Sintered neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention relates to the technical field of neodymium-iron-boron magnets, in particular to a sintered neodymium-iron-boron magnet and a preparation method thereof.The sintered neodymium-iron-boron magnet is prepared from, by mass, 85%-95% of main phase alloy and 5%-15% of rare earth-rich phase alloy, and the main phase alloy comprises Nd, Pr, Fe, B and M elements; the rare earth-rich phase alloy comprises the following chemical components: Nd, Pr, Dy, Tb and B elements. The neodymium-iron-boron magnet prepared by the invention has excellent residual magnetism and coercive force performance.

Description

Technical Field

[0001] The present invention relates to the technical field of neodymium iron boron magnets, and particularly relates to a sintered neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Sintered neodymium iron boron permanent magnetic materials are widely used in the fields of electronics, automobiles, aerospace, etc. due to their excellent magnetic properties. With the continuous improvement of application requirements, higher requirements are put forward for the performance of neodymium iron boron magnets. In traditional preparation methods, the main phase alloy and the rare earth-rich phase alloy are usually mixed during the preparation of the flake, and then formed and sintered after mixing. The magnets prepared by this mixing method have insufficient performance.

[0003] In the prior art, a Chinese invention patent application (publication number CN119132771A) discloses a method for improving the coercivity of neodymium iron boron magnets. The raw materials of each element of the neodymium iron boron magnet are taken according to the component ratio, and the flake is obtained after melting and casting; the flake is subjected to vacuum heat treatment at a temperature of 450-600 °C. The vacuum heat-treated flake is hydrogenated and pulverized by a jet mill to obtain powder, the powder is oriented and formed to obtain a green body, the green body is cold isostatically pressed, and finally vacuum sintered to obtain a neodymium iron boron magnet. The mixing method described above is difficult to achieve uniform distribution of rare earth elements inside the magnet, resulting in insufficient performance consistency of the magnet, which limits the improvement of the magnet performance.

[0004] Therefore, there is still room for improvement and development in the prior art. Summary of the Invention

[0005] The object of the present invention is to provide a sintered neodymium iron boron magnet and a preparation method thereof, and the obtained material has excellent remanence and coercivity performance.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A sintered neodymium iron boron magnet is made of the following components by mass content, including 85-95% of the main phase alloy and 5-15% of the rare earth-rich phase alloy. The main phase alloy includes elements Nd, Pr, Fe, B, and M, where Nd is 21-25%, Pr is 7-8.5%, B is 0.85-1.1%; M is 0-2%, and M is selected from any one or more of Ti, V, Cr, Co, Ga, Cu, Mn, Si, Al, Zr, W, and Mo, and the balance is Fe; the chemical composition of the rare earth-rich phase alloy includes elements Nd, Pr, Dy, Tb, and B, where Dy is 3-10%, Tb is 2-8%, Nd is 16-23%, Pr is 5.5-8%, B is 0.9-1.2%, and the balance is Fe.

[0007] The present invention also provides a preparation method of a sintered neodymium iron boron magnet, including the following steps: (1)Weigh the raw materials according to the composition ratio of the main-phase alloy, melt the raw materials in an argon environment, and then pour them onto the surface of a rapidly cooled copper roller. The rotational speed of the rapidly cooled copper roller is 30 - 50 r / min, and rapid cooling is carried out under argon protection to obtain the main-phase alloy flakes. (2)Weigh the raw materials according to the composition ratio of the rare-earth-rich phase alloy, melt the raw materials separately in an argon environment, and then pour them onto the surface of a rapidly cooled copper roller. The rotational speed of the rapidly cooled copper roller is 25 - 45 r / min, and rapid cooling is carried out under argon protection to obtain the rare-earth-rich phase alloy flakes. (3)Hydrogenate the above-mentioned main-phase alloy flakes and rare-earth-rich phase alloy flakes respectively. The hydrogen content of the hydrogenated powder of the main-phase alloy is controlled at 500 - 1500 ppm, and the hydrogen content of the hydrogenated powder of the rare-earth-rich phase alloy is controlled at 1500 - 3500 ppm. (4)Add lubricant to the hydrogenated powder of the main-phase alloy and stir it to make powder on a jet mill. The oxygen content is controlled at 1 - 6 ppm. The SMD particle size of the main-phase alloy powder after the jet mill is 2.8 - 3.4 μm, and the particle size distribution X90 / X10 is 3.95 - 4.3. (5)Add lubricant to the hydrogenated powder of the rare-earth-rich phase alloy and stir it to make powder on a jet mill. The oxygen content is controlled at 1 - 5 ppm. The SMD particle size of the rare-earth-rich phase alloy powder after the jet mill is 2 - 2.5 μm, and the particle size distribution X90 / X10 is 3.5 - 4. (6)Uniformly lay the main-phase alloy powder obtained in step (4) in a forming die through a powder spreading device to form the first-layer main-phase alloy powder layer. Above the first-layer main-phase alloy powder layer, uniformly lay the rare-earth-rich phase alloy powder prepared in step (5) on the surface of the main-phase alloy powder layer to form the rare-earth-rich phase alloy powder layer. Above the rare-earth-rich phase alloy powder layer, lay another layer of the main-phase alloy powder obtained in step (4) to form a complete three-layer structure. (7)Perform orientation compaction under the action of a magnetic field to form a green compact, so that the powder particles are arranged in the same direction in the magnetic field direction, and the green compact is obtained.

[0008] (8)Put the green compact into a sintering furnace under nitrogen protection and sinter it in a vacuum state. Temper the green compact after vacuum sintering to obtain a sintered blank.

[0009] According to the above scheme, the melting temperatures in step (1) and step (2) are both 1450 - 1520 °C, and the melted main-phase alloy and rare-earth-rich phase alloy are respectively kept static and heat-insulated for 10 - 15 minutes to achieve homogenization.

[0010] According to the above scheme, the surface temperatures of the rapidly cooled copper rollers in step (1) and step (2) are both 5 - 35 °C.

[0011] According to the above scheme, the thickness of the main-phase alloy flakes in step (1) is 0.2 - 0.4 mm.

[0012] According to the above solution, the thickness of the rare earth-rich phase alloy flakes in step (2) is 0.3-0.5 mm.

[0013] According to the above solution, in step (6), the powder spreading weight of the first main phase alloy powder spreading layer is 42.5-47.5% of the total powder spreading weight, the powder spreading weight of the rare earth-rich phase alloy powder spreading layer is 5-15% of the total powder spreading weight, and the powder spreading weight of the third main phase alloy powder spreading layer is the balance of the total powder spreading amount.

[0014] According to the above solution, the forming pressure in step (7) is 5-20 MPa.

[0015] According to the above solution, the sintering temperature in step (8) is 1000°C - 1100°C, and the sintering time is 4-6 h.

[0016] According to the above solution, in step (8), the green compact is subjected to two-stage tempering treatment in a vacuum or inert protective gas environment. The first-stage tempering aging temperature is 840-930°C, and the holding time is 2-4 h. The second-stage tempering aging temperature is 440-550°C, and the holding time is 4-7 h. After tempering, the green compact is cooled to room temperature to obtain a sintered blank.

[0017] The beneficial effects of the present invention are as follows: In the present invention, the main phase alloy and the rare earth-rich phase alloy are respectively made into flakes, hydrogenated and pulverized, and then mixed. During the forming process, the easy magnetization axis of the main phase alloy grains in the main phase alloy powder is arranged along the magnetic field direction, forming a highly oriented texture to ensure high remanence performance. By using the rare earth-rich phase alloy powder as the intermediate layer for powder spreading and forming under the interaction of the magnetic field and pressure, the rare earth-rich phase alloy is given a directional extrusion migration. During the sintering stage, the rare earth-rich phase alloy is fully melted, promoting the complete diffusion of the rare earth-rich phase along the grain boundaries, and finally forming a continuous network grain boundary isolation layer, enabling the rare earth-rich phase alloy to continuously and uniformly wrap the main phase alloy grains, forming an effective grain boundary isolation, improving the coercivity, thus realizing the optimization of the remanence performance and the coercivity performance, and further preparing a low-cost and high-performance NdFeB permanent magnetic material. Specific embodiments

[0018] The technical solutions of the present invention will be described below in conjunction with the embodiments.

[0019] Example 1 A sintered NdFeB magnet, comprising 95% of a main phase alloy and 5% of a rare earth-rich phase alloy. The main phase alloy comprises elements Nd, Pr, Fe, B, and M, where Nd is 21.75%, Pr is 8%, B is 0.92%, and the balance is Fe; the chemical composition of the rare earth-rich phase alloy comprises elements Nd, Pr, Dy, Tb, and B, where Dy is 3%, Tb is 2%, Nd is 22.5%, Pr is 7.5%, B is 0.9%, and the balance is Fe.

[0020] The preparation method of the sintered NdFeB magnet comprises the following steps: (1) Weigh the raw materials according to the component ratio of the main phase alloy, place the raw materials in a melting furnace at 1450 °C, melt in an argon environment, keep the melted main phase alloy standing and insulated for 10 minutes to achieve homogenization, then pour it onto the surface of a rapid-cooling copper roller at 5 °C. The rotation speed of the rapid-cooling copper roller is 30 r / min, and it is rapidly cooled under argon protection to obtain a main phase alloy flake with a thickness of 0.2 mm. (2) Weigh the raw materials according to the component ratio of the rare earth-rich phase alloy, place the raw materials in a melting furnace at 1450 °C, melt in an argon environment, keep the melted rare earth-rich phase alloy standing and insulated for 10 minutes to achieve homogenization, then pour it onto the surface of a rapid-cooling copper roller at 5 °C. The rotation speed of the rapid-cooling copper roller is 25 r / min, and it is rapidly cooled under argon protection to obtain a rare earth-rich phase alloy flake with a thickness of 0.3 mm. (3) Hydrogenate the above-mentioned main phase alloy flakes and rare earth-rich phase alloy flakes respectively. The hydrogen content of the hydrogenated powder of the main phase alloy is controlled at 500 ppm, and the hydrogen content of the hydrogenated powder of the rare earth-rich phase alloy is controlled at 1500 ppm. (4) Add a lubricant to the hydrogenated powder of the main phase alloy and stir to make powder on a jet mill, control the oxygen content at 1 ppm. The SMD particle size of the main phase alloy powder after the jet mill is 2.8 μm, and the particle size distribution X90 / X10 is 3.95. (5) Add a lubricant to the hydrogenated powder of the rare earth-rich phase alloy and stir to make powder on a jet mill, control the oxygen content at 1 ppm. The SMD particle size of the rare earth-rich phase alloy powder after the jet mill is 2.5 μm, and the particle size distribution X90 / X10 is 3.5. (6) Powder the above-prepared main phase alloy powder and rare earth-rich phase alloy powder under nitrogen protection. The total powdering amount is 600 g. Take 255 g of the main phase alloy powder obtained in step (4), and evenly distribute it into the cavity of a square mold through a vibrating powdering device to form a first-layer main phase alloy powdering layer. Above the first-layer main phase alloy powdering layer, take 30 g of the rare earth-rich phase alloy powder prepared in step (5) and evenly lay it on the surface of the main phase alloy powdering layer to form a rare earth-rich phase alloy powdering layer. Then take 315 g of the main phase alloy powder obtained in step (4) again and lay it above the rare earth-rich phase alloy powdering layer to form a complete three-layer structure. (7) Orient and compact under a magnetic field to form a green compact, aligning the powder particles in the direction of the magnetic field, with a forming pressure of 5 MPa, to obtain the green compact; (8) Place the green compact into a sintering furnace under nitrogen protection, sinter at 1000 °C in a vacuum state for 4 h, and perform two-stage tempering treatment on the green compact in a vacuum or inert protective gas environment. The first-stage tempering aging temperature is 840 °C, and the holding time is 2 h. The second-stage tempering aging temperature is 440 °C, and the holding time is 4 h. Cool the green compact to room temperature after tempering to obtain the NdFeB permanent magnetic material.

[0021] Example 2 A sintered NdFeB magnet, including 90% main phase alloy and 10% rare earth-rich phase alloy. The main phase alloy includes elements Nd, Pr, Fe, B, and M, where Nd is 24%, Pr is 7%, and B is 0.98%; Cr is 0.3%, Co is 0.3%, Si is 0.4%, Cu is 0.25%, and the balance is Fe; The chemical composition of the rare earth-rich phase alloy includes elements Nd, Pr, Dy, Tb, and B, where Dy is 6%, Tb is 4.5%, Nd is 18%, Pr is 7%, and B is 1%, and the balance is Fe.

[0022] The preparation method of the sintered NdFeB magnet includes the following steps: (1) Weigh the raw materials according to the component ratio of the main phase alloy, place the raw materials in a melting furnace at 1485 °C, melt in an argon environment, keep the melted main phase alloy static and insulated for 13 minutes to achieve homogenization, and then pour it onto the surface of a 20 °C rapid-cooling copper roller. The rotation speed of the rapid-cooling copper roller is 40 r / min, and it is rapidly cooled under argon protection to obtain 0.3 mm main phase alloy flakes; (2) Weigh the raw materials according to the component ratio of the rare earth-rich phase alloy, place the raw materials in a melting furnace at 1485 °C, melt in an argon environment, keep the melted rare earth-rich phase alloy static and insulated for 13 minutes to achieve homogenization, and then pour it onto the surface of a 20 °C rapid-cooling copper roller. The rotation speed of the rapid-cooling copper roller is 35 r / min, and it is rapidly cooled under argon protection to obtain 0.4 mm rare earth-rich phase alloy flakes; (3) Hydrogenate the above-mentioned main phase alloy flakes and rare earth-rich phase alloy flakes respectively. The hydrogen content of the hydrogenated powder of the main phase alloy is controlled at 1000 ppm, and the hydrogen content of the hydrogenated powder of the rare earth-rich phase alloy is controlled at 2500 ppm; (4) Add a lubricant to the hydrogenated powder of the main phase alloy and stir to make powder on a jet mill, control the oxygen content to be 3.5 ppm, and the SMD particle size of the main phase alloy powder after the jet mill is 3.1 μm, and the particle size distribution X90 / X10 is 4.05; (5) Add lubricant to the hydrogenated and pulverized rare-earth-rich alloy powder above and stir. Then, pulverize it on a jet mill, control the oxygen content to 3 ppm. The SMD particle size of the rare-earth-rich alloy powder after the jet mill is 2.25 μm, and the particle size distribution X90 / X10 is 3.75; (6) Powder the obtained main-phase alloy powder and rare-earth-rich alloy powder under nitrogen protection. The total powdering amount is 600 g. Take 270 g of the main-phase alloy powder obtained in step (4) and evenly distribute it into the cavity of a square mold through a vibrating powdering device to form the first layer of the main-phase alloy powdering layer. Above the first layer of the main-phase alloy powdering layer, take another 60 g of the rare-earth-rich alloy powder prepared in step (5) and evenly lay it on the surface of the main-phase alloy powdering layer to form the rare-earth-rich alloy powdering layer. Then, take another 270 g of the main-phase alloy powder obtained in step (4) and lay it above the rare-earth-rich alloy powdering layer to form a complete three-layer structure; (7) Perform orientation compaction under the action of a magnetic field to obtain a green compact, making the powder particles arranged in the same direction in the magnetic field direction. The compaction pressure is 12.5 MPa; (8) Put the green compact into a sintering furnace under nitrogen protection and sinter it at 1050 °C in a vacuum state for 5 h. Perform two-stage tempering treatment on the green compact in a vacuum or inert protective gas environment. The first-stage tempering aging temperature is 885 °C, and the holding time is 3 h. The second-stage tempering aging temperature is 495 °C, and the holding time is 5.5 h. Cool the green compact to room temperature after tempering to obtain the NdFeB permanent magnet material.

[0023] Example 3 A sintered NdFeB magnet, including 85% main-phase alloy and 15% rare-earth-rich alloy. The main-phase alloy includes elements Nd, Pr, Fe, B, and M, where Nd is 21%, Pr is 7%, and B is 1.1%; Cu is 0.2%, Mn is 0.3%, Al is 0.1%, Zr is 0.2%, W is 0.3%, Mo is 0.15%, and the balance is Fe; The chemical composition of the rare-earth-rich alloy includes elements Nd, Pr, Dy, Tb, and B, where Dy is 10%, Tb is 8%, Nd is 16.5%, Pr is 5.5%, B is 1.2%, and the balance is Fe.

[0024] The preparation method of the sintered NdFeB magnet includes the following steps: (1) Weigh the raw materials according to the composition ratio of the main-phase alloy, place the raw materials in a melting furnace at 1520 °C, melt them in an argon environment, keep the melted main-phase alloy still and insulated for 15 minutes to achieve homogenization, and then pour it onto the surface of a 35 °C rapid-cooling copper roller. The rotation speed of the rapid-cooling copper roller is 50 r / min, and it is rapidly cooled under argon protection to obtain 0.4 mm main-phase alloy flakes; (2) Weigh the raw materials according to the component ratio of the rare earth-rich phase alloy, place the raw materials in a melting furnace at 1520 °C, melt them in an argon environment, let the melted rare earth-rich phase alloy stand and heat preserve for 15 minutes to achieve homogenization, and then pour it onto the surface of a rapidly cooled copper roller at 35 °C. The rotation speed of the rapidly cooled copper roller is 45 r / min, and it is rapidly cooled under argon protection to obtain 0.5 mm rare earth-rich phase alloy flakes; (3) Hydrogenate the above-mentioned main phase alloy flakes and rare earth-rich phase alloy flakes respectively. The hydrogen content of the hydrogenated powder of the main phase alloy is controlled at 1500 ppm, and the hydrogen content of the hydrogenated powder of the rare earth-rich phase alloy is controlled at 3500 ppm; (4) Add lubricant to the above-mentioned hydrogenated powder of the main phase alloy and stir it to make powder on a jet mill, control the oxygen content to be 6 ppm, the SMD particle size of the main phase alloy powder after the jet mill is 3.4 μm, and the particle size distribution X90 / X10 is 4.3; (5) Add lubricant to the above-mentioned hydrogenated powder of the rare earth-rich phase alloy and stir it to make powder on a jet mill, control the oxygen content to be 5 ppm, the SMD particle size of the rare earth-rich phase alloy powder after the jet mill is 2.5 μm, and the particle size distribution X90 / X10 is 4; (6) Spread the above-mentioned prepared main phase alloy powder and rare earth-rich phase alloy powder under nitrogen protection. The total spreading amount is 600 g. Take 285 g of the main phase alloy powder obtained in step (4), and evenly spread it into the cavity of a square mold through a vibrating powder spreading device to form the first layer of main phase alloy powder spreading layer. Above the first layer of main phase alloy powder spreading layer, then take 90 g of the rare earth-rich phase alloy powder prepared in step (5), and evenly lay it on the surface of the main phase alloy powder spreading layer to form a rare earth-rich phase alloy powder spreading layer. Then take 225 g of the main phase alloy powder obtained in step (4) again, and lay it above the rare earth-rich phase alloy powder spreading layer to form a complete three-layer structure; (7) Carry out orientation pressing to form a green compact under the action of a magnetic field, so that the powder particles are arranged in the same direction in the magnetic field direction, and the forming pressure is 20 MPa to obtain a green compact; (8) Put the green compact into a sintering furnace under nitrogen protection, sinter it at 1100 °C in a vacuum state for 6 h, carry out two-stage tempering treatment on the green compact in an inert protective gas environment. The first-stage tempering aging temperature is 930 °C, and the holding time is 4 h. The second-stage tempering aging temperature is 550 °C, and the holding time is 7 h. Cool the tempered green compact to room temperature to obtain a NdFeB permanent magnetic material.

[0025] Comparative Example 1 This comparative example is basically the same as Example 2, except that: 1) the flakes of the main phase alloy and the rare earth-rich phase alloy are mixed in a weight ratio of 9:1 and then hydrogen-crushed; 2) the hydrogen content of the hydrogen-crushed powder is controlled at 600ppm, and the powder particle size SMD obtained by air flow grinding is 2.9μm, and X90 / X10 is 4.05; 3) the mixed powder obtained by air flow grinding is placed in a mold and filled with powder at one time and then oriented and formed.

[0026] Testing Trials Performance evaluation methods and implementation standards: The remanence and intrinsic coercivity of the materials obtained in Examples 1-3 and Comparative Example 1 were tested by using the hysteresis loop method.

[0027] Table 1 Performance test results of NdFeB permanent magnet materials As can be seen from the above table, compared with the NdFeB permanent magnet material prepared by the conventional method of Comparative Example 1, the remanence of Example 2 is increased by 0.25KGs, and the intrinsic coercive force is increased by 2.7kOe. The obtained NdFeB permanent magnet material with high remanence and high coercive force effectively solves the technical problem of inconsistent performance of NdFeB materials and achieves the optimization of remanence performance and coercive force performance.

[0028] The above description is only a preferred embodiment of the present invention, so all equivalent changes or modifications made according to the structure, characteristics and principles described in the scope of the patent application of the present invention are included in the scope of the patent application of the present invention.

Claims

1. A sintered NdFeB magnet, characterized in that: It is made of the following components by mass content, including 85-95% of the main phase alloy and 5-15% of the rare earth-rich phase alloy. The main phase alloy includes elements Nd, Pr, Fe, B, and M, where Nd is 21-25%, Pr is 7-8.5%, B is 0.85-1.1%; M is 0-2%, and M is selected from any one or several of Ti, V, Cr, Co, Ga, Cu, Mn, Si, Al, Zr, W, Mo, and the balance is Fe; the chemical composition of the rare earth-rich phase alloy includes elements Nd, Pr, Dy, Tb, and B, where Dy is 3-10%, Tb is 2-8%, Nd is 16-23%, Pr is 5.5-8%, B is 0.9-1.2%, and the balance is Fe.

2. A method for preparing a sintered neodymium iron boron magnet as described in claim 1, characterized in that, It includes the following steps: (1) Weigh the raw materials according to the composition ratio of the main phase alloy, melt the raw materials in an argon environment and then pour them onto the surface of a rapidly cooled copper roller. The rotation speed of the rapidly cooled copper roller is 30-50 r / min, and it is rapidly cooled under argon protection to obtain the main phase alloy flakes. (2) Weigh the raw materials according to the composition ratio of the rare earth-rich phase alloy, melt the raw materials separately in an argon environment and then pour them onto the surface of a rapidly cooled copper roller. The rotation speed of the rapidly cooled copper roller is 25-45 r / min, and it is rapidly cooled under argon protection to obtain the rare earth-rich phase alloy flakes. (3) Hydrogenate the above-mentioned main phase alloy flakes and rare earth-rich phase alloy flakes respectively. The hydrogen content of the hydrogenated powder of the main phase alloy is controlled at 500-1500 ppm, and the hydrogen content of the hydrogenated powder of the rare earth-rich phase alloy is controlled at 1500-3500 ppm. (4) Add lubricant to the hydrogenated powder of the above-mentioned main phase alloy and stir it to make powder on a jet mill, control the oxygen content to be 1-6 ppm, and the SMD particle size of the main phase alloy powder after the jet mill is 2.8-3.4 μm, and the particle size distribution X90 / X10 is 3.95-4.

3. (5) Add lubricant to the hydrogenated powder of the above-mentioned rare earth-rich phase alloy and stir it to make powder on a jet mill, control the oxygen content to be 1-5 ppm, and the SMD particle size of the rare earth-rich phase alloy powder after the jet mill is 2-2.5 μm, and the particle size distribution X90 / X10 is 3.5-4. (6) Uniformly lay the main phase alloy powder obtained in step (4) in a molding die through a powder spreading device to form the first layer of the main phase alloy powder spreading layer. Above the first layer of the main phase alloy powder spreading layer, then uniformly lay the rare earth-rich phase alloy powder prepared in step (5) on the surface of the main phase alloy powder spreading layer to form the rare earth-rich phase alloy powder spreading layer. Above the rare earth-rich phase alloy powder spreading layer, lay another layer of the main phase alloy powder obtained in step (4) again to form a complete three-layer structure. (7) Perform orientation pressing under the action of a magnetic field to form a green compact, so that the powder particles are arranged uniformly in the magnetic field direction to obtain the green compact. (8) Put the green compact into a sintering furnace under nitrogen protection and sinter it in a vacuum state. Temper the green compact after vacuum sintering to obtain a sintered blank.

3. The preparation method of a sintered neodymium iron boron magnet according to claim 2, wherein, The melting temperatures in steps (1) and (2) are both 1450-1520 °C, and the melted main phase alloy and rare earth-rich phase alloy are respectively kept static and insulated for 10-15 minutes to achieve homogenization.

4. The preparation method of a sintered neodymium iron boron magnet according to claim 2, characterized in that, The surface temperatures of the rapid-cooling copper rollers in the steps (1) and (2) are both 5 - 35°C.

5. The preparation method of a sintered neodymium iron boron magnet according to claim 4, characterized in that, The thickness of the main-phase alloy flakes in the step (1) is 0.2 - 0.4 mm.

6. The preparation method of a sintered neodymium iron boron magnet according to claim 4, characterized in that, The thickness of the rare-earth-rich phase alloy flakes in the step (2) is 0.3 - 0.5 mm.

7. The method for preparing a sintered neodymium iron boron magnet according to claim 2, characterized in that, In the step (6), the powder spreading weight of the first-layer main-phase alloy powder layer is 42.5 - 47.5% of the total powder spreading weight, the powder spreading weight of the rare-earth-rich phase alloy powder layer is 5 - 15% of the total powder spreading weight, and the powder spreading weight of the third-layer main-phase alloy powder layer is the balance of the total powder spreading amount.

8. The preparation method of a sintered neodymium iron boron magnet according to claim 2, characterized in that, The forming pressure in the step (7) is 5 - 20 MPa.

9. The preparation method of a sintered neodymium iron boron magnet according to claim 2, characterized in that, The sintering temperature in the step (8) is 1000°C - 1100°C, and the sintering time is 4 - 6 h.

10. The preparation method of a sintered neodymium iron boron magnet according to claim 2, characterized in that, In the step (8), the green compact is subjected to two-stage tempering treatment in a vacuum or inert protective gas environment. The first-stage tempering aging temperature is 840 - 930°C, and the holding time is 2 - 4 h. The second-stage tempering aging temperature is 440 - 550°C, and the holding time is 4 - 7 h. After tempering, the green compact is cooled to room temperature to obtain a sintered blank.

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