Neodymium-iron-boron magnet and preparation method for improving orientation degree of sintered neodymium-iron-boron magnet

Abstract

The invention belongs to the technical field of rare earth permanent magnet material preparation, and provides a neodymium-iron-boron magnet and a preparation method for improving the orientation degree of the sintered neodymium-iron-boron magnet, and the preparation method comprises the step of sintering a neodymium-iron-boron green body in a magnetic field. Preferably, the magnetic field is a direct-current magnetic field, and the magnetic induction intensity of the direct-current magnetic field is 10-13T. The high-intensity magnetic field can magnetize magnet powder particles in the sintering process, so that a magnetic chain is formed among the powder particles, the binding force among the particles is improved, and the powder particles cannot rotate due to the generation of a liquid phase. The neodymium-iron-boron powder particles are arranged according to the magnetic field direction in the sintering process, so that the high orientation degree of the magnet is ensured, and the high-performance neodymium-iron-boron magnet is obtained.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet material preparation technology, specifically, it relates to a neodymium iron boron magnet and a method for improving the orientation degree of sintered neodymium iron boron magnets. Background Technology

[0002] The C-axis (easy magnetization axis) orientation of NdFeB magnets is one of the important parameters affecting their magnetic properties; the higher the degree of orientation, the better the magnetic properties. In the preparation of sintered NdFeB magnets, C-axis orientation is usually achieved through magnetic field orientation. The degree of magnet orientation is affected by both the pressing orientation and sintering processes, and many factors influence these processes. During the pressing orientation process, the magnet is oriented using an orientation magnetic field. However, van der Waals forces, positive friction, rolling friction, static repulsion, and external magnetic field forces exist simultaneously between the powder particles, making complete orientation difficult to achieve. When the mold applies pressure to the magnet powder, relative movement occurs between the mold and the powder, causing the originally perfectly oriented powder to deflect and shift. During sintering, the NdFeB-rich phase melts to produce a liquid phase, which flows into the pores, causing the powder particles to move. Factors such as increasing temperature, grain growth, and gradual densification of the blank can all disrupt the magnet's orientation, thus affecting its performance.

[0003] Existing technologies, such as Chinese patent publication number "CN 115050564 A", disclose a high-orientation neodymium iron boron magnet and its preparation method. This patent mixes neodymium iron boron powder with acrylic emulsion to obtain a magnetic powder slurry, which is then oriented in a magnetic field. The green body after the first orientation is then immersed in a low-pressure bath and oriented a second time to obtain a high-orientation neodymium iron boron magnet. Because other materials are added during the molding orientation process and need to be removed, the subsequent processes are more complicated.

[0004] For example, Chinese patent publication number "CN 115621028 A" discloses a highly oriented sintered NdFeB magnet and its preparation method. This technical solution specifically discloses placing NdFeB powder in a mold equipped with an ultrasonic transducer for orientation, placing the mold in an alternating magnetic field for pre-orientation, and then adjusting the magnetic field to a constant magnetic field for final orientation. Ultrasonic vibration is used during the orientation process to increase the displacement of the magnetic powder, ensuring that the magnetic powder particles do not interfere with each other, thus obtaining a highly oriented NdFeB magnet. This invention avoids the shortcomings of incomplete magnet orientation caused by additives in traditional processes, resulting in good stability after orientation. However, this invention requires secondary orientation and introduces ultrasonic vibration to assist in orientation, increasing the complexity of the equipment and process.

[0005] For example, Chinese patent publication number "CN 114823114 A" discloses a method for preparing high-performance NdFeB magnets with improved orientation. Specifically, it discloses annealing the sintered NdFeB magnet blank in a magnetic field environment. During annealing, a DC magnetic field is introduced, and fluid flow generates an induced current. Charged particles in the magnetic field are subjected to Lorentz force and orient themselves according to the magnetic field, further improving the magnet's orientation. The magnetic field affects the magnetic domain structure and magnetic properties of the material during annealing, and can be used as a post-processing method for sintered magnetic materials. However, during the annealing stage, the NdFeB sintered body has already undergone densification, the grains have grown and are difficult to rotate, and the annealing temperature is higher than the Curie temperature of the magnet. At this point, the magnet changes from ferromagnetism to paramagnetism, making it difficult for the magnetic field to restrict the magnet's orientation. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a neodymium iron boron magnet and a method for preparing sintered neodymium iron boron magnets with improved orientation, so as to solve the problems of insufficient orientation and complex preparation process in the prior art and improve the orientation of neodymium iron boron magnets.

[0007] To address the aforementioned technical problems, this invention provides a method for improving the orientation of sintered NdFeB magnets, the method comprising: sintering a NdFeB green blank in a magnetic field.

[0008] Furthermore, the magnetic field is a DC magnetic field, and the magnetic induction intensity of the DC magnetic field is 10⁻¹³ T.

[0009] Furthermore, the sintering step of the NdFeB green compact includes: Under the presence of an external magnetic field, the temperature of the neodymium iron boron green compact is raised to the Curie temperature of the green compact and held for heat treatment to obtain an intermediate product; The intermediate product is subjected to sintering treatment. Before the sintering treatment, the temperature is raised to the sintering temperature by gradually increasing the temperature.

[0010] Furthermore, the conditions for the heat preservation treatment include: a vacuum degree of 1×10⁻⁶. -2 -1×10 -3 Pa, time is 50-70 min.

[0011] Furthermore, the stepwise heating includes subjecting the intermediate product to a first-stage heating treatment followed by a second-stage heating treatment, wherein; The temperature after the first heating treatment is 600-700℃, and the holding time after the first heating treatment is 80-100min. The temperature after the second heating treatment is 1030-1080℃, and the holding time after the second heating treatment is 6-12h.

[0012] Furthermore, the preparation method further includes: cooling the sintered product using a room temperature inert gas.

[0013] Furthermore, the preparation method also includes: tempering the product obtained by sintering.

[0014] Furthermore, the tempering process is performed under a vacuum or argon atmosphere, and the tempering process includes a primary tempering process and a secondary tempering process: The conditions for the first-stage tempering treatment include: a temperature of 850-950℃ and a time of 1-2 hours; The conditions for the secondary tempering process include: a temperature of 400-650℃ and a time of 1-3 hours.

[0015] Furthermore, the preparation steps of the NdFeB green blank include: Neodymium iron boron powder is oriented under a magnetic field, then vacuum-sealed after applying a demagnetizing field in the opposite direction, and subjected to pressure holding treatment to obtain the neodymium iron boron green blank. Preferably, the pressure holding treatment is a static pressure holding treatment, and the conditions for the pressure holding treatment include: a pressure value of 200-250 MPa.

[0016] The present invention also provides a neodymium iron boron magnet prepared by the above preparation method.

[0017] The beneficial effects of the present invention through the above solution are as follows: This invention places neodymium iron boron green blanks in a magnetic field for sintering. Due to the presence of an external strengthening magnetic field during the sintering process, the C-axis orientation of the magnet powder always remains in the direction of the magnetic field, avoiding the problem of orientation degree being destroyed during the pressing orientation and sintering process. This can improve the orientation degree of the magnet, and the operation is simple, requiring no multiple orientations or additional additives.

[0018] During the liquid phase sintering process of NdFeB magnets, the magnet particles are affected by the strong magnetic field, causing changes in their distribution area. This results in the pores being distributed along the direction of the magnetic field. The liquid NdFeB-rich phase diffuses and fills the pores along the direction of the strong magnetic field, increasing the density of the material, improving the microstructure of the magnet, and thus enhancing the performance of the NdFeB magnet.

[0019] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0020] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only, and the scope of protection of the present invention is not limited to the specific embodiments described below.

[0021] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0022] This invention provides a method for improving the orientation degree of sintered NdFeB magnets. The method involves sintering NdFeB green blanks in a magnetic field. Due to the presence of an external strong magnetic field during sintering, the C-axis orientation of the magnet powder remains aligned with the magnetic field direction, avoiding the orientation degree loss caused by pressing and sintering. This improves the magnet's orientation degree and is simple to operate, requiring no multiple orientation steps or additional additives. During liquid-phase sintering, the magnet particles are affected by the strong magnetic field, causing changes in their distribution area. This results in pores distributed along the magnetic field direction. The liquid NdFeB-rich phase diffuses and fills these pores along the strong magnetic field direction, increasing the material density, improving the magnet's microstructure, and thus enhancing the performance of the NdFeB magnet.

[0023] Furthermore, the sintering step of the NdFeB green blank in the preparation method of the present invention includes: S1. Under the presence of an external magnetic field, the temperature of the NdFeB green compact is raised to the Curie temperature of the green compact and held for heat treatment to obtain an intermediate product. At this time, the thermal motion of the molecules is relatively intense, which is conducive to the directional alignment of the magnetic dipoles, so that the magnetization direction of the material is consistent with the external magnetic field, ensuring that the NdFeB magnet is fully oriented at this temperature.

[0024] In step S1, the external magnetic field is a DC magnetic field with a magnetic induction intensity of 10⁻¹³ T; the heat preservation conditions include a vacuum degree of 1 × 10⁻¹³ T. -2 -1×10 -3 Pa, time is 50-70 min.

[0025] S2. The intermediate product is subjected to sintering treatment. Before the sintering treatment, the temperature is raised to the sintering temperature by gradually increasing the temperature.

[0026] In step S2, the stepwise heating includes a first-stage heating treatment followed by a second-stage heating treatment of the intermediate product. The temperature after the first-stage heating treatment is 600-700℃, and the holding time after the first-stage heating treatment is 80-100 min. During this process, the NdFeB green compact begins to dehydrogenate, removing free hydrogen from the powder through heating. At this point, the sintering temperature is much higher than the Curie temperature of the magnet, the ferromagnetism of the material disappears, the ordered arrangement of magnetic domains is destroyed, the magnetic field cannot effectively orient or confine the magnetic domain structure, and the anisotropic effect of the magnetic field no longer exists, allowing the external magnetic field to be turned off. The temperature after the second-stage heating treatment is 1030-1080℃, and the holding time after the second-stage heating treatment is 6-12 h.

[0027] It should be noted that the external magnetic field added during the sintering process should be added below the Curie temperature of the green body.

[0028] Furthermore, the preparation method of the present invention also includes: S3. After step S2 is completed, the sintered magnet is cooled to room temperature using a room temperature inert gas. Preferably, high-purity argon gas is introduced into the vacuum sintering furnace, and a blower is turned on for air cooling to room temperature to obtain a neodymium iron boron magnet semi-finished product, so as to further improve the magnet performance.

[0029] S4. The sintered product (neodymium iron boron magnet semi-finished product) is tempered to obtain the finished neodymium iron boron magnet.

[0030] Preferably, the tempering treatment is carried out under a vacuum or argon atmosphere, and the tempering treatment includes a first-stage tempering treatment and a second-stage tempering treatment. The second tempering treatment effectively improves the magnet performance. The conditions for the first-stage tempering treatment include: a temperature of 850-950℃ and a time of 1-2 hours; The conditions for the secondary tempering process include: a temperature of 400-650℃ and a time of 1-3 hours.

[0031] It should be noted that the preparation steps of NdFeB green blanks include: Neodymium iron boron powder is oriented under a magnetic field, then vacuum-sealed after applying a demagnetizing field in the opposite direction, and subjected to pressure holding treatment to obtain the neodymium iron boron green blank; preferably, the pressure holding treatment is a static pressure holding treatment, and the conditions of the pressure holding treatment include: a pressure value of 200-250 MPa.

[0032] The following specific embodiments further illustrate the preparation method of the high orientation degree sintering method for improving the orientation degree of sintered NdFeB magnets provided by the present invention.

[0033] It should be noted that the NdFeB powder used in the following examples was prepared according to conventional preparation processes, with a particle size of 3-4 μm, an average particle size of 3.5 μm, and a loose powder density of 1.5 g / cm³. 3 The composition is (Pr, Nd). 18 .2Ce 13 Co0.3Cu0.3Zr0. 25 Ti0.2Al0.1Ga0.1-B0. 91 Febal. Sintered NdFeB magnetic powder is oriented under a magnetic field of 1.5T, and a demagnetizing magnetic field in the opposite direction is applied to obtain a demagnetized green blank. The green blank is then vacuum-sealed and placed in an oil isostatic press. The powder is compacted and arranged under a pressure of 225MPa for 25s to form a NdFeB green blank.

[0034] Example 1 The neodymium iron boron green blanks were sintered in a vacuum sintering furnace with an external magnetic field. The magnetic field was a direct current magnetic field with a magnetic induction intensity of 10T. The sintering furnace was then evacuated to a vacuum of 1×10⁻⁶. -2 Pa, then the temperature was increased to 600℃ at a rate of 10℃ / min, held for 60min and then the magnetic field was turned off; The intermediate product after heat preservation is first heated to 650℃ and kept at that temperature for 90 minutes. The furnace chamber was heated to 1060℃ in two stages at a heating rate of 8℃ / min and held at that temperature for 10 hours. Turn off the heating, introduce high-purity argon gas into the vacuum sintering furnace, turn on the blower to cool it to room temperature, and obtain the neodymium iron boron magnet semi-finished product; The neodymium iron boron semi-finished product was subjected to a two-stage tempering heat treatment. Under a high-purity argon atmosphere, the first-stage tempering temperature was 850°C for 2 hours, and the second-stage tempering temperature was 400°C for 2 hours. The neodymium iron boron magnet was obtained.

[0035] The magnetic properties of the obtained neodymium iron boron magnets were tested and characterized. The characteristics were: Br = 14.94 kGs, Hci = 906.6 kA / m, and (BH)max = 430.2 kJ / m. 3 .

[0036] Example 2 The neodymium iron boron green blanks were sintered in a vacuum sintering furnace with an external magnetic field. The magnetic field was a direct current magnetic field with a magnetic induction intensity of 10T. The sintering furnace was then evacuated to a vacuum of 1×10⁻⁶. -2 Pa, then the temperature was increased to 600℃ at a rate of 10℃ / min, held for 60min and then the magnetic field was turned off; The intermediate product after heat preservation is first heated to 650℃ and kept at that temperature for 90 minutes. The furnace chamber was heated to 1030℃ in two stages at a heating rate of 8℃ / min and held at that temperature for 10 hours. Turn off the heating, introduce high-purity argon gas into the vacuum sintering furnace, turn on the blower to cool it to room temperature, and obtain the neodymium iron boron magnet semi-finished product; The neodymium iron boron semi-finished product was subjected to a two-stage tempering heat treatment. Under a high-purity argon atmosphere, the first-stage tempering temperature was 850°C for 2 hours, and the second-stage tempering temperature was 400°C for 2 hours. The neodymium iron boron magnet was obtained.

[0037] The magnetic properties of the obtained neodymium iron boron magnets were tested and characterized. The characteristics were: Br = 15.07 kGs, Hci = 903.6 kA / m, and (BH)max = 443.4 kJ / m. 3 .

[0038] Example 3 The neodymium iron boron green blanks were sintered in a vacuum sintering furnace with an external magnetic field. The magnetic field was a direct current magnetic field with a magnetic induction intensity of 12T. The sintering furnace was then evacuated to a vacuum of 1×10⁻⁶. -2 Pa, then the temperature was increased to 600℃ at a rate of 10℃ / min, held for 60min and then the magnetic field was turned off; The intermediate product after heat preservation is first heated to 650℃ and kept at that temperature for 90 minutes. The furnace chamber was heated to 1060℃ in two stages at a heating rate of 8℃ / min and held at that temperature for 10 hours. Turn off the heating, introduce high-purity argon gas into the vacuum sintering furnace, turn on the blower to cool it to room temperature, and obtain the neodymium iron boron magnet semi-finished product; The neodymium iron boron semi-finished product was subjected to a two-stage tempering heat treatment. Under a high-purity argon atmosphere, the first-stage tempering temperature was 850°C for 2 hours, and the second-stage tempering temperature was 400°C for 2 hours. The neodymium iron boron magnet was obtained.

[0039] The magnetic properties of the obtained neodymium iron boron magnets were tested and characterized. The characteristics were: Br = 15.11 kGs, Hci = 863.7 kA / m, and (BH)max = 451.4 kJ / m. 3 .

[0040] Example 4 The neodymium iron boron green blanks were sintered in a vacuum sintering furnace with an external magnetic field. The magnetic field was a direct current magnetic field with a magnetic induction intensity of 13T. The sintering furnace was then evacuated to a vacuum of 1×10⁻⁶. -2 Pa, then the temperature was increased to 600℃ at a rate of 10℃ / min, held for 60min and then the magnetic field was turned off; The intermediate product after heat preservation is first heated to 650℃ and kept at that temperature for 90 minutes. The furnace chamber was heated to 1060℃ in two stages at a heating rate of 8℃ / min and held at that temperature for 10 hours. Turn off the heating, introduce high-purity argon gas into the vacuum sintering furnace, turn on the blower to cool it to room temperature, and obtain the neodymium iron boron magnet semi-finished product; The neodymium iron boron semi-finished product was subjected to a two-stage tempering heat treatment. Under a high-purity argon atmosphere, the first-stage tempering temperature was 850°C for 2 hours, and the second-stage tempering temperature was 400°C for 2 hours. The neodymium iron boron magnet was obtained.

[0041] The magnetic properties of the obtained neodymium iron boron magnets were tested and characterized. The characteristics were: Br = 15.18 kGs, Hci = 861.7 kA / m, and (BH)max = 453.3 kJ / m. 3 .

[0042] As can be seen from the above embodiments, the present invention sintersects NdFeB green blanks in a magnetic field environment, and hard-orients the NdFeB magnets by using an external strong magnetic field, maintaining the constraint of the external strong magnetic field on the powder orientation. Under the action of the external magnetic field, the domain walls move, causing the domains to grow and rearrange, forming a stable and consistent domain structure, thus solving the problem of orientation destruction caused by powder movement during molding.

[0043] In the early stages of sintering, the magnetic powder particles are small in size and the blank is not densified. Under the action of the external magnetic field, the powder is aligned along the direction of the magnetic field, avoiding the powder rotation caused by the removal of additives.

[0044] During sintering, an external magnetic field magnetizes the powder particles, forming magnetic chains between them and increasing the interparticle bonding force. The powder particles do not rotate due to the formation of a liquid phase. As the sintering temperature gradually approaches the Curie temperature of the magnet, the thermal motion of the molecules becomes more intense, which is conducive to the directional alignment of the magnetic dipoles. This ensures that the magnetization direction of the material is consistent with the external magnetic field, maintaining a high degree of orientation and thus obtaining a high-performance neodymium iron boron magnet.

[0045] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0046] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0047] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing sintered NdFeB magnets with improved orientation, characterized in that, The preparation method includes: sintering a neodymium iron boron green blank in a magnetic field.

2. The preparation method according to claim 1, characterized in that, The magnetic field is a DC magnetic field with a magnetic induction intensity of 10⁻¹³ T.

3. The preparation method according to claim 1, characterized in that, The sintering steps of the NdFeB green blank include: Under the presence of an external magnetic field, the temperature of the neodymium iron boron green compact is raised to the Curie temperature of the green compact and held for heat treatment to obtain an intermediate product; The intermediate product is subjected to sintering treatment. Before the sintering treatment, the temperature is raised to the sintering temperature by gradually increasing the temperature.

4. The preparation method according to claim 3, characterized in that, The conditions for the heat preservation treatment include: a vacuum degree of 1×10⁻⁶. -2 -1×10 -3 Pa, time is 50-70 min.

5. The preparation method according to claim 3, characterized in that, The stepwise heating process includes subjecting the intermediate product to a first-stage heating treatment followed by a second-stage heating treatment, wherein; The temperature after the first heating treatment is 600-700℃, and the holding time after the first heating treatment is 80-100min. The temperature after the second heating treatment is 1030-1080℃, and the holding time after the second heating treatment is 6-12h.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The preparation method further includes: cooling the sintered product with a room temperature inert gas.

7. The preparation method according to any one of claims 1 to 5, characterized in that, The preparation method further includes: tempering the product obtained by sintering.

8. The preparation method according to claim 7, characterized in that, The tempering process is carried out under a vacuum or argon atmosphere, and includes a primary tempering process and a secondary tempering process: The conditions for the first-stage tempering treatment include: a temperature of 850-950℃ and a time of 1-2 hours; The conditions for the secondary tempering process include: a temperature of 400-650℃ and a time of 1-3 hours.

9. The preparation method according to any one of claims 1 to 5, characterized in that, The preparation steps of the NdFeB green blank include: Neodymium iron boron powder is oriented under a magnetic field, then vacuum-sealed after applying a demagnetizing field in the opposite direction, and subjected to pressure holding treatment to obtain the neodymium iron boron green blank. Preferably, the pressure holding treatment is a static pressure holding treatment, and the conditions for the pressure holding treatment include: a pressure value of 200-250 MPa.

10. A neodymium iron boron magnet prepared by the preparation method according to any one of claims 1 to 9.