High-performance sintered neodymium-iron-boron magnet and method for producing same

Abstract

The application belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a high-performance sintered neodymium-iron-boron magnet and a preparation method thereof. The method specifically comprises the following steps: designing a composite grain boundary diffusion source composed of low-melting-point rare earth metal alloy powder, heavy rare earth metal alloy powder and an organic dispersing agent, coating the composite grain boundary diffusion source on the surface of a sintered neodymium-iron-boron sintered substrate by spraying, dipping or screen printing, and preparing a high-performance sintered neodymium-iron-boron magnet with a greatly widened grain boundary phase by adopting a multi-stage stepwise heating vacuum heat treatment. The preparation method of the composite grain boundary diffusion source and the high-performance sintered neodymium-iron-boron magnet realizes the regulation and control of the diffusion capacity of heavy rare earth elements. Through the optimized design of the diffusion source and the diffusion process, the amount of heavy rare earth elements can be greatly reduced, and the coercivity of the sintered neodymium-iron-boron magnet can be greatly improved. The method is suitable for batch production of high-performance sintered neodymium-iron-boron magnets.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a high-performance sintered neodymium-iron-boron magnet and a preparation method thereof. BACKGROUND

[0002] Neodymium-iron-boron (Nd2Fe 14 B) permanent magnets have high remanence, high coercivity and high magnetic energy product, and are the highest comprehensive performance rare earth permanent magnet material known today. With the rapid development of high-end popular fields such as wind power generation, variable frequency compressors and new energy passenger cars in recent years, the performance requirements for sintered neodymium-iron-boron magnets are becoming higher and higher. Therefore, the research on the preparation of high-performance sintered neodymium-iron-boron permanent magnets has become a current hotspot. In order to obtain high-performance sintered neodymium-iron-boron permanent magnets, a large amount of heavy rare earth metals is often used. However, heavy rare earth resources are not only expensive but also have limited reserves. Therefore, the development of a preparation method for high-performance sintered neodymium-iron-boron magnets with less heavy rare earth metal has become the focus of the world's rare earth magnet field.

[0003] At present, the preparation of high-performance sintered neodymium-iron-boron magnets mainly adopts the grain boundary diffusion of heavy rare earth elements process method. The current mainstream grain boundary diffusion methods that can be mass-produced mainly include magnetron sputtering and spraying. The magnetron sputtering process requires a specific magnetron sputtering device, which is extremely expensive and has a low utilization rate of heavy rare earth target material, resulting in a significant increase in the production cost of the magnet. Therefore, the spraying diffusion process method with lower production cost has developed rapidly. Chinese invention patent 202010185809.1 discloses a coating material for infiltrating magnets and a preparation method of high-coercivity neodymium-iron-boron magnets. The high-coercivity neodymium-iron-boron magnets are obtained by covering the surface of the magnets with a slurry containing heavy rare earth metal powder and non-rare earth metal powder for grain boundary diffusion. However, in this method, the proportion of heavy rare earth metal powder is too high, resulting in waste of heavy rare earth metal and increasing the preparation cost. Chinese invention patent 201711448520.9 discloses a method for grain boundary diffusion of neodymium-iron-boron magnets and rare earth magnets. The improvement value of the coercivity of the magnet is regulated by mixing Re 1-y-z Al y M z alloy powder with an organic solvent and a binder to form a coating material, coating the surface of the magnet, and performing heat treatment at multiple temperature stages. However, in this method, the improvement value of the coercivity of the magnet is very limited, and it is not suitable for mass production. Therefore, it is necessary to develop a process method that can greatly reduce the amount of heavy rare earth metal and greatly improve the coercivity of sintered neodymium-iron-boron magnets, and is suitable for batch production of high-performance sintered neodymium-iron-boron magnets. SUMMARY

[0004] The present application provides a high-performance sintered neodymium-iron-boron magnet and a preparation method thereof, and the preparation method can realize the regulation and control of heavy rare earth diffusion capacity, greatly reduce the amount of heavy rare earth and greatly improve the coercivity of the sintered neodymium-iron-boron magnet through the optimization design of the diffusion source and diffusion process, and is suitable for batch production of high-performance sintered neodymium-iron-boron magnets, and has important significance for the development of sintered neodymium-iron-boron permanent magnet material industry.

[0005] In order to solve the above technical problems, the technical scheme of the present application is as follows: a preparation method of a high-performance sintered neodymium-iron-boron magnet, which specifically comprises the following process steps:

[0006] S1) first mix low-melting-point rare earth metal alloy powder, heavy rare earth metal alloy powder and organic dispersant in a certain proportion to obtain a composite grain boundary diffusion source;

[0007] S2) then coat the composite grain boundary diffusion source obtained in S1) on the surface of the sintered state substrate of the sintered neodymium-iron-boron by spraying, dipping or screen printing;

[0008] S3) then perform multi-stage temperature rising vacuum heat treatment to obtain the high-performance sintered neodymium-iron-boron magnet.

[0009] Further, the mass ratio of the low-melting-point rare earth alloy powder to the heavy rare earth metal alloy powder in S1) is 1:1 to 10:1, and the organic dispersant accounts for 30% to 70% of the total mass of the composite diffusion source;

[0010] The average particle size of the low-melting-point rare earth metal powder is 1-10 μm; and the average particle size of the heavy rare earth metal alloy powder is 1-10 μm.

[0011] Further, the chemical formula of the low-melting-point rare earth alloy powder 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.

[0012] Further, the chemical formula of the heavy rare earth metal alloy powder is (La a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tbd Ho e Gd 1-c-d-e ) z M 1-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 any one or more of the elements Al, Cu, Ga, In, Sn, Fe, Co or Zr.

[0013] Furthermore, the organic dispersant is one or more of alcohols, ketones, and lipids.

[0014] Furthermore, both the low-melting-point rare earth alloy powder and the heavy rare earth metal alloy powder are prepared by using a rapid solidification process to obtain rapid solidification flakes, which are then ground into corresponding metal powders by an air jet mill.

[0015] Furthermore, the multi-stage stepped heating vacuum heat treatment process in S3) is as follows:

[0016] S3.1) When the vacuum of the equipment is ≤10 -1 When the temperature reaches 100-150℃, the holding time is 1-2 hours. When the temperature reaches 200-300℃, the holding time is 1-2 hours.

[0017] S3.2) When the temperature continues to rise to 700℃, the holding time is 1-2 hours; when the temperature reaches 800℃, the holding time is 1-2 hours.

[0018] S3.3) Continue heating to 900-1000℃, hold for 10-30 hours. After holding, cool to room temperature with argon gas. Then, ensure the vacuum level of the equipment is ≤10℃. -1 At Pa, the temperature is increased at a certain rate to 400-600℃, and held for 2-5 hours. After the holding period, the temperature is cooled to room temperature by argon air.

[0019] Furthermore, the heating rate in S3.1) and S3.3) is 2-10℃ / min.

[0020] Furthermore, in step S3), after undergoing multi-stage stepped heating in vacuum heat treatment, the low-melting-point rare-earth metal alloy powder preferentially melts and enters the grain boundaries, forming a particle size of 10nm-5μm with a composition of (La) at the grain boundaries. a Ce 1-a ) p (Pr b Nd 1-b ) q M 1-p-qThe phases, wherein 0≤a≤1, 0≤b≤1, 0≤p≤1, 0≤q≤1 and 0.4≤p+q≤1, and M is one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr;

[0021] The heavy rare earth alloy powder reacts with molten 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 Gd 1-c-d-e ) z M 1-x-y-z The molten alloy enters the interior of the magnet, 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 any one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr, and then reacts with the edge of the main phase of the magnet, forming a composition of (La) at the boundary of the main phase. i Ce 1-i ) m (Pr k Nd 1-k ) n (Dy l Tb f Ho h Gd 1-l-f-h ) t M 1-m-n-t The phase has a thickness of 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 or Zr.

[0022] A high-performance sintered NdFeB magnet is prepared using the above-described preparation method.

[0023] The sintered matrix in S2) is a magnet that has not undergone tempering heat treatment.

[0024] Compared with the prior art, the advantages of the present invention include:

[0025] 1. This invention employs a composite grain boundary diffusion source composed of low-melting-point rare-earth metal alloy powder, heavy rare-earth alloy powder, and an organic dispersant. During vacuum heat treatment, holding at 100-150℃ and 200-300℃ effectively decomposes and removes the organic dispersant. At 700℃, the low-melting-point rare-earth metal alloy powder melts and enters the grain boundaries, reacting with the magnet to generate a product at the grain boundaries whose main component is (La). a Ce 1-a ) x (Pr b Nd 1-b ) y M 1-x-y The phase, with a size of 10 nm-5 μm, greatly broadens the matrix grain boundary size, thereby opening the grain boundary diffusion channel of the magnet. When held at 800℃, the heavy rare earth alloy powder reacts with the molten 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 Gd 1-c-d-e ) z M 1-x-y-z The molten alloy enters the magnet through diffusion channels, reacting with the main phase. Finally, during holding at 900-1000℃, more and more heavy rare earth alloys and molten low-melting-point rare earth metals react and liquefy, entering deeper into the magnet through the opened diffusion channels to react with the deeper main phase. At the main phase boundary, a phase with a composition of (La) begins to form. a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e Gd 1-c-d-e ) z M 1-x-y-z The phase, with a thickness of 1-3 μm, significantly improves the coercivity of sintered NdFeB magnets and also successfully controls the diffusion ability of heavy rare earth elements.

[0026] 2. The proportion of heavy rare earth alloy powder in the composite grain boundary diffusion source used in this invention can be very low, which can significantly reduce the amount of heavy rare earth metal used, thereby significantly reducing the production cost of high-performance sintered NdFeB magnets.

[0027] 3. The present invention can coat the composite grain boundary diffusion source onto the surface of the magnet by spraying, dip coating, screen printing and other methods, and is suitable for mass production of magnets. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating a method for preparing a high-performance sintered NdFeB magnet according to the present invention.

[0029] Figure 2 This is an electron microscope schematic diagram of a high-performance sintered NdFeB magnet produced in Example 1 using the preparation method of the present invention. Detailed implementation method:

[0030] In the following description, embodiments of the composite grain boundary diffusion source and the method for preparing high-performance sintered NdFeB magnets of the present invention will be described in detail. These embodiments are exemplary, and the disclosure of the present invention is not limited thereto.

[0031] In some embodiments of the present invention, the composite grain boundary diffusion source includes: low-melting-point rare earth metal alloy powder, heavy rare earth metal alloy powder, and organic dispersant.

[0032] The low melting point rare earth metal alloy (La) a Ce 1-a ) x (Pr b Nd 1-b ) y M 1-x-y , where 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 the elements Al, Cu, Ga, In, Sn, Fe, Co, Zr, etc.;

[0033] The heavy rare earth metal alloy is (La) a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e Gd 1-c-d-e ) z M 1-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 any one or more of the elements Al, Cu, Ga, In, Sn, Fe, Co, Zr, etc.

[0034] The organic dispersant is one or more of alcohols, ketones, and esters;

[0035] Some embodiments of the present invention can greatly broaden the grain boundaries of the magnet matrix by adding low-melting-point rare earth metal alloy powder as part of the composite grain boundary diffusion material, thereby opening the grain boundary diffusion channels of the matrix and regulating the diffusion ability of heavy rare earth metal elements in the matrix. The low-melting-point rare earth metal powder content in the composite grain boundary diffusion source is very high, which greatly reduces the amount of heavy rare earth elements used and significantly reduces production costs.

[0036] Low-melting-point rare earth metal alloy powder, heavy rare earth alloy powder and organic solvent are physically mixed. Physical mixing is carried out in a nitrogen atmosphere. There are no restrictions on the physical mixing method, such as a three-dimensional mixer.

[0037] In some embodiments of the present invention, the mass ratio of low-melting-point rare-earth alloy powder to heavy rare-earth metal alloy powder in the composite grain boundary diffusion source is preferably 5:1 to 10:1, and the organic dispersant preferably accounts for 40% to 60% of the total mass of the composite diffusion source. The proportion of low-melting-point rare-earth metal powder has a significant impact on the diffusion ability of heavy rare-earth elements in the magnet matrix. If the proportion of low-melting-point rare-earth metal alloy powder is too low, it cannot effectively widen the grain boundaries in the magnet matrix, thus failing to effectively control the diffusion ability of heavy rare-earth elements and failing to reduce costs. If the proportion of low-melting-point rare-earth metal powder is too high, there will be too few heavy rare-earth elements, which will reduce the coercivity of the magnet.

[0038] In some embodiments of the present invention, the average particle size of the low-melting-point rare earth metal powder and the heavy rare earth alloy powder is 1-3 μm. The finer particle size is beneficial to the uniform distribution of the powder in the organic dispersant in the composite grain boundary diffusion source and to prevent it from settling. It is also beneficial to the powder to be more easily liquefied during diffusion heat treatment, resulting in more uniform element diffusion and better diffusion effect. It is further preferred that the average particle size of the low-melting-point rare earth metal powder and the heavy rare earth alloy powder is 1-2.5 μm.

[0039] In some embodiments of the present invention, the low-melting-point rare earth metal alloy is one of rare earth metal elements such as La, Ce, Pr, and Nd. Rare earth elements such as La, Ce, Pr, and Nd are also commonly used elements in the preparation of magnet matrices. The use of rare earth elements such as La, Ce, Pr, and Nd in the composite grain boundary greatly widens the grain boundary of the magnet matrix, thereby opening the channel for grain boundary diffusion. This allows the magnet matrix, which was originally unsuitable for diffusion due to its low total rare earth content and few grain boundary phases, to achieve a significant increase in coercivity in the method of the present invention.

[0040] In some embodiments of the present invention, the preparation method of high-performance sintered NdFeB magnets includes the following steps: preparing a sintered NdFeB magnet matrix to be diffused by sequentially passing through rapid solidification and spinning, hydrogen crushing, air jet milling, additive stirring, magnetic field orientation forming, sintering densification, and machining processes; covering the surface of the sintered NdFeB matrix with a composite grain boundary diffusion source by spraying; and performing vacuum heat treatment to obtain a high-performance sintered NdFeB magnet.

[0041] In some embodiments of the present invention, there are many ways to cover the composite grain boundary diffusion source onto the surface of the magnet substrate, such as spraying, dip coating, and screen printing. The present invention preferably uses spraying, that is, spraying the composite grain boundary diffusion source onto the surface of the magnet substrate using a spray gun. The present invention does not impose a particular limitation on the weight of the sprayed diffusion source, which can be adjusted according to the shape and thickness of the magnet substrate. Preferably, the weight of the composite grain boundary diffusion source in the present invention is 1-4 wt% of the weight of the magnet substrate.

[0042] In some embodiments of the present invention, the multi-stage stepped heating vacuum heat treatment process is as follows: when the vacuum of the equipment is ≤8*10 -2 The temperature rises from point Pa. During the rise, the holding time is 1-2 hours at 120-150℃, 1-2 hours at 200-250℃, 1-2 hours at 700℃, 1-2 hours at 800℃, and 10-20 hours at 900-950℃. The heating rate between the stepped temperatures is 2-6℃ / min. After the holding time is completed, the equipment is cooled to room temperature with argon gas. The vacuum level of the equipment is then ≤8*10⁻⁶. -2 Start heating to 450-550℃ at Pa, hold for 2-5 hours, and then cool to room temperature with argon gas after holding.

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0044] Example 1

[0045] like Figure 1 As shown, the specific steps of the preparation method are as follows:

[0046] First, the heavy rare earth alloy powder Tb 0.8 Cu 0.2 The composite grain boundary diffusion source was prepared by physical mixing (10 wt%) with organic dispersant as the balance in a glove box filled with nitrogen atmosphere.

[0047] The sintered matrix I of NdFeB to be diffused was prepared by sequentially performing rapid solidification flake spinning, hydrogen crushing, air jet milling, additive stirring, magnetic field orientation molding, sintering densification, and machining processes. The matrix size was Φ10*3mm.

[0048] The composite grain boundary diffusion source was sprayed onto the upper surface of the substrate I using a spray gun, and then dried in an oven. The diffusion source was then sprayed onto the lower surface of the magnet substrate and dried again in an oven. The amount of the composite grain boundary diffusion source was controlled to be 3 wt% of the magnet substrate. The magnet substrate covered with the diffusion source was then placed in a sintering furnace and evacuated to a vacuum of 8*10. -2 Pa then begins heating. During the heating process, the holding time is as follows: 120℃ for 1 hour, 200℃ for 2 hours, 700℃ for 1 hour, 800℃ for 1 hour, 900℃ for 1 hour, and 920℃ for 20 hours. The heating rate between each step is 5℃ / min. After heating, the magnet is air-cooled to room temperature, then heated to 500℃ at a rate of 5℃ / min for tempering and holding for 4 hours. After tempering, the magnet is air-cooled to room temperature, resulting in a high-performance sintered NdFeB magnet. Figure 2 As shown.

[0049] Example 2

[0050] First, the low-melting-point rare earth metal Pr 0.25 Nd 0.75 Powder (50wt%), heavy rare earth alloy powder Tb 0.8 Cu 0.2 The composite grain boundary diffusion source was prepared by physical mixing (10 wt%) with organic dispersant as the balance in a glove box filled with nitrogen atmosphere.

[0051] The sintered matrix I of NdFeB to be diffused was prepared by sequentially performing rapid solidification flake spinning, hydrogen crushing, air jet milling, additive stirring, magnetic field orientation molding, sintering densification, and machining processes. The matrix size was Φ10*3mm.

[0052] The composite grain boundary diffusion source was sprayed onto the upper surface of the substrate I using a spray gun, and then dried in an oven. The diffusion source was then sprayed onto the lower surface of the magnet substrate and dried again in an oven. The amount of the composite grain boundary diffusion source was controlled to be 3 wt% of the magnet substrate. The magnet substrate covered with the diffusion source was then placed in a sintering furnace and evacuated to a vacuum of 8*10. -2 Pa started heating, and during the heating process, the holding time was 2 hours at 120℃, 1 hour at 200℃, 2 hours at 700℃, 2 hours at 800℃, 2 hours at 900℃, and 20 hours at 920℃. The heating rate between the stepped temperatures was 5℃ / min. After heating, the magnet was air-cooled to room temperature, and then heated to 500℃ at 5℃ / min for tempering and holding for 4 hours. After heating, the magnet was air-cooled to room temperature to obtain a high-performance sintered NdFeB magnet 2.

[0053] Example 3

[0054] First, mix low-melting-point rare earth metal Nd powder (45wt%) and heavy rare earth alloy powder Dy 0.7 Fe 0.25 Al 0.05 The composite grain boundary diffusion source was prepared by physical mixing (8 wt%) with organic dispersant as the balance in a glove box filled with nitrogen atmosphere.

[0055] The sintered matrix II of NdFeB to be diffused was prepared by sequentially performing rapid solidification flake spinning, hydrogen crushing, air jet milling, additive stirring, magnetic field orientation molding, sintering densification, and machining processes. The matrix size was Φ10*4mm.

[0056] The composite grain boundary diffusion source was sprayed onto the upper surface of the substrate II using a spray gun, and then dried in an oven. The diffusion source was then sprayed onto the lower surface of the magnet substrate and dried again in an oven. The amount of the composite grain boundary diffusion source was controlled to be 2 wt% of the magnet substrate. The magnet substrate covered with the diffusion source was then placed in a sintering furnace and evacuated to a vacuum of 8*10. -2 Pa started heating and raising the temperature. During the heating process, the holding time was 2 hours at 120℃, 2 hours at 200℃, 1 hour at 700℃, 2 hours at 800℃, 1 hour at 900℃, and 20 hours at 930℃. The heating rate between the stepped temperatures was 5℃ / min. After heating, the temperature was cooled to room temperature by air, and then heated to 520℃ by 5℃ / min for tempering and holding for 3 hours. After heating, the temperature was cooled to room temperature by air to obtain a high-performance sintered NdFeB magnet 3.

[0057] Example 4

[0058] First, mix low-melting-point rare earth metal Pr powder (45wt%) and heavy rare earth alloy powder Tb. 0.75 Al 0.25 The composite grain boundary diffusion source was prepared by physical mixing (5 wt%) with organic dispersant as the balance in a glove box filled with nitrogen atmosphere.

[0059] The sintered matrix III of NdFeB to be diffused was prepared by sequentially performing rapid solidification flake spinning, hydrogen crushing, air jet milling, additive stirring, magnetic field orientation molding, sintering densification, and machining processes. The matrix size was Φ10*5mm.

[0060] The composite grain boundary diffusion source was sprayed onto the upper surface of the substrate III using a spray gun, and then dried in an oven. The diffusion source was then sprayed onto the lower surface of the magnet substrate and dried again in an oven. The amount of the composite grain boundary diffusion source was controlled to be 4 wt% of the magnet substrate. The magnet substrate covered with the diffusion source was then placed in a sintering furnace and evacuated to a vacuum of 8*10. -2Pa started heating, and during the heating process, the holding time was 1 hour at 120℃, 2 hours at 200℃, 1 hour at 700℃, 2 hours at 800℃, 1 hour at 900℃, and 30 hours at 940℃. The heating rate between the stepped temperatures was 5℃ / min. After heating, the magnet was air-cooled to room temperature, and then heated to 480℃ at 5℃ / min for tempering and holding for 4 hours. After heating, the magnet was air-cooled to room temperature to obtain a high-performance sintered NdFeB magnet 4.

[0061] The magnetic properties of the sintered NdFeB magnets prepared above were tested, and the data are shown in the table below:

[0062] Magnet Remanence (kGs) Intrinsic coercivity (kOe) Maximum energy product (MGOe) Matrix I 14.85 10.53 52.90 Matrix II 13.87 14.17 47.30 Matrix III 14.45 11.22 50.47 Magnet 1 14.57 16.45 51.79 Magnet 2 14.52 23.53 50.86 Magnet 3 13.68 23.26 46.21 Magnet 4 14.09 25.33 48.79

[0063] The comparison of the magnetic properties of magnets 1 and 2 in the table above shows that when the total rare earth content of the matrix is ​​low and there is no low-melting-point rare earth metal Nd in the composite grain boundary diffusion source, the increase in coercivity of the matrix after diffusion is limited. With the presence of low-melting-point rare earth metal Nd, the coercivity of the matrix increases significantly. The addition of low-melting-point rare earth metal is beneficial to the diffusion of heavy rare earth elements in the matrix, and the effect is significant. The analysis of the magnetic properties of magnets 2, 3 and 4 shows that the presence of low-melting-point rare earth metal in the composite grain boundary diffusion source is not only beneficial to the increase of matrix coercivity, but also beneficial to significantly reduce the amount of heavy rare earth.

[0064] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a high-performance sintered NdFeB magnet, characterized in that, The preparation method specifically includes the following process steps: S1) First, mix low-melting-point rare earth metal alloy powder, heavy rare earth metal alloy powder and organic dispersant in a certain proportion to obtain a composite grain boundary diffusion source. The mass ratio of the low-melting-point rare earth alloy powder to the heavy rare earth metal alloy powder is 1:1 to 10:1, and the organic dispersant accounts for 30% to 70% of the total mass of the composite diffusion source; The chemical formula of the low-melting-point rare earth alloy powder is (La a Ce 1-a ) x (Pr b Nd 1-b ) y M 1-x-y Where 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; The chemical formula of the heavy rare earth metal alloy powder is (La a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e Gd 1-c-d-e ) z M 1-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 any one or more of the elements Al, Cu, Ga, In, Sn, Fe, Co or Zr; The low-melting-point rare earth metal powder has an average particle size of 1-10 μm; the heavy rare earth metal alloy powder has an average particle size of 1-10 μm. S2) The composite grain boundary diffusion source obtained in S1) is then coated onto the sintered matrix surface of sintered NdFeB by spraying, dip coating or screen printing. S3) Then, a multi-stage stepped heating vacuum heat treatment is performed to obtain a high-performance sintered NdFeB magnet. The multi-stage stepped heating vacuum heat treatment process is as follows: S3.1) When the vacuum of the equipment is ≤10 -1 When the temperature reaches 100-150℃, the holding time is 1-2 hours. When the temperature reaches 200-300℃, the holding time is 1-2 hours. S3.2) When the temperature continues to rise to 700℃, the holding time is 1-2 hours; when the temperature reaches 800℃, the holding time is 1-2 hours. S3.3) Continue heating to 900-1000℃, hold for 10-30 hours. After holding, cool to room temperature with argon gas. Then, ensure the vacuum level of the equipment is ≤10. -1 When Pa, the temperature is increased at a certain rate to 400-600℃, and held for 2-5 hours. After the holding period, the temperature is cooled to room temperature by argon air. In step S3), the low-melting-point rare-earth metal alloy powder, after undergoing multi-stage stepped heating in a vacuum heat treatment, melts and enters the grain boundaries, forming a particle size of 10nm-5μm with a composition of (La). a Ce 1-a ) p (Pr b Nd 1-b ) q M 1-p-q The phases, wherein 0≤a≤1, 0≤b≤1, 0<p≤1, 0<q≤1 and 0.4≤p+q≤1, and M is one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr; The heavy rare earth alloy powder reacts with molten 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 Gd 1-c-d-e ) z M 1-x-y-z The molten alloy enters the interior of the magnet, 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 any one or more of Al, Cu, Ga, In, Sn, Fe, Co or Zr, and then reacts with the edge of the main phase of the magnet, forming a composition of (La) at the boundary of the main phase. i Ce 1-i ) m (Pr k Nd 1-k ) n (Dy l Tb f Ho h Gd 1-l-f-h ) t M 1-m-n-t The phase has a thickness of 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 or Zr.

2. The preparation method according to claim 1, characterized in that, The organic dispersant is one or more of alcohols, ketones, and lipids.

3. The preparation method according to claim 1, characterized in that, The preparation process of the low-melting-point rare earth alloy powder and heavy rare earth metal alloy powder is as follows: First, low-melting-point rare earth metal alloys or heavy rare earth metal alloys are prepared into rapidly solidified flakes using a rapid solidification process, and then ground into corresponding metal powders using an air jet mill.

4. A high-performance sintered NdFeB magnet, characterized in that, The high-performance sintered NdFeB magnet is prepared using the preparation method described in any one of claims 1-3.

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