High-coercivity sintered neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention discloses a high-coercivity sintered neodymium-iron-boron magnet and a preparation method thereof, and the method comprises the following steps: depositing an aluminum film on the surface of a to-be-diffused sintered neodymium-iron-boron magnet to obtain a semi-finished product I; heavy rare earth powder is sprayed on the surface of the aluminum film through the thermal spraying technology, and a semi-finished product II is obtained; and performing high-temperature heat treatment on the semi-finished product II, and cooling to obtain the high-coercivity sintered neodymium-iron-boron magnet. The low-melting-point metal aluminum film is deposited on the surface of the magnet in advance, then the heavy rare earth powder is bonded to the surface of the magnet through the thermal spraying technology, the low-melting-point metal aluminum serves as an adhesive, the utilization rate of a diffusion source is increased, and the coercive force improving effect is improved. According to the method, the adverse effect of the organic binder in the high-temperature diffusion process is avoided, the diffusion process is further optimized through the two-stage heat treatment technology of low-temperature alloying and high-temperature diffusion, and the comprehensive performance of the magnet is improved.

Description

Technical Field

[0001] The present invention relates to the field of rare earth permanent magnetic materials, in particular to a high-coercivity sintered NdFeB magnet and a preparation method thereof. Background Art

[0002] During the preparation of sintered NdFeB magnets, increasing their coercivity is a key goal for enhancing magnetic properties. Currently, commonly used methods for increasing coercivity include directly adding heavy rare earth elements (such as Dy and Tb) during alloy smelting, adding powder containing heavy rare earth elements to the powder through a dual alloying method, and introducing heavy rare earth elements into the magnet through grain boundary diffusion. Of these, grain boundary diffusion has become the most widely used method due to its lower cost and higher performance improvement.

[0003] Currently, grain boundary diffusion technologies primarily include magnetron sputtering-diffusion and spray-diffusion. The magnetron sputtering-diffusion method uses a magnetron sputtering device to deposit a diffusion source rich in heavy rare earth elements on the magnet surface, followed by a diffusion heat treatment. However, this method operates in a vacuum environment, and some of the sputtered heavy rare earth atoms are extracted by the vacuum system. As a result, the amount of diffusion source actually deposited on the magnet surface is only about 50% of the target material consumed, resulting in a low utilization rate.

[0004] The spray-diffusion method uses a spray coating to apply a diffusion source rich in heavy rare earth elements mixed with an organic binder to the magnet surface, followed by a diffusion heat treatment. However, during the high-temperature diffusion process, the organic binder chemically reacts with the diffusion source, causing some of the diffusion source to be carbonized, nitrided, or oxidized, thereby reducing the diffusion efficiency and the increase in coercivity. Summary of the Invention

[0005] In light of this, the present invention provides a high-coercivity sintered NdFeB magnet and its preparation method. This method pre-deposits a low-melting-point aluminum film on the magnet surface, then thermally sprays a heavy rare earth-rich powder onto the magnet surface. Using the low-melting-point aluminum as a binder, this method improves diffusion source utilization and enhances coercivity. This method not only avoids the adverse effects of organic binders during high-temperature diffusion, but also, through a two-stage heat treatment process involving low-temperature alloying and high-temperature diffusion, further optimizes the diffusion process and improves the overall performance of the magnet.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention discloses a method for preparing a high coercivity sintered NdFeB magnet, comprising the following steps:

[0008] Deposit aluminum film on the surface of the NdFeB magnet to be diffused and sintered to obtain a semi-finished product I ;

[0009] Use thermal spraying process to spray heavy rare earth powder on the surface of aluminum film to obtain semi-finished products II ;

[0010] The semi-finished product II After high-temperature heat treatment and cooling, a high-coercivity sintered NdFeB magnet is obtained.

[0011] Further solution: the NdFeB magnet to be diffused and sintered is RE2Fe 14 B is the main magnetic phase, and its volume accounts for no less than 95% of the total volume of the magnet.

[0012] The present invention pre-deposits a layer of low-melting-point metal aluminum film on the surface of a sintered NdFeB magnet, then thermally sprays rich heavy rare earth powder, utilizes the heat of the rich heavy rare earth powder to melt the aluminum film layer in contact with the rich heavy rare earth powder, thereby achieving adhesion of the rich heavy rare earth powder to the magnet surface, and then performs a two-stage heat treatment of low-temperature alloying and high-temperature diffusion. The heat is kept below the melting point of the metal aluminum for a period of time to promote an alloying reaction between the rich heavy rare earth powder and the metal aluminum, thereby preventing the problem of diffusion source powder falling off due to melting of the metal aluminum caused by direct heating to above the melting point of the metal aluminum. After the alloying reaction, the temperature is raised to a diffusion temperature above the melting point of the metal aluminum, so that aluminum atoms can diffuse into the grain boundary phase of the magnet, lowering the melting point of the grain boundary phase, promoting the diffusion movement of heavy rare earth metal atoms from the magnet surface to the inside of the magnet, and improving the coercive force of the magnet.

[0013] The diffusion sintered NdFeB magnets mentioned in this article refer to RE2Fe 14 A magnet with B phase as the main magnetic phase, wherein RE is at least one of the rare earth elements, and the rare earth element can be neodymium (Nd), dysprosium (Dy), praseodymium (Pr), etc., without special restrictions; the preparation of the diffusion-sintered NdFeB magnet has no special restrictions and can be carried out using conventional preparation processes in the art. In one or more embodiments of the present invention, the diffusion-sintered NdFeB magnet is prepared by a powder metallurgy process.

[0014] A further solution is that the thickness of the aluminum film is 0.5-2 μm. There is no particular limitation on the coating surface of the metal aluminum film layer on the NdFeB magnet to be diffused and sintered. It can be any one surface or any multiple surfaces such as two, three, or four surfaces. The coating surface can be selected based on the shape of the NdFeB magnet to be diffused and sintered and the diffusion requirements. The main function of the metal aluminum film is to bond the rich heavy rare earth diffusion source to the magnet surface. It should not be too thick or too thin. Generally speaking, the thickness of the metal aluminum film layer is controlled to be above 0.5 μm and below 2 μm, otherwise it will affect the subsequent penetration effect.

[0015] A further solution: the average particle size D50 of the heavy rare earth-rich powder is 5 to 20 μm, and it is at least one of a heavy rare earth element, a heavy rare earth hydride, and a heavy rare earth alloy; in the heavy rare earth-rich powder, the heavy rare earth element accounts for more than 50% of the total weight; the heavy rare earth is selected from at least one of dysprosium and terbium.

[0016] Because the aluminum film is only a thin layer, it can only adhere to a layer of heavy rare earth-rich powder on the magnet surface. The particle size of the heavy rare earth-rich powder directly affects the amount of diffusion source attached (the larger the powder particle size, the greater the attachment amount; the smaller the powder particle size, the less attachment amount). The amount of diffusion source attached can be adjusted by adjusting the powder particle size. Generally speaking, the thickness of the magnet to be diffused is 2-5mm, the amount of diffusion source attached is 0.3-1.0% of the weight of the magnet to be diffused, and the corresponding average particle size D50 of the heavy rare earth-rich powder is 6-50μm.

[0017] A further solution is described: the thermal spraying temperature is 700-900°C, the spray gun pressure is 0.3-0.8 MPa, and the medium gas is selected from argon or helium with a gas purity of >99.999%. To promote the adhesion of the heavy rare earth-rich powder to the magnet surface, the semi-finished product (I) can be heated to 300-600°C before thermal spraying. The heavy rare earth-rich powder that does not adhere to the magnet surface can be collected and reused. The heavy rare earth-rich powder is thermally sprayed onto any one or more surfaces of the semi-finished product (I) covered with the low-melting-point metal aluminum film.

[0018] In order to ensure the adhesion strength between the metal aluminum film and the magnet to be diffused, before depositing the low-melting-point metal aluminum film, the magnet to be diffused can be subjected to necessary surface cleaning treatment to remove oil stains, rust, etc. that may exist on the surface of the magnet. The treatment methods include mechanical grinding, ultrasonic pickling, sandblasting, etc.

[0019] A further solution: the high-temperature heat treatment is carried out in a vacuum or inert gas environment, including two stages: low-temperature alloying and high-temperature diffusion; wherein:

[0020] The low temperature alloying temperature is 550-650°C, and the holding time is 5-10h;

[0021] The temperature of the high-temperature diffusion is 850° C.-950° C., and the insulation time is 5-40 hours.

[0022] The high-temperature heat treatment is carried out in a vacuum or argon environment and is divided into two stages: low-temperature alloying and high-temperature diffusion. The temperature of the low-temperature alloying is 550°C-650°C, and the holding time is 5-10h. The temperature of the high-temperature diffusion is 850°C-950°C, and the holding time is 5-40h. After the high-temperature diffusion treatment, a heat treatment step is also included, the purpose of which is to further optimize the internal structure of the grain boundary phase and improve the coercive force of the magnet. It can adopt conventional temperatures in this field, and the holding time can be adjusted as needed. In one or more embodiments of the present invention, the temperature of the heat treatment is 460-600°C, and the time is 3-6h.

[0023] A further solution: after the high-temperature diffusion treatment, a heat treatment step is further included, wherein the heat treatment temperature is 460-600° C. and the time is 3-6 hours.

[0024] A further solution: the aluminum film exists on any one or more surfaces of the semi-finished product I.

[0025] In a second aspect, the present invention discloses a high-coercivity sintered NdFeB magnet obtained using the aforementioned preparation method. When the heavy rare earth in the sprayed heavy rare earth-rich powder is dysprosium, the coercivity of the magnet is increased by more than 6 kOe compared to a pre-diffusion sintered NdFeB magnet; when the heavy rare earth in the sprayed heavy rare earth-rich powder is terbium, the coercivity is increased by more than 9 kOe compared to a pre-diffusion sintered NdFeB magnet.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention deposits a low-melting-point aluminum film on the surface of a sintered NdFeB magnet and uses a thermal spray process to bond heavy rare earth-rich powder to the magnet surface. Using the low-melting-point aluminum as an adhesive, the coercive force of the magnet is significantly improved. The specific technical effects are as follows:

[0028] Using low-melting-point aluminum as a binder: Compared to traditional organic binders, this method effectively prevents carbonization, nitridation, or oxidation of organic binders during high-temperature diffusion, thereby improving diffusion source utilization and coercivity. Furthermore, aluminum as a binder promotes the bonding of heavy rare earth-rich powders to the magnet surface, enhancing the coating's adhesion.

[0029] Two-stage heat treatment process of low-temperature alloying and high-temperature diffusion: This method incorporates a two-stage heat treatment process of low-temperature alloying and high-temperature diffusion. During the low-temperature alloying stage, aluminum metal and heavy rare earth-rich powders undergo an alloying reaction, forming a stable alloy layer. This prevents the diffusion source powder from falling out due to melting of the aluminum metal during the high-temperature diffusion stage. During the high-temperature diffusion stage, the temperature is raised above the melting point of aluminum metal to promote the diffusion of heavy rare earth metal atoms from the magnet surface to the interior, thereby increasing the coercive force of the magnet.

[0030] Improved diffusion source utilization: Compared to the traditional spray-diffusion method, this method uses low-melting-point aluminum as a binder, effectively reducing diffusion source loss and improving diffusion source utilization. Furthermore, this method allows for the collection and reuse of heavy rare earth-rich powder that has not adhered to the magnet surface, further reducing costs.

[0031] Optimizing the heat treatment process: This method controls the temperature and duration of the heat treatment to better control the diffusion behavior of the diffusion sources, thereby improving the coercivity of the magnet. For example, the low-temperature alloying temperature is 550°C-650°C, and the holding time is 5-10 hours; the high-temperature diffusion temperature is 850°C-950°C, and the holding time is 5-40 hours. This optimized heat treatment process ensures uniform distribution and effective diffusion of the diffusion sources.

[0032] Improved overall magnet performance: Through these innovations, this method significantly increases the coercivity of sintered NdFeB magnets by 6kOe-12kOe compared to conventional methods. Furthermore, this method increases the magnet's remanence and maximum magnetic energy product, thereby enhancing its overall performance. DETAILED DESCRIPTION

[0033] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0035] Example 1

[0036] For the magnet I with the finished specifications of 40mm×30mm×3mm 10 (The brand is N52, the main component is Nd 30.5 Fe 68.55 B0.95 , subscripts are wt.%) were subjected to ultrasonic pickling treatment and two ultrasonic water washings in sequence to remove the oil and oxide layer on the surface of the magnet. A metal aluminum film with a thickness of 0.5 μm was formed on two surfaces of the magnet with a size of 40 mm × 30 mm after cleaning using a magnetron sputtering coating device to obtain a semi-finished product I 11 .

[0037] In semi-finished product I 11 The surfaces of the two metal aluminum film layers were thermally sprayed with dysprosium hydride powder with an average particle size of D50 = 10 μm. The thermal spraying temperature was 800°C, the spray gun pressure was 0.5 MPa, the medium gas was argon, and the gas purity was >99.999%, to obtain a semi-finished product II. 11 .

[0038] Semi-finished products in vacuum environment II 11 A two-stage heat treatment was performed: low-temperature alloying and high-temperature diffusion. The low-temperature alloying was performed at 600°C for 7 hours, and the high-temperature diffusion was performed at 880°C for 10 hours. After the high-temperature diffusion treatment, a further low-temperature heat treatment was performed at 480°C for 4 hours. After cooling, a high-coercivity sintered NdFeB magnet was obtained, designated as Example 1.

[0039] Comparative Example 1-1

[0040] The semi-finished product I obtained in Example 1 was prepared by magnetron sputtering coating equipment. 11 A heavy rare earth metal Dy layer was deposited on the surface of two 40 mm × 30 mm pieces of the magnet. The weight of the metal Dy layer was the same as the weight of the dysprosium hydride powder covering the magnet surface in Example 1 to obtain a semi-finished product II. 11-1 The semi-finished product II was treated under the same environment and heat treatment temperature as in Example 1. 11-1 The mixture was heat treated and cooled to obtain a high coercive force sintered NdFeB magnet, which was labeled as Comparative Example 1-1.

[0041] Comparative Example 1-2

[0042] For the same magnet 1 as in Example 1 10 The same ultrasonic acid cleaning treatment and two ultrasonic water washings as in Example 1 were performed in sequence. Then, a heavy rare earth metal Dy layer was deposited on two 40 mm × 30 mm surfaces of the cleaned magnet using a magnetron sputtering coating device. The weight of the metal Dy layer was the same as the weight of the dysprosium hydride powder covering the magnet surface in Example 1, to obtain a semi-finished product II. 11-2 The semi-finished product II was treated under the same environment and heat treatment temperature as in Example 1. 11-2 Heat treatment was performed and high coercivity sintered NdFeB magnets were obtained after cooling, which were marked as Comparative Example 1-2.

[0043] Comparative Examples 1-3

[0044] For the same magnet 1 as in Example 1 10 The same ultrasonic acid cleaning treatment and two ultrasonic water washings as in Example 1 were performed in sequence. Then, rosin was used as a binder to spray dysprosium hydride powder on two 40 mm × 30 mm surfaces of the cleaned magnet using a spraying device. The weight of the dysprosium hydride powder was the same as the weight of the dysprosium hydride powder covering the magnet surface in Example 1 to obtain a semi-finished product II. 11-3 The semi-finished product II was treated under the same environment and heat treatment temperature as in Example 1. 11-3 Heat treatment was performed and high coercivity sintered NdFeB magnets were obtained after cooling, which were marked as Comparative Examples 1-3.

[0045] Comparative Examples 1-4

[0046] For the same magnet 1 as in Example 1 10 The same ultrasonic pickling treatment and two ultrasonic water washings as in Example 1 were performed in sequence. Then, rosin was used as a binder to spray dysprosium aluminum alloy powder on two 40 mm × 30 mm surfaces of the cleaned magnet using a spraying device. The weight of dysprosium in the dysprosium aluminum alloy powder was the same as the weight of dysprosium in the dysprosium hydride powder covering the magnet surface in Example 1, and the weight of aluminum in the dysprosium aluminum alloy powder was the same as the weight of the aluminum film covering the magnet surface in Example 1, to obtain a semi-finished product II. 11-4 The semi-finished product II was treated under the same environment and heat treatment temperature as in Example 1. 11-4 After heat treatment and cooling, high coercivity sintered NdFeB magnets were obtained, which were marked as Comparative Examples 1-4.

[0047] Comparative Examples 1-5

[0048] The same semi-finished product II as in Example 1 was subjected to a vacuum environment. 11 A high-temperature diffusion treatment was performed at 880°C for 17 hours. Following the high-temperature diffusion treatment, a low-temperature heat treatment was performed at 480°C for 4 hours. After cooling, high-coercivity sintered NdFeB magnets were obtained, designated Comparative Examples 1-5.

[0049] Example 2

[0050] For the magnet I with the finished specifications of 50mm×25mm×4mm 20 (The brand is 50M, the main component is Nd 31 Fe 68.08 B 0.92 , subscripts are wt.%) were subjected to ultrasonic pickling treatment and two ultrasonic water washings in sequence to remove the oil and oxide layer on the surface of the magnet. A metal aluminum film with a thickness of 0.8 μm was formed on two surfaces of the magnet with a size of 50 mm × 25 mm after cleaning using a magnetron sputtering coating device to obtain a semi-finished product I 21 .

[0051] In semi-finished product I 21 The surfaces of the two metal aluminum film layers are thermally sprayed with metal terbium (Tb) powder with an average particle size D50 = 15 μm. The thermal spraying temperature is 765°C, the spray gun pressure is 0.6 MPa, the medium gas is argon, and the gas purity is >99.999%, to obtain a semi-finished product II. 21 .

[0052] Semi-finished products in vacuum environment II 21 A two-stage heat treatment was performed: low-temperature alloying and high-temperature diffusion. The low-temperature alloying was performed at 625°C for 5 hours, and the high-temperature diffusion was performed at 850°C for 16 hours. After the high-temperature diffusion treatment, a further low-temperature heat treatment was performed at 460°C for 3 hours. After cooling, a high-coercivity sintered NdFeB magnet was obtained, designated as Example 2.

[0053] Comparative Example 2-1

[0054] The semi-finished product I obtained in Example 2 was prepared by magnetron sputtering coating equipment. 21 A heavy rare earth metal terbium layer was deposited on the surface of two 50 mm × 25 mm pieces of the magnet. The weight of the metal terbium layer was the same as the weight of the metal terbium powder covering the surface of the magnet in Example 2 to obtain a semi-finished product II. 21-1 The semi-finished product II was treated under the same environment and heat treatment temperature as in Example 2. 21-1 The mixture was heat treated and cooled to obtain a high coercive force sintered NdFeB magnet, which was labeled as Comparative Example 2-1.

[0055] Comparative Example 2-2

[0056] For the same magnet 1 as in Example 2 20 The same ultrasonic acid cleaning treatment and ultrasonic water washing as in Example 2 were performed in sequence, and then a heavy rare earth metal terbium layer was deposited on two 50 mm × 25 mm surfaces of the cleaned magnet using a magnetron sputtering coating device. The weight of the metal terbium layer was the same as the weight of the metal terbium powder covering the magnet surface in Example 2, to obtain a semi-finished product II. 21-2 The semi-finished product II was treated under the same environment and heat treatment temperature as in Example 2. 21-2 After heat treatment and cooling, a high coercive force sintered NdFeB magnet was obtained, which was marked as Comparative Example 2-2.

[0057] Comparative Examples 2-3

[0058] For the same magnet 1 as in Example 2 20The same ultrasonic acid cleaning treatment and two ultrasonic water washings as in Example 2 were performed in sequence. Then, metal terbium powder was sprayed on two 50 mm × 25 mm surfaces of the cleaned magnet using rosin as a binder using a spraying device. The weight of the metal terbium powder was the same as the weight of the metal terbium powder covering the magnet surface in Example 2 to obtain a semi-finished product II. 21-3 The semi-finished product II was treated under the same environment and heat treatment temperature as in Example 2. 21-3 Heat treatment was performed and high coercivity sintered NdFeB magnets were obtained after cooling, which were marked as Comparative Example 2-3.

[0059] Comparative Examples 2-4

[0060] For the same magnet 1 as in Example 2 20 The same ultrasonic pickling treatment and two ultrasonic water washings as in Example 2 were performed in sequence, and then terbium aluminum alloy powder was sprayed on two 50 mm × 25 mm surfaces of the cleaned magnet using rosin as a binder using a spraying device. The weight of terbium in the terbium aluminum alloy powder was the same as the weight of terbium in the metal terbium powder covering the magnet surface in Example 2, and the weight of aluminum in the terbium aluminum alloy powder was the same as the weight of the aluminum film covering the magnet surface in Example 2, to obtain a semi-finished product II. 21-4 The semi-finished product II was treated under the same environment and heat treatment temperature as in Example 2. 21-4 After heat treatment and cooling, high coercivity sintered NdFeB magnets were obtained, which were marked as Comparative Examples 2-4.

[0061] Comparative Examples 2-5

[0062] The same semi-finished product II as in Example 2 was subjected to vacuum treatment. 21 A high-temperature diffusion treatment was performed at 850°C for 21 hours. Following the high-temperature diffusion treatment, a low-temperature heat treatment was performed at 460°C for 3 hours. After cooling, high-coercivity sintered NdFeB magnets were produced, designated Comparative Examples 2-5.

[0063] Example 3

[0064] For the magnet I with the finished specifications of 30mm×25mm×5mm 30 (The brand is N54, the main component is Nd 30 Fe 69.05 B 0.95 , subscripts are wt.%) were sequentially subjected to ultrasonic pickling treatment and two ultrasonic water washings to remove oil stains and oxide layers on the surface of the magnet. A metal aluminum film with a thickness of 1.7 μm was formed on two surfaces of the cleaned magnet with a size of 30 mm × 25 mm using a magnetron sputtering coating device to obtain a semi-finished product I 31 .

[0065] In semi-finished product I31 The surfaces of the two metal aluminum film layers were thermally sprayed with terbium hydride powder with an average particle size D50 = 17 μm. The thermal spraying temperature was 730°C, the spray gun pressure was 0.7 MPa, the medium gas was argon, and the gas purity was >99.999%, to obtain a semi-finished product II. 31 .

[0066] Semi-finished product II in argon environment 31 A two-stage heat treatment was performed: low-temperature alloying and high-temperature diffusion. The low-temperature alloying was performed at 650°C for 6 hours, and the high-temperature diffusion was performed at 910°C for 20 hours. After the high-temperature diffusion treatment, a low-temperature heat treatment was performed again at 500°C for 5 hours. After cooling, a high-coercivity sintered NdFeB magnet was produced, designated as Example 3.

[0067] Example 4

[0068] For the finished magnet I with the specification of 40mm×35mm×6mm 40 (The brand is 52M, the main component is Dy1Nd 29 Fe 69.05 B 0.95 , subscripts are wt.%) were sequentially subjected to ultrasonic pickling treatment and two ultrasonic water washings to remove the oil and oxide layer on the surface of the magnet. A metal aluminum film with a thickness of 2 μm was formed on two surfaces of the magnet with a size of 40 mm × 35 mm after cleaning using a magnetron sputtering coating device to obtain a semi-finished product I 41 .

[0069] In semi-finished product I 41 The surfaces of the two metal aluminum film layers are thermally sprayed with metal dysprosium powder with an average particle size D50 = 20 μm. The thermal spraying temperature is 700°C, the spray gun pressure is 0.8 MPa, the medium gas is helium, and the gas purity is >99.999%, to obtain a semi-finished product II. 41 .

[0070] Semi-finished product II in argon environment 41 A two-stage heat treatment was performed: low-temperature alloying and high-temperature diffusion. The low-temperature alloying was performed at 625°C for 8 hours, and the high-temperature diffusion was performed at 860°C for 40 hours. After the high-temperature diffusion treatment, a further low-temperature heat treatment was performed at 550°C for 6 hours. After cooling, a high-coercivity sintered NdFeB magnet was obtained, designated as Example 4.

[0071] Example 5

[0072] For the magnet I with the finished specifications of 30mm×20mm×2mm 50 (The brand is N56, the main component is Nd 29.5 Fe69.55 B 0.95 , subscripts are wt.%) were subjected to ultrasonic pickling treatment and two ultrasonic water washings in sequence to remove the oil and oxide layer on the surface of the magnet. A metal aluminum film with a thickness of 1.1 μm was formed on a surface of the cleaned magnet with a size of 30 mm × 20 mm using a magnetron sputtering coating device to obtain a semi-finished product I 51 .

[0073] In semi-finished product I 51 The surface of the metal aluminum film layer is thermally sprayed with terbium-iron alloy powder with an average particle size D50 = 8 μm. The thermal spraying temperature is 850°C, the spray gun pressure is 0.4 MPa, the medium gas is helium, and the gas purity is >99.999%, to obtain a semi-finished product II 51 .

[0074] Semi-finished product II in helium environment 51 A two-stage heat treatment was performed: low-temperature alloying and high-temperature diffusion. The low-temperature alloying was performed at 550°C for 9 hours, and the high-temperature diffusion was performed at 950°C for 5 hours. After the high-temperature diffusion treatment, a low-temperature heat treatment was performed again at 600°C for 4 hours. After cooling, a high-coercivity sintered NdFeB magnet was produced, designated as Example 5.

[0075] Example 6

[0076] For the finished magnet I with the specifications of 35mm×30mm×1.5mm 60 (The brand is 54M, the main component is Tb1Nd 28.5 Fe 69.55 B 0.95 , subscripts are wt.%) were subjected to ultrasonic pickling treatment and two ultrasonic water washings in sequence to remove the oil and oxide layer on the surface of the magnet. A metal aluminum film with a thickness of 0.8 μm was formed on a surface of the cleaned magnet with a size of 35 mm × 30 mm using a magnetron sputtering coating device to obtain a semi-finished product I 61 .

[0077] In semi-finished product I 61 The surface of the metal aluminum film layer is thermally sprayed with dysprosium-iron alloy powder with an average particle size D50 = 5 μm. The thermal spraying temperature is 900°C, the spray gun pressure is 0.3 MPa, the medium gas is helium, and the gas purity is >99.999%, to obtain a semi-finished product II 61 .

[0078] Semi-finished product II in helium environment 61A two-stage heat treatment was performed: low-temperature alloying and high-temperature diffusion. The low-temperature alloying was performed at 575°C for 10 hours, and the high-temperature diffusion was performed at 920°C for 8 hours. After the high-temperature diffusion treatment, a low-temperature heat treatment was performed again at 580°C for 5 hours. After cooling, a high-coercivity sintered NdFeB magnet was produced, designated Example 6.

[0079] The consumption, attachment, and recovery amounts of different types of diffusion sources during the experiment were weighed (because the amount of diffusion source attachment of a single magnet is small and difficult to accurately weigh, 100 magnets were selected for weighing in the experiment), and the loss rate of the diffusion source was calculated; using a magnetic property tester, in accordance with the requirements of GB / T 3217-2013 Permanent Magnetic (Hard Magnetic) Materials - Magnetic Test Methods, the coercive forces of Examples 1 to 6 and Comparative Examples 1-1 to 2-4 were compared and tested at room temperature (23±1°C); the oxygen, nitrogen, and carbon contents of Examples 1 to 6 and Comparative Examples 1-1 to 2-4 were tested using oxygen, nitrogen, hydrogen, and carbon-sulfur testers. The results are shown in Table 1.

[0080] Table 1 Parameter comparison of Examples 1 to 6 and Comparative Examples 1-1 to 2-4

[0081]

[0082] According to the test results in Table 1, it can be seen that: (1) Using the technical solution of Example 1 herein, its diffusion source loss rate is less than that of Comparative Examples 1-1 and 1-2, and is equivalent to Comparative Examples 1-3 and 1-4; its coercive force increase is higher than that of Comparative Examples 1-2, 1-3, and 1-4, and is equivalent to Comparative Example 1-1; its oxygen and carbon content is equivalent to that of Comparative Examples 1-1 and 1-2, and lower than that of Comparative Examples 1-3 and 1-4. Because rosin does not contain nitrogen, the nitrogen content in Example 1 and Comparative Examples 1-3 and 1-4 is not much different; its coercive force increase is greater than that of Comparative Example 1-5 subjected to direct diffusion heat treatment. (2) Using the technical solution of Example 2 herein, its diffusion source loss rate is less than that of Comparative Examples 2-1 and 2-2, and is equivalent to that of Comparative Examples 2-3 and 2-4; its coercive force increase is higher than that of Comparative Examples 2-2, 2-3, and 2-4, and is equivalent to that of Comparative Example 2-1; its oxygen and carbon content is equivalent to that of Comparative Examples 2-1 and 2-2, and lower than that of Comparative Examples 2-3 and 2-4. Because rosin does not contain nitrogen, the nitrogen content in Example 2 and Comparative Examples 2-3 and 2-4 is not much different; the increase in coercivity is greater than that in Comparative Examples 2-5, which are treated with direct diffusion heat treatment. (3) Compared with the magnetron sputtering diffusion source coating process, the technical solutions of Examples 1 to 6 reduce the loss rate of the diffusion source; compared with the organic adhesive spray coating diffusion source process, the technical solutions of Examples 1 to 6 reduce the oxygen and carbon content in the diffused magnet and increase the coercivity of the magnet.

[0083] Although this specification is described according to implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0084] Therefore, the above description is only a preferred embodiment of the present application and is not intended to limit the scope of implementation of the present application; that is, all equivalent modifications made according to the scope of the claims of the present application are within the scope of protection of the claims of the present application.

Claims

1. A method for preparing a high coercive force sintered NdFeB magnet, characterized in that: The following steps are involved: Depositing an aluminum film on the surface of the NdFeB magnet to be diffused and sintered to obtain a semi-finished product I; Using a thermal spraying process to spray heavy rare earth-rich powder on the surface of the aluminum film, a semi-finished product II is obtained; The semi-finished product II is subjected to high-temperature heat treatment and then cooled to obtain a high-coercivity sintered NdFeB magnet.

2. The preparation method according to claim 1, characterized in that The NdFeB magnet to be diffused and sintered is made of RE2Fe 14 B is the main magnetic phase, and its volume accounts for no less than 95% of the total volume of the magnet.

3. The preparation method according to claim 1, characterized in that The thickness of the aluminum film is 0.5-2 μm.

4. The preparation method according to claim 1, characterized in that The average particle size D50 of the heavy rare earth-rich powder is 5 to 20 μm, and the powder is at least one of a heavy rare earth element, a heavy rare earth hydride, and a heavy rare earth alloy; in the heavy rare earth-rich powder, the heavy rare earth element accounts for more than 50% of the total weight; the heavy rare earth is selected from at least one of dysprosium and terbium.

5. The preparation method according to claim 1, characterized in that The temperature of the thermal spraying process is 700-900° C., the spray gun pressure is 0.3-0.8 MPa, and the medium gas is argon or helium.

6. The preparation method according to claim 1, characterized in that The high-temperature heat treatment is carried out in a vacuum or inert gas environment and includes two stages: low-temperature alloying and high-temperature diffusion; wherein: The low temperature alloying temperature is 550-650°C, and the holding time is 5-10h; The temperature of the high-temperature diffusion is 850° C.-950° C., and the insulation time is 5-40 hours.

7. The preparation method according to claim 1, characterized in that After the high-temperature diffusion treatment, a heat treatment step is further included, wherein the heat treatment temperature is 460-600° C. and the time is 3-6 hours.

8. The preparation method according to claim 1, characterized in that The aluminum film exists on any one or more surfaces of the semi-finished product I.

9. A high-coercivity sintered NdFeB magnet obtained by the preparation method according to any one of claims 1 to 8. When the heavy rare earth in the sprayed heavy rare earth-rich powder is dysprosium, the coercivity of the magnet is increased by more than 6 kOe compared to the NdFeB magnet to be diffused and sintered; when the heavy rare earth in the sprayed heavy rare earth-rich powder is terbium, the coercivity of the magnet is increased by more than 9 kOe compared to the NdFeB magnet to be diffused and sintered.

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