Preparation method of neodymium iron boron diffusion magnet

Abstract

The invention belongs to the technical field of high-performance sintered neodymium-iron-boron magnets, and particularly discloses a preparation method of a neodymium-iron-boron diffusion magnet. According to the preparation method, through the design of a layered structure, composite diffusion sources with different components are placed on the two faces of the magnet, then thermal diffusion treatment is conducted, and the grain boundary diffusion magnet is obtained after annealing. The high-performance magnet is prepared through dry or wet diffusion, the intrinsic coercive force of the magnet can be remarkably improved, and heavy rare earth resources are saved. According to the method, in the preparation process of the grain boundary diffusion magnet, the layered structure design is matched with the grain boundary diffusion technology, the grain boundary phase composition of the magnet can be well enriched, the utilization rate of heavy rare earth resources is remarkably increased, and the diffusion magnet product prepared through the method is good in performance consistency and high in yield. The method can be applied to working conditions with high requirements for magnetic performance, and is suitable for industrialization.

Description

Technical Field

[0001] The invention belongs to the technical field of high-performance sintered NdFeB magnets, and more specifically, relates to a method for preparing a NdFeB diffusion magnet. Background Art

[0002] Grain boundary diffusion technology is an effective method for preparing high-performance sintered NdFeB magnets. High-performance sintered NdFeB magnets with high remanence and coercivity prepared by grain boundary diffusion technology are widely used in many fields. In the automotive field, grain boundary diffusion magnets are widely used in drive motors, generators and high-quality audio systems for new energy vehicles; in consumer electronics, grain boundary diffusion magnets are used in vibration motors in smartphones, micro cameras, and high-quality micro audio systems in tablet computers; industrial robots also have high performance requirements for magnets, such as stators or outer rotors of high-precision motors, which require high-performance grain boundary diffusion magnets; grain boundary diffusion magnets are also widely used in computers, 5G network base stations, energy-saving home appliances, wind power, industrial motors and other fields. These fields have different performance requirements for magnets, but grain boundary diffusion magnets can provide better solutions. At present, the preparation of high-performance magnets by grain boundary diffusion technology and their wide application in many fields have become an important development direction in the field of high-performance magnetic materials.

[0003] The technical principle of grain boundary diffusion technology is to form a layer of heavy rare earth diffusion film on the surface of magnetic steel, and then enter the interior of the magnet along the grain boundary phase through vacuum heat treatment. In this process, heavy rare earth atoms will replace Nd atoms around the main phase grains of NdFeB, forming a high coercive force shell around the main phase grains. This unique microstructure can greatly improve the coercive force of the magnet on the basis of extremely low remanence drop value. Compared with traditional non-diffused magnets, grain boundary diffusion technology can greatly reduce the use of heavy rare earth elements such as dysprosium (Dy) and terbium (Tb), thereby reducing costs. Grain boundary diffusion technology can produce magnets with high comprehensive magnetic properties, such as 50EH, 52UH and other high-performance magnets that traditional processes cannot achieve. However, the preparation of grain boundary diffusion magnets directly through heavy rare earth diffusion sources usually also leads to the enrichment of a large amount of expensive heavy rare earth elements on the surface of the magnet, reducing the utilization efficiency of the heavy rare earth diffusion source. In order to further open the diffusion channel of the magnet substrate, enrich the grain boundary phase of the magnet, and improve the coercive force and comprehensive magnetic properties of the magnet, the present invention prepares a composite diffusion source by adding a low melting point metal for grain boundary diffusion, which is used to optimize the diffusion channel of the magnet substrate and further enrich the grain boundary phase of the magnet substrate, so that the magnet can achieve a higher magnetocrystalline anisotropy field. In addition, the present invention can optimize the grain boundary diffusion technology by preparing a composite diffusion source of metal powder and quartz sand powder, provide more flow channels for the diffusion source, and then improve the utilization rate of heavy rare earths such as dysprosium and terbium, so as to achieve the purpose of improving the comprehensive magnetic properties of the magnet and saving heavy rare earth resources. Summary of the invention

[0004] In order to reduce the usage of heavy rare earth in the diffusion source and improve the comprehensive magnetic properties of the magnet, such as the coercive force, the present invention provides a method for preparing high-performance sintered NdFeB magnets by diffusion of low-melting-point metal composite films, which can greatly improve the utilization rate of heavy rare earth resources, make the diffusion source diffuse more evenly during the diffusion process, make the grain boundary phase distribution of the NdFeB magnet more abundant, and greatly improve the magnetocrystalline anisotropy field of the magnet.

[0005] The technical solution of the present invention is: a method for preparing a NdFeB diffused magnet, the preparation method specifically comprising the following steps:

[0006] S1) preparing a composite diffusion source;

[0007] S2) placing the composite diffusion source prepared in S1) and the sintered NdFeB magnet substrate in a mold in a certain manner;

[0008] S3) Then, pressing, heat treatment diffusion, annealing and grinding and polishing are performed to obtain a diffusion magnet with a diffusion layer attached to the surface; and high-precision grinding is performed to obtain a smooth sintered NdFeB diffusion magnet.

[0009] Further, the method for preparing the composite diffusion source in S1) is a dry process or a dry process;

[0010] The dry process is specifically as follows: low-melting-point metal powder and inorganic material of a certain mesh size are weighed and mixed according to the designed proportion, so as to obtain the powder of the diffusion source;

[0011] The dry process is specifically as follows: low-melting-point metal powder of a certain mesh size, metal powder containing heavy rare earth and liquid agent are weighed separately according to the designed proportion, and fully mixed to obtain a slurry of the composite diffusion source.

[0012] Furthermore, the mass percentage of the low melting point metal powder in the dry process is 1 to 30% by weight, and the mass percentage of the inorganic material is 70 to 99% by weight;

[0013] The low melting point metal powder is one or more of gallium, aluminum, tin, indium and bismuth;

[0014] The inorganic material is quartz sand.

[0015] Furthermore, the mass percentage of the low melting point metal powder in the dry process is 10-70.wt% and / or the mass percentage of the metal powder containing heavy rare earth is 10-70.wt%, and the mass percentage of the chemical reagent is 30-90% .wt%;

[0016] The low melting point metal powder is one or more of gallium, aluminum, tin, indium and bismuth (Bi);

[0017] The heavy rare earth-containing metal powder is a heavy rare earth alloy powder or a heavy rare earth hydrogenated powder;

[0018] The chemical reagent is ethanol or glycerol.

[0019] Further, the specific process steps of S2) are: firstly, the diffusion source powder is made into a thin layer; the diffusion source powder thin layer, the sintered NdFeB magnet substrate and the diffusion source powder thin layer are placed in a mold in the order of being used;

[0020] or

[0021] First, place the inorganic material at the bottom of the mold, then drip the diffusion source slurry on the surface of the inorganic material. After sufficient penetration, place the NdFeB magnet substrate in the middle of the pre-prepared mold, then take a certain amount of inorganic material and place it on the upper surface of the NdFeB magnet substrate and drip the composite diffusion source slurry evenly on the surface of the inorganic material again to form a double-sided diffusion source thin layer.

[0022] Further, the mass ratio of the slurry to the inorganic material is in the range of 5% to 50%.wt.;

[0023] The inorganic material is quartz sand.

[0024] Further, the specific process parameters in S3) are:

[0025] The vacuum degree should be less than 1.0×10 -3 crouch;

[0026] The temperature of heat treatment diffusion is 800-1020°C, and the heat treatment time is 8-24h;

[0027] The annealing process temperature is 450-600°C, and the annealing process time is 2-5h;

[0028] The pressure required for pressing by dry process is 2.5M Pa to 10.0M Pa;

[0029] The pressure required for pressing in the wet process is the same as that in the dry process;

[0030] Furthermore, the particle size of the low melting point metal powder in the dry process is less than 400 mesh; the particle size of the inorganic material is 38 microns;

[0031] The diffusion source slurry contains one or more of low melting point metal powder or heavy rare earth metal powder, and the particle size is required to be less than 400 mesh, 38 microns (μm);

[0032] Furthermore, the intrinsic coercive force increase of the NdFeB diffused magnet prepared by the preparation method is 5 kOe to 10 kOe.

[0033] A NdFeB diffused magnet is prepared by the above-mentioned preparation method.

[0034] The beneficial effects of the present invention are as follows: due to the adoption of the above technical solution, the present invention adopts a composite diffusion source in the process of preparing a grain boundary diffusion magnet, and the layered structure design is combined with the grain boundary diffusion technology, which can better enrich the grain boundary phase composition of the magnet, significantly improve the intrinsic coercive force of the magnet, and improve the utilization rate of heavy rare earth resources. The diffused magnet product prepared by the present invention has good performance consistency, can be used in working conditions with high magnetic performance requirements, and is suitable for industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a flowchart of a method for preparing a NdFeB diffusion magnet. DETAILED DESCRIPTION

[0036] In order to clarify the technical solutions and advantages of the present application, the present application will be further described below in conjunction with the embodiments. It should be understood that the described embodiments are only part of the implementation cases of the present application, rather than all the embodiments. The preparation process of the specific embodiment is as follows:

[0037] The grain boundary diffusion method provided by the present invention is divided into a dry method and a wet method. First, in the dry process, a low-melting point metal powder and quartz sand powder of a certain mesh size are fully mixed to prepare a composite diffusion source; another pre-prepared mold is taken, and the diffusion source powder thin layer, the sintered NdFeB magnet substrate and the diffusion source powder thin layer are placed in sequence, and then pressing, heat treatment diffusion, annealing and grinding and polishing processes are performed to obtain a diffusion magnet; the dry process composite diffusion source film is subjected to a grain boundary diffusion process. First, a low-melting point metal powder of a certain mesh size, a metal powder containing heavy rare earths and a liquid agent are fully mixed to prepare a composite diffusion source slurry; another quartz sand fine powder is taken and placed in a pre-prepared mold and the diffusion source slurry is evenly dripped for full penetration, and then the NdFeB magnet substrate is placed on the surface of the composite diffusion source thin layer, and a composite diffusion source thin layer containing quartz sand fine powder is placed in the same manner to form a double-sided diffusion source thin layer, and then pressing, drying, heat treatment diffusion, annealing and grinding and polishing processes are performed to obtain a diffusion magnet;

[0038] Preferably, a composite diffusion source film is prepared by a dry process, wherein the chemical composition of the diffusion source is one or more of low melting point metals of gallium (Ga), aluminum (Al), tin (Sn), indium (In) and bismuth (Bi) and high temperature resistant quartz sand fine powder. The mass percentage of the low melting point metal and the high temperature resistant quartz sand fine powder is in the following range: x is 1 to 30% by weight of the low melting point metal, y is 70 to 99% by weight of the quartz sand, and x+y is 100%;

[0039] Preferably, the particle size of the metal powder, low melting point metal powder and quartz sand powder used in the dry process composite diffusion source film is required to be less than 38 microns (μm);

[0040] Preferably, the mold used in the dry process is an open mold with a demoulding accessory, which does not leak after being closed, and can be processed according to the thickness of the magnet and the thickness of the diffusion source thin layer. The pressure required for pressing is 2.5Mpa to 10.0Mpa;

[0041] Preferably, the temperature range required for the heat treatment diffusion process is 800-1020°C, and the temperature range required for the annealing process is 450-600°C; the vacuum required for the heat treatment diffusion process and the annealing process should be less than 1.0×10 -3 Pa, after annealing, the diffused magnet is obtained by rapid cooling in an argon atmosphere;

[0042] Preferably, the wet process can prepare a composite diffusion source slurry, which contains one or more of low melting point metals of gallium (Ga), aluminum (Al), tin (Sn), indium (In) and bismuth (Bi), wherein the heavy rare earth metal powder can be one or more of dysprosium (Dy), terbium (Tb), heavy rare earth alloy powder and hydrogenated powder. The mass percentage of each component in the diffusion source slurry is as follows: x is 10-70.wt% of low melting point metal, y is 10-70.wt% of heavy rare earth metal powder, z is 30-90% .wt% of chemical reagent (such as ethanol, glycerol, etc.), x+y+z=100%;

[0043] Preferably, the wet process requires that the diffusion source slurry be uniformly dripped onto the surface of the quartz sand, and the mass ratio of the diffusion source slurry to the quartz sand is in the range of 5% to 50%.wt.

[0044] Preferably, the prepared diffusion source film is pressed and then dried, and the drying temperature is 80-120°C; the temperature range required for the heat treatment diffusion process is 800-1020°C, and the temperature range required for the annealing process is 450-600°C; the vacuum required for the heat treatment diffusion process and the annealing process is less than 1.0×10 -3 Pa, after annealing, the diffused magnet is obtained by rapid cooling in an argon atmosphere;

[0045] Example 1

[0046] According to the dry process, 0.1g of aluminum powder and 4.9g of quartz sand powder are mixed evenly. The particle size of aluminum powder and quartz sand is 20-30μm. Put them into the prepared mixing bottle for mixing to prepare a uniform composite diffusion source. Use the pre-prepared mold to first put the module 1 cylinder (diameter 14.75mm, thickness 30.00mm) into module 2 (diameter 14.80mm, hole thickness 60.00mm), completely insert, take 2.0g of the mixed diffusion source powder and spread it on the surface of the above cylindrical mold, shake it evenly, and put the prepared or commercially purchased cylindrical magnet (N48 or N55, etc.) into the mold. The diameter of the magnet substrate is 14.70mm and the thickness is 5.0mm. The specific thickness can be customized according to needs. Take 2.0g of the mixed diffusion source fine powder and spread it on the top of the above cylindrical magnet. Finally, place module 3 into the prepared module 2. The diameter of the cylindrical part of module 3 is the same as that of module 1, and the thickness is 50.0mm. In actual working conditions, the diameter and thickness of the required mold can be customized according to actual needs. Place the diffusion source powder layer, sintered NdFeB magnet substrate and diffusion source powder layer in order and press them. The pressure is 3.0Mpa and the pressing time is 5min. Put the prepared magnet module assembly as a whole into a horizontal vacuum sintering furnace for heat treatment diffusion. The required vacuum degree needs to be less than 1.0×10 -3 pa, heat treatment temperature 800℃, time 4h. After the heat treatment, annealing is carried out, annealing temperature 520℃, time 2h. After annealing, the magnet is ground and polished to obtain a grain boundary diffusion magnet. A comparative experiment was carried out in this case. Comparative Example 1 is a conventional method, in which a composite diffusion source prepared by 0.2g aluminum powder and 9.8g quartz sand fine powder is sampled and sprayed on the surface of the magnet for thermal diffusion; in Comparative Example 2, the diffusion source is a composite diffusion source prepared by 0.2g aluminum powder and 4.8g quartz sand fine powder, and the remaining conditions are the same as the preparation process of Comparative Example 1.

[0047] Table 1. Comprehensive magnetic properties of grain boundary diffused NdFeB magnets in Example 1

[0048]

[0049]

[0050] Example 2

[0051] According to the dry process, the magnet is a rectangular magnetic sheet with a certain thickness. Take 0.2g aluminum powder and 9.8g quartz sand fine powder and mix them evenly. The particle size of aluminum powder and quartz sand is 20-30μm. Put them into the prepared mixing bottle for mixing to prepare a uniform composite diffusion source. The subsequent steps are the same as Example 1. The mold is prepared in advance. The columnar hole size of the mold (module 2) is 16.00mm long, 4.50mm wide, and 200.00mm high. First, the module 1 cuboid (15.95mm long, 4.45mm wide, and 50.00mm high) is placed in module 2 and completely inserted. Take 1.0g of the mixed diffusion source fine powder and spread it on the surface of the above cuboid mold. Put the prepared or commercially purchased rectangular magnet (N48H or N50H, etc.) into the mold. The magnet substrate is also a cuboid, 15.90mm long, 4.30mm wide, and 5.00mm high. Take 1.0g of the mixed diffusion source fine powder and spread it on the top of the above rectangular magnet. Finally, place module 3 into the prepared module 2. The rectangular part of module 3 is 15.95mm long, 4.45mm wide and 200.0mm high. Modules 1 and 3 can be demolded under pressure. In actual working conditions, the size of the required mold can be customized according to actual needs. Place the diffusion source powder layer, sintered NdFeB magnet substrate and diffusion source powder layer in order and press them. The pressure is 5.0Mpa and the pressing time is 5min. Put the prepared magnet module assembly as a whole into a horizontal vacuum sintering furnace for heat treatment diffusion. The required vacuum degree needs to be less than 1.0×10 -3 pa, heat treatment temperature 800℃, time 4h. Annealing is carried out after the heat treatment, annealing temperature 520℃, time 2h. After annealing, the magnet is ground and polished to obtain a grain boundary diffusion magnet. A comparative experiment was carried out in this case. In comparative example 1, the diffusion source is a composite diffusion source prepared by 0.15g aluminum powder and 9.85g quartz sand fine powder, and the magnet is a rectangular magnetic sheet. After conventional pulping and spraying, grain boundary diffusion is carried out; in comparative example 2, the diffusion source is a composite diffusion source prepared by 0.25g aluminum powder and 9.75g quartz sand fine powder. The influence on the comprehensive magnetic properties of the magnet, the experimental conditions are the same as the preparation process of comparative example 1.

[0052] Table 2. Comprehensive magnetic properties of grain boundary diffused NdFeB magnets in Example 2 and Comparative Examples

[0053]

[0054]

[0055] Example 3

[0056] According to the wet process, 1.6 g of terbium aluminum alloy powder (Tb 70 Al 30), 1.2g of fine copper powder and 7.2g of liquid diffusant are evenly mixed to prepare a uniform composite diffusion source slurry. The fine particle sizes of terbium aluminum alloy powder and copper powder are both 1-3μm. Take 0.6g of the above mixed slurry and add it dropwise to 4.0g of quartz sand fine powder to mix evenly to obtain the diffusion source fine powder. The particle size of the quartz sand fine powder is 1-3μm. Use the same mold as Example 1 to carry out the thermal diffusion process. First, place the module 1 cylinder (diameter 14.75mm, thickness 30.00mm) into module 2 (diameter 14.80mm, hole thickness 60.00mm), completely insert it, take 1.5g of the mixed diffusion source fine powder and spread it on the surface of the above cylindrical module 1, shake it evenly, and place the prepared or commercially purchased cylindrical magnet (N50M or N52M) into the mold. The diameter of the magnet substrate is 14.70mm and the thickness is 5.0mm. The specific thickness can be customized according to needs. Take another 1.5g of the mixed diffusion source fine powder and spread it on the surface of the cylindrical magnet. Finally, place module 3 into the prepared module 2. The diameter of the cylindrical part of module 3 is the same as that of module 1, and the thickness is 50.0mm. Place the diffusion source powder layer, sintered NdFeB magnet substrate and diffusion source powder layer in the order of each layer and press them. The pressure is 3.0Mpa and the pressing time is 5min. Dry the magnet together with the mold at 100℃, and then place the prepared magnet module assembly as a whole in a horizontal vacuum sintering furnace for heat treatment diffusion. The required vacuum degree needs to be less than 1.0×10 -3 pa, heat treatment temperature 800℃, time 4h. After the heat treatment, annealing is performed at 520℃, time 2h. After annealing, the magnet is ground and polished to obtain a grain boundary diffusion magnet. This case conducted a comparative experiment. In comparative example 1, the diffusion source is 1.3g terbium aluminum alloy powder (Tb 70 Al 30 ), 1.2g fine copper powder and 7.5g liquid diffusing agent were mixed evenly to prepare a composite diffusion source slurry, which was directly sprayed and then heat treated and tempered; in Comparative Example 2, the diffusion source was 1.8g terbium aluminum alloy powder (Tb 70 Al 30 ), 1.1g of fine copper powder and 7.1g of liquid diffusing agent were mixed evenly to prepare a composite diffusion source slurry; the other experimental conditions were the same as those in Comparative Example 1.

[0057] Comprehensive magnetic properties of grain boundary diffused NdFeB magnets in Example 3

[0058]

[0059]

[0060] The technical solution for preparing diffusion magnets provided by the present invention includes two methods, dry method and wet method. Both methods require the use of a diffusion mold for diffusion. After the diffusion process uses low-melting-point metal and quartz sand to prepare a composite diffusion source, a grain boundary diffusion treatment is performed. In the dry diffusion process, directly performing grain boundary diffusion after pressing to form a diffusion source film can make the grain boundary phase distribution of the magnet more uniform during the thermal diffusion treatment process, and the diffusion source dispersion is more obvious, thereby improving the comprehensive magnetic properties of the magnet, such as the coercive force. In the present invention, the wet process mainly first needs to prepare a diffusion source slurry containing a low-melting-point metal, and then the slurry is evenly added to the quartz sand fine powder to prepare a composite diffusion source film. Grain boundary diffusion is performed through processes such as pressing and thermal diffusion treatment, and finally a magnet with higher comprehensive magnetic properties is obtained. The present invention includes but is not limited to the NdFeB magnets provided in the above-mentioned embodiments, which can be applied to the grain boundary diffusion treatment of various magnets and has universal applicability.

[0061] The above is a detailed introduction to the preparation method of a NdFeB diffused magnet 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 a NdFeB diffusion magnet, characterized in that: The preparation method specifically comprises the following steps: S1) preparing a composite diffusion source; S2) placing the composite diffusion source prepared in S1) and the sintered NdFeB magnet substrate in a mold in a certain manner; S3) The whole is pressed, heat-treated, diffused, annealed and polished to obtain a diffused magnet with a diffusion layer attached to the surface; and then high-precision polishing is performed to obtain a NdFeB diffused magnet.

2. The preparation method according to claim 1, characterized in that: The method for preparing the composite diffusion source in S1) is a dry process or a wet process; The dry process is specifically as follows: low-melting-point metal powder and inorganic material of a certain mesh size are weighed and mixed according to the designed proportion, so as to obtain the powder of the diffusion source; The wet process is specifically as follows: low-melting-point metal powder of a certain mesh size, metal powder containing heavy rare earth and liquid reagent are weighed separately according to the designed proportion, and fully mixed to obtain a slurry of the composite diffusion source.

3. The preparation method according to claim 2, characterized in that: The mass percentage of the low melting point metal powder in the dry process is 1 to 30% by weight, and the mass percentage of the inorganic material is 70 to 99% by weight; The low melting point metal powder is one or more of gallium, aluminum, tin, indium and bismuth; The inorganic material is quartz sand.

4. The preparation method according to claim 2, characterized in that: The mass percentage of the low melting point metal powder in the dry process is 10-70.wt% and the mass percentage of the metal powder containing heavy rare earth is 10-70.wt%, and the mass percentage of the chemical reagent is 30-90% .wt%; The low melting point metal powder is one or more of gallium, aluminum, tin, indium and bismuth; The heavy rare earth-containing metal powder is a heavy rare earth alloy powder or a heavy rare earth hydrogenated powder; The chemical reagent is ethanol or glycerol.

5. The preparation method according to claim 2, characterized in that: The specific process steps of S2) are: firstly, the diffusion source powder is made into a thin layer; the diffusion source powder thin layer, the sintered NdFeB magnet substrate and the diffusion source powder thin layer are placed in a mold in the order of being used; or First, place the inorganic material at the bottom of the mold, then drip the diffusion source slurry on the surface of the inorganic material. After sufficient penetration, place the NdFeB magnet substrate in the middle of the pre-prepared mold, then take a certain amount of inorganic material and place it on the upper surface of the NdFeB magnet substrate and drip the composite diffusion source slurry evenly on the surface of the inorganic material again to form a double-sided diffusion source thin layer.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the slurry to the inorganic material is in the range of 5% to 50%.wt; The inorganic material is quartz sand.

7. The preparation method according to claim 1, characterized in that: The specific process parameters in S3) are: The vacuum degree should be less than 1.0×10 -3 crouch; The temperature of heat treatment diffusion is 800-1020°C, and the heat treatment time is 8-24h; The annealing process temperature is 450-600°C, and the annealing process time is 2-5h; The pressure required for pressing by both dry process and wet process is 2.5M Pa-10.0M Pa.

8. The preparation method according to claim 2, characterized in that: The particle size of the low melting point metal powder is less than 400 mesh; the particle size of the inorganic material is 38 microns; The particle size of the heavy rare earth metal powder is required to be less than 400 mesh.

9. The preparation method according to claim 2, characterized in that: The intrinsic coercive force increase of the NdFeB diffusion magnet prepared by the preparation method is 5 kOe to 10 kOe.

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

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