A method for manufacturing grain boundary diffusion thick NdFeB magnets

Abstract

The present invention relates to the technical field of preparation of NdFeB magnets, and particularly to a method for manufacturing thick NdFeB magnets with grain boundary diffusion. After the magnet steel sheets are ion-etched and sputter-coated, they are polished and stacked in the same direction, and then hot-pressed and composited, followed by grain boundary diffusion, to form thick NdFeB magnets with grain boundary diffusion. The hot-pressed composite technology of the same direction stacking, combined with the synergistic effect of ion etching and sputtering coating, enhances the grain boundary diffusion of the NdFeB magnet without adding other reagents or alloy powders, thereby significantly improving the coercive force of the thick NdFeB magnets, alleviating the problem of reduced remanence of the magnets due to the diffusion of heavy rare earth elements, and improving the overall magnetic properties.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of NdFeB magnetic steel, and in particular to a method for manufacturing grain boundary diffusion thick NdFeB magnetic steel. Background Art

[0002] Neodymium iron boron (NdFeB), a third-generation permanent magnet, is widely used in electronics, wind power generation, medical equipment, robotics, and other fields. After decades of development, the residual magnetization of sintered NdFeB has approached 90% of the theoretical limit, but the coercivity still falls significantly short of the theoretical value. With the rapid development of new energy vehicles in recent years, market demand for sintered NdFeB magnets, a key component in electric motors, has been increasing. Furthermore, the heat generated by the high-speed operation of the motors causes the magnets to operate at relatively high temperatures, requiring NdFeB magnets to possess both higher temperature resistance and higher coercivity.

[0003] Grain boundary diffusion (GBD) is a method for effectively increasing the coercivity of sintered NdFeB magnets by incorporating heavy rare earth elements into the magnet, forming a heavy rare earth shell with a highly anisotropic field on the surface of the NdFeB grains. In the face of soaring heavy rare earth prices, GBD can effectively increase the utilization rate of heavy rare earth elements compared to traditional smelting addition techniques, thereby significantly reducing costs. However, for thick NdFeB magnets with a thickness of more than 11mm, the diffusion depth of GBD is far from reaching the design depth required.

[0004] In order to improve the interface diffusion depth of NdFeB magnets, for example, the invention patent with patent application number 202410592008.5 specifically discloses a grain boundary diffusion method for thick NdFeB magnets. By using a first alloy powder and a second alloy powder for zone printing on the orientation surface of the NdFeB magnet, a printed magnet is obtained, thereby solving the common problems of grain boundary diffusion technology such as insufficient diffusion depth and surface enrichment of heavy rare earths, which lead to waste of heavy rare earths. However, the use of the first alloy powder and the second alloy powder still greatly increases the manufacturing cost.

[0005] In addition, the invention patent with patent application number 201810921550.5 also specifically discloses a method for preparing low-cost large-scale NdFeB magnets by grain boundary diffusion, which specifically involves selecting dysprosium, terbium, iron, aluminum, copper, and gallium alloy powders as diffusion sources, coating them on oriented or non-oriented surfaces of 2 to 8 mm, and then selecting an appropriate number of magnets based on the final size of the finished product, stacking them and placing them in a sintering furnace for diffusion bonding treatment to obtain large-scale high-performance sintered magnets. However, when alloy powder is directly used as a diffusion source for coating, the diffusion depth of the alloy powder cannot reach the preset depth when it diffuses at the grain boundaries, and there will still be a problem of enrichment of diffusion elements, resulting in waste of alloy powder.

[0006] On the other hand, there is also a method of using glue to bond small magnets to produce large magnets, but this method has high requirements on the quality of the glue, and the introduction of expensive glue will inevitably increase production costs.

[0007] Therefore, in order to solve the above problems, it is necessary to develop a method for manufacturing grain boundary diffusion thick NdFeB magnets without using excess binder or alloy powder. Summary of the Invention

[0008] In response to the existing technical problems, the present invention aims to provide a method for improving the grain boundary diffusion of NdFeB magnets by utilizing the same-direction stacking hot pressing composite technology, in combination with the synergistic effect of ion etching and sputtering coating, without adding other reagents and alloy powders, so as to significantly improve the coercive force of NdFeB magnets with large thickness, and alleviate the problem of reduced remanence of the magnets due to the diffusion of heavy rare earth elements, thereby improving the overall magnetic properties.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A method for manufacturing grain boundary diffusion thick NdFeB magnets, comprising the following steps:

[0011] Step S1: Loading the magnets. Hoist the magnetic steel sheet to be prepared onto the turret system. During hoisting, the magnetic steel sheet is set vertically, and the orientation plane A of the magnetic steel sheet in the magnetic field orientation direction is set toward the central axis B of the turret system. After loading is completed, close the sealed door of the etching and coating machine.

[0012] Step S2: Preheat etching. Turn on the mechanical pump, Roots pump and molecular pump in the vacuum pump group in sequence to make the vacuum degree of the working chamber of the etching and coating machine reach 1.0×10 -2 pa~2.0×10 -2 After pa, the electric heating system and the ion etching system are respectively turned on to preheat and etch the magnetic steel sheet to remove impurities on the surface of the magnetic steel sheet. During etching, the Ar gas concentration at the cylindrical target in the working chamber is higher than the Ar gas concentration in the working chamber. Specifically, the gas pressure reflects the Ar gas concentration. The gas pressure at the cylindrical target is 5.0×10 -2 pa~8.0×10 -2 Pa, and the air pressure in the working chamber is 3.0×10 -2 pa~3.5×10 -2 pa;

[0013] Step S3, sputtering coating: After etching is completed, the ion etching system is turned off, the electric heating system is kept running, Ar gas is again introduced into the working chamber, and the sputtering system is turned on. The cylindrical target and the pancake target are both Dy metal targets. The cylindrical target and the pancake target emit Dy plasma, which is deposited on the surface of the magnetic steel sheet of the turret system to form a coating;

[0014] Step S4: Polishing treatment: Take the coated magnetic steel sheet out of the etching and coating machine, polish and clean the magnetic steel sheet to form edge magnetic steel sheet and middle magnetic steel sheet. The edge magnetic steel sheet is the magnetic steel sheet with the orientation surface A polished, and the middle magnetic steel sheet is the magnetic steel sheet with both orientation surfaces polished. The polishing treatment is to make the magnetic steel sheets fit better when they are composited.

[0015] Step S5: stacking. The edge magnetic steel sheets and the middle magnetic steel sheets are stacked in the magnetic field orientation direction in the stacking manner of edge magnetic steel sheet-middle magnetic steel sheet-edge magnetic steel sheet to form a magnetic sheet stack. During stacking, the polished surface of the edge magnetic steel sheet is placed in contact with the polished surface of another edge magnetic steel sheet or the middle magnetic steel sheet, and the number N of the middle magnetic steel sheets is an integer ≥ 0. The stacking thickness of the edge magnetic steel sheets and the middle magnetic steel sheets depends on the design thickness requirement. After the stacking thickness reaches the design requirement, the number N of the middle magnetic steel sheets can be 0.

[0016] Step S6, composite treatment, applying a pressure of 0.5~12MPa in the magnetic field orientation direction of the magnetic sheet stack, and performing heat treatment at a temperature of 800~1050℃ in vacuum or inert atmosphere for 10~40h, and tempering the magnetic sheet stack at a temperature of 440~640℃ for 5~15h after heat treatment to obtain grain boundary diffusion thick NdFeB magnets. The remanence of grain boundary diffusion thick NdFeB magnets with a thickness of ≥11mm reaches more than 14.12kG, and the coercive force reaches more than 23.75kOe. The sintering composite process is also a process of grain boundary diffusion. Increasing the pressure can, on the one hand, avoid the diffusion depth being limited due to too low pressure, and only a small amount of heavy rare earth elements diffuse into the deeper area of the magnet, and the coercive force is not increased much. On the other hand, it can further promote the mutual bonding between the magnetic steel sheets. At the same time, it is also necessary to avoid excessive pressure causing heavy rare earth elements to diffuse into the interior of the grains, which causes a significant decrease in remanence.

[0017] As an improvement, the preheat etching includes the following steps:

[0018] Step T1: preheating, turning on the electric heating system to raise the temperature in the working chamber to 200-250°C;

[0019] Step T2: sealing the cylindrical target and activating the sleeve module surrounding the cylindrical target to seal and isolate the cylindrical target from the working chamber;

[0020] Step T3: Filling Ar gas into the sleeve module and the working chamber respectively, so that the pressure in the sleeve module is 5.0×10 -2 pa~8.0×10 -2 Pa, synchronously, the air pressure in the working chamber is 3.0×10 -2 pa~3.5×10 -2 pa;

[0021] Step T4: etching arc initiation: the first arc initiation needle 51 next to the cylindrical target 5 rotates and swings, and instantly touches the cylindrical target, short-circuiting the arc initiation power supply on the cylindrical target, and discharging the Ar gas in the sleeve module to start the arc and emit a glow, forming Ar positive ions and electrons;

[0022] Step T5: Opening the anode ring. Simultaneously with step T4, the partition door assembly on the sleeve module is opened, forming a gap on the side of the sleeve module facing away from the turret system. Simultaneously, an anode ring is formed at the gap. The anode ring performs a bunching and acceleration process on Ar positive ions and electrons, pulling the Ar positive ions and electrons out of the sleeve module through the gap.

[0023] Step T6, anode pulling: Synchronously with step T4, the anode power supply supplies power to the pancake target. The pancake target pulls and accelerates the electrons released in step T4, which collide with the Ar gas in the working chamber to form Ar positive ions. The operating current and voltage of the anode power supply are 30A / 60V.

[0024] Step T7, etching, the bias power supply supplies power to the turret system, the turret system pulls Ar positive ions, and the Ar positive ions collide with the surface of the magnetic steel sheet on the turret system. The working current and voltage of the bias power supply are as follows: the working voltage is 50V to 250V, the current is 0.2A to 10A, and the working time is 25min to 45min.

[0025] Preferably, in step T2, the air pressure in the sleeve module is 6.0×10 -2 Pa, the air pressure in the working chamber is 3.2×10 -2 pa.

[0026] Preferably, in step T3, the initial voltage of the arc starting power supply is 150-250V, and the working current and voltage after arc stabilization are 100A / 20V.

[0027] Preferably, in step T6, the current of the anode power supply is gradually increased from 30A to 100A.

[0028] Preferably, in step T7, the voltage of the bias power supply is gradually increased from 50V to 250V.

[0029] As an improvement, the sputtering coating includes the following steps:

[0030] Step U1: heating and heat preservation: maintaining the operation of the electric heating system, raising the temperature in the working chamber to 550-650° C., and heat preservation;

[0031] Step U2: Filling Ar gas into the working chamber to maintain the vacuum degree in the working chamber at 2.5×10 -1 Pa~4.5×10 -1 Pa;

[0032] Step U3: gap switching, adjusting the partition door assembly on the sleeve module so that a gap is formed on the side of the sleeve module facing the turret system;

[0033] Step U4, glow sputtering: the first arc-starting needle at the cylindrical target rotates and swings to instantly touch the cylindrical target, and the second arc-starting needle at the pancake target touches the pancake target, respectively short-circuiting the arc-starting power supply and the anode power supply, causing the Ar gas in the working chamber to discharge and start an arc to emit a glow, and the cylindrical target and the pancake target sputter to overflow Dy plasma;

[0034] Step U5, coating, bias power supply supplies power to the turret system, the working voltage is 100V, the turret system draws Dy plasma to adhere to the surface of the magnetic steel sheet on the turret system, forming a coating with a thickness of 2.5 to 3 μm, and the working time is 45 to 50 minutes.

[0035] Preferably, in step U2, the vacuum degree in the working chamber is maintained at 3.5×10 -1 Pa.

[0036] Preferably, in step U4, the operating current and voltage of the arc starting power supply and the anode power supply are 180A / 25V.

[0037] Preferably, in step S6, a pressure of 6 MPa is applied to the magnetic field orientation direction of the magnetic sheet stack, and heat treatment is carried out at a temperature of 950°C in a vacuum or inert atmosphere for 35 hours. After the heat treatment, the magnetic sheet stack is tempered at a temperature of 550°C for 10 hours to obtain grain boundary diffusion thick NdFeB magnets. The remanence of the grain boundary diffusion thick NdFeB magnets with a thickness of ≥11 mm reaches more than 14.12 kG, and the coercive force reaches more than 23.75 kOe.

[0038] The beneficial effects of the present invention are:

[0039] (1) The present invention utilizes the same-direction stacking hot pressing composite technology, combined with the synergistic effect of ion etching and sputtering coating, to enhance the grain boundary diffusion of NdFeB magnets without adding other reagents and alloy powders, thereby significantly improving the coercive force of thick NdFeB magnets;

[0040] (2) The ion etching of the present invention utilizes reactive gas to react with the material in a plasma or reactive ion etching environment. This etching process etches the surface and near-surface of the material, removes part of the material, and exposes more grain boundaries. After the grain boundaries are exposed, more channels and contact areas are provided for subsequent diffusion, which is beneficial for the diffusion of substances along the grain boundaries. In addition, the bombardment of ions will produce defects in the material, such as vacancies and dislocations. These defects will affect the crystal structure and atomic arrangement of the material, change the atomic structure at the grain boundaries, and increase the activity of the grain boundaries. At the same time, ion etching will also generate stress in the material. The existence of stress will promote the migration and diffusion of atoms, which is beneficial to opening the diffusion channel of the grain boundaries.

[0041] (3) The present invention combines ion etching with sputtering coating, so that the etching and sputtering coating of the magnetic steel sheet are carried out in the same working chamber. The magnetic steel sheet does not need to switch the working chamber, thereby maintaining the working temperature of the magnetic steel sheet. There is no need to cool down and transfer the etched magnetic steel sheet, thereby ensuring the cleanliness of the surface of the magnetic steel sheet after etching. In addition, during the etching process, in order to expose more grain boundaries, the Ar gas concentration in the working chamber is adjusted to form partitions, so that the Ar gas concentration at the cylindrical target is much higher than the Ar gas concentration in the working chamber. Therefore, during etching, the number of Ar positive ions generated by the excitation is guaranteed, and the blocking of the Ar atoms on the magnetic steel sheet is reduced, so that the Ar positive ions can better impact the surface of the magnetic steel sheet and expose the grain boundaries.

[0042] (4) During the sputtering coating process of the present invention, the bombardment of high-energy particles will cause the structure of the substrate surface to change, such as generating roughness and forming nano-scale pores. These changes in surface structure will increase the contact area between the grain boundary and the outside world, providing more entry channels for diffusing substances. In addition, the deposition coating is carried out by plasma deposition of heavy rare earth element Dy, which can form a high coercive force shell at the grain boundary, thereby improving the magnetic properties of the material.

[0043] (5) The present invention utilizes the same-direction stacking hot pressing composite technology to pressurize and composite the edge magnetic steel sheets and the middle magnetic steel sheets of the stack, without the need for adhesives, thus saving production costs. Furthermore, the pressurization treatment is performed during the grain boundary diffusion process, which is beneficial to improving the diffusion depth and post-diffusion performance, thereby increasing the utilization rate of heavy rare earths. The grain boundary diffusion process and the magnet assembly splicing process are performed simultaneously, which can effectively simplify the production process.

[0044] In summary, the coercive force of the grain boundary diffused thick NdFeB magnet prepared by the present invention is significantly improved, which overcomes the problem of reduced remanence of the magnet caused by the diffusion of heavy rare earth elements, and the comprehensive magnetic properties are significantly improved. It is particularly suitable for the field of paint technology for the preparation of grain boundary diffused thick NdFeB magnets. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the manufacturing method of the present invention;

[0046] Figure 2 Schematic diagram of the edge magnetic steel sheet of the present invention;

[0047] Figure 3 This is a schematic diagram of the middle magnetic steel sheet of the present invention;

[0048] Figure 4 This is a schematic diagram of a magnetic sheet stack according to the present invention;

[0049] Figure 5 A top view of the rotary system of the present invention;

[0050] Figure 6 This is a schematic diagram of the three-dimensional structure of the etching and coating integrated machine of the present invention;

[0051] Figure 7 This is a schematic diagram of the top view of the etching and coating integrated machine of the present invention;

[0052] Figure 8 This is a schematic diagram of the power connection of the etching and coating integrated machine of the present invention;

[0053] Figure 9 This is a schematic diagram of the power supply connection of the cylindrical target of the present invention;

[0054] Figure 10 This is a schematic cross-sectional view of the etching and coating integrated machine of the present invention;

[0055] Figure 11 This is a schematic diagram of the three-dimensional structure of the cylindrical target material of the present invention;

[0056] Figure 12 This is a schematic diagram of the front view structure of the cylindrical target material of the present invention;

[0057] Figure 13 This is a schematic diagram of the top view of the pillar target material of the present invention;

[0058] Figure 14 Schematic diagram of the anode ring structure of the present invention.

[0059] The reference numerals in the figure are: 10. magnetic steel sheet, 101. edge magnetic steel sheet, 102. middle magnetic steel sheet, 103. magnetic sheet stack, 1. turret system, 11. bias power supply, 2. etching and coating integrated machine, 20. working chamber, 21. sealing door, 3. vacuum pump group, 4. electric heating system, 5. cylindrical target, 51. first arcing needle, 52. arc starting power supply, 6. pancake target, 61. anode power supply, 62. second arcing needle, 7. sleeve module, 70. sleeve, 701. opening, 71. partition door assembly, 711. partition door, 712. gear, 72. notch, 73. drive unit, 731. drive motor, 732. drive gear, 8. anode ring, 81. anode strip, 82. anode connecting strip. DETAILED DESCRIPTION

[0060] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0062] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0063] Example:

[0064] like Figure 1 As shown, a method for manufacturing grain boundary diffused thick NdFeB magnets comprises the following steps:

[0065] Step S1: Loading the magnets. Hoist the magnetic steel sheet 10 to be prepared onto the turret system 1. During hoisting, the magnetic steel sheet 10 is vertically arranged, and the orientation plane A of the magnetic steel sheet 10 in the magnetic field orientation direction is all arranged toward the central axis B of the turret system 1. After loading is completed, close the sealing door 21 of the etching and coating machine 2.

[0066] Step S2: Preheat etching. Turn on the mechanical pump, Roots pump and molecular pump in the vacuum pump group 3 in sequence to make the vacuum degree of the working chamber 20 of the etching and coating machine 2 reach 1.0×10 -2 pa~2.0×10 -2 After pa, the electric heating system 4 and the ion etching system are respectively turned on to preheat and etch the magnetic steel sheet 10 to remove impurities on the surface of the magnetic steel sheet 10. During etching, the Ar gas concentration at the cylindrical target 5 in the working chamber 20 is higher than the Ar gas concentration at other areas in the working chamber 20. Specifically, the gas pressure reflects the Ar gas concentration. The gas pressure at the cylindrical target 5 is 5.0×10 -2 pa~8.0×10 -2 pa, while the pressure in the rest of the working chamber 20 is 3.0×10 -2 pa~3.5×10 -2 pa;

[0067] Step S3, sputtering coating. After etching is completed, the ion etching system is turned off, the electric heating system 4 is kept running, Ar gas is again introduced into the working chamber 20, and the sputtering system is turned on. The cylindrical target 5 and the pancake target 6 are both Dy metal targets. The cylindrical target 5 and the pancake target 6 are excited to generate Dy plasma, which is deposited on the surface of the magnetic steel sheet 10 of the turret system 1 to form a coating.

[0068] Step S4, polishing treatment, taking the coated magnetic steel sheet 10 out of the etching and coating machine 2, polishing and cleaning the magnetic steel sheet 10 to form an edge magnetic steel sheet 101 and an intermediate magnetic steel sheet 102, wherein the edge magnetic steel sheet 101 is a magnetic steel sheet with the orientation surface A polished, and the intermediate magnetic steel sheet 102 is a magnetic steel sheet with both orientation surfaces polished. The polishing treatment is to enable the magnetic steel sheets to fit better when they are composited. Although the polished surfaces of the edge magnetic steel sheet 101 and the intermediate magnetic steel sheet 102 are polished, there is still a Dy metal coating on the polished surfaces, and the interior of the polished surfaces has also been deposited and infiltrated with Dy metal elements during the coating process;

[0069] Step S5: stacking. The edge magnetic steel sheets 101 and the middle magnetic steel sheets 102 are stacked in the magnetic field orientation direction in the stacking manner of edge magnetic steel sheet-middle magnetic steel sheet-edge magnetic steel sheet to form a magnetic sheet stack 103. During stacking, the polished surface of the edge magnetic steel sheet 101 is aligned with the polished surface of another edge magnetic steel sheet 101 or the middle magnetic steel sheet 102, and the number N of the middle magnetic steel sheets 102 is an integer ≥ 0. The stacking thickness of the edge magnetic steel sheets 101 and the middle magnetic steel sheets 102 depends on the design thickness requirement. After the stacking thickness reaches the design requirement, the number N of the middle magnetic steel sheets can be 0.

[0070] Step S6, composite treatment, after stacking, the magnetic sheet stack 103 is placed in a sintering furnace, a pressure of 0.5 to 12 MPa is applied in the magnetic field orientation direction of the magnetic sheet stack, and heat treatment is carried out at a temperature of 800 to 1050°C in a vacuum or inert atmosphere for 10 to 40 hours. After heat treatment, the magnetic sheet stack is tempered at a temperature of 440 to 640°C for 5 to 15 hours to obtain grain boundary diffusion thick NdFeB magnets. The remanence of the grain boundary diffusion thick NdFeB magnets with a thickness of ≥11 mm reaches more than 14.12 kG, and the coercive force reaches more than 23.75 kOe. The sintering composite process is also a process of grain boundary diffusion. On the one hand, increasing the pressure can avoid the diffusion depth being limited due to too low pressure, and only a small amount of heavy rare earth elements diffuse into the deeper area of the magnet, and the coercive force is not increased much. On the other hand, it can further promote the mutual bonding between the magnetic steel sheets. At the same time, it is also necessary to avoid excessive pressure causing heavy rare earth elements to diffuse into the interior of the grains, which significantly reduces the remanence.

[0071] Preferably, in step S6, a pressure of 6 MPa is applied to the magnetic field orientation direction of the magnetic sheet stack, and heat treatment is performed at 950°C in a vacuum or inert atmosphere for 35 hours. After the heat treatment, the magnetic sheet stack is tempered at 550°C for 10 hours.

[0072] First of all, it should be noted that the columnar target 5 and the pancake target 6 in this application are both Dy metal targets or Dy alloy targets, and in the ion etching system, the columnar target 5 is used as a cathode, and the pancake target 6 is used as an anode. The columnar target 5, the pancake target 6 and the turntable system 1 form an ion etching system.

[0073] Furthermore, the pressure applied in the magnetic field orientation direction of the magnetic sheet stack cannot be too large, because sintered NdFeB magnets are a material with high hardness and brittleness, and are very easy to be damaged due to uneven force during processing. Therefore, it is necessary to ensure that the magnetic sheet stack is not crushed while ensuring that the pressure on the magnetic sheet stack is uniform, and to avoid excessive pressure causing the Dy element to diffuse into the interior of the grains and reduce the residual magnetism.

[0074] In addition, the temperature of the diffusion heat treatment is controlled to be carried out under low temperature conditions, that is, the temperature is 950℃. On the one hand, it can avoid the lattice diffusion of more Dy elements and the enrichment of Dy elements on the surface of the magnet due to excessively high temperature, which affects the grain boundary diffusion depth of Dy, reduces the saturation magnetization intensity of the magnet and the content of Dy elements diffused into the interior of the magnet, and avoids the ultimate decrease in the remanence of the magnet and a small increase in the coercive force. On the other hand, it can avoid the slow diffusion rate due to excessively low temperature, and avoid only a small amount of Dy elements diffusing into the magnet.

[0075] It should be emphasized that the heavy rare earth elements used for grain boundary diffusion in this application are not limited to Dy elements. All heavy rare earth elements that meet the requirements of this application are within the scope of protection of this application, such as the heavy rare earth element terbium (Tb).

[0076] In the present invention, the thickness of the grain boundary diffusion thick NdFeB magnet is ≥11 mm, for example, it can be 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 or 20 mm, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0077] like Figures 1 to 14 As shown, the preheat etching includes the following steps:

[0078] Step T1: preheating, turning on the electric heating system 4 to raise the temperature in the working chamber 20 to 200-250° C.;

[0079] Step T2: closing the cylindrical target and starting the sleeve module 7 surrounding the cylindrical target 5 to seal and isolate the cylindrical target 5 from the working chamber 20;

[0080] Step T3: Filling Ar gas into the sleeve module 7 and the working chamber 20 respectively, so that the pressure in the sleeve module 7 is 5.0×10 -2 pa~8.0×10 -2 pa, synchronously, the air pressure in the working chamber 20 is 3.0×10 -2 pa~3.5×10 -2 pa;

[0081] Step T4: etching arc initiation: the first arc initiation needle 51 next to the cylindrical target 5 rotates and swings, and momentarily touches the cylindrical target 5, short-circuiting the arc initiation power supply 52 on the cylindrical target 5, and discharging the Ar gas in the sleeve module 7 to start an arc and emit a glow, forming Ar positive ions and electrons;

[0082] Step T5: Opening the anode ring. Simultaneously with step T4, the partition door assembly 71 on the sleeve module 7 is opened, forming a gap 72 on the side of the sleeve module 7 facing away from the turret system 1. Simultaneously, an anode ring 8 is formed at the gap 72. The anode ring 8 performs a bunching and acceleration process on the Ar positive ions and electrons, pulling the Ar positive ions and electrons out of the sleeve module 7 through the gap 72.

[0083] Step T6, anode pulling. Synchronously with step T4, the anode power supply 61 supplies power to the pancake target 6. The pancake target 6 pulls and accelerates the electrons released in step T4, which collide with the Ar gas in the working chamber 20 to form Ar positive ions. The operating current and voltage of the anode power supply 61 are 30A / 60V.

[0084] Step T7, etching, the bias power supply 11 supplies power to the turret system 1, the turret system 1 pulls Ar positive ions, and the Ar positive ions collide with the surface of the magnetic steel sheet 10 on the turret system 1. The working current and voltage of the bias power supply 11 are as follows: the working voltage is 50V~250V, the current is 0.2A~10A, and the working time is 25min~45min.

[0085] Furthermore, in step T2, the air pressure in the sleeve module 7 is 6.0×10 -2 Pa, the air pressure in the working chamber is 3.2×10 -2 pa.

[0086] Furthermore, in step T3, the initial voltage of the arc starting power supply 52 is 150-250V, and the working current and voltage after arc stabilization are 100A / 20V.

[0087] Furthermore, in step T6 , the current of the anode power supply 61 is gradually increased from 30A to 100A.

[0088] In addition, in step T7, the voltage of the bias power supply 11 is gradually increased from 50V to 250V.

[0089] It should be noted that the Ar gas concentration in the sleeve module 7 is high, while the Ar gas concentration in the working chamber 20 is low. This is because the Ar gas concentration in the working chamber 20 is too high. When Ar atoms are not hit by electrons to form Ar positive ions, they will hinder the migration of the already formed Ar positive ions, especially the Ar atoms at the turntable system 1, which directly affects the etching and cleaning effect of the magnetic steel sheet. Conventional ion etching systems have this problem, and the magnetic steel sheet cannot be fully hit by Ar positive ions, exposing the grain boundaries and affecting the subsequent Dy plasma precipitation penetration.

[0090] It is further explained that in the invention patent with patent application number 201810885211.6, an ion source multi-arc column arc composite PVD coating system and method are disclosed, which is similar to the present invention. The Ar gas is ionized by the arc starting of the cylindrical target to form Ar positive ions, and the Ar positive ions and electrons are pulled by the anode of the pancake target to make the Ar positive ions jump. Finally, relying on the bias power supply, the Ar positive ions hit the workpiece to form etching. However, since this application requires sufficient impact on the magnetic steel sheet to expose the grain boundary, and the above-mentioned ion source multi-arc column arc composite PVD coating system is provided with a protective cover at the cylindrical target after arc starting, it is difficult for the Ar positive ions and electrons to escape from the protective cover area when they are pulled by the anode, resulting in difficulty in the transition of the Ar positive ions and electrons. At the same time, the Ar gas concentration in the entire vacuum chamber is consistent. It is difficult to form a high concentration of Ar positive ions when the cylindrical target is etched and the arc is started, and the remaining Ar atoms in the vacuum chamber will still hinder the Ar positive ions.

[0091] However, the present application fully considers the barrier effect of the protective cover on Ar positive ions and electrons, while retaining the function of the protective cover, thereby avoiding contamination of the cylindrical target by impurities generated during the etching process.

[0092] Specifically, the present application first uses the sleeve module 7 to seal and isolate the cylindrical target 5 after the etching and coating integrated machine completes vacuuming and heating. Then, when Ar gas is filled into the external gas supply device, two Ar gas environments with different concentrations are formed inside and outside the sleeve module 7. Then, when the cylindrical target starts arcing and discharging, the sleeve module 7 forms a gap 72 to connect to the working chamber 20, and at the same time, an anode ring 8 is formed at the gap 72. The anode ring 8 pulls the Ar positive ions and electrons in the sleeve module 7 before the pancake target. At the same time, since there are a large number of Ar positive ions and electrons in the sleeve module 7, the anode ring 8 bunches them. The Ar positive ions and electrons are extracted from the sleeve module 7 and then pulled by the anode of the pancake target 6 to make a transition. Since the Ar positive ions and electrons have separated from the sleeve module 7, the path of their being pulled by the anode will no longer be blocked. Moreover, a large number of Ar positive ions and electrons are formed at the moment of arc discharge of the cylindrical target. The concentration of the remaining Ar atoms in the working chamber 20 has no effect of blocking the Ar positive ions while playing the role of inert gas protection. The Ar positive ions can quickly and fully transition to the turntable system 1 to impact-etch and clean the magnetic steel sheet, completely exposing the grain boundaries.

[0093] In addition, due to the obstruction and restriction of the sleeve module 7, the arc discharge in a small space has a better ionization effect on the Ar gas. At the same time, it can also prevent the cylindrical target from igniting the magnetic steel sheet at the moment of arc discharge, thereby avoiding burning of the magnetic steel sheet.

[0094] Specifically, the sputtering coating includes the following steps:

[0095] Step U1: heating and heat preservation: maintaining the operation of the electric heating system, raising the temperature in the working chamber to 550-650° C., and heat preservation;

[0096] Step U2: Filling Ar gas into the working chamber to maintain the vacuum degree in the working chamber at 2.5×10 -1 Pa~4.5×10 -1 Pa;

[0097] Step U3: gap switching, adjusting the partition door assembly on the sleeve module so that a gap is formed on the side of the sleeve module facing the turret system;

[0098] Step U4, glow sputtering: the first arc-starting needle 51 of the cylindrical target 5 rotates and swings to instantly touch the cylindrical target, and the second arc-starting needle 62 of the pancake target 6 touches the pancake target, respectively short-circuiting the arc-starting power supply and the anode power supply, and igniting the Ar gas discharge in the working chamber to emit a glow arc, and the cylindrical target and the pancake target sputter out Dy plasma;

[0099] Step U5, coating, the bias power supply 11 supplies power to the turret system 1, the working voltage is 100V, the turret system draws the Dy plasma to adhere to the surface of the magnetic steel sheet on the turret system, forming a coating with a thickness of 2.5 to 3 μm, and the working time is 45 to 50 minutes.

[0100] Preferably, in step U2, the vacuum degree in the working chamber is maintained at 3.5×10 -1 Pa.

[0101] Preferably, in step U4, the operating current and voltage of the arc starting power supply and the anode power supply are 180A / 25V.

[0102] It should be noted that when sputtering coating is performed, the cylindrical target 5 and the pancake target 6 discharge and strike an arc at the same time, and the arc is used to form multiple arc spots on the surface of the cylindrical target 5 and the pancake target 6, so that the Dy element of the cylindrical target 5 and the pancake target 6 escapes directly in the form of plasma, forming an evaporation ion source, and the evaporation ion source is used to perform sputter coating on the magnetic steel sheet on the turntable system 1.

[0103] It is further explained that when the cylindrical target material 5 is used as an evaporation ion source to sputter-coat the magnetic steel sheet, the sleeve module 7 forms a gap on the side facing the turntable system 1. The Dy plasma can directly jump to the turntable system 1 through the gap without any interference, and the Dy plasma can quickly penetrate into the interior of the magnetic steel sheet.

[0104] Specifically, the sleeve module 7 includes a sleeve 70, a partition door assembly 71 and a driving unit 73;

[0105] The sleeve 70 is coaxially sleeved on the outer side of the cylindrical target 5 , and the sleeve 70 is provided with openings 701 on the side facing and the side facing away from the turret system 1 ;

[0106] The partition door assembly 71 is symmetrically arranged. There are two groups of partition door assemblies 71. The two groups of partition door assemblies 71 are respectively arranged at the corresponding openings 701. The two groups of partition doors 711 in the partition door assembly 71 are rotated around the inner ring of the sleeve 71. The lower ends of the partition doors 711 in the same group are meshed with each other through gears 712.

[0107] The driving unit 73 includes a driving motor 731 and a driving gear 732. The driving motor 731 is configured to cooperate with the gear 712 through the driving gear 732. The driving gear 732 is a toothless gear. The driving unit 73 switches forward and reverse to drive the partition door assembly 71 to open the corresponding gap 72.

[0108] Furthermore, anode bars 81 are arranged in parallel at the upper and lower edges of the opening 701 on the side of the sleeve 70 facing away from the turret system 1, and anode connecting bars 82 are respectively arranged at the edges of the two groups of partition doors 711 facing the resin. The upper and lower ends of the anode connecting bar 82 are respectively slidably arranged on the anode bar 81, and the anode connecting bar 82 and the anode bar 81 are conductively arranged in contact with each other. When the partition door 711 is opened, the anode bar 81 and the anode connecting bar 82 are combined to form an anode ring 8, and the middle part of the anode bar 81 is connected to the arc starting power supply 52. The current of the arc starting power supply 52 flows through the anode ring 8, forming a voltage / current at the anode ring 8 that is higher than that at the cylindrical target material 5.

[0109] It should also be noted here that when the cylindrical target 5 is used as the ion etching cathode to discharge and start the arc, the partition door 711 is gradually opened to form a gap 72, and the synchronous anode connecting bar 82 moves on the anode bar 81 to form the anode ring 8. Since the opening of the anode ring 8 is gradually formed from small to large, the traction and bunching effect also changes from strong to weak in the process of the anode ring 8 pulling the Ar positive ions and electrons, which is inversely proportional to the density of the Ar positive ions and electrons in the sleeve module 7. The pulling effect of the anode ring 8 on the Ar positive ions and electrons is exactly the same as the anode traction at the pancake-shaped target 6 (the current of the anode power supply 61 is gradually increased from 30A to 100A, and the anode traction effect becomes stronger and stronger), forming a complementary effect.

[0110] In addition, the structure of the etching and coating all-in-one machine of the present invention can refer to the structure of an ion source multi-arc column arc composite PVD coating system disclosed in the invention patent 201810885211.6, which will not be described in detail here.

[0111] Examples 1-4:

[0112] The manufacturing method of the grain boundary diffusion thick NdFeB magnets of Examples 1-4 is the same as that of the embodiment. The specific parameters of the manufacturing method are shown in Table 1 below:

[0113] Table 1

[0114] Parameter name Example 1 Example 2 Example 3 Example 4 Vacuum degree <![CDATA[1.0×10 -2 so]]> <![CDATA[1.5×10 -2 so]]> <![CDATA[1.5×10 -2 so]]> <![CDATA[2.0×10 -2 so]]> Preheating temperature 200℃ 225℃ 225℃ 250℃ Air pressure inside sleeve module <![CDATA[5.0×10 -2 so]]> <![CDATA[5.5×10 -2 so]]> <![CDATA[6.0×10 -2 so]]> <![CDATA[8.0×10 -2 so]]> Air pressure in the working chamber <![CDATA[3.0×10 -2 so]]> <![CDATA[3.2×10 -2 so]]> <![CDATA[3.2×10 -2 so]]> <![CDATA[3.5×10 -2 so]]> Arc starting voltage of arc starting power supply 150V 200V 200V 250V Arc starting power supply arc stabilization voltage / current 100A / 20V 100A / 20V 100A / 20V 100A / 20V Anode power supply etching working current / voltage 30A / 60V 30A / 60V 30A / 60V 30A / 60V Bias power supply etching working current / voltage 50V / 0.2A~250V / 10A 50V / 0.2A~250V / 10A 50V / 0.2A~250V / 10A 50V / 0.2A~250V / 10A Etching working time 25min 30min 30min 45min Sputtering operating temperature 550℃ 600℃ 600℃ 650℃ Sputtering vacuum <![CDATA[2.5×10 -1 Well]]> <![CDATA[3.5×10 -1 Well]]> <![CDATA[3.5×10 -1 Well]]> <![CDATA[4.5×10 -1 Well]]> Arc starting power supply, anode power supply sputtering working current / voltage 180A / 25V 180A / 25V 180A / 25V 180A / 25V Bias power supply sputtering operating voltage 100V 100V 100V 100V Coating thickness 2.5μm 2.8μm 2.8μm 3μm Sputtering time 45min 48 minutes 48 minutes 50min Magnetic field orientation pressure 0.5MPa 6MPa 6MPa 12MPa Heat treatment temperature 800℃ 900℃ 950℃ 1050℃ Heat treatment time 10h 20h 20h 40h Tempering temperature 440℃ 500℃ 580℃ 640℃ Tempering time 5h 8h 8h 15h

[0115] Example 5:

[0116] Example 5 is the same as Example 3, except that the magnetic field orientation pressure is 4 MPa.

[0117] Example 6:

[0118] Example 6 is the same as Example 3, except that the heat treatment temperature is 800°C.

[0119] Example 7:

[0120] Example 7 is the same as Example 3, except that during ion etching, no anode ring is provided at the cylindrical target.

[0121] Comparative Examples 1-4:

[0122] The specific parameters of the NdFeB magnet manufacturing method of Comparative Examples 1-4 are shown in Table 2 below:

[0123] Table 2

[0124] Parameter name Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Vacuum degree <![CDATA[1.0×10 -2 so]]> <![CDATA[1.5×10 -2 so]]> <![CDATA[1.5×10 -2 so]]> <![CDATA[2.0×10 -2 so]]> Preheating temperature 200℃ 225℃ 225℃ 250℃ Air pressure inside sleeve module <![CDATA[4.0×10 -2 so]]> <![CDATA[5.5×10 -2 so]]> 0 <![CDATA[9.0×10 -2 so]]> Air pressure in the working chamber <![CDATA[3.0×10 -2 so]]> <![CDATA[3.2×10 -2 so]]> <![CDATA[3.2×10 -2 so]]> <![CDATA[3.5×10 -2 so]]> Arc starting voltage of arc starting power supply 150V 200V 200V 250V Arc starting power supply arc stabilization voltage / current 100A / 20V 100A / 20V 100A / 20V 100A / 20V Anode power supply etching working current / voltage 30A / 60V 30A / 60V 30A / 60V 30A / 60V Bias power supply etching working current / voltage 50V / 0.2A~250V / 10A 50V / 0.2A~250V / 10A 50V / 0.2A~250V / 10A 50V / 0.2A~250V / 10A Etching working time 25min 30min 30min 45min Sputtering operating temperature 550℃ 600℃ 600℃ 650℃ Sputtering vacuum <![CDATA[2.5×10 -1 Well]]> <![CDATA[3.5×10 -1 Well]]> <![CDATA[3.5×10 -1 Well]]> <![CDATA[4.5×10 -1 Well]]> Arc starting power supply, anode power supply sputtering working current / voltage 180A / 25V 180A / 25V 180A / 25V 180A / 25V Bias power supply sputtering operating voltage 100V 100V 100V 100V Coating thickness 2.5μm 2.8μm 2.8μm 3μm Sputtering time 45min 48 minutes 48 minutes 50min Magnetic field orientation pressure 0.5MPa 0MPa 6MPa 12MPa Heat treatment temperature 700℃ 900℃ 950℃ 1150℃ Heat treatment time 10h 20h 20h 40h Tempering temperature 440℃ 500℃ 580℃ 640℃ Tempering time 5h 8h 8h 15h

[0125] The coercivity Hcj (kOe) and remanence Br (kG) of the diffused NdFeB magnets obtained in Examples 1-6 and Comparative Examples 1-4 were measured using a TD8330 permanent magnet material testing system. The test results are shown in Table 3.

[0126] Table 3

[0127] coercive force remanence Original magnet 14.35 16.02 Example 1 14.12 23.75 Example 2 14.19 25.01 Example 3 14.20 25.07 Example 4 14.13 23.93 Example 5 14.17 24.93 Example 6 14.18 24.95 Example 7 14.13 23.78 Comparative Example 1 14.09 22.78 Comparative Example 2 14.07 21.45 Comparative Example 3 14.15 23.96 Comparative Example 4 14.11 22.96

[0128] As can be seen from Table 3, by comparing the coercive force and remanence data of Examples 1-6 with the coercive force and remanence data of the original magnet, it can be seen that the method for manufacturing grain boundary diffusion thick NdFeB magnets provided by the present invention can make the coercive force of NdFeB magnets (thickness ≥ 11 mm) reach above 23.75 kOe. In the best embodiment, the coercive force reaches 25.07 kOe, which can be increased by 9.05 kG compared to the coercive force of the original magnet, and the remanence can reach above 14.12 kG. In the best embodiment, the remanence can reach 14.20 kG, which can control the remanence reduction to 0.15 kG compared to the remanence of the original magnet.

[0129] Through the horizontal comparison of Examples 1-4, the separate comparison of Example 2 and Example 3, the separate comparison of Example 3 and Example 5, and the comparison of Example 3 and Example 6, it can be seen that appropriately increasing the Ar gas concentration in the sleeve module during etching, the magnetic field orientation pressure during composite treatment, and the heat treatment temperature can further improve the comprehensive magnetic properties of the diffused NdFeB magnet.

[0130] By comparing Example 1, Example 3 with Example 4, comparing Comparative Example 1 with Example 1, and comparing Comparative Example 4 with Example 4, it can be seen that when the Ar gas concentration in the sleeve module and the working chamber is too high, the Ar positive ions in the etching process will be blocked by Ar atoms when exposing the grain boundaries of the magnetic steel sheet, reducing the grain boundary exposure of the magnetic steel sheet and weakening the ability to open the grain boundary diffusion channel during the later grain boundary diffusion. When the Ar gas concentration in the sleeve module and the working chamber is too low, the ionization rate of the Ar positive ions in the etching process is too low, and too few Ar positive ions are formed, which will also reduce the grain boundary exposure of the magnetic steel sheet and weaken the ability to open the grain boundary diffusion channel during the later grain boundary diffusion.

[0131] At the same time, excessively high magnetic field orientation pressure and heat treatment temperature will cause more Dy elements to diffuse into the lattice and enrich Dy elements on the surface of the magnet, affecting the grain boundary diffusion depth of Dy, reducing the saturation magnetization intensity of the magnet and the content of Dy elements diffused into the interior of the magnet, and ultimately causing the remanence of the magnet to decrease, and the coercive force to increase slightly. Excessively low magnetic field orientation pressure and heat treatment temperature will lead to a slower diffusion rate, with only a small amount of Dy elements diffusing into the magnet, and the grain boundary diffusion effect is poor.

[0132] By comparing Example 2 with Comparative Example 2, it can be seen that when the magnetic field orientation pressure is canceled, the grain boundary diffusion depth of Dy will be reduced, the saturation magnetization intensity of the magnet and the content of Dy elements diffused into the interior of the magnet will be reduced, and ultimately the remanence of the magnet will decrease, and the coercive force will not be increased much.

[0133] By comparing Example 3 with Comparative Example 3, it can be seen that during ion etching, when the Ar gas concentration zoning setting is not performed, the Ar gas concentration at the columnar target is too low, and the rate of generated Ar positive ions is too low, which will affect the grain boundary exposure rate of the magnetic steel sheet. If the Ar gas concentration at the columnar target is too high, the generated Ar positive ions will be hindered by the Ar atoms in the working chamber, which will also affect the grain boundary exposure rate of the magnetic steel sheet.

[0134] By comparing Example 3 with Example 7, it can be seen that during ion etching, if an anode ring is not provided to accelerate, bunch, guide and pull the Ar positive ions and electrons generated at the cylindrical target, the Ar positive ion overflow rate at the cylindrical target will be relatively low, and the grain boundary exposure rate of the magnetic steel sheet will be reduced, affecting the grain boundary diffusion of thick NdFeB magnets.

[0135] In summary, the ion etching of the present invention adopts an Ar concentration zoning setting, combined with the synergistic effect of the same-direction stacking hot pressing composite, which can effectively improve the grain boundary exposure rate of the magnetic steel sheet, promote the opening of the grain boundary channel of the magnetic steel sheet during diffusion, and also enable more Dy elements to diffuse in the lattice. The grain boundary diffusion depth of Dy is deeper than that of the existing technology, and is more suitable for the grain boundary diffusion of thick NdFeB magnets, thereby improving the saturation magnetization intensity of the magnet and the content of Dy elements diffused into the interior of the magnet, and improving the comprehensive magnetic properties of the thick NdFeB magnets, such as remanence and coercive force.

[0136] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for manufacturing grain boundary diffused thick NdFeB magnets, characterized in that: The following steps are involved: Step S1: Loading the magnets. Hoist the magnetic steel sheet to be prepared onto the turret system. During hoisting, the magnetic steel sheet is set vertically, and the orientation plane A of the magnetic steel sheet in the magnetic field orientation direction is set toward the central axis B of the turret system. After loading is completed, close the sealed door of the etching and coating machine. Step S2: Preheat etching. Turn on the mechanical pump, Roots pump and molecular pump in the vacuum pump group in sequence to make the vacuum degree of the working chamber of the etching and coating machine reach 1.0×10 -2 pa~2.0×10 -2 After pa, the electric heating system and the ion etching system are respectively turned on to preheat and etch the magnetic steel sheet to remove impurities on the surface of the magnetic steel sheet. During etching, after the etching and coating integrated machine completes vacuuming and heating, the cylindrical target is sealed and isolated. Then, when Ar gas is filled into the external gas supply device, two Ar gas environments with different concentrations are formed inside and outside the sleeve module. The Ar gas concentration at the cylindrical target in the working chamber is higher than the Ar gas concentration in the working chamber. When the cylindrical target starts arcing and discharging, a gap is formed in the sleeve module to connect to the working chamber, and an anode ring is formed at the gap. The anode ring pulls the Ar positive ions and electrons in the sleeve module before the pancake target. Step S3, sputtering coating. After etching is completed, the ion etching system is turned off, the electric heating system is kept running, Ar gas is again introduced into the working chamber, and the sputtering system is turned on. The cylindrical target and the pancake target emit Dy plasma, which is deposited on the magnetic steel sheet of the turret system for coating. Before the sputtering, the partition door assembly on the sleeve module is adjusted so that a gap is formed on the side of the sleeve module facing the turret system. When the cylindrical target acts as an evaporation ion source to sputter the magnetic steel sheet, the Dy plasma can directly jump to the turret system through the gap. Step S4: Polishing treatment: Take the coated magnetic steel sheet out of the etching and coating machine, polish and clean the magnetic steel sheet to form edge magnetic steel sheets and middle magnetic steel sheets. The edge magnetic steel sheet is the magnetic steel sheet with the orientation surface A polished, and the middle magnetic steel sheet is the magnetic steel sheet with both orientation surfaces polished. Step S5: stacking the edge magnetic steel sheets and the middle magnetic steel sheets in the direction of the magnetic field orientation in the order of edge magnetic steel sheet-middle magnetic steel sheet-edge magnetic steel sheet. During stacking, the polished surface of the edge magnetic steel sheet is aligned with the polished surface of another edge magnetic steel sheet or the middle magnetic steel sheet, and the number N of the middle magnetic steel sheets is an integer ≥ 0. Step S6, composite treatment, applying a pressure of 0.5 to 12 MPa in the magnetic field orientation direction of the magnetic sheet stack, and performing heat treatment at a temperature of 800 to 1050°C in a vacuum or inert atmosphere for 10 to 40 hours. After the heat treatment, the magnetic sheet stack is tempered at a temperature of 440 to 640°C for 5 to 15 hours to obtain grain boundary diffusion thick NdFeB magnets. The remanence of the grain boundary diffusion thick NdFeB magnets with a thickness of ≥11 mm reaches more than 14.28 kG, and the coercive force reaches more than 22.87 kOe.

2. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 1, characterized in that: The preheat etching comprises the following steps: Step T1: preheating, turning on the electric heating system to raise the temperature in the working chamber to 200-250°C; Step T2: sealing the cylindrical target and activating the sleeve module surrounding the cylindrical target to seal and isolate the cylindrical target from the working chamber; Step T3: Filling Ar gas into the sleeve module and the working chamber respectively, so that the pressure in the sleeve module is 5.0×10 -2 pa~8.0×10 -2 Pa, synchronously, the air pressure in the working chamber is 3.0×10 -2 pa~3.5×10 - 2 pa; Step T4, etching arc initiation: the first arc initiation needle next to the cylindrical target rotates and swings, and instantly touches the cylindrical target, short-circuiting the arc initiation power supply on the cylindrical target, and discharging the Ar gas in the sleeve module to start the arc and emit a glow, forming Ar positive ions and electrons; Step T5: Opening the anode ring. Simultaneously with step T4, the partition door assembly on the sleeve module is opened, forming a gap on the side of the sleeve module facing away from the turret system. Simultaneously, an anode ring is formed at the gap. The anode ring performs a bunching and acceleration process on Ar positive ions and electrons, pulling the Ar positive ions and electrons out of the sleeve module through the gap. Step T6, anode pulling: Synchronously with step T4, the anode power supply supplies power to the pancake target. The pancake target pulls and accelerates the electrons released in step T4, which collide with the Ar gas in the working chamber to form Ar positive ions. The operating current and voltage of the anode power supply are 30A / 60V. Step T7, etching, the bias power supply supplies power to the turret system, the turret system pulls Ar positive ions, and the Ar positive ions collide with the surface of the magnetic steel sheet on the turret system. The working current and voltage of the bias power supply are as follows: the working voltage is 50V to 250V, the current is 0.2A to 10A, and the working time is 25min to 45min.

3. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 2, characterized in that: In step T2, the air pressure in the sleeve module is 6.0×10 -2 Pa, the air pressure in the working chamber is 3.2×10 -2 pa; The sleeve module includes a sleeve, a partition door assembly and a drive unit. The sleeve is coaxially sleeved on the outer side of the cylindrical target. The sleeve is provided with openings on the side opposite to the turret system and the side opposite to the turret system. The partition door assembly is symmetrically arranged, and there are two groups of partition door assemblies. The two groups of partition door assemblies are respectively arranged at the corresponding openings. The two groups of partition doors in the partition door assembly are rotated around the inner ring of the sleeve, and the lower ends of the partition doors in the same group are engaged by gears; The driving unit includes a driving motor and a driving gear. The driving motor is arranged in cooperation with the gear through the driving gear. The driving gear is a toothless gear. The driving unit switches forward and reverse to drive the partition door assembly to open the corresponding gap. Anode bars are arranged in parallel at the upper and lower edges of the opening on the side of the sleeve facing away from the turret system, and anode connecting bars are respectively arranged at the edges of the two groups of partition doors facing the resin. The upper and lower ends of the anode connecting bars are respectively slidably arranged on the anode bars, and the anode connecting bars are conductively arranged to contact the anode bars. When the partition door is opened, the anode bars and the anode connecting bars are combined to form an anode ring, and the middle part of the anode bar is connected to the arc starting power supply. The current of the arc starting power supply flows through the anode ring, forming a voltage / current at the anode ring that is higher than that at the cylindrical target material.

4. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 2, characterized in that: In step T4, the initial voltage of the arc starting power supply is 150-250V, and the working current and voltage after arc stabilization are 100A / 20V.

5. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 2, characterized in that: In step T6, the current of the anode power supply is gradually increased from 30A to 100A.

6. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 2, characterized in that: In step T7, the voltage of the bias power supply is gradually increased from 50V to 250V.

7. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 1, characterized in that: The sputtering coating comprises the following steps: Step U1: heating and heat preservation: maintaining the operation of the electric heating system, raising the temperature in the working chamber to 550-650° C., and heat preservation; Step U2: Filling Ar gas into the working chamber to maintain the vacuum degree in the working chamber at 2.5×10 -1 Pa~4.5×10 -1 Pa; Step U3, glow sputtering: the first arc-starting needle at the cylindrical target rotates and swings to instantly touch the cylindrical target, and the second arc-starting needle at the pancake target touches the pancake target, respectively short-circuiting the arc-starting power supply and the anode power supply, causing the Ar gas in the working chamber to discharge and start an arc to emit a glow, and the cylindrical target and the pancake target sputter to overflow Dy plasma; Step U4, coating, bias power supply supplies power to the turret system, the working voltage is 100V, the turret system draws Dy plasma to adhere to the surface of the magnetic steel sheet on the turret system, forming a coating with a thickness of 2.5 to 3 μm, and the working time is 45 to 50 minutes.

8. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 7, characterized in that: In step U2, the vacuum degree in the working chamber is maintained at 3.5×10 -1 Pa.

9. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 7, characterized in that: In step U3, the operating current and voltage of the arc starting power supply and the anode power supply are 180A / 25V.

10. The method for manufacturing a grain boundary diffused thick NdFeB magnet according to claim 1, characterized in that: In the step S6, a pressure of 6 MPa is applied to the magnetic field orientation direction of the magnetic sheet stack, and a heat treatment is performed at a temperature of 950°C in a vacuum or inert atmosphere for 35 hours. After the heat treatment, the magnetic sheet stack is tempered at a temperature of 550°C for 10 hours to obtain grain boundary diffusion thick NdFeB magnets. The remanence of the grain boundary diffusion thick NdFeB magnets with a thickness of ≥11 mm reaches more than 14.12 kG, and the coercive force reaches more than 23.75 kOe.

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