A high coercive force neodymium iron boron magnet and its preparation method

Abstract

The present invention discloses a high-coercivity NdFeB magnet and its preparation method. The preparation method of the high-coercivity NdFeB magnet comprises: uniformly mixing NdFeB magnetic powder with a micron-sized metal wire having a melting point of less than 1100°C, and then sequentially performing orientation pressing and sintering heat treatment to obtain a sintered blank; subjecting the sintered blank to a tempering heat treatment to obtain an easily diffused substrate with multiple through-hole channels; heating and evaporating the diffusion source metal, and allowing the formed metal gas-phase atoms or molecules to penetrate into the multiple through-hole channels of the easily diffused substrate and deposit inside the easily diffused substrate; subjecting the easily diffused substrate with the diffusion source metal deposited therein to a grain boundary diffusion treatment to obtain a high-coercivity NdFeB magnet. The present invention uses a metal wire and NdFeB metallurgical reaction to form a through-hole structure, so that the gas-phase atoms or molecules of the diffusion source metal penetrate to a greater depth inside the magnet, and the metal wire uses a metal component that is beneficial to optimizing the grain boundary structure, without excessively damaging the magnet performance.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a high-coercivity neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] The widespread development of NdFeB magnets in high-tech industries such as wind power generation, new energy vehicles, energy-saving home appliances, industrial robots, high-speed and maglev trains, etc., has provided important support for the development of the rare earth permanent magnet materials industry and considerable industry growth potential. As the reliability requirements for NdFeB magnet applications continue to increase, magnets are required to possess excellent anti-demagnetization capabilities and high temperature stability. Grain boundary diffusion technology can effectively improve the coercive force of magnets, thereby enhancing the magnet's anti-demagnetization capabilities and service stability. The principle is to attach a diffusion source containing modified elements to the surface of the magnet. After a certain heat treatment process, the diffusion source diffuses into the interior of the magnet along the grain boundary channel, repairing surface defects of the grains or increasing the anisotropy field of the grains, thereby achieving the purpose of improving the coercive force of the magnet. However, since the diffusion behavior obeys Fick's law of diffusion, the driving force for element migration comes from the concentration gradient, and the diffusion substrate lacks effective diffusion channels, resulting in a large number of diffusion sources accumulating on the surface of the magnet during the diffusion process. The depth of grain boundary diffusion modification is very limited, making the diffusion technology only suitable for small-sized or thin magnets, and it is difficult to meet the requirements of large-sized or thicker magnets for grain boundary diffusion modification effects.

[0003] Patent CN109360728B proposes a method for enhancing the coercive force of NdFeB magnets by evaporative grain boundary diffusion. Compared to conventional diffusion source attachment methods (surface coating, electrodeposition, sputtering, etc.), this method utilizes an evaporation process to allow the diffusion source gas-phase atoms to penetrate into the magnet interior, increasing the thickness of the grain boundary diffused magnet from the conventional 4mm to 6mm. However, in this method, the diffusion substrate is a pre-sintered magnet, and a large number of pore channels are non-through-hole structures, making it difficult for the diffusion source components to penetrate deeply into the magnet interior. At the same time, the number of permeable pore channels is very sensitive to the pre-sintering temperature, resulting in a narrow process control window for pre-sintering and diffusion. The subsequent densification process is relatively cumbersome and difficult to operate, making it difficult to further increase the thickness of the diffused magnet and unable to meet the grain boundary diffusion modification requirements of large-sized or thicker magnets exceeding 6mm.

[0004] In summary, the invention of a diffusion treatment method suitable for large-sized or thicker magnets effectively increases the diffusibility of the diffusion substrate, greatly improves the diffusion depth of the modified diffusion source, and significantly enhances the coercive force of large-sized or thicker magnets. It is the only way to meet the service application requirements of large-sized NdFeB magnets in the field of high technology, and has far-reaching significance for promoting the rapid development of the rare earth permanent magnet field. Summary of the Invention

[0005] The main purpose of the present invention is to provide a high coercive force NdFeB magnet and a preparation method thereof, so as to overcome the deficiencies in the prior art.

[0006] To achieve the aforementioned object of the invention, the technical solutions adopted in the embodiments of the present invention include:

[0007] The present invention provides a method for preparing a high coercive force neodymium iron boron magnet, comprising:

[0008] The NdFeB magnetic powder is uniformly mixed with a micron-sized metal wire having a melting point of less than 1100°C, and then subjected to orientation pressing and sintering heat treatment in sequence to obtain a sintered blank;

[0009] The sintered compact is subjected to a tempering heat treatment to obtain an easily diffusible substrate having multiple through-hole channels, wherein the through-hole channels of the easily diffusible substrate penetrate the easily diffusible substrate in a thickness direction;

[0010] heating and evaporating the diffusion source metal, and allowing the formed metal gas-phase atoms or molecules to penetrate into the multi-through-hole channels of the easy-diffusion substrate and be deposited inside the easy-diffusion substrate;

[0011] A high coercive force NdFeB magnet is obtained by performing grain boundary diffusion treatment on an easily diffusible substrate with a diffusion source metal deposited inside.

[0012] Furthermore, the mass ratio of the NdFeB magnetic powder to the micron-sized metal wire is 95-99.5:5-0.5, wherein the particle size of the NdFeB magnetic powder is 2-5 μm.

[0013] Furthermore, the diameter of the micron-sized metal wire is 5 to 70 microns, and the length is 0.5 to 3 times the thickness of the easily diffusible substrate; and the material of the micron-sized metal wire includes any one or more of Cu, Al or Ag;

[0014] Furthermore, the specific process of the orientation pressing is: the magnetic field used is between 1.8 and 2.0 T, and the pressing pressure is between 15 and 25 MPa.

[0015] Furthermore, the specific process of the sintering heat treatment is: heating to 750℃~900℃ and keeping it for 0.5~2 hours, then heating to 1000℃~1100℃ and keeping it for 4~8 hours, and finally cooling rapidly to room temperature, and the vacuum degree during this process is less than 9×10 -3 Pa.

[0016] Furthermore, the tempering heat treatment specifically includes: keeping the sintered blank at 900°C to 1000°C for 0.5 to 2 hours, then keeping it at 750°C to 850°C for 0.5 to 2 hours, and finally keeping it at 450°C to 650°C for 0.5 to 2 hours, and the vacuum degree during this process is less than 9×10 -3 Pa.

[0017] Furthermore, the specific process of the evaporation treatment is as follows: placing the diffusion source metal into the tungsten boat of the vacuum chamber of the vacuum coating machine, placing the easily diffusible substrate on the sample stage of the vacuum coating machine, and evacuating the vacuum to a vacuum degree of less than 3×10 -3 Pa, turn on the tungsten boat heating power supply, adjust the output current to 170A to 200A, control the deposition time to 0.5 to 10h, and then introduce argon gas to induce the metal gas phase atoms or molecules to enter the multi-channel through holes of the easily diffusible substrate and deposit.

[0018] Furthermore, the chemical formula of the diffusion source metal is RE a M b , wherein RE includes at least one of the rare earth elements Pr, Nd, Dy, Tb, Ho, Gd, La, Ce, and Y, M includes at least one of Cu, Al, Ga, Co, Fe, Ni, Zn, and Ti, a and b are mass percentages, satisfying 60≤a≤100, and a+b=100.

[0019] Furthermore, the grain boundary diffusion treatment specifically includes: placing the easily diffused substrate after evaporation deposition treatment under a vacuum degree of less than 8×10 -3 Pa conditions, keep warm at 900℃~950℃ for 4~10 hours, then keep warm at 450~550℃ for 2~8 hours.

[0020] The present invention also provides a high-coercivity NdFeB magnet, which is prepared by the above method.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention utilizes the rare earth components between the NdFeB crystals in the liquid phase sintering process to undergo a metallurgical reaction with the introduced metal wire, and can extract the metal at the wire position through reactive diffusion and form a porous channel with a through-hole structure. Further application of evaporation deposition technology can allow the gaseous atoms or molecules of the diffusion source metal to penetrate into the magnet to a greater depth through the through-hole channel. Subsequently, grain boundary diffusion treatment can be performed to effectively increase the diffusion depth, greatly improve the coercive force, and especially significantly enhance the grain boundary diffusion modification effect of large-sized or thicker magnets. In addition, the large-sized diffused magnet products prepared by the present invention have good performance consistency, the process flow is easy to control, and are suitable for mass production.

[0023] (2) The metal wire with a diameter of micron-level in the present invention uses metal components such as Cu and Al that are beneficial to optimizing the grain boundary structure. Its introduction will not excessively damage the performance of the magnet. In addition, the production and preparation technology of micron-level wires such as Cu and Al on the market is quite mature. The cost of preparing the easily diffusible substrate using the present invention is relatively low, which is conducive to industrial development. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a schematic diagram of the preparation process of the high coercivity NdFeB magnet in Example 1 of the present application.

[0026] Figure 2 This is a schematic diagram of the preparation process of the high coercivity NdFeB magnet in Comparative Example 1 of the present application.

[0027] Figure 3 This is a microscopic morphology of the easily diffusible substrate in one embodiment of the present application ((a) surface area; (b) fracture morphology; (c) observation magnification of the area near the through-hole channel).

[0028] Figure 4 This is the microstructure and composition distribution near the through-hole channel inside the magnet after grain boundary diffusion treatment. DETAILED DESCRIPTION

[0029] In order to overcome the problem that the existing NdFeB magnet grain boundary diffusion technology lacks effective diffusion channels in the diffusion substrate, a large number of diffusion sources accumulate on the surface of the magnet during the diffusion process, and the depth of grain boundary diffusion modification is very limited, making it difficult to meet the demand for grain boundary diffusion modification effects for large-sized or thicker magnets, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice. The present invention mainly provides a high-coercivity NdFeB magnet and its preparation method. During the magnetic powder sintering process, a low-melting-point micron-sized metal wire is introduced, and the metallurgical properties of rare earth and metal elements are used to extract the metal components at the wire position, thereby constructing an easy-diffusion substrate with multiple through-hole channels. Subsequently, the diffusion source is infiltrated into the interior of the magnet through the multiple through-hole channels in the form of gas-phase free atoms or molecules, and further grain boundary diffusion treatment is performed, so that the diffusion sources on the surface and inside of the magnet diffuse to the surrounding area at the same time, comprehensively improving the grain boundary structure of the magnet surface and deep inside, and achieving the purpose of significantly improving the coercivity of the magnet. The following will further explain the technical solution, its implementation process and principles.

[0030] One aspect of an embodiment of the present invention provides a method for preparing a high coercivity NdFeB magnet, comprising:

[0031] The NdFeB magnetic powder is uniformly mixed with a micron-sized metal wire having a melting point of less than 1100°C, and then subjected to orientation pressing and sintering heat treatment in sequence to obtain a sintered blank;

[0032] The sintered compact is subjected to a tempering heat treatment to obtain an easily diffusible substrate having multiple through-hole channels, wherein the through-hole channels of the easily diffusible substrate penetrate the easily diffusible substrate in a thickness direction;

[0033] heating and evaporating the diffusion source metal, and allowing the formed metal gas-phase atoms or molecules to penetrate into the multi-through-hole channels of the easy-diffusion substrate and be deposited inside the easy-diffusion substrate;

[0034] A high coercive force NdFeB magnet is obtained by performing grain boundary diffusion treatment on an easily diffusible substrate with a diffusion source metal deposited inside.

[0035] In some embodiments, the mass ratio of the NdFeB magnetic powder to the micron-sized metal wire is 95-99.5:5-0.5, wherein the particle size of the NdFeB magnetic powder is 2-5 μm.

[0036] In some embodiments, the diameter of the micron-sized metal wire is 5 to 70 microns, and the length is 0.5 to 3 times the thickness of the easily diffusible substrate; and the composition of the low-melting-point micron-sized metal wire can include any one or more of Cu, Al, Ag, etc., but is not limited thereto.

[0037] In some embodiments, the specific process of the orientation pressing is: the magnetic field used is between 1.8 and 2.0 T, and the pressing pressure is between 15 and 25 MPa.

[0038] In some preferred embodiments, the specific process of the sintering heat treatment is: heating to 750℃~900℃ and keeping it for 0.5~2 hours, then heating to 1000℃~1100℃ and keeping it for 4~8 hours, and finally cooling rapidly to room temperature, and the vacuum degree during this process is less than 9×10 -3 Pa.

[0039] In some embodiments, the tempering heat treatment specifically includes: keeping the sintered blank at 900°C to 1000°C for 0.5 to 2 hours, then keeping it at 750°C to 850°C for 0.5 to 2 hours, and finally keeping it at 450°C to 650°C for 0.5 to 2 hours, and the vacuum degree during this process is less than 9×10 -3 Pa.

[0040] In some embodiments, the method for preparing the high coercivity NdFeB magnet further includes: cleaning the surface of the sintered blank after the tempering heat treatment.

[0041] In some more preferred embodiments, the surface cleaning may include alcohol ultrasonic cleaning and pressure air gun washing.

[0042] In some embodiments, the thickness of the easily diffusible substrate along the diffusion direction is 3 mm to 12 mm.

[0043] In some embodiments, the specific process of the evaporation treatment is as follows: placing the diffusion source metal into the tungsten boat of the vacuum chamber of the vacuum coating machine, placing the easily diffusible substrate on the sample stage of the vacuum coating machine, and evacuating the vacuum to a vacuum degree of less than 3×10 -3 Pa, turn on the tungsten boat heating power supply, adjust the output current to 170A to 200A, control the deposition time to 0.5 to 10h, and then introduce argon gas to induce the metal gas phase atoms or molecules to enter the multi-channel through holes of the easily diffusible substrate and deposit.

[0044] In some embodiments, the chemical formula of the diffusion source metal is RE a M b , wherein RE includes at least one of the rare earth elements Pr, Nd, Dy, Tb, Ho, Gd, La, Ce, and Y, M includes at least one of Cu, Al, Ga, Co, Fe, Ni, Zn, and Ti, a and b are mass percentages, satisfying 60≤a≤100, and a+b=100.

[0045] In some embodiments, the grain boundary diffusion treatment specifically includes: placing the easily diffusible substrate after evaporation deposition treatment under a vacuum degree of less than 8×10 -3 Pa conditions, keep warm at 900℃~950℃ for 4~10 hours, then keep warm at 450~550℃ for 2~8 hours.

[0046] Another aspect of the embodiments of the present invention further provides a high coercive force NdFeB magnet, which is prepared by the above method.

[0047] The technical solution of the present invention is further explained and illustrated below in conjunction with specific embodiments and illustrative drawings to facilitate a full understanding of the present invention by those skilled in the art. However, this explanation and illustration does not further limit the technical solution of the present invention. The improved technical solution of simple numerical replacement and conventional adjustment made on the basis of the present invention falls within the scope of protection of the present invention.

[0048] Example 1

[0049] This embodiment provides a method for preparing a high coercive force NdFeB magnet. Figure 1 As shown, the following steps are included:

[0050] (1) In the case of nominal composition (PrNd) 29.5 (Zr, Co, Cu, Ga, Al) 1.1 B 0.98 Fe balA copper wire with a diameter of 30 μm was added to the NdFeB powder (wt.%), with the copper wire accounting for 1.5% of the total mass. After being mixed evenly, the mixture was subjected to orientation pressing in a magnetic field of 1.8 T and a pressure of 20 MPa. The mixture was then placed in a heat treatment furnace and heated to a vacuum of 5×10 -3 Pa, the temperature was raised to 800°C, kept at this temperature for 1 hour, then raised to 1080°C, kept at this temperature for another 6 hours, and then rapidly cooled to room temperature to obtain a pre-sintered green body;

[0051] (2) The pre-sintered green body was kept at 900°C for 2 hours, cooled to room temperature, kept at 750°C for 2 hours, cooled to room temperature, and kept at 500°C for 2 hours; machined to a thickness direction (diffusion direction) of 6.5 mm, and cleaned with 360W alcohol ultrasonic wave for 15 minutes, and then flushed with a pressure air gun to obtain an easily diffusible substrate, numbered 1#;

[0052] (3) Diffusion source metal Tb 80 Cu 10 Al 10 The tungsten boat (wt%) was placed in the vacuum chamber of the vacuum coating machine, and the easily diffusible substrate was placed on the sample stage of the vacuum coating machine, and the vacuum was evacuated to a vacuum degree of 2×10 -3 Pa, turn on the tungsten boat heating power supply, adjust the output current to 180A, set the deposition time to 4h, and then introduce argon gas for cooling to complete the evaporation; (4) After the evaporation, the sample was kept at 900℃ in a vacuum sintering furnace for 8 hours, cooled to room temperature under argon atmosphere, and then kept at 500℃ for 2 hours to obtain a diffused magnet. The vacuum degree was 6×10 -4 Pa, numbered 2#;

[0053] (5) The magnetic properties of 1# and 2# NdFeB magnets were measured using a pulsed magnetometer (PFM), as shown in Table 1.

[0054] Table 1 Comparison of magnetic properties of samples 1# and 2#

[0055]

[0056]

[0057] The microscopic morphology of the easily diffusible substrate 1# sample in this embodiment is as follows Figure 3 As shown in the figure, it can be seen that there are evenly distributed through holes in the easy-diffusion substrate, which can meet the needs of gas molecules to enter and deposit. The microstructure and composition distribution near the internal through hole channel of the magnet sample 2# after grain boundary diffusion treatment in this embodiment are shown in FIG. Figure 4 As shown, it can be seen that Tb atoms are deposited near the through-hole channel and grain boundary diffusion occurs, and the Tb element concentration is distributed in a gradient divergent manner.

[0058] Comparative Example 1

[0059] This comparative example provides a method for preparing a neodymium iron boron magnet. Figure 2 As shown, the following steps are included:

[0060] (1) The nominal composition is (PrNd) 29.5 (Zr, Co, Cu, Ga, Al) 1.1 B 0.98 Fe bal (wt.%) NdFeB powder is oriented and pre-fired in vacuum to form a pre-sintered green body, wherein the operation and process conditions of the oriented green body and vacuum pre-fired are the same as those in Example 1;

[0061] (2) The pre-sintered green body was kept at 900°C for 2 hours, cooled to room temperature, kept at 750°C for 2 hours, cooled to room temperature, and kept at 500°C for 2 hours; machined to a thickness direction (diffusion direction) of 6.5 mm, and cleaned with 360W alcohol ultrasonic wave for 15 minutes, and then flushed with a pressure air gun to obtain a diffusion matrix, numbered 3#;

[0062] (3) Diffusion source metal Tb 80 Cu 10 Al 10 The tungsten boat (wt%) was placed in the vacuum chamber of the vacuum coating machine, and the easily diffusible substrate was placed on the sample stage of the vacuum coating machine, and the vacuum was evacuated to a vacuum degree of 2×10 -3 Pa, turn on the tungsten boat heating power supply, adjust the output current to 180A, set the deposition time to 4h, and then introduce argon gas for cooling to complete the evaporation.

[0063] (4) After the evaporation, the sample was kept at 900 °C in a vacuum sintering furnace for 8 hours, cooled to room temperature under an argon atmosphere, and then kept at 500 °C for 2 hours to obtain a diffused magnet. The vacuum degree was 6×10 -4 Pa, numbered 4#;

[0064] (5) The magnetic properties of 3# and 4# NdFeB magnets were measured using a pulsed magnetometer (PFM), as shown in Table 2.

[0065] Table 2 Comparison of magnetic properties of samples 3# and 4#

[0066]

[0067] It can be seen from the results in Table 1 and Table 2 that the magnet obtained by adopting the technical solution of the present invention has higher diffusion coercivity increase and final coercivity performance.

[0068] Example 2

[0069] (1) In the case of nominal composition (PrNd) 29.5 (Zr, Co, Cu, Ga, Al) 1.1B 0.98 Fe bal A copper wire with a diameter of 30 μm was added to the NdFeB powder (wt.%), with the copper wire accounting for 0.8% of the total mass. After being mixed evenly, the mixture was subjected to orientation pressing in a magnetic field of 2.0 T and a pressure of 25 MPa. The mixture was then placed in a heat treatment furnace and heated to a vacuum of 3×10 -3 Pa, the temperature was raised to 850 ° C, kept at this temperature for 0.5 hours, then raised to 1090 ° C, kept at this temperature for another 4 hours, and then quickly cooled to room temperature to obtain a pre-sintered green body;

[0070] (2) The pre-sintered green body was kept at 900°C for 2 hours, cooled to room temperature, kept at 750°C for 2 hours, cooled to room temperature, and kept at 500°C for 2 hours; machined to a thickness direction (diffusion direction) of 7 mm, and cleaned with 360W alcohol ultrasonic wave for 15 minutes, and then flushed with a pressure air gun to obtain an easily diffusible substrate, numbered 5#;

[0071] (3) Diffusion source metal Tb 70 Cu 30 (wt%) was placed in a tungsten boat in the vacuum chamber of a vacuum coating machine, and the easily diffusible substrate was placed on the sample stage of the vacuum coating machine and evacuated to a vacuum degree of 9×10 -4 Pa, turn on the tungsten boat heating power supply, adjust the output current to 200A, set the deposition time to 6h, and then introduce argon gas for cooling to complete the evaporation.

[0072] (4) After the evaporation, the sample was kept at 900 °C in a vacuum sintering furnace for 8 hours, cooled to room temperature under an argon atmosphere, and then kept at 500 °C for 2 hours to obtain a diffused magnet. The vacuum degree was 6×10 -4 Pa, numbered 6#;

[0073] (5) The magnetic properties of 5# and 6# NdFeB magnets were measured using a pulsed magnetometer (PFM), as shown in Table 3.

[0074] Table 3 Comparison of magnetic properties of samples 5# and 6#

[0075]

[0076] Comparative Example 2

[0077] (1) The nominal composition is (PrNd) 29.5 (Zr, Co, Cu, Ga, Al) 1.1 B 0.98 Fe bal (wt.%) NdFeB powder is oriented and pre-fired in vacuum to form a pre-sintered green body, wherein the operation and process conditions of the oriented green body and vacuum pre-fired are the same as those in Example 2;

[0078] (2) The pre-sintered green body was kept at 900°C for 2 hours, cooled to room temperature, kept at 750°C for 2 hours, cooled to room temperature, and kept at 500°C for 2 hours; machined to a thickness direction (diffusion direction) of 7 mm, and cleaned with 360W alcohol ultrasonic wave for 15 minutes, and then flushed with a pressure air gun to obtain a diffusion matrix, numbered 7#;

[0079] (3) Diffusion source metal Tb 70 Cu 30 (wt%) was placed in a tungsten boat in the vacuum chamber of a vacuum coating machine, and the easily diffusible substrate was placed on the sample stage of the vacuum coating machine and evacuated to a vacuum degree of 9×10 -4 Pa, turn on the tungsten boat heating power supply, adjust the output current to 200A, set the deposition time to 6h, and then pass argon gas for cooling to complete the evaporation;

[0080] (4) After the evaporation, the sample was kept at 900 °C in a vacuum sintering furnace for 8 hours, cooled to room temperature under an argon atmosphere, and then kept at 500 °C for 2 hours to obtain a diffused magnet. The vacuum degree was 6×10 -4 Pa, numbered 8#;

[0081] (5) The magnetic properties of 7# and 8# NdFeB magnets were measured using a pulsed magnetometer (PFM), as shown in Table 4.

[0082] Table 4 Comparison of magnetic properties of samples 7# and 8#

[0083]

[0084] It can be seen from the results in Table 3 and Table 4 that the magnet obtained by adopting the technical solution of the present invention has a higher diffusion coercive force increase and final coercive force performance.

[0085] Example 3

[0086] (1) The nominal composition is (PrNd) 23.5 Ce7Fe bal (Zr, Co, Cu, Gd, Ga, Al) 2.4 B 0.92 Metal copper wire with a diameter of 20 μm was added to the iron-boron powder (wt.%), and the copper wire accounted for 2.5% of the total mass. After being mixed evenly, the oriented pressing was completed under a magnetic field of 1.8 T and a pressure of 15 MPa. Then, the oriented pressing was carried out in a heat treatment furnace and the vacuum degree was 3×10 -3 Pa, heating to 900 ° C, keeping it warm for 1 hour, then heating to 1100 ° C, keeping it warm for another 8 hours, and then rapidly cooling to room temperature to obtain a pre-sintered green body;

[0087] (2) The pre-sintered green body was kept at 900°C for 1.5 hours, cooled to room temperature, kept at 750°C for 1.5 hours, cooled to room temperature, and kept at 550°C for 1.5 hours; machined to a thickness direction (diffusion direction) of 6.5 mm, and cleaned with alcohol ultrasonic cleaning at a power of 360 W for 15 minutes, and then flushed with a pressure air gun to obtain an easily diffusible substrate, numbered 9#;

[0088] (3) Diffusion source metal Tb 80 Al 20 (wt%) was placed in a tungsten boat in the vacuum chamber of a vacuum coating machine, and the easily diffusible substrate was placed on the sample stage of the vacuum coating machine and evacuated to a vacuum degree of 9×10 -4 Pa, turn on the tungsten boat heating power supply, adjust the output current to 190A, set the deposition time to 8h, and then pass argon gas for cooling to complete the evaporation;

[0089] (4) After the evaporation, the sample was kept at 900 °C in a vacuum sintering furnace for 10 hours, cooled to room temperature under an argon atmosphere, and then kept at 500 °C for 2 hours to obtain a diffused magnet. The vacuum degree was 5×10 -4 Pa, numbered 10#;

[0090] (5) The magnetic properties of 9# and 10# NdFeB magnets were measured using a pulsed magnetometer (PFM), as shown in Table 5.

[0091] Table 5 Comparison of magnetic properties of samples 9# and 10#

[0092]

[0093] Comparative Example 3

[0094] (1) The nominal composition is (PrNd) 23.5 Ce7 (Zr, Co, Cu, Gd, Ga, Al) 2.4 B0. 92 Fe bal (wt.%) NdFeB powder is oriented and pre-fired in vacuum to form a pre-sintered green body, wherein the operation and process conditions of the oriented green body and vacuum pre-fired are the same as those in Example 3;

[0095] (2) The pre-sintered green body was kept at 900°C for 1.5 hours, cooled to room temperature, kept at 750°C for 1.5 hours, cooled to room temperature, and kept at 550°C for 1.5 hours; machined to a thickness direction (diffusion direction) of 6.5 mm, and cleaned with alcohol ultrasonic cleaning at a power of 360 W for 15 minutes, and then flushed with a pressure air gun to obtain a diffusion matrix, numbered 11#;

[0096] (3) Diffusion source metal Tb 80 Al 20(wt%) was placed in a tungsten boat in the vacuum chamber of a vacuum coating machine, and the easily diffusible substrate was placed on the sample stage of the vacuum coating machine and evacuated to a vacuum degree of 9×10 -4 Pa, turn on the tungsten boat heating power supply, adjust the output current to 190A, set the deposition time to 8h, and then introduce argon gas for cooling to complete the evaporation.

[0097] (4) After the evaporation, the sample was kept at 900 °C in a vacuum sintering furnace for 10 hours, cooled to room temperature under an argon atmosphere, and then kept at 500 °C for 2 hours to obtain a diffused magnet. The vacuum degree was 5×10 -4 Pa, numbered 12#;

[0098] (5) The magnetic properties of 11# and 12# NdFeB magnets were measured using a pulsed magnetometer (PFM), as shown in Table 6.

[0099] Table 6 Comparison of magnetic properties of samples 11# and 12#

[0100]

[0101] It can be seen from the results in Table 5 and Table 6 that the magnet obtained by adopting the technical solution of the present invention has a higher diffusion coercive force increase and final coercive force performance.

[0102] Example 4

[0103] (1) The nominal composition is (PrNd) 23.5 Ce7Fe bal (Zr, Co, Cu, Gd, Ga, Al) 2.4 B 0.92 A copper wire with a diameter of 70 μm was added to the iron-boron powder (wt.%), and the copper wire accounted for 0.5% of the total mass. After being mixed evenly, the oriented pressing was completed under a magnetic field of 2.0 T and a pressure of 25 MPa. The oriented pressing was then placed in a heat treatment furnace and the vacuum degree was 3×10- 3 Pa, the temperature was raised to 900 ° C, kept at this temperature for 1 hour, then raised to 1090 ° C, kept at this temperature for another 8 hours, and then quickly cooled to room temperature to obtain a pre-sintered green body;

[0104] (2) The pre-sintered green body was kept at 1000°C for 0.5 hours, cooled to room temperature, kept at 850°C for 0.5 hours, cooled to room temperature, and kept at 450°C for 2 hours; machined to a thickness direction (diffusion direction) of 12 mm, and cleaned with alcohol ultrasonic wave at a power of 360 W for 15 minutes, and then flushed with a pressure air gun to obtain an easily diffusible substrate, numbered 13#;

[0105] (3) Diffusion source metal Tb 80 Al 20(wt%) was placed in a tungsten boat in the vacuum chamber of a vacuum coating machine, and the easily diffusible substrate was placed on the sample stage of the vacuum coating machine and evacuated to a vacuum degree of 9×10 -4 Pa, turn on the tungsten boat heating power supply, adjust the output current to 190A, set the deposition time to 8h, and then introduce argon gas for cooling to complete the evaporation.

[0106] (4) After the evaporation, the sample was kept at 900 °C in a vacuum sintering furnace for 10 hours, cooled to room temperature under an argon atmosphere, and then kept at 500 °C for 2 hours to obtain a diffused magnet. The vacuum degree was 5×10 -4 Pa, numbered 14#;

[0107] (5) The magnetic properties of 13# and 14# NdFeB magnets were measured using a pulsed magnetometer (PFM), as shown in Table 7.

[0108] Table 7 Comparison of magnetic properties of samples 13# and 14#

[0109]

[0110] Example 5

[0111] (1) The nominal composition is (PrNd) 23.5 Ce7Fe bal (Zr, Co, Cu, Gd, Ga, Al) 2.4 B 0.92 Metal copper wire with a diameter of 5 μm was added to the iron-boron powder (wt.%), and the copper wire accounted for 1% of the total mass. After mixing evenly, the oriented pressing was completed under a magnetic field of 1.9 T and a pressure of 22 MPa. Then, the oriented pressing was carried out in a heat treatment furnace and the vacuum degree was 3×10 -3 Pa, the temperature was raised to 900 ° C, kept at this temperature for 1 hour, then raised to 1090 ° C, kept at this temperature for another 8 hours, and then quickly cooled to room temperature to obtain a pre-sintered green body;

[0112] (2) The pre-sintered green body was kept at 950°C for 1 hour, cooled to room temperature, kept at 800°C for 1 hour, cooled to room temperature, and kept at 500°C for 1 hour; machined to a thickness direction (diffusion direction) of 3 mm, and cleaned with 360W alcohol ultrasonic wave for 15 minutes, and then flushed with pressure air gun to obtain a diffusion-friendly substrate, numbered 15#;

[0113] (3) Diffusion source metal Tb 80 Al 20 (wt%) was placed in a tungsten boat in the vacuum chamber of a vacuum coating machine, and the easily diffusible substrate was placed on the sample stage of the vacuum coating machine and evacuated to a vacuum degree of 9×10 -4 Pa, turn on the tungsten boat heating power supply, adjust the output current to 190A, set the deposition time to 8h, and then introduce argon gas for cooling to complete the evaporation.

[0114] (4) After the evaporation, the sample was kept at 900 °C in a vacuum sintering furnace for 10 hours, cooled to room temperature under an argon atmosphere, and then kept at 500 °C for 2 hours to obtain a diffused magnet. The vacuum degree was 5×10 -4 Pa, numbered 16#;

[0115] (5) The magnetic properties of 13# and 14# NdFeB magnets were measured using a pulsed magnetometer (PFM), as shown in Table 8.

[0116] Table 8 Comparison of magnetic properties of samples 15# and 16#

[0117]

[0118] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0119] Although the present invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions, and / or additions may be made and that substantial equivalents may be substituted for the elements of the embodiments without departing from the spirit and scope of the present invention. Additionally, many modifications may be made to adapt specific circumstances or materials to the teachings of the present invention without departing from the scope of the present invention. Therefore, it is not intended herein to limit the present invention to the disclosed specific embodiments for carrying out the present invention, but rather to include all embodiments within the scope of the appended claims. Furthermore, unless specifically stated, any use of the terms first, second, etc. does not indicate any order or importance, but rather uses the terms first, second, etc. to distinguish one element from another.

Claims

1. A method for preparing a high coercive force neodymium iron boron magnet, characterized in that: include: The NdFeB magnetic powder is uniformly mixed with a micron-sized metal wire having a melting point of less than 1100°C, and then subjected to orientation pressing and sintering heat treatment in sequence to obtain a sintered blank; The sintered compact is subjected to a tempering heat treatment to obtain a diffusion-prone substrate having multiple through-hole channels; Performing an evaporation treatment on the easily diffusible substrate, heating and evaporating the diffusion source metal, and allowing the formed metal gas-phase atoms or molecules to penetrate into the multi-through-hole channels of the easily diffusible substrate and be deposited inside the easily diffusible substrate; A high coercive force NdFeB magnet is obtained by performing grain boundary diffusion treatment on a diffusion-prone substrate with a diffusion source metal deposited inside. The mass ratio of the NdFeB magnetic powder to the micron-sized metal wire is 95-99.5:5-0.5, the particle size of the NdFeB magnetic powder is 2-5 μm, the diameter of the micron-sized metal wire is 5-70 μm, and the length is 0.5 to 3 times the thickness of the easily diffusible substrate, and the material of the micron-sized metal wire includes any one or more of Cu, Al or Ag.

2. The method for preparing a high coercive force NdFeB magnet according to claim 1, wherein: The specific process of the orientation pressing is as follows: the magnetic field used is between 1.8 and 2.0 T, and the pressing pressure is between 15 and 25 MPa.

3. The method for preparing a high coercive force NdFeB magnet according to claim 1, wherein: The specific process of sintering heat treatment is: heating to 750℃~900℃ and keeping it for 0.5~2 hours, then heating to 1000℃~1100℃ and keeping it for 4~8 hours, and finally cooling quickly to room temperature. The vacuum degree during sintering heat treatment is less than 9×10 -3 Pa.

4. The method for preparing a high coercive force NdFeB magnet according to claim 1, wherein: The tempering heat treatment specifically includes: keeping the sintered blank at 900℃~1000℃ for 0.5~2 hours, then keeping it at 750℃~850℃ for 0.5~2 hours, and finally keeping it at 450℃~650℃ for 0.5~2 hours, and the vacuum degree during the tempering heat treatment is less than 9×10 -3 Pa.

5. The method for preparing a high coercive force NdFeB magnet according to claim 1 or 4, characterized in that: Also includes: The surface of the sintered blank after the tempering heat treatment is cleaned, and the surface cleaning includes alcohol ultrasonic cleaning and pressure air gun flushing.

6. The method for preparing a high coercive force NdFeB magnet according to claim 5, wherein: The thickness of the easily diffusible substrate along the diffusion direction is 3 mm to 12 mm.

7. The method for preparing a high coercive force NdFeB magnet according to claim 1, wherein: The specific process of the evaporation treatment is as follows: the diffusion source metal is placed in the tungsten boat of the vacuum chamber of the vacuum coating machine, the diffusion-prone substrate is placed on the sample stage of the vacuum coating machine, and the vacuum is evacuated to a vacuum degree of less than 3×10 -3 Pa, turn on the tungsten boat heating power supply, adjust the output current to 170A to 200A, control the deposition time to 0.5~10h, and then introduce argon gas to induce the metal gas phase atoms or molecules to enter the multi-channel through holes of the easily diffusible substrate and deposit.

8. The method for preparing a high coercive force NdFeB magnet according to claim 1, wherein: The chemical formula of the diffusion source metal is RE a M b , wherein RE includes at least one of the rare earth elements Pr, Nd, Dy, Tb, Ho, Gd, La, Ce, and Y, M includes at least one of Cu, Al, Ga, Co, Fe, Ni, Zn, and Ti, a and b are mass percentages, satisfying 60≤a≤100, and a+b=100.

9. The method for preparing a high coercive force NdFeB magnet according to claim 1, wherein: The grain boundary diffusion treatment specifically includes: placing the easily diffused substrate after evaporation deposition treatment under a vacuum degree of less than 8×10 -3 Pa conditions, keep at 900℃~950℃ for 4~10 hours, then keep at 450~550℃ for 2~8 hours.

10. A high coercive force neodymium iron boron magnet, characterized in that: The high coercive force NdFeB magnet is prepared by the method according to any one of claims 1 to 9.

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