 0.15-0.45 mm; The powder preparation process includes sequentially subjecting alloy flakes to hydrogen crushing, air jet milling, and ball milling to obtain magnetic powder. The particle size of the coarse alloy powder obtained by hydrogen decomposition is 10-100 μm; The air jet milling is performed in an inert gas atmosphere; The air jet mill specifically includes: controlling the feed rate V of the alloy coarse powder and grinding it under the grinding pressure P to obtain air jet mill powder, wherein 0.10MPa≤P≤0.50MPa, 1kg / min≤V≤5kg / min; The unit output q of the air jet mill and the feed rate V satisfy the following relationship: 0.9≤q / V≤1.1; The average particle size of the air jet mill powder is 2.6~3.6μm; The ball milling process includes: mixing the air jet mill powder with metal balls, optionally adding or not adding an antioxidant, and mixing to obtain ball mill magnetic powder, with a mixing time T of 60~120 min; The particle size distribution of the ball-milled magnetic powder has a ratio of X90 to X10, X90 / X10, which is u. The unit output q of the air jet mill and the particle size distribution of the ball-milled magnetic powder satisfy the relationship II: 1≤Ln(q*60) / u≤1.

25.

7. The preparation method according to any one of claims 4-6, characterized in that, The molding process includes: dry molding or wet molding of magnetic powder in a magnetic field to obtain a molded body; The heat treatment process includes: sintering the obtained molded body under vacuum conditions or an inert atmosphere; The temperature of the heat treatment process is 950~1150℃; The heat treatment process takes 1-20 hours.

8. The application of the sintered NdFeB magnetic matrix according to any one of claims 1-3 in the preparation of permanent magnets.

9. A permanent magnet, wherein the raw material of the permanent magnet is selected from the sintered NdFeB magnetic matrix as described in any one of claims 1-3.

10. The application of the permanent magnet of claim 9 in the fields of motors, loudspeakers, magnetic separators, computer disk drives, and magnetic resonance imaging equipment.

Images