A grain boundary diffusion method and magnetic force adsorption deposition equipment for neodymium-iron-boron magnets

Abstract

The application belongs to the technical field of Nd-Fe-B magnets, and relates to a grain boundary diffusion method and a magnetic adsorption deposition equipment for a Nd-Fe-B magnet deposited by magnetic adsorption. The application discloses a grain boundary diffusion method for a Nd-Fe-B magnet deposited by magnetic adsorption, which comprises the following steps: after the Nd-Fe-B magnet is magnetized to be oversaturated, the magnet is subjected to thermal demagnetization, then the magnet is subjected to diffusion source powder adhesion and diffusion heat treatment, and finally the magnet after the grain boundary diffusion is obtained. The application further discloses a magnetic adsorption deposition equipment, which comprises a thermal demagnetization tank, a dust removal and cooling tank, an adhesion chamber and a transition cabin which are sequentially and closably connected, and a magnet moves in the magnetic adsorption deposition equipment through a transmission group. According to the application, after the magnet is magnetized to be oversaturated, the magnet is subjected to thermal demagnetization, so that the magnet has a non-magnetic saturated state with suitable residual magnetism and surface magnetism distribution; on this basis, the diffusion source powder is adhered and diffusion heat treatment is performed, so that batch production of diffusion magnets with high performance and high consistency can be realized.

Description

Technical Field

[0001] This invention belongs to the field of neodymium iron boron magnet technology, and relates to a grain boundary diffusion method and magnetic adsorption deposition equipment for neodymium iron boron magnets deposited by magnetic adsorption. Background Technology

[0002] With the in-depth application of grain boundary diffusion technology in NdFeB permanent magnet materials, high-coercivity, high-performance NdFeB magnets have developed rapidly and have become an indispensable key functional material in high-tech fields such as rail transportation and new energy vehicles. A complete grain boundary diffusion technology typically includes the following processes: ① preparing a diffusion source of a specific composition; ② attaching the diffusion source to the surface of the target magnet; ③ placing the magnet with the attached diffusion source into a heat treatment furnace for diffusion heat treatment; ④ performing surface processing on the diffused magnet to achieve a smooth and bright surface. In terms of diffusion source development, after long-term exploration, multi-element rare earth alloy diffusion sources with multiple elements have gradually replaced rare earth elements and their simple compounds (oxides, hydrides, fluorides). Due to their lower raw material costs and better diffusion modification effects, they are considered the most promising diffusion source system. To adapt to the development and application of diffusion source systems based on multi-component rare earth alloys, the mainstream process has become one of preparing multi-component rare earth alloys into powders, then thoroughly mixing them with organic solvents (adhesives) to form a slurry, and finally attaching the diffusion source using spraying and screen printing. In this process, although organic solvents or adhesives can, to some extent, prevent excessive oxidation of the rare earth alloy powder and achieve the effect of adhering the diffusion source powder to the magnet surface, the introduction of organic solvents inevitably leads to an increase in impurities such as carbon and hydrogen, preventing the grain boundary diffusion technology from achieving the expected performance enhancement.

[0003] Recent studies have shown that introducing appropriate amounts of ferromagnetic elements such as Fe and Co into the diffusion source of multi-component rare earth alloys is beneficial to improving the defects of the diffusion interface, thereby optimizing the remanence of the magnet, and at the same time, it will enable the multi-component rare earth alloy to have a certain degree of ferromagnetism. By utilizing the intrinsic magnetic force of magnetized neodymium iron boron (NdFeB) magnets to adsorb ferromagnetic diffusion source powders (containing elements such as Fe and Co), the problem of residual diffusion impurities caused by the introduction of organic solvents or adhesives can be fundamentally avoided. However, this technology requires strict control over the magnetization process. The magnetization process uses a magnetic field to perform unsaturated magnetization (pre-magnetization / pre-aperture) on the NdFeB magnets, which requires tedious experiments and calculations of the appropriate magnitude of the magnetization magnetic field. The magnetization deflection angle must be strictly controlled. During magnetization, the magnetic deflection angle between the normal of the magnetization coil and the C-axis must be strictly less than 5 degrees, otherwise it will lead to uneven surface magnetic distribution and affect the final adsorption effect. Even under the same magnetization magnetic field conditions, the remanence (external magnetic moment / magnetic attraction force) obtained can vary greatly, resulting in poor consistency in the amount of diffusion source powder adsorbed in batches or the final magnet diffusion performance. Furthermore, for NdFeB magnets with varying coercivity, it is difficult to precisely set the magnetizing current parameters during the magnetization process using a magnetizer to achieve the target surface magnetic distribution. Even NdFeB magnets prepared in the same batch exhibit coercivity fluctuations. Magnets with slight differences in coercivity, when magnetized with unsaturated current, can also result in significant differences in their surface magnetic distribution, making it difficult to ensure the consistency of the diffusion source powder adsorption quality in batches of magnets. In addition, the above-mentioned technical solutions rely relatively heavily on manual operation, resulting in low diffusion source adhesion efficiency, which is difficult to match the growing demand for large-scale supply of high-performance diffused NdFeB magnets.

[0004] Therefore, it is necessary to develop a grain boundary diffusion method for NdFeB magnets based on the principle of magnetic adsorption deposition, to achieve efficient and automated attachment of ferromagnetic diffusion sources containing elements such as Fe and Co, and to achieve the goal of mass production of high-performance and highly consistent diffused NdFeB magnets. This is of great significance to the development of high-performance NdFeB permanent magnet materials. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a grain boundary diffusion method for NdFeB magnets using magnetic adsorption deposition. Through magnetic adsorption deposition, diffusion source powder is attached to the surface of the magnet to be attached, which is obtained by thermal demagnetization after saturation magnetization. This significantly improves the magnetic properties while meeting the requirements for efficient mass production.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for grain boundary diffusion of NdFeB magnets deposited by magnetic adsorption includes: supersaturating the NdFeB magnets and then thermally demagnetizing them, followed by attachment of diffusion source powder and diffusion heat treatment to obtain NdFeB magnets with grain boundary diffusion.

[0008] Preferably, the grain boundary diffusion method for depositing NdFeB magnets using magnetic adsorption includes:

[0009] (1) After the neodymium iron boron magnet is oversaturated and magnetized, it is detachably fixed on the detachable magnet fixture to obtain the magnet assembly to be attached;

[0010] (2) The magnet assembly to be attached is transferred to the magnetic adsorption deposition equipment, and thermal demagnetization, dust removal and cooling are performed in sequence. The diffusion source powder is attached to the magnet surface by circulating powder to obtain the magnet to be diffused.

[0011] (3) The magnet to be diffused is subjected to diffusion heat treatment to obtain a neodymium iron boron magnet after grain boundary diffusion.

[0012] Preferably, after thermal demagnetization, the surface magnetic field of the pole face of the magnet is 800–1100 Gs.

[0013] Further optimization revealed that, after thermal demagnetization, the magnetic difference between the pole surfaces of magnets in the same batch was 0–20 Gs.

[0014] After thermal demagnetization, the magnet forms a uniform surface magnetic distribution, and the surface magnetic intensity can adsorb an appropriate amount of ferromagnetic diffusion source powder.

[0015] Preferably, the neodymium iron boron magnet is a neodymium iron boron magnet with a coercivity performance of N to AH or higher.

[0016] Preferably, the neodymium iron boron magnet undergoes surface treatment before oversaturation magnetization, and the surface treatment includes at least one of alkaline washing, acid washing, and sandblasting.

[0017] Preferably, the magnetizing capacitor is greater than 4800μF and the magnetizing voltage is greater than 3200V during the oversaturation magnetization process.

[0018] Preferably, the oxygen content in the magnetic adsorption deposition equipment is less than 150 ppm.

[0019] Preferably, the thermal demagnetization temperature is 200–350℃ and the time is 0.1–30 min.

[0020] Further optimization involves using a thermal demagnetization temperature of 260–300°C and a time of 10–15 minutes.

[0021] Further optimization reveals that the thermal demagnetization temperature of NdFeB magnets with coercivity performance in the N to M range is 260 to 270°C, the thermal demagnetization temperature of NdFeB magnets with coercivity performance in the H to SH range is 270 to 280°C, the thermal demagnetization temperature of NdFeB magnets with coercivity performance in the UH to EH range is 280 to 290°C, and the thermal demagnetization temperature of NdFeB magnets with coercivity performance in the AH range and above is 290 to 300°C.

[0022] Preferably, the method for grain boundary diffusion of NdFeB magnets deposited by magnetic adsorption includes: after the NdFeB magnet is oversaturated and magnetized, it is thermally demagnetized at 260-300°C, and then subjected to diffusion source powder attachment and diffusion heat treatment to obtain NdFeB magnets with grain boundary diffusion.

[0023] As a preferred embodiment, in the circulating powder lifting process, the motor unit driving the rolling inner cavity of the attachment chamber rotates the rolling inner cavity of the attachment chamber, which in turn drives the powder-lifting blades in the inner cavity of the attachment chamber to circulate and lift the diffusion source powder.

[0024] Preferably, during diffusion source powder attachment, the adsorption load of diffusion source powder on the NdFeB magnet is 1 to 3 wt% of the mass of the NdFeB magnet after diffusion source powder attachment.

[0025] Preferably, the average particle size of the diffusion source powder is 3–50 μm.

[0026] Preferably, the diffusion source powder is a ferromagnetic diffusion source powder with the chemical formula R1. a R2 b M1 c M2 d Wherein, R1 is at least one of Pr, Nd, La, Ce, and Y; R2 is at least one of Dy, Tb, Ho, and Gd; M1 is at least one of Fe, Co, and Ni; M2 is at least one of Cu, Al, Ga, Zr, Ti, and Nb; and a, b, c, and d are the atomic percentages of the corresponding components, satisfying 0≤a≤40, 20≤b≤70, 60≤a+b≤80, 20≤c≤40, 0≤d≤20, and a+b+c+d=100.

[0027] Preferably, the diffusion heat treatment includes a two-stage heat treatment with a vacuum degree ≤10. -2 Pa; The heating rate of the first stage heat treatment is 0.1~5℃ / min, the holding temperature is 880~920℃, and the holding time is 1~12h; after cooling to room temperature, the second stage heat treatment is carried out, the heating rate of the second stage heat treatment is 5~15℃ / min, the holding temperature is 460~520℃, and the holding time is 1~12h.

[0028] A magnetic adsorption deposition device includes a thermal demagnetization box, a dust removal and cooling box, an attachment chamber, and a transition chamber that are sequentially and enclosedly connected. The magnet moves within the magnetic adsorption deposition device via a transmission assembly.

[0029] Preferably, the transmission assembly includes a detachable magnetic clamp assembly, an upper drive motor, a lower drive motor, an upper rotating gear assembly, a lower rotating gear assembly, an upper transmission chain shaft, and a lower transmission chain shaft.

[0030] The upper and lower drive chain shafts are vertically fixed at the upper and lower ends of the detachable magnetic clamp assembly. The upper drive motor causes the upper rotating gear set to rotate, which drives the upper drive chain shaft to move. The lower drive motor causes the lower rotating gear set to rotate, which drives the lower drive chain shaft to move.

[0031] Further optimization involves adjusting the output power of the upper and lower drive motors to cause the detachable magnetic clamp to exhibit a "left-right swaying" posture, with a maximum bidirectional swaying angle difference of 60°.

[0032] Further preferred, the detachable magnet clamp includes two clamping meshes with clamping frame edging, and the magnet is detachably fixed in the two clamping meshes by fixing bolts. The upper end of the clamping frame is provided with an upper clamping connector, which is connected to the upper drive chain shaft through an elastic component of the upper drive chain shaft. The lower end of the clamping frame is provided with a lower clamping connector, which is connected to the lower drive chain shaft through an elastic component of the lower drive chain shaft.

[0033] Further optimization is made of high-temperature resistant stainless steel for the detachable magnet clamps.

[0034] Preferably, the thermal demagnetizing box is connected to a first inert gas source; the dust removal and cooling box is connected to a cooling gas source; and the transition chamber is connected to a second inert gas source.

[0035] Further optimization involves using an air pressure of 0.05–0.2 MPa in the thermal demagnetization box, 0.05–0.5 MPa in the dust removal cooling box, and 0.05–0.2 MPa in the transition chamber.

[0036] Further optimization involves using a temperature of 260–300°C in the thermal demagnetizing chamber.

[0037] Preferably, the attachment chamber includes an outer support box and a rolling inner cavity. The rolling inner cavity has tapered tightening ports with a taper of 10–45° at both ends. Several inclined powder-lifting blades are evenly distributed inside the rolling inner cavity. The top of the outer support box has a closable gate, and the top of the rolling inner cavity has a closable gate. Diffusion source powder enters the rolling inner cavity sequentially through both the closable gates. A motor unit drives the rolling inner cavity to rotate, causing the powder-lifting blades to circulate and lift the diffusion source powder. The linear velocity of the bottom edge of the powder-lifting blades is 0.1–5.0 m / s.

[0038] Preferably, the oxygen content in the rolling inner cavity of the attachment chamber and the transition chamber is less than 150 ppm.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. This invention involves oversaturating the magnet with magnetization followed by thermal demagnetization, resulting in a non-magnetically saturated state with suitable remanence and surface magnetic distribution. Based on this, diffusion source powder is attached and diffusion heat treatment is performed, enabling the mass production of high-performance, highly consistent diffusion magnets.

[0041] 2. Compared to directly magnetizing the magnet to the target magnetization level, the method of this invention does not require tedious experiments and calculations of the appropriate magnetization magnetic field size. It directly uses the largest possible magnetic field to magnetize the NdFeB magnet, bringing it to magnetic saturation, thus simplifying the magnetization process. Subsequently, the thermal demagnetization characteristics of NdFeB permanent magnet materials are utilized for heat treatment, transforming the magnet from a magnetically saturated state to a non-magnetically saturated state with appropriate remanence (external magnetic moment effect / magnetic attraction). During this process, since NdFeB materials with similar microstructures have nearly uniform thermal demagnetization characteristics, only a reasonable heat treatment temperature needs to be designed to ensure that a batch of magnets obtains consistent and appropriate remanence (external magnetic moment effect / magnetic attraction), thereby obtaining a batch of high-performance diffusion magnets with consistent performance.

[0042] 3. This invention does not require control of the magnetization deflection angle because saturating the magnet with magnets will eliminate the negative impact of magnetic deflection angle on the distribution and uniformity of surface magnetism. During the technical magnetization process of the magnet, when the external magnetic field is large enough to achieve a state of supersaturation, the positive domains in the magnet, or "positive magnetic moments," will uniformly and consistently turn towards the magnetization direction. After removing the external magnetic field, all magnetic domains will basically transfer to the easy magnetization direction of the magnet, i.e., the "direction of lowest energy," which is the easy axis direction of the magnet. At this time, there is no result of uneven distribution of magnetic moments in multiple directions caused by magnetic deflection angle. Therefore, this invention adopts saturation magnetization first, followed by thermal demagnetization (thermal demagnetization can achieve uniform weakening of magnetic moment directions), which can avoid the magnetic deflection angle problem caused by the unsaturated magnetization process. Therefore, this invention does not require control of the magnetic deflection angle during the magnetization or technical magnetization process.

[0043] 4. The grain boundary diffusion method of NdFeB magnets deposited by magnetic adsorption in this invention can effectively improve magnetic properties and meet the requirements of efficient mass production.

[0044] 5. In this invention, the diffusion source powder is circulated and dispersed in the attachment chamber, and combined with the bidirectional swinging motion of the detachable magnet clamp, the diffusion source powder is uniformly attached to the magnet surface.

[0045] 6. In the magnetic adsorption deposition equipment of the present invention, tapered tightening ports with a taper of 10 to 45° are provided at both ends of the rolling inner cavity of the attachment chamber. The function of these ports is that the diffusion source powder raised by the powder-flicking blades in the attachment chamber can slide down along the inner wall of the tapered tightening port after it falls and re-enters the bottom of the rolling inner cavity of the attachment chamber, which can effectively prevent the diffusion source powder from overflowing.

[0046] 7. This invention uses a magnetic adsorption deposition device to process magnets, enabling mass production of magnets and meeting batch consistency requirements. Attached Figure Description

[0047] Figure 1 This is a simplified diagram of the magnetic adsorption deposition apparatus of the present invention.

[0048] Figure 2 This is a cross-sectional view of the attachment chamber in the magnetic adsorption deposition apparatus of the present invention.

[0049] Figure 3 This is a simplified diagram of the detachable magnet clamp assembly in the magnetic adsorption deposition apparatus of the present invention.

[0050] In the diagram: 1. Upper drive motor; 2. Upper rotating gear set; 3. Detachable magnet clamp set; 4. Lower rotating gear set; 5. Lower drive motor; 6. Upper transmission chain shaft; 7. Lower transmission chain shaft; 8. Thermal demagnetization box; 9. First inert gas source; 10. Dust removal cooling box; 11. Cooling gas source; 12. Attachment chamber support outer box; 13. Attachment chamber rolling inner cavity; 14. Attachment chamber inner cavity closable gate; 15. Attachment chamber inner cavity powder-removing blade; 16. Attachment chamber outer box closable gate; 17. Diffusion source powder; 18. Inductive positioning control system; 19. Attachment chamber rolling inner cavity drive motor set; 20. Second inert gas source; 21. Transition chamber; 22. Magnet; 23. Clamp upper connector; 24. Clamping frame; 25. Fixing bolt; 26. Lower transmission chain shaft elastic component; 27. Upper transmission chain shaft elastic component; 28. Clamping mesh; 29. ​​Clamp lower connector. Detailed Implementation

[0051] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0052] Unless otherwise specified, the materials used in this invention are commercially available products, and the methods used are conventional technical means.

[0053] The magnetic adsorption deposition equipment of the present invention includes a thermal demagnetizing box 8, a dust removal and cooling box 10, an attachment chamber, and a transition chamber 21 that can be sequentially and enclosedly connected; the magnet moves in the magnetic adsorption deposition equipment through a transmission assembly.

[0054] When the magnet moves in the magnetic adsorption deposition equipment via the transmission assembly, the ambient oxygen content is less than 150 ppm.

[0055] The thickness of the magnet is 1 to 30 mm to ensure that the magnet is stably fixed in the detachable magnet clamp assembly; the thickness of the magnet is further preferably 1 to 10 mm.

[0056] The transmission assembly includes a detachable magnetic clamp assembly 3, an upper drive motor 1, a lower drive motor 5, an upper rotating gear assembly 2, a lower rotating gear assembly 4, an upper transmission chain shaft 6, and a lower transmission chain shaft 7.

[0057] The upper drive chain shaft 6 and the lower drive chain shaft 7 are vertically fixed at the upper and lower ends of the detachable magnetic clamp group 3. The upper drive motor 1 causes the upper rotating gear group 2 to rotate, which drives the upper drive chain shaft 6 to move. The lower drive motor 5 causes the lower rotating gear group 4 to rotate, which drives the lower drive chain shaft 7 to move.

[0058] Adjust the output power of the upper drive motor 1 and the lower drive motor 5 to drive the detachable magnetic clamp to present a "left and right swinging" posture (the maximum angle difference between the two swinging directions is 60°).

[0059] The detachable magnet clamp includes two meshes 28 with a clamping frame 24 as the rim. The magnet 22 is detachably fixed in the two meshes 28 by a fixing bolt 25. The upper end of the clamping frame 24 is provided with an upper clamping connector 23, which is connected to the upper drive chain shaft 6 through an upper drive chain shaft elastic component 27. The lower end of the clamping frame 24 is provided with a lower clamping connector 29, which is connected to the lower drive chain shaft 7 through a lower drive chain shaft elastic component 26.

[0060] The thermal demagnetizing box 8 is connected to a first inert gas source 9; the dust removal and cooling box 10 is connected to a cooling gas source 11; and the transition chamber 21 is connected to a second inert gas source 20.

[0061] The attachment chamber includes an outer support box 12 and a rolling inner cavity 13. The rolling inner cavity 13 has tapered tightening ports with a taper of 10–45° at both ends. Several inclined powder-lifting blades 15 are evenly distributed inside the rolling inner cavity 13. The top of the outer support box 12 has a closable gate 16, and the top of the rolling inner cavity 13 has a closable gate 14. Diffusion source powder 17 enters the rolling inner cavity 13 sequentially through the closable gate 16 and the closable gate 14. A motor 19 drives the rolling inner cavity to rotate the rolling inner cavity 13, causing the powder-lifting blades 15 to circulate and lift the diffusion source powder 17. The linear velocity of the bottom edge of the powder-lifting blades is 0.1–5.0 m / s.

[0062] The attachment chamber is also connected to a sensor positioning control system 18, which is used to detect the remaining amount of diffusion source powder and control the addition of supplementary diffusion source powder.

[0063] Example 1

[0064] 200 N55(N) grade magnets with a diameter of 25mm×12mm×4mm were sequentially pickled and sandblasted. Then, the magnets were oversaturated magnetized using a magnetizer. The magnetizing capacitor was 5200μF and the magnetizing voltage was 3600V. After magnetization, the magnets were detachably fixed on a detachable magnet fixture to obtain the magnet assembly to be attached.

[0065] The magnet assembly to be attached is placed in the transmission assembly and transferred to the magnetic adsorption deposition equipment. The transmission assembly in the magnetic adsorption deposition equipment is used to move the magnet assembly to be attached, so that it passes through the thermal demagnetization box 8, the dust removal and cooling box 10, the attachment chamber, and the transition chamber 21 in sequence.

[0066] The transmission assembly includes a detachable magnetic clamp assembly 3, an upper drive motor 1, a lower drive motor 5, an upper rotating gear assembly 2, a lower rotating gear assembly 4, an upper transmission chain shaft 6, and a lower transmission chain shaft 7. The upper and lower ends of the detachable magnetic clamp assembly 3 are vertically fixed on the upper transmission chain shaft 6 and the lower transmission chain shaft 7. The upper drive motor 1 causes the upper rotating gear assembly 2 to rotate, which drives the upper transmission chain shaft 6 to move. The lower drive motor 5 causes the lower rotating gear assembly 4 to rotate, which drives the lower transmission chain shaft 7 to move.

[0067] The thermal demagnetizing box 8 is connected to a first inert gas source 9, which fills the thermal demagnetizing box 8 with argon gas and sets the temperature to 260°C. The magnet group to be attached stays in the thermal demagnetizing box 8 for 15 minutes. Then the magnet group to be attached is moved to the dust removal and cooling box by the transmission group.

[0068] The dust removal and cooling box 10 is connected to a cooling gas source 11, which fills the box with nitrogen gas at a pressure of 0.1 MPa. The magnets to be attached stay in the dust removal and cooling box 10 for 5 minutes. Then the magnets to be attached are moved to the attachment chamber by the transmission group.

[0069] In the attachment chamber, the output power of the upper drive motor 1 and the lower drive motor 5 is adjusted to drive the magnet group to be attached to present a "left and right swinging" posture, with a bidirectional swinging angle difference of 0 to 60°.

[0070] The attachment chamber includes an outer support box 12 and a rolling inner cavity 13. The rolling inner cavity 13 has tapered tightening ports with a taper of 25° at both ends. The top of the outer support box 12 has a closable gate 16, and the top of the rolling inner cavity 13 has a closable gate 14. The chemical formula is Pr7Nd. 23 Tb 15 Dy 15 Fe 25 Ga5Al 10The diffusion source powder 17 (atomic ratio) enters the attachment chamber rolling cavity 13 through the closable gate 14 of the outer casing of the attachment chamber and the closable gate of the inner cavity of the attachment chamber; several inclined powder-lifting blades 15 are evenly distributed inside the rolling cavity of the attachment chamber; the attachment chamber rolling cavity drive motor 19 rotates the attachment chamber rolling cavity 13, which drives the powder-lifting blades 15 of the inner cavity of the attachment chamber to circulate and lift the diffusion source powder 17; the linear velocity of the bottom edge of the powder-lifting blades of the inner cavity of the attachment chamber is set to 2.0 m / s.

[0071] The magnet assembly to be attached is kept in the attachment chamber for 8 minutes. The average adsorption load of the diffusion source powder on the surface of the magnet assembly to be attached is 1.5 wt% of the total mass. Then it is moved to the transition chamber 21 to obtain the magnet assembly to be diffused.

[0072] The transition chamber 21 is connected to a second inert gas source 20 and is filled with argon. The oxygen content in the rolling inner cavity of the attachment chamber and the transition chamber is 80 ppm.

[0073] The magnet assembly to be diffused was transferred to a vacuum heat treatment furnace via a movable glove box filled with argon gas. The vacuum level in the furnace was 2.5 × 10⁻⁶. -3 Pa was heated to 900℃ at a rate of 4℃ / min, held for 8 hours, and then rapidly cooled to room temperature by air cooling. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min, held for 8 hours, and then rapidly cooled to room temperature by air cooling to obtain a NdFeB magnet with grain boundary diffusion.

[0074] Ten magnets were randomly selected after passing through the thermal demagnetization box for surface magnetic distribution testing of their pole faces. The average surface magnetic intensity (absolute value) of their pole faces were 852 Gs, 845 Gs, 848 Gs, 850 Gs, 850 Gs, 852 Gs, 847 Gs, 850 Gs, 855 Gs, and 849 Gs, respectively.

[0075] Ten NdFeB magnets were randomly selected from 200 NdFeB magnets after grain boundary diffusion for magnetic performance testing. The results of remanence (Br), coercivity (Hcj), and squareness (Hk / Hcj) of the original magnets and the sampled magnets after grain boundary diffusion are shown in Table 1 below.

[0076] Table 1. Magnetic property data of original N55(N) magnets and sampled magnets after grain boundary diffusion.

[0077]

[0078] The test data above show that the NdFeB magnets prepared by the method of this embodiment after grain boundary diffusion can significantly improve coercivity while meeting the requirements for efficient mass production.

[0079] Example 2

[0080] Compared with Example 1, the difference is that 200 pieces of 30mm×10mm×3.5mm 50H grade magnets are acid-washed and sandblasted, and then oversaturated magnetized using a magnetizer. The magnetizing capacitor is 5100μF and the magnetizing voltage is 3550V. After magnetization, they are detachably fixed on a detachable magnet fixture to obtain the magnet assembly to be attached. The magnet assembly to be attached is placed in the transmission group and transferred to the magnetic adsorption deposition equipment. The transmission group in the magnetic adsorption deposition equipment moves the magnet assembly to be attached, so that it passes through the thermal demagnetization box 8, the dust removal and cooling box 10, the attachment chamber, and the transition chamber 21 in sequence.

[0081] The thermal demagnetizing box 8 is connected to a first inert gas source 9, which fills the thermal demagnetizing box 8 with argon gas and sets the temperature to 270°C. The magnet group to be attached stays in the thermal demagnetizing box 8 for 15 minutes. Then the magnet group to be attached is moved to the dust removal and cooling box by the transmission group.

[0082] The dust removal and cooling box 10 is connected to a cooling gas source 11, which fills the box with nitrogen gas at a pressure of 0.2 MPa. The magnets to be attached stay in the dust removal and cooling box 10 for 5 minutes. Then the magnets to be attached are moved to the attachment chamber by the transmission group.

[0083] The chemical formula is Pr 40 Dy 25 Fe 15 Co 10 The diffusion source powder 17 of Cu5Al5 (atomic ratio) enters the attachment chamber rolling cavity 13 through the closable gate 14 of the outer casing of the attachment chamber and the closable gate of the inner cavity of the attachment chamber; several inclined powder-lifting blades 15 are evenly distributed inside the rolling cavity of the attachment chamber; the attachment chamber rolling cavity drive motor 19 drives the attachment chamber rolling cavity 13 to rotate, thereby driving the powder-lifting blades 15 inside the attachment chamber to circulate and lift the diffusion source powder 17; the linear velocity of the bottom edge of the powder-lifting blades inside the attachment chamber is set to 1.5m / s.

[0084] The magnet assembly to be attached is placed in the attachment chamber for 8 minutes, and the average adsorption loading of the diffusion source powder on the surface of the NdFeB magnet is 2.0 wt% of the total mass. It is then moved to the transition chamber 21 to obtain the magnet assembly to be diffused. The transition chamber 21 is connected to a second inert gas source 20 and is filled with argon. The oxygen content in the rolling inner cavity of the attachment chamber and the transition chamber is 80 ppm.

[0085] The magnet assembly to be diffused was transferred to a vacuum heat treatment furnace using a moving glove box filled with argon gas. The vacuum level in the furnace was 2.5 × 10⁻⁶. -3 Pa was heated to 900℃ at a rate of 4℃ / min, held for 8 hours, and then rapidly cooled to room temperature by air cooling. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min, held for 8 hours, and then rapidly cooled to room temperature by air cooling to obtain a NdFeB magnet with grain boundary diffusion.

[0086] Ten magnets were randomly selected after passing through the thermal demagnetization box for surface magnetic distribution testing of their pole faces. The average surface magnetic intensity (absolute value) of their pole faces were 919Gs, 912Gs, 916Gs, 917Gs, 912Gs, 915Gs, 919Gs, 915Gs, 917Gs, and 912Gs, respectively.

[0087] Ten NdFeB magnets were randomly selected from 200 NdFeB magnets after grain boundary diffusion for magnetic performance testing. The results of remanence (Br), coercivity (Hcj), and squareness (Hk / Hcj) of the original magnets and the sampled magnets after grain boundary diffusion are shown in Table 2 below.

[0088] Table 2. Magnetic property data of the original 50H magnet and sampled magnets after grain boundary diffusion.

[0089]

[0090] The test data above show that the NdFeB magnets prepared by the method of this embodiment after grain boundary diffusion can significantly improve coercivity while meeting the requirements for efficient mass production.

[0091] Comparative Example 1

[0092] Two hundred N55(N) grade magnets, each measuring 25mm × 12mm × 4mm, were sequentially acid-washed and sandblasted. Based on the surface magnetic distribution of the magnets and tests of the optimal ferromagnetic powder adsorption capacity, the required surface magnetic field size for an average adsorption load of 2% of the diffusion source powder, as well as the external magnetic field or magnetizer parameters required to obtain this surface magnetic field, were determined. The magnets were then subjected to unsaturated magnetization using a magnetizer with a 2000μF magnetizing capacitor, a 1000V magnetizing voltage, and a magnetization deflection angle controlled to be less than 5 degrees, to obtain the magnets to be attached. The magnetized magnets were then buried in a Pr7Nd atmosphere under a protective gas environment. 23 Tb 10 Dy 20 Fe 25 Ga5Al 10 In a diffusion source powder of (atomic ratio), the diffusion source powder is completely adsorbed onto the surface of the magnetized magnet, and then removed to obtain the magnet to be diffused. The magnet to be diffused is then transferred to a vacuum heat treatment furnace under argon protection, at a vacuum degree of 2.5 × 10⁻⁶. -3 Under Pa conditions, the temperature was increased to 900℃ at a rate of 4℃ / min, held for 8 hours, and then rapidly cooled to room temperature by air cooling. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min, held for 8 hours, and then rapidly cooled to room temperature by air cooling to obtain the final target diffusion magnet.

[0093] Ten magnets were randomly selected from those magnets after unsaturation magnetization for surface magnetic distribution testing of their pole faces. The average surface magnetic intensities (absolute values) of the magnet pole faces were 821 Gs, 869 Gs, 807 Gs, 791 Gs, 847 Gs, 801 Gs, 833 Gs, 815 Gs, 850 Gs, and 816 Gs, respectively.

[0094] Ten magnets were randomly selected from 200 magnets after grain boundary diffusion for magnetic performance testing. The results of remanence (Br), coercivity (Hcj), and squareness (Hk / Hcj) of the original magnets and the sampled magnets after grain boundary diffusion are shown in Table 3 below.

[0095] Table 3. Magnetic performance data of original N55(N) magnets and sampled magnets after conventional magnetic adsorption and diffusion.

[0096]

[0097] The test data above shows that, compared with the method in Example 1, the magnetic properties of the magnets after traditional magnetic adsorption and diffusion in this comparative example fluctuate greatly (Hcj of the same batch of magnets differs by 1.93), which cannot meet the strict batch consistency requirements.

[0098] Comparative Example 2

[0099] Compared with Example 1, the difference is that the internal temperature of the thermal demagnetizing box is 305°C.

[0100] Ten magnets were randomly selected after passing through the thermal demagnetization box for surface magnetic distribution testing of their pole faces. The average surface magnetic intensity (absolute value) of their pole faces were 329Gs, 335Gs, 332Gs, 327Gs, 341Gs, 335Gs, 329Gs, 339Gs, 337Gs, and 329Gs, respectively.

[0101] Ten magnets were randomly selected from 200 magnets after grain boundary diffusion for magnetic performance testing. The results of remanence (Br), coercivity (Hcj), and squareness (Hk / Hcj) of the original magnets and the sampled magnets after grain boundary diffusion are shown in Table 4 below.

[0102] Table 4. Magnetic property data of original N55(N) magnets and sampled magnets after grain boundary diffusion.

[0103]

[0104] The test data above show that when the thermal demagnetization temperature is set higher than the parameter range of the present invention, the coercivity of the obtained magnet after grain boundary diffusion is significantly reduced, and the consistency of magnetic properties deteriorates.

[0105] This is because when the thermal demagnetization temperature is higher than the temperature range of the technical solution of this invention, the magnetic moment or surface magnetic field of the magnet diminishes too much, and the surface magnetic intensity of the magnet is less than the strength required for magnetic adsorption of a suitable amount of diffusion source powder. As a result, the adsorbed powder becomes too little or uneven, leading to a poor final diffusion amplification effect.

[0106] Comparative Example 3

[0107] Compared with Example 1, the difference is that the internal temperature of the thermal demagnetizing box is 250°C.

[0108] Ten magnets were randomly selected from 200 magnets after grain boundary diffusion for magnetic performance testing. The results of remanence (Br), coercivity (Hcj), and squareness (Hk / Hcj) of the original magnets and the sampled magnets after grain boundary diffusion are shown in Table 5 below.

[0109] Ten magnets were randomly selected from those that had passed through the thermal demagnetization chamber for surface magnetic distribution testing of their pole faces. The average surface magnetic intensities (absolute values) of the magnet pole faces were: 1875 Gs, 1853 Gs, 1912 Gs, 1897 Gs, 1905 Gs, 1897 Gs, 1882 Gs, 1932 Gs, 1869 Gs, and 1892 Gs, respectively.

[0110] Table 5. Magnetic property data of the original N55(N) magnet and sampled magnets after grain boundary diffusion.

[0111]

[0112] The test data above shows that when the thermal demagnetization temperature is set below the parameter range of the present invention, the remanence of the obtained magnet after grain boundary diffusion is significantly reduced, and the consistency of magnetic properties deteriorates.

[0113] Comparative Example 4

[0114] Compared with Example 1, the difference is that the magnetizing capacitor is 4500μF and the magnetizing voltage is 2800V.

[0115] Ten magnets were randomly selected from those that had passed through the thermal demagnetization chamber for surface magnetic distribution testing of their pole faces. The average surface magnetic intensities (absolute values) of the magnet pole faces were 829 Gs, 795 Gs, 763 Gs, 812 Gs, 805 Gs, 781 Gs, 765 Gs, 746 Gs, 792 Gs, and 813 Gs, respectively.

[0116] Ten magnets were randomly selected from 200 magnets after grain boundary diffusion for magnetic performance testing. The results of remanence (Br), coercivity (Hcj), and squareness (Hk / Hcj) of the original magnets and the sampled magnets after grain boundary diffusion are shown in Table 6 below.

[0117] Table 6. Magnetic property data of original N55(N) magnets and sampled magnets after grain boundary diffusion.

[0118]

[0119] The test data above shows that, compared with the method in Example 1, the magnetization voltage and capacitance of this comparative example are too small, and the magnetic properties of the magnets after magnetic adsorption deposition diffusion are less consistent, which cannot meet the strict batch consistency requirements.

[0120] Comparative Example 5

[0121] Two hundred N55(N) grade magnets, each measuring 25mm × 12mm × 4mm, were sequentially acid-washed and sandblasted. The magnets were then unsaturatedly magnetized using a magnetizer with a 2000μF magnetizing capacitor and a 1000V magnetizing voltage, controlling the magnetization angle to be less than 5 degrees. These magnets were then evenly arranged and fixed in a detachable magnet fixture to form a magnet assembly. Finally, following the method described in Example 1, the assembly was placed in the attachment chamber of a magnetic adsorption deposition apparatus and subjected to diffusion heat treatment to obtain the final target diffusion magnet.

[0122] Ten magnets were randomly selected from those that had passed through the thermal demagnetization chamber for surface magnetic distribution testing of their pole faces. The average surface magnetic intensities (absolute values) of the magnet pole faces were 181 Gs, 172 Gs, 151 Gs, 193 Gs, 169 Gs, 203 Gs, 179 Gs, 186 Gs, 212 Gs, and 166 Gs, respectively.

[0123] Ten magnets were randomly selected from 200 magnets after grain boundary diffusion for magnetic performance testing. The results of remanence (Br), coercivity (Hcj), and squareness (Hk / Hcj) of the original magnets and the sampled magnets after grain boundary diffusion are shown in Table 7 below.

[0124] Table 7. Magnetic performance data of the original N55(N) magnet and the sampled magnet after grain boundary diffusion.

[0125]

[0126] The test data above shows that, compared with the method in Example 1, the magnetization voltage and capacitance of this comparative example are further reduced, resulting in poorer magnetic properties of the magnet after magnetic adsorption deposition diffusion and further reduced batch consistency.

[0127] In summary, the grain boundary diffusion method of NdFeB magnets deposited by magnetic adsorption in this invention can effectively improve magnetic properties; and the use of magnetic adsorption deposition equipment to process the magnets enables mass production of magnets while meeting batch consistency requirements.

[0128] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for grain boundary diffusion of NdFeB magnets deposited by magnetic adsorption, characterized in that, Includes the following steps: (1) After the neodymium iron boron magnet is oversaturated and magnetized, it is detachably fixed on the detachable magnet fixture to obtain the magnet assembly to be attached; Neodymium iron boron magnets are neodymium iron boron magnets with coercivity performance in the N~AH range and above; Oversaturation magnetization, over-magnetization capacitance greater than 4800μF, magnetization voltage greater than 3200V; (2) The magnet assembly to be attached is transferred to the magnetic adsorption deposition equipment, and thermal demagnetization, dust removal and cooling are performed in sequence. The diffusion source powder is attached to the magnet surface by circulating powder to obtain the magnet to be diffused. The thermal demagnetization temperature is 260~300℃, and the time is 10~15min; After thermal demagnetization, the surface magnetic field of the pole face of the neodymium iron boron magnet is 800~1100Gs, and the surface magnetic difference of the pole face of the neodymium iron boron magnet in the same batch is 0~20Gs. The magnetic adsorption deposition equipment includes, in sequence, a thermally demagnetizing box that can be sealed and connected, a dust removal and cooling box, an attachment chamber, and a transition chamber; The oxygen content in the magnetic adsorption deposition equipment is less than 150 ppm; Inside the attachment chamber, several inclined powder-lifting blades are evenly distributed inside the rolling inner cavity of the attachment chamber. The motor unit driving the rolling inner cavity of the attachment chamber rotates the rolling inner cavity of the attachment chamber, which in turn drives the powder-lifting blades inside the attachment chamber to circulate and lift the diffusion source powder. The detachable magnet clamp exhibits a left-right swinging posture, with a maximum bidirectional swing angle difference of 60°. The adsorption loading of the diffusion source powder on the magnet is 1~3 wt% of the mass of the NdFeB magnet after the diffusion source powder is attached; (3) The magnet to be diffused is subjected to diffusion heat treatment to obtain a neodymium iron boron magnet after grain boundary diffusion; The diffusion heat treatment includes a two-stage heat treatment with a vacuum degree ≤10. -2 Pa; The heating rate of the first stage heat treatment is 0.1~5℃ / min, the holding temperature is 880~920℃, and the holding time is 1~12h; after cooling to room temperature, the second stage heat treatment is carried out, the heating rate of the second stage heat treatment is 5~15℃ / min, the holding temperature is 460~520℃, and the holding time is 1~12h.

2. A magnetic adsorption deposition apparatus capable of applying the grain boundary diffusion method for NdFeB magnets deposited by magnetic adsorption deposition as described in claim 1, characterized in that, It includes, in sequence, a heat-demagnetizing box that can be sealed and connected, a dust removal and cooling box, an attachment chamber, and a transition chamber. The neodymium iron boron magnet moves in the magnetic adsorption deposition equipment through a transmission assembly. The transmission assembly includes a detachable magnet clamp assembly, an upper drive motor, a lower drive motor, an upper rotating gear assembly, a lower rotating gear assembly, an upper transmission chain shaft, and a lower transmission chain shaft. Adjusting the output power of the upper and lower drive motors causes the detachable magnetic clamp to swing left and right, with a maximum bidirectional swing angle difference of 60°.

3. The magnetic adsorption deposition apparatus according to claim 2, characterized in that, The upper and lower drive chain shafts are vertically fixed to the upper and lower ends of the detachable magnetic clamp assembly. The upper drive motor rotates the upper rotating gear set, which drives the upper drive chain shaft to move. The lower drive motor rotates the lower rotating gear set, which drives the lower drive chain shaft to move.

4. The magnetic adsorption deposition apparatus according to claim 2, characterized in that, The detachable magnet clamp includes two clamping meshes with a clamping frame edging. The magnet is detachably fixed in the two clamping meshes by fixing bolts. An upper clamping connector is provided at the upper end of the clamping frame. The upper clamping connector is connected to the upper transmission chain shaft through an elastic component of the upper transmission chain shaft. A lower clamping connector is provided at the lower end of the clamping frame. The lower clamping connector is connected to the lower transmission chain shaft through an elastic component of the lower transmission chain shaft.

5. The magnetic adsorption deposition apparatus according to claim 2, characterized in that, The thermal demagnetizing box is connected to a first inert gas source; the dust removal and cooling box is connected to a cooling gas source; and the transition chamber is connected to a second inert gas source. The air pressure in the thermal demagnetization box is 0.05~0.2MPa; the air pressure in the dust removal cooling box is 0.05~0.5MPa; and the air pressure in the transition chamber is 0.05~0.2MPa.

6. The magnetic adsorption deposition apparatus according to claim 2, characterized in that, The dust removal cooling box is connected to a cooling gas source and filled with nitrogen at a pressure of 0.1 MPa. The magnets to be attached stay in the dust removal cooling box for 5 minutes. Then the magnets to be attached are moved to the attachment chamber by the transmission group.

7. The magnetic adsorption deposition apparatus according to claim 2, characterized in that, The attachment chamber includes an outer support box and a rolling inner cavity. The rolling inner cavity has tapered tightening ports with a taper of 10-45° at both ends. Several inclined powder-lifting blades are evenly distributed inside the rolling inner cavity. The top of the outer support box has a closable gate, and the top of the rolling inner cavity has a closable gate. Diffusion source powder enters the rolling inner cavity sequentially through both the closable gates. A motor drives the rolling inner cavity to rotate, causing the powder-lifting blades to circulate and lift the diffusion source powder. The linear velocity of the bottom edge of the powder-lifting blades is 0.1-5.0 m / s.

8. The magnetic adsorption deposition apparatus according to claim 7, characterized in that, The oxygen content in the rolling inner cavity of the attachment chamber and the transition chamber is less than 150 ppm.

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