Manufacturing method for R-Fe-B sintered magnets

Abstract

The present invention belongs to the field of rare earth permanent magnet materials and discloses a large-sized R-Fe-B sintered magnet and its manufacturing method and application. The thickness of the R-Fe-B sintered magnet in the orientation direction of the present invention is more than 10 mm, and any one of the cross sections along the orientation direction is a diffusion cross section area, and the side of the diffusion cross section area close to the outer surface of the R-Fe-B sintered magnet is the diffusion cross section area surface, and the difference in coercivity between the diffusion cross section area surface and the point 5 mm away from the diffusion cross section area surface is ΔH, and ΔH≦50 kA / m. Compared with the conventional grain boundary diffusion method, the manufacturing method of the present invention solves the problems that the current large-sized sintered magnet is too thick, which makes it difficult for heavy rare earth to diffuse into the magnet, the difference in coercivity between the magnet surface and the inside after diffusion treatment is large, and the heavy rare earth is consumed in large amounts by diffusion and the diffusion period is long.

Description

Detailed Description of the Invention

[0001] (Technical field) This application claims priority from a prior patent application bearing patent application number 202211734983.2 and entitled "Large-sized R-Fe-B sintered magnet, its manufacturing method and application," filed with the State Intellectual Property Office of the People's Republic of China on December 30, 2022. The prior application is incorporated herein by reference in its entirety.

[0002] The present invention relates to large-sized R-Fe-B sintered magnets and their manufacturing methods and applications, belonging to the field of rare earth permanent magnetic materials.

[0003] (Background technology) Under the current global trend toward a low-carbon economy and energy revolution, countries are increasingly focusing on green energy. Reducing fossil fuel combustion and accelerating the development and utilization of renewable energy are becoming the direction of action for countries around the world. Wind power, a technologically mature and environmentally friendly renewable energy source, is widely used around the world. Along with traditional hydroelectric power, it has become the most widely used renewable energy source. Current wind power technology has gradually improved, and the installed capacity of onshore and offshore wind power plants has increased year by year. Both wind turbines use neodymium-iron-boron sintered permanent magnets, accounting for nearly one-third of the generator's cost. At the same time, the increasing size of construction machinery has led to increased demand for neodymium-iron-boron permanent magnets for motors. These applications require relatively large magnets, typically with thicknesses of 10 mm or more.

[0004] As the use of rare earth permanent magnet materials increases, the scarcity of heavy rare earth materials has led to a significant rise in their prices. Reducing the amount of heavy rare earth materials used in large-sized sintered magnets is an urgent issue that must be addressed. In the field of sintered neodymium-iron-boron magnets, mass production has been achieved using the grain boundary diffusion method, which refines the microstructure by diffusing heavy rare earth elements Dy and Tb placed on the magnet surface into the magnet along the grain boundaries. By improving the coercivity of sintered neodymium-iron-boron magnets and reducing the magnetic exchange coupling at the grain boundaries, the grain boundaries are magnetically hardened, significantly improving the magnet's coercivity while maintaining minimal loss of remanence. Grain boundary diffusion involves placing heavy rare earth elements on the magnet surface, and then, under high-temperature conditions, the grain boundary phase melts, utilizing the difference in concentration of heavy rare earth elements between the magnet's surface and interior as a diffusion force. In magnets with small thicknesses, heavy rare earth elements can easily diffuse all the way to the center of the magnet, and the distribution of the diffused heavy rare earth elements at the grain boundaries on the magnet's surface and within the magnet is uniform. However, as the magnet becomes thicker, the heavy rare earth elements become less able to diffuse into the magnet's interior, and increasing the amount of heavy rare earth elements placed on the magnet's surface results in a rapid rise in product costs. Therefore, the development of grain boundary diffusion processes and methods for large-sized sintered magnets has relatively high application value.

[0005] (Summary of the Invention) The present invention provides a sintered R-Fe-B magnet having a thickness of 10 mm or more in the orientation direction, a diffusion cross-sectional region at any one cross section along the orientation direction, a diffusion cross-sectional region surface at the side of the diffusion cross-sectional region closest to the outer surface of the sintered R-Fe-B magnet, and a difference ΔH between the coercivity at the diffusion cross-sectional region surface and a coercivity at a point 5 mm away from the diffusion cross-sectional region surface, where ΔH≦50 kA / m. In the present invention, the diffusion cross-sectional region surface is preferably a portion 1 mm away from the outer surface of the sintered R-Fe-B magnet.

[0006] According to an embodiment of the present invention, ΔH is, for example, 45 kA / m or less, for example, 42 kA / m, 38 kA / m.

[0007] According to an embodiment of the present invention, the thickness in the orientation direction is, for example, 10 mm to 20 mm, for example, 11 mm, 15 mm.

[0008] According to an embodiment of the present invention, the raw materials of the R-Fe-B sintered magnet include R, B, Fe, and M, among which: The mass content of R is 27 to 34 wt%, preferably 29 to 32 wt%, for example 30.2 wt%.

[0009] The mass content of M is 0 to 5 wt%, preferably 0 to 3 wt%, for example 2 wt%.

[0010] According to an embodiment of the present invention, R is at least one selected from the rare earth elements Nd, Pr, Tb, Dy, Gd, and Ho.

[0011] According to an embodiment of the present invention, M is at least one selected from Ti, V, Cr, Mn, Co, Ga, Cu, Si, Al, Zr, Nb, W, and Mo.

[0012] The present invention further provides a method for producing the above-mentioned R—Fe—B sintered magnet, the method comprising the steps of: (1) producing a billet of R-Fe-B magnet having a thickness of ≥ 10 mm; (2) Arranging a diffusion section: arranging diffusion sections on at least two surfaces of the billet obtained in step (1) in the orientation direction, the diffusion sections including at least one RH layer and one M layer, the M layer being in direct contact with the billet surface, and at least one M layer being spaced between the RH layer and the billet; (3) Diffusion Heat Treatment: The billet on which the diffusion layer has been disposed in step (2) is subjected to a diffusion heat treatment to obtain the R—Fe—B sintered magnet.

[0013] According to an embodiment of the present invention, in step (1), the R-Fe-B magnet billet is obtained by preparing the raw material for the R-Fe-B sintered magnet by a method known in the art, and is not particularly limited by the present invention.

[0014] According to an embodiment of the present invention, in step (2), the diffusion section has RH layers and M layers alternately arranged, and at least one M layer is separated between the RH layer and the billet, and the number of the RH layers is 1 to 3, and the number of the M layers is 1 to 3.

[0015] According to an exemplary embodiment of the present invention, the diffusion portion includes one M layer and one RH layer.

[0016] According to an exemplary embodiment of the present invention, the diffusion section includes two M layers and two RH layers, which are arranged in the following order from the surface of the billet: first M layer, first RH layer, second M layer, and second RH layer. Preferably, the first M layer and second M layer may be the same or different. Preferably, the first RH layer and second RH layer may be the same or different.

[0017] According to an embodiment of the present invention, in the diffusion section, the thickness of each RH layer is 1 μm to 70 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, or 50 μm.

[0018] According to an embodiment of the present invention, the method for manufacturing the RH layer specifically includes disposing an RH slurry on two surfaces of the billet in the orientation direction, and then drying the RH layer.

[0019] According to an embodiment of the present invention, the RH slurry includes a heavy rare earth element, an organic solid, and a solvent.

[0020] According to an embodiment of the present invention, in the RH slurry, the mass ratio of the heavy rare earth element, the organic solid, and the solvent is (40-70):(0.5-12):(0-50), for example, 62:8:30 or 60:8:32.

[0021] According to an embodiment of the present invention, the heavy rare earth element includes at least one of metallic dysprosium, metallic terbium, dysprosium hydride, terbium hydride, dysprosium fluoride, terbium fluoride, dysprosium oxide, and terbium oxide.

[0022] According to an embodiment of the present invention, the organic solid is at least one selected from a rosin-modified alkyd resin, a thermoplastic phenolic resin, a urea resin, and polyvinyl butyral.

[0023] According to an embodiment of the present invention, the solvent is at least one selected from an alcohol-based solvent (e.g., methanol, ethanol), an ether-based solvent (e.g., ethyl ether), and an aromatic hydrocarbon-based solvent (e.g., benzene), and the solvent is preferably ethanol.

[0024] According to an embodiment of the present invention, in the diffusion section, the thickness of each M layer is less than 20 μm and greater than 0.1 μm, preferably less than or equal to 10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm.

[0025] According to an embodiment of the present invention, in the diffusion section, the thickness ratio of each RH layer to each M layer is (1 to 70):(0.1 to 20), for example, 50:3, 40:3, 35:3, 40:2, or 35:2.

[0026] According to an embodiment of the present invention, the manufacturing method of the M layer specifically includes disposing a slurry containing M powder on two surfaces of the billet in the orientation direction, and then drying the slurry to obtain the M layer.

[0027] According to an embodiment of the present invention, the M powder-containing slurry includes M powder, an organic solid, and a solvent.

[0028] According to an embodiment of the present invention, in the M powder-containing slurry, the mass ratio of M powder, organic solid, and solvent is (20-70):(1-10):(0-50), for example, 60:5:35, 55:5:40.

[0029] According to an embodiment of the present invention, the M powder includes at least one of graphite powder, titanium powder, zirconium powder, molybdenum powder, tungsten powder, titanium oxide, zirconium oxide, molybdenum oxide, and tungsten oxide, and the content of oxygen element in the M powder is less than 3%, preferably less than 1%.

[0030] According to an embodiment of the present invention, the M powder includes powders with particle sizes less than 5 μm, of which the powders with particle sizes between 0.5 μm and 1.8 μm account for 50% or more, preferably more than 65%, of the total mass of the powder.

[0031] Generally, as diffusion progresses, the heavy rare earth elements on the magnet surface are consumed, and as the amount of heavy rare earth elements on the magnet surface decreases, the concentration difference decreases, making it impossible for the heavy rare earth elements to diffuse into the magnet interior (e.g., in the portion of the magnet with a thickness of 5 mm or more). In this case, as the thickness increases, the amount of heavy rare earth elements used on the magnet surface and the thickness of the RH layer both increase significantly. However, increasing the magnet orientation thickness significantly lengthens the diffusion path. Conventional methods for diffusing large magnets extend the diffusion time, but the effect of increasing thickness is becoming less clear. Therefore, it is necessary to control the heavy rare earth concentration during the diffusion process. In this invention, the inventors have discovered that by alternating M and RH layers and placing at least one M layer between the billet and the RH layer, the heavy rare earth concentration of the RH can be adjusted. Furthermore, in the present invention, the melting points of the M powders are all above 1000°C, and therefore no melting or other chemical reactions occur during the diffusion heat treatment. Therefore, the M layer forms a concentration-adjusting layer between the RH layer and the billet, and at high temperatures, the heavy rare earth elements in the RH layer can be adjusted by the M layer to adjust the concentration of the heavy rare earth elements. The inventors have found that the particle size distribution of the M powder is an important factor in adjusting the concentration; if the powder particle size is too large, it will corrode the billet and cause pits on the magnet surface; and if the powder particle size is too small, the resulting powder will be too dense, resulting in a low concentration of the heavy rare earth elements, making it difficult to effectively adjust the concentration of the heavy rare earth elements. At the same time, if the thickness is too large, the concentration of the heavy rare earth will be too low; if it is too small, the effect of adjusting the concentration of the heavy rare earth will not be achieved. When diffusing large-sized magnets, the diffusion thickness is too large, so the heavy rare earth elements need to form relatively stable distribution channels at the magnet grain boundaries. If the diffusion concentration is too large, heavy rare earths will be enriched on the magnet surface, blocking the diffusion of the heavy rare earths into the magnet interior. If the diffusion concentration is too small, the diffusion power will be insufficient, significantly increasing the diffusion heat retention time and increasing production costs. When the powder in the M layer meets the conditions of the present invention, the diffusion heat treatment effect is most excellent.Furthermore, the inventors also discovered that the neodymium and praseodymium present at the grain boundaries are highly chemically active, and that the neodymium and praseodymium present at the grain boundaries on the magnet surface are prone to substitution reactions with oxygen, trapping oxygen at the grain boundaries. Increased content of impurities such as oxygen at the grain boundaries disrupts the molten state, reducing the wettability of the diffusion paths and reducing the uniformity of the coercivity on the surface and inside of the diffused magnet. While this can be compensated for by appropriately extending the diffusion time if the magnet is not thick enough, if the magnet is thicker than 10 mm in the diffusion direction, the smoothness of the diffusion paths due to oxygen entering the grain boundaries is significantly impaired, resulting in the loss of uniformity of the coercivity on the magnet surface and inside. Prolonging the diffusion time only slightly improves uniformity and significantly increases manufacturing costs. Therefore, in the present invention, the oxygen content of M powder is 3% or less, preferably 1% or less.

[0032] According to an embodiment of the present invention, in step (3), the diffusion heat treatment includes at least a DW heat treatment and an ST heat treatment.

[0033] According to an embodiment of the present invention, the conditions for the DW heat treatment specifically include heating to the DW temperature and then maintaining the temperature for a certain period of time. Preferably, the DW temperature is 280°C to 480°C, more preferably 320°C to 400°C. Preferably, the DW heat treatment time is 2 hours or more, for example, 3 hours, 5 hours, or 10 hours. The inventors have found that during the DW heat treatment process, most of the organic solids and solvents in the diffusion zone are desorbed, and since the melting points of the powders in the M layer are both 1000°C or higher, after the organic solids and solvents are desorbed, the M powder comes into direct contact with the billet, i.e., the M layer forms a powdery concentration adjustment layer.

[0034] In an embodiment of the present invention, the DW heat treatment is performed under vacuum conditions.

[0035] According to an embodiment of the present invention, in step (3), the ST heat treatment includes a low-temperature heat treatment and a high-temperature heat treatment, wherein the temperature of the low-temperature heat treatment is 750°C to 890°C (e.g., 830°C), and the temperature of the high-temperature heat treatment is 830°C to 970°C (e.g., 870°C, 890°C), the difference between the low-temperature heat treatment temperature and the high-temperature heat treatment temperature is more than 30°C, and the time of the low-temperature heat treatment and / or the high-temperature heat treatment is 50 hours or less, wherein the heat-retention time is ≥ 2 hours. Preferably, the temperature rise rate from the low-temperature heat treatment to the high-temperature heat treatment is 4 to 10°C / min, e.g., 5°C / min.

[0036] Preferably, the low-temperature heat treatment includes raising the temperature to the low-temperature heat treatment temperature and then maintaining the temperature for a certain period of time. Preferably, the high-temperature heat treatment includes raising the temperature to the high-temperature heat treatment temperature and then maintaining the temperature for a certain period of time. Preferably, the temperature rise rate in the low-temperature heat treatment and the high-temperature heat treatment is not specifically limited, but is, for example, 4 to 10°C / min, e.g., 5°C / min.

[0037] According to a preferred embodiment of the present invention, in step (3), the ST heat treatment includes alternating low-temperature heat treatment and high-temperature heat treatment.

[0038] According to an embodiment of the present invention, the time for the ST heat treatment is 2 hours or more, for example, 3 hours, 5 hours, or 10 hours.

[0039] According to an embodiment of the present invention, the ST heat treatment is performed in a vacuum or in an inert gas atmosphere, for example, the inert gas atmosphere may be selected from nitrogen gas, argon gas, and the like.

[0040] According to an exemplary embodiment of the present invention, in step (3), the ST heat treatment includes a first temperature-rise stage, a first temperature-holding heat treatment, a second temperature-rise stage, and a second temperature-holding heat treatment, wherein the first temperature-rise stage includes a temperature rise from 400°C to 790°C over 70 min and a first temperature-holding heat treatment includes a temperature-holding heat treatment at 790°C for 480 min, the second temperature-rise stage includes a temperature rise from 790°C to 940°C over 30 min, and a second temperature-holding heat treatment includes a temperature-holding heat treatment at 940°C for 720 min.

[0041] According to an exemplary embodiment of the present invention, in step (3), the ST heat treatment includes a first temperature rise stage, a first temperature retention heat treatment, a second temperature rise stage, a second temperature retention heat treatment, a third temperature rise stage, and a third temperature retention heat treatment, wherein the first temperature rise stage includes a temperature rise from 420°C to 750°C over 70 min and a first temperature retention heat treatment comprising maintaining the temperature at 750°C for 300 min; the second temperature rise stage includes a temperature rise from 750°C to 810°C over 30 min and a second temperature retention heat treatment comprising maintaining the temperature at 810°C for 420 min; the third temperature rise stage includes a temperature rise from 780°C to 870°C over 40 min and a third temperature retention heat treatment comprising maintaining the temperature at 870°C for 900 min.

[0042] In conventional techniques, diffusion heat treatment of large-sized sintered magnets (thickness in the orientation direction ≥ 10 mm) tends to employ a single temperature, typically between 870 and 970°C. Because different temperatures provide different diffusion forces, the conventional approach to accommodate increasing product thickness is to increase the diffusion temperature to enhance the diffusion force and thereby achieve deeper diffusion of the heavy rare earth elements. However, when the diffusion thickness (i.e., orientation thickness) reaches 10 mm or more, direct contact between the magnet and the heavy rare earth elements can easily lead to supersaturation of the heavy rare earth elements on the magnet surface, allowing the heavy rare earth elements to easily penetrate into the main phase of the crystal grains. However, the formation of a heavy rare earth layer on the magnet surface can also hinder subsequent diffusion of the heavy rare earth elements. The present invention overcomes this problem by increasing the M layer to achieve controlled adjustment of the heavy rare earth elements. At the same time, the inventors also found that alternating low- and high-temperature heat treatment during ST heat treatment significantly improves diffusion depth, particularly when the ST heat treatment conditions of the present invention are adopted. This is because, during the low-temperature heat treatment diffusion process, if the heat treatment temperature is lower than 750°C, the heavy rare earth RH located on the magnet surface is too low to diffuse effectively. However, if the heat treatment temperature is higher than 890°C, the diffusion efficiency is too high, preventing sufficient substitution of heavy rare earth and Nd at the grain boundaries. This leads to the enrichment of heavy rare earth elements at the magnet surface, reducing the RH diffusion depth. Meanwhile, during the high-temperature heat treatment diffusion process, if the heat treatment temperature is higher than 970°C, the heavy rare earth elements located on the surface directly enter the main phase, preventing grain boundary diffusion.

[0043] According to an embodiment of the present invention, rapid cooling and temperature reduction are required after the ST heat treatment. Rapid cooling and temperature reduction can be performed by a method known in the art, for example, a vacuum cooling method without heating power output.

[0044] According to an embodiment of the present invention, before disposing the diffusion portion, the billet may be washed sequentially with an acid solution and deionized water, followed by a drying process. The acid solution may be selected from acid solutions known in the art, such as aqueous hydrogen chloride solutions and aqueous nitric acid solutions.

[0045] According to an embodiment of the present invention, the manufacturing method further includes (4) performing an aging heat-holding treatment after the rapid cooling and temperature decrease, wherein the conditions for the aging heat-holding treatment are that the aging heat-holding temperature is between 430 and 650°C, the aging heat-holding time is longer than 30 minutes, and the aging heat-holding is followed by rapid cooling to room temperature.

[0046] According to an embodiment of the present invention, the aging heat treatment is carried out in a vacuum or an inert gas atmosphere.

[0047] The present invention further provides applications of the above R-Fe-B sintered magnet in the fields of wind power generation, household motors, automobiles, medical equipment, or mobile communication electrical equipment, and is preferably applied in the field of wind power generation.

[0048] (beneficial effects) (1) The present invention provides a large-sized R-Fe-B sintered magnet and a manufacturing method thereof. Compared to the conventional grain boundary diffusion method, the present invention solves the problems that current large-sized sintered magnets are too thick, making it difficult for heavy rare earth elements to diffuse into the magnet, resulting in a large difference in coercivity between the magnet's surface and interior after diffusion treatment, a large amount of heavy rare earth elements consumed by diffusion, and a long diffusion period.

[0049] (2) This invention employs a diffusion zone including an M layer and an RH layer on the surface of a magnet billet, which undergoes diffusion heat treatment including DW and ST heat treatments. After the organic solids and solvents in the diffusion layer are removed during the DW heat treatment, a concentration-adjusting layer is formed, thereby adjusting the heavy rare earth concentration in the RH. During the ST heat treatment, the heavy rare earth elements in the RH layer first pass through the powder in the M layer before reaching the magnet surface. The presence of the M layer prevents the heavy rare earth elements from coming into direct contact with the magnet, preventing the problem of excessive heavy rare earth concentrations on the magnet surface accumulating at grain boundaries and clogging diffusion paths. Furthermore, the heavy rare earth concentrations are adjusted and controlled after passing through the M layer during the diffusion process, preventing excessive concentrations due to a relatively large amount of heavy rare earth elements being distributed on the magnet surface at the beginning of diffusion. By optimizing the diffusion zone structure and combining the diffusion heat treatment process, this invention achieves diffusion heat treatment for large-sized sintered magnets, resulting in more uniform internal coercivity in the resulting sintered magnets. [Brief explanation of the drawings]

[0050] [Figure 1] FIG. 10 is a diagram showing the state of the diffusion portion after undergoing DW in the heat treatment process. [Figure 2] 1 is a schematic diagram of sample collection positions for the sintered magnet of Example 1. Units of illustration: mm. (Modes for Carrying Out the Invention) The technical solutions of the present invention will be described in more detail below with reference to specific examples. It should be understood that the following examples are merely intended to exemplify and explain the present invention, and should not be construed as limiting the scope of the claims of the present invention. Any technologies realized based on the above content of the present invention are included within the scope of the claims of the present invention.

[0051] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0052] Example 1 The manufacturing method of the big size sintered magnet is as follows: (1) A neodymium-iron-boron magnet (R-Fe-B magnet) was prepared by arranging raw materials with the desired composition, specifically, 29.1% Nd, 1.2% Dy, 1.5% Co, 0.2% Al, 0.1% Ga, 0.2% Ti, 0.17% Cu, 0.98% B, and the remainder Fe. The raw materials were melt-spinned in a melting furnace to obtain a neodymium-iron-boron alloy sheet with a thickness of 0.1 to 0.5 mm. The alloy sheet was coarsely crushed using a hydrogen embrittlement process to obtain powder. The powder was then crushed in a jet mill to obtain a fine powder with an SMD of 2.85 μm. The fine powder was then magnetically aligned and press-molded to obtain a green compact with a density of 3.98 g / cm3. The green compact was then sintered and aged in a sintering furnace to obtain a base body. After processing the element body, the billet was washed with a nitric acid solution and deionized water, and then dried to obtain a neodymium-iron-boron billet A1. The dimensions of the billet A1 were 80 mm × 40 mm × 11 mm, with a dimensional tolerance of ±0.03 mm. The thickness Z along the orientation direction of the billet A1 was 11 mm.

[0053] (2) Arrangement of the diffusion section: The diffusion section is arranged on two surfaces of the billet A1 in the orientation direction, and the diffusion section has a two-layer structure, including an M layer and an RH layer, of which the M layer is in direct contact with the surface of the billet A1, and the RH layer is arranged on the surface of the M layer. The specific process is as follows:

[0054] (a) The manufacturing process of the M layer includes preparing a first slurry using graphite powder (oxygen content of the powder is 0.07%), organic solid rosin-modified alkyd resin, and ethanol, in which the weight percentages of the graphite powder, organic solid rosin-modified alkyd resin, and ethanol are 55 wt%, 2 wt%, and 43 wt%, respectively. The first slurry is sprayed onto the surface of the billet A1, and then dried with hot air at 60°C. After drying, an M layer is obtained, the thickness of which is 3±2 μm.

[0055] (b) Then, an RH layer was placed on the surface of the dried M layer. The process for preparing the RH layer included preparing a second slurry using terbium hydride powder, organic solid rosin-modified alkyd resin, and ethanol, where the weight percentages of the terbium hydride powder, organic solid rosin-modified alkyd resin, and ethanol were 62 wt%, 3 wt%, and 35 wt%, respectively. Similarly, the second slurry was sprayed onto the surface of the M layer. After spray application was completed, the layer was again dried with hot air at 60°C. After drying, an RH layer was obtained, with a thickness of 50±15 μm. That is, after the placement of the surface diffusion portion of billet A1 was completed, billet A2 was formed.

[0056] (3) Diffusion heat treatment: The billet A2 is placed in a graphite case and subjected to diffusion heat treatment. The diffusion heat treatment process begins with heating in a vacuum state, with a vacuum level of ≦10 Pa. The diffusion heat treatment process mainly includes heating, DW, ST, and cooling processes. The specific diffusion heat treatment process is as follows: 1) Temperature increase: The temperature was increased to 400°C over 80 min; 2) DW: maintained at 400℃ for 240 min; 3) Temperature increase: The temperature was increased from 400°C to 850°C over 70 min; 4) ST1: maintained at 850℃ for 480 min; 5) Temperature increase: The temperature was increased from 850°C to 940°C over 30 min; 6) ST2: maintained at 940℃ for 1080 min; (4) Aging treatment: After the diffusion heat treatment was completed, the material was filled with argon gas, and the blower was turned on to rapidly cool it to below 80°C. After rapid cooling, the material was heated to 500°C and aged (the heating rate was 5°C / min and the temperature holding time was 120 min. Aging treatment refers to a heat treatment process in which the alloy workpiece, after undergoing solid solution treatment, cold plastic deformation, casting, or forging, is left at a relatively high temperature or at room temperature to maintain its performance, shape, and dimensions, and change over time). After the aging treatment was completed, the material was filled with argon gas again, and the blower was turned on to rapidly cool it to 80°C, yielding the final neodymium iron boron sintered magnet A3.

[0057] Figure 1 shows the state of the diffusion zone after DW in the heat treatment process. After the DW process, the organic solids and solvents in the M layer escape from the diffusion zone. At this time, the M layer of the diffusion zone is mainly graphite powder, and the RH layer is mainly terbium hydride powder.

[0058] (5) The neodymium-iron-boron sintered magnet A3 was inspected as follows.

[0059] 1) Sampling: As shown in Figure 2, the neodymium-iron-boron sintered magnet A3 was cut along its orientation to obtain a diffusion cross-sectional area. Samples measuring 1 mm x 1 mm x 1 mm were taken from the surface of the sintered magnet in the diffusion cross-sectional area and from a position 5 mm away from the surface. These samples were designated H1-1 and H1-2.

[0060] The performance of samples H1-1 and H1-2 in Example 1 was measured and compared. The measurement results are shown in Table 1.

[0061] 2) The measurement conditions are as follows: Sample size: 1 mm × 1 mm × 1 mm, tolerance ±0.03 mm; Measurement temperature: 23℃ Inspection equipment: UK HIRST PFM06 (maximum coercive force measurement possible: 60 kOe, temperature range: 16~40℃, minimum inspection possible for B1×1×1 sample).

[0062] [Table 1]

[0063] Example 2 The manufacturing method of the big size sintered magnet is as follows: (1) A neodymium-iron-boron magnet (R-Fe-B magnet) was prepared by arranging raw materials with the desired composition: 28.6% PrNd, 1.5% Dy, 1.0% Co, 0.1% Al, 0.2% Ga, 0.12% Ti, 0.10% Cu, 0.98% B, and the remainder Fe. The raw materials were melt-spinned in a melting furnace to obtain a neodymium-iron-boron alloy sheet with a thickness of 0.1 to 0.5 mm. The alloy sheet was coarsely crushed using a hydrogen embrittlement process to obtain powder. The powder was then crushed in a jet mill to obtain a fine powder with an SMD of 2.85 μm. The fine powder was then magnetically aligned and press-molded to a green compact with a density of 3.95 g / cm. The green compact was then sintered and aged in a sintering furnace to obtain a blank. After processing, the billet was washed with a nitric acid solution and deionized water, and then dried to obtain a neodymium-iron-boron billet B1. The dimensions of the billet B1 were 100 mm × 50 mm × 15 mm, with a dimensional tolerance of ±0.03 mm, and the thickness Z in the orientation direction of the billet A1 was 15 mm.

[0064] (2) Arrangement of the diffusion section: The diffusion section was arranged on the surface of the billet B1, and the diffusion section had a four-layer structure, consisting of an M1 layer, an RH1 layer, an M2 layer, and an RH2 layer, in that order from the surface of the billet B1, of which the first layer, M1, was in direct contact with the billet B1. The specific process was as follows:

[0065] (a) The manufacturing process of the M1 layer includes preparing a first slurry using molybdenum powder (oxygen content of the powder is 0.65%), organic solid polyvinyl butyral, and ethanol, in which the weight percentages of the molybdenum powder, organic solid polyvinyl butyral, and ethanol are 60 wt%, 5 wt%, and 35 wt%, respectively. The first slurry is sprayed onto the surface of billet B1, and then dried with hot air at 60°C. After drying, an M1 layer is obtained, with a thickness of 3±2 μm.

[0066] (b) After drying, an RH1 layer was placed on the surface of the M1 layer. The manufacturing process for the RH1 layer included preparing a second slurry using dysprosium hydride powder, organic solid polyvinyl butyral, and ethanol, where the weight percentages of the dysprosium hydride powder, organic solid polyvinyl butyral, and ethanol in the second slurry were 60 wt%, 8 wt%, and 32 wt%, respectively. Similarly, the second slurry was sprayed onto the surface of the M1 layer. After spray application was completed, the second slurry was again dried with hot air at 60°C. After drying, an RH2 layer was obtained, with a thickness of 40±15 μm.

[0067] (c) After drying is completed, the above steps (a) and (b) are repeated to sequentially deposit one M2 layer and one RH2 layer. The M2 layer and the RH2 layer are formed using the first and second slurries in steps (a) and (b), respectively. After drying, the M2 layer has a thickness of 2±1 μm, and the RH2 layer has a thickness of 35±15 μm. After the surface diffusion portion of the billet body B1 is completely deposited, billet B2 is formed.

[0068] (3) Diffusion heat treatment: The billet B2 is placed in a graphite case and subjected to diffusion heat treatment. The diffusion heat treatment process begins with heating in a vacuum state, with a vacuum level of ≦10 Pa. The diffusion heat treatment process mainly includes heating, DW, ST, and cooling processes. The specific diffusion heat treatment process is as follows: 1) Temperature increase: The temperature was increased from 50°C to 420°C over 80 min; 2) DW: maintained at 420℃ for 240 min; 3) Temperature increase: The temperature was increased from 420°C to 750°C over 70 min; 4) ST1: maintained at 750℃ for 300 min; 5) Temperature increase: The temperature was increased from 750°C to 810°C over 30 min; 6) ST2: maintained at 810℃ for 420 min; 7) Temperature increase: The temperature was increased from 780°C to 870°C over 40 min; 8) ST3: maintained at 870℃ for 1200 min; (4) Aging treatment: After the diffusion heat treatment was completed, the material was filled with argon gas, and the blower was turned on to rapidly cool it to below 80°C. After rapid cooling, the material was heated to 520°C and aged (the heating rate was 5°C / min and the temperature holding time was 300 min. Aging treatment refers to a heat treatment process in which the alloy workpiece, after undergoing solid solution treatment, cold plastic deformation, casting, or forging, is left at a relatively high temperature or at room temperature to maintain its performance, shape, and dimensions, and change over time). After the aging treatment was completed, the material was filled with argon gas again, and the blower was turned on to rapidly cool it to 80°C, yielding the final neodymium iron boron based sintered magnet B3.

[0069] (5) The neodymium-iron-boron sintered magnet B3 of this example was measured with reference to Example 1, except that A3 was replaced with B3, and the resulting samples were designated H2-1 and H2-2. The measurement results are shown in Table 2.

[0070] [Table 2]

[0071] (Comparative Example 1) In this comparative example, a billet was manufactured using the same sample manufacturing process as in Example 1, with the following differences.

[0072] (2) Diffusion sections were placed: Diffusion sections were placed on two surfaces of the billet A1 in the orientation direction, and an RH layer was directly placed on the diffusion sections. The manufacturing process for the RH layer included preparing a slurry using terbium hydride powder, organic solid rosin-modified alkyd resin, and ethanol, where the weight percentages of the terbium hydride powder, organic solid rosin-modified alkyd resin, and ethanol were 62 wt%, 3 wt%, and 35 wt%, respectively. The slurry was then sprayed directly onto the surface of the billet A1. After spraying, the slurry was dried again with hot air at 60°C. After drying, an RH layer was obtained, with a thickness of 50±15 μm.

[0073] The other steps (1), (3) and (4) were the same as in Example 1, and in this comparative example, a neodymium-iron-boron sintered magnet C3 was finally obtained.

[0074] (5) Neodymium-iron-boron sintered magnet C3 was inspected with reference to Example 1, except that A3 was replaced with C3, and samples D3-1 and D3-2 of Comparative Example 1 were obtained.

[0075] [Table 3]

[0076] (Comparative Example 2) In this comparative example, a billet was manufactured using the same sample manufacturing process as in Example 2, with the following differences.

[0077] (2) A diffusion portion was provided: the oxygen element content in the molybdenum powder used in the M layer was 5.5%, and the oxygen element content in the molybdenum powder used in Example 2 was 0.65%.

[0078] The other steps (1), (2), and (4) were the same as in Example 2, and this comparative example ultimately produced neodymium-iron-boron sintered magnet D4, and samples D4-1 and D4-2 of Comparative Example 2. The results showed that the performance of the entire sample had deteriorated, and the uniformity of the coercive force had also deteriorated.

[0079] [Table 4]

[0080] (Comparative Example 3) This comparative example is basically the same as Example 2, except that the diffusion heat treatment process in step (3) is specifically as follows: 1) Temperature increase: The temperature was increased from 50°C to 420°C over 80 min; 2) DW: maintained at 420℃ for 240 min; 3) Temperature increase: The temperature was increased from 420°C to 870°C over 140 min; 4) ST: Maintained at 870°C for 900 min.

[0081] The other steps (1), (2), and (4) were the same as in Example 1, and in this comparative example, a neodymium-iron-boron sintered magnet E5 was finally obtained.

[0082] (5) The neodymium-iron-boron sintered magnet E5 of this example was measured with reference to Example 1, except that A3 was replaced with E5, resulting in samples E5-1 and E5-2. The measurement results are shown in Table 5.

[0083] [Table 5]

[0084] Although exemplary embodiments of the present invention have been described above, the scope of the claims of the present application is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art without departing from the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for producing an R-Fe-B sintered magnet, comprising the steps of: (1) producing a billet of R-Fe-B magnet with a thickness of ≥ 10 mm; (2) Arranging a diffusion section: arranging diffusion sections on at least two surfaces of the billet obtained in step (1) in the orientation direction, the diffusion sections including at least one RH layer and one M layer, the M layer being in direct contact with the billet surface, and at least one M layer being spaced between the RH layer and the billet; (3) Diffusion Heat Treatment: Diffusion heat treatment of the billet on which the diffusion layer has been disposed in step (2) to obtain the R—Fe—B sintered magnet; Specifically, the method for producing the M layer includes disposing a slurry containing M powder on two surfaces of the billet in the orientation direction, and then drying the slurry to obtain the M layer; The M powder-containing slurry contains M powder, an organic solid, and optionally a solvent; In the M powder-containing slurry, the mass ratio of M powder, organic solid, and solvent is (20-70):(1-10):(0-50), the M powder includes at least one of graphite powder, titanium powder, zirconium powder, molybdenum powder, tungsten powder, titanium oxide, zirconium oxide, molybdenum oxide, and tungsten oxide, and the content of oxygen element in the M powder is less than 3% or less than 1%; a thickness of the R-Fe-B sintered magnet in the orientation direction of the magnet of 10 mm or more, or 10 mm to 20 mm; a diffusion cross-sectional region at any one cross section along the orientation direction; a diffusion cross-sectional region surface at a side of the diffusion cross-sectional region closer to the outer surface of the R-Fe-B sintered magnet; a difference in coercivity between the diffusion cross-sectional region surface and a point 5 mm away from the diffusion cross-sectional region surface of the magnet of ΔH, wherein ΔH≦50 kA / m or ΔH is 45 kA / m or less.

2. A manufacturing method as described in claim 1, characterized in that in step (2), the diffusion section has RH layers and M layers arranged alternately, and at least one M layer is separated between the RH layer and the billet, the RH layers include 1 to 3 layers, and the M layers include 1 to 3 layers.

3. The diffusion section includes one M layer and one RH layer, or 3. The manufacturing method according to claim 2, wherein the diffusion section includes two M layers and two RH layers, which are arranged in the order of a first M layer, a first RH layer, a second M layer, and a second RH layer from the surface of the billet, the first M layer and the second M layer being homologous or different, and the first RH layer and the second RH layer being homologous or different.

4. The manufacturing method according to claim 1, wherein in the diffusion section, each RH layer has a thickness of 1 μm to 70 μm.

5. The manufacturing method of the RH layer specifically includes disposing an RH slurry on two surfaces of the billet in the orientation direction, and then drying the RH slurry to obtain the RH layer; the RH slurry contains a heavy rare earth element, an organic solid, and optionally a solvent; In the RH slurry, the mass ratio of the heavy rare earth element, the organic solid, and the solvent is (40-70):(0.5-12):(0-50); the heavy rare earth element includes at least one of metallic dysprosium, metallic terbium, dysprosium hydride, terbium hydride, dysprosium fluoride, terbium fluoride, dysprosium oxide, and terbium oxide; the organic solid is at least one selected from a rosin-modified alkyd resin, a thermoplastic phenolic resin, a urea resin, and polyvinyl butyral; 2. The method according to claim 1, wherein the solvent is at least one selected from the group consisting of alcohol-based solvents, ether-based solvents, and aromatic hydrocarbon-based solvents.

6. In the diffusion section, the thickness of each M layer is less than 20 μm and greater than 0.1 μm; 2. The manufacturing method according to claim 1, wherein the ratio of the thickness of each RH layer to the thickness of each M layer in the diffusion section is (1-70):(0.1-20).

7. The manufacturing method described in claim 1, characterized in that the M powder includes powder having a particle size of less than 5 μm, and powder having a particle size between 0.5 μm and 1.8 μm accounts for more than 50% or more than 65% of the total mass of the powder.

8. In step (3), the diffusion heat treatment includes at least a DW heat treatment and an ST heat treatment, Specifically, the conditions of the DW heat treatment include heating to a DW temperature and then maintaining the temperature for a certain period of time, the DW temperature being 280°C to 480°C or 320°C to 400°C, and the DW heat treatment time being 2 hours or more; 2. The method of claim 1, wherein the DW heat treatment is performed under vacuum conditions.

9. In step (3), the ST heat treatment includes a low-temperature heat treatment and a high-temperature heat treatment, wherein the temperature of the low-temperature heat treatment is 750°C to 890°C, and the temperature of the high-temperature heat treatment is 830°C to 970°C, the difference between the low-temperature heat treatment temperature and the high-temperature heat treatment temperature is more than 30°C, and the time of the low-temperature heat treatment and / or the high-temperature heat treatment is 50 hours or less, wherein the heat-keeping time is ≥ 2 hours, and the temperature rise rate from the low-temperature heat treatment to the high-temperature heat treatment is 4 to 10°C / min, The low-temperature heat treatment includes increasing the temperature to a low-temperature heat treatment temperature and then maintaining the temperature for a certain period of time, and the high-temperature heat treatment includes increasing the temperature to a high-temperature heat treatment temperature and then maintaining the temperature for a certain period of time, In step (3), the ST heat treatment includes alternating low-temperature heat treatment and high-temperature heat treatment, The time of the ST heat treatment is 2 hours or more in all cases, 9. The manufacturing method according to claim 8, wherein the ST heat treatment is performed in a vacuum or in an inert gas atmosphere.

10. Before disposing the diffusion portion, the billet is washed successively with an acid solution and deionized water, and then dried; The manufacturing method further includes (4) performing an aging heat-retention treatment after the quenching and temperature-lowering, wherein the conditions of the aging heat-retention treatment are that the aging heat-retention temperature is between 430 and 650°C, the aging heat-retention time is longer than 30 minutes, and the aging heat-retention is followed by quenching to room temperature after the aging heat-retention is completed; 2. The method according to claim 1, wherein the aging heat treatment is carried out in a vacuum or inert gas atmosphere.

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