Preparation method of rare earth permanent magnet material and obtained material

Abstract

The invention provides a preparation method of a rare earth permanent magnet material and the obtained material. The preparation method comprises the steps that a Ca metal film and a heavy rare earth element metal film are sequentially formed on the surface of a neodymium iron boron sintered body, or the heavy rare earth element metal film and the Ca metal film are sequentially formed, or a Ca-heavy rare earth element alloy film is formed, and a diffusion precursor is obtained; and performing diffusion heat treatment on the diffusion precursor to obtain the rare earth permanent magnetic material. The rare earth permanent magnet material prepared by the method can improve the intrinsic coercive force while keeping the residual magnetic induction intensity and the rectangularity.

Description

Technical Field

[0001] The present application relates to the technical field of rare earth permanent magnet materials, and in particular to a method for preparing a rare earth permanent magnet material and a rare earth permanent magnet material having excellent magnetic properties obtained thereby. Background Art

[0002] Rare earth permanent magnet materials are permanent magnet materials based on intermetallic compounds formed by rare earth metals and other transition metals. For example, neodymium iron boron permanent magnet materials are the permanent magnet materials with the highest magnetic properties at present. Rare earth permanent magnet materials are widely used in new energy, home appliances, medical equipment and consumer electronics. In recent years, with the rapid development of industries such as electric vehicles and wind power, higher requirements have been placed on the magnetic properties of rare earth permanent magnet materials. That is, it is hoped that the residual magnetic induction intensity (B r ) and rectangularity (H k / H cj ) while increasing the intrinsic coercivity (H cj ).

[0003] The related art cannot make the magnetic properties of rare earth permanent magnet materials meet the above requirements. Therefore, there is a need to provide rare earth permanent magnet materials with further improved performance. Summary of the Invention

[0004] In view of this, the main purpose of the present application is to provide a method for preparing a rare earth permanent magnet material, wherein the rare earth permanent magnet material prepared by the method can improve the intrinsic coercive force while maintaining the residual magnetic induction intensity and rectangularity.

[0005] In order to achieve the above objectives, this application provides the following technical solutions.

[0006] The first aspect of the present application provides a method for preparing a rare earth permanent magnet material, comprising: sequentially forming a Ca metal film and a heavy rare earth element metal film on the surface of a NdFeB sintered body, or sequentially forming the heavy rare earth element metal film and the Ca metal film, or forming a Ca-heavy rare earth element alloy film to obtain a diffusion precursor; and performing diffusion heat treatment on the diffusion precursor to obtain the rare earth permanent magnet material.

[0007] According to some embodiments of the present application, the Ca metal film, the heavy rare earth element metal film, and the Ca-heavy rare earth element alloy film are formed by physical vapor deposition; preferably, the physical vapor deposition is magnetron sputtering.

[0008] According to some embodiments of the present application, in the diffusion precursor, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.0005~0.0055):1; preferably, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.001~0.0040):1.

[0009] According to some embodiments of the present application, in the diffusion precursor, the mass ratio of the heavy rare earth element in the heavy rare earth element metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.002-0.015):1.

[0010] According to some embodiments of the present application, in the NdFeB sintered body, the mass fraction of the oxygen element is 350ppm~2000ppm; and / or, in the NdFeB sintered body, the mass fraction of the carbon element is 450ppm~1500ppm; and / or, in the NdFeB sintered body, the mass fraction of the nitrogen element is 300ppm~800ppm.

[0011] According to some embodiments of the present application, in the diffusion precursor, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the oxygen element in the NdFeB sintered body is (0.2-5.0):1.

[0012] According to some embodiments of the present application, the heavy rare earth element is selected from one or more of Dy, Tb, and Ho.

[0013] According to some embodiments of the present application, the diffusion heat treatment is performed in an inert gas, wherein the inert gas is argon and / or nitrogen; preferably, the pressure of the inert gas is 1×10 -9 MPa~0.1MPa; More preferably, the pressure of the inert gas is 1×10 -6 MPa~0.05MPa.

[0014] According to some embodiments of the present application, the diffusion heat treatment includes a first heat treatment and a second heat treatment; preferably, the temperature of the first heat treatment is 750°C to 950°C, the time of the first heat treatment is 5 hours to 24 hours, the temperature of the second heat treatment is 450°C to 650°C, and the time of the second heat treatment is 3 hours to 10 hours.

[0015] A second aspect of the present application provides a rare earth permanent magnet material prepared by the method of any of the above embodiments.

[0016] The method for preparing rare earth permanent magnet material of the present application deposits Ca metal element and heavy rare earth element metal film, or deposits Ca-heavy rare earth element alloy film on the surface of NdFeB sintered body, and then performs diffusion heat treatment, which can increase the content of rare earth-rich phase in grain boundaries and improve the continuity of rare earth-rich phase in grain boundaries, thereby improving the diffusion of heavy rare earth elements, so that the obtained rare earth permanent magnet material has improved intrinsic coercive force while maintaining residual magnetic induction intensity and rectangularity.

[0017] In addition to the technical problems solved by this application, the technical features that constitute the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions described above, other technical problems that can be solved by this application, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further described in detail in the specific implementation methods below. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 This is a process flow chart of the preparation method of the rare earth permanent magnet material of Example 1 of the present application. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions of this application in conjunction with specific implementation methods. Obviously, the implementation methods described are only part of the implementation methods of this application, not all of the implementation methods. Based on the implementation methods in this application, all other implementation methods obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] Throughout this specification, unless otherwise specified, the terms used herein should be understood as having the same meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. In the event of any conflict, the present specification shall take precedence.

[0022] It should be noted that, in this application, the term "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that a method or apparatus comprising a series of elements includes not only the elements explicitly stated, but also other elements not explicitly listed, or also includes elements inherent to the implementation of the method or apparatus.

[0023] Except in any operating examples, or where otherwise indicated, all numerals representing component amounts, reaction conditions, etc. used in the specification and claims are to be understood as being modified by the term "about" in all cases. Unless otherwise indicated, the numerical parameters set forth in the following specification and the appended claims are approximate values, which can vary according to the desired properties to be obtained by the application. Although the numerical ranges and parameters setting forth the broad scope of the application are approximate values, the numerical values ​​set forth in the specific embodiments are reported as accurately as possible.

[0024] The above steps are divided only for clarity of description. When implemented, they can be combined into one step or some steps can be split and decomposed into multiple steps. As long as they include the same logical relationship, they are all within the scope of protection of this patent.

[0025] Definition of terms

[0026] As used herein, the term "NdFeB sintered body" refers to a sintered body made of Nd2Fe 14 The sintered body consists of B main phase grains and Nd-rich grain boundary phase between the main phase grains. The chemical formula of the NdFeB sintered body is R a Fe b B c M d , wherein R includes Nd and one or more selected from Pr, La, Ce, Gd, Ho, Dy, Tb, Sm, Yb, Sc, Er, Eu, Lu, and Tm, M is selected from one or more selected from Al, Cu, Zr, Co, Ga, Nb, V, and Ti, a is 28.0 to 35.0, c is 0.8 to 0.97, d is 0.1 to 5, and b = 100-acd.

[0027] As used herein, the term "heavy rare earth elements" refers to Gd, Ho, Dy, Tb, Er, Tm, Yb, Lu, and Y.

[0028] Adding heavy rare earth elements (HREs) to NdFeB sintered bodies through grain boundary diffusion (GBD) is an advanced technique for increasing coercivity and reducing HRE usage. This method enables rare earth permanent magnets to meet the requirements for high-temperature use. This technique involves forming a HRE-containing film on the surface of the NdFeB sintered body. After heat treatment, the HREs diffuse along the grain boundaries into the sintered body, surrounding the main phase grains to form a high-coercivity shell. This microstructure enhances the intrinsic coercivity of the rare earth permanent magnet while maintaining or slightly decreasing the residual magnetic induction intensity. This reduces the amount of HREs used. However, current preparation methods limit the depth of HRE diffusion from the surface into the NdFeB sintered body, limiting the magnitude of the increase in intrinsic coercivity of the resulting rare earth permanent magnet. Furthermore, the resulting diffused HREs exhibit a significant decrease in squareness compared to the diffused precursor.

[0029] To address the above issues, CN113963931A discloses a method for preparing rare earth permanent magnets. The method comprises: preparing a slurry comprising, in addition to at least one rare earth compound selected from the group consisting of rare earth suboxides, rare earth fluorides, and rare earth hydrides, reducing metal elements such as Al, Zn, Ca, and Fe; screen-printing the slurry onto the surface of a sintered body to form a deposited film layer; and heat-treating the sintered body in a vacuum sintering furnace to reduce the rare earth elements in the rare earth suboxides and diffuse them into the interior of the sintered magnet, thereby producing a series of rare earth permanent magnets with reduced rectangularity. However, the inventors have discovered that, in this process, the reducing metal elements have a limited reduction effect on the rare earth compounds, resulting in a limited diffusion depth and a limited improvement in intrinsic coercivity.

[0030] Therefore, there is still a need to provide improved rare earth permanent magnet materials and preparation methods thereof, so as to improve the performance of the rare earth permanent magnet materials and simplify the preparation process.

[0031] Based on this, the present application provides a rare earth permanent magnet material and a preparation method thereof.

[0032] Preparation method of rare earth permanent magnet material

[0033] The present application provides a method for preparing a rare earth permanent magnet material, comprising: sequentially forming a Ca metal film and a heavy rare earth element metal film, or sequentially forming the heavy rare earth element metal film and the Ca metal film, or forming a Ca-heavy rare earth element alloy film, on the surface of a NdFeB sintered body to obtain a diffusion precursor; and performing diffusion heat treatment on the diffusion precursor to obtain the rare earth permanent magnet material.

[0034] The grain boundary diffusion process mainly uses grain boundaries to provide diffusion channels. The continuity of the grain boundaries determines the diffusion efficiency and diffusion depth. In the preparation process of NdFeB sintered bodies, elements such as O, C, and N are inevitably introduced. The oxides, carbides, and nitrides present in the grain boundaries will affect the continuity of the grain boundaries and hinder the diffusion of heavy rare earth elements, thereby reducing the intrinsic coercivity of the obtained rare earth permanent magnet material. This application deposits Ca metal elements and heavy rare earth element films on the surface of the NdFeB sintered body before the diffusion heat treatment, or deposits a Ca-heavy rare earth element alloy film. Since the Ca metal element in the above-mentioned film layer has a strong ability to diffuse at the grain boundary and has high reducibility, after entering the NdFeB sintered body along the grain boundary, it reacts with the oxides, carbides, nitrides, etc. in the grain boundary, which can effectively remove the oxides, carbides, nitrides, etc. in the diffusion channel. On the one hand, it can release rare earth elements in the form of oxides, carbides, nitrides, etc., significantly increase the content of rare earth-rich phases in the grain boundary and improve the continuity of rare earth-rich phases in the grain boundary. On the other hand, it can repair discontinuous grain boundaries, make the diffusion channel of heavy rare earth elements more unobstructed, and improve the diffusion efficiency and depth of heavy rare earth elements. Compared with the heavy rare earth element diffusion process of the prior art, the present application improves the diffusion efficiency and depth of heavy rare earth elements by the composite diffusion of Ca and heavy rare earth elements present in the metal film or alloy film on the surface of the sintered body, while maintaining the residual magnetic induction intensity and rectangularity, significantly improving the intrinsic coercive force H. cj In some embodiments, compared to using heavy rare earth metal film alone, the H content of the rare earth permanent magnet material obtained by the method of the present application is cj It can be increased by more than 1.5kOe.

[0035] The NdFeB sintered body described herein can be prepared by conventional methods in the art. An exemplary preparation method includes: preparing raw materials according to the chemical formula of the NdFeB sintered body, smelting the raw materials (for example, using a vacuum induction melting furnace) to obtain a melt; preparing the melt into an alloy sheet by a rapid solidification strip process; grinding the alloy sheet into a fine powder by hydrogen crushing and air flow grinding; pressing the fine powder under a magnetic field for orientation pressing, optionally, further isostatic pressing to obtain an embryo; and sintering the embryo under vacuum or in an inert gas to obtain a NdFeB sintered body. Optionally, the NdFeB sintered body can be cut according to the required size. In the preparation process of the above-mentioned NdFeB sintered body, elements such as O, C, and N are inevitably introduced, and the presence of these elements will affect the effect of the subsequent grain boundary diffusion process.

[0036] According to one embodiment of the present application, the preparation method further includes, before forming the metal film or alloy film, performing a surface chemical pretreatment on the NdFeB sintered body by degreasing, cleaning, and pickling. This removes the surface of the NdFeB sintered body rich in elements such as O, C, and N, thereby facilitating the subsequent grain boundary diffusion process.

[0037] According to one embodiment of the present application, the oxygen content in the NdFeB sintered body is 350ppm to 2000ppm. For example, the oxygen content in the NdFeB sintered body is 350ppm, 400ppm, 600ppm, 800ppm, 1000ppm, 1200ppm, 1400ppm, 1600ppm, 1800ppm, 2000ppm, or a range between any two values, but is not limited thereto. This helps increase the depth of grain boundary diffusion and improves the intrinsic coercivity of the permanent magnet material.

[0038] The oxygen content mentioned in this application can be measured by conventional determination methods in the art, for example, by a nitrogen, oxygen, and hydrogen analyzer.

[0039] According to one embodiment of the present application, the carbon content in the NdFeB sintered body is 400ppm to 1500ppm. Exemplarily, the carbon content in the NdFeB sintered body is 400ppm, 650ppm, 850ppm, 1050ppm, 1250ppm, 1500ppm, or a range consisting of any two values, but not limited thereto. This helps increase the depth of grain boundary diffusion and improves the intrinsic coercivity of the permanent magnet material.

[0040] The carbon content mentioned in this application can be measured by conventional determination methods in the art, for example, by spark direct reading spectrometer or carbon-sulfur analyzer.

[0041] According to one embodiment of the present application, the NdFeB sintered body has a nitrogen content of 300 ppm to 800 ppm. Exemplarily, the nitrogen content in the NdFeB sintered body is 300 ppm, 400 ppm, 600 ppm, 800 ppm, or a range consisting of any two of these values, but is not limited thereto. This helps increase the depth of grain boundary diffusion and improves the intrinsic coercivity of the permanent magnet material.

[0042] The nitrogen content mentioned in this application can be measured by conventional determination methods in the art, for example, by a nitrogen, oxygen, and hydrogen analyzer.

[0043] According to one embodiment of the present application, the Ca metal film, the heavy rare earth metal film, and the Ca-heavy rare earth alloy film are formed by physical vapor deposition (PVD). For example, the physical vapor deposition includes vacuum evaporation coating, sputtering coating, ion plating, etc. Before the diffusion heat treatment, the Ca metal film, the heavy rare earth metal film, or the Ca-heavy rare earth alloy film is pre-formed by physical vapor deposition, which is beneficial to improve the contact between the above-mentioned film layer and the surface of the NdFeB sintered body, and control the thickness and uniformity of the film layer, thereby helping to improve the performance of the obtained rare earth permanent magnet material while saving heavy rare earth, and improving the stability of the subsequent diffusion process. In particular, a good grain boundary diffusion effect can be obtained for sintered bodies with an oxygen content of less than 2000ppm.

[0044] According to one embodiment of the present application, the physical vapor deposition is magnetron sputtering. The magnetron sputtering is a process in which a metal used to form a film is used as a cathode target and a neodymium iron boron sintered body is used as an anode in an appropriate amount of inert gas (usually argon). A DC voltage or a radio frequency voltage is applied between the two electrodes to ionize the inert gas to form a plasma (for example, Ar). + ions and electrons); at the same time, a magnetic field perpendicular to the electric field is applied between the two poles. The magnetic field will generate a Lorentz force on the electrons, causing the electrons to spiral near the target surface, extending the electron's movement path and increasing the probability of collision between the electrons and the inert gas atoms, thereby improving the ionization efficiency of the inert gas; the positive ions in the plasma are accelerated by the electric field to bombard the cathode target surface, sputtering the target atoms from its surface. These sputtered neutral target atoms carry high kinetic energy, fly to the anode and deposit on the anode surface, forming a dense and uniform thin film. Compared with other types of PVD processes, the use of magnetron sputtering coating technology saves the amount of target material, and the film layer has stronger bonding strength and more uniform thickness, thereby further improving the magnet performance and process stability.

[0045] According to one embodiment of the present application, in the diffusion precursor, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.0005-0.0055):1. This is beneficial to improving the intrinsic coercive force of the magnet. For example, the mass ratio of the Ca element to the NdFeB sintered body is 0.0005:1, 0.0010:1, 0.0015:1, 0.0020:1, 0.0025:1, 0.0030:1, 0.0035:1, 0.0040:1, 0.0045:1, 0.0050:1, 0.0055:1 or a value between the ranges consisting of any two values, but is not limited thereto. Preferably, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.0010-0.0040):1.

[0046] According to one embodiment of the present application, in the diffusion precursor, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the oxygen element in the NdFeB sintered body is (0.2 to 5.0):1. This is conducive to releasing the rare earth elements in the rare earth oxide and improving the diffusion efficiency of the heavy rare earth elements. Exemplarily, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the oxygen element in the NdFeB sintered body is 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 4.0:1, 5.0:1 or a value between the ranges consisting of any two values, but is not limited thereto.

[0047] According to one embodiment of the present application, the heavy rare earth element is selected from one or more of Dy, Tb, and Ho.

[0048] According to one embodiment of the present application, in the diffusion precursor, the mass ratio of the heavy rare earth element in the heavy rare earth element metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.002-0.015):1. This is beneficial to improving the intrinsic coercive force of the material, while Br is hardly reduced. If the content of heavy rare earth elements is too low, it will not play a role in enhancing the coercive force; if the content of heavy rare earth elements is too high, the content of heavy rare earth elements in the shallow layer will be too high, and the heavy rare earth elements will enter the interior of the grains from the grain boundaries, greatly reducing B. r . Exemplarily, the mass ratio of the heavy rare earth element to the NdFeB sintered body is 0.002:1, 0.005:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, 0.011:1, 0.012:1, 0.013:1, 0.015:1, or a value between any two values, but not limited thereto. Preferably, the mass ratio of the heavy rare earth element in the heavy rare earth metal film or the Ca-heavy rare earth alloy film to the NdFeB sintered body is (0.007-0.012):1.

[0049] According to one embodiment of the present application, the diffusion heat treatment is performed in an inert gas, such as argon and / or nitrogen. This helps reduce oxidation, thereby avoiding ineffective consumption of rare earth elements and improving grain boundary diffusion.

[0050] According to one embodiment of the present application, the pressure in the inert gas is 1×10 -9 MPa~0.1MPa, which is beneficial to reduce oxidation and improve grain boundary diffusion effect, thereby increasing the intrinsic coercivity of the magnet. For example, the pressure in the inert gas is 1×10 -9 MPa, 1×10-8 MPa, 1×10 -7 MPa, 1×10 -6 MPa, 1×10 -5 MPa, 1×10 -4 MPa, 1×10 -3 MPa, 0.01 MPa, 0.03 MPa, 0.05 MPa, 0.07 MPa, 0.1 MPa or a value between any two values, but not limited thereto. Preferably, the pressure in the inert gas is 1×10 -6 MPa~0.05MPa.

[0051] According to one embodiment of the present application, the diffusion heat treatment includes a first heat treatment and a second heat treatment; preferably, the first heat treatment temperature is 750°C to 950°C for 5 to 24 hours, and the second heat treatment temperature is 450°C to 650°C for 3 to 10 hours. This helps improve grain boundaries and enhance intrinsic coercivity.

[0052] Rare earth permanent magnet materials

[0053] The present application provides a rare earth permanent magnet material produced by the production method of any of the above embodiments, and thus has at least the same advantages as mentioned in the description of the above production method.

[0054] In some embodiments, the mass percentage of the Ca element in the rare earth permanent magnet material is 0.01% to 0.4%, the thickness of the diffusion from the surface to the inside of the rare earth permanent magnet material is 3.00 mm to 12.0 mm, and the rectangularity of the rare earth permanent magnet material obtained after diffusion is less than 3% lower than that of the diffusion precursor. Compared with the grain boundary diffusion of heavy rare earth elements alone, the H of the rare earth permanent magnet material obtained by the composite diffusion of the present application is cj It can be increased by more than 1.5kOe.

[0055] Example

[0056] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0057] Examples 1 to 8

[0058] refer to Figure 1 , the rare earth permanent magnet material is prepared according to the following steps.

[0059] 1. Preparation of alloy castings:

[0060] According to the mass ratio of Nd 33.00 Fe 64.7 B 0.90 Co 1.00 Cu 0.20 Al 0.20 Chemical formula, prepare raw materials.

[0061] The prepared raw materials were placed in a vacuum quick-setting furnace and heated to 1×10 -2 The smelting is carried out under vacuum conditions of 0.05 Pa and a temperature of 1460° C., and a molten liquid is obtained after complete melting. After refining for 5 minutes, a casting sheet with a thickness of 0.2 mm is produced by a rapid solidification strip spinning process.

[0062] 2. Flour making:

[0063] First, the cast sheet was coarsely crushed into a coarse powder with an average particle size of 150 μm using a hydrogen crushing furnace, and then the antioxidant XLDK-1 (Guangzhou Xiangdeling New Materials Co., Ltd.) was added to the coarse powder and mixed evenly. Then, the fine powder was finely pulverized using a jet mill, and the Fisher particle size was 3.0 μm.

[0064] 3. Pressing:

[0065] The above-mentioned fine powder was subjected to orientation pressing in a magnetic field of 2.0T, with a pressing time of 10 seconds and a pressing pressure of 25MPa; and then isostatic pressing was performed, with a pressing time of 15 seconds and a pressing pressure of 180MPa, to form a density of about 4.3g / cm 3 of the embryo.

[0066] 4. Sintering and aging treatment:

[0067] The green body is placed in a sintering furnace for sintering and aging treatment: -3 Pa vacuum conditions at 1060 ° C for 5 h, and then at 3.0 × 10 -2 Pa vacuum conditions at 900 ° C for 3 h, and finally at 3.5 × 10 -2 Pa under vacuum conditions and 520 ° C for 5 hours to form a NdFeB sintered body.

[0068] 5. Slicing:

[0069] The NdFeB sintered body was cut into a size of 25 mm×25 mm×6 mm (the thickness in the orientation direction was 6 mm).

[0070] 6. Surface treatment:

[0071] The cut NdFeB sintered body is subjected to surface chemical pretreatment by degreasing, cleaning and pickling.

[0072] The oxygen content and nitrogen content of the NdFeB sintered body after surface chemical pretreatment were measured by a nitrogen, oxygen and hydrogen analyzer (Shandong Hengmei Electronic Technology Co., Ltd., model: HM-ONH), and the carbon content was measured by a carbon and sulfur analyzer (Gangyan Nak Testing Technology Co., Ltd., model: CS5500T). The results are shown in Table 1.

[0073] The residual magnetic induction intensity B of the NdFeB sintered body after surface chemical pretreatment was measured by a permanent magnet measuring instrument (manufactured by the China Institute of Metrology, NIM-620000). r , intrinsic coercivity H cj , rectangularity H k / H cj , the results are shown in Table 2.

[0074] 6. Magnetron sputtering coating:

[0075] The metal Ca target and the NdFeB sintered body were installed in the chamber of the MSI-100-UHV magnetron sputtering equipment. The distance between the target and the NdFeB sintered body was 55 mm. The chamber was evacuated to a vacuum degree of 1.0×10 -5 Pa, argon gas was introduced to control the pressure to 1 Pa, a DC power supply of 300 W was selected, and the temperature was adjusted to 80°C. A metal Ca film was sputtered on the surface of the NdFeB sintered body. The quality of the Ca metal film was measured by scanning electron microscopy. Different mass ratios of the Ca metal film to the NdFeB sintered body were obtained by controlling the sputtering time in different embodiments, as shown in Table 1.

[0076] The metal Ca target in the chamber of the magnetron sputtering equipment is replaced with a metal Dy target, and sputtering is continued on the Ca metal film to obtain a Dy metal film to obtain a diffusion precursor. The mass ratio of the sputtered Dy metal film to the NdFeB sintered body is 0.01:1.

[0077] 7. Diffusion heat treatment:

[0078] The diffusion precursor was placed in a heat treatment furnace and evacuated to a vacuum degree of 1.5×10 -2 The first heat treatment is carried out at 895° C. for 10 hours at 400° C.; the second heat treatment is carried out at 500° C. for 6 hours; and the rare earth permanent magnet material is obtained after cooling to room temperature.

[0079] The residual magnetic induction intensity B of the rare earth permanent magnet material was measured by a permanent magnet measuring instrument (manufactured by the China Institute of Metrology, NIM-620000). r , intrinsic coercivity H cj , rectangularity H k / H cj , as shown in Table 2.

[0080] Example 9

[0081] The rare earth permanent magnet material was prepared in the same manner as in Example 1, with the only difference being that the metal Dy target was replaced with a Tb metal target during magnetron sputtering coating.

[0082] Example 10

[0083] The rare earth permanent magnet material was prepared in the same manner as in Example 2, with the only difference being that during magnetron sputtering coating, a Dy metal film was first sputtered, and then a Ca metal film was sputtered.

[0084] Example 11

[0085] The rare earth permanent magnet material was prepared in the same manner as in Example 1, with the only difference being that during magnetron sputtering coating, a DyCa alloy target (wherein the mass ratio of Dy to Ca was 10:1) was used instead of the separate metal Ca target and metal Dy target.

[0086] Comparative Example 1

[0087] The rare earth permanent magnet material was prepared in the same manner as in Example 1, except that no Dy metal film was sputtered during magnetron sputtering coating.

[0088] Comparative Example 2

[0089] The rare earth permanent magnet material was prepared in the same manner as in Example 1, except that no Ca metal film was sputtered during magnetron sputtering coating.

[0090] Comparative Example 3

[0091] The rare earth permanent magnet material was prepared in the same manner as in Comparative Example 2, except that the NdFeB sintered body was cut into a size of 25 mm×25 mm×3 mm after sintering.

[0092] Comparative Example 4

[0093] After preparing the NdFeB sintered body in the same manner as in Example 1, 53.8 g of DyCl3 was dissolved in water to prepare a solution with a concentration of 0.2 mol / L. In the solution, DyCl3 was hydrolyzed to form rare earth hydroxides. The solution was heated to 85°C to promote hydrolysis and prepare a Dy(OH)3 sol. The surface-treated sintered NdFeB magnet was immersed in the aforementioned sol solution and then taken out to form a Dy(OH)3 film on the magnet surface. The solvent was removed by drying. This process was repeated several times so that the mass ratio of the Dy element in the coated Dy(OH)3 to the mass ratio of the sintered body reached 0.01:1. During the grain boundary diffusion treatment, the metal Ca particles were first placed in a 75 mm × 75 mm × 60 mm molybdenum sagger, and then the molybdenum sagger and the diffusion precursor were placed in a heat treatment furnace and evacuated to a vacuum degree of 1.5×10 -2 Pa, argon gas with a pressure of 0.05MPa is filled as an inert gas, and the first heat treatment is carried out at a temperature of 890°C for 10 hours, so that the Dy(OH)3 film is reduced by the vapor formed by the metal Ca particles; then a second heat treatment is carried out at a temperature of 500°C for 6 hours; finally, the rare earth permanent magnet material is obtained after cooling to room temperature.

[0094] Comparative Example 5

[0095] The rare earth permanent magnet material was prepared in the same manner as in Comparative Example 4, except that the NdFeB sintered body was cut into a size of 25 mm×25 mm×3 mm after sintering.

[0096] Comparative Example 6

[0097] The rare earth permanent magnet material was prepared in the same manner as in Example 11, with the only difference being that during magnetron sputtering coating, a DyAl alloy target (wherein the mass ratio of Dy to Al was 7:3) was used instead of a DyCa alloy target (wherein the mass ratio of Dy to Ca was 7:3).

[0098] Comparative Example 7

[0099] The rare earth permanent magnet material was prepared in the same manner as in Comparative Example 6, except that the NdFeB sintered body was cut into a size of 25 mm×25 mm×3 mm after sintering.

[0100] The compositions of the NdFeB sintered bodies and diffusion precursors prepared in the above examples and comparative examples are shown in Table 1. The magnetic property test results of the NdFeB sintered bodies and rare earth permanent magnet materials are shown in Table 2.

[0101] Table 1

[0102]

[0103] Here, “ / ” indicates that it is difficult to determine the mass of Ca element from metallic calcium vapor that participates in the composite diffusion.

[0104] Table 2

[0105]

[0106] It can be seen from the above data that for oxygen content below 2000ppm, compared with the grain boundary diffusion of heavy rare earth metal alone, the present application uses Ca metal film and heavy rare earth metal film or Ca-heavy rare earth alloy film for composite diffusion, and the rectangularity of the rare earth permanent magnet material obtained after diffusion is reduced by less than 3% compared with the diffusion precursor; the grain boundary diffusion effect is significantly improved. The rare earth permanent magnet materials of the embodiments of the present application are all based on 6mm thick NdFeB sintered bodies. Compared with the rare earth permanent magnet materials of Comparative Examples 1, 2, 4, and 6, which are also based on 6mm thick NdFeB sintered bodies, H cj The increase is more than 1.5kOe, while maintaining the residual magnetic induction intensity and rectangularity.

[0107] Examples 12-13

[0108] Rare earth permanent magnet materials were prepared using the same method as in Example 2, with the only difference being that during magnetron sputtering, the mass ratios of the sputtered Dy metal film to the NdFeB sintered body were 0.011:1 and 0.007:1, respectively. The compositions of the NdFeB sintered bodies and diffusion precursors prepared in Example 2 and Examples 12-13 are shown in Table 3.

[0109] Table 3

[0110]

[0111] The magnetic property test results of the NdFeB sintered bodies and rare earth permanent magnet materials prepared in Example 2 and Examples 12-13 are shown in Table 4.

[0112] Table 4

[0113]

[0114] From the above data, it can be seen that when the mass ratio of heavy rare earth elements to sintered body is within the above range, the rare earth permanent magnet materials prepared by the method of the present application can improve the grain boundary diffusion effect and increase the H cj .

[0115] The above descriptions are merely some specific embodiments of the present application, which are intended to illustrate the present application and are not intended to limit the scope of protection claimed in the present application. All modifications, substitutions, or direct / indirect applications in other related technical fields made using the description of the present application under the inventive concept of the present application are included in the scope of protection claimed in the present application.

Claims

1. A method for preparing a rare earth permanent magnet material, comprising: On the surface of the NdFeB sintered body, a Ca metal film and a heavy rare earth element metal film are sequentially formed, or the heavy rare earth element metal film and the Ca metal film are sequentially formed, or a Ca-heavy rare earth element alloy film is formed to obtain a diffusion precursor; as well as The diffusion precursor is subjected to diffusion heat treatment to obtain the rare earth permanent magnet material.

2. The method according to claim 1, characterized in that The Ca metal film, the heavy rare earth element metal film, and the Ca-heavy rare earth element alloy film are formed by physical vapor deposition; preferably, the physical vapor deposition is magnetron sputtering.

3. The method according to claim 1, characterized in that In the diffusion precursor, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.0005~0.0055):1; preferably, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.0010~0.0040):

1.

4. The method according to claim 1, wherein In the diffusion precursor, the mass ratio of the heavy rare earth element in the heavy rare earth element metal film or the Ca-heavy rare earth element alloy film to the NdFeB sintered body is (0.002-0.015):

1.

5. The method according to claim 1, wherein In the NdFeB sintered body, the mass fraction of oxygen element is 350ppm to 2000ppm; and / or, in the NdFeB sintered body, the mass fraction of carbon element is 450ppm to 1500ppm; and / or, in the NdFeB sintered body, the mass fraction of nitrogen element is 300ppm to 800ppm.

6. The method according to any one of claims 1 to 5, characterized in that In the diffusion precursor, the mass ratio of the Ca element in the Ca metal film or the Ca-heavy rare earth element alloy film to the oxygen element in the NdFeB sintered body is (0.2-5.0):

1.

7. The method according to claim 1, characterized in that The heavy rare earth element is selected from one or more of Dy, Tb, and Ho.

8. The method according to claim 1, characterized in that The diffusion heat treatment is carried out in an inert gas, which is argon and / or nitrogen. Preferably, the pressure of the inert gas is 1×10 -9 MPa~0.1MPa; More preferably, the pressure of the inert gas is 1×10 -6 MPa~0.05MPa.

9. The method according to claim 1, characterized in that The diffusion heat treatment includes a first heat treatment and a second heat treatment; preferably, the temperature of the first heat treatment is 750℃~950℃, the time of the first heat treatment is 5 hours to 24 hours, the temperature of the second heat treatment is 450℃~650℃, and the time of the second heat treatment is 3 hours to 10 hours.

10. A rare earth permanent magnet material prepared by the method according to any one of claims 1 to 9.

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