Forming method of high-density magnet and high-density magnet

Abstract

The invention provides a forming method of a high-density magnet and the high-density magnet. The forming method of the high-density magnet comprises the following steps that NdFeB magnetic powder with the residual magnetism Br of 13.5-14.5 kGs and the maximum magnetic energy product (BH) max of 38-42 MGOe is smashed, and the particle size of the smashed NdFeB magnetic powder ranges from 30 micrometers to 150 micrometers; the NdFeB magnetic powder is subjected to HDDR treatment; manufacturing a blank body; and the blank body is put into a forming press with the temperature, the magnetic field and the explosion field, explosive cladding is carried out under the conditions that the temperature is 100-150 DEG C, the magnetic field intensity is larger than or equal to 1 T and the instantaneous pressure generated by the high-energy explosion field is 5000-10000 MPa, the magnetic powder is tightly formed, and the high-density magnet is obtained. According to the method, the high-density and high-magnetic-performance magnet is rapidly prepared through multi-field synergistic compounding of the temperature field, the magnetic field, the explosion field and the pressure field, the technological process is remarkably shortened, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of manufacturing and processing rare earth permanent magnet materials, specifically to a method for forming a high-density magnet and a high-density magnet. Background Technology

[0002] Neodymium iron boron (NdFeB) is currently the most superior permanent magnet material in terms of magnetic properties. It typically contains about 30% rare earth elements such as neodymium (Nd) and praseodymium (Pr). In the electronics and information industry, it is used in hard disk drives, optical disc drives, mobile phone speakers, and microphones. In the automotive industry, it is a core component of electric vehicle drive motors, power steering sensors, and starters. In the industrial and energy sectors, it is widely used in wind turbines, magnetic separators, and CNC machine tools. In addition, it is ubiquitous in medical devices (such as MRI) and everyday consumer products, demonstrating its wide range of applications.

[0003] Patent CN202410773062.X discloses a method for preparing anisotropic bonded NdFeB magnets, comprising the following steps: mixing and granulating anisotropic NdFeB magnetic powder with binder resin; forming a preform from the mixed and granulated magnetic powder; placing the preform into a magnetic field forming press mold, starting ultrasonic welding, setting the ultrasonic energy to 800-1500J, the time to 4-10s, and applying an orientation magnetic field; pressing, curing, cooling, and ejecting from the mold to obtain anisotropic bonded NdFeB magnets with radial orientation. This patent innovatively employs magnetic field molding and ultrasonic welding, meeting the temperature requirements for magnetic powder orientation and binder curing in a very short time, while avoiding prolonged heating and oxidation of the magnetic powder; after stopping ultrasonic welding and applying pressure, the binder resin cures rapidly, resulting in high magnet forming efficiency and good orientation. However, due to the presence of resin, the magnetic properties remain relatively low. Patent 200510030737.9 utilizes the shock wave and pressure generated by an explosion to bond and compact nanocrystalline NdFeB powder. This nanocrystalline NdFeB powder is isotropic, with nanoscale, non-oriented grains, and the explosion does not damage its magnetic properties. In contrast, HDDR NdFeB magnetic powder has larger and more brittle particle sizes; the instantaneous high pressure generated by an explosion would disrupt the anisotropic structure of the magnet, leading to a sharp drop in magnetic properties.

[0004] There is currently no process for forming HDDR neodymium iron boron magnetic powder using an explosive method. Summary of the Invention

[0005] The problem solved by this invention is to provide a method for forming high-density magnets by using a multi-field synergistic combination of temperature field, magnetic field, pressure field and explosion field to obtain a method for rapidly preparing high-density, high-magnetic-performance anisotropic neodymium iron boron magnets.

[0006] To address the above problems, the present invention provides a method for forming a high-density magnet, comprising the following steps:

[0007] Step (1): The remanence Br is 13.5~14.5kGs, and the maximum magnetic energy product (BH) is obtained. max NdFeB magnetic powder with a density of 38–42 MGOe was pulverized to obtain a particle size of 30–150 μm; the NdFeB magnetic powder was then subjected to HDDR treatment.

[0008] Step (2): Making the blank;

[0009] Step (3): Place the blank into a molding press with temperature, magnetic field and explosion field. Under the conditions of temperature of 100 to 150°C, magnetic field strength ≥ 1T and instantaneous pressure of 5000 to 10000 MPa generated by high energy explosion field, the magnetic powder is tightly formed to obtain the high density magnet.

[0010] HDDR is short for Hydrogenation–Disproportionation–Desorption–Recombination, a process used to prepare anisotropic NdFeB magnetic powder. Its core process consists of four stages: first, rare earth intermetallic compounds absorb hydrogen (hydrogenation), then disproportionation decomposition occurs, followed by forced dehydrogenation, and finally, the disproportionation products are recombined and reorganized. This process ultimately refines the grains and forms a crystal structure along the C-axis of the main phase, thereby obtaining anisotropic NdFeB magnetic powder with excellent magnetic properties.

[0011] The strong magnetic field of this invention causes the easy magnetization axis of anisotropic magnetic powder particles to be spatially aligned along the field strength direction, thus establishing orientation. While applying the magnetic field, the blank is heated to assist in optimization. The instantaneous high pressure generated by the explosion completes the densification of the blank. This invention achieves multi-field synergistic combination of temperature field, magnetic field, explosion field and pressure field by establishing orientation with magnetic field, assisting optimization with temperature field, and instantaneous high-density solidification with pressure field, thereby improving magnet density and optimizing magnet performance.

[0012] Furthermore, step (1) also includes mixing the pulverized NdFeB magnetic powder with one or more magnetic powders of SmFeN, SmCo, and FeO to obtain a mixed powder.

[0013] In this invention, a roller mill is preferably used to pulverize NdFeB magnetic powder; the pulverized NdFeB magnetic powder is preferably mixed with one or two magnetic powders of SmFeN and SmCo to obtain a mixed powder.

[0014] The raw materials for NdFeB magnetic powder are rare earth materials such as neodymium oxide and praseodymium oxide. The raw materials are scarce and difficult to refine, resulting in high production costs. In contrast, the main raw material for SmFeN magnetic powder is samarium oxide, while FeO magnetic powder is mainly composed of iron, which is inexpensive.

[0015] In one embodiment of the present invention, HDDR neodymium iron boron powder and SmFeN magnetic powder are mixed at a mass ratio of 70%:30%, and the high-density magnet is obtained by multi-field synergistic composite of temperature field, magnetic field, pressure field and explosion field. The magnetic properties do not change significantly, but the production cost is significantly reduced.

[0016] In this invention, a mixer is preferably used to mix the powders.

[0017] Furthermore, the mass content of NdFeB in the mixed powder is 30% to 100% wt.

[0018] Furthermore, the particle sizes of the SmFeN, SmCo, and FeO magnetic powders are 10–50 μm, 50 μm–100 μm, and 100 μm–200 μm, respectively.

[0019] This invention mixes magnetic powders of different particle sizes to fill gaps and improve the density of the magnet after molding.

[0020] Furthermore, the mass content of NdFeB in the mixed powder is 50% to 100% wt, more preferably 70% to 100%.

[0021] In this invention, the magnetic properties of SmFeN, SmCo and FeO magnetic powders are all lower than those of NdFeB magnetic powder, and excessive addition will lead to a significant decrease in the magnetic properties of the magnet.

[0022] Furthermore, the magnetic field strength in step (3) is 1.0 to 2.0 T.

[0023] Furthermore, in step (3), the temperature is 120-150℃, the magnetic field strength is 2.0T, and the instantaneous pressure generated by the high-energy explosion field is 10000MPa.

[0024] Generally, the higher the magnetic field strength, the better the magnet orientation. However, magnetic fields exceeding 2.0T are difficult to obtain in industrial production, and the improvement in magnet performance gradually decreases after this threshold. Therefore, in practical applications, the magnetic field strength usually does not exceed 2.0T.

[0025] The present invention uses appropriate temperature and pressure to help increase magnet density; however, excessively high temperature will cause the magnetic powder to oxidize, which will lead to a decrease in magnet performance. Moreover, when the pressure exceeds the critical value, the magnet density will no longer increase, but will instead destroy the magnetic powder orientation structure, resulting in a decrease in magnet performance.

[0026] The present invention also provides a high-density magnet, which is prepared according to the molding method described above.

[0027] Furthermore, the density of the magnet is not less than 6.0 g / cm³. 3(BH) max Above 20 MGOe.

[0028] Compared with existing technologies, the high-density magnet forming method and the high-density magnet of the present invention have the following advantages:

[0029] This invention uses HDDR neodymium iron boron magnetic powder and improves the density of anisotropic neodymium iron boron magnets through the synergistic combination of multiple fields such as temperature field, magnetic field, explosion field, and pressure field, thus rapidly preparing anisotropic neodymium iron boron magnets with high density and high magnetic performance. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0031] Anisotropic HDDR NdFeB magnetic powder can be prepared through a hydrogenation-disproportionation-dehydrogenation-recombination process (HDDR). Mass production of HDDR NdFeB magnetic powder materials has been achieved. Currently, the main forming methods for HDDR NdFeB magnetic powder are bonding molding and hot pressing / hot deformation molding. Bonding molding involves mixing HDDR magnetic powder with a binder (such as epoxy resin) and then molding it through processes such as molding and injection. This method has lower production costs and simpler equipment. However, in this process, the magnetic powder particles are separated by the non-magnetic binder, resulting in a lower overall density and relatively lower magnetic properties, typically around 10 MGOe. Hot pressing / hot deformation molding involves loading HDDR magnetic powder into a mold and then applying high pressure (unidirectional or bidirectional pressure) at high temperature for densification sintering. This method can obtain a fully dense magnet with a density close to the theoretical density. Therefore, its magnetic properties are significantly higher than bonded magnets, falling between bonded and sintered NdFeB magnets, with a magnetic energy product typically reaching 25–45 MGOe. However, in actual production, the process is long and costly because it requires hot pressing followed by sintering.

[0032] This invention employs a multi-field synergistic combination of temperature field, magnetic field, pressure field, and explosion field to obtain an anisotropic neodymium iron boron magnet with a simple preparation process and the ability to rapidly prepare magnetic properties superior to bonded magnets.

[0033] Example 1

[0034] Material preparation: High-performance anisotropic HDDR Nd-Fe-B powder was selected, with initial magnetic properties of Br = 13.5–14.5 kGs (BH). max =38~42MGOe, particle size 30~150μm.

[0035] HDDR magnetic powder is molded into a blank under a pressure of 4MPa.

[0036] The blank is placed in a press and formed under a pressure of 5000MPa in a magnetic field and an explosion field at a temperature of 100℃~150℃, to obtain the high-density magnet.

[0037] The high-density magnet (BH) prepared in Example 1 was tested. max =25 MGOe, density is 6.5 g / cm³ 3 .

[0038] Example 2

[0039] Material preparation: High-performance anisotropic HDDR Nd-Fe-B powder was selected, with initial magnetic properties of Br = 13.5–14.5 kGs (BH). max =38~42MGOe, particle size 30~150μm; SmFeN magnetic powder particle size 30~50μm, its initial magnetic properties Br=12~13kGs, (BH) max =30~40MGOe; HDDR neodymium iron boron powder and SmFeN magnetic powder are mixed at a mass ratio of 70%:30% to obtain mixed magnetic powder.

[0040] The mixed magnetic powder is molded into a blank under a pressure of 4 MPa.

[0041] The blank is placed in a press and formed under a pressure of 10000MPa in a magnetic field and an explosion field at 120℃~150℃ to obtain the high-density magnet.

[0042] The high-density magnet (BH) prepared in Example 2 was tested. max =28 MGOe, density is 6.3 g / cm³ 3 .

[0043] HDDR NdFeB powder has a complex preparation process, high rare earth content, and is 50 times more expensive than SmFeN magnetic powder. This invention uses relatively inexpensive SmFeN to partially replace HDDR Nd-Fe-B, with little change in density (BH). max The increase was slight, but the production cost was significantly reduced.

[0044] Example 3

[0045] Material preparation: High-performance anisotropic HDDR Nd-Fe-B powder was selected, with initial magnetic properties of Br = 13.5–14.5 kGs (BH). max =38~42MGOe, particle size 30~150μm; SmFeN magnetic powder particle size 30~50μm, its initial magnetic properties Br=12~13kGs, (BH) max=30~40MGOe; SmCo magnetic powder has a particle size of 50~100μm, and its initial magnetic properties are Br=7~12kGs, (BH) max =18~24MGOe; HDDR neodymium iron boron powder, SmFeN magnetic powder and SmCo magnetic powder are mixed in a mass ratio of 50%:30%:20% to obtain mixed magnetic powder.

[0046] The mixed magnetic powder is molded into a blank under a pressure of 4 MPa.

[0047] The blank is placed in a press and formed under a pressure of 10000MPa in a magnetic field and an explosion field at 120℃~150℃ to obtain the high-density magnet.

[0048] The high-density magnet (BH) prepared in Example 3 was tested. max =26 MGOe, density is 6.65 g / cm³ 3 .

[0049] Example 4

[0050] Material preparation: High-performance anisotropic HDDR Nd-Fe-B powder was selected, with initial magnetic properties of Br = 13.5–14.5 kGs (BH). max =38~42MGOe, particle size 30~150μm; SmFeN magnetic powder particle size 30~50μm, its initial magnetic properties Br=12~13kGs, (BH) max =30~40MGOe; SmCo magnetic powder has a particle size of 50~100μm, and its initial magnetic properties are Br=7~12kGs, (BH) max =18~24MGOe; FeO magnetic powder particle size is 100~200μm, and its initial magnetic properties are Br=1.0~4.0kGs, (BH) max =3~5MGOe; HDDR neodymium iron boron powder, SmFeN magnetic powder, SmCo magnetic powder and FeO magnetic powder are mixed in a mass ratio of 50%:20%:10%:10% to obtain a mixed magnetic powder. This reduces costs.

[0051] The mixed magnetic powder is molded into a blank under a pressure of 4 MPa.

[0052] The blank is placed in a press and formed under a pressure of 10000MPa in a magnetic field and an explosion field at 120℃~150℃ to obtain the high-density magnet.

[0053] The high-density magnet (BH) prepared in Example 4 was tested and confirmed. max =22 MGOe, density is 6.0 g / cm³ 3 .

[0054] Comparative Example 1

[0055] Material preparation: High-performance anisotropic HDDR Nd-Fe-B powder was selected, with initial magnetic properties of Br = 13.5–14.5 kGs (BH). max =38~42MGOe, particle size 30~150μm.

[0056] Mixed with adhesives (epoxy resin, nitrile rubber, silicone rubber, nylon, etc.), and molded under a magnetic field, bonded NdFeB magnets are produced (BH). max The range is 10–12 MGOe.

[0057] Comparative Example 2

[0058] Material preparation: High-performance anisotropic HDDR Nd-Fe-B powder was selected, with initial magnetic properties of Br = 13.5–14.5 kGs (BH). max =38~42MGOe, particle size 30~150μm; SmFeN magnetic powder particle size 30~50μm, its initial magnetic properties Br=12~13kGs, (BH) max =30~40MGOe; HDDR neodymium iron boron powder and SmFeN magnetic powder are mixed at a mass ratio of 70%:30% to obtain mixed magnetic powder.

[0059] The mixed magnetic powder is molded into a blank under a pressure of 4 MPa.

[0060] The blank is placed in a press and formed under a magnetic field of 2T and an explosion field of 10000MPa to obtain anisotropic neodymium iron boron magnets.

[0061] The magnet (BH) prepared in Comparative Example 2 was tested. max =23MGOe, density is 6.35 g / cm³ 3 .

[0062] Applying a certain temperature and pressure can help increase the magnet density. However, excessively high temperatures can cause active metal elements to react with oxygen to form a non-magnetic oxide layer, leading to the oxidation of magnetic powder and thus significantly reducing the magnet's performance.

[0063] Comparative Example 3

[0064] Material preparation: High-performance anisotropic HDDR Nd-Fe-B powder was selected, with initial magnetic properties of Br = 13.5–14.5 kGs (BH). max=38~42MGOe, particle size 30~150μm; SmFeN magnetic powder particle size 30~50μm, its initial magnetic properties Br=12~13kGs, (BH) max =30~40MGOe; HDDR neodymium iron boron powder and SmFeN magnetic powder are mixed at a mass ratio of 70%:30% to obtain mixed magnetic powder.

[0065] The mixed magnetic powder is molded into a blank under low pressure.

[0066] The blank is placed in a press and formed under a magnetic field of 0.5T and an explosion field of 10000MPa to obtain anisotropic neodymium iron boron magnets.

[0067] The magnet (BH) prepared in Comparative Example 3 was tested. max =22 MGOe, density is 6.3 g / cm³ 3 .

[0068] If the magnetic field is too low, it cannot effectively drive the magnetic moments of anisotropic NdFeB and SmFeN magnetic powders to align in a uniform direction, resulting in a decrease in the anisotropy of the magnet and a reduction in the magnet's performance.

[0069] Comparative Example 4

[0070] Material preparation: High-performance anisotropic HDDR Nd-Fe-B powder was selected, with initial magnetic properties of Br = 13.5–14.5 kGs (BH). max =38~42MGOe, particle size 30~150μm; SmFeN magnetic powder particle size 30~50μm, its initial magnetic properties Br=12~13kGs, (BH) max =30~40MGOe; HDDR neodymium iron boron powder and SmFeN magnetic powder are mixed at a mass ratio of 70%:30% to obtain mixed magnetic powder.

[0071] The mixed magnetic powder is molded into a blank under low pressure.

[0072] The blank is placed in a press and formed under a magnetic field of 2T and an explosion field of 15000MPa to obtain anisotropic neodymium iron boron magnets.

[0073] The magnet (BH) prepared in Comparative Example 4 was tested. max =26 MGOe, density is 6.5 g / cm³ 3 .

[0074] Normally, higher pressure results in higher magnet density, thus improving performance. However, when the pressure exceeds the critical threshold, excessive pressure will destroy the ordered orientation structure of the magnetic powder, leading to disordered magnetic domain arrangement. At this point, the magnet density no longer increases with increasing pressure, but instead, the magnetic performance decreases due to the deterioration of orientation.

[0075] The high-density magnets obtained by this invention have magnetic properties superior to bonded NdFeB magnets ((BH)max is typically 10–15 MGOe) and close to sintered NdFeB magnets ((BH) max Typically above 30 MGOe), with excellent magnetic properties; the preparation process adopted in this invention innovatively combines temperature field, magnetic field, pressure field and explosion field to rapidly prepare magnets, with a simple and efficient process that significantly reduces production process costs.

[0076] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for forming a high-density magnet, characterized in that, Includes the following steps: Step (1): The remanence Br is 13.5~14.5kGs, and the maximum magnetic energy product (BH) is obtained. max NdFeB magnetic powder with a density of 38–42 MGOe was pulverized to obtain a particle size of 30–150 μm; the NdFeB magnetic powder was then subjected to HDDR treatment. Step (2): Making the blank; Step (3): Place the blank into a molding press with temperature, magnetic field and explosion field. Under the conditions of temperature of 100 to 150°C, magnetic field strength ≥ 1T and instantaneous pressure of 5000 to 10000 MPa generated by high energy explosion field, the magnetic powder is tightly formed to obtain the high density magnet.

2. The method for forming a high-density magnet according to claim 1, characterized in that, Step (1) further includes mixing the pulverized NdFeB magnetic powder with one or more magnetic powders of SmFeN, SmCo, and FeO to obtain a mixed powder.

3. The method for forming a high-density magnet according to claim 2, characterized in that, The mass content of NdFeB in the mixed powder is 30% to 100% wt.

4. The method for forming a high-density magnet according to claim 2, characterized in that, The particle sizes of the SmFeN, SmCo, and FeO magnetic powders are 10–50 μm, 50 μm–100 μm, and 100 μm–200 μm, respectively.

5. The method for forming a high-density magnet according to claim 2, characterized in that, The mass content of NdFeB in the mixed powder is 50% to 100% wt.

6. The method for forming a high-density magnet according to any one of claims 1 to 5, characterized in that, In step (3), the temperature is 120-150℃, the magnetic field strength is 2.0T, and the instantaneous pressure generated by the high-energy explosion field is 10000MPa.

7. A high-density magnet, characterized in that, It is prepared by the molding method according to claim 1.

8. A high-density magnet according to claim 7, characterized in that, The density of the magnet is not less than 6.0 g / cm³. 3 (BH) max Above 20 MGOe.