A corrosion-resistant sintered NdFeB magnetic material, its preparation process, and a cylindrical magnetic block made of the NdFeB magnetic material

Abstract

This application relates to the field of neodymium iron boron magnetic material production. More specifically, it relates to a corrosion-resistant sintered neodymium iron boron magnetic material, its preparation process, and a cylindrical magnet block made of the neodymium iron boron magnetic material. A corrosion-resistant sintered neodymium iron boron magnetic material, by weight percentage, includes PrNd: 25 - 29%, Cu: 0 - 2%, Zr: 1 - 2%, Co: 0 - 2%, Nb: 0 - 2%, Al: 1 - 2%, Ga: 0 - 2%, Y and / or Sc: 1 - 5%, Si: 2 - 4%, C: 0.1 - 0.2%, B: 1 - 1.5%, with the balance being Fe and unavoidable impurities; A preparation process for a corrosion-resistant sintered neodymium iron boron magnetic material, including the preparation steps of melt spinning, hydrogen decrepitation grinding, pressing forming, and sintering processing; A cylindrical magnet block made of the above-mentioned sintered neodymium iron boron magnetic material. This application can effectively improve the corrosion resistance of sintered neodymium iron boron magnetic materials.

Description

Technical Field

[0001] The present application relates to the field of neodymium iron boron magnetic material production. More specifically, it relates to a corrosion-resistant sintered neodymium iron boron magnetic material, its preparation process, and a cylindrical magnet block made of the neodymium iron boron magnetic material. Background Art

[0002] Neodymium iron boron, as the third-generation rare earth permanent magnet material, is the permanent magnet second only to holmium magnet at absolute zero and is also the most commonly used rare earth magnet. It is widely used in fields such as electroacoustics, national defense, aerospace, automobiles, energy, and medical devices. Neodymium iron boron magnetic materials can be divided into sintered neodymium iron boron magnetic materials and bonded neodymium iron boron magnetic materials. Among them, the sintered neodymium iron boron magnetic material has relatively good magnetic properties and is the most widely used, but the sintered neodymium iron boron magnetic material has poor corrosion resistance.

[0003] Regarding the above related technologies, the inventor believes that in order to further promote the application fields of neodymium iron boron magnetic materials, the market's requirements for the comprehensive performance of neodymium iron boron magnetic materials are continuously increasing, especially the requirements for their corrosion resistance. The poor corrosion resistance of sintered neodymium iron boron magnetic materials limits the further expansion of their applications. Summary of the Invention

[0004] In order to improve the corrosion resistance of sintered neodymium iron boron magnetic materials, the present application provides a corrosion-resistant sintered neodymium iron boron magnetic material and its preparation process.

[0005] A corrosion-resistant sintered neodymium iron boron magnetic material and its preparation process provided by the present application adopt the following technical solutions: In the first aspect, the present application provides a corrosion-resistant sintered neodymium iron boron magnetic material, adopting the following technical solutions:

[0006] A corrosion-resistant sintered neodymium iron boron magnetic material, by weight percentage, includes PrNd: 25 - 29%, Cu: 0 - 2%, Zr: 1 - 2%, Co: 0 - 2%, Nb: 0 - 2%, Al: 1 - 2%, Ga: 0 - 2%, Y and / or Sc: 1 - 5%, Si: 2 - 4%, C: 0.1 - 0.2%, B: 1 - 1.5%, and the balance is Fe and unavoidable impurities.

[0007] By adopting the above technical solutions, Zr is added to improve the corrosion resistance of NdFeB magnetic materials. However, Zr will absorb a large amount of O in the air when heated, introducing too much O into the magnetic materials. A large amount of rare earth oxides agglomerate at the grain boundaries, and a large number of pores are generated inside the magnetic materials, resulting in a decrease in the mechanical properties of the magnetic materials. By using the combination of Si and O, the O in the NdFeB magnetic materials is removed, making the material integrity better and the crystal polymerization degree higher. However, too much Si will coarsen the grains of the magnetic materials, resulting in larger pores between the grains. A certain amount of C is added. C cooperates with Al to generate the intermediate phase Al4C3, making the melt mix evenly during melting, refining the grains of the magnetic materials, restricting the increase of pores, and ensuring the mechanical properties of the magnetic materials while ensuring the corrosion resistance of the magnetic materials.

[0008] Preferably, B2O3 - SiO2 sintering aids are added during sintering processing.

[0009] By adopting the above technical solutions, the porosity inside the sintered NdFeB magnetic materials is relatively high, and O2 is easy to enter the pores of the NdFeB magnetic materials, causing oxidation corrosion of the magnetic materials and resulting in poor corrosion resistance of the NdFeB magnetic materials. Before sintering processing, B2O3 - SiO2 sintering aids are added. The eutectic temperature of the B2O3 - SiO2 sintering aids is 438 °C. The B2O3 - SiO2 sintering aids melt into a liquid state at the sintering temperature. The liquid B2O3 - SiO2 sintering aids infiltrate the surface of the NdFeB powder, causing the NdFeB powder to bond. During the later pressing and forming process, the NdFeB magnetic materials gradually become denser, and the B2O3 - SiO2 sintering aids are inside the NdFeB magnetic materials, filling the gaps between the NdFeB powders.

[0010] Preferably, the added weight of the B2O3 - SiO2 sintering aids accounts for 1 - 2% of the sintered NdFeB magnetic materials.

[0011] By adopting the above technical solutions, as the content of the B2O3 - SiO2 sintering aids increases, the porosity of the NdFeB magnetic materials decreases. The eutectic temperature of the B2O3 - SiO2 sintering aids is 438 °C. However, since the sintering temperature of the NdFeB powder is much higher than the eutectic temperature of the B2O3 - SiO2 sintering aids, part of the liquid B2O3 - SiO2 sintering aids evaporate at high temperatures, leaving more closed pores in the NdFeB matrix. Control the addition amount of the B2O3 - SiO2 sintering aids to avoid damaging the densification degree of the NdFeB while ensuring the reduction of porosity.

[0012] Preferably, the weight ratio of B2O3:SiO2 in the B2O3 - SiO2 sintering aids is 9:1.

[0013] By adopting the above technical solution, when the SiO2 content is too high, the B2O3-SiO2 sintering aid has a relatively high viscosity and low fluidity after melting into a liquid state, cannot fully wet the surface of the neodymium iron boron, and is difficult to penetrate between the neodymium iron borons to fill the pores during the sintering process.

[0014] Preferably, the particle size of the B2O3-SiO2 sintering aid is 50-70μm.

[0015] By adopting the above technical solution, the smaller the particle size of the B2O3-SiO2 sintering aid, the higher the melting efficiency, the larger the contact area with the neodymium iron boron magnetic material, and the better the wetting effect of the melted sintering aid on the surface of the neodymium iron boron magnetic material. However, if the particle size of the B2O3-SiO2 sintering aid is too small, agglomeration is likely to occur, affecting the wetting effect. Therefore, in this application, the particle size of the B2O3-SiO2 sintering aid is controlled to be 50-70μm, which can prevent the B2O3-SiO2 sintering aid from agglomerating while ensuring the wetting effect.

[0016] In a second aspect, the present application provides a preparation process for a corrosion-resistant sintered neodymium iron boron magnetic material, adopting the following technical solution:

[0017] A preparation process for a corrosion-resistant sintered neodymium iron boron magnetic material includes the following steps:

[0018] Melting and strip casting: PrNd, Cu, Zr, Co, Nb, Al, Ga, Y and / or Sc, Fe, Si are added to a vacuum melting furnace according to a specified weight ratio, melted at a high temperature under argon protection, and then strip cast;

[0019] Hydrogen decrepitation and grinding: The strip-cast flakes are first subjected to hydrogen decrepitation in a hydrogen decrepitation furnace and then made into powder in a jet mill;

[0020] Compression molding: The powder obtained from hydrogen decrepitation and grinding is placed in rubber molds of different shapes according to requirements, compression molded and vacuum encapsulated, and then isostatically pressed to obtain a sintered green body. The obtained sintered green body includes but is not limited to cylinders;

[0021] Sintering process: The sintered green body obtained from compression molding is placed in a vacuum sintering furnace for sintering under the protection of nitrogen, and then subjected to tempering aging heat treatment to obtain a sintered neodymium iron boron magnetic material, and the surface of the obtained sintered neodymium iron boron magnetic material is processed.

[0022] By adopting the above technical solution, directly pressing the powder obtained from hydrogen decrepitation and grinding into different shapes is more simple and rapid compared to obtaining products of different sizes and shapes through machining.

[0023] Preferably, in melting and strip casting, the vacuum melting furnace is evacuated to a vacuum degree ≤1 Pa before melting.

[0024] By adopting the above technical solution, when the vacuum degree is too high, the degassing of the vacuum melting furnace is incomplete, and the raw materials are prone to react with O and oxidize, resulting in a decrease in the coercivity of the finished NdFeB magnetic material. The vacuum degree is maintained at ≤1 Pa to limit the oxidation of the raw materials.

[0025] Preferably, in hydrogen decrepitation grinding, an antioxidant is added to the NdFeB coarse powder after hydrogen decrepitation, and then jet milling is carried out.

[0026] By adopting the above technical solution, an antioxidant is added to reduce the probability of the formation of oxides between the Nd-rich phase and O, and limit the number of pores in the grain boundaries, thereby improving the corrosion resistance of the product.

[0027] Preferably, in hydrogen decrepitation grinding, the particle size of the magnetic powder after jet milling is 2-6 μm.

[0028] By adopting the above technical solution, as the particle size of the magnetic powder decreases, the coercivity of the sintered magnetic material continuously increases. However, when the particle size of the magnetic powder is too small, the specific surface area of the magnetic powder is too large, and the Nd-rich phase is prone to react with O to form oxides during the sintering process, resulting in an increase in the number of grain boundary pores and a decrease in the remanence. The particle size of the magnetic powder after jet milling is limited to limit the excessive number of grain boundary pores in the magnetic material while ensuring the coercivity of the magnetic material.

[0029] In a third aspect, the present application provides a cylindrical magnetic block made of the sintered NdFeB magnetic material according to any one of claims 1-5.

[0030] In summary, the present application has the following beneficial effects:

[0031] 1. The present application adds Zr to improve the corrosion resistance of the NdFeB magnetic material, adds a certain amount of Si to combine with O to remove the O that Zr absorbs in large amounts during heating, thereby ensuring the integrity of the magnetic material and reducing the number of pores inside the magnetic material. Since too much Si will coarsen the grains of the magnetic material, a certain amount of C is added to cooperate with Al to form an intermediate phase Al4C3, making the melt mix evenly during melting and refining the grains of the magnetic material, limiting the increase in pores. Generally speaking, while ensuring the corrosion resistance of the magnetic material, the mechanical properties of the magnetic material are ensured;

[0032] 2. The present application preferably further adds a B2O3-SiO2 sintering aid before sintering the NdFeB magnetic material. The B2O3-SiO2 sintering aid melts into a liquid state at the sintering temperature, and the liquid B2O3-SiO2 sintering aid wets the surface of the NdFeB powder, causing the NdFeB powder to bond. During the subsequent pressing process, the NdFeB magnetic material gradually densifies, and the B2O3-SiO2 sintering aid is inside the NdFeB magnetic material, filling the gaps between the NdFeB powder. Detailed Embodiments

[0033] The present application will be further described in detail below with reference to examples and comparative examples.

[0034] Raw material introduction

[0035] Praseodymium-neodymium powder: It is made by mixing praseodymium powder and neodymium powder. The purity of both praseodymium powder and neodymium powder is ≥99.99%. The weight of praseodymium powder accounts for 15.5% of the total amount of praseodymium-neodymium powder, and its particle size can be adjusted as needed. In this embodiment, it is specifically illustrated with 4-6μm as an example.

[0036] Iron powder: The iron content is ≥98.8%, and its particle size can be adjusted as needed. In this embodiment, it is illustrated with 4.8-5.5μm as an example.

[0037] Ferro-boron powder: Low-carbon ferro-boron powder (C≤0.1%), the boron content is 20%, and its particle size can be adjusted as needed. In this embodiment, it is illustrated with 4-6μm as an example.

[0038] Metal powders of lanthanide elements such as terbium, dysprosium, erbium, dysprosium, terbium, cerium, erbium, etc.: The metal content is ≥99.99%, and its particle size can be adjusted as needed. In this embodiment, it is specifically illustrated with 4-6μm as an example.

[0039] Metal powders of elements such as zirconium, aluminum, copper, cobalt, niobium, gallium, yttrium, scandium, etc. that can be used to assist in improving the performance of NdFeB magnetic materials: The metal content is ≥99.99%, and its particle size can be adjusted as needed. In this embodiment, it is specifically illustrated with 4-6μm as an example.

[0040] Silicon powder: The purity of silicon powder is ≥95%, and its particle size can be adjusted as needed. In this embodiment, it is specifically illustrated with 0.1-0.3μm as an example.

[0041] Carbon powder: The purity of carbon powder is ≥95%, and its particle size can be adjusted as needed. In this embodiment, it is specifically illustrated with 4-6μm as an example.

[0042] The B2O3-SiO2 sintering aid is prepared by mixing boron oxide powder and silicon dioxide powder.

[0043] Boron oxide powder: The purity of boron oxide powder is ≥99.99%, and its particle size can be adjusted as needed. In this embodiment, it is specifically illustrated with particle sizes of 10-30μm, 50-70μm, and 70-100μm as examples.

[0044] Silicon dioxide powder: The purity of silicon dioxide powder is ≥99.99%, and its particle size can be adjusted as needed. In this embodiment, it is specifically illustrated with particle sizes of 10-30μm, 50-70μm, and 70-100μm as examples.

[0045] The following further describes the present application in detail with reference to embodiments.

[0046] Embodiment

[0047] Example 1

[0048] A NdFeB magnetic material comprises the following components (by weight percentage): PrNd: 25%, Cu: 1%, Zr: 1%, Co: 1%, Nb: 1%, Al: 1.5%, Ga: 1%, Y: 2%, Sc: 3%, Si: 2%, C: 0.1%, B: 1%, and the balance is Fe and unavoidable impurities.

[0049] The method for preparing the above-mentioned NdFeB magnetic material comprises the following steps:

[0050] ①, Melting and spinning: According to the components of the above-mentioned NdFeB magnetic materials, weigh the corresponding weight ratio of praseodymium-neodymium powder, copper powder, zirconium powder, cobalt powder, niobium powder, aluminum powder, gallium powder, yttrium powder, and scandium powder and put them into a vacuum melting furnace. When the vacuum value is ≤1.5Pa, heat it. After the vacuum is evacuated to ≤1Pa, fill it with argon gas, melt the raw materials under the protection of argon gas, pour the obtained molten liquid onto the cooling roller for spinning, and obtain spinning thin sheets;

[0051] ② Hydrogen crushing and grinding: Place the molten belt flakes prepared in the molten belt in a hydrogen crushing furnace, evacuate to a vacuum degree of ≤1Pa, fill with hydrogen until the vacuum value is 0.2Mpa, and perform hydrogen crushing for 4 hours. After nitrogen is filled into the airflow mill to discharge oxygen until the pressure value is 0.25Mpa, the hydrogen crushed material obtained after hydrogen crushing is placed in the airflow mill and made into powder in the airflow mill. The particle size of the magnetic powder after airflow grinding is 2-6μm;

[0052] ③. Compression molding: nitrogen is filled in the mold, and the magnetic powder obtained after airflow grinding is placed in the mold. Molds of different shapes can be used according to actual needs. In Example 1 of the present application, a cylindrical mold is used. The magnetic powder is pressed by a 6T pulse magnetic field, and the pressed product is placed in a nitrogen bag for sealing, and then placed in an isostatic press, and pressed under 280Mpa oil pressure to obtain a sintered green body with a diameter of 4-10mm. The obtained sintered green body includes but is not limited to a cylinder;

[0053] ④. Sintering process: Put the sintered green body obtained in the sintering into a vacuum sintering furnace, and in a nitrogen atmosphere, first increase the temperature from room temperature to 800°C at 3°C / min, keep it warm for 2.5 hours, and then increase the temperature to 1100°C at 5°C / min, and keep it warm for 1.5 hours. After sintering, wait for the temperature of the vacuum sintering furnace to drop to room temperature, and then increase the temperature to 480°C at 5°C / min for tempering and aging heat treatment. When the treatment is completed, when the temperature drops to 75°C, first exhaust the gas to the outside, and then inflate the vacuum sintering furnace to normal pressure, take out the sintered green body, and obtain the sintered NdFeB magnet after the sintered green body cools to room temperature. After grinding and surface treatment of the above sintered NdFeB magnet, a cylindrical magnet block is obtained.

[0054] Embodiment 2-6

[0055] The main differences between Examples 2-6 and Example 1 lie in the different raw material ratios, and the specific ratios are shown in Table 1.

[0056] Table 1 Schematic Diagram of Raw Material Ratios in Examples 2-6

[0057]

[0058]

[0059] Examples 7-11

[0060] In Examples 7-11, the composition and dosage of the basic raw materials are generally the same as those in Example 5. However, different from Example 5, B2O3-SiO2 sintering aids are added during the sintering process. The weight of the B2O3-SiO2 sintering aids added in Example 7 accounts for 0.1% of the total weight of the neodymium iron boron magnetic powder, the weight of the B2O3-SiO2 sintering aids added in Example 8 accounts for 1% of the total weight of the neodymium iron boron magnetic powder, the weight of the B2O3-SiO2 sintering aids added in Example 9 accounts for 1.5% of the total weight of the neodymium iron boron magnetic powder, the weight of the B2O3-SiO2 sintering aids added in Example 10 accounts for 2% of the total weight of the neodymium iron boron magnetic powder, and the weight of the B2O3-SiO2 sintering aids added in Example 11 accounts for 4% of the total weight of the neodymium iron boron magnetic powder.

[0061] Comparative Examples

[0062] Comparative Example 1

[0063] The difference between Comparative Example 1 and Example 1 is that Si and C are not added in Comparative Example 1.

[0064] Comparative Example 2

[0065] The difference between Comparative Example 2 and Example 1 is that Si is not added in Comparative Example 2.

[0066] Comparative Example 3

[0067] The difference between Comparative Example 3 and Example 1 is that C is not added in Comparative Example 3.

[0068] Comparative Example 4

[0069] In Comparative Example 4, the composition and dosage of the basic raw materials are generally the same as those in Example 5. However, different from Example 5, Y and Sc are not added in Comparative Example 4, and the weight percentage of PrNd is 29%.

[0070] Performance Detection Test

[0071] 1. Corrosion Resistance

[0072] For the cylindrical magnets provided in Examples 1-6 and Comparative Examples 1-3 of the present application, place the cylindrical magnets in a sealed box with a constant temperature set at 90 °C, and the O2 concentration in the sealed box is set at 50%, and test the time when rust spots first appear on the surface of the magnetic material.

[0073] For the cylindrical magnets provided in Examples 1-6 and Comparative Example 1 of the present application, place the cylindrical magnets in a sealed box with a constant temperature set at 23 °C, and the relative humidity in the sealed box is constantly set at 70%, and test the time when rust spots first appear on the surface of the magnetic material.

[0074] 2. Magnetic properties: Perform magnetic property detection on the cylindrical magnets provided in Examples 1-6 and Comparative Examples 1-3 of the present application according to the magnetic test method for permanent magnet (hard magnet) materials in GB / T 3217. The test results are shown in Table 2.

[0075] Table 2 Performance detection data table of Examples 1-6 and Comparative Examples 1-3

[0076]

[0077] As can be seen from Table 2, the corrosion resistance of Examples 1-6 is better than that of Comparative Examples 1-3. Zr will absorb a large amount of O in the air when heated. As the content of Zr increases, too much O is introduced into the magnetic material, and a large amount of rare earth oxides agglomerate at the grain boundaries, resulting in a large number of pores inside the magnetic material, and the oxidation resistance of the magnetic material decreases in high-temperature or high-humidity environments. By using the combination of Si and O to remove O in the cylindrical magnet, the integrity of the magnet is better and the crystal polymerization degree is higher. However, too much Si will coarsen the grains of the NdFeB magnetic material, resulting in larger pores between the grains, thus affecting the coercivity. Adding a certain amount of C, in cooperation with Al, generates the intermediate phase Al4C3, making the melt mix evenly during melting, and refining the grains of the magnetic material and restricting the increase of pores.

[0078] Perform the above corrosion resistance test and magnetic property detection on the cylindrical magnets prepared in Comparative Example 4. The test results are shown in Table 3.

[0079] Table 3 Performance detection data table of Example 5 and Comparative Example 4

[0080]

[0081] As can be seen from Table 3, without adding Y and Sc, the impact on the corrosion resistance of the cylindrical magnet is not significant, but the costs of Y and Sc are relatively low. Adding a part of Y and / or Sc to replace part of Nd can effectively reduce the production cost of the cylindrical magnet.

[0082] Perform the above corrosion resistance test and magnetic property detection on the cylindrical magnets prepared in Examples 7-11. The test results are shown in Table 4.

[0083] Table 4 Performance Test Data Sheet of Example 5 and Examples 7 - 12

[0084]

[0085] As can be seen from Table 4, the corrosion resistance of Examples 7 - 11 is better than that of Example 5. Due to the relatively high porosity inside the cylindrical magnet block, O₂ easily enters the pores of the cylindrical magnet block. Before sintering processing, B₂O₃ - SiO₂ sintering aids are added. At this time, the B₂O₃ - SiO₂ sintering aids melt into a liquid state at the sintering temperature. The liquid B₂O₃ - SiO₂ sintering aids come into full contact with the surface of the NdFeB green body and infiltrate the surface of the NdFeB green body. During the sintering process, as the NdFeB green body densifies, the liquid B₂O₃ - SiO₂ sintering aids are squeezed into the interior of the NdFeB green body and fill the voids.

[0086] In Example 7, due to the relatively small amount of B₂O₃ - SiO₂ sintering aids added, the infiltration rate of the B₂O₃ - SiO₂ sintering aids is relatively low. In Examples 8 - 10, the amount of B₂O₃ - SiO₂ sintering aids added is more appropriate, and the infiltration rate of the B₂O₃ - SiO₂ sintering aids is good. When the amount of B₂O₃ - SiO₂ sintering aids added in Example 11 is large, since the sintering temperature of the NdFeB powder is much higher than the eutectic temperature (438 °C) of the B₂O₃ - SiO₂ sintering aids, part of the liquid B₂O₃ - SiO₂ sintering aids evaporate at high temperature, leaving more closed pores in the NdFeB matrix, which affects the densification degree of the cylindrical magnet block.

[0087] To further study the influence of each component and preparation parameters on the performance of the cylindrical magnet block, based on the preparation method of Example 1, the following examples are further carried out for verification in this application.

[0088] Examples 12, 13

[0089] In Examples 12 and 13, the composition and dosage of the basic raw materials are generally the same as those in Example 10. However, different from Example 10, the weight ratio of B₂O₃:SiO₂ in the B₂O₃ - SiO₂ sintering aids is different. In Example 12, the weight ratio of B₂O₃:SiO₂ is 3:1; in Example 13, the weight ratio of B₂O₃:SiO₂ is 12:1.

[0090] The cylindrical magnet blocks prepared in Example 12 and Example 13 are subjected to the above corrosion resistance test and magnetic property detection, and the test results are shown in Table 5.

[0091] Table 5 Performance Test Data Sheet of Example 10 and Examples 12, 13

[0092]

[0093] As can be seen from Table 5, the corrosion resistance of Example 10 is better than that of Example 12 and Example 13. In Example 12, when the content of SiO2 is too high, the viscosity of the B2O3-SiO2 sintering aid is relatively large after melting into a liquid state, and the fluidity is relatively low, making it difficult to penetrate between neodymium iron boron to fill the pores. In Example 10, when the weight ratio of B2O3 and SiO2 is appropriate, the fluidity of the B2O3-SiO2 sintering aid is better. In Example 13, when the content of SiO2 is too low, the effect of the B2O3-SiO2 sintering aid in filling the pores is relatively poor.

[0094] Examples 14 and 15

[0095] In Examples 14 and 15, the composition and dosage of the basic raw materials are generally the same as those in Example 10. However, different from Example 10, the particle sizes of the B2O3-SiO2 sintering aid are different. In Example 14, the particle sizes of both B2O3 and SiO2 are 10 - 30 μm, and in Example 15, the particle sizes of both B2O3 and SiO2 are 70 - 100 μm.

[0096] The cylindrical magnets prepared in Examples 14 - 15 were subjected to the above corrosion resistance test and magnetic property detection, and the test results are shown in Table 6.

[0097] Table 6 Performance detection data table of Example 10 and Examples 14 and 15

[0098]

[0099]

[0100] The smaller the average particle size of the B2O3-SiO2 sintering aid, the higher the melting efficiency, the larger the contact area with the neodymium iron boron magnetic material, the better the effect of the melted sintering aid in wetting the surface of the neodymium iron boron magnetic material, and the better the corrosion resistance of the finally obtained cylindrical magnet. However, if the average particle size of the B2O3-SiO2 sintering aid is too small, agglomeration is likely to occur, affecting the wetting effect. Therefore, in this application, the particle size of the B2O3-SiO2 sintering aid is controlled to be 50 - 70 μm, while ensuring the wetting effect and preventing agglomeration of the B2O3-SiO2 sintering aid.

[0101] Example 16

[0102] In Example 16, the composition and dosage of the basic raw materials are generally the same as those in Example 10. However, different from Example 10, during hydrogen breaking and grinding, an antioxidant is added to the hydrogen broken material after hydrogen breaking, and then airflow grinding is carried out.

[0103] The cylindrical magnet prepared in Example 16 was subjected to the above corrosion resistance test and magnetic property detection, and the test results are shown in Table 7.

[0104] Table 7 Performance Test Data Sheet of Example 10 and Example 16

[0105]

[0106] As can be seen from Table 7, the corrosion resistance of Example 16 is better than that of Example 10. After mixing the antioxidant and the NdFeB coarse powder after hydrogen breaking and carrying out air flow grinding together, the addition of the antioxidant reduces the probability of the rich Nd phase reacting with O to form oxides and limits the number of pores in the grain boundary, thereby improving the corrosion resistance of the product.

[0107] This specific embodiment is only an interpretation of the present application and does not limit the present application. Those skilled in the art can make modifications to this embodiment without creative contributions according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A corrosion-resistant sintered NdFeB magnetic material, characterized in that: By weight percentage, it includes PrNd: 25 - 29%, Cu: 0 - 2%, Zr: 1 - 2%, Co: 0 - 2%, Nb: 0 - 2%, Al: 1 - 2%, Ga: 0 - 2%, Y and / or Sc: 1 - 5%, Si: 2 - 4%, C: 0.1 - 0.2%, B: 1 - 1.5%, and the balance is Fe and unavoidable impurities; B2O3 - SiO2 sintering aids are added during sintering processing; The added weight of the B2O3 - SiO2 sintering aids accounts for 1 - 2% of the sintered Nd - Fe - B magnetic material; The weight ratio of B2O3:SiO2 in the B2O3 - SiO2 sintering aids is 9:1; The particle size of the B2O3 - SiO2 sintering aids is 50 - 70μm.

2. The preparation process of a corrosion-resistant sintered NdFeB magnetic material according to claim 1, characterized in that, It includes the following steps: Melt spinning: Add PrNd, Cu, Zr, Co, Nb, Al, Ga, Y and / or Sc, Fe, Si into a vacuum melting furnace according to the specified weight ratio. After high - temperature melting under argon protection, perform melt spinning; Hydrogen decrepitation and grinding: First, perform hydrogen decrepitation on the melt - spun thin sheets in a hydrogen decrepitation furnace, and then make them into powders in a jet mill; Compression molding: Place the powders obtained from hydrogen decrepitation and grinding into rubber molds of different shapes according to requirements, perform compression molding and vacuum packaging, and then perform isostatic pressing treatment to obtain a sintered green compact. The obtained sintered green compact includes, but is not limited to, cylinders; Sintering processing: Place the sintered green compact obtained from compression molding into a vacuum sintering furnace for sintering under the protection of nitrogen, and then perform tempering aging heat treatment to obtain a sintered Nd - Fe - B magnetic material, and perform surface processing on the obtained sintered Nd - Fe - B magnetic material.

3. The preparation process of a corrosion-resistant sintered NdFeB magnetic material according to claim 2, characterized in that: In the step of melt spinning, evacuate the vacuum melting furnace to a vacuum degree ≤1 Pa before melting.

4. The preparation process of a corrosion-resistant sintered NdFeB magnetic material according to claim 2, characterized in that: In the step of hydrogen decrepitation and grinding, add an antioxidant to the Nd - Fe - B coarse powder after hydrogen decrepitation, and then perform jet grinding.

5. The preparation process of a corrosion-resistant sintered NdFeB magnetic material according to claim 2, characterized in that: In the step of hydrogen decrepitation and grinding, the particle size of the magnetic powder after jet grinding is 2 - 6μm.

6. A cylindrical magnetic block, characterized in that: It is made of the sintered Nd - Fe - B magnetic material as described in claim 1.

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