Rare earth permanent magnet and method for manufacturing the same

Abstract

The present invention discloses a rare earth permanent magnet and a manufacturing method thereof. The rare earth permanent magnet M and manufacturing method thereof provided by the present invention effectively improve the grain boundary anisotropy of the magnet, provide more diffusion channels for the heavy rare earth diffusion source to enter the magnet, allow the heavy rare earth diffusion source to diffuse into the magnet more effectively, and further significantly improve the intrinsic coercivity of the magnet, thereby obtaining a magnet N with high intrinsic coercivity. Compared with the prior art, even if the amount of heavy rare earth diffusion source used is the same, the present invention can obtain a magnet N with a larger increase in intrinsic coercivity, and the manufacturing cost of the magnet can be reduced.

Description

Detailed Description of the Invention

[0001] This application claims the priority of a prior application with patent application number 202011628718.7, titled "Rare Earth Permanent Magnet and Its Manufacturing Method", which was filed by the applicant with the China National Intellectual Property Administration on December 30, 2020. The above prior application is incorporated herein by reference in its entirety.

[0002] 〔Technical Field〕 The present invention belongs to the technical field of manufacturing rare earth permanent magnets and relates to rare earth permanent magnets and their manufacturing methods.

[0003] 〔Background Art〕 Currently, the application of neodymium iron boron sintered rare earth permanent magnets in the new energy field is continuously expanding, and both the scope of application and the consumption volume are increasing year by year. However, considering that the intrinsic coercive force Hcj of neodymium iron boron magnets is significantly reduced at high temperatures and further causes irreversible thermal demagnetization, the intrinsic coercive force level of neodymium iron boron magnets must be increased to meet the requirements for the use of magnets at high temperatures. In contrast, the heavy rare earth grain boundary diffusion process has been widely used in recent years. This process allows the heavy rare earth diffusion source coated outside the magnet to diffuse into the magnet along the liquid grain boundary phase at high temperature through a heat treatment process at a certain temperature and time. Moreover, the heavy rare earth elements are mainly distributed along the grain boundaries or the outer shell layer of the main phase crystal grains and do not clearly enter the core part of the main phase crystal grains. Therefore, it is possible to achieve the effect of significantly improving the coercive force of the magnet without significantly reducing the residual magnetism of the magnet.

[0004] Since the increase in the coercive force of rare earth permanent magnets after the heavy rare earth diffusion process is significantly larger than the improvement in coercive force by adding the same proportion of heavy rare earth elements to the smelting formula, finding a method to more effectively improve the increase in diffusion coercive force is of extremely important significance for the effective improvement of magnet performance and the reduction of product cost.

[0005] Patent Document 1 (CN104159685A) discloses a method of sandblasting on the outer periphery of a chill roll. This method can remove the deposits on the outer peripheral surface of the cooling roll, suppress the decrease in the cooling rate, reduce the deviation of the crystal structure, and improve the uniformity of the crystal structure.

[0006] Patent Document 2 (CN105261473A) discloses that by sandblasting and polishing the surface of a copper roll, the damaged area of the copper roll surface is reduced, the service life is extended, and the strip obtained by cooling the sandblasted and polished copper roll is cooled uniformly, and the internal columnar crystals and neodymium-rich phases are more uniformly distributed.

[0007] Patent Document 3 (CN1306527C) discloses a method for improving the uniformity of the distribution of rare earth-rich phases at grain boundaries. Among them, by adjusting the roughness of the chill roll surface represented by the ten-point average roughness (Rz) to the range of 5 to 100 microns, the volume ratio of the fine rare earth-rich phase region of the alloy sheet is reduced, and the uniformity of the rare earth-rich phase of the flakes is improved.

[0008] Patent Document 4 (JP09001296A) discloses a method for adjusting the roughness of the wear-resistant metal layer on the chill roll surface. By adjusting the surface roughness Ra1 at the central part on the roll outer peripheral surface composed of the wear-resistant metal layer of the chill roll to be larger than the surface roughness Ra2 at both sides, the uniformity of the crystal structure can be improved, and the residual magnetism and intrinsic coercive force of the magnet can be increased.

[0009] Non-Patent Document 5 (Acta Materialia, 2016, 112: 59 - 66) studies the anisotropy of the diffusion process. The shell layer structure enriched with heavy rare earths is more easily formed at the interface parallel to the

[0001] direction (c-axis direction) of the main phase crystal grains.

[0010] All of the above Patent Documents 1 to 4 achieve the improvement of the uniformity of the structure of the sintered magnet and the enhancement of the performance of the sintered magnet by adjusting the surface state of the rapid-cooling roll. However, none of them touch upon how the grain boundary anisotropy distribution of the sintered rare-earth permanent magnet obtained by any manufacturing method is more suitable for the diffusion of the heavy rare-earth grain boundary, how the coercivity is further increased significantly, and how to make the content distribution of the heavy rare-earth in the magnet after diffusion more reasonable.

[0011] Non-Patent Document 5 studies the difference in diffusion anisotropy due to the anisotropy of the Re2Fe 14 B matrix lattice, but similarly does not touch upon the influence on diffusion due to grain boundary anisotropy.

[0012] Considering that the diffusion rates of heavy rare-earth elements are clearly different in magnets with different distribution characteristics of the grain boundary structure, in the conventional process method, although the grain boundary structure is significantly improved in terms of uniformity, the distribution of grain boundary anisotropy is poor. Furthermore, when the magnet undergoes a heavy rare-earth diffusion process, the heavy rare-earth elements still hardly effectively enter the magnet interior. Although the coercivity can be increased, the increase range is often small.

[0013] Effectively optimizing the anisotropy of the grain boundary structure distribution, increasing the increase range of the coercivity of the magnet in the diffusion process, reducing the heavy rare-earth content of the magnet, and reducing the manufacturing cost of the magnet are the technical problems to be solved.

[0014] 〔Summary of the Invention〕 The present invention provides a rare-earth permanent magnet, denoted as rare-earth permanent magnet M. The rare-earth permanent magnet M is obtained by orientation press molding and sintering in a magnetic field. The size of the magnet in the direction perpendicular to both the press direction and the magnetic field orientation direction is denoted as a1 after pressing and a2 after sintering. The size of the magnet in the press direction is denoted as b1 after pressing and b2 after sintering. The size of the magnet in the magnetic field orientation direction is denoted as c1 after pressing and c2 after sintering. Each size of the rare earth permanent magnet M satisfies the formula (1): c2 / c1 ≦ 1.25 × b2 / b1 + 1.1 × a2 / a1 - 1.26 (1), and / or Define the texture anisotropy coefficient of the rare earth permanent magnet M as A = (105 × c2 / c1) / (a2 / a1 + b2 / b1), and it satisfies the formula (2): A ≦ 44.5 (2).

[0015] According to an embodiment of the present invention, c2 / c1 ≦ 0.75, for example, c2 / c1 ≦ 0.74, preferably 0.65 < c2 / c1 ≦ 0.73, and illustratively, c2 / c1 = 0.697, 0.699, 0.701, 0.706, 0.712, 0.724.

[0016] According to an embodiment of the present invention, the data range of b2 / b1 is 0.80 to 0.95, for example, 0.83 to 0.92, and illustratively, 0.86, 0.862, 0.863, 0.864, 0.87, 0.88, 0.888.

[0017] According to an embodiment of the present invention, the data range of a2 / a1 is 0.75 to 0.90, for example, 0.805 to 0.84, and illustratively, 0.807, 0.808, 0.811, 0.813, 0.815, 0.82, 0.83, 0.839.

[0018] According to an embodiment of the present invention, the data range of A may be 40 ≦ A ≦ 44.2, for example, the data range of A is 43, 43.5, 43.59, 43.82, 43.94, 44.02, 44.1.

[0019] According to an embodiment of the present invention, the oxygen content inside the rare earth permanent magnet M is 1500 ppm or less, for example, 1000 ppm or less, and more preferably 800 ppm or less. For the rare earth permanent magnet M, a low oxygen content means that the amount of rare earth-rich oxide enriched in the grain boundary triple point region is small, which increases the diffusion rate in the grain boundary phase of the heavy rare earth diffusion source and helps to improve the performance of the diffusion magnet (i.e., the rare earth permanent magnet N described later).

[0020] According to an embodiment of the present invention, in the orientation press forming process, the magnetic field strength is ≥ 1.5 T so that the magnetic field orientation process in the press forming process of the magnet is ensured to be in a saturated state. In this case, the grain boundary phase deflects together with the main phase particles and is concentrated and distributed in the plane parallel to the orientation, which is more helpful for the diffusion and entry of heavy rare earths into the magnet.

[0021] The rare earth permanent magnet M satisfying the conditions of formula (1) and / or formula (2) has more obvious anisotropic characteristics in the distribution of its grain boundary phase inside the magnet, that is, more grain boundary phases are distributed in the plane parallel to the orientation direction as diffusion channels in the heavy rare earth diffusion process. Therefore, with the same usage amount of the heavy rare earth diffusion source, it can diffuse more into the magnet along the diffusion channels, effectively improving the increase range of the coercivity of the magnet before and after diffusion, and increasing the intrinsic coercivity of the magnet after diffusion (i.e., the rare earth permanent magnet N described below).

[0022] The present invention further provides a rare earth permanent magnet, denoted as rare earth permanent magnet N. The average content of heavy rare earths at a location 0.08 - 0.12 mm (preferably 0.1 mm) from the magnet surface along the magnetic field orientation direction into the magnet is denoted as x (wt%), and the average content of heavy rare earths at a location 0.98 - 1.02 mm (preferably 1 mm) from the magnet surface along the magnetic field orientation direction into the magnet is denoted as y (wt%). The total thickness of the rare earth permanent magnet N is denoted as z. When z ≤ 6, x - y ≤ 1.3^(z + 0.5) + 0.3 (3) When z > 6, x - y ≤ 5.5 + z / 13 (4).

[0023] Among them, the above total thickness refers to the thickness of the magnet along the magnetic field orientation direction.

[0024] Preferably, the above rare earth permanent magnet N is obtained after the above rare earth permanent magnet M is diffused by a heavy rare earth diffusion source.

[0025] According to an embodiment of the present invention, when z ≤ 6, x - y ≤ 6, and illustratively, x - y = 0.3, 1.4, 2.5, or 3.4.

[0026] According to an embodiment of the present invention, when z > 6, x - y ≤ 8, and illustratively, x - y = 2.4, 4.5, or 6.2.

[0027] The grain boundary microstructure of the rare earth permanent magnet M satisfying the above formula is further useful for the entry into the magnet during the diffusion process of the heavy rare earth diffusion source. When using the same weight of the diffusion source, the content of the heavy rare earth present on the magnet surface is decreased, but the content of the heavy rare earth entering the magnet interior is increased. Therefore, the difference in the content of the heavy rare earth at the positions of 0.1 mm and 1 mm from the magnet surface along the magnetic field orientation direction into the magnet interior becomes smaller. As a result, the increase amplitude and consistency of the coercivity of the magnet before and after diffusion are effectively improved, and the intrinsic coercivity of the diffusion magnet (i.e., the rare earth permanent magnet N) is increased.

[0028] According to an embodiment of the present invention, the oxygen content in the above rare earth permanent magnet N is 1500 ppm or less, for example, 1000 ppm or less, and more preferably 800 ppm or less. The heavy rare earth diffusion source on the surface of the rare earth permanent magnet M with a low oxygen content enters more into the magnet interior, the concentration difference of the heavy rare earth inside and outside the magnet is further decreased, and the increase amplitude of the intrinsic coercivity of the rare earth permanent magnet N obtained by performing the diffusion process on the magnet becomes larger.

[0029] The present invention (1) Supplying a molten alloy containing raw materials for manufacturing a rare earth permanent magnet M to a rapid cooling roll, solidifying the molten alloy to obtain an alloy sheet, The surface roughness Ra and Rz of the outer peripheral surface of the rapid cooling roll respectively satisfy the step where the range of Ra is 0.5 to 15 μm and the range of Rz is 0.5 to 45 μm, (2) Powdering the alloy sheet obtained in step (1), performing orientation press molding, and sintering to obtain a rare earth permanent magnet M, provides a method for manufacturing the above rare earth permanent magnet M, including the above steps.

[0030] According to an embodiment of the present invention, the raw materials for manufacturing the rare earth permanent magnet M described above are raw materials known in the art.

[0031] For example, the raw materials for manufacturing the rare earth permanent magnet M described above contain elements R, Fe, and B. Among them, R is one, two, or more of Nd, Pr, Ce, Ho, Dy, or Tb. The weight ratio of R in the raw materials is 25-35%, the weight ratio of B in the raw materials is 0.8-1.5%, and the above raw materials further contain one, two, or more additive elements among Co, Ti, Ga, Cu, Al, and Zr. The weight ratio of the above additive elements in the raw materials is 0.5-5%, and the balance is Fe.

[0032] Preferably, in terms of weight percentage, in the raw materials for manufacturing the rare earth permanent magnet M described above, the PrNd content is 19-35%, the Dy content is 0-6%, the Co content is 0.3-4%, the Cu content is 0.01-0.4%, the Ga content is 0.01-0.5%, the Al content is 0.01-1.2%, the Zr content is 0.01-0.2%, the Ti content is 0.01-0.3%, the B content is 0.8-1.2%, and the rest is Fe. The total content of Co, Cu, Ga, Al, Zr, and Ti is within the range of 0.5-5% of the mass of the above raw materials.

[0033] Exemplarily, in terms of weight percentage, in the raw materials for manufacturing the rare earth permanent magnet M described above, the PrNd content is 27%, the Dy content is 4%, the Co content is 2%, the Cu content is 0.1%, the Ga content is 0.1%, the Al content is 0.4%, the Zr content is 0.1%, the B content is 1%, and the rest is Fe.

[0034] According to an embodiment of the present invention, in step (1), the surface of the chill roll can be treated by treatment methods such as shot blasting, shot peening, sand blasting, and sandpaper polishing so that the surface roughness Ra and Rz of the outer peripheral surface of the chill roll satisfy the above requirements.

[0035] According to an embodiment of the present invention, in step (1), the surface roughness Ra of the outer peripheral surface of the above-mentioned rapid cooling roll ranges from 1 to 12 μm, for example, 3 μm, 4 μm, 4.5 μm, 5 μm, 10 μm.

[0036] According to an embodiment of the present invention, in step (1), the surface roughness Rz of the outer peripheral surface of the above-mentioned rapid cooling roll ranges from 3 to 30 μm. Also, for example, the range of Rz is from 3 to 25 μm, for example, 7 μm, 7.3 μm, 7.9 μm, 8 μm, 10 μm, 10.6 μm, 12 μm, 13 μm, 15 μm, 20 μm, 25 μm.

[0037] According to an embodiment of the present invention, in step (1), the average thickness of the above-mentioned alloy sheet is 0.15 to 0.5 μm, for example, 0.2 to 0.4 μm, and illustratively 0.15 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm.

[0038] According to an embodiment of the present invention, step (2) includes performing a hydrogen storage treatment on the above-mentioned alloy sheet to obtain coarse powder, further adding an antioxidant and a lubricant to the above-mentioned coarse powder to obtain mixed powder, subjecting the above-mentioned mixed powder to oriented press molding to obtain a compact, and sintering the above-mentioned compact to obtain the rare earth permanent magnet M.

[0039] Among them, the above-mentioned antioxidant and lubricant may be selected from reagents known in the art. Further, the total amount of the above-mentioned antioxidant and lubricant is 3 to 6 wt% of the raw materials for manufacturing the above-mentioned rare earth permanent magnet M, for example, 4 to 5.5 wt%, and illustratively 5 wt% or 5.5 wt%.

[0040] Among them, the pressure of the above-mentioned hydrogen storage treatment is 0.1 to 0.4 MPa, for example, 0.15 to 0.3 MPa, and illustratively 0.2 MPa.

[0041] Among them, the time of the above-mentioned hydrogen storage treatment is 3 to 6 h, for example, 4 to 5 h, and illustratively 3 h, 4 h, 4.5 h, 5 h or 6 h.

[0042] Among them, the temperature of the above hydrogen storage treatment is 500 to 660 °C, for example 530 to 600 °C, and illustratively 550 °C.

[0043] Among them, the above-mentioned coarse powder can be obtained by manufacturing with jet milling. For example, the surface average diameter (SMD, also called the Sauter average diameter) of the above-mentioned coarse powder is 2 to 4 μm, for example 2.5 to 3.5 μm, and illustratively 2.8 μm.

[0044] Among them, in the process of the above-mentioned orientation pressing, the magnetic field strength ≥ 1.5 T, for example the magnetic field strength ≥ 2 T, and illustratively 2 T. The magnetic field strength can ensure that the magnetic field orientation process in the press forming process of the magnet is in a saturated state. In this case, the grain boundary phase deflects together with the main phase particles and is concentrated and distributed in the plane parallel to the orientation direction, which is more helpful for the entry of heavy rare earth diffusion into the magnet.

[0045] Among them, those skilled in the art can select the form of the press as needed. For example, the hydrostatic press method is selected. Furthermore, the pressure of the above hydrostatic press is 160 to 180 MPa, for example 165 to 175 MPa, and illustratively 170 MPa.

[0046] Among them, the above sintering is vacuum sintering, for example, it is carried out in a vacuum heat treatment furnace. Preferably, before heating and sintering, the vacuum degree in the furnace reaches 10 -2 Pa, and the oxygen content is less than 100 ppm.

[0047] Among them, the above sintering is vacuum sintering aging. Preferably, the sintering temperature is 1000 to 1150 °C, for example 1030 to 1100 °C, and illustratively 1070 °C. Preferably, the temperature of the primary aging is 800 to 950 °C, for example 850 to 930 °C, and illustratively 900 °C. Preferably, the temperature of the secondary aging is 470 to 550 °C, for example 500 to 540 °C, and illustratively 520 °C.

[0048] The present invention further provides an application of the rare earth permanent magnet M in the manufacture of a rare earth permanent magnet with a large increase in intrinsic coercive force.

[0049] Preferably, the rare earth permanent magnet with a large increase in intrinsic coercive force is the rare earth permanent magnet N.

[0050] Preferably, the increase in intrinsic coercive force is at least 10 kOe, for example, the increase is 10.2 - 15 kOe.

[0051] The present invention (a) placing a heavy rare earth diffusion source on the surface of the rare earth permanent magnet M; (b) after completion of step (a), heat-treating the magnet with heavy rare earth on its surface to obtain the rare earth permanent magnet N; and further provides a method for manufacturing the rare earth permanent magnet N.

[0052] According to an embodiment of the present invention, in step (a), the heavy rare earth diffusion source includes at least one of pure metals Tb, Dy, and an alloy of Tb and / or Dy and other metals, preferably Tb and / or Dy.

[0053] According to an embodiment of the present invention, in step (a), the heavy rare earth diffusion source can be placed on the surface of the rare earth permanent magnet M by methods known in the art, such as spraying, vapor deposition, coating, magnetron sputtering, embedding, dipping, etc.

[0054] According to an embodiment of the present invention, in step (b), the heat treatment may include a two-stage heat treatment process. For example, the temperature of the primary heat treatment is 800 - 1000 °C, for example 850 - 950 °C, and illustratively 900 °C. For example, the holding time of the primary heat treatment is at least 3 h, for example 3 - 35 h, preferably 5 - 30 h, and illustratively 10 h, 20 h, 30 h. For example, the temperature of the secondary heat treatment is 400 - 650 °C, for example 450 - 600 °C, and illustratively 400 °C, 500 °C, 600 °C. For example, the holding time of the secondary heat treatment is 1 - 10 h, for example 2 - 8 h, and illustratively 3 h, 5 h, 7 h.

[0055] Advantageous effects of the present invention: In order to solve the above problems, the inventor has conducted in-depth research. As a result, it has been found that the rare earth permanent magnet having the characteristics of the magnet M described in the present invention has a significantly larger increase in coercivity after the heavy rare earth diffusion than that of a general permanent magnet. In addition, when manufacturing an alloy sheet by the processing method of a quenching roll in the manufacturing process of the magnet M, the surface roughness Ra of the outer peripheral surface of the quenching roll should be controlled within the range of 0.5 - 15 μm, and the surface roughness Rz should be controlled within the range of 0.5 μm - 45 μm so as to achieve an increase in the increase range of the intrinsic coercivity after diffusion.

[0056] The rare earth permanent magnet M and its manufacturing method provided by the present invention can effectively improve the grain boundary anisotropy of the magnet, provide more diffusion channels for the heavy rare earth diffusion source to enter the magnet, more effectively diffuse the heavy rare earth diffusion source into the magnet, and significantly improve the intrinsic coercivity of the magnet, so as to obtain a magnet N with a high intrinsic coercivity.

[0057] Compared with the prior art, when the usage amount of the heavy rare earth diffusion source is the same, the present invention can obtain a magnet N with a larger increase range of intrinsic coercivity, and the manufacturing cost of the magnet is reduced.

[0058] 〔Embodiments for Carrying Out the Invention〕 The R-T-B series sintered magnets have typical anisotropic properties. In addition to magnetic properties, this property is also present in their electrical resistivity and thermal expansion coefficient. However, through experiments, the inventor found that, depending on the direction, the increase in intrinsic coercivity in the heavy rare earth diffusion process is significantly different for the magnet. Along the c-axis direction with the richest grain boundary phase, the increase in the intrinsic coercivity of the magnet after diffusion is the highest. That is, it was found that there are also obvious anisotropic properties in the diffusion process of the heavy rare earth diffusion source. Therefore, by focusing on the optimal direction of diffusion anisotropy, the present invention provides a magnet (i.e., rare earth permanent magnet M) with more diffusion channels inside, allowing more heavy rare earth diffusion sources to enter the magnet through more diffusion channels, reducing the concentration difference of heavy rare earths between the surface layer and the subsurface layer of the magnet, and further improving the increase in the coercivity of the heavy rare earth diffused material.

[0059] Regarding the anisotropy of the grain boundary structure, it is difficult to characterize it by directly measuring specific parameters. In the present invention, mainly, the change rate c2 / c1 from the size after magnetic field orientation pressing in each direction of the magnet to the size after sintering completion is used as the measurement criterion for the grain boundary anisotropy distribution. The anisotropy of the grain boundary structure directly affects the size shrinkage in the orientation direction, pressing direction, and the third direction perpendicular to the orientation direction and pressing direction during the sintering of the magnet. The main reason is that the grain boundary phase is concentratedly distributed between columnar crystals parallel to the c-axis in the strip-cast alloy flakes after smelting. In the hydrogen crushing and hydrogen absorption process, the columnar crystal structure is broken into a plurality of polyhedrons along the c-axis direction. The plane parallel to the c-axis has a relatively large distribution of grain boundary phases because the grain boundary phase between the columnar crystals during smelting remains. However, the cross-section perpendicular to the c-axis has very few grain boundary phases. Such anisotropic distribution characteristics of the grain boundary phase are strengthened in the process of orientation pressing. As a result, the shrinkage in the sintering process in the orientation direction, pressing direction, and the third direction perpendicular to the orientation direction and pressing direction will have obvious anisotropy.

[0060] In addition, through a large number of experiments, the inventor found that when manufacturing an alloy sheet by the processing method of a chill roll in the manufacturing process of the magnet M, it is necessary to control the surface roughness Ra of the outer peripheral surface of the chill roll within the range of 0.5 to 15 μm and the surface roughness Rz within the range of 0.5 to 45 μm. In this way, the texture anisotropy of the grain boundary phase of the alloy flakes can be effectively improved. The number of grain boundary phases in the plane parallel to the orientation direction increases, while the number of grain boundary phases in the plane perpendicular to the orientation direction decreases. Due to the heredity of the structure, the improvement of such grain boundary distribution anisotropy is transmitted to the sintered magnet, and finally the increase range of the diffusion coercive force of the diffusion magnet (i.e., magnet N) becomes significantly larger.

[0061] The anisotropy of such a structure does not actually significantly improve the magnetic properties of the sintered magnet (i.e., magnet M). This is probably because the total amount of the grain boundary phase has not increased. The increased grain boundary phases in the plane parallel to the orientation direction actually originate from the grain boundary phases in the plane perpendicular to the orientation direction. As a result of the enhancement of the magnetic separation effect between crystal particles in the parallel plane and the weakening of the magnetic separation effect in the perpendicular plane overlapping each other, the coercive force level of the sintered magnet cannot be effectively improved. However, unexpectedly, such a magnet with a strong grain boundary anisotropy distribution has obvious advantages in the heavy rare earth diffusion process. The heavy rare earth diffusion source is more easily diffused into the magnet along the orientation direction, the difference in the heavy rare earth content between the surface layer and the subsurface layer of the magnet is reduced, and the increase range of the coercive force of the magnet obtained in the heavy rare earth diffusion process is improved.

[0062] For the permanent magnet M manufactured by the present invention, the ratio of the size after sintering to the size after pressing in its orientation direction satisfies c2 / c1 ≧ 1.25×b2 / b1 + 1.1×a2 / a1 - 1.26. If c2 / c1 is too large, the grain boundary phase decreases in the plane parallel to the orientation in the magnet, affecting the improvement effect of the diffusion coercive force. The anisotropy coefficient A of the permanent magnet M is A = (105×c2 / c1) / (a2 / a1 + b2 / b1), and it satisfies A ≦ 44.5. If A is too large, the grain boundaries tend to be more isotropically distributed around the crystal particles, and the diffusion rate of the heavy rare earth diffusion source decreases.

[0063] The permanent magnet N manufactured by the present invention has a content of heavy rare earths of x (wt%) at a position 0.08 to 0.12 mm from the magnet surface into the magnet along the magnetic field orientation direction, and a content of heavy rare earths of y (wt%) at a position 0.98 to 1.02 mm from the magnet surface into the magnet along the magnetic field orientation direction. The total thickness of the rare earth permanent magnet N has the following relationship: When z ≤ 6, x - y ≤ 1.3^(z + 0.5) + 0.3 When z > 6, x - y ≤ 5.5 + z / 13.

[0064] If x - y is too large, the heavy rare earths will be excessively concentrated and distributed on the magnet surface, resulting in insufficient diffusion of heavy rare earths in the center, which will affect the intrinsic coercivity of the magnet.

[0065] In the test of the magnet processing standard sample of 10 × 10 mm after diffusion, the magnetic properties are tested with a NIM-62000 device, and by a fluorescent X-ray analyzer (XRF), x (taking a total of 5 measurement points at the 4 corners + the center, and taking the average value of the heavy rare earth contents at these 5 positions), which is the content of heavy rare earths at a position 0.08 to 0.12 mm from the magnet surface into the magnet along the magnetic field orientation direction in the above permanent magnet, and y (taking a total of 5 measurement points at the 4 corners + the center, and taking the average value of the heavy rare earth contents at these 5 positions), which is the content of heavy rare earths at a position 0.98 to 1.02 mm from the magnet surface into the magnet along the magnetic field orientation direction, are measured. Hereinafter, in accordance with specific embodiments, the technical solution of the present invention will be described in more detail. The following embodiments are merely illustrative explanations and interpretations of the present invention and should not be construed as limiting the scope of the claims of the present invention. Any technology realized based on the above content of the present invention is included within the scope of the claims of the present invention.

[0066] Unless otherwise specified, all raw materials and reagents used in the following embodiments are commercially available products or can be manufactured by known methods.

[0067] Example 1 Raw materials of a neodymium-iron-boron sintered permanent magnet were prepared with the following weight percentages: PrNd is 27%, Dy is 4%, Co is 2%, Cu is 0.1%, Ga is 0.1%, Al is 0.4%, Zr is 0.1%, B is 1%, and the balance is Fe. The above raw materials were manufactured into alloy flakes by rapid solidification strip casting. Among them, the surface of the chill roll in the strip casting furnace was treated by sandblasting, and the surface roughness Ra of the outer peripheral surface of the chill roll was controlled to be 5 μm, and the surface roughness Rz was 32 μm.

[0068] The obtained rapidly solidified alloy flakes were subjected to hydrogen storage treatment, with the hydrogen storage pressure being 0.2 MPa and the dehydrogenation temperature being 550 °C. Then, jet milling was performed to obtain powder with SMD = 2.8 μm. After adding a lubricant accounting for 0.05 wt% of the raw materials, it was mixed in a mixer for 1 h and pulverized by jet milling. A lubricant and an antioxidant, which in total accounted for 0.5 wt% of the raw materials, were further added to the obtained powder, and then the mixing continued for 3 h.

[0069] The uniformly mixed fine alloy powder was orientation pressed in a magnetic field, with the orientation magnetic field strength controlled to be 2 T. Next, isostatic pressing at 170 MPa was performed.

[0070] The green compact was placed in a vacuum heat treatment furnace, and the vacuum degree in the furnace reached 20 Pa or less, and the oxygen content was less than 300 ppm, the sintering temperature was 1065 °C, the primary annealing temperature was 900 °C, and the secondary annealing temperature was controlled to be 520 °C.

[0071] The sintered blank was machined to 10 - 10 - 2 mm by machining. Among them, the size along the magnetic field orientation direction was 2 mm, and it was denoted as rare earth permanent magnet M1.

[0072] By magnetron sputtering, heavy rare earth terbium (Tb) was placed on the surface of magnet M1, and then heat treatment was carried out. The heat treatment process included a primary heat treatment of holding at a diffusion temperature of 900 °C for 30 h and a subsequent secondary heat treatment of holding at 500 °C for 10 h. A rare earth permanent magnet N1 was obtained. The properties of magnet N1 were detected.

[0073] Example 2 Raw materials for a neodymium-iron-boron-based sintered permanent magnet were prepared in the following weight percentages: PrNd was 27%, Dy was 4%, Co was 2%, Cu was 0.1%, Ga was 0.1%, Al was 0.4%, Zr was 0.1%, B was 1%, and the balance was Fe. The above raw materials were manufactured into alloy flakes by rapid solidification strip casting. Among them, the surface of the quench roll in the strip casting furnace was treated by shot peening, and the surface roughness Ra of the outer peripheral surface of the quench roll was 4.1 μm, and the surface roughness Rz was 21 μm was controlled.

[0074] The obtained rapidly solidified alloy flakes were subjected to hydrogen storage treatment with a hydrogen storage pressure of 0.2 MPa and a dehydrogenation temperature of 550 °C. Then, jet milling was carried out to obtain powder with SMD = 2.8 μm. After adding a lubricant accounting for 0.05 wt% of the raw materials, it was mixed in a mixer for 1 h and then pulverized by jet milling. A lubricant and an antioxidant, which in total accounted for 0.5 wt% of the raw materials, were further added to the obtained powder, and then mixing was continued for 3 h.

[0075] The uniformly mixed alloy fine powder was orientation pressed in a magnetic field, and the orientation magnetic field strength was controlled to 2 T. Then, isostatic pressing at 170 MPa was carried out.

[0076] The green compact was placed in a vacuum heat treatment furnace, and the vacuum degree in the furnace reached 20 Pa or less, and the oxygen content was less than 300 ppm, the sintering temperature was 1065 °C, the primary annealing temperature was 900 °C, and the secondary annealing temperature was 520 °C.

[0077] The sintered substrate was machined to 10 - 10 - 2 mm by mechanical processing, among which the size in the orientation direction was 2 mm, denoted as rare - earth permanent magnet M2.

[0078] By vapor deposition, heavy rare - earth terbium (Tb) was disposed on the surface of magnet M2, and then heat treatment was carried out. The heat treatment process included a primary heat treatment of holding for 30 h at a diffusion temperature of 900 °C and a subsequent secondary heat treatment of holding for 10 h at 500 °C. Rare - earth permanent magnet N2 was obtained. The properties of magnet N2 were detected.

[0079] Example 3 Raw materials of neodymium - iron - boron - based sintered permanent magnets in weight percentages were prepared: PrNd was 27%, Dy was 4%, Co was 2%, Cu was 0.1%, Ga was 0.1%, Al was 0.4%, Zr was 0.1%, B was 1%, and the balance was Fe. The above raw materials were manufactured into alloy flakes by rapid solidification strip casting. Among them, the surface of the quench roll in the strip casting furnace was treated by shot blasting, and the surface roughness Ra of the outer peripheral surface of the quench roll was 3.1 μm, and the surface roughness Rz was 13 μm was controlled.

[0080] The obtained rapidly solidified alloy flakes were subjected to hydrogen storage treatment with a hydrogen storage pressure of 0.2 MPa and a dehydrogenation temperature of 550 °C. Then jet milling was carried out to obtain powder with SMD = 2.8 μm. After adding a lubricant accounting for 0.05 wt% of the raw materials, it was mixed in a mixer for 1 h and then milled into powder by jet milling. After further adding a lubricant and an antioxidant accounting for a total of 0.5 wt% of the raw materials to the obtained powder, mixing was continued for 3 h.

[0081] The uniformly mixed fine alloy powder was orientation - pressed in a magnetic field with the orientation magnetic field strength controlled to 2 T, and then isostatic pressing at 170 MPa was carried out.

[0082] The green compact was placed in a vacuum heat treatment furnace until the vacuum degree in the furnace reached 20 Pa or less and the oxygen content was 300 It was controlled so that it was less than ppm, the sintering temperature was 1065 °C, the primary annealing temperature was 900 °C, and the secondary annealing temperature was 520 °C.

[0083] The sintered substrate was machined to 10 - 10 - 6 mm by machining, among which, the size in the orientation direction was 6 mm, and it was denoted as rare earth permanent magnet M3.

[0084] By coating, heavy rare earth terbium (Tb) was arranged on the surface of magnet M3, and then heat treatment was performed. The heat treatment process included a primary heat treatment of holding at a diffusion temperature of 900 °C for 30 h and a subsequent secondary heat treatment of holding at 500 °C for 10 h. Rare earth permanent magnet N3 was obtained. The properties of magnet N3 were detected.

[0085] Example 4 Raw materials of neodymium - iron - boron - based sintered permanent magnets with the following weight percentages were prepared: PrNd was 27%, Dy was 4%, Co was 2%, Cu was 0.1%, Ga was 0.1%, Al was 0.4%, Zr was 0.1%, B was 1%, and the balance was Fe. The above raw materials were manufactured into alloy flakes by rapid solidification strip casting. Among them, the surface of the quenching roll in the strip casting furnace was treated by shot peening, and the surface roughness Ra of the outer peripheral surface of the quenching roll was 3.3 μm, and the surface roughness Rz was 18 μm was controlled.

[0086] The obtained rapidly solidified alloy flakes were subjected to hydrogen storage treatment with a hydrogen storage pressure of 0.2 MPa and a dehydrogenation temperature of 550 °C. Then jet milling was performed to obtain powder with SMD = 2.8 μm. After adding a lubricant accounting for 0.05 wt% of the raw materials, it was mixed in a mixer for 1 h and then pulverized by jet milling. A lubricant and an antioxidant, which in total accounted for 0.5 wt% of the raw materials, were further added to the obtained powder, and then the mixing was continued for 3 h.

[0087] The uniformly mixed alloy fine powder was orientation - pressed in a magnetic field, and the orientation magnetic field strength was controlled to 2 T. Then, isostatic pressing at 170 MPa was performed.

[0088] The compacted powder was placed in a vacuum heat treatment furnace, and the degree of vacuum inside the furnace was reached to 20 Pa or less, and the oxygen content was 300 ppm or less, the sintering temperature was 1065 °C, the primary annealing temperature was 900 °C, and the secondary annealing temperature was controlled to be 520 °C.

[0089] The sintered compacted powder was machined to 10 - 10 - 6 mm by machining. Among them, the size in the orientation direction was 6 mm, and it was denoted as the rare earth permanent magnet M4.

[0090] By spraying, heavy rare earth terbium (Tb) was arranged on the surface of the magnet M4, and then heat treatment was performed. The heat treatment process included a primary heat treatment of holding for 30 h at a diffusion temperature of 900 °C and a subsequent secondary heat treatment of holding for 10 h at 500 °C. The rare earth permanent magnet N4 was obtained. The characteristics of the magnet N4 were detected.

[0091] Comparative Example 1 In this comparative example, the surface roughness Ra of the outer peripheral surface of the chill roll was 7 μm, and the surface roughness Rz was 52 μm was controlled. Other manufacturing steps were the same as those in Example 1.

[0092] Comparative Example 2 In this comparative example, the surface roughness Ra of the outer peripheral surface of the chill roll was 12 μm, and the surface roughness Rz was 90 μm was controlled. Other manufacturing steps were the same as those in Example 1.

[0093] Comparative Example 3 In this comparative example, the surface roughness Ra of the outer peripheral surface of the chill roll was 17 μm, and the surface roughness Rz was 122 μm was controlled, and the ratio of the heavy rare earth diffusion material used in the diffusion process was half of that in the example. Other manufacturing steps were the same as those in Example 2.

[0094] Table 1 shows the roughness of the chill roll of the magnet M obtained in the examples and comparative examples, the size after three - direction pressing of the substrate, the size after sintering, and the anisotropy coefficient A.

[0095]

Table 1

[0096] Table 2 shows whether the heavy rare earth concentrations in the surface layer and the subsurface layer along the diffusion direction of magnet N obtained in Examples 1 to 4 and Comparative Examples 1 to 3 satisfy the evaluation of formula (1), the evaluation of formula (2), the evaluation of formula (3), Br after diffusion, Hcj after diffusion, and the increase width of Hcj in the diffusion process.

[0097]

Table 2

[0098] As can be seen from Table 1 and Table 2 above, by controlling the surface roughness Ra and Rz of the outer peripheral surface of the rapid cooling roll, magnets with higher distribution characteristics of grain boundary anisotropy can be obtained, but this does not mean that the lower the shrinkage ratio c2 / c1 in the orientation c direction, the higher the distribution characteristics of the grain boundary anisotropy. For example, in Example 4, although the c2 / c1 ratio is the highest among the examples, it is lower than the shrinkage ratios a2 / a1 and b2 / b1 in the a and b directions. Therefore, magnets with higher distribution characteristics of grain boundary anisotropy can also be manufactured, and the increase width of the coercive force after diffusion also has the same advantageous characteristics.

[0099] By controlling the ranges of the surface roughness Ra and the surface roughness Rz of the outer peripheral surface of the rapid cooling roll, as can be seen from the comparison of the detection data of Comparative Example 1 and Comparative Example 2, when the relational expression (1) is satisfied, the improvement of grain boundary anisotropy is achieved, the heavy rare earth can enter more effectively into the magnet along the grain boundary, and the increase width of the coercive force of the magnet before and after diffusion is improved.

[0100] From the detection data of Example 1 and Comparative Example 1, when the change in the magnet size before and after pressing satisfies the relational expression (1) and the anisotropy coefficient A satisfies the relational expression (2), along the c-axis direction where the grain boundary phase is most enriched, more heavy rare earth diffusion sources can enter the magnet through more diffusion channels, reducing the concentration difference of heavy rare earths between the surface layer and the subsurface layer of the magnet, and further improving the increase in the coercive force of the heavy rare earth diffused material. Therefore, it can be seen that the △Hcj of the rare earth permanent magnet is greatly improved compared to the magnet that does not satisfy the relational expression (1) and the relational expression (2).

[0101] From the detection data of Comparative Example 2 and Comparative Example 3, by reducing the ratio of the heavy rare earth in the diffusion material used in the diffusion process, the concentration difference of the heavy rare earth between the surface layer and the subsurface layer can be effectively reduced, and the relationship of the relational expression (3) can be satisfied. However, since the increase in the coercive force before and after diffusion is much smaller than the normal level, it can be seen that the practical effect is worse. As described above, the rare earth permanent magnet manufactured by the present invention has a larger shrinkage in the orientation direction than the other two directions, and the characteristics of grain boundary anisotropy are more obvious. Since more heavy rare earth diffusion sources enter the magnet after diffusion, the increase in the intrinsic coercive force is significantly improved.

[0102] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made 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

A method for manufacturing a rare earth permanent magnet M, comprising: (1) Supplying a molten alloy containing raw materials for manufacturing the rare earth permanent magnet M to a chill roll, and solidifying the molten alloy to obtain an alloy sheet; Among them, the surface roughness Ra and Rz of the outer peripheral surface of the chill roll respectively satisfy the range of Ra of 0.5 to 15 μm and the range of Rz of 0.5 to 45 μm; (2) Pulverizing the alloy sheet obtained in step (1), subjecting it to orientation press molding, and sintering to obtain the rare earth permanent magnet M; Characterized by including: The rare earth permanent magnet M is: A rare earth permanent magnet, which is denoted as the rare earth permanent magnet M. The rare earth permanent magnet M is obtained by orientation press molding and sintering in a magnetic field; In the manufacturing process of the rare earth permanent magnet M, an alloy sheet is manufactured using a chill roll treatment method. The surface roughness Ra and Rz of the outer peripheral surface of the chill roll respectively satisfy the range of Ra of 0.5 to 15 μm and the range of Rz of 0.5 to 45 μm; The size of the magnet in the direction perpendicular to both the press direction and the magnetic field orientation direction is denoted as a1 after pressing and a2 after sintering; The size of the magnet in the press direction is denoted as b1 after pressing and b2 after sintering; The size of the magnet in the magnetic field orientation direction is denoted as c1 after pressing and c2 after sintering; Each size of the rare earth permanent magnet M satisfies the following formula: c2 / c1 ≦ 1.25×b2 / b1 + 1.1×a2 / a1 - 1.26 (1); And / or Defining the texture anisotropy coefficient of the rare earth permanent magnet M as A = (105×c2 / c1) / (a2 / a1 + b2 / b1), and satisfying the following formula: A≦44.5 （2）、 It is the rare earth permanent magnet M as described above. Manufacturing method.

2. c2 / c1 ≦ 0.75, The value range of b2 / b1 is 0.80 to 0.95, The data range of a2 / a1 is 0.75 to 0.90, The oxygen content inside the rare earth permanent magnet M is 1500 ppm or less. The manufacturing method according to claim 1, characterized by the above.

3. In step (1), the surface of the chill roll is treated by a treatment method such as shot blasting, shot peening, sand blasting or sandpaper polishing; In step (1), the range of the surface roughness Ra of the outer peripheral surface of the chill roll is 1 to 12 μm; In step (1), the range of the surface roughness Rz of the outer peripheral surface of the chill roll is 3 to 30 μm. In step (1), the average thickness of the alloy sheet is 0.15 to 0.5 μm, The manufacturing method according to claim 1, characterized in that.

4. Step (2) includes performing a hydrogen storage treatment on the alloy sheet to obtain coarse powder, further adding an antioxidant and a lubricant to the coarse powder to obtain mixed powder, subjecting the mixed powder to oriented press molding to obtain a green compact, and sintering the green compact to obtain the rare earth permanent magnet M. In the process of the oriented press molding, the magnetic field strength ≥ 1.5 T, The oriented press molding is isostatic press molding, The sintering is vacuum sintering, which is carried out in a vacuum heat treatment furnace. Before heat sintering, the vacuum degree in the furnace reaches 10 -2 Pa, and the oxygen content is less than 100 ppm. The manufacturing method according to claim 1, characterized in that.

5. A method for manufacturing a rare earth permanent magnet N, The rare earth permanent magnet N is A rare earth permanent magnet, which is denoted as rare earth permanent magnet N, The rare earth permanent magnet N is obtained by treating the rare earth permanent magnet M with a heavy rare earth diffusion source, The rare earth permanent magnet N is such that the average content of heavy rare earths at a location 0.08 to 0.12 mm from the magnet surface along the magnetic field orientation direction into the magnet interior is denoted as x (wt%), and the average content of heavy rare earths at a location 0.98 to 1.02 mm from the magnet surface along the magnetic field orientation direction into the magnet interior is denoted as y (wt%). The total thickness of the rare earth permanent magnet N is denoted as z (mm). When z ≤ 6, x - y ≤ 1.3^(z + 0.5) + 0.3 (3) When z > 6, x - y ≤ 5.5 + z / 13 (4), It is such a rare earth permanent magnet N, (a) A step of disposing a heavy rare earth diffusion source on the surface of the rare earth permanent magnet M, After completion of step (a), (b) a step of heat-treating the magnet with heavy rare earths on the surface to obtain the rare earth permanent magnet N, Characterized by including, The rare earth permanent magnet M is A rare earth permanent magnet, which is denoted as rare earth permanent magnet M. The rare earth permanent magnet M is obtained by oriented press molding and sintering in a magnetic field. In the manufacturing process of the rare earth permanent magnet M, an alloy sheet is manufactured using a rapid cooling roll treatment method. The surface roughness Ra and Rz of the outer peripheral surface of the rapid cooling roll respectively satisfy the range of Ra being 0.5 to 15 μm and the range of Rz being 0.5 to 45 μm. The size of the magnet in the direction perpendicular to both the press direction and the magnetic field orientation direction is denoted as a1 after pressing and a2 after sintering. The size of the magnet in the press direction is denoted as b1 after pressing and b2 after sintering. The size in the magnetic field orientation direction of the magnet is denoted as c1 after pressing and c2 after sintering. Each size of the rare earth permanent magnet M satisfies the following formula: c2 / c1 ≦ 1.25×b2 / b1 + 1.1×a2 / a1 - 1.26 (1), and / or Define the texture anisotropy coefficient of the rare earth permanent magnet M as A = (105×c2 / c1) / (a2 / a1 + b2 / b1), and it satisfies the following formula: A≦44.5 （2）、 Such a rare earth permanent magnet M. Manufacturing method.

6. When z ≦ 6, x - y ≦ 6, When z > 6, x - y ≦ 8, The oxygen content inside the rare earth permanent magnet N is 1500 ppm or less. The manufacturing method according to claim 5, characterized by this.

7. In step (a), the heavy rare earth diffusion source includes at least one of pure metals Tb, Dy, and an alloy of Tb and / or Dy and other metals. In step (a), the heavy rare earth diffusion source is disposed on the surface of the rare earth permanent magnet M by spraying, vapor deposition, coating, magnetron sputtering, or embedding method. In step (b), the heat treatment includes a two-step heat treatment process. The manufacturing method according to claim 5, characterized by this.

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