Preparation method of low-cost sintered neodymium-iron-boron grain boundary diffusion source

Abstract

The invention relates to the technical field of magnetic materials, in particular to a preparation method of a low-cost sintered neodymium-iron-boron grain boundary diffusion source, which comprises the following steps: S1, preparing an alloy throwing sheet: preparing diffusion source alloy raw materials in percentage by weight: 0.5-3% of Co, 2-8% of A < l >, 1-5% of Cu, 0.2-3% of Ga, 2-8% of N and the balance of terbium or dysprosium; the raw materials are smelted into alloy throwing sheets under the protection of inert gas. Starting from the principle of improving the coercive force of the neodymium-iron-boron magnetic steel, the intrinsic coercive force of the magnetic steel prepared through the new diffusion source is greatly improved by ingeniously designing the alloy permeation diffusion source of grain boundary permeation, the magnetic performance mark of the magnetic steel is improved by four grades, the residual magnetism is almost unchanged, and compared with traditional pure heavy rare earth hydride or fluoride, the magnetic performance of the magnetic steel is greatly improved. And the cost is reduced by 10-25%.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and more specifically, to a method for preparing a low-cost sintered neodymium iron boron grain boundary diffusion source. Background Art

[0002] The third-generation sintered neodymium iron boron rare earth permanent magnet materials are known as the "magnetic king" due to their high magnetic properties. Their magnetic indicators mainly include remanence (Br), intrinsic coercivity (Hcj), maximum magnetic energy product (BH)max, etc. The remanence and maximum magnetic energy product represent the "energy" that the magnetic steel can output. The higher their values, the smaller the volume and weight of the magnetic steel required under the same demand conditions. The higher the intrinsic coercivity, the stronger the demagnetization resistance ability of the magnetic steel, and the higher the temperature at which it can be applied. If the magnetic steel is applied to an electric motor, the magnetic steel with high coercivity can be used for higher motor speeds.

[0003] Since the discovery of neodymium iron boron, it has experienced more than 40 years of development. Due to its good comprehensive performance, it has been widely used in fields such as wind power generation, industrial motors, communication electronic equipment, and new energy vehicles. With the rapid development of intelligentization and digitization in recent years and the development of industrialization, it is necessary to keep up with the rhythm, and at the same time, the demand for higher-performance magnetic steel is becoming increasingly intense. At present, the main means to improve the performance (intrinsic coercivity) of sintered neodymium iron boron magnets are: optimizing the formula composition, grain refinement, and grain boundary penetration technology. The formula optimization is limited by scientific principles and has reached its limit at present. It is very difficult to improve the intrinsic coercivity of the magnet through this means without reducing the remanence. Grain refinement has also reached a bottleneck at present, and this technology has very strict requirements for equipment and oxygen control technology. The grain boundary penetration technology is currently the most effective and popular technology to improve the performance of neodymium iron boron. By coating the surface of the magnetic steel with hydrides or fluorides of heavy metals Tb and Dy and then performing heat treatment, a heavy rare earth grain boundary penetration layer is formed on the surface of the magnetic steel, thereby greatly improving the magnetic performance of the magnetic steel. However, with the rapid development of the industry, the intensifying international trade war, and the competition for rare earth resources, how to use less heavy rare earth and develop high-performance sintered neodymium iron boron magnetic steel at low cost has become an extremely important matter.

[0004] Therefore, we propose a method for preparing a low-cost sintered neodymium iron boron grain boundary diffusion source to solve the above problems. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides a method for preparing a low-cost sintered neodymium iron boron grain boundary diffusion source to solve the problems raised in the above background art.

[0006] To achieve the above object, the present invention provides the following technical solution: A method for preparing a low-cost sintered neodymium iron boron grain boundary diffusion source, comprising the following steps:

[0007] Step S1: Preparation of alloy sputtering pieces: Prepare diffusion source alloy raw materials according to weight percentages, including:

[0008] Co: 0.5% - 3%, Al: 2% - 8%, Cu: 1% - 5%, Ga: 0.2% - 3%, Ni: 2% - 8%, with the balance being terbium or dysprosium;

[0009] Melt the raw materials into alloy sputtering pieces under the protection of inert gas;

[0010] Step S2: Preparation of alloy powder: Subject the alloy sputtering pieces to ultra-high pressure hydrogen absorption and crushing (hydrogen pressure 20 MPa - 25 MPa), and then perform high-energy ball milling under the protection of a mixed protective agent of terpineol and isopropyl alcohol (mass ratio 1:1 - 3) and high-purity argon gas to obtain alloy powder with an average particle size of 1 - 2 μm;

[0011] Step S3: Preparation of slurry: Mix the alloy powder, polymer resin, and protective agent in a mass ratio of 1:1 - 1.5:1 - 1.8, and stir evenly to obtain an alloy slurry;

[0012] Step S4: Coating: Uniformly apply the slurry on the surface of the magnetic steel, with the coating weight gain ratio being 0.3% - 1%, and dry it at 70 - 120 °C to form a coating;

[0013] Step S5: Heat treatment: Subject the coated magnetic steel to the following treatments in a vacuum furnace in sequence:

[0014] Heat to 500 °C - 600 °C and hold for 1 h - 3 h, then cool to 400 °C - 450 °C at a rate of 3 °C / min - 5 °C / min and hold for 0.5 h - 1 h;

[0015] Heat to 680 °C - 750 °C and hold for 2 h - 6 h, then cool to 400 °C - 450 °C at a rate of 3 °C / min - 5 °C / min and hold for 0.5 h - 1 h;

[0016] Heat to 780 °C - 960 °C and hold for 6 h - 12 h for infiltration heat treatment, rapidly cool, then temper at 400 °C - 650 °C for 1 h - 6 h, and rapidly air-cool to room temperature to obtain a sintered neodymium iron boron magnetic steel.

[0017] In a preferred embodiment, the inert gas in Step S1 is argon with a purity ≥ 99.999%, and the thickness of the alloy sputtering pieces is 0.18 mm - 0.25 mm.

[0018] In a preferred embodiment, the mass ratio of the protective agent to the alloy powder in Step S2 is 1:0.1 - 0.5, and the hydrogen pressure for ultra-high pressure hydrogen absorption and crushing is 22 MPa - 24 MPa.

[0019] In a preferred embodiment, in step S3, the polymer resin is polyurethane or epoxy resin, and the slurry viscosity is 1000 mPa·s to 3000 mPa·s.

[0020] In a preferred embodiment, in step S4, the coating thickness in the magnet orientation direction is 0.5 mm to 20 mm, and the drying time is 3 minutes to 10 minutes.

[0021] In a preferred embodiment, in step S5, the vacuum degree in the infiltration heat treatment stage is ≤10 -3 Pa, and the vacuum degree in the tempering stage is ≤10 -2 Pa.

[0022] In a preferred embodiment, in step S5, the infiltration heat treatment temperature is 820 °C to 900 °C, and the holding time is 8 h to 10 h.

[0023] In a preferred embodiment, the Co content in the alloy powder is 0.8% to 2.5%, the Al content is 3% to 6%, and the Ga content is 0.5% to 2%.

[0024] In a preferred embodiment, the intrinsic coercivity of the finally sintered neodymium iron boron magnet is increased by ≥10 kOe compared with the base material, and the remanence change rate is ≤2%.

[0025] In a preferred embodiment, a low-cost sintered neodymium iron boron magnet has a hexavalent chromium content of ≤10 ppm, an intrinsic coercivity of ≥25 kOe, and the production cost is reduced by 10% to 25% compared with the traditional process.

[0026] Technical effects and advantages of the present invention:

[0027] Starting from the principle of improving the coercivity of neodymium iron boron magnets, the present invention cleverly designs the alloy infiltration diffusion source for grain boundary infiltration. The intrinsic coercivity of the magnet prepared with the new diffusion source is greatly improved (when calculating the infiltration alloy magnetic powder with an increment of 1 gram of magnet coating, the intrinsic coercivity increases by 32.68 kOe). The magnetic property grade of the magnet rises by 4 grades, and the remanence remains almost unchanged. Compared with traditional pure heavy rare earth hydrides or fluorides, the cost is reduced by 10 - 25%. Description of the drawings

[0028] Figure 1 It is a process flow schematic diagram of a preparation method for a low-cost sintered neodymium iron boron grain boundary infiltration diffusion source;

[0029] Figure 2 It is a schematic diagram of the performance indexes of Examples 1 - 4 and Comparative Examples 1 - 4 in the present invention. Detailed implementation manners

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] Refer to Figure 1 , (1) Preparation of alloy sputtering flakes

[0032] Prepare the diffusion source alloy raw materials according to the following weight percentages: Co: 0.5% - 3%, Al: 2% - 8%, Cu: 1% - 5%, Ga: 0.2% - 3%, Ni: 2% - 8%, and the balance is Tb or Dy;

[0033] Under the protection of high-purity (99.999%) argon, the prepared diffusion source alloy raw materials are melted to obtain alloy sputtering flakes, and the thickness of the sputtering flakes is controlled at 0.18 - 0.25 mm;

[0034] (2) Preparation of alloy powder

[0035] The alloy sputtering flakes are subjected to hydrogen breaking treatment by a special ultra-high pressure device (the hydrogen absorption pressure reaches 20 - 25 MPa). After hydrogen breaking, the alloy powder, under the protection of terpineol and isopropyl alcohol (protective agent) (terpineol: isopropyl alcohol = 1: 1 - 3), the weight ratio of protective agent: alloy powder = 1: 0.1 - 0.5, and at the same time under the protection of high-purity argon (the purity of argon is 99.999%), alloy powder is prepared by high-energy ball milling, and the average particle size of the prepared alloy powder is 1 μm - 2 μm.

[0036] (3) Preparation of slurry

[0037] A certain proportion of polymer resin is added to the alloy powder together with the protective agent. The component ratio of the slurry is polymer resin: protective agent: alloy powder = 1: 1 - 1.5: 1 - 1.8, and it is uniformly stirred by a stirrer to prepare an alloy slurry.

[0038] (4) Film coating

[0039] The alloy slurry is evenly coated on the surface of the magnetic steel. The thickness in the magnetic steel orientation direction is controlled at 0.5 mm - 20 mm, and the coating weight gain ratio is controlled at 0.3% - 1%. Then, it is baked in an oven at 70°C - 120°C for 3 minutes - 10 minutes to form a neodymium iron boron magnetic steel with an alloy film coating.

[0040] (5) Heat treatment

[0041] The coated NdFeB permanent magnet is heated from room temperature to 500 - 600 °C in a vacuum furnace and held for 1 - 3 h, then cooled at a rate of 3 - 5 °C / min to 400 - 450 °C and held for 0.5 - 1 h, then reheated to 680 - 750 °C and held for 2 - 6 h, and then cooled at a rate of 3 - 5 °C / min to 400 - 450 °C and held for 0.5 - 1 h, and then reheated to 780 - 960 °C and held for 6 - 12 h for infiltration heat treatment, and then rapidly cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10⁻³. Subsequently, it is reheated to 400 °C - 650 °C for 1 h - 6 h of tempering treatment and rapidly air-cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10⁻² to obtain the final sintered NdFeB permanent magnet.

[0042] The magnetic properties of the sintered NdFeB magnet prepared by the new diffusion source are as follows: remanence Br = 14.45 kGs, maximum magnetic energy product (BH)max = 50.85 MGOe, intrinsic coercivity Hcj = 32.31 kOe. Compared with the magnetic properties of the base material, remanence Br = 14.55 kGs, maximum magnetic energy product (BH)max = 52.50 MGOe, intrinsic coercivity Hcj = 15.12 kOe. After the grain boundary infiltration of the new diffusion source, Hcj increases by 17.76 kOe. Calculated by coating 1 g of infiltration alloy magnetic powder on the permanent magnet, the intrinsic coercivity increases by 32.68 kOe, and the magnetic property grade of the permanent magnet rises by 4 grades, and the remanence remains almost unchanged.

[0043] Hereinafter, it will be further described in conjunction with specific embodiments.

[0044] Example 1

[0045] (1) Preparation of alloy flakes

[0046] Prepare the diffusion source alloy raw materials according to the following weight percentages: Co: 0.98%, Al: 3.5%, Cu: 1.5%, Ga: 1.8%, Ni: 3%, and the balance is Tb;

[0047] Under the protection of high-purity (99.999%) argon, the prepared diffusion source alloy raw materials are melted to obtain alloy flakes, and the thickness of the flakes is controlled at 0.2 mm;

[0048] (2) Preparation of alloy powder

[0049] The alloy flakes are subjected to hydrogen breaking treatment by a special ultra-high pressure device (hydrogen absorption pressure reaches 22 MPa). After hydrogen breaking, the alloy powder is protected by terpineol and isopropyl alcohol (protective agent) (terpineol: isopropyl alcohol = 1:1.8), and the weight ratio of the protective agent to the alloy powder is 1:0.45. At the same time, under the protection of high-purity argon (argon purity 99.999%), alloy powder is prepared by high-energy ball milling, and the average particle size of the prepared alloy powder is 1.55 μm.

[0050] (3) Preparation of Slurry

[0051] A certain proportion of polymer resin is added to the alloy powder together with the protective agent. The component ratio of the slurry is: polymer resin: protective agent: alloy powder = 1:1.35:1.68. After being fully stirred evenly by a stirrer, an alloy slurry is prepared.

[0052] (4) Coating

[0053] The alloy slurry is evenly coated on the surface of the magnetic steel. The magnetic steel used is 52M magnetic steel purchased on the market. Its detailed magnetic properties are shown in Table 1. The thickness in the orientation direction of the magnetic steel is controlled at 1.8 mm. The slurry is evenly coated on both sides in the orientation direction, and the coating weight gain ratio is controlled at 0.07 g. Then, it is baked in an oven at 85 °C for 6 minutes to form a neodymium iron boron magnetic steel with an alloy coating.

[0054] (5) Heat Treatment

[0055] For the coated neodymium iron boron magnetic steel, in a vacuum furnace, it is heated from room temperature to 550 °C and held for 1.8 h, then cooled at 4.5 °C / min to 420 °C and held for 1 h, then heated to 680 °C and held for 4 h, and then cooled at 3 °C / min to 435 °C and held for 1 h, and then heated to 860 °C and held for 10 h for infiltration heat treatment, and then quickly cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-3. Subsequently, it is heated to 420 °C for 5.5 h tempering treatment and quickly air-cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-2 to obtain the final sintered neodymium iron boron magnetic steel.

[0056] The magnetic properties of the sintered neodymium iron boron magnetic steel prepared according to Example 1 are: remanence Br = 14.43 kGs, maximum magnetic energy product (BH)max = 50.85 MGOe, and intrinsic coercivity Hcj = 32.31 kOe.

[0057] Example 2

[0058] (1) Preparation of Alloy Sputtering Targets

[0059] Prepare the diffusion source alloy raw materials according to the following weight percentages: Co: 1.8%, Al: 6.2%, Cu: 2.2%, Ga: 0.8%, Ni: 4.6%, and the balance is Tb;

[0060] Under the protection of high-purity (99.999%) argon, the prepared diffusion source alloy raw materials are melted to obtain alloy sputtering targets, and the thickness of the sputtering targets is controlled at 0.24 mm;

[0061] (2) Preparation of Alloy Powder

[0062] The alloy flakes are subjected to hydrogen rupture treatment by special ultra-high pressure equipment (hydrogen absorption pressure reaches 20MPa). The alloy powder after hydrogen rupture is protected by pine alcohol and isopropyl alcohol (protective agent) (pine alcohol: isopropyl alcohol = 1:1.5), the weight ratio of protective agent: alloy powder = 1:0.25, and at the same time, under the protection of high-purity argon (argon purity 99.999%), high-energy ball milling is used to prepare alloy powder. The average particle size of the prepared alloy powder is 2μm.

[0063] (3) Preparation of slurry

[0064] A certain proportion of polymer resin is added to the alloy powder and the protective agent. The composition ratio of the slurry is polymer resin: protective agent: alloy powder = 1:1:1.25. The alloy slurry is prepared by fully stirring with a stirrer.

[0065] (4) Lamination

[0066] The alloy slurry is evenly coated on the surface of the magnet. The magnet adopts 52M magnet purchased from the market. Its detailed magnetic properties are shown in Table 1. The thickness of the magnet in the orientation direction is controlled at 5mm, and the weight gain ratio of the coating is controlled at 0.05g. Then it is baked in an oven at 110℃ for 5 minutes to form a NdFeB magnet with an alloy coating.

[0067] (5) Heat treatment

[0068] The coated NdFeB magnet is heated from room temperature to 540℃ in a vacuum furnace for 2h, then cooled to 415℃ at 3.5℃ / min and kept for 0.8h, then heated to 705℃ and kept for 3.5h, then cooled to 425℃ at 4℃ / min and kept for 0.6h, then heated to 820℃ and kept for 8h for infiltration heat treatment, then quickly cooled to room temperature, the vacuum degree of the whole heat treatment process is controlled within 10-3, then heated to 480℃ for 5h tempering treatment, and quickly air-cooled to room temperature, the vacuum degree of the whole heat treatment process is controlled within 10-2, and the final sintered NdFeB magnet is obtained.

[0069] The magnetic properties of the sintered NdFeB magnet prepared according to Example 2 are: remanence Br=14.45 kGs, maximum magnetic energy product (BH) max=50.83 MGOe, intrinsic coercive force Hcj=26.33 kOe.

[0070] Example 3

[0071] (1) Preparation of alloy sheets

[0072] The diffusion source alloy raw material is prepared according to the following weight percentages: Co: 0.88%, Al: 2.5%, Cu: 1.8%, Ga: 2.1%, Ni: 2.8%, and the balance is Dy;

[0073] The prepared diffusion source alloy raw material is smelted under the protection of high-purity (99.999%) argon gas to obtain alloy flakes, and the thickness of the flakes is controlled at 0.19 mm;

[0074] (2) Preparation of alloy powder

[0075] The alloy flakes were subjected to hydrogen rupture treatment by special ultra-high pressure equipment (hydrogen absorption pressure reached 23MPa). The alloy powder after hydrogen rupture was protected by pine alcohol and isopropyl alcohol (protective agent) (pine alcohol: isopropyl alcohol = 1:1.7), the weight ratio of protective agent: alloy powder = 1:0.43, and at the same time, under the protection of high-purity argon (argon purity 99.999%), high-energy ball milling was performed to prepare alloy powder. The average particle size of the prepared alloy powder was 1.75μm.

[0076] (3) Preparation of slurry

[0077] A certain proportion of polymer resin is added to the alloy powder and the protective agent. The composition ratio of the slurry is polymer resin: protective agent: alloy powder = 1:1.3:1.7. The alloy slurry is prepared by fully stirring with a stirrer.

[0078] (4) Lamination

[0079] The alloy slurry is evenly coated on the surface of the magnetic steel. The magnetic steel adopts 52M magnetic steel purchased from the market. Its detailed magnetic properties are shown in Table 1. The thickness of the magnetic steel in the orientation direction is controlled at 1.8mm. The slurry is evenly coated on both sides of the orientation direction. The coating weight gain ratio is controlled at 0.06g. Then it is baked in an oven at 85℃ for 6 minutes to form a NdFeB magnet with an alloy coating.

[0080] (5) Heat treatment

[0081] The coated NdFeB magnet is heated from room temperature to 530℃ in a vacuum furnace for 1.6h, then cooled to 425℃ at 4.4℃ / min for 0.8h, then heated to 685℃ for 3.5h, then cooled to 415℃ at 3.5℃ / min for 1h, then heated to 875℃ for 11h for infiltration heat treatment, then quickly cooled to room temperature, the vacuum degree of the whole heat treatment process is controlled within 10-3, then heated to 440℃ for 5h tempering treatment, and quickly air-cooled to room temperature, the vacuum degree of the whole heat treatment process is controlled within 10-2, and the final sintered NdFeB magnet is obtained.

[0082] The magnetic properties of the sintered NdFeB magnet prepared according to Example 3 are: remanence Br=14.41 kGs, maximum magnetic energy product (BH) max=50.78 MGOe, intrinsic coercive force Hcj=25.35 kOe.

[0083] Example 4

[0084] (1) Preparation of alloy sputtering flakes

[0085] Prepare the diffusion source alloy raw materials according to the following weight percentages: Co: 2.5%, Al: 6.8%, Cu: 2.4%, Ga: 0.9%, Ni: 3.6%, and the balance is Dy;

[0086] Under the protection of high-purity (99.999%) argon, melt the prepared diffusion source alloy raw materials to obtain alloy sputtering flakes, and the thickness of the sputtering flakes is controlled at 0.2 mm;

[0087] (2) Preparation of alloy powder

[0088] Hydrogen break the alloy sputtering flakes with a special ultra-high pressure device (hydrogen absorption pressure reaches 21 MPa). After hydrogen breaking, the alloy powder, under the protection of terpineol and isopropyl alcohol (protective agent) (terpineol: isopropyl alcohol = 1:1.45), the weight ratio of protective agent to alloy powder = 1:0.35, and at the same time under the protection of high-purity argon (argon purity 99.999%), prepare alloy powder through high-energy ball milling. The average particle size of the prepared alloy powder is 2 μm.

[0089] (3) Preparation of slurry

[0090] Add a certain proportion of polymer resin to the alloy powder together with the protective agent. The component ratio of the slurry is polymer resin: protective agent: alloy powder = 1:1:1.15, and prepare an alloy slurry by fully stirring with a stirrer.

[0091] (4) Coating

[0092] Evenly coat the alloy slurry on the surface of the magnetic steel. The magnetic steel is a 52M magnetic steel purchased on the market. Its detailed magnetic properties are shown in Table 1. The thickness of the magnetic steel in the orientation direction is controlled at 12 mm, and the coating weight gain ratio is controlled at 0.045 g. Then, bake in an oven at 100 °C for 6 minutes to form a neodymium iron boron magnetic steel with an alloy coating.

[0093] (5) Heat treatment

[0094] For the coated neodymium iron boron magnetic steel, in a vacuum furnace, heat from room temperature to 535 °C and hold for 2 h, then cool at 3.5 °C / min to 435 °C and hold for 0.6 h, then heat to 705 °C and hold for 3 h, then cool at 4 °C / min to 425 °C and hold for 1 h, then heat to 900 °C and hold for 10 h for infiltration heat treatment, and then quickly cool to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-3. Subsequently, heat to 460 °C for 5 h tempering treatment and quickly air-cool to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-2 to obtain the final sintered neodymium iron boron magnetic steel.

[0095] The magnetic properties of the sintered NdFeB magnet prepared according to Example 4 are as follows: remanence Br = 14.40 kGs, maximum magnetic energy product (BH)max = 50.75 MGOe, and intrinsic coercivity Hcj = 21.68 kOe.

[0096] <Comparative Example 1>

[0097] A preparation method of a low-cost sintered NdFeB grain boundary penetration diffusion source

[0098] (1) Preparation of alloy flakes

[0099] The diffusion source alloy raw material is pure terbium hydride;

[0100] The prepared diffusion source alloy raw material is melted under the protection of high-purity (99.999%) argon to obtain alloy flakes, and the thickness of the flakes is controlled at 0.2 mm;

[0101] (2) Preparation of alloy powder

[0102] The alloy flakes are subjected to hydrogen breaking treatment by a special ultra-high pressure device (hydrogen absorption pressure reaches 22 MPa). After hydrogen breaking, the alloy powder is protected by terpineol and isopropanol (protective agent) (terpineol: isopropanol = 1:1.8), and the weight ratio of the protective agent to the alloy powder = 1:0.45. At the same time, under the protection of high-purity argon (purity of argon 99.999%), alloy powder is prepared by high-energy ball milling. The average particle size of the prepared alloy powder is 1.55 μm.

[0103] (3) Preparation of slurry

[0104] A certain proportion of polymer resin is added to the alloy powder together with the protective agent. The component ratio of the slurry is polymer resin: protective agent: alloy powder = 1:1.35:1.68, and it is fully stirred evenly by a stirrer to prepare an alloy slurry.

[0105] (4) Coating

[0106] The alloy slurry is evenly coated on the surface of the magnet. The magnet used is a 52M magnet purchased on the market. Its detailed magnetic properties are shown in Table 1. The thickness of the magnet in the orientation direction is controlled at 1.8 mm. The slurry is evenly coated on both sides in the orientation direction, and the coating weight gain ratio is controlled at 0.07 g. Then it is baked in an oven at 85 °C for 6 minutes to form a NdFeB magnet with an alloy coating.

[0107] (5) Heat treatment

[0108] The coated NdFeB permanent magnet is heated from room temperature to 550 °C in a vacuum furnace and held for 1.8 h, then cooled at a rate of 4.5 °C / min to 420 °C and held for 1 h, then heated to 680 °C and held for 4 h, then cooled at a rate of 3 °C / min to 435 °C and held for 1 h, and then heated to 860 °C and held for 10 h for infiltration heat treatment, and then rapidly cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-3. Subsequently, it is heated to 420 °C for tempering treatment for 5.5 h and rapidly air-cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-2 to obtain the final sintered NdFeB permanent magnet.

[0109] <Comparative Example 2>

[0110] A preparation method of a low-cost sintered NdFeB grain boundary infiltration diffusion source

[0111] (1) Preparation of alloy flakes

[0112] The diffusion source alloy raw material is pure terbium fluoride;

[0113] The prepared diffusion source alloy raw material is melted under the protection of high-purity (99.999%) argon to obtain alloy flakes, and the thickness of the flakes is controlled at 0.24 mm;

[0114] (2) Preparation of alloy powder

[0115] The alloy flakes are hydrogenated under a special ultra-high pressure device (hydrogen absorption pressure reaches 20 MPa). After hydrogenation, the alloy powder is under the protection of terpineol and isopropanol (protective agent) (terpineol: isopropanol = 1:1.5), and the weight ratio of the protective agent to the alloy powder is 1:0.25. At the same time, under the protection of high-purity argon (argon purity 99.999%), alloy powder is prepared by high-energy ball milling, and the average particle size of the prepared alloy powder is 2 μm.

[0116] (3) Preparation of slurry

[0117] A certain proportion of polymer resin is added to the alloy powder together with the protective agent. The component ratio of the slurry is polymer resin: protective agent: alloy powder = 1:1:1.25, and it is uniformly stirred by a stirrer to prepare an alloy slurry.

[0118] (4) Coating

[0119] The alloy slurry is evenly coated on the surface of the permanent magnet. The permanent magnet uses a 52M permanent magnet purchased on the market, and its detailed magnetic properties are shown in Table 1. The thickness in the orientation direction of the permanent magnet is controlled at 5 mm, and the coating weight gain ratio is controlled at 0.05 g. Then it is baked in an oven at 110 °C for 5 minutes to form a NdFeB permanent magnet with an alloy coating.

[0120] (5) Heat treatment

[0121] The coated NdFeB magnet is heated from room temperature to 540℃ in a vacuum furnace for 2h, then cooled to 415℃ at 3.5℃ / min and kept for 0.8h, then heated to 705℃ and kept for 3.5h, then cooled to 425℃ at 4℃ / min and kept for 0.6h, then heated to 820℃ and kept for 8h for infiltration heat treatment, then quickly cooled to room temperature, the vacuum degree of the whole heat treatment process is controlled within 10-3, then heated to 480℃ for 5h tempering treatment, and quickly air-cooled to room temperature, the vacuum degree of the whole heat treatment process is controlled within 10-2, and the final sintered NdFeB magnet is obtained.

[0122] <Comparative Example 3>

[0123] A method for preparing a low-cost sintered NdFeB grain boundary infiltration diffusion source.

[0124] (1) Preparation of alloy sheets

[0125] The diffusion source alloy raw material is pure hydrogenated entropy;

[0126] The prepared diffusion source alloy raw material is smelted under the protection of high-purity (99.999%) argon gas to obtain alloy flakes, and the thickness of the flakes is controlled at 0.19 mm;

[0127] (2) Preparation of alloy powder

[0128] The alloy flakes were subjected to hydrogen rupture treatment by special ultra-high pressure equipment (hydrogen absorption pressure reached 23MPa). The alloy powder after hydrogen rupture was protected by pine alcohol and isopropyl alcohol (protective agent) (pine alcohol: isopropyl alcohol = 1:1.7), the weight ratio of protective agent: alloy powder = 1:0.43, and at the same time, under the protection of high-purity argon (argon purity 99.999%), high-energy ball milling was performed to prepare alloy powder. The average particle size of the prepared alloy powder was 1.75μm.

[0129] (3) Preparation of slurry

[0130] A certain proportion of polymer resin is added to the alloy powder and the protective agent. The composition ratio of the slurry is polymer resin: protective agent: alloy powder = 1:1.3:1.7. The alloy slurry is prepared by fully stirring with a stirrer.

[0131] (4) Lamination

[0132] The alloy slurry is evenly coated on the surface of the magnetic steel. The magnetic steel adopts 52M magnetic steel purchased from the market. Its detailed magnetic properties are shown in Table 1. The thickness of the magnetic steel in the orientation direction is controlled at 1.8mm. The slurry is evenly coated on both sides of the orientation direction. The coating weight gain ratio is controlled at 0.06g. Then it is baked in an oven at 85℃ for 6 minutes to form a NdFeB magnet with an alloy coating.

[0133] (5) Heat treatment

[0134] For the coated NdFeB permanent magnet, in a vacuum furnace, it is heated from room temperature to 530 °C and held for 1.6 h, then cooled at 4.4 °C / min to 425 °C and held for 0.8 h, then heated to 685 °C and held for 3.5 h, and then cooled at 3.5 °C / min to 415 °C and held for 1 h, and then heated to 875 °C and held for 11 h for infiltration heat treatment, and then rapidly cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-3. Subsequently, it is heated to 440 °C for 5 h of tempering treatment and rapidly air-cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-2 to obtain the final sintered NdFeB permanent magnet.

[0135] <Comparative Example 4>

[0136] A preparation method of a low-cost sintered NdFeB grain boundary infiltration diffusion source,

[0137] (1) Preparation of alloy flakes

[0138] The diffusion source alloy raw material is pure terbium fluoride;

[0139] The prepared diffusion source alloy raw material is melted under the protection of high-purity (99.999%) argon to obtain alloy flakes, and the thickness of the flakes is controlled at 0.2 mm;

[0140] (2) Preparation of alloy powder

[0141] The alloy flakes are subjected to hydrogen breaking treatment by a special ultra-high pressure device (the hydrogen absorption pressure reaches 21 MPa). After hydrogen breaking, the alloy powder is under the protection of terpineol and isopropyl alcohol (protective agent) (terpineol: isopropyl alcohol = 1:1.45), and the weight ratio of the protective agent to the alloy powder = 1:0.35. At the same time, under the protection of high-purity argon (the purity of argon is 99.999%), alloy powder is prepared by high-energy ball milling. The average particle size of the prepared alloy powder is 2 μm.

[0142] (3) Preparation of slurry

[0143] A certain proportion of polymer resin is added to the alloy powder together with the protective agent. The component ratio of the slurry is polymer resin: protective agent: alloy powder = 1:1:1.15, and it is uniformly stirred by a stirrer to prepare an alloy slurry.

[0144] (4) Coating

[0145] The alloy slurry is uniformly coated on the surface of the permanent magnet. The permanent magnet uses a 52M permanent magnet purchased on the market. Its detailed magnetic properties are shown in Table 1. The thickness of the permanent magnet in the orientation direction is controlled at 12 mm, and the coating weight gain ratio is controlled at 0.045 g. Then, it is baked in an oven at 100 °C for 6 minutes to form a NdFeB permanent magnet with an alloy coating.

[0146] (5) Heat treatment

[0147] The coated neodymium iron boron permanent magnet is heated from room temperature to 535 °C in a vacuum furnace and held for 2 h, then cooled at 3.5 °C / min to 435 °C and held for 0.6 h, then heated to 705 °C and held for 3 h, then cooled at 4 °C / min to 425 °C and held for 1 h, then heated to 900 °C and held for 10 h for infiltration heat treatment, and then rapidly cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-3. Subsequently, it is heated to 460 °C for 5 h tempering treatment and rapidly air-cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10-2 to obtain the final sintered neodymium iron boron permanent magnet.

[0148] In order to conveniently verify the preparation method of a low-cost sintered neodymium iron boron grain boundary infiltration diffusion source in this invention patent, the performance indexes of Examples 1 to 4 and Comparative Examples 1 to 4 are respectively listed in the attached Figure 2 as shown. It can be seen that the present invention provides a preparation method of a low-cost sintered neodymium iron boron grain boundary infiltration diffusion source. The intrinsic coercivity Hcj of the permanent magnet prepared with the new diffusion source is greatly improved, the remanence Br remains almost unchanged, and the performance grade of the permanent magnet can be increased from 52M to 52EH at most, with a 4-grade improvement. Compared with the traditional diffusion source, the cost can be reduced by 23%, which is very suitable for commercial promotion.

[0149] Finally: The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a low-cost sintered Nd-Fe-B grain boundary diffusion source, characterized in that; It includes the following steps: Step S1: Preparation of alloy sputtering pieces: Prepare diffusion source alloy raw materials according to weight percentages, including: Co: 0.5% - 3%, Al: 2% - 8%, Cu: 1% - 5%, Ga: 0.2% - 3%, Ni: 2% - 8%, and the balance is terbium or dysprosium; Melt the raw materials into alloy sputtering pieces under the protection of inert gas; Step S2: Preparation of alloy powder: Subject the alloy sputtering pieces to ultra-high pressure hydrogen absorption and crushing (hydrogen pressure 20 MPa - 25 MPa), and then carry out high-energy ball milling under the protection of a mixed protective agent of terpineol and isopropyl alcohol (mass ratio 1:1 - 3) and high-purity argon to obtain alloy powder with an average particle size of 1 - 2 μm; Step S3: Preparation of slurry: Mix the alloy powder, polymer resin, and protective agent according to a mass ratio of 1:1 - 1.5:1 - 1.8, and stir evenly to obtain an alloy slurry; Step S4: Coating: Uniformly apply the slurry on the surface of the magnetic steel, with a coating weight gain ratio of 0.3% - 1%, and dry it at 70 - 120 °C to form a coating; Step S5: Heat treatment: Subject the coated magnetic steel to the following treatments in a vacuum furnace in sequence: Heat to 500 °C - 600 °C and hold for 1 h - 3 h, cool to 400 °C - 450 °C at a rate of 3 °C / min - 5 °C / min and hold for 0.5 h - 1 h; Heat to 680 °C - 750 °C and hold for 2 h - 6 h, then cool to 400 °C - 450 °C at a rate of 3 / min - 5 °C / min and hold for 0.5 h - 1 h; Heat to 780 °C - 960 °C and hold for 6 h - 12 h for infiltration heat treatment, after rapid cooling, then temper at 400 °C - 650 °C for 1 h - 6 h, and rapidly air-cool to room temperature to obtain a sintered neodymium iron boron magnetic steel.

2. The preparation method of a low-cost sintered Nd-Fe-B grain boundary diffusion source according to claim 1, characterized in that: In step S1, the inert gas is argon with a purity ≥ 99.999%, and the thickness of the alloy sputtering pieces is 0.18 mm - 0.25 mm.

3. The preparation method of a low-cost sintered neodymium iron boron grain boundary diffusion source according to claim 1, characterized in that: In step S2, the mass ratio of the protective agent to the alloy powder is 1:0.1 - 0.5, and the hydrogen pressure for ultra-high pressure hydrogen absorption and crushing is 22 MPa - 24 MPa.

4. The preparation method of a low-cost sintered Nd-Fe-B grain boundary diffusion source according to claim 1, characterized in that: In step S3, the polymer resin is polyurethane or epoxy resin, and the viscosity of the slurry is 1000 mPa·s - 3000 mPa·s.

5. The preparation method of a low-cost sintered neodymium iron boron grain boundary diffusion source according to claim 1, wherein: In step S4, the coating thickness in the magnetic steel orientation direction is 0.5 mm - 20 mm, and the drying time is 3 minutes - 10 minutes.

6. The preparation method of a low-cost sintered neodymium iron boron grain boundary diffusion source according to claim 1, wherein: The vacuum degree in the infiltration heat treatment stage in step S5 ≤ 10 -3 Pa, and the vacuum degree in the tempering stage ≤ 10 -2 Pa.

7. The preparation method of a low-cost sintered neodymium iron boron grain boundary diffusion source according to claim 1, characterized in that: In step S5, the temperature for infiltration heat treatment is 820 °C - 900 °C, and the holding time is 8 h - 10 h.

8. The preparation method of a low-cost sintered Nd-Fe-B grain boundary diffusion source according to claim 1, wherein: The Co content in the alloy powder is 0.8% - 2.5%, the Al content is 3% - 6%, and the Ga content is 0.5% - 2%.

9. The preparation method of a low-cost sintered neodymium iron boron grain boundary diffusion source according to claim 1, characterized in that: The intrinsic coercivity of the final sintered neodymium iron boron magnetic steel is increased by ≥ 10 kOe compared with the base material, and the remanence change rate ≤ 2%.

10. A low-cost sintered NdFeB permanent magnet, characterized in that, Prepared by the method according to any one of claims 1 - 9, its hexavalent chromium content ≤ 10 ppm, intrinsic coercivity ≥ 25 kOe, and the production cost is reduced by 10% - 25% compared with the traditional process.

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