A neodymium iron boron magnet with ultra-high coercivity and its preparation method and application

Abstract

The present invention discloses a neodymium iron boron magnet with ultra-high coercivity, and its preparation method and application. The preparation method comprises: providing a neodymium iron boron compact; and performing a liquid phase sintering treatment on the neodymium iron boron compact to prepare a neodymium iron boron magnet with ultra-high coercivity; wherein the liquid phase sintering treatment comprises pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion treatment; the magnet main phase grains in the pre-diffused magnet obtained by the pre-diffusion treatment have a core-shell structure, and the magnet main phase grains in the neodymium iron boron magnet with ultra-high coercivity have an inner and outer double-layer heavy rare earth magnetic hardened shell structure. The present invention utilizes the segmented process control of the liquid phase sintering process to optimize the sintering and diffusion processes, realizes the high-quality utilization of heavy rare earths, and prepares an ultra-high coercivity neodymium iron boron magnet with simple operation and convenient production.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth permanent magnet materials, and in particular relates to a neodymium iron boron magnet with ultra-high coercivity, a preparation method thereof, and an application thereof. Background Art

[0002] As a third-generation rare earth permanent magnet, NdFeB (NdFeB) boasts high coercivity, high remanence, and high magnetic energy product, making it the permanent magnet material with the highest overall magnetic properties discovered to date. The rapid development of emerging sectors such as new energy vehicles, magnetic levitation trains, wind power generation, and energy-saving home appliances is placing higher demands on the magnetic properties of NdFeB permanent magnets, particularly their resistance to demagnetization. However, the actual coercivity of ternary NdFeB magnets currently achievable is less than half of the theoretical value, necessitating further enhancement of their coercivity. Heavy rare earth grain boundary diffusion (GBI) is an effective method for increasing the coercivity of magnets. This involves attaching a diffusion source containing heavy rare earth elements to the magnet surface. Through a specific heat treatment, the heavy rare earth elements are introduced into the magnet along the grain boundaries of the NdFeB magnet, forming a magnetically hardened shell with a higher anisotropy field on the grain surface. This inhibits the nucleation of reverse magnetization domains (reverse magnetic domains) on the grain surface, thereby increasing the magnet's coercivity. After years of development, the forms of diffusion sources used in diffusion technology have become diverse, including heavy rare earth elements, oxides, fluorides, hydrides, and alloys. Simultaneously, the methods for attaching the diffusion sources have also continued to expand, including electrophoretic deposition, spray coating, magnetron sputtering, and vapor deposition. Despite this increasing diversity of diffusion processes, practice has shown that conventional heavy rare earth grain boundary diffusion techniques offer limited improvements in coercivity, typically failing to achieve increases exceeding 10 kOe after diffusion. Therefore, providing NdFeB magnets with ultrahigh coercivity and methods for their preparation are pressing challenges. Summary of the Invention

[0003] The main purpose of the present invention is to provide a neodymium iron boron magnet with ultra-high coercivity and a preparation method and application thereof, so as to overcome the deficiencies of the prior art.

[0004] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0005] An embodiment of the present invention provides a method for preparing a neodymium iron boron magnet with ultrahigh coercivity, which comprises:

[0006] Provide NdFeB compacts;

[0007] and performing liquid phase sintering on the NdFeB compact to produce a NdFeB magnet with ultra-high coercivity;

[0008] Among them, the liquid phase sintering treatment includes pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion treatment; the main phase grains of the magnet in the pre-diffused magnet obtained by the pre-diffusion treatment have a core-shell structure, and the main phase grains of the magnet in the NdFeB magnet with ultra-high coercivity have an inner and outer double-layer heavy rare earth magnetic hardened shell structure.

[0009] An embodiment of the present invention also provides a neodymium iron boron magnet with ultra-high coercivity obtained by the aforementioned preparation method, wherein the magnet main phase grains in the neodymium iron boron magnet with ultra-high coercivity include an inner heavy rare earth magnetic hardening shell layer and an outer heavy rare earth magnetic hardening shell layer sequentially formed on the surface of the core structure.

[0010] The embodiments of the present invention further provide uses of the aforementioned NdFeB magnets with ultra-high coercivity in the fields of new energy vehicles, magnetic levitation trains, wind power generation or energy-saving home appliances.

[0011] The high-performance NdFeB magnets prepared by the present invention using traditional grain boundary diffusion technology have a magnetic hardening shell rich in heavy rare earths only present on the surface of the grains. During the actual demagnetization process, although this shell has a certain pinning effect on the reversal and transfer of anti-magnetization domains between grains, anti-magnetization nucleation is more likely to form inside the grains. Once the volume fraction of the anti-magnetization domains inside the grains reaches a certain proportion, the magnetic hardening effect of the shell on the grain surface will not be sufficient to continue to block the magnetic exchange coupling between the grains. This means that the traditional intergranular diffusion technology has limited effect on improving the coercive force. The present invention is based on a large number of practical studies, combined with the growth characteristics of the main phase of NdFeB, and uses the segmented process control of the liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion) to achieve a typical structure in which the main phase of the magnet grain has an inner and outer double-layer heavy rare earth magnetic hardening shell. The inner shell can effectively inhibit the nucleation of reverse magnetization in the weak area inside the grain, and the outer shell can effectively block the transfer of reverse magnetization domains between grains, ultimately achieving the purpose of preparing ultra-high coercive force NdFeB magnets.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] (1) The present invention successfully prepares NdFeB grains with a double-layer heavy rare earth shell, forming magnetic hardening and strengthening structural units on the surface and inside of the magnet grains, effectively inhibiting the nucleation and migration of reverse magnetization domains, and optimizing and improving the coercive force of NdFeB magnets;

[0014] (2) The main phase grains of the NdFeB magnets with ultra-high coercivity in the present invention have an inner and outer double-layer heavy rare earth magnetic hardening shell. The thickness and heavy rare earth content of the inner shell can be controlled and adjusted by controlling the pre-diffusion process (heavy rare earth pre-diffusion source composition and dosage), which can achieve the expected design of raw material cost and coercivity improvement effect;

[0015] (3) The present invention not only realizes the advantages of grain boundary diffusion technology in saving heavy rare earth usage and production costs, but also achieves the characteristics of traditional heavy rare earth alloying smelting and adding method in strengthening the overall anti-demagnetization ability of NdFeB main phase grains, and has strong practicality and creativity;

[0016] (4) The preparation method provided by the present invention is simple and easy to operate, and the prepared product has good consistency and stability. It can prepare ultra-high coercive force NdFeB magnets and is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a schematic diagram of the principle of preparing a neodymium iron boron magnet with ultra-high coercivity in a typical embodiment of the present invention. DETAILED DESCRIPTION

[0019] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The technical solution of the present invention will be clearly and completely described below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making any creative effort shall fall within the scope of protection of the present invention.

[0020] Specifically, as one aspect of the technical solution of the present invention, a method for preparing a neodymium iron boron magnet with ultra-high coercivity includes:

[0021] Provide NdFeB compacts;

[0022] and performing liquid phase sintering on the NdFeB compact to produce a NdFeB magnet with ultra-high coercivity;

[0023] Among them, the liquid phase sintering treatment includes pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion treatment; the main phase grains of the magnet in the pre-diffused magnet obtained by the pre-diffusion treatment have a core-shell structure, and the main phase grains of the magnet in the NdFeB magnet with ultra-high coercivity have an inner and outer double-layer heavy rare earth magnetic hardened shell structure.

[0024] In some preferred embodiments, the schematic diagram of the principle of preparing NdFeB magnets with ultra-high coercivity in the present invention is as follows: Figure 1 shown.

[0025] In some preferred embodiments, the method for preparing the NdFeB magnet with ultra-high coercivity comprises: preparing raw materials according to the composition of the final desired sintered NdFeB magnet, smelting the alloy to obtain NdFeB alloy flakes, hydrogen-crushing the NdFeB alloy flakes to obtain hydrogen-crushed coarse powder; jet milling the hydrogen-crushed coarse powder to obtain NdFeB fine powder with uniform particle size distribution; performing orientation pressing and isostatic pressing to obtain NdFeB compacts; and subjecting the NdFeB compacts to Liquid phase sintering treatment includes pre-sintering, pre-diffusion, densification sintering and grain boundary diffusion treatment; first, the NdFeB compact is pre-sintered to obtain a relatively dense pre-sintered magnet; then the pre-sintered magnet is pre-diffusion treated to form a core-shell structure in the main phase grains of the magnet; the above magnet is further sintered to densify the magnet, and finally grain boundary diffusion is performed to obtain an ultra-high coercive force NdFeB magnet with an inner and outer double layer of heavy rare earth magnetic hardening shell in the main phase grains of the magnet.

[0026] In some preferred embodiments, the preparation method comprises: pre-sintering the NdFeB compact at 900-1020° C. for 2-5 hours to obtain a pre-sintered magnet; wherein the grain size of the pre-sintered magnet is 3-5 μm.

[0027] Furthermore, the purpose of the pre-sintering is to prevent excessive growth of grains, and the grain size is 3-5 μm at this time.

[0028] In some preferred embodiments, the preparation method includes: coating a pre-diffusion source on the surface of the pre-sintered magnet and performing a pre-diffusion treatment for 2-8 hours under vacuum conditions at a temperature of 800-950°C to obtain a pre-diffusion magnet; wherein the pre-diffusion treatment at least causes the main phase grains of the obtained pre-diffusion magnet to form a core-shell structure.

[0029] Furthermore, the pre-diffusion source includes a rare earth alloy diffusion source, and the chemical formula of the rare earth alloy diffusion source is H x R y M 100-x-y , wherein H is selected from any one or a combination of two or more of Tb, Dy, and Ho, R is selected from any one or a combination of two or more of Pr, Nd, Y, Ce, and La, and M is selected from any one or a combination of two or more of Cu, Al, Fe, Ga, Zn, Mg, and Mn. x and y represent the atomic percentage content of each component in the rare earth alloy diffusion source, and x is 0-30 and y is 20-80.

[0030] Furthermore, raw materials are prepared according to the composition of the pre-diffusion source, and the required pre-diffusion source is prepared through processes such as arc melting, wire cutting, hydrogen blasting, and air flow milling.

[0031] In some preferred embodiments, the preparation method comprises: performing a densification sintering treatment on the pre-diffused magnet at 1000-1100° C. for 2-10 hours to obtain a densified sintered magnet; wherein the grain size of the densified sintered magnet is 5-10 μm.

[0032] Furthermore, the densification sintering process is to increase the temperature to allow the grains to grow.

[0033] In some preferred embodiments, the preparation method includes: coating the surface of the densified sintered magnet with a diffusion source and performing a diffusion treatment at 800-950°C for 2-8 hours, followed by a tempering treatment at 400-600°C for 2-4 hours to obtain a NdFeB magnet with ultra-high coercivity.

[0034] Furthermore, the diffusion source includes a rare earth alloy diffusion source, and the chemical formula of the rare earth alloy diffusion source is H x R y M 100-x-y , wherein H is selected from any one or a combination of two or more of Tb, Dy, and Ho, R is selected from any one or a combination of two or more of Pr, Nd, Y, Ce, and La, and M is selected from any one or a combination of two or more of Cu, Al, Fe, Ga, Zn, Mg, and Mn. x and y represent the atomic percentage content of each component in the rare earth alloy diffusion source, and x is 0-30 and y is 20-80.

[0035] Furthermore, raw materials are prepared according to the composition of the diffusion source, and the required diffusion source is prepared through processes such as arc melting, wire cutting, hydrogen blasting, and air flow milling.

[0036] In some preferred embodiments, the preparation method comprises:

[0037] Providing raw materials for preparing NdFeB compacts and performing alloy smelting treatment to obtain NdFeB alloy flakes;

[0038] performing hydrogen crushing treatment on the NdFeB alloy flakes to obtain hydrogen crushed coarse powder;

[0039] Performing jet milling on the hydrogen-crushed coarse powder to obtain NdFeB fine powder;

[0040] Furthermore, the NdFeB fine powder is subjected to orientation compression molding and isostatic pressing to obtain a NdFeB compact.

[0041] Furthermore, the chemical formula of the composition of the NdFeB compact is R x Fe y M z B α; Wherein, R is selected from any one or a combination of two or more of La, Ce, Tb, Dy, Ho, Y, Gd, Nd, and Pr, M is selected from any one or a combination of two or more of Cu, Al, Ga, Mg, Ni, Ti, Co, and Zr, x is 28-33wt%, y is 60-75wt%, z is 0-5wt%, α is 0.9-1.2wt%, and x+y+z+α=100.

[0042] Furthermore, the thickness of the NdFeB alloy sheet is 200-300 μm.

[0043] Furthermore, the grinding gas pressure used in the jet mill treatment is 0.5-0.7 MPa, and the rotating speed of the classifying wheel is 3500-5000 rpm.

[0044] Furthermore, the average particle size D50 of the NdFeB fine powder is 1 μm≤D50≤2 μm.

[0045] The pre-diffusion source and the diffusion source in the present invention may be the same or different.

[0046] In some more specific embodiments, the method for preparing the NdFeB magnet with ultrahigh coercivity comprises:

[0047] (1) preparing raw materials according to the composition of the final desired sintered NdFeB magnet, smelting the alloy to obtain NdFeB alloy flakes, and hydrogen-crushing the NdFeB alloy flakes to obtain hydrogen-crushed coarse powder;

[0048] (2) jet milling the hydrogen-crushed coarse powder to obtain NdFeB fine powder with uniform particle size distribution;

[0049] (3) performing isostatic pressing after orientation compression molding to obtain a NdFeB compact;

[0050] (4) pre-sintering the NdFeB compact to obtain a relatively dense pre-sintered magnet;

[0051] (5) performing a pre-diffusion treatment on the pre-sintered magnet to form a core-shell structure in the main phase grains of the magnet;

[0052] (6) The magnet is subjected to a sintering densification treatment and finally subjected to grain boundary diffusion to obtain an ultra-high coercive force NdFeB magnet having an inner and outer double-layer heavy rare earth magnetic hardening shell.

[0053] Furthermore, the NdFeB alloy thin sheet is obtained by spinning in a rapid solidification furnace and has a thickness of 200-300 μm.

[0054] Another aspect of the embodiments of the present invention further provides a neodymium iron boron magnet with ultra-high coercivity obtained by the aforementioned preparation method, wherein the magnet main phase grains in the neodymium iron boron magnet with ultra-high coercivity include an inner heavy rare earth magnetic hardening shell layer and an outer heavy rare earth magnetic hardening shell layer sequentially formed on the surface of the core structure;

[0055] Furthermore, the thickness of the inner heavy rare earth magnetic hardening shell layer is 0.5-3 μm.

[0056] Furthermore, the thickness of the outer heavy rare earth magnetic hardening shell layer is 0.2-0.5 μm.

[0057] Another aspect of the embodiments of the present invention further provides uses of the NdFeB magnet with ultra-high coercivity in the fields of new energy vehicles, magnetic levitation trains, wind power generation or energy-saving home appliances.

[0058] The present invention designs a method for preparing ultra-high coercivity NdFeB magnets. By optimizing and improving the base magnet preparation process and the subsequent diffusion process, NdFeB grains with a double-layer heavy rare earth shell are prepared. Magnetic hardening and strengthening structural units are simultaneously formed on the surface and inside of the magnet grains, effectively suppressing the nucleation and migration of reverse magnetization domains. This method has far-reaching significance for improving the coercivity of NdFeB magnets and promoting the rapid development of the NdFeB industry and the rare earth permanent magnet field.

[0059] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0060] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0061] Example 1:

[0062] According to the matrix alloy composition of Nd 30.5 Fe 68.42 Al 0.1 Cu 0.2 Co 0.5 Zr 0.2 Ga 0.1 B 0.98, the raw materials are melted and poured onto a copper roller using a rapid solidification process to obtain a casting with an average thickness of 0.3mm. The casting is placed in a hydrogen crushing furnace, hydrogenated and crushed, and kept at 450℃ for 10 hours for dehydrogenation treatment to obtain a coarse crushed powder. The coarse crushed powder is then ground in a nitrogen atmosphere-protected air flow mill to obtain air flow-milled magnetic powder with an average particle size of 2.0μm; the NdFeB fine powder is subjected to an oriented pressing process to obtain a NdFeB green billet. The NdFeB green billet is formed into a grain structure with an inner and outer double-layer heavy rare earth magnetic hardened shell through a liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion); the pre-sintering treatment is to place the NdFeB pressed billet in a vacuum heat treatment furnace and heat it to 1020℃ at a heating rate of 10℃ / min and keep it for 4 hours, followed by gas quenching and air cooling. The pre-diffusion treatment is to cut the sintered NdFeB magnet into Preparation of diffusion source Tb 15 Pr 60 Cu 15 Al 10 Multi-element alloy block, the raw materials are placed in a vacuum induction melting furnace for melting, and the smelted alloy ingots are cut into Remove the surface oxide scale of the thin film, keep the surface flat and rinse with alcohol to dry. 15 Pr 60 Cu 15 Al 10 The sintered NdFeB magnet was then placed in a crucible and diffused in a vacuum heat treatment furnace at 900°C for 8 hours. After pre-sintering and pre-diffusion, the magnet was heated to 1080°C for 8 hours. After the vacuum heat treatment furnace cooled to room temperature, the diffused magnet was removed and the diffusion sheet was applied to the upper and lower surfaces of the diffused magnet. The diffusion process was then continued at 900°C for 8 hours and tempered at 500°C for 2 hours to obtain an ultra-high coercivity NdFeB magnet.

[0063] Comparative Example 1

[0064] According to the matrix alloy composition Nd 30.5 Fe 68.42 Al 0.1 Cu 0.2 Co 0.5 Zr 0.2 Ga 0.1 B 0.98, the raw materials are melted and poured onto a copper roller using a rapid solidification process to obtain a casting with an average thickness of 0.3mm. The casting is placed in a hydrogen crushing furnace, hydrogenated and crushed, and kept at 450℃ for 10 hours for dehydrogenation treatment to obtain coarse crushed powder. The coarse crushed powder is then ground in a nitrogen atmosphere-protected air flow mill to obtain air flow-ground magnetic powder with an average particle size of 2.0μm; the NdFeB fine powder is subjected to oriented pressing treatment to obtain NdFeB green billets. The NdFeB green billets are placed in a vacuum heat treatment furnace and heated to 1080℃ at a rate of 10℃ / min and kept at that temperature for 8 hours, followed by gas quenching and air cooling. The grain boundary diffusion treatment is to cut the sintered NdFeB magnets into Preparation of diffusion source Tb 15 Pr 60 Cu 15 Al 10 Multi-element alloy block, the raw materials are placed in a vacuum induction melting furnace for melting, and the smelted alloy ingots are cut into Remove the surface oxide scale of the thin film, keep the surface flat and rinse with alcohol to dry. 15 Pr 60 Cu 15 Al 10 The mixture is coated on a sintered NdFeB magnet, placed in a crucible and placed in a vacuum heat treatment furnace for a diffusion process at 900°C for 8 hours and a tempering treatment at 500°C for 2 hours to obtain a high coercive force NdFeB magnet.

[0065] Backscattered structural observations of the two samples of Example 1 and Comparative Example 1 revealed that the main phase grains of the sample of Example 1 formed an inner and outer double-layer heavy rare earth magnetic hardening shell, with an inner shell thickness of 1.2 μm and an outer shell thickness of 0.4 μm. The sample of Comparative Example 1 did not have this double-layer structure. A comparison of the performance data of Example 1 and Comparative Example 1 is shown in Table 1:

[0066] Table 1 Performance data of NdFeB magnets prepared by different methods

[0067] Magnet type Coercive force (kOe) Remanence (kGs) Magnetic energy product (MGOe) Example 1 25.85 14.13 48.44 Comparative Example 1 22.32 14.17 48.57

[0068] By comparison, it can be seen that the present invention has obvious advantages. The coercive force of the embodiment is significantly higher than that of the comparative example. Through the segmented process control of liquid phase sintering (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion), the main phase grains of the magnet form an inner and outer double-layer heavy rare earth magnetic hardening shell. The thickness and heavy rare earth content of the inner shell can be adjusted by controlling the composition and dosage of the heavy rare earth pre-diffusion source. In this way, the expected design of raw material cost and coercive force improvement effect can be achieved, and the production cost can be reduced while improving the coercive force.

[0069] Example 2:

[0070] According to the matrix alloy composition Nd25.5 Tb 5.5 Fe 66.33 Cu 0.15 Co1Zr 0.1 Ga 0.5 B 0.92 , the raw materials are melted and poured onto a copper roller using a rapid solidification process to obtain a casting with an average thickness of 0.3mm. The casting is placed in a hydrogen crushing furnace, hydrogenated and crushed, and kept at 450℃ for 12 hours for dehydrogenation treatment to obtain a coarse crushed powder. The coarse crushed powder is then ground in a nitrogen atmosphere-protected air flow mill to obtain air flow-milled magnetic powder with an average particle size of 1.5μm; the NdFeB fine powder is subjected to an oriented pressing process to obtain a NdFeB green billet. The NdFeB green billet is formed into a grain structure with an inner and outer double-layer heavy rare earth magnetic hardened shell through a liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion); the pre-sintering treatment is to place the NdFeB pressed billet in a vacuum heat treatment furnace and heat it to 1020℃ at a heating rate of 10℃ / min and keep it for 4 hours, followed by gas quenching and air cooling. The pre-diffusion treatment is to cut the sintered NdFeB magnet into Preparation of diffusion source Tb 15 Pr 55 Al 15 Ga 15 Multi-element alloy block, the raw materials are placed in a vacuum induction melting furnace for melting, and the smelted alloy ingots are cut into Remove the surface oxide scale of the thin film, keep the surface flat and rinse with alcohol to dry. 15 Pr 55 Al 15 Ga 15 The sintered NdFeB magnet was then placed in a crucible and diffused in a vacuum heat treatment furnace at 900°C for 8 hours. After pre-sintering and pre-diffusion, the magnet was heated to 1080°C for 8 hours. After the vacuum heat treatment furnace cooled to room temperature, the diffused magnet was removed and the diffusion sheet was applied to the upper and lower surfaces of the diffused magnet. The diffusion process was then continued at 900°C for 8 hours and tempered at 500°C for 2 hours to obtain an ultra-high coercivity NdFeB magnet.

[0071] Comparative Example 2:

[0072] In order to compare the advantages of the present invention, comparative example 2 uses jet milled magnetic powder with an average particle size of 4.0 μm; after oriented compression molding, liquid phase sintering treatment (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion) is performed to obtain a high coercive force sintered NdFeB magnet. After the treatment, magnetic properties are tested. The performance data of Example 2 and comparative example 2 are compared as shown in Table 2:

[0073] Table 2 Performance data of NdFeB magnets prepared by different methods

[0074] Magnet type Coercive force (kOe) Remanence (kGs) Magnetic energy product (MGOe) Example 2 42.08 12.42 37.59 Comparative Example 2 39.27 12.51 37.71

[0075] Comparison shows that the present invention has obvious advantages. The coercive force of the embodiment is significantly higher than that of the comparative example. By using air flow to grind the magnetic powder, the coercive force is greatly improved. The process is simple and easy to operate, suitable for industrial production, and can produce ideal ultra-high coercive force NdFeB magnets.

[0076] Example 3:

[0077] According to the matrix alloy composition Pr 16.43 Nd 5.47 Ce 8.6 Fe 65.94 Gd 1.5 Al 0.5 Cu 0.2 Co 0.2 Zr 0.12 Ga 0.12 B 0.92 , the raw materials are melted and poured onto a copper roller using a rapid solidification process to obtain a casting with an average thickness of 0.2mm. The casting is placed in a hydrogen crushing furnace, hydrogenated and crushed, and kept at 430℃ for 12h for dehydrogenation treatment to obtain a coarse crushed powder. The coarse crushed powder is then ground in a nitrogen atmosphere-protected air flow mill to obtain air flow-milled magnetic powder with an average particle size of 2.0μm; the NdFeB fine powder is subjected to an oriented pressing process to obtain a NdFeB green billet. The NdFeB green billet is formed into a grain structure with an inner and outer double-layer heavy rare earth magnetic hardened shell through a liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion); the pre-sintering treatment is to place the NdFeB pressed billet in a vacuum heat treatment furnace and heat it to 1020℃ at a heating rate of 10℃ / min and keep it for 4h, followed by gas quenching and air cooling. The pre-diffusion treatment is to cut the sintered NdFeB magnet into Preparation of diffusion source Dy 25 Pr 45 Cu 15 Ga 15 Multi-element alloy block, the raw materials are placed in a vacuum induction melting furnace for melting, and the smelted alloy ingots are cut into Remove the surface oxide scale of the thin film, keep the surface flat and rinse with alcohol to dry. 15 Pr 55 Cu 15 Ga 15The diffuser is then applied to a sintered NdFeB magnet, placed in a crucible and placed in a vacuum heat treatment furnace for a diffusion process at 950°C for 10 hours. After pre-sintering and pre-diffusion, the magnet is heated to 1080°C for 8 hours. After the vacuum heat treatment furnace cools to room temperature, the diffused magnet is removed and the diffuser is applied to the diffused magnet. The diffusion process is then repeated at 950°C for 10 hours, followed by a tempering treatment at 500°C for 2 hours to produce an ultra-high coercivity NdFeB magnet.

[0078] Comparative Example 3:

[0079] In order to compare the advantages of the present invention, comparative example 3 uses air flow milled magnetic powder with an average particle size of 2.0 μm. The air flow milled magnetic powder is oriented and pressed into shape before liquid phase sintering in a segmented process (pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion). The diffusion source used in the pre-diffusion and grain boundary diffusion processes is Dy 25 Pr 10 Cu 30 Ga 35 Finally, a high coercivity sintered NdFeB magnet was obtained. After the treatment, magnetic properties were tested. The performance data comparison between Example 3 and Comparative Example 3 is shown in Table 3:

[0080] Table 3 Performance data of NdFeB magnets prepared by different methods

[0081] Magnet type Coercive force (kOe) Remanence (kGs) Magnetic energy product (MGOe) Example 3 24.97 11.95 35.88 Comparative Example 3 20.84 12.03 35.93

[0082] By comparison, it can be seen that the present invention has obvious advantages. The coercive force of the embodiment is significantly higher than that of the comparative example, the heavy rare earth content is reduced, the high-quality utilization of heavy rare earth is achieved, and the production cost is reduced. At the same time, the coercive force of the sintered NdFeB magnet is greatly improved. The process is simple and the operation is convenient, and it can be applied to industrial production.

[0083] Example 4

[0084] According to the matrix alloy composition of Nd 30.5 Fe 68.42 Al 0.1 Cu 0.2 Co 0.5 Zr 0.2 Ga 0.1 B 0.98, the raw materials are melted and poured onto a copper roller using a rapid solidification process to obtain a casting with an average thickness of 0.3mm. The casting is placed in a hydrogen crushing furnace, hydrogenated and crushed, and kept at 450℃ for 10 hours for dehydrogenation treatment to obtain a coarse crushed powder. The coarse crushed powder is then ground in a nitrogen atmosphere-protected air flow mill to obtain air flow-milled magnetic powder with an average particle size of 2.0μm; the NdFeB fine powder is subjected to an oriented pressing process to obtain a NdFeB green billet. The NdFeB green billet is formed into a grain structure with an inner and outer double-layer heavy rare earth magnetic hardened shell through a liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion); the pre-sintering treatment is to place the NdFeB pressed billet in a vacuum heat treatment furnace and heat it to 1020℃ at a heating rate of 10℃ / min and keep it for 4 hours, followed by gas quenching and air cooling. The pre-diffusion treatment is to cut the sintered NdFeB magnet into Preparation of diffusion source Tb 15 Pr 60 Cu 15 Al 10 Multi-element alloy block, the raw materials are placed in a vacuum induction melting furnace for melting, and the smelted alloy ingots are cut into Remove the surface oxide scale of the thin film, keep the surface flat and rinse with alcohol to dry. 15 Pr 60 Cu 15 Al 10 The sintered NdFeB magnet was then placed in a crucible and diffused in a vacuum heat treatment furnace at 800°C for 8 hours. After pre-sintering and pre-diffusion, the magnet was heated to 1080°C for 8 hours. After the vacuum heat treatment furnace cooled to room temperature, the diffused magnet was removed and the diffusion sheet was applied to the upper and lower surfaces of the diffused magnet. The diffusion process was then continued at 800°C for 8 hours and tempered at 400°C for 2 hours to produce an ultra-high coercivity NdFeB magnet.

[0085] Table 4 Performance data of NdFeB magnets prepared by different methods

[0086] Magnet type Coercive force (kOe) Remanence (kGs) Magnetic energy product (MGOe) Example 4 24.05 14.23 48.64

[0087] Example 5

[0088] According to the matrix alloy composition of Nd 30.5 Fe 68.42 Al 0.1 Cu 0.2 Co 0.5 Zr 0.2 Ga 0.1 B 0.98, the raw materials are melted and poured onto a copper roller using a rapid solidification process to obtain a casting with an average thickness of 0.3mm. The casting is placed in a hydrogen crushing furnace, hydrogenated and crushed, and kept at 450℃ for 10 hours for dehydrogenation treatment to obtain a coarse crushed powder. The coarse crushed powder is then ground in a nitrogen atmosphere-protected air flow mill to obtain air flow-milled magnetic powder with an average particle size of 2.0μm; the NdFeB fine powder is subjected to an oriented pressing process to obtain a NdFeB green billet. The NdFeB green billet is formed into a grain structure with an inner and outer double-layer heavy rare earth magnetic hardened shell through a liquid phase sintering process (pre-sintering, pre-diffusion, densification sintering, grain boundary diffusion); the pre-sintering treatment is to place the NdFeB pressed billet in a vacuum heat treatment furnace and heat it to 1020℃ at a heating rate of 10℃ / min and keep it for 4 hours, followed by gas quenching and air cooling. The pre-diffusion treatment is to cut the sintered NdFeB magnet into Preparation of diffusion source Tb 15 Pr 60 Cu 15 Al 10 Multi-element alloy block, the raw materials are placed in a vacuum induction melting furnace for melting, and the smelted alloy ingots are cut into Remove the surface oxide scale of the thin film, keep the surface flat and rinse with alcohol to dry. 15 Pr 60 Cu 15 Al 10 The sintered NdFeB magnet was then placed in a crucible and placed in a vacuum heat treatment furnace for a diffusion process at 950°C for 8 hours. After pre-sintering and pre-diffusion, the magnet was heated to 1110°C for 8 hours. After the temperature was raised and the vacuum heat treatment furnace cooled to room temperature, the diffused magnet was removed and the diffusion sheet was applied to the upper and lower surfaces of the diffused magnet. The diffusion process was then continued at 950°C for 8 hours and tempered at 600°C for 2 hours to obtain an ultra-high coercivity NdFeB magnet.

[0089] Table 5 Performance data of NdFeB magnets prepared by different methods

[0090] Magnet type Coercive force (kOe) Remanence (kGs) Magnetic energy product (MGOe) Example 5 24.21 14.11 47.73

[0091] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0092] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical variations made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a neodymium iron boron magnet with ultra-high coercivity, characterized in that include: Provide NdFeB compacts; and performing liquid phase sintering on the NdFeB compact to produce a NdFeB magnet with ultra-high coercivity; The liquid phase sintering treatment includes pre-sintering, pre-diffusion, densification sintering, and grain boundary diffusion treatment; the magnet main phase grains in the pre-diffused magnet obtained by the pre-diffusion treatment have a core-shell structure, and the magnet main phase grains in the NdFeB magnet with ultra-high coercivity have an inner and outer double-layer heavy rare earth magnetic hardened shell structure; The temperature of the pre-sintering treatment is 900-1020° C., and the grain size of the pre-sintered magnet obtained by the pre-sintering treatment is 3-5 μm; The pre-diffusion treatment at least forms a core-shell structure in the main phase grains of the obtained pre-diffusion magnet; the pre-diffusion source used in the pre-diffusion treatment includes a rare earth alloy diffusion source, and the chemical formula of the rare earth alloy diffusion source is H x R y M 100-x-y , wherein H is selected from any one or a combination of two or more of Tb, Dy, and Ho, R is selected from any one or a combination of two or more of Pr, Nd, Y, Ce, and La, and M is selected from any one or a combination of two or more of Cu, Al, Fe, Ga, Zn, Mg, and Mn, and x and y represent the atomic percentage content of each component in the rare earth alloy diffusion source, and x is 0-30, x is not 0, and y is 20-80; The densification sintering process is to increase the temperature to allow the grains to grow; The diffusion source used in the grain boundary diffusion treatment includes a rare earth alloy diffusion source, and the chemical formula of the rare earth alloy diffusion source is H x R y M 100-x-y , wherein H is selected from any one or a combination of two or more of Tb, Dy, and Ho, R is selected from any one or a combination of two or more of Pr, Nd, Y, Ce, and La, and M is selected from any one or a combination of two or more of Cu, Al, Fe, Ga, Zn, Mg, and Mn, and x and y represent the atomic percentage content of each component in the rare earth alloy diffusion source, and x is 0-30, x is not 0, and y is 20-80.

2. The preparation method according to claim 1, wherein: The pre-sintering treatment time is 2-5 hours.

3. The preparation method according to claim 2, wherein include: The pre-diffusion source is coated on the surface of the pre-sintered magnet and a pre-diffusion treatment is performed under vacuum conditions at a temperature of 800-950° C. for 2-8 hours to obtain a pre-diffusion magnet.

4. The preparation method according to claim 3, characterized in that include: The pre-diffused magnet is subjected to densification sintering treatment at 1000-1100° C. for 2-10 hours to obtain a densified sintered magnet; wherein the grain size of the densified sintered magnet is 5-10 μm.

5. The preparation method according to claim 4, characterized in that include: The diffusion source is coated on the surface of the densified sintered magnet and subjected to diffusion treatment at 800-950° C. for 2-8 hours, followed by tempering treatment at 400-600° C. for 2-4 hours to obtain a neodymium iron boron magnet with ultra-high coercivity.

6. The preparation method according to claim 1, characterized in that include: Providing raw materials for preparing NdFeB compacts and performing alloy smelting treatment to obtain NdFeB alloy flakes; performing hydrogen crushing treatment on the NdFeB alloy flakes to obtain hydrogen crushed coarse powder; Performing jet milling on the hydrogen-crushed coarse powder to obtain NdFeB fine powder; Furthermore, the NdFeB fine powder is subjected to orientation compression molding and isostatic pressing to obtain a NdFeB compact.

7. The preparation method according to claim 6, characterized in that: The chemical formula of the NdFeB compact is R x Fe y M z B α ; Wherein, R is selected from any one or a combination of two or more of La, Ce, Tb, Dy, Ho, Y, Gd, Nd, and Pr, M is selected from any one or a combination of two or more of Cu, Al, Ga, Mg, Ni, Ti, Co, and Zr, x is 28-33wt%, y is 60-75wt%, z is 0-5wt%, α is 0.9-1.2wt%, and x+y+z+α=100.

8. The preparation method according to claim 6, characterized in that: The thickness of the NdFeB alloy sheet is 200-300 μm; And / or, the grinding gas pressure used in the jet mill treatment is 0.5-0.7 MPa, and the classifying wheel speed is 3500-5000 rpm; And / or, the average particle size D50 of the NdFeB fine powder is 1 μm≤D50≤2 μm.

9. A neodymium iron boron magnet with ultrahigh coercivity obtained by the method according to any one of claims 1 to 8, characterized in that: The magnet main phase grains in the NdFeB magnet with ultra-high coercivity include an inner heavy rare earth magnetic hardening shell layer and an outer heavy rare earth magnetic hardening shell layer sequentially formed on the surface of the core structure.

10. The NdFeB magnet with ultra-high coercivity according to claim 9, characterized in that: The thickness of the inner heavy rare earth magnetic hardening shell layer is 0.5-3 μm; the thickness of the outer heavy rare earth magnetic hardening shell layer is 0.2-0.5 μm.

11. Use of the NdFeB magnet with ultrahigh coercivity according to claim 9 or 10 in the fields of new energy vehicles, magnetic levitation trains, wind power generation or energy-saving home appliances.

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