Method for preparing neodymium-iron-boron magnet through diffusion welding

Abstract

The invention belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a method for preparing a neodymium-iron-boron magnet through diffusion welding. The method comprises the following steps: coating the surface of a neodymium-iron-boron magnet with a low-melting-point rare earth metal alloy target material through magnetron sputtering equipment, and continuously coating the surface of the magnet with a high-melting-point heavy rare earth metal alloy target material through magnetron sputtering equipment, stacking two magnets which have the same surface size and are coated with the upper surface and the lower surface together to obtain a sample, putting the sample into a diffusion welding furnace for vacuum heat treatment and pressure welding, and tempering in a vacuum sintering furnace to prepare the magnet of which the thickness is expanded; by means of the double diffusion sources, the diffusivity of heavy rare earth elements is regulated and controlled, a liquid phase needed by diffusion welding is provided, the magnet can be welded while being subjected to grain boundary diffusion successfully, the problem that the thickness of a traditional grain boundary diffusion magnet is limited within 10 mm is solved, and the service life of the magnet is prolonged. And the application of the grain boundary diffusion magnet in the fields of wind power generation and the like is widened.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth permanent magnet materials, and in particular relates to a method for preparing a neodymium iron boron magnet by diffusion welding. Background Art

[0002] Neodymium Iron Boron (Nd2Fe 14 B) Permanent magnets have high remanence, high coercive force and high magnetic energy product. They are the rare earth permanent magnet materials with the highest comprehensive performance known today. With the rapid development in high-end popular fields such as wind power generation, variable frequency compressors and new energy passenger vehicles in recent years, not only the performance requirements of NdFeB magnets are getting higher and higher, but also the thickness of high-performance NdFeB diffused magnets is required to be thicker and thicker.

[0003] At present, in order to obtain high-performance NdFeB magnets, on the one hand, the traditional process method is used, which requires a large amount of heavy rare earth metals, but heavy rare earth resources are not only expensive but also have limited reserves, and the cost is high. On the other hand, the grain boundary diffusion method is used, such as magnetron sputtering, spraying, screen printing, dip coating, etc. This method can effectively reduce the use of heavy rare earth to obtain high-performance magnets, but the thickness of the magnet is greatly restricted and generally cannot exceed 10mm. Chinese invention patent CN109192493 A discloses a method of using magnetron sputtering to plate a rare earth alloy film on the upper and lower surfaces of a NdFeB magnet, and then subjecting it to grain boundary diffusion and vacuum tempering heat treatment to improve the coercive force of the magnet. Chinese invention patent 202010185809.1 discloses a method of obtaining a high coercive force NdFeB magnet by covering the surface of a magnet with a slurry containing heavy rare earth metal powder and non-rare earth metal powder for grain boundary diffusion. However, the above methods all face the problem that the thickness of the diffused magnet cannot exceed 10 mm. Therefore, it has become a market necessity to develop a process method that can significantly reduce the amount of heavy rare earth metal used to obtain high-performance NdFeB magnets, while at the same time breaking through the thickness constraints of the diffused magnets to a certain extent. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the present invention provides a method for preparing NdFeB magnets by diffusion welding. The preparation method of the present invention can realize the regulation of the diffusion capacity of heavy rare earths. Through the optimization design of the diffusion source and the diffusion welding process, the amount of heavy rare earths can be greatly reduced and the coercive force of the NdFeB magnet can be greatly improved. While obtaining high-performance NdFeB magnets, the restriction of the thickness of the diffusion magnets is effectively broken through, which is of great significance to the development of the NdFeB permanent magnet material industry.

[0005] In order to solve the above technical problems, the technical solution of the present invention is: a method for preparing NdFeB magnets by diffusion welding, the method specifically comprising the following process steps:

[0006] S1) pre-treating the surfaces of two NdFeB magnets to be welded, and then coating the upper and lower surfaces of two NdFeB magnets to be welded having the same surface size with a low melting point rare earth metal alloy target by magnetron sputtering equipment;

[0007] S2) using a magnetron sputtering device to coat the high melting point heavy rare earth metal alloy target material on the upper and lower surfaces of the two NdFeB magnets to be welded obtained after the treatment in S1);

[0008] S3) stacking the two NdFeB magnets to be welded after the treatment in S2) together to obtain a sample, and then placing the sample in a vacuum diffusion welding furnace for vacuum heat treatment with multiple step-by-step temperature increase and pressure welding;

[0009] S4) The sample obtained in S3) is then tempered, and after cooling, a NdFeB magnet with grain boundary diffusion is obtained.

[0010] Further, the chemical formula of the low melting point rare earth metal alloy in S1) is (La a Ce 1-a ) x (Pr b Nd 1-b ) y M 1-x-y , wherein 0≤a≤1, 0≤b≤1, 0≤x≤1, 0≤y≤1 and 0.2≤x+y≤1, and M is one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr.

[0011] Further, the chemical formula of the high melting point heavy rare earth metal alloy in S2) is (La a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e G 1-c-d-e ) z M 1-x-y-z ; wherein 0≤a≤1, 0≤b≤1, 0≤x≤1, 0≤y≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0≤z≤1 and 0.2≤x+y+z≤1; M is any one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr elements.

[0012] Furthermore, the coating thickness of the low melting point rare earth metal alloy in said S1) is 1-100 microns.

[0013] Furthermore, the coating of the high melting point heavy rare earth metal alloy in S2).

[0014] Furthermore, the specific process of the multi-stage step-by-step temperature increase vacuum heat treatment and pressure welding in S3) is as follows:

[0015] S3.1) Place the sample into the diffusion welding equipment and start evacuating the vacuum;

[0016] S3.2) When the vacuum of the equipment is ≤10 -2 Pa, the temperature is raised at a certain rate, and when the temperature reaches 700°C, the holding time is 1-2h, and when the temperature continues to rise to 800°C, the holding time is 1-2h;

[0017] S3.3) When the temperature continues to rise to 900-1000°C, the pressure is increased to 2-60MPa, so that the grain boundary diffusion and pressure welding processes are carried out simultaneously. The heat preservation and pressure holding time is 10-30h. After the heat preservation is completed, argon gas is filled and cooled to room temperature.

[0018] Further, the heating rate in S3.2) is 2-10°C / min;

[0019] The pressurization rate in S3.3) is 2-10 MPa / min.

[0020] Further, the tempering equipment in S4) is a vacuum furnace, the tempering temperature is 400-600°C, the holding time is 2-5h, and the vacuum degree is ≤10 -2 Pa, the heating rate is 2-10℃ / min.

[0021] Furthermore, the thickness of the NdFeB magnet prepared by the preparation method is 6-20 mm; and the composition is (La i Ce 1-i ) m (Pr k Nd 1-k ) n (Dy l Tb f Ho h G 1-l-f-h ) t M 1-m-n-t phase, the thickness of which is 1-3 μm; wherein 0≤i≤1, 0≤k≤1, 0≤m≤1, 0≤n≤1, 0≤l≤1, 0≤f≤1, 0≤h≤1, 0≤t≤1 and 0.4≤m+n+t<1; M is any one or more of Al, Cu, Ga, In, Sn, Fe, Co, and Zr.

[0022] A high-performance NdFeB magnet is prepared by the above method.

[0023] Compared with the prior art, the advantages of the present invention include:

[0024] 1. The present invention adopts a low melting point rare earth metal alloy and a high melting point heavy rare earth alloy. When vacuum heat treatment and pressure welding are performed, when the temperature is kept at 700°C, the low melting point rare earth metal alloy melts into the interior of the magnet grain boundary, greatly widening the size of the matrix grain boundary, thereby opening the grain boundary diffusion channel of the magnet. When the temperature is kept at 800°C, the heavy rare earth alloy reacts with the melted low melting point rare earth metal alloy powder to generate (La a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e G 1-c-d-e ) z M 1-x-y-z The alloy liquid enters the interior of the magnet along the diffusion channel and reacts with the main phase of the magnet. Finally, when the temperature is kept at 900-1000℃ and the pressure is maintained, more and more high-melting-point heavy rare earth alloys and melted low-melting-point rare earth metals react and liquefy. The alloy liquid not only provides the liquid phase required for welding, so that the upper and lower magnets with the same surface size begin to weld, but also the alloy liquid enters deeper into the magnet along the opened diffusion channel and reacts with the main phase of the deeper magnet. At the boundary of the main phase, a liquid with a composition of (La i Ce 1-i ) m (Pr k Nd 1-k ) n (Dy l Tb f Ho h G 1-l-f-h ) t M 1-m-n-t The phase has a thickness of 1-3μm, which greatly improves the coercivity of the sintered NdFeB magnet. It also successfully regulates the diffusion capacity of heavy rare earth elements and successfully prepares diffused magnets with a thickness of 6-20mm.

[0025] 2. The high melting point heavy rare earth alloy used in the present invention can have a very low proportion, which can greatly reduce the usage of heavy rare earth metals, thereby greatly reducing the production cost of high-performance NdFeB magnets;

[0026] 3. The present invention uses a diffusion welding furnace to weld two magnets of the same surface size while performing grain boundary diffusion, so that the thickness of the obtained diffused magnets is superimposed, effectively breaking through the restriction of 10 mm thickness of the diffused magnets, and broadening the application of grain boundary diffused magnets in the fields of wind power generation, new energy vehicles, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a flowchart of a method for preparing NdFeB magnets by diffusion welding. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the method for preparing a NdFeB magnet by diffusion welding of the present invention will be described in detail. These embodiments are exemplary and the disclosure of the present invention is not limited thereto.

[0029] like Figure 1 As shown, the present invention provides a method for preparing NdFeB magnets by diffusion welding, and the preparation method specifically includes the following process steps:

[0030] S1) pre-treating the surface of the NdFeB magnet to be welded to remove the oil and scale on the surface of the magnet to keep the magnet clean and tidy, and then coating the low melting point rare earth metal alloy target on the upper and lower surfaces of two NdFeB magnets to be welded with the same surface size by magnetron sputtering equipment;

[0031] S2) using a magnetron sputtering device to coat the high melting point heavy rare earth metal alloy target material on the upper and lower surfaces of the two magnets obtained in S1);

[0032] S3) stacking the two magnets in S2) together to obtain a sample, and placing the sample in a vacuum diffusion welding device for vacuum heat treatment with multiple step-by-step temperature increases and pressure welding;

[0033] S4) The sample obtained in S3) is then tempered in a vacuum sintering furnace to obtain a high performance NdFeB magnet.

[0034] The chemical formula of the low melting point rare earth alloy target is (La a Ce 1-a ) x (Pr b Nd 1-b ) y M 1-x-y , wherein 0≤a≤1, 0≤b≤1, 0≤x≤1, 0≤y≤1 and 0.2≤x+y≤1, and M is one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr.

[0035] The chemical formula of the high melting point heavy rare earth metal alloy target is (La a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e G 1-c-d-e ) z M1-x-y-z ; where 0≤a≤1, 0≤b≤1, 0≤x≤1, 0≤y≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0≤z≤1 and 0.2≤x+y+z≤1; M is Al, Cu, Ga, In, Sn, Fe,

[0036] Any one or more of Co and Zr elements.

[0037] The coating thickness in S1) is 1-100 microns.

[0038] The coating thickness in S2) is 1-100 microns.

[0039] The mass ratio of the low melting point rare earth alloy to the high melting point heavy rare earth metal alloy coated on the magnet is 1:1 to 10:1;

[0040] The thickness of the NdFeB magnet is 1-10 mm;

[0041] The multi-stage step-by-step vacuum heat treatment and pressure welding process in S3) is as follows:

[0042] S3.1) Place the sample into the diffusion welding equipment and start evacuating the vacuum;

[0043] S3.2) When the vacuum of the equipment is ≤10 -2 Pa, the temperature is raised at a certain rate, and when the temperature reaches 700℃, the holding time is 1-2h, and when it reaches 800℃, the holding time is 1-2h;

[0044] S3.3) When the temperature continues to rise to 900-1000°C, the pressure is increased to 2-60MPa, so that the grain boundary diffusion and pressure welding process are carried out simultaneously. The heat preservation and pressure holding time is 10-30h. After the heat preservation is completed, argon gas is filled and cooled to room temperature;

[0045] The tempering temperature of the vacuum tube furnace tempering in S4) is 400-600°C, the holding time is 2-5h, and the vacuum degree is ≤10 -2 Pa;

[0046] The heating rates in S3.2) and S3.3) are both 2-10°C / min.

[0047] The pressurization rate in S3.3) is 2-10 MPa / min.

[0048] The thickness of the high performance NdFeB magnet in S4) is 6-20 mm.

[0049] In the multi-stage step-type vacuum heat treatment and welding process, the low-melting-point rare earth metal alloy first melts to form a liquid phase, which preferentially enters the interior of the magnet grain boundary, and then the high-melting-point heavy rare earth alloy reacts with the melted low-melting-point rare earth metal alloy to generate (La a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e G 1-c-d-e ) z M 1-x-y-z Alloy liquid, wherein 0≤a≤1, 0≤b≤1, 0≤x≤1, 0≤y≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0≤z≤1 and 0.2≤x+y+z≤1; M is any one or more of elements such as Al, Cu, Ga, In, Sn, Fe, Co, Zr, etc., the alloy liquid not only provides the liquid phase required for welding in the welding process, but also the alloy liquid enters the interior of the magnet along the grain boundary, reacts with the edge of the main phase of the magnet to carry out the grain boundary diffusion process, and forms a composition of (La i Ce 1-i ) m (Pr k Nd 1-k ) n (Dy l Tb f Ho h G 1-l-f-h ) t M 1-m-n-t The thickness of the phase is 1-3 μm; wherein 0≤i≤1, 0≤k≤1, 0≤m≤1, 0≤n≤1, 0≤l≤1, 0≤f≤1, 0≤h≤1, 0≤t≤1 and 0.4≤m+n+t<1; M is any one or more of Al, Cu, Ga, In, Sn, Fe, Co, Zr and the like;

[0050] Some embodiments of the present invention can greatly widen the grain boundaries of the magnet and open up the grain boundary diffusion channels of the magnet by introducing a low-melting-point rare earth metal alloy, thereby regulating the diffusion capacity of heavy rare earth metal elements in the matrix, while the proportion of the second diffusion source is very low, thereby reducing the use of heavy rare earth elements and greatly reducing production costs.

[0051] In some embodiments of the present invention, the method for preparing the NdFeB magnet matrix comprises the following steps: sequentially preparing the NdFeB magnet matrix to be diffused through the steps of rapid solidification and sheeting, hydrogen crushing, air flow milling, additive stirring, magnetic field orientation molding, sintering densification, and machining;

[0052] The technical solution of the present invention is further described below in conjunction with specific embodiments, and the protection scope of the present invention is not limited by the following embodiments;

[0053] Example 1

[0054] Firstly, the tempered matrix I of sintered NdFeB to be diffused is prepared in sequence through the steps of rapid solidification and flinging, hydrogen crushing, air flow grinding, agent addition and stirring, magnetic field orientation molding, sintering densification and machining. The matrix size is Φ20*3mm, and the surface of the NdFeB magnet matrix is ​​pretreated to remove the oil and oxide scale on the magnet surface to keep the magnet clean and tidy.

[0055] The high melting point heavy rare earth metal alloy Tb 0.8 Cu 0.2 The target diffusion source is coated with a film of about 20 microns on the surface of the magnet substrate by a magnetron sputtering device. Then two magnets with a thickness of 5 mm and the same surface size and both coated on the upper and lower surfaces are stacked together to obtain a sample. The sample is placed in a diffusion welding furnace and vacuum is started. When the vacuum of the equipment is ≤10 -2 Pa, the temperature was raised at a certain heating rate. When the temperature reached 700℃, the holding time was 1.5h, and when it reached 800℃, the holding time was 1h. After the temperature was further raised to 900℃, the pressure was increased to 10MPa, and grain boundary diffusion and welding were carried out at the same time. The holding time was 15h. After the holding was completed, argon was filled and cooled to room temperature. The heating rate between the step temperatures was 5℃ / min, and the pressure rate was 2MPa / min. Then, the furnace was tempered in a vacuum tube furnace, and the temperature was raised to 480℃ at 5℃ / min. The holding time was 2h, and the vacuum degree was ≤10 - 2 Pa, and then air-cooled to room temperature after heating to obtain a high-performance diffusion-sintered NdFeB magnet 1 with a thickness of about 10 mm.

[0056] Example 2

[0057] Firstly, the tempered matrix I of sintered NdFeB to be diffused is prepared in sequence through the steps of rapid solidification and flinging, hydrogen crushing, air flow grinding, agent addition and stirring, magnetic field orientation molding, sintering densification and machining. The matrix size is Φ20*3mm, and the surface of the NdFeB magnet matrix is ​​pretreated to remove the oil and oxide scale on the magnet surface to keep the magnet clean and tidy.

[0058] The low melting point rare earth metal alloy Pr 0.25 Nd 0.75 The first diffusion source of the target material is coated with a film of about 16 microns on the surface of the NdFeB magnet by a magnetron sputtering device, and the high melting point heavy rare earth metal alloy Tb 0.8 Cu 0.2The second diffusion source of the target material is coated on the surface of the magnet substrate by a magnetron sputtering device for about 4 microns. Then, two magnets with a thickness of 5 mm and the same surface size and both coated on the upper and lower surfaces by the double diffusion source are stacked together to obtain a sample. The sample is placed in a diffusion welding device and vacuum is started. When the vacuum of the device is ≤10 -2 Pa, the temperature was raised at a certain heating rate. When the temperature reached 700℃, the holding time was 1.5h, and when it reached 800℃, the holding time was 1h. After the temperature was further raised to 900℃, the pressure was increased to 10MPa, and grain boundary diffusion and welding were carried out at the same time. The holding time was 15h. After the holding was completed, argon was filled and cooled to room temperature. The heating rate between the step temperatures was 5℃ / min, and the pressure rate was 2MPa / min. Then, the furnace was tempered in a vacuum tube furnace, and the temperature was raised to 480℃ at 5℃ / min. The holding time was 2h, and the vacuum degree was ≤10 -2 Pa, and then air-cooled to room temperature after heating to obtain a high-performance diffusion-sintered NdFeB magnet 2 with a thickness of about 10 mm.

[0059] Example 3

[0060] Firstly, the tempered matrix II of sintered NdFeB to be diffused is prepared in sequence through the steps of rapid solidification and flinging, hydrogen crushing, air flow grinding, agent addition and stirring, magnetic field orientation molding, sintering densification and machining. The matrix size is Φ20*5mm, and the surface of the NdFeB magnet matrix is ​​pretreated to remove the oil and oxide scale on the magnet surface to keep the magnet clean and tidy.

[0061] The first diffusion source of the low melting point rare earth metal alloy Pr target is coated on the surface of the NdFeB magnet by magnetron sputtering equipment for about 29 microns, and the high melting point heavy rare earth metal alloy Tb 0.75 Al 0.25 The second diffusion source of the target material is coated on the surface of the magnet substrate by a magnetron sputtering device for about 7 microns. Then, two magnets with the same surface size and thickness of 5 mm and 7 mm, which are both coated on the upper and lower surfaces of the double diffusion source, are stacked together to obtain a sample. The sample is placed in a diffusion welding device and vacuum is started. When the vacuum of the device is ≤10 -2 Pa, the temperature was raised at a certain heating rate. When the temperature reached 700℃, the holding time was 1h, and when it reached 800℃, the holding time was 2h. After the temperature was further raised to 930℃, the pressure was increased to 15MPa, and grain boundary diffusion and welding were carried out at the same time. The holding time was 20h. After the holding was completed, argon was filled and cooled to room temperature. The heating rate between the step temperatures was 5℃ / min, and the pressure rate was 3MPa / min. Then, the furnace was tempered in a vacuum tube furnace, the temperature was raised to 520℃ at 7℃ / min, the holding time was 3h, and the vacuum degree was ≤10 -2Pa, and then air-cooled to room temperature after heating to obtain a high-performance diffusion-sintered NdFeB magnet 3 with a thickness of about 12 mm.

[0062] Example 4

[0063] Firstly, the tempered matrix III of the sintered NdFeB to be diffused is prepared through the steps of rapid solidification and flinging, hydrogen crushing, air flow grinding, agent addition and stirring, magnetic field orientation molding, sintering densification and machining. The matrix size is Φ20*6mm, and the surface of the NdFeB magnet matrix is ​​pretreated to remove the oil and oxide scale on the magnet surface to keep the magnet clean and tidy.

[0064] The first diffusion source of the low melting point rare earth metal alloy Nd target is coated with a 35 micron film on the surface of the NdFeB magnet through a magnetron sputtering device, and the high melting point heavy rare earth metal alloy Dy 0.7 Fe 0.25 Al 0.05 The second diffusion source of the target material is coated with a 5-micron film on the surface of the magnet substrate by a magnetron sputtering device. Then, two magnets with the thickness of 6 mm and 7 mm and the same size and both coated on the upper and lower surfaces are stacked together to obtain a sample. The sample is placed in a diffusion welding device and vacuum is started. When the vacuum of the device is ≤10 -2 Pa, the temperature was raised at a certain heating rate. When the temperature reached 700℃, the holding time was 1h, and at 800℃, the holding time was 1.5h. After continuing to heat up to 910℃, the pressure was increased to 20MPa, and grain boundary diffusion and welding were carried out at the same time. The holding time was 30h. After the holding was completed, argon was filled and cooled to room temperature. The heating rate between the step temperatures was 6℃ / min, and the pressure rate was 5MPa / min. Then, tempering was carried out in a vacuum tube furnace, the temperature was raised to 500℃ at 5℃ / min, the holding time was 2.5h, and the vacuum degree was ≤10 -2 Pa, and then air-cooled to room temperature after heating to obtain a high-performance diffusion-sintered NdFeB magnet 4 with a thickness of about 13 mm.

[0065] The sintered NdFeB magnets prepared above were tested for magnetic properties, and the data are shown in the following table:

[0066]

[0067]

[0068] From the comparison of the magnetic properties data of Magnet 1 and Magnet 2 in the above table, it can be seen that when the total rare earth content of the magnet matrix itself is low and there is no low-melting-point rare earth metal alloy in the diffusion source, the coercive force of the magnet after diffusion increases only slightly. After being plated with the low-melting-point rare earth metal Nd, the coercive force of the magnet increases significantly, indicating that the addition of low-melting-point rare earth metals is beneficial to the diffusion of heavy rare earth elements in the matrix, thereby significantly increasing the coercive force. By analyzing the magnetic properties of Magnet 2, Magnet 3 and Magnet 4, it can be seen that the use of this patented method and process can not only obtain NdFeB magnets with low heavy rare earth metal usage and high performance, but also solve the problem of thickness restriction of traditional grain boundary diffusion magnets within 10 mm, and prepare diffusion magnets with a thickness of more than 10 mm.

[0069] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

[0070] The above is a detailed introduction to a method for preparing NdFeB magnets by diffusion welding provided in the embodiment of the present application. The description of the above embodiment is only used to help understand the method and its core idea of ​​the present application; at the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present application.

[0071] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different nouns to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. As mentioned throughout the specification and claims, "including" and "comprising" are open-ended terms, so they should be interpreted as "including / including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect. The subsequent description of the specification is a preferred embodiment of the present application, but the description is for the purpose of illustrating the general principles of the present application, and is not used to limit the scope of the present application. The scope of protection of the present application shall be determined by the definition of the attached claims.

[0072] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0073] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0074] The above description shows and describes several preferred embodiments of the present application, but as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present application, and should be within the scope of protection of the claims attached to the present application.

Claims

1. A method for preparing NdFeB magnets by diffusion welding, characterized in that: The method specifically comprises the following process steps: S1) pre-treating the surfaces of the two NdFeB magnets to be welded, and then coating the low melting point rare earth metal alloy target on the upper and lower surfaces of the two NdFeB magnets to be welded respectively by magnetron sputtering equipment; S2) coating the high melting point heavy rare earth metal alloy target material on the upper and lower surfaces of the two NdFeB magnets to be welded obtained after the treatment in S1) by magnetron sputtering equipment; S3) stacking the two NdFeB magnets to be welded after the treatment in S2) together to obtain a sample, and then placing the sample in a vacuum diffusion welding furnace for vacuum heat treatment with multiple step-by-step temperature increase and pressure welding; S4) The sample obtained in S3) is then tempered and cooled to obtain a NdFeB diffusion magnet.

2. The method according to claim 1, characterized in that: The chemical formula of the low melting point rare earth metal alloy in S1) is (La a Ce 1-a ) x (Pr b Nd 1-b ) y M 1-x-y , wherein 0≤a≤1, 0≤b≤1, 0≤x≤1, 0≤y≤1, and 0.2≤x+y≤1, and M is one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr.

3. The method according to claim 1, characterized in that: The chemical formula of the high melting point heavy rare earth metal alloy in S2) is (La a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e G 1-c - d-e ) z M 1-x-y-z ; wherein 0≤a≤1, 0≤b≤1, 0≤x≤1, 0≤y≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0≤z≤1 and 0.2≤x+y+z≤1; M is any one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr elements.

4. The method according to claim 1, characterized in that The coating thickness of the low melting point rare earth metal alloy in S1) is 1-100 microns.

5. The method according to claim 1, characterized in that The coating of the high melting point heavy rare earth metal alloy in S2).

6. The method according to claim 1, characterized in that The specific process of the multi-stage step-by-step temperature increase vacuum heat treatment and pressure welding in S3) is as follows: S3.1) Place the sample into the diffusion welding equipment and start evacuating the vacuum; S3.2) When the vacuum of the equipment is ≤10 -2 Pa, the temperature is raised at a certain rate, and when the temperature reaches 700°C, the holding time is 1-2h, and when the temperature continues to rise to 800°C, the holding time is 1-2h; S3.3) When the temperature continues to rise to 900-1000°C, the pressure is increased to 2-60MPa, so that the grain boundary diffusion and pressure welding processes are carried out simultaneously. The heat preservation and pressure holding time is 10-30h. After the heat preservation is completed, argon gas is filled and cooled to room temperature.

7. The method according to claim 6, characterized in that The heating rate in S3.2) is 2-10°C / min; The pressurization rate in S3.3) is 2-10 MPa / min.

8. The method according to claim 1, characterized in that The tempering equipment in S4) is a vacuum furnace, the tempering temperature is 400-600°C, the insulation time is 2-5h, and the vacuum degree is ≤10 -2 Pa, the heating rate is 2-10℃ / min.

9. The method according to claim 1, characterized in that: The thickness of the NdFeB magnet prepared by the method is 6-20 mm; and the composition is (La i Ce 1-i ) m (Pr k Nd 1-k ) n (Dy l Tb f Ho h G 1-l-f-h ) t M 1-m-n-t phase, the thickness of which is 1-3 μm; wherein 0≤i≤1, 0≤k≤1, 0≤m≤1, 0≤n≤1, 0≤l≤1, 0≤f≤1, 0≤h≤1, 0≤t≤1 and 0.4≤m+n+t<1; M is any one or more of Al, Cu, Ga, In, Sn, Fe, Co, and Zr.

10. A neodymium iron boron magnet, characterized in that: The NdFeB magnet is prepared by the method according to any one of claims 1 to 9.

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