High-temperature-resistant neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention relates to the technical field of permanent magnet preparation, and particularly discloses a high-temperature-resistant neodymium-iron-boron magnet and a preparation method thereof. The high-temperature-resistant neodymium-iron-boron magnet comprises the following elements in percentage by mass: 17.4%-19.5% of Nd, 0.66%-0.72% of B, 38.37%-41.19% of Fe, 0.36%-4.8% of Dy, 0.18%-0.3% of Nb, 0.18%-0.3% of Al, 0.03%-0.09% of Cu, 29.1%-34.8% of an alloy rapid hardening sheet and the balance of unremovable impurities, wherein the alloy rapid hardening sheet contains Pr, Tb, Bi and Sn; the preparation method comprises the following steps: grinding the surface of an alloy rapid hardening sheet to be bright, mixing the alloy rapid hardening sheet with a pretreated magnet block, adding zirconium oxide balls, putting into a reaction kettle of a rotary diffusion furnace, vacuumizing the reaction kettle, introducing argon, rotating at the rotating speed of 4-6r / min, keeping the temperature at 700-704 DEG C for 3-7h, and carrying out rotary diffusion, so as to obtain the zirconium oxide-based composite material. And then carrying out heat preservation at 850-950 DEG C for 2-4 hours for high-temperature diffusion and heat preservation at 450-550 DEG C for 2-4 hours for tempering heat treatment by using a vacuum tube furnace in a vacuum environment. The high-temperature-resistant neodymium-iron-boron magnet has the advantage that the defect that heat resistance of a conventional neodymium-iron-boron magnet is still insufficient is overcome.

Description

Technical Field

[0001] This application relates to the field of permanent magnet preparation technology, and more specifically, to a high-temperature resistant neodymium iron boron magnet and its preparation method. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets, as the world's most outstanding rare-earth permanent magnet material in terms of comprehensive performance, possess excellent properties such as high energy product and high remanence, earning them the reputation of "King of Permanent Magnets." They have broad application prospects in fields such as information and communication, new energy, and medical devices. With the adjustment of my country's economic structure and the advancement of energy conservation and emission reduction policies, emerging industries such as new energy vehicles and wind power generation are rapidly rising, significantly increasing the market demand for high-performance NdFeB permanent magnets. This is also driving innovation in NdFeB magnet manufacturing technology, especially with increasingly stringent requirements for long-term service at high operating temperatures, meaning that the overall magnetic properties of NdFeB magnets need to reach a new level.

[0003] Intrinsic coercivity (H) cj The intrinsic coercivity H of neodymium iron boron magnets at room temperature has always been one of the most important technical parameters. cj The higher the value, the better the stability at high temperatures, thus enabling operation at even higher temperatures, which improves the intrinsic coercivity H of NdFeB magnets. cj Heavy rare earth elements are often added to the formulation. However, these elements are scarce resources, leading to an imbalance in the utilization of rare earth resources and increasing the cost of raw materials. Adding cobalt (Co) is also used to improve the temperature coefficient of NdFeB magnets. However, adding Co easily forms a soft magnetic phase at grain boundaries, thereby reducing the intrinsic coercivity (H) of the magnet. cj Therefore, there is an urgent need for a new technical method to improve the heat resistance of neodymium iron boron magnets. Summary of the Invention

[0004] To address the shortcomings of conventional NdFeB magnets in terms of heat resistance, this application provides a high-temperature resistant NdFeB magnet and its preparation method.

[0005] In the first aspect, this application provides a high-temperature resistant neodymium iron boron magnet, which adopts the following technical solution:

[0006] A high-temperature resistant neodymium iron boron magnet comprises the following elements by mass percentage: Nd 17.4-19.5%, B 0.66-0.72%, Fe 38.37-41.19%, Dy 0.36-4.8%, Nb 0.18-0.3%, Al 0.18-0.3%, Cu 0.03-0.09%, alloy quick-setting flakes 29.1-34.8%, with the balance being non-removable impurities, wherein the alloy quick-setting flakes contain Pr, Tb, Bi, and Sn.

[0007] Because heavy rare earth element Tb is a scarce resource with high production costs and relatively low utilization, while the addition of Pr can improve the magnetic properties of magnets at high temperatures, enabling the magnets to maintain stable magnetic properties over a wide temperature range, the partial replacement of Tb with Pr can reduce the amount of heavy rare earth element Tb added without affecting the high-temperature stability of NdFeB magnets.

[0008] Meanwhile, both Bi and Sn have low melting points. The low-melting-point metal BiSn alloy is conducive to promoting the uniform distribution of grain boundary phases. The wettability of the grain boundary phases is enhanced, which promotes the diffusion of Tb into the interior of the magnet and forms a core-shell structure with a high magnetocrystalline anisotropy field. This improves the coercivity of the magnet and reduces the degradation of the magnet's magnetic properties at high temperatures.

[0009] Preferably, the alloy quick-setting sheet comprises the following elements by mass percentage: Pr 26-30%, Tb 0.7-1.3%, Bi 0.9-1.2%, and Sn 0.8-1%.

[0010] Preferably, the alloy quick-setting sheet is added via rotary diffusion.

[0011] Rotational diffusion is essentially vapor deposition diffusion. Vapor deposition involves placing heavy rare earth elements and their compounds along with sheet-like permanent magnet samples inside a vapor deposition furnace. High-temperature heating causes the heavy rare earth elements to sublimate and deposit onto the surface of the diffusion sample under the induction of their gas. Simultaneously, this high-temperature environment promotes the diffusion of heavy rare earth elements into the interior of the magnet, and the high-temperature treatment helps stabilize the internal structure of the magnet, reducing the degradation of magnetic properties after heat treatment, thereby helping to maintain high coercivity at high temperatures.

[0012] Preferably, the alloy quick-setting sheet also contains Mo and Ti.

[0013] Due to the poor corrosion resistance of NdFeB magnets, they are prone to electrochemical corrosion, oxidative corrosion, and hydrogen absorption corrosion during use, resulting in poor environmental stability and greatly limiting their use in complex environments such as high temperature and humidity. The presence of Cu in NdFeB magnets reduces the potential difference between phases and improves corrosion resistance. At the same time, during corrosion, unoxidized Cu forms a barrier layer, which helps to prevent the migration of point defects and thus slows down the corrosion rate. Mo has a more significant effect on the corrosion resistance of magnets in acidic solutions than Cu. Adding Mo to the alloy helps to increase the corrosion potential and reduce the corrosion current density. Ti has a high passivation ability. In most aqueous solutions, Ti exhibits a low critical passivation potential and a wide passivation region, thus having excellent corrosion resistance.

[0014] Preferably, the mass percentage of Mo is 0.6-0.9%, and the mass percentage of Ti is 0.1-0.4%.

[0015] Preferably, the preparation method of the alloy quick-setting sheet is as follows: Pr, Tb, Bi, Sn, Mo and Ti are loaded into the quick-setting furnace according to the ratio, vacuum is gradually drawn, low-power preheating is used to remove the moisture and adsorbed impurities of the furnace charge, vacuum is continued, argon gas is introduced, medium-frequency current is introduced to melt the furnace charge, heating is carried out, stirring is performed for 3-5 minutes, the alloy liquid is poured onto the surface of a water-cooled copper roller with a roller speed of 1.1-1.3 m / s, and finally cooled to obtain the alloy quick-setting sheet.

[0016] Secondly, this application provides a method for preparing a high-temperature resistant neodymium iron boron magnet, which adopts the following technical solution:

[0017] A method for preparing a high-temperature resistant neodymium iron boron magnet includes the following steps:

[0018] S1: Nd, B, Fe, Dy, Nb, Al, and Cu are added to a vacuum atmosphere sintering furnace in a certain proportion and nitrogen is introduced. The mixture is then smelted to obtain a strip, which is then milled by hydrogen crushing and grinding to obtain neodymium iron boron magnetic powder.

[0019] S2: Place neodymium iron boron magnetic powder in a molding die and press it to obtain a green blank, and then press it in a static press to obtain a pre-treated magnet block;

[0020] S3: The pretreated magnet block is acid-washed in a 3.5%-4.5% nitric acid solution, then ultrasonically cleaned with deionized water, and finally poured into anhydrous ethanol to dehydrate and dry for later use.

[0021] S4: After polishing the surface of the alloy quick-setting sheet to a bright finish, mix it with the pretreated magnet block, add zirconia balls, and place it in the reaction vessel of a rotary diffusion furnace. Evacuate the reaction vessel, then introduce argon gas and rotate it at a speed of 4-6 r / min. Hold it at 700-704℃ for 3-7 hours for rotary diffusion. Then, use a vacuum tube furnace to perform high-temperature diffusion at 850-950℃ for 2-4 hours and tempering heat treatment at 450-550℃ for 2-4 hours in a vacuum environment.

[0022] Preferably, the mass ratio of the alloy quick-setting sheet, the pretreated magnet block, and the zirconia ball is (1-3):(0.5-1.5):(0.5-1.5).

[0023] Zirconia balls can assist in stirring and have the characteristics of high temperature resistance and high wear resistance. Reacting alloy quick-setting sheets, pretreated magnet blocks and zirconia balls in a mass ratio of (1-3):(0.5-1.5):(0.5-1.5) helps to improve the uniform distribution of elements in the magnet, thereby improving the coercivity of the magnet.

[0024] In summary, this application has the following beneficial effects:

[0025] 1. Since the production cost of heavy rare earth element Tb is too high and the utilization rate is relatively low as a scarce resource, while the addition of Pr can improve the magnetic properties of magnets at high temperatures, so that the magnets can maintain stable magnetic properties over a wide temperature range, the use of Pr to partially replace Tb can reduce the amount of heavy rare earth element Tb added without affecting the high-temperature stability of NdFeB magnets.

[0026] Meanwhile, both Bi and Sn have low melting points. The low-melting-point metal BiSn alloy is conducive to promoting the uniform distribution of grain boundary phases. The wettability of the grain boundary phases is enhanced, which promotes the diffusion of Tb into the interior of the magnet and forms a core-shell structure with a high magnetocrystalline anisotropy field. This improves the coercivity of the magnet and reduces the degradation of the magnet's magnetic properties at high temperatures.

[0027] 2. Rotational diffusion is essentially vapor deposition diffusion. Vapor deposition involves placing heavy rare earth elements and their compounds along with sheet-like permanent magnet samples in the chamber of a vapor deposition furnace. High-temperature heating causes the heavy rare earth elements to sublimate and deposit onto the surface of the diffusion sample under the induction of their gas. At the same time, this high-temperature environment promotes the diffusion of heavy rare earth elements into the interior of the magnet, and the high-temperature treatment helps stabilize the internal structure of the magnet, reducing the degradation of magnetic properties after heat treatment, thereby helping to maintain high coercivity at high temperatures.

[0028] 3. Due to the poor corrosion resistance of NdFeB magnets, they are prone to electrochemical corrosion, oxidative corrosion, and hydrogen absorption corrosion during use, resulting in poor environmental stability and greatly limiting their use in complex environments such as high temperature and humidity. The presence of Cu in NdFeB magnets reduces the potential difference between phases and improves corrosion resistance. At the same time, during corrosion, unoxidized Cu forms a barrier layer, which helps to prevent the migration of point defects and thus slows down the corrosion rate. Mo has a more significant effect on the corrosion resistance of magnets in acidic solutions than Cu. Adding Mo to the alloy helps to increase the corrosion potential and reduce the corrosion current density. Ti has a high passivation ability. In most aqueous solutions, Ti exhibits a low critical passivation potential and a wide passivation region, thus having excellent corrosion resistance. Detailed Implementation

[0029] The present application will be further described in detail below with reference to Examples 1-10 and Comparative Examples 1-3.

[0030] raw material

[0031] Nd, B, Fe, Dy, Nb, Al, Cu, Pr, Tb, Bi, Sn, Mo, and Ti were all purchased from Chengdu Lingliu Biotechnology Co., Ltd.; Nitric acid CAS: 7697-37-2; Anhydrous ethanol CAS: 64-17-5; Zirconia spheres were purchased from Hangzhou Jiuli Biomaterials Co., Ltd.

[0032] Example

[0033] Example 1

[0034] A high-temperature resistant neodymium iron boron magnet comprises the following elements by mass percentage: Nd 18.45%, B 0.69%, Fe 39.78%, Dy 2.58%, Nb 0.24%, Al 0.24%, Cu 0.06%, alloy quick-setting flakes 31.95%, with the balance being non-removable impurities.

[0035] Specifically, the preparation method of high-temperature resistant NdFeB magnets includes the following steps:

[0036] S1: 18.45% Nd, 0.69% B, 39.78% Fe, 2.58% Dy, 0.24% Nb, 0.24% Al, and 0.06% Cu were added to a vacuum atmosphere sintering furnace and nitrogen gas was introduced. The mixture was smelted to obtain a strip, which was then milled by hydrogen gas to obtain 3.15μm NdFeB magnetic powder.

[0037] S2: Place neodymium iron boron magnetic powder in a molding die and press it to obtain a green blank, and then press it in a static press to obtain a pre-treated magnet block;

[0038] S3: The pretreated magnet block is acid-washed in a 4% nitric acid solution, then ultrasonically cleaned with deionized water, and finally poured into anhydrous ethanol to dehydrate and dry for later use.

[0039] S4: After polishing the surface of the alloy quick-setting sheet to a bright finish, mix it with the pretreated magnet block and add zirconia balls. The mass ratio of the alloy quick-setting sheet, the pretreated magnet block and the zirconia balls is 2:1:1. Then, place it in the reactor of a rotary diffusion furnace, first evacuate to 6×10-3 Pa, then introduce argon gas as a protective atmosphere, rotate at a speed of 5 r / min and hold at 702℃ for 5 h for rotary diffusion, then use a vacuum tube furnace to perform high-temperature diffusion at 900℃ for 3 h and tempering heat treatment at 500℃ for 3 h in a vacuum environment, and finally cool to obtain high-temperature resistant NdFeB magnets.

[0040] The preparation method of the alloy rapid solidification sheet is as follows: 28% Pr, 1% Tb, 1.05% Bi, 0.9% Sn, 0.75% Mo, and 0.25% Ti are loaded into the crucible of a vacuum induction melting rapid solidification furnace. The furnace door is then closed, and the vacuum is gradually evacuated to 10⁻³ Pa. Low-power preheating is used to remove moisture and adsorbed impurities from the furnace charge. At this point, the vacuum level decreases, and the vacuum is further evacuated to 10⁻³ Pa. High-purity argon gas (purity exceeding 99.9%) is introduced, and a medium-frequency current is introduced to melt the furnace charge. Then, high-power heating is used to melt and clear all the furnace charge. Electromagnetic refining and stirring are performed for 3-5 minutes to ensure uniform alloy composition. The molten alloy is then poured through the nozzle of an tundish onto the surface of a water-cooled copper roller with a roller speed of 1.2 m / s. Finally, cooling is performed to obtain an alloy rapid solidification sheet with a thickness of approximately 0.5 mm.

[0041] Example 2-3

[0042] The difference from Example 1 is that the mass percentages of each component in the high-temperature resistant NdFeB magnet are different, as shown in Table 1.

[0043] Table 1. Mass percentage of each component in the high-temperature resistant NdFeB magnets of Examples 1-3 (%)

[0044] Example 1 Example 2 Example 3 Nd 18.45 17.4 19.5 B 0.69 0.72 0.66 Fe 39.78 41.19 38.37 Dy 2.58 0.36 4.8 Nb 0.24 0.18 0.3 Al 0.24 0.3 0.18 Cu 0.06 0.03 0.09 Alloy quick-setting tablets 31.95 34.8 29.4 impurities margin margin margin

[0045] Example 4

[0046] The difference from Example 1 is that Pr, Tb, Bi, Sn, Mo and Ti are mixed with Nd, B, Fe, Dy, Nb, Al and Cu to prepare neodymium iron boron magnetic powder;

[0047] The preparation method of NdFeB magnetic powder is as follows: Nd, B, Fe, Dy, Nb, Al, Cu, Pr, Tb, Bi, Sn, Mo and Ti are added to a vacuum atmosphere sintering furnace in a certain proportion and nitrogen gas is introduced. The mixture is then smelted to obtain a strip, which is then milled by hydrogen gas to obtain NdFeB magnetic powder.

[0048] Example 5

[0049] The difference from Example 1 is that Pr, Tb, Bi, and Sn are added in the form of alloy quick-setting tablets, and Mo and Ti are also added in the form of alloy quick-setting tablets.

[0050] The preparation method of PrTbBiSn alloy quick-setting sheet is as follows: Pr, Tb, Bi and Sn are loaded into a quick-setting furnace according to the ratio, vacuum is gradually drawn, low-power preheating is used to remove the moisture and adsorbed impurities of the furnace charge, vacuum is continued, argon gas is introduced, medium frequency current is introduced to melt the furnace charge, heating is carried out, stirring is carried out for 4 minutes, the alloy liquid is poured onto the surface of a water-cooled copper roller with a roller speed of 1.2m / s, and finally cooled to obtain PrTbBiSn alloy quick-setting sheet;

[0051] Preparation method of MoTi alloy rapid solidification sheet: Mo and Ti are loaded into the rapid solidification furnace according to the ratio, the furnace is gradually evacuated, the furnace charge is preheated at low power to remove moisture and adsorbed impurities, the furnace charge is evacuated again, argon gas is introduced, medium frequency current is introduced to melt the furnace charge, the furnace charge is heated and stirred for 4 minutes, the alloy liquid is poured onto the surface of a water-cooled copper roller with a roller speed of 1.2 m / s, and finally cooled to obtain MoTi alloy rapid solidification sheet.

[0052] Preparation method of high temperature resistant NdFeB magnets: After polishing the surfaces of PrTbBiSn alloy quick-setting sheets and MoTi alloy quick-setting sheets, they are mixed together with pretreated magnet blocks and zirconia balls are added. The mass ratio of PrTbBiSn alloy quick-setting sheets, MoTi alloy quick-setting sheets, pretreated magnet blocks and zirconia balls is 1:1:1:1. The mixture is placed in the reactor of a rotary diffusion furnace, the reactor is evacuated, and then argon gas is introduced. The reactor is rotated at a speed of 5 r / min and held at 702℃ for 5 h for rotary diffusion. Then, a vacuum tube furnace is used to perform high temperature diffusion at 900℃ for 3 h and tempering heat treatment at 500℃ for 3 h in a vacuum environment.

[0053] Example 6

[0054] The difference from Example 1 is that the alloy quick-setting sheet is added by grain boundary diffusion.

[0055] Examples 7-8

[0056] The difference from Example 1 is that the mass percentage of each component in the alloy quick-setting sheet is different, as shown in Table 2.

[0057] Table 2. Mass percentage of each component in the alloy rapid-setting sheets of Examples 1 and 7-8 (%)

[0058] Example 1 Example 7 Example 8 Pr 28 26 30 Tb 1 0.7 1.3 Bi 1.05 1.2 0.9 Sn 0.9 0.8 1 Mo 0.75 0.9 0.6 Ti 0.25 0.4 0.1

[0059] Examples 9-10

[0060] The difference from Example 1 is that the mass ratio of the alloy quick-setting sheet, the pretreated magnet block, and the zirconia ball is different, as shown in Table 3.

[0061] Table 3. Mass ratio of alloy quick-setting sheet, pretreated magnet block and zirconia ball in Examples 1 and 9-10

[0062] Example 1 Example 9 Example 10 Alloy quick-setting tablets 2 1 3 Pre-processed magnet blocks 1 1.5 0.5 Zirconia spheres 1 0.5 1.5

[0063] Comparative Example

[0064] Comparative Example 1

[0065] The difference from Example 1 is that no alloy quick-setting tablets are added.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that Pr, Tb, Bi, and Sn are no longer added.

[0068] Comparative Example 3

[0069] The difference from Example 1 is that Mo and Ti are no longer added.

[0070] Performance testing

[0071] Detection methods

[0072] I. High Temperature Resistance Test

[0073] Three samples were taken from Examples 1-10 and Comparative Examples 1-3 respectively. The high-temperature magnetic properties of the samples were then tested in accordance with GB / T13560-2017 "Sintered NdFeB Permanent Magnet Materials", and the average value was taken.

[0074] The test data are shown in Table 4.

[0075] Table 4. High-Temperature Resistance Test Results of Examples 1-10 and Comparative Examples 1-3

[0076] Innate coercivity (kOe) Maximum operating temperature (°C) Example 1 35.72 257 Example 2 35.65 254 Example 3 35.66 255 Example 4 34.52 241 Example 5 34.81 245 Example 6 34.93 247 Example 7 35.70 253 Example 8 35.68 251 Example 9 35.61 249 Example 10 35.65 250 Comparative Example 1 33.14 192 Comparative Example 2 33.56 213 Comparative Example 3 35.47 252

[0077] II. Corrosion Resistance Test

[0078] Three samples were taken from Examples 1-10 and Comparative Examples 1-3 respectively. The samples were immersed in a sodium chloride aqueous solution with a concentration of 50 g / L for a neutral salt spray test at a temperature of 30°C. After immersion, the weight loss rate of the neodymium iron boron magnet was calculated as: weight loss rate = (mass before immersion - mass after immersion) / mass before immersion, and the average value was taken.

[0079] The test data are shown in Table 5.

[0080] Table 5. Corrosion resistance test results (%) for Examples 1-10 and Comparative Examples 1-3

[0081] 24-hour weightlessness rate 72h weightlessness rate 144h weightlessness rate Example 1 0.009 0.027 0.053 Example 2 0.012 0.031 0.058 Example 3 0.011 0.029 0.057 Example 4 0.028 0.046 0.077 Example 5 0.017 0.035 0.066 Example 6 0.015 0.032 0.064 Example 7 0.013 0.03 0.059 Example 8 0.014 0.033 0.061 Example 9 0.016 0.036 0.065 Example 10 0.018 0.039 0.067 Comparative Example 1 0.041 0.071 0.108 Comparative Example 2 0.022 0.037 0.069 Comparative Example 3 0.038 0.056 0.087

[0082] Combining Example 1 and Comparative Example 1 with Tables 4-5, it can be seen that, compared with Example 1, the intrinsic coercivity and maximum operating temperature of Comparative Example 1 are significantly reduced. At the same time, the weight loss rate of Comparative Example 1 at 24h, 72h and 144h is significantly increased. This shows that, compared with conventional NdFeB magnets, the addition of alloy quick-setting sheets can effectively improve the high temperature resistance and corrosion resistance of NdFeB magnets.

[0083] Combining Example 1 and Comparative Example 2 with Tables 4-5, it can be seen that, compared with Example 1, the intrinsic coercivity and maximum operating temperature of Comparative Example 2 are significantly reduced. At the same time, the weight loss rate of Comparative Example 2 at 24h, 72h and 144h is also increased. This shows that, compared with not adding Pr, Tb, Bi and Sn, adding Pr, Tb, Bi and Sn can effectively improve the high temperature resistance of NdFeB magnets and affect the corrosion resistance of NdFeB magnets to a certain extent.

[0084] The reason for this is that both Bi and Sn have low melting points. Low-melting-point BiSn alloys are conducive to promoting the uniform distribution of grain boundary phases. The wettability of the grain boundary phases is enhanced, which promotes the diffusion of Tb into the interior of the magnet, forming a core-shell structure with a high magnetocrystalline anisotropy field. This improves the coercivity of the magnet and reduces the degradation of the magnet's magnetic properties at high temperatures.

[0085] Based on Example 1 and Comparative Example 3, and referring to Tables 4-5, it can be seen that, compared to Example 1, the intrinsic coercivity and maximum operating temperature of Comparative Example 3 are both reduced. At the same time, the weight loss rate of Comparative Example 3 at 24h, 72h, and 144h is significantly increased. This indicates that, compared to not adding Mo and Ti, adding Mo and Ti can effectively improve the corrosion resistance of NdFeB magnets and, to some extent, affect the high-temperature resistance of NdFeB magnets.

[0086] The presence of Cu in NdFeB magnets reduces the potential difference between phases and improves corrosion resistance. During corrosion, unoxidized Cu forms a barrier layer, which helps prevent the migration of point defects and thus slows down the corrosion rate. Mo has a more significant effect on the corrosion resistance of magnets in acidic solutions than Cu. Adding Mo to the alloy helps to increase the corrosion potential and reduce the corrosion current density. Ti has a high passivation capability. In most aqueous solutions, Ti exhibits a low critical passivation potential and a wide passivation region, thus possessing excellent corrosion resistance.

[0087] Combining Examples 1 and 2-3 with Tables 4-5, it can be seen that, compared with Example 1, the intrinsic coercivity and maximum operating temperature of Examples 2 and 3 are both reduced, and the weight loss rates of Examples 2 and 3 at 24h, 72h, and 144h are also increased. This indicates that the mass percentage of each component of the high-temperature resistant NdFeB magnet affects the high-temperature resistance and corrosion resistance of the NdFeB magnet.

[0088] Combining Examples 1 and 4 with Tables 4-5, it can be seen that, compared with Example 1, the intrinsic coercivity and maximum operating temperature of Example 4 are significantly reduced. At the same time, the weight loss rate of Example 4 at 24h, 72h and 144h is also significantly increased. This indicates that directly mixing Pr, Tb, Bi, Sn, Mo and Ti with Nd, B, Fe, Dy, Nb, Al and Cu to prepare NdFeB magnetic powder will reduce the high temperature resistance and corrosion resistance of NdFeB magnets.

[0089] Combining Examples 1 and 5 with Tables 4-5, it can be seen that, compared with Example 1, the intrinsic coercivity and maximum operating temperature of Example 5 are both reduced. At the same time, the weight loss rate of Example 5 at 24h, 72h and 144h is also increased. This indicates that adding Pr, Tb, Bi, Sn and Mo, Ti in the form of alloy quick-setting flakes affects the high temperature resistance and corrosion resistance of NdFeB magnets to a certain extent.

[0090] Combining Examples 1 and 6 with Tables 4-5, it can be seen that, compared with Example 1, the intrinsic coercivity and maximum operating temperature of Example 6 are both reduced. At the same time, the weight loss rate of Example 6 at 24h, 72h, and 144h is also increased. This indicates that, compared with adding alloy quick-setting sheets by grain boundary diffusion, the rotational diffusion method can more effectively improve the high-temperature resistance and corrosion resistance of NdFeB magnets.

[0091] The reason for this is that the essence of rotational diffusion is vapor deposition diffusion. Vapor deposition involves placing heavy rare earth elements and their compounds along with sheet-like permanent magnet samples in the chamber of a vapor deposition furnace. High-temperature heating causes the heavy rare earth elements to sublimate and deposit onto the surface of the diffusion sample under the induction of their gas. At the same time, this high-temperature environment promotes the diffusion of heavy rare earth elements into the interior of the magnet, and the high-temperature treatment helps stabilize the internal structure of the magnet, reducing the degradation of magnetic properties after heat treatment, thereby helping to maintain high coercivity at high temperatures.

[0092] Combining Examples 1 and 7-8 with Tables 4-5, it can be seen that, compared with Example 1, the intrinsic coercivity and maximum operating temperature of Examples 7 and 8 are both reduced. At the same time, the weight loss rates of Examples 7 and 8 at 24h, 72h and 144h are also increased. This indicates that the mass percentage of each component in the alloy quick-setting sheet also affects the high-temperature resistance and corrosion resistance of NdFeB magnets to a certain extent.

[0093] Combining Examples 1 and 9-10 with Tables 4-5, it can be seen that, compared with Example 1, the intrinsic coercivity and maximum operating temperature of Examples 9 and 10 have decreased. At the same time, the weight loss rates of Examples 9 and 10 at 24h, 72h, and 144h have increased. This indicates that the mass ratio of gold quick-setting sheet, pretreated magnet block, and zirconia ball affects the high-temperature resistance and corrosion resistance of NdFeB magnets to a certain extent.

[0094] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-temperature resistant neodymium iron boron magnet, characterized in that, The alloy comprises the following elements by mass percentage: Nd 17.4-19.5%, B 0.66-0.72%, Fe 38.37-41.19%, Dy 0.36-4.8%, Nb 0.18-0.3%, Al 0.18-0.3%, Cu 0.03-0.09%, and alloy quick-setting flakes 29.1-34.8%, with the balance being non-removable impurities. The alloy quick-setting flakes contain Pr, Tb, Bi, and Sn.

2. The high-temperature resistant neodymium iron boron magnet according to claim 1, characterized in that: The alloy quick-setting sheet comprises the following elements by mass percentage: Pr 26-30%, Tb 0.7-1.3%, Bi 0.9-1.2%, and Sn 0.8-1%.

3. A high-temperature resistant neodymium iron boron magnet according to claim 2, characterized in that: The alloy quick-setting sheet is added via rotary diffusion.

4. A high-temperature resistant neodymium iron boron magnet according to claim 3, characterized in that: The alloy quick-setting sheet also contains Mo and Ti.

5. A high-temperature resistant neodymium iron boron magnet according to claim 4, characterized in that: The mass percentage of Mo is 0.6-0.9%, and the mass percentage of Ti is 0.1-0.4%.

6. A high-temperature resistant neodymium iron boron magnet according to claim 5, characterized in that, The preparation method of the alloy quick-setting sheet is as follows: Pr, Tb, Bi, Sn, Mo and Ti are loaded into the quick-setting furnace according to the ratio, the furnace is gradually evacuated, and the furnace charge is preheated at low power to remove moisture and adsorbed impurities. The furnace charge is then evacuated again, argon gas is introduced, and medium frequency current is introduced to melt the furnace charge. The furnace charge is heated and stirred for 3-5 minutes. The alloy liquid is then poured onto the surface of a water-cooled copper roller with a roller speed of 1.1-1.3 m / s. Finally, the furnace charge is cooled to obtain the alloy quick-setting sheet.

7. A method for preparing a high-temperature resistant neodymium iron boron magnet according to any one of claims 1-6, characterized in that, Includes the following steps: S1: Nd, B, Fe, Dy, Nb, Al, and Cu are added to a vacuum atmosphere sintering furnace in a certain proportion and nitrogen is introduced. The mixture is then smelted to obtain a strip, which is then milled by hydrogen crushing and grinding to obtain neodymium iron boron magnetic powder. S2: Place neodymium iron boron magnetic powder in a molding die and press it to obtain a green blank, and then press it in a static press to obtain a pre-treated magnet block; S3: The pretreated magnet block is acid-washed in a 3.5%-4.5% nitric acid solution, then ultrasonically cleaned with deionized water, and finally poured into anhydrous ethanol to dehydrate and dry for later use. S4: After polishing the surface of the alloy quick-setting sheet to a bright finish, mix it with the pretreated magnet block, add zirconia balls, and place it in the reaction vessel of a rotary diffusion furnace. Evacuate the reaction vessel, then introduce argon gas and rotate it at a speed of 4-6 r / min. Hold it at 700-704℃ for 3-7 hours for rotary diffusion. Then, use a vacuum tube furnace to perform high-temperature diffusion at 850-950℃ for 2-4 hours and tempering heat treatment at 450-550℃ for 2-4 hours in a vacuum environment.

8. The method for preparing a high-temperature resistant neodymium iron boron magnet according to claim 7, characterized in that: The mass ratio of the alloy quick-setting sheet, the pretreated magnet block, and the zirconia spheres is (1-3):(0.5-1.5):(0.5-1.5).