Preparation method of double-high-performance sintered NdFeB (neodymium iron boron)

Abstract

The invention discloses a preparation method of double-high-performance sintered NdFeB. The preparation method comprises the following steps: preparing alloy melt-spinning according to requirements, preparing powder, carrying out orientation forming, carrying out vacuum sintering heat treatment, carrying out hot isostatic pressing treatment, processing into finished product sizes required by the market, cleaning magnetic steel, coating heavy rare earth alloy slurry, and finally carrying out grain boundary permeation heat treatment. Through reasonable design of raw material components, an airflow grinding process and a step-by-step addition mode of additives, uniform components are ensured, magnetic powder orientation forming and vacuum sintering heat treatment are performed, then ultrahigh-pressure hot isostatic pressing treatment is performed, then the magnetic steel is processed to be close to the size of a finished product, and after magnetic steel is cleaned, alloy slurry is coated, and then permeation heat treatment is performed. Compared with magnetic steel prepared by a traditional process, the intrinsic coercive force of the magnetic steel prepared by the method is greatly improved, the residual magnetism is almost unchanged, and the magnetic steel is very suitable for commercial popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and particularly relates to a preparation method of double high-performance sintered neodymium iron boron. Background Art

[0002] As the third-generation rare-earth permanent magnet, sintered neodymium iron boron has become a key support for the development of related fields towards intelligence, miniaturization, and lightweight due to its high magnetic properties at room temperature. Currently, the pursuit of "double high" high coercivity and high remanence (high maximum magnetic energy product (BH)max) is the research and development direction of sintered neodymium iron boron. At present, its (BH)max has reached 59.5 MGOe, which is close to its theoretical value. However, the coercivity of the magnet is quite different from its theoretical value, resulting in poor temperature stability. Usually, a certain amount of heavy rare earths Dy and Tb are added during alloy melting to improve the coercivity of the magnet. However, the addition of Dy or Tb will cause a decrease in the remanence and maximum magnetic energy product of the material; especially, the prices of Dy and Tb elements are much higher than that of Nd (Tb is about 14 times that of Nd), resulting in a substantial increase in the production cost of the magnet. Due to the intensifying international trade war and the competition for rare earth resources, how to use less heavy rare earths and develop high-performance sintered neodymium iron boron magnets at low cost has become a matter of life and death for the industry's development. Summary of the Invention

[0003] Aiming at the problems proposed in the background art, the present invention provides a preparation method of double high-performance sintered neodymium iron boron. Starting from the principle of improving the coercivity of neodymium iron boron magnets, the present invention forms a Dy or Tb alloy coating layer on the magnet close to the customer's finished product by means of coating through a special process, and then cooperates with an alloy infiltration heat treatment system to form an alloy infiltration layer on the surface of the magnet, so as to significantly improve the coercivity of the magnet. Combining with the process of hot isostatic pressing, while ensuring the unchanged remanence of the magnet, the research and production of double high-performance sintered neodymium iron boron are realized.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A preparation method of double high-performance sintered neodymium iron boron includes the following steps:

[0006] S1. Prepare alloy sputtering flakes: Prepare diffusion source alloy raw materials according to the following weight percentages: PrNd: 24 - 32%, Al: 0.2 - 0.6%, Cu: 0.1 - 0.3%, Co: 0.2 - 3%, Zr: 0.1 - 1%, Ga: 0.1 - 0.3%, B: 0.8 - 1%, Dy: 0 - 4%, Tb: 0 - 1%, and the balance is Fe. Under the protection of inert gas, the prepared raw materials are melted at high temperature to obtain alloy sputtering flakes;

[0007] S2. Preparation of alloy magnetic powder: After the alloy flakes prepared in S1 are hydrogenated and crushed, they are immediately processed by a jet mill to prepare uniformly distributed alloy magnetic powder;

[0008] S3. Preparation of NdFeB green compact: The magnetic powder prepared in S2 is oriented and formed in a closed press to obtain an NdFeB green compact;

[0009] S4. Vacuum sintering heat treatment: The NdFeB green compact prepared in step (3) is placed in a vacuum heat treatment furnace, and the vacuum is controlled at 10 -2 above. After the heat treatment is completed, it is quickly air-cooled to room temperature to obtain the final sintered NdFeB permanent magnet;

[0010] S5. Hot isostatic pressing treatment: The NdFeB permanent magnet obtained in step (4) is subjected to hot isostatic pressing treatment;

[0011] S6. Machining: The NdFeB permanent magnet obtained in step S5 is machined into the required finished size specifications;

[0012] S7. Coating and drying: The surface of the NdFeB permanent magnet obtained in step S6 is cleaned, coated with a self-developed heavy metal alloy slurry, and dried;

[0013] S8. Alloy infiltration heat treatment: The permanent magnet obtained in step S7 is placed in a vacuum heat treatment furnace, and the vacuum degree during the entire heat treatment process is controlled at 10 -2 inside. After the heat treatment is completed, it is quickly air-cooled to room temperature to obtain the NdFeB permanent magnet.

[0014] As a further step in the method of the present invention, in S1, the melting and casting of the alloy flakes are both carried out under the protection of high-purity (99.999%) argon.

[0015] As a further step in the method of the present invention, in S1, the thickness of the flakes is controlled at 0.2 - 0.25 mm.

[0016] As a further step in the method of the present invention, in S2, after the strip is hydrogenated and crushed, the average particle size SMD of the alloy powder prepared by the jet mill is 2.5 - 3 μm, and the additives in the powder preparation process are added in a distributed manner. The prepared magnetic powder is then mixed in nitrogen for 3 - 5 h.

[0017] As a further step in the method of the present invention, in S3, the forming is carried out in a closed press under nitrogen protection, and the orientation magnetic field is controlled above 1.8 T.

[0018] As a further step in the method of the present invention, in S4, it is heated from room temperature to 280 - 350 °C and kept warm for 1 - 3 h, then heated to 480 - 600 °C and kept warm for 2 - 6 h, then heated to 780 - 900 °C and kept warm for 2 - 6 h, then heated to 1000 - 1020 °C and kept warm for 0.5 - 1 h, and finally heated to 1050 - 1100 °C and kept warm for 3 - 8 h.

[0019] As a further step in the method of the present invention, in S5, the conditions for hot isostatic pressing treatment are: under a pressure of 160 - 220 Mpa, kept warm at 1050 - 1100 °C for 1 - 3 h.

[0020] As a further step in the method of the present invention, in S6, the processed size is the size specification of a conventional square - shaped finished product required by the market, and the size is: 20 - 50 mm * 10 - 30 mm * 0.5 - 8 mm.

[0021] As a further step in the method of the present invention, in S7, the weight gain ratio is controlled at 0.01 - 0.8 g, and then dried at 80 - 120 °C.

[0022] As a further step in the method of the present invention, in S8, it is heated from room temperature to 500 - 600 °C and kept warm for 1 - 3 h, then cooled at 3 - 5 °C / min to 400 - 450 °C and kept warm for 0.5 - 1 h, then heated to 680 - 750 °C and kept warm for 2 - 6 h, then cooled at 3 - 5 °C / min to 400 - 450 °C and kept warm for 0.5 - 1 h, then heated to 780 - 960 °C and kept warm for 6 - 12 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. After the above heat treatment process, it is quickly cooled to room temperature, and then heated to 400 - 650 °C for 1 - 6 h of tempering treatment.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] The intrinsic coercivity of the sintered Nd - Fe - B permanent magnet prepared by this invention method is greatly improved (when calculating the infiltration alloy magnetic powder with an increment of 1 g in the magnetic steel coating, the intrinsic coercivity increases by 32.68 kOe). The magnetic property grade of the magnetic steel rises by 4 grades, and the remanence remains unchanged (or slightly increases), which has good economic benefits and is suitable for industrialization. Specific Embodiments

[0025] Referring to the following detailed description of the preferred embodiments of the present invention and the included examples, the content of the present invention can be more easily understood. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. When there is a contradiction, the definition in this specification shall prevail.

[0026] As used herein, the term "comprising" is synonymous with "including". As used herein, the terms "comprising", "including", "having", "containing", or any other variation thereof, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises the recited elements need not be limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0027] The transitional phrase "consisting of" excludes any unrecited element, step, or ingredient. When used in a claim, this phrase renders the claim closed-ended, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the claim body rather than immediately following the subject, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0028] When an equivalent, concentration, or other value or parameter is expressed as a range, preferably a range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, whether or not those ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within that range.

[0029] The singular forms include plural referents unless the context clearly dictates otherwise. "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0030] Approximating language, as used in the specification and claims, is used to modify a quantity, indicating that the present invention is not limited to the specific quantity and also includes modified portions that are close to that quantity and are acceptable without causing a change in the relevant basic function. Accordingly, modifying a numerical value with terms such as "about", "approximately", etc. means that the present invention is not limited to the exact value. In some instances, the approximating language may correspond to the precision of the instrument for measuring the value. In the specification and claims of the present application, range limitations may be combined and / or interchanged, and these ranges include all sub-ranges subsumed therein if not otherwise stated.

[0031] In addition, the indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirements (i.e., the number of occurrences) of the elements or components. Therefore, "a" or "an" should be construed to include one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers to the singular form.

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with 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.

[0033] A preparation method of double high-performance sintered neodymium iron boron includes the following steps:

[0034] (1) Preparation of alloy flakes

[0035] Prepare the diffusion source alloy raw materials according to the following weight percentages: PrNd: 24 - 32%, Al: 0.2 - 0.6%, Cu: 0.1 - 0.3%, Co: 0.2 - 3%, Zr: 0.1 - 1%, Ga: 0.1 - 0.3%, B: 0.8 - 1%, Dy: 0 - 4%, Tb: 0 - 1%, and the balance is Fe;

[0036] Perform the prepared diffusion source alloy raw materials under the protection of high-purity (99.999%) argon, and the thickness of the secondary flakes is controlled at 0.2 - 0.25 mm.

[0037] (2) Powder making

[0038] After the strip casting is hydrogenated and crushed, the average particle size SMD of the alloy powder prepared by the jet mill is 2.5 - 3 μm, and the additives in the powder making process are added in a distributed manner, and the prepared magnetic powder is mixed in nitrogen for 3 - 5 h.

[0039] (3) Orientation forming

[0040] The forming is carried out in a closed press under nitrogen protection, and the orientation magnetic field is controlled above 1.8 T.

[0041] (4) Vacuum sintering heat treatment

[0042] The prepared neodymium iron boron green body is heated from room temperature to 280 - 350 °C in a vacuum furnace and held for 1 - 3 h, then heated to 480 - 600 °C and held for 2 - 6 h, then heated to 780 - 900 °C and held for 2 - 6 h, then heated to 1000 - 1020 °C and held for 0.5 - 1 h, and finally heated to 1050 - 1100 °C and held for 3 - 8 h, and then rapidly air-cooled to room temperature to obtain the final sintered neodymium iron boron magnet;

[0043] (5) Hot isostatic pressing treatment

[0044] The magnet steel after vacuum heat treatment is subjected to hot isostatic pressing under the following conditions: maintaining at 1050 - 1100 °C for 1 - 3 h under a pressure of 160 - 220 Mpa.

[0045] (6) Machining

[0046] The blank after hot isostatic pressing is machined to the size specifications of conventional square sheet finished products required by the market, with the size being: 20 - 50 mm * 10 - 30 mm * 0.5 - 8 mm.

[0047] (7) Coating

[0048] The machined NdFeB magnet steel is cleaned on the surface and coated with a heavy metal alloy slurry independently developed, with the weight gain ratio controlled at 0.01 - 0.8 g, and then dried at 80 - 120 °C.

[0049] (8) Alloy infiltration heat treatment

[0050] The NdFeB magnet steel coated with heavy metal slurry is placed in a vacuum heat treatment furnace, heated from room temperature to 500 - 600 °C and maintained for 1 - 3 h, then cooled at 3 - 5 °C / min to 400 - 450 °C and maintained for 0.5 - 1 h, then heated to 680 - 750 °C and maintained for 2 - 6 h, and then cooled at 3 - 5 °C / min to 400 - 450 °C and maintained for 0.5 - 1 h, and then heated to 780 - 960 °C 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. After the above heat treatment process is completed, it is rapidly cooled to room temperature, and then reheated to 400 - 650 °C for 1 - 6 h for tempering treatment. The vacuum degree during the whole heat treatment process is controlled within 10⁻². After the above heat treatment process is completed, the magnet steel is rapidly air-cooled to room temperature to obtain the NdFeB magnet steel.

[0051] The magnetic properties of the sintered NdFeB magnet prepared by the process of the present invention are: remanence Br = 14.56 kGs, maximum magnetic energy product (BH)max = 52.55 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 new diffusion source grain boundary infiltration, Hcj increases by 17.76 kOe. Calculated by coating 1 g of infiltration alloy magnetic powder on the magnet steel, the intrinsic coercivity increases by 32.68 kOe, and the magnetic property grade of the magnet steel rises by 4 grades, and the remanence remains unchanged.

[0052] Hereinafter, it will be further described in conjunction with specific embodiments.

[0053] Example 1

[0054] (1) Preparation of Alloy Flakes

[0055] Prepare the diffusion source alloy raw materials according to the following weight percentages: PrNd: 29.2%, Al: 0.21%, Cu: 0.15%, Co: 1%, Zr: 0.15%, Ga: 0.2%, B: 0.895%, and the balance is Fe;

[0056] 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 0.22 mm;

[0057] (2) Powder Making

[0058] After the strip casting is hydrogenated and crushed, the average particle size SMD of the alloy powder prepared by the jet mill is 2.55 μm, and the additives in the powder making process are added in a distributed manner. The prepared magnetic powder is then mixed in nitrogen for 3.5 h.

[0059] (3) Orientation Forming

[0060] The forming is carried out in a closed press under nitrogen protection, and the orientation magnetic field is controlled at 2.0 T.

[0061] (4) Vacuum Sintering Heat Treatment

[0062] The prepared NdFeB green compact is heated from room temperature to 300 °C in a vacuum furnace and held for 2.5 h, then heated to 550 °C and held for 4 h, then heated to 850 °C and held for 4 h, then heated to 1000 °C and held for 1 h, and finally heated to 1060 °C and held for 5 h, and then quickly air-cooled to room temperature to obtain the final sintered NdFeB permanent magnet;

[0063] (5) Hot Isostatic Pressing Treatment

[0064] The magnet after vacuum heat treatment is subjected to hot isostatic pressing treatment. The conditions of the hot isostatic pressing treatment are: at a pressure of 220 Mpa and held at 1060 °C for 2 h.

[0065] (6) Machining

[0066] The size of the blank after hot isostatic pressing treatment is the size specification of the conventional square piece finished product required by the market, and the size is: 25 mm * 10 mm * 1.8 mm.

[0067] (7) Coating

[0068] The surface of the processed NdFeB permanent magnet is cleaned, and a self-developed heavy metal Tb alloy slurry is coated. The weight gain ratio is controlled at 0.07 g, and then dried at 100 °C.

[0069] (8) Alloy Penetration Heat Treatment

[0070] 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 5.5 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.

[0071] The magnetic properties of the sintered NdFeB permanent magnet prepared according to Example 1 are: remanence Br = 14.56 kGs, maximum magnetic energy product (BH)max = 52.55 MGOe, and intrinsic coercivity Hcj = 32.31 kOe.

[0072] Example 2

[0073] (1) Preparation of alloy flakes

[0074] Prepare the diffusion source alloy raw materials according to the following weight percentages: PrNd: 30%, Al: 0.1%, Cu: 0.2%, Co: 2%, Zr: 0.15%, Ga: 0.3%, B: 0.9%, and the balance is Fe;

[0075] The prepared diffusion source alloy raw materials are carried out under the protection of high-purity (99.999%) argon gas, and the thickness of the flake is controlled at 0.2 mm.

[0076] (2) Powder making

[0077] After the strip casting is hydrogenated and crushed, the average particle size SMD of the alloy powder prepared by the jet mill is 2.8 μm, and the additives in the powder making process are added in a distributed manner. The prepared magnetic powder is mixed in nitrogen for 3.5 h.

[0078] (3) Orientation forming

[0079] The forming is carried out in a closed press under nitrogen protection, and the orientation magnetic field is controlled at 1.8 T.

[0080] (4) Vacuum sintering heat treatment

[0081] The prepared NdFeB green body is heated from room temperature to 280 °C in a vacuum furnace and held for 1 h, then heated to 480 °C and held for 2.5 h, then heated to 785 °C and held for 4 h, then heated to 1000 °C and held for 1 h, and finally heated to 1050 °C and held for 3.5 h, and then rapidly air-cooled to room temperature to obtain the final sintered NdFeB permanent magnet;

[0082] (5) Hot isostatic pressing treatment

[0083] The magnet steel after vacuum heat treatment is subjected to hot isostatic pressing under the following conditions: at a pressure of 180 Mpa and holding at 1050 °C for 1.5 h.

[0084] (6) Machining

[0085] The blank after hot isostatic pressing is machined to the size specifications of the conventional square sheet finished products required by the market, with the size of 20 mm * 10 mm * 0.6 mm.

[0086] (7) Coating

[0087] The machined NdFeB magnet steel is cleaned on the surface and coated with a heavy metal Dy alloy slurry independently developed, with the weight gain ratio controlled at 0.3 g, and then dried at 80 °C.

[0088] (8) Alloy infiltration heat treatment

[0089] The NdFeB magnet steel coated with the heavy metal slurry is placed in a vacuum heat treatment furnace, heated from room temperature to 500 °C and held for 1 h, then cooled at 3 °C / min to 400 °C and held for 0.5 h, then heated to 680 °C and held for 2 h, then cooled at 3 °C / min to 450 °C and held for 1 h, and then heated to 785 °C and held for 6.5 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. After the above heat treatment process is completed, it is quickly cooled to room temperature, and then heated to 450 °C for 2 h tempering treatment. The vacuum degree during the whole heat treatment process is controlled within 10-2. After the above heat treatment process is completed, the magnet steel is quickly air-cooled to room temperature to obtain the NdFeB magnet steel.

[0090] The magnetic properties of the sintered NdFeB magnet steel prepared according to Example 2 are: remanence Br = 14.45 kGs, maximum magnetic energy product (BH)max = 50.83 MGOe, and intrinsic coercivity Hcj = 23.35 kOe.

[0091] Example 3

[0092] (1) Preparation of alloy sputtering flakes

[0093] Prepare the diffusion source alloy raw materials according to the following weight percentages: PrNd: 30%, Al: 0.1%, Cu: 0.2%, Co: 2%, Zr: 0.15%, Ga: 0.3%, B: 0.9%, and the balance is Fe;

[0094] The prepared diffusion source alloy raw materials are carried out under the protection of high-purity (99.999%) argon gas, and the thickness of the sputtering flakes is controlled at 0.2 mm.

[0095] (2) Powder making

[0096] After the strip is hydrogenation pulverized, the average particle size SMD of the alloy powder prepared by jet milling is 2.8 μm. Moreover, the additives in the powder preparation process are added in a distributed manner, and the prepared magnetic powder is then mixed for 3.5 h under the protection of nitrogen.

[0097] (3) Orientation forming

[0098] The forming is carried out in a closed press under the protection of nitrogen, and the orientation magnetic field is controlled at 1.8 T.

[0099] (4) Vacuum sintering heat treatment

[0100] The prepared NdFeB green compact is heated from room temperature to 280 °C in a vacuum furnace and held for 1 h, then heated to 480 °C and held for 2.5 h, then heated to 785 °C and held for 4 h, then heated to 1000 °C and held for 1 h, and finally heated to 1050 °C and held for 3.5 h, and then quickly air-cooled to room temperature to obtain the final sintered NdFeB permanent magnet;

[0101] (5) Hot isostatic pressing treatment

[0102] The permanent magnet after vacuum heat treatment is subjected to hot isostatic pressing treatment. The conditions of the hot isostatic pressing treatment are: at a pressure of 180 Mpa and held at 1050 °C for 1.5 h.

[0103] (6) Machining

[0104] The blank after hot isostatic pressing treatment is machined to the size of the conventional square piece finished product required by the market, and the size is: 20 mm * 10 mm * 0.6 mm.

[0105] (7) Coating

[0106] The machined NdFeB permanent magnet is cleaned on the surface, coated with the self-developed heavy metal Tb alloy slurry, and the weight gain ratio is controlled at 0.04 g, and then dried at 100 °C.

[0107] (8) Alloy infiltration heat treatment

[0108] The NdFeB permanent magnet coated with the heavy metal slurry is placed in a vacuum heat treatment furnace, heated from room temperature to 550 °C and held for 2 h, then cooled at 3.5 °C / min to 400 °C and held for 1 h, then heated to 720 °C and held for 3 h, then cooled at 4 °C / min to 450 °C and held for 1.5 h, then heated to 850 °C and held for 6.5 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. After the above heat treatment process is completed, it is quickly cooled to room temperature, and then heated to 520 °C for 3 h tempering treatment. The vacuum degree during the whole heat treatment process is controlled within 10-2. After the above heat treatment process is completed, the permanent magnet is quickly air-cooled to room temperature to obtain the NdFeB permanent magnet.

[0109] The magnetic properties of the sintered NdFeB magnet prepared according to Example 3 are: remanence Br = 14.46 kGs, maximum magnetic energy product (BH)max = 50.78 MGOe, and intrinsic coercivity Hcj = 25.78 kOe.

[0110] Example 4

[0111] (1) Preparation of alloy flakes

[0112] Prepare the diffusion source alloy raw materials according to the following weight percentages: PrNd: 24.5%, Al: 0.2%, Cu: 0.15%, Co: 0.2%, Zr: 0.15%, Ga: 0.25%, B: 0.9%, Dy: 4%, Tb: 0.2%, and the balance is Fe;

[0113] Carry out the prepared diffusion source alloy raw materials under the protection of high-purity (99.999%) argon gas, and the thickness of the secondary flakes is controlled at 0.24 mm.

[0114] (2) Powder making

[0115] After the strip casting is hydrogenated and crushed, the average particle size SMD of the alloy powder prepared by the jet mill is 2.8 μm, and the additives in the powder making process are added in a distributed manner. The prepared magnetic powder is then mixed in nitrogen for 5 h.

[0116] (3) Orientation and forming

[0117] The forming is carried out in a closed press under nitrogen protection, and the orientation magnetic field is controlled above 2.2 T.

[0118] (4) Vacuum sintering heat treatment

[0119] The prepared NdFeB green compact is heated from room temperature to 295 °C in a vacuum furnace and held for 2.8 h, then heated to 540 °C and held for 5.5 h, then heated to 880 °C and held for 5 h, then heated to 1015 °C and held for 1 h, and finally heated to 1058 °C and held for 7 h, and then quickly air-cooled to room temperature to obtain the final sintered NdFeB magnet;

[0120] (5) Hot isostatic pressing treatment

[0121] The magnet after vacuum heat treatment is subjected to hot isostatic pressing treatment. The conditions of the hot isostatic pressing treatment are: at a pressure of 200 Mpa and held at 1058 °C for 2.5 h.

[0122] (6) Machining

[0123] The size of the blank after hot isostatic pressing treatment is the size specification of the conventional square sheet finished product required by the market, and the size is: 30 mm * 15 mm * 2 mm.

[0124] (7) Coating

[0125] The processed neodymium-iron-boron permanent magnet is cleaned on the surface and coated with a heavy metal Dy alloy slurry independently developed, and the weight gain ratio is controlled at 0.2 g, and then dried at 80 - 120 °C.

[0126] (8) Alloy infiltration heat treatment

[0127] The neodymium-iron-boron permanent magnet coated with the heavy metal slurry is placed in a vacuum heat treatment furnace, heated from room temperature to 540 °C and held for 2 h, then cooled at 4.5 °C / min to 440 °C and held for 1 h, then heated to 695 °C and held for 4 h, then cooled at 3 °C / min to 440 °C and held for 1 h, and then heated to 900 °C and held for 11 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. After the above heat treatment process is completed, it is quickly cooled to room temperature, and then heated to 450 °C for 4 h tempering treatment. The vacuum degree during the whole heat treatment process is controlled within 10-2. After the above heat treatment process is completed, the permanent magnet is quickly air-cooled to room temperature to obtain the neodymium-iron-boron permanent magnet.

[0128] The magnetic properties of the sintered neodymium-iron-boron permanent magnet prepared according to Example 4 are: remanence Br = 13.75 kGs, maximum magnetic energy product (BH)max = 45.75 MGOe, and intrinsic coercivity Hcj = 31.68 kOe.

[0129] <Comparative Example 1>

[0130] A preparation method of a low-cost sintered neodymium-iron-boron grain boundary infiltration diffusion source is the same as that in Example 1, except that it does not undergo hot isostatic pressing treatment.

[0131] <Comparative Example 2>

[0132] A preparation method of a low-cost sintered neodymium-iron-boron grain boundary infiltration diffusion source is the same as that in Example 2, except that it does not undergo hot isostatic pressing treatment.

[0133] <Comparative Example 3>

[0134] A preparation method of a low-cost sintered neodymium-iron-boron grain boundary infiltration diffusion source is the same as that in Example 3, except that it does not undergo hot isostatic pressing treatment.

[0135] <Comparative Example 4>

[0136] A preparation method of a low-cost sintered neodymium-iron-boron grain boundary infiltration diffusion source is the same as that in Example 4, except that it does not undergo hot isostatic pressing treatment.

[0137] For the convenience of verifying the preparation method of a low-cost sintered NdFeB grain boundary penetration diffusion source in this invention patent, the performance indexes of Examples 1 to 4 and Comparative Examples 1 to 4 are listed in Table 1 below; it can be seen that the present invention provides a preparation method of double-high-performance sintered NdFeB. The intrinsic coercivity Hcj of the magnetic steel prepared by this invention process has been greatly improved, the remanence Br remains unchanged, and the performance grade of the magnetic steel can be increased from 52M to 52EH at most, with a 4-grade improvement, realizing the process development of double-high-performance NdFeB, which is very suitable for commercial promotion.

[0138]

[0139]

[0140] The examples involved in this article are only illustrative and are used to explain some features of the method described in the present invention. The appended claims are intended to claim the broadest scope possible, and the embodiments presented herein are only illustrative of the selected embodiments according to the combination of all possible embodiments. Therefore, the applicant's intention is that the appended claims are not limited by the selection of examples that illustrate the features of the present invention. Some of the numerical ranges used in the claims also include sub-ranges within them, and variations within these ranges should also be interpreted as being covered by the appended claims whenever possible.

Claims

1. A preparation method of double high-performance sintered neodymium iron boron, characterized in that, The following steps are involved: S1. Preparation of alloy flakes: prepare diffusion source alloy raw materials according to the following weight percentages: PrNd: 24-32%, Al: 0.2-0.6%, Cu: 0.1-0.3%, Co: 0.2-3%, Zr: 0.1-1%, Ga: 0.1-0.3%, B: 0.8-1%, Dy: 0-4%, Tb: 0-1%, and the balance is Fe. The prepared raw materials are smelted at high temperature under the protection of inert gas to obtain alloy flakes; S2, preparing alloy magnetic powder: the alloy flakes prepared in S1 are crushed by hydrogen absorption, and then processed by air jet milling to prepare uniformly distributed alloy magnetic powder; S3, preparing NdFeB green compacts: orienting and molding the magnetic powder prepared in S2 in a closed press to obtain NdFeB green compacts; S4. Vacuum sintering heat treatment: Place the NdFeB green compact prepared in step (3) in a vacuum heat treatment furnace. During the entire heat treatment process, the vacuum is controlled at 10 -2 above. After the heat treatment is completed, quickly air-cool to room temperature to obtain the final sintered NdFeB magnet; S5, hot isostatic pressing: subjecting the NdFeB magnet obtained in step (4) to hot isostatic pressing; S6, processing: processing the NdFeB magnet obtained in step S5 into the size specifications of the finished product according to the requirements; S7, coating and drying: clean the surface of the NdFeB magnet obtained in step S6, coat it with the self-developed heavy metal alloy slurry, and dry it; S8. Alloy infiltration heat treatment: Place the magnetic steel obtained in step S7 into a vacuum heat treatment furnace, and control the vacuum degree within 10 during the entire heat treatment process. -2 After the heat treatment is completed, quickly air-cool it to room temperature to obtain a neodymium iron boron magnetic steel.

2. The preparation method of a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S1, the melting and casting of the alloy flakes are carried out under the protection of high-purity (99.999%) argon.

3. The preparation method of a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S1, the thickness of the film is controlled at 0.2-0.25 mm.

4. The preparation method of a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S2, after the belt is broken by hydrogen absorption, the average particle size SMD of the alloy powder prepared by the air flow mill is 2.5-3μm, and the additives in the powder making process are added in a distributed manner. The prepared magnetic powder is then mixed for 3-5h under the protection of nitrogen.

5. The preparation method of a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S3, the molding is carried out in a closed press protected by nitrogen, and the orientation magnetic field is controlled above 1.8T.

6. The preparation method of a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S4, heat from room temperature to 280-350℃ and keep it for 1-3h, then heat to 480-600℃ and keep it for 2-6h, then heat to 780-900℃ and keep it for 2-6h, then heat to 1000-1020℃ and keep it for 0.5-1h, and finally heat to 1050-1100℃ and keep it for 3-8h.

7. A method for preparing a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S5, the hot isostatic pressing treatment conditions are: 160-220Mpa pressure, 1050-1100°C insulation for 1-3h.

8. The preparation method of a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S6, the processed size is the size specification of the conventional square piece finished product required by the market, which is: 20-50mm*10-30mm*0.5-8mm.

9. The preparation method of a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S7, the weight gain ratio is controlled at 0.01-0.8 g, and then dried at 80-120°C.

10. The preparation method of a double high-performance sintered neodymium iron boron according to claim 1, characterized in that, In S8, it is heated from room temperature to 500 - 600 °C and held for 1 - 3 h, then cooled at 3 - 5 °C / min to 400 - 450 °C and held for 0.5 - 1 h, then heated to 680 - 750 °C and held for 2 - 6 h, then cooled at 3 - 5 °C / min to 400 - 450 °C and held for 0.5 - 1 h, then heated to 780 - 960 °C and held for 6 - 12 h for infiltration heat treatment, then rapidly cooled to room temperature. The vacuum degree during the whole heat treatment process is controlled within 10⁻³. After the above heat treatment process, it is rapidly cooled to room temperature, and then heated to 400 - 650 °C for 1 - 6 h tempering treatment.

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