Sintered r-fe-b permanent magnet, and preparation method and use thereof

Abstract

The present invention provides a sintered R-Fe-B permanent magnet, and a preparation method and use thereof.SOLUTION: The main phase grains in the surface layer of the sintered R-Fe-B permanent magnets of the present invention are referred to as surface layer grains, the size of the surface layer grains is referred to as D1, the main phase grains in the core of the sintered R-Fe-B permanent magnets along the easy magnetic direction are referred to as core grains, the size of the core grains is referred to as Dn, and D1 - Dn ≤ 0.34. The present invention improves the size consistency of the main phase grains in the sintered R-Fe-B permanent magnet, thereby improving the magnetic properties of the sintered R-Fe-B permanent magnet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of manufacturing rare earth permanent magnet materials, and in particular to a sintered R-Fe-B permanent magnet manufactured by grain boundary diffusion, as well as its manufacturing method and use. [Background technology]

[0002] Improving energy utilization efficiency is an important path to effectively solving energy problems. Statistics show that motors have always accounted for a relatively high proportion of electrical energy consumption in the industrial sector. Therefore, improving motor efficiency is crucial for conserving power resources. Compared to conventional motors, permanent magnet motors have relatively high motor efficiency. Permanent magnet motors are widely used in many industrial fields, such as electric vehicles and elevators. Sintered neodymium-iron-boron permanent magnet motors offer advantages such as high efficiency, low noise, and compact size, making them the ideal material for manufacturing high-efficiency permanent magnet motors. However, during motor operation, Nd-Fe-B magnets are exposed to high temperatures due to eddy currents. As the temperature increases, the magnet's performance deteriorates, ultimately reducing motor efficiency and increasing energy consumption. Improving the inherent coercivity of neodymium-iron-boron magnets can improve their high-temperature resistance, increasing motor power density and torque density and preventing motor efficiency degradation.

[0003] There are many ways to improve the intrinsic coercivity of neodymium iron boron magnets. Among them, grain refinement and heavy rare earth grain boundary diffusion technology are currently the most effective and simplest methods to implement. By further performing diffusion treatment on a magnet with refined crystal grains as the base material, the coercivity of the magnet can be significantly improved. However, when the crystal grains are refined, the number of crystal grains per unit volume increases, and the penetration resistance of heavy rare earth elements rises. In order to obtain a better diffusion effect and ensure that the same heavy rare earth elements exist in the surface layer and the core of the magnet, a longer diffusion time is required for the diffusion source element to diffuse into the magnet. At high temperatures during the diffusion process, the atoms at the boundary layer of the main phase crystal grains of the magnet are in a high-energy state. When they come into contact with elements such as high-concentration rare earths in the thermally activated state in the grain boundary phase for a long time, the main phase crystal grains will grow spontaneously and inevitably. In particular, due to the abnormal growth of the surface crystal grains of the magnet that come into contact with the heavy rare earth diffusion source first, the diffusion channels become smaller, preventing the diffusion source from diffusing deeper into the magnet. As a result, the contact between the main phase crystal grains in the core and the diffusion source elements decreases, and the original crystal grain size and performance are maintained. Thereby, a large difference occurs in the dimensions of the main phase crystal grains on the surface and in the core of the magnet, deteriorating the magnetic properties, rectangularity, and mechanical properties of the magnet.

Summary of the Invention

Problems to be Solved by the Invention

[0004] To solve the above drawbacks, the technical solution of the present invention is as follows.

Means for Solving the Problems

[0007] In an embodiment of the present invention, in the core, the average size of the core crystal grains closer to the surface of the permanent magnet is larger, and the average size of the core crystal grains closer to the geometric center point of the permanent magnet is smaller.

[0008] According to an embodiment of the present invention, the core can be divided into multiple parts along the easy magnetization direction of the sintered R-Fe-B permanent magnet. For example, it can be divided evenly into a first core, a second core, and a third core, and the first, second, and third cores have the same thickness, the first core is closer to the surface of the permanent magnet, and the third core is closer to the geometric center of the permanent magnet. Preferably, the average size of the first core crystal grains in the first core is D2, the average size of the second core crystal grains in the second core is D3, and the average size of the third core crystal grains in the third core is D4. Preferably, D4≦D3≦D2. Furthermore, 0 <D1-D2≦0.34、かつ0<D1-D3≦0.34、かつ0<D1-D4≦0.34である。

[0009] According to an embodiment of the present invention, the thickness of the sintered R—Fe—B permanent magnet is not particularly limited, and any thickness known in the art, such as 3.0 mm or 3.1 mm, can be selected.

[0010] According to an exemplary embodiment of the present invention, the thickness of the sintered R-Fe-B permanent magnet is 3 mm, and the core includes a first core, a second core, and a third core, arranged in that order along the easy magnetization direction of the sintered R-Fe-B permanent magnet. Preferably, the first core refers to the region extending from 0.3 mm away from the surface of the permanent magnet to 0.7 mm away from the surface of the permanent magnet, and the average size of the first core grains corresponding to this region is D2. The second core refers to the region extending from 0.7 mm away from the surface of the permanent magnet to 1.1 mm away from the surface of the permanent magnet, and the average size of the second core grains corresponding to this region is D3. The third core refers to the region extending from 1.1 mm away from the surface of the permanent magnet to 1.5 mm away from the surface of the permanent magnet, and the average size of the third core grains corresponding to this region is D4. Furthermore, D1-D2≦0.34, D1-D3≦0.34, and D1-D4≦0.34.

[0011] According to an embodiment of the present invention, as shown in Figure 1, the sintered R-Fe-B permanent magnet includes a main phase and a grain boundary phase, wherein the grain boundary phase includes a Zr-B phase, and the Zr-B phase exhibits an acicular structure. Preferably, the length of the acicular Zr-B phase is 20 nm to 1000 nm, for example, 100 nm or 500 nm. Preferably, the acicular Zr-B phase is uniformly dispersed in the grain boundary phase, changing the grain boundary state.

[0012] According to an embodiment of the present invention, the Zr-B phase exhibits an acicular structure and can also be expressed as an acicular Zr-B phase.

[0013] According to an embodiment of the present invention, the needle-like structure is known in the art. For example, the needle-like structure may refer to a structure whose length is greater than the maximum width (e.g., diameter) of its cross section, and the shape of the cross section is not particularly limited, including but not limited to, a circle, an ellipse, a rectangle, and a polygon. Preferably, the length of the needle-like structure is 5 times or more, for example, 10 times, 50 times, or 100 times, the maximum width of the cross section.

[0014] According to an embodiment of the present invention, the magnetic performance of the sintered R—Fe—B permanent magnet is as follows:

[0015] (1) Br is 1.41T or more, for example, 1.419T, 1.420T, or 1.421T; (2) Hcj is 1900 KA / m or more, for example, 1910 KA / m, 1920 KA / m, 1930 KA / m, 1940 KA / m, 1950 KA / m, 1960 KA / m, 1970 KA / m, 1980 KA / m, or 1990 KA / m.

[0016] According to an embodiment of the present invention, the raw materials for the sintered R—Fe—B permanent magnet contain Zr and B. Preferably, the mass contents of Zr and B in the raw materials are [Zr] and [B], respectively, and satisfy the relationship 0.13≦[Zr] / [B]≦0.55. The mass content of Zr in the raw materials is 0.15 wt% or more. This ensures the formation of acicular Zr-B phases in the grain boundary phase, thereby achieving grain boundary phase transformation.

[0017] According to an embodiment of the present invention, the raw material of the sintered R—Fe—B permanent magnet includes R, M1, B, Zr, and the remaining Fe and unavoidable impurity elements, R is at least one or more elements selected from Sm, La, Ce, Y, Nd, Pr, Ho, Gd, Dy, and Tb, and the mass content of R is 28 wt% or more and 35 wt% or less; M1 is at least one or more selected from Co, Ga, Cu, Al, Nb, Zr, and Ti, and the mass content of M1 is 0.5 wt% or more and 5 wt% or less; The B content is 0.95 wt% or more and 1.3 wt% or less, The Zr content is 0.15 wt% or more, preferably 0.15 wt% or more and 0.5 wt% or less, for example, 0.45 wt%.

[0018] The present invention further provides a method for producing the above-mentioned sintered R—Fe—B permanent magnet, the method comprising the steps of: Step (1): Mixing raw materials in a corresponding mass ratio to produce a neodymium-iron-boron alloy strip cast ribbon, and then pulverizing it to obtain a magnetic powder of a target particle size; Step (2) of press-molding the obtained magnetic powder and pressing it by cold isostatic pressing to obtain a green body; (3) subjecting the compact to a sintering and aging treatment to obtain a sintered NdFeB matrix; and (4) subjecting the sintered neodymium iron boron matrix to a high temperature diffusion treatment to obtain the sintered R-Fe-B permanent magnet.

[0019] According to an embodiment of the present invention, in step (1), the raw material refers to the raw material of the sintered R—Fe—B permanent magnet described above.

[0020] According to an embodiment of the present invention, in step (1), the neodymium-iron-boron alloy strip-cast ribbon is produced by a method known in the art, such as strip casting and melt spinning. Illustratively, the neodymium-iron-boron alloy strip-cast ribbon is produced by heating and melting the raw materials to 1300-1600°C by electromagnetic induction, casting the molten alloy onto a chill roll (preferably a polished chill roll), and then further cooling it in a water-cooled bath to obtain a neodymium-iron-boron alloy strip-cast ribbon.

[0021] According to an embodiment of the present invention, in step (1), the pulverization step specifically includes subjecting the neodymium-iron-boron alloy strip cast ribbon to hydrogen pulverization to obtain a coarsely pulverized powder, and then pulverizing the coarsely pulverized powder in a high-energy ball milling process or a jet mill using a jet milling process to obtain a magnetic powder. Preferably, a lubricant may be added during pulverization. Any lubricant known in the art may be used as the lubricant, and the present invention does not particularly limit the lubricant. Furthermore, the amount of the lubricant added is 0.1 to 1 wt %, for example, 0.1 to 0.5 wt %, of the magnetic powder.

[0022] For example, in step (1), the pulverization step is as follows: the neodymium-iron-boron alloy strip cast ribbon is subjected to hydrogen pulverization to obtain coarsely pulverized powder, which is then pulverized in a jet mill to obtain magnetic powder of a target particle size. Optionally, after obtaining the magnetic powder of the target particle size, 0.1 to 0.5 wt % of a lubricant may be added and mixed, for example, for 0.1 to 5 hours to uniformly mix the magnetic powder.

[0023] In the present invention, the hydrogen pulverization, high energy ball milling process, and jet milling process can all be carried out using process conditions known in the art, as long as the magnetic powder is obtained.

[0024] According to an embodiment of the present invention, in step (1), the target particle size of the magnetic powder is 1 to 8 μm, for example, 5 μm.

[0025] According to an embodiment of the present invention, in step (2), the press molding includes orienting the magnetic powder in a magnetic field and then press-molding. Preferably, the magnetic field is a magnetic field known in the art, for example, having a magnetic field strength of 2 T.

[0026] According to an embodiment of the present invention, in step (2), the cold isostatic pressing may be performed under cold isostatic pressing conditions known in the art, and the present invention does not particularly limit the conditions.

[0027] According to an embodiment of the present invention, in step (3), the sintering treatment includes sintering the compact at a high temperature of 1055°C to 1090°C in a vacuum environment.

[0028] According to an embodiment of the present invention, in step (3), the aging treatment refers to performing a tempering treatment at 1000°C or less after sintering, which may be performed under conditions known in the art, such as 910°C and 520°C for 4 hours, respectively.

[0029] According to an embodiment of the present invention, in step (4), the sintered NdFeB matrix may first be mechanically processed to form an R—Fe—B black ribbon having a target size.

[0030] According to an embodiment of the present invention, in step (4), the sintered NdFeB matrix (e.g., R-Fe-B black ribbon) may be washed first, and the washing may be performed by a method known in the art. For example, the sintered NdFeB matrix (e.g., R-Fe-B black ribbon) may be washed with an acid having a volume concentration of 1% to 5% to remove oxide impurities and oil stains on the surface of the sintered NdFeB matrix (e.g., R-Fe-B black ribbon).

[0031] According to an embodiment of the present invention, in step (4), the high-temperature diffusion treatment specifically includes applying a heavy rare earth element to the surface of the sintered neodymium iron boron matrix (for example, R-Fe-B black ribbon) so that the heavy rare earth element is uniformly distributed on the surface of the sintered neodymium iron boron matrix (for example, R-Fe-B black ribbon); and performing a two-stage heat treatment diffusion in a vacuum atmosphere, with the temperature range of the first-stage heat treatment being 790°C to 930°C (preferably 900°C or less, for example, 800°C, 850°C, or 900°C), the temperature range of the second-stage heat treatment being 440°C to 530°C (preferably 520°C or less, for example, 450°C, 500°C, or 520°C), and the degree of vacuum being 10. -2 ~10 -4 The inventors have found that when the two-stage heat treatment diffusion of the present invention is employed, the temperature during diffusion is reduced because a lower vacuum is used, and therefore the Zr-B phase does not dissolve during the diffusion step.

[0032] According to an embodiment of the present invention, the heavy rare earth element is provided by a diffusion source. Preferably, the diffusion source includes heavy rare earth powder particles, an antioxidant, and an organic solvent. Preferably, the diffusion source is applied to the surface of a sintered neodymium iron boron matrix (e.g., an R-Fe-B black ribbon) in the form of a slurry. Preferably, the heavy rare earth powder particles include a mixture of at least one of dysprosium, dysprosium hydride, dysprosium oxide, dysprosium fluoride, terbium, terbium hydride, terbium oxide, and terbium fluoride.

[0033] According to an embodiment of the present invention, the heavy rare earth powder particles have an average particle size of 2 to 100 μm (for example, 10 μm, 50 μm), and D90 / D10 is 1.2 to 5.1 (for example, 2, 3, 4).

[0034] The inventors have discovered the following: To prevent Zr from dissolving in the neodymium-rich phase at high temperatures and alloying with other trace elements, which would prevent magnetic separation and inhibit the growth of the main phase crystal grains, it is necessary to diffuse at a lower diffusion temperature to ensure that the Zr-B phase in the grain boundary phase of the permanent magnet does not dissolve after diffusion and forms elongated tubes together with the main phase crystal grains, strengthening the capillary force and facilitating the penetration of the diffusion source into the interior of the permanent magnet. For this reason, a high vacuum (≥ 10 -2 A relatively low diffusion temperature is achieved by using a pressure of 100 Pa. The average particle size of the powder particles in the diffusion source is within the range of 2 to 100 μm, and the D90 / D10 ratio is within the range of 1.2 to 5.1, ensuring synchronous melting of the diffusion source during the diffusion process, maximizing the concentration difference between the diffusion source on the surface and inside of the magnet, increasing the driving force for diffusion, promoting penetration of the diffusion source into the interior of the permanent magnet, shortening the diffusion time, and suppressing abnormal growth of surface particles while ensuring magnetic performance.

[0035] The present invention also provides a sintered R—Fe—B permanent magnet produced by the above-mentioned production method, and the sintered R—Fe—B permanent magnet has the above-mentioned meaning.

[0036] The present invention also provides the use of the above-mentioned sintered R—Fe—B permanent magnet, preferably for use in a motor. [Effects of the Invention]

[0037] The beneficial effects are as follows:

[0038] Compared to conventional fine-grained diffusion magnets, the permanent magnets of the present invention exhibit a change in grain boundary structure, with the presence of acicular Zr-B phases formed by Zr and B in the raw materials. The formation of relatively thin channels between the acicular Zr-B phases and the main phase crystal grains reduces the diffusion barrier, strengthens capillary forces, accelerates the migration of heavy rare earth elements from the diffusion source into the permanent magnet, reduces the accumulation of heavy rare earth elements in the grain boundary phase, and suppresses the growth of main phase crystal grains. The present invention improves the dimensional uniformity of the main phase crystal grains in sintered R-Fe-B permanent magnets, further improving their magnetic performance. Furthermore, the use of low-temperature diffusion treatment conditions under high vacuum reduces the melting point of the grain boundary phase. The large-grain diffusion source particles with a concentrated grain size distribution are synchronously melted at a relatively low temperature, which promotes the formation of a larger concentration difference between the diffusion source elements on the surface and inside of the magnet, further accelerating the diffusion of the heavy rare earth elements into the magnet's interior, reducing the accumulation of diffusion sources in the grain boundary phase, suppressing grain growth, and ensuring consistent sizes of the main phase crystal grains in the permanent magnet after the diffusion of the fine-grain magnet. [Brief explanation of the drawings]

[0039] [Figure 1] 1 is a TEM of the sintered Nd—Fe—B permanent magnet obtained in Example 1. [Figure 2] FIG. 2 is a schematic diagram of the regions corresponding to the surface layer and core of a sintered R—Fe—B permanent magnet. [Figure 3] FIG. 2 is a schematic diagram of main phase crystal grains corresponding to different regions along the thickness direction in the cross section of a sintered R—Fe—B permanent magnet. [Figure 4] FIG. 1 is a schematic diagram of sampling points of surface crystal grains. [Figure 5] 1 is a TEM of the sintered Nd—Fe—B permanent magnets obtained in Comparative Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0040] The following will further describe the technical solutions of the present invention in detail with reference to specific examples. It should be understood that the following examples are only intended to exemplify and explain the present invention, and should not be construed as limiting the protection scope of the present invention. Any technology realized based on the above content of the present invention is included in the protection scope of the present invention.

[0041] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0042] Example 1 The manufacturing method for high performance sintered Nd-Fe-B permanent magnets includes the following steps: (1) The raw materials required for the Nd-Fe-B alloy were melted in the target composition in an argon atmosphere at 1400°C and held for 15 minutes to ensure homogenization. After that, they were cast onto the surface of a rotating quench roll to obtain a Nd-Fe-B alloy strip cast ribbon approximately 0.3 mm thick. Here, the Nd-Fe-B alloy contained 31.3 wt% Nd, 1.0 wt% B, 0.45 wt% Zr, 0.10 wt% Al, 0.2 wt% Ga, and 1.0 wt% Co, with the remainder being Fe and unavoidable impurities. (2) The Nd-Fe-B alloy strip cast ribbon from step (1) was coarsely crushed in a hydrogen crushing furnace and then removed under argon protection to reduce oxidation of the coarse powder. The coarse powder after hydrogen crushing was directly polished in a jet mill to obtain magnetic powder with particle sizes of 1 to 8 μm and an average particle size of 2.8 μm. (3) 0.15 wt% of fatty acid ester as an antioxidant was added to the magnetic powder obtained in step (2), and mechanical stirring was continued for 4 h until it was uniformly dispersed. (4) The magnetic powder of step (3) was press-molded in the direction of magnetic field orientation under conditions of vacuum and magnetic field strength of 2 T, and then pressed by cold isostatic pressing at 170 MPa to obtain a compact. (5) The compact from step (4) was placed in a vacuum sintering furnace and sintered at 1065°C for 3 hours, and then tempered at 910°C and 520°C for 4 hours to obtain a sintered Nd—Fe—B substrate. (6) The sintered Nd-Fe-B permanent magnet produced in step (5) was mechanically processed into a black ribbon with a thickness of 3.1 mm, length of 35 mm, and width of 21 mm, where the thickness direction was the easy magnetization direction of the magnet. The black ribbon was pickled with 3% diluted nitric acid to remove oil stains and then dried. (7) The washed black ribbon obtained in step (6) was coated with heavy rare earth elements in an atmospheric environment, and a slurry containing a Dy diffusion source was coated on the two large surfaces of the black ribbon in an amount of 0.7% based on the weight of the black ribbon. The weight ratio of Dy powder particles to fatty acid ester and organic solvent in the slurry was 80:15:5, the average particle size of the Dy powder was 4.7 μm, and D90 / D10 = 3.1. (8) For the black thin strip coated with heavy rare earth elements obtained in step (7), 2 × 10 -3 A two-stage heat treatment diffusion was performed in a vacuum atmosphere of 870°C for 6 hours in the first stage and 460°C for 4 hours in the second stage to obtain a sintered Nd-Fe-B permanent magnet. In this example, a lower heat treatment temperature than the usual two-stage heat treatment diffusion (900°C and 520°C) is adopted, which prevents Zr element from dissolving in the neodymium-rich phase and alloying with other trace elements, thereby ensuring the formation of a Zr-B phase in the grain boundary phase. Performance test: A test ribbon with a thickness of 3 mm, length of 7 mm, and width of 7 mm was cut from the center of the black ribbon after diffusion, and was magnetized to saturation in a pulsed magnetic field of 5 T. The demagnetization curve of the obtained magnet at 20°C was then tested using a NIM-10000 measuring instrument. Testing the dimensions of magnet crystal grains (i.e., the main phase crystal grains of the permanent magnet): After diffusion, the magnet was polished evenly in all directions by 0.05 mm to remove any surface Dy diffusion sources that had not penetrated the magnet. Positions 0.3 mm, 0.7 mm, 1.1 mm, and 1.4 mm from the outer surface of the permanent magnet were selected and cut along a direction perpendicular to the easy axis of magnetization (also shown as the thickness direction and orientation direction of the permanent magnet). The cut positions are indicated by dotted lines in Figure 3. The main phase crystal grains at different cross sections corresponding to the dotted lines were examined. In the present invention, D1 is the size of the magnet crystal grains in a region 0.3 mm from the outer surface of the cross section, D2 is the size of the magnet crystal grains in a region 0.7 mm from the outer surface of the permanent magnet (referred to as the second core), D3 is the size of the magnet crystal grains in a region 1.1 mm from the surface of the permanent magnet (referred to as the third core), and D4 is the size of the magnet crystal grains in a region 1.5 mm from the surface of the permanent magnet (referred to as the fourth core), and the above D1, D2, D3, and D4 are all average values ​​of the magnet crystal grains measured at six arbitrary points selected from the corresponding cross section. Figure 4 shows the six sampling points for D1.

[0043] Comparative Example 1-1 Comparative Example 1-1 was almost the same as the manufacturing method of Example 1, except that the Zr content in the Nd-Fe-B alloy in step (1) of Example 1 was changed to 0.10%, and the remaining conditions were the same as in Example 1, to obtain a Nd-Fe-B alloy strip-cast ribbon having a thickness of approximately 0.3 mm. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic properties of the sintered Nd-Fe-B permanent magnet obtained in this example at 20° C. and the size of the crystal grains at each position were tested.

[0044] Comparative Example 1-2 The manufacturing method of Comparative Example 1-2 was almost the same as that of Example 1, except that the blending for producing the strip cast ribbon in step (1) of Example 1 did not contain Zr element, and the rest was the same. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic properties of the sintered Nd-Fe-B permanent magnet obtained in this example at 20° C. and the size of the crystal grains at each position were tested.

[0045] Comparative Examples 1-3 Comparative Example 1-3 was almost the same as the manufacturing method of Example 1, except that in step (8) of Example 1, a vacuum of 5×10 was applied to the black thin strip coated with heavy rare earth. -2 The difference is that the two-stage heat treatment diffusion was carried out in a Pa atmosphere. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic properties of the sintered Nd-Fe-B permanent magnet obtained in this example at 20° C. and the size of the crystal grains at each position were tested.

[0046] Comparative Examples 1-4 The manufacturing method of Comparative Examples 1-4 was almost the same as that of Example 1, except that the average particle size of the Dy powder used in the slurry containing the heavy rare earth element Dy in step (7) of Example 1 was set to 1.8 μm, and the particle size distribution was set to D90 / D10=5.5. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic properties of the sintered Nd-Fe-B permanent magnet obtained in this example at 20° C. and the size of the crystal grains at each position were tested.

[0047] Comparative Examples 1-5 Comparative Example 1-5 was almost the same as the manufacturing method of Example 1, except that the Zr content in the Nd-Fe-B alloy in step (1) of Example 1 was 0.1%, and the heavy rare earth-coated black ribbon in step (8) of Example 1 was vacuum-treated at a degree of 2×10 -2 The difference is that the two-stage heat treatment diffusion is carried out in an atmosphere of Pa. The average particle size of the Dy powder used as the diffusion source is still 4.7 μm. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic properties of the sintered Nd-Fe-B permanent magnet obtained in this example at 20° C. and the size of the crystal grains at each position were tested.

[0048] Comparative Examples 1-6 Comparative Example 1-6 was almost the same as the manufacturing method of Example 1, except that the Zr content in the Nd-Fe-B alloy in step (1) of Example 1 was 0.1%, and the heavy rare earth-coated black ribbon in step (8) of Example 1 was vacuum-treated at a degree of 2×10 -2 The difference is that the two-stage heat treatment diffusion is performed in a Pa atmosphere, with the first heat treatment temperature at 900°C and the time period being 6 hours, and the second heat treatment temperature at 520°C and the time period being 4 hours. The average particle size of the Dy powder diffusion source used is still 1.8 μm. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic properties of the sintered Nd-Fe-B permanent magnet obtained in this example at 20° C. and the size of the crystal grains at each position were tested.

[0049] Comparative Examples 1-7 Comparative Example 1-7 was almost the same as the manufacturing method of Example 1, except that the process of applying a heavy rare earth element in step (7) of Example 1 and the diffusion of the heavy rare earth element as a diffusion source were not performed, and the black ribbon processed in step (6) was subjected to 2×10 -3 The difference is that the two-stage heat treatment diffusion is directly carried out in a vacuum atmosphere of 860°C for 6 hours in the first heat treatment, and the temperature of the second heat treatment is 460°C for 4 hours. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic properties of the sintered Nd-Fe-B permanent magnet obtained in this example at 20° C. and the size of the crystal grains at each position were tested.

[0050] Example 2 The manufacturing method of Example 2 was almost the same as that of Example 1, except that the Zr content in the Nd-Fe-B alloy in step (1) of Example 1 was changed to 0.25%, and the black ribbon coated with heavy rare earth elements in step (8) of Example 1 was heated under a vacuum of 2×10 -3 The difference is that the two-stage heat treatment diffusion was performed in a Pa atmosphere, the average particle size of the Dy powder used as the diffusion source was 11 μm, and D90 / D10=3.4. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic performance of the sintered Nd-Fe-B permanent magnet obtained in this example was tested at 20°C.

[0051] Example 3 The manufacturing method of Example 3 was almost the same as that of Example 1, except that the Zr content in the Nd-Fe-B alloy in step (1) of Example 1 was changed to 0.25%, and the black ribbon coated with heavy rare earth elements in step (8) of Example 1 was heated under a vacuum of 2×10 -4 The difference is that the two-stage heat treatment diffusion is carried out in an atmosphere of Pa, and the average particle size of the diffusion source Dy powder used is still 54 μm, where D90 / D10=3.2. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic performance of the sintered Nd-Fe-B permanent magnet obtained in this example was tested at 20°C.

[0052] Example 4 The manufacturing method of Example 4 was almost the same as that of Example 1, except that the Zr content in the Nd-Fe-B alloy in step (1) of Example 1 was changed to 0.55%, and the black ribbon coated with heavy rare earth elements in step (8) of Example 1 was heated under a vacuum of 2×10 -4 The difference is that the two-stage heat treatment diffusion is carried out in an atmosphere of Pa, and the average particle size of the diffusion source Dy powder used is still 54 μm, where D90 / D10=3.1. The remaining parts were treated in the same manner as in Example 1 to obtain a sintered Nd—Fe—B permanent magnet. According to the method described in Example 1, the magnetic performance of the sintered Nd-Fe-B permanent magnet obtained in this example was tested at 20°C.

[0053] In Example 1 and Comparative Examples 1 to 6, the grain boundary phase was analyzed using TEM, and the following was observed.

[0054] Figure 1 is a TEM image of the sintered Nd-Fe-B permanent magnet obtained in Example 1. The white areas at the grain boundaries in the image are Zr-B phases. It was found that needle-shaped Zr-B phases were formed in the grain boundary phase of the sintered Nd-Fe-B permanent magnet produced in this example, and that the Zr-B phases were uniformly and completely distributed within the grain boundary phase.

[0055] Figure 5 shows TEM images of the sintered Nd-Fe-B permanent magnets obtained in Comparative Examples 1 to 6. Figure 5 shows that Zr-B is distributed discretely in the grain boundary phase, and the Zr-B phase does not form an elongated needle-like structure.

[0056] Table 1 shows the magnetic properties at 20° C. and the crystal grain size at each position of the sintered Nd—Fe—B permanent magnets of the above examples and comparative examples.

[0057] [Table 1]

[0058] From the above table, it can be seen that for the sintered Nd—Fe—B permanent magnets produced in Examples 1 to 4 of the present invention, D1-Dn≦0.34, where Dn refers to D2, D3, and D4, while for the sintered Nd—Fe—B permanent magnets produced in Comparative Examples 1 to 6, D1-Dn was all greater than 0.34. Comparing the Examples and Comparative Examples, it was found that when the D1-Dn of the diffused products was less than 0.34 and greater than 0, the products had high grain size consistency and superior magnetic performance.

[0059] Although the conventional diffusion process can significantly improve the magnetic properties of permanent magnets during the diffusion process, when the diffusion temperature is high, the atoms in the boundary layer of the main-phase crystal grains of the permanent magnet are in a high-energy state. When they come into contact with elements such as a high concentration of rare earths in the thermally activated state in the grain boundary phase for a long time, the main-phase crystal grains, especially the surface crystal grains, grow spontaneously and inevitably, and the growth of the surface crystal grains is considered to affect the further improvement of magnetic properties.

[0060] The sintered R-Fe-B permanent magnet manufactured by the present invention can control the excessive growth of surface crystal grains. Therefore, the dimensions of the crystal grains corresponding to different positions in the sintered R-Fe-B permanent magnet are uniform, that is, 0 < D1 - Dn ≤ 0.34. The reasons are as follows. (1) The Zr element content is the basis for ensuring the formation of large needle-shaped Zr-B phases. The needle-shaped Zr-B phases change the state of the grain boundary phase, ensure that the diffusion source elements quickly enter the magnet during the diffusion process, shorten the contact time between the diffusion source elements and the surface crystal grains of the magnet, and suppress the growth of the crystal grains. (2) Due to the high diffusion vacuum degree, the elements in the diffusion source complete diffusion at a relatively low temperature, ensuring that the Zr-B phases in the grain boundary phase do not dissolve. (3) Due to the uniformity of the particle size dimensions and distribution of the diffusion source powder, it melts at a relatively low diffusion temperature, realizes synchronous diffusion of the diffusion source, and shortens the diffusion time by maximizing the concentration difference inside and outside the magnet. From the above, it is found that the three factors of the Zr element content, the diffusion vacuum degree, and the particle size dimensions and distribution of the diffusion source act synergistically to prevent the diffusion of the diffusion source elements into the magnet, thereby avoiding the abnormal growth of the magnet crystal grains caused by the long-term contact between the surface crystal grains of the magnet and the diffusion source at high temperature. Specifically, it is as follows.

[0061] Comparing Comparative Examples 1-1, 1-2, 1-3, and 1-4, it was found that when the acicular Zr-B phase could not be formed, the degree of diffusion vacuum was low, and the particle size of the diffusion source was abnormal and not distributed centrally, the diffusion of the diffusion source elements into the interior of the magnet was hindered, making it difficult for the diffusion source elements to penetrate into the interior of the magnet. As a result, the main phase crystal grains and diffusion source elements on the surface of the magnet and the elements in the grain boundary phase underwent long-term mass and heat transfer processes at high temperatures, ultimately resulting in different degrees of grain growth in different positions of the magnet and a more significant decrease in the Hcj@20°C of the magnet.

[0062] Comparing Comparative Examples 1 to 5 with Example 1, it was found that when any two of the three factors, Zr element content, diffusion vacuum level, and particle size of the diffusion source, were changed, the performance of the magnet deteriorated more significantly, the crystal grains at different positions of the magnet became larger, and the size difference became larger.

[0063] Therefore, the inventors believe that the synergistic effect of the three factors of Zr element content, diffusion vacuum level, and grain size of the diffusion source is the key to producing high-performance magnets with uniform crystal grain size.

[0064] Comparing Comparative Examples 1 to 6 with Example 1, it was found that the Zr element content and the two-stage low-temperature diffusion process affect the formation of the acicular Zr-B phase, which in turn affects the diffusion rate of the diffusion source elements into the interior of the magnet, and ultimately leads to a consistent grain size of the magnet.

[0065] From Examples 2, 3, and 4, it was found that within the scope of the present invention, when the Zr element content, diffusion vacuum level, and particle size and distribution of the diffusion source were changed, there was no significant effect on the formation of the acicular Zr-B phase at the grain boundaries, but the rapid diffusion of the diffusion source into the interior of the magnet was effectively ensured, and the abnormal growth of the magnet crystal grains was suppressed, with little effect on the performance and crystal grain size of the magnet, all within a small variation range.

[0066] The above describes exemplary embodiments of the present invention. However, the scope of protection of the present application is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principle 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, wherein the main phase crystal grains in the surface layer of the sintered R—Fe—B permanent magnet are called surface crystal grains, the size of the surface crystal grains is called D1, the main phase crystal grains in the core portion along the easy magnetization direction of the sintered R—Fe—B permanent magnet are called core crystal grains, the size of the core crystal grains is called Dn, and 0<D1-Dn≦0.34, where n is an integer greater than 1, and the easy magnetization direction of the sintered R—Fe—B permanent magnet is the thickness direction.

2. The sintered R—Fe—B permanent magnet according to claim 1, characterized in that the sintered R—Fe—B permanent magnet includes a main phase and a grain boundary phase, the grain boundary phase includes a Zr—B phase, and the Zr—B phase exhibits an acicular structure.

3. The magnetic properties of the sintered R—Fe—B permanent magnet are as follows: (1) Br is 1.41 T or more; (2) The sintered R—Fe—B permanent magnet according to claim 1, characterized in that Hcj is 1900 KA / m or more.

4. The sintered R—Fe—B permanent magnet according to claim 1, characterized in that the raw materials of the sintered R—Fe—B permanent magnet contain Zr and B elements, the mass contents of Zr and B in the raw materials are [Zr] and [B], respectively, and satisfy the relationship 0.13≦[Zr] / [B]≦0.55, and the mass content of Zr in the raw materials is 0.15 wt % or more.

5. A method for producing a sintered R—Fe—B permanent magnet according to any one of claims 1 to 4, comprising: Step (1): Mixing raw materials in a corresponding mass ratio to produce a neodymium-iron-boron alloy strip cast ribbon, and then pulverizing it to obtain a magnetic powder of a target particle size; Step (2) press-molding the obtained magnetic powder and pressing it by cold isostatic pressing to obtain a molded body; (3) subjecting the compact to a sintering and aging treatment to obtain a sintered NdFeB matrix; and (4) subjecting the sintered neodymium iron boron matrix to a high temperature diffusion treatment to obtain the sintered R—Fe—B permanent magnet.

6. In step (1), the pulverizing step specifically includes subjecting the neodymium-iron-boron alloy strip cast ribbon to hydrogen pulverization to obtain coarsely pulverized powder, and then pulverizing the coarsely pulverized powder in a high-energy ball milling process or a jet milling process to obtain magnetic powder; And / or, in step (1), the target particle size of the magnetic powder is 1 to 8 μm.

7. In step (2), the press molding includes orienting the magnetic powder in a magnetic field and press molding it; and / or in step (3), the sintering treatment includes sintering the compact at a high temperature of 1055°C to 1090°C in a vacuum environment; And / or, in step (3), the aging treatment refers to performing a tempering treatment at 1000°C or less after a sintering treatment.

8. In step (4), the high-temperature diffusion treatment is specifically performed by applying a heavy rare earth element to the surface of the sintered neodymium iron boron matrix so that the heavy rare earth element is uniformly distributed on the surface of the sintered neodymium iron boron matrix, and then performing a two-stage heat treatment diffusion in a vacuum atmosphere, with the temperature range of the first heat treatment being 790°C to 930°C, the temperature range of the second heat treatment being 440°C to 530°C, and the degree of vacuum being 10. －２ ~10 －４ and Pa.

9. the heavy rare earth element is provided by a diffusion source; the diffusion source includes heavy rare earth element powder particles, an antioxidant, and an organic solvent; the heavy rare earth element powder particles contain at least one or more of dysprosium, dysprosium hydride, dysprosium oxide, dysprosium fluoride, terbium, terbium hydride, terbium oxide, and terbium fluoride; 9. The method according to claim 8, wherein the heavy rare earth element powder particles have an average particle size of 2 to 100 μm and a D90 / D10 ratio of 1.2 to 5.

1.

10. Use of the sintered R-Fe-B permanent magnet according to any one of claims 1 to 4 in a motor.

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