High-stability high-magnetic energy product rare earth permanent magnet material and preparation method thereof

Abstract

The invention relates to the field of magnetic materials, in particular to a high-stability high-magnetic-energy-product rare earth permanent magnet material and a preparation method thereof. The main alloy of the rare earth permanent magnet material with high stability and high magnetic energy product comprises the following components in percentage by atom: (NdaLa1-a) xFe100-w-x-y-zCowMyBz, m is selected from Cr, Al and Cu; a, w, x, y and z satisfy the following relations: 0.8 < = a < = 1, 0.5 < = w < = 1.5, 11 < = x < = 16, 0 < = y < = 1.5, 4.5 < = z < = 6.5; the grain boundary phase alloy comprises the following components in percentage by atom: Ho100-uTau, and u is more than or equal to 10 and less than or equal to 20; the neodymium-iron-boron magnet material disclosed by the invention has excellent magnetic performance and can have ultrahigh residual magnetism and high coercive force at the same time. And the highest working temperature can be greater than or equal to 240 DEG C.

Description

Technical Field

[0001] The present invention relates to the field of magnetic materials, and in particular to a rare earth permanent magnetic material with high stability and high magnetic energy product, and a preparation method and application thereof. Background Art

[0002] Neodymium iron boron permanent magnets are the magnetic materials with the highest magnetic properties to date. Due to their extremely high magnetic energy product, coercivity, and energy density, they are known as the "King of Magnets" and have been widely used in emerging technologies such as wind power generation, maglev trains, and new energy vehicles. These new fields also place higher demands on the stability and other properties of neodymium iron boron permanent magnets. Studies have shown that partial substitution (or doping) of alloying elements can improve the stability of neodymium iron boron permanent magnets and further enhance their magnetic properties. For example, the Curie temperature and coercivity of sintered rare earth permanent magnets can be increased by adding Cu, Al, etc., thereby improving the thermal stability of the magnets. However, the addition of these elements will lead to a decrease in the remanence and magnetic energy product of the magnets. The grain boundary diffusion technology that emerged in the early 21st century penetrates heavy rare earth elements or rare earth alloys into the magnets by grain boundary diffusion. While significantly reducing the amount of heavy rare earth elements to reduce costs, it effectively improves the coercivity and magnetic energy product of the magnets.

[0003] The development of the above-mentioned technology has attracted widespread attention in the industry and has been industrialized. However, this field still needs continued research on magnetic materials with higher stability and coercive force performance to meet the continuous pursuit of high-performance magnetic materials in future technological development and promote the continuous progress of related industries. Summary of the Invention

[0004] The present invention aims to provide a NdFeB magnet material with both stability and high coercivity, as well as a preparation method and application thereof. The NdFeB magnet material of the present invention has excellent magnetic properties and can have both ultra-high remanence and high coercivity.

[0005] The inventors of the present invention have discovered that using zinc oxide nanoparticles as an additive to prepare rare earth permanent magnet materials can enable the zinc oxide nanoparticles to effectively pin grain boundaries, inhibit irregular grain growth, improve the wettability of grain boundary phases and main phase grains, inhibit the nucleation of reverse magnetization domains, and significantly improve the boundary structure and magnetic properties of the rare earth permanent magnet materials. As a result, the rare earth permanent magnet materials have good high-temperature anti-demagnetization properties while having increased remanence and magnetic energy product.

[0006] The inventors of the present invention further discovered that, under the premise of zinc oxide nanoparticles pinning grain boundaries, the introduction of tantalum (Ta) elements can further inhibit grain coarsening, promote grain isolation, and form finer and more uniform grains. By optimizing the overall grain morphology and grain boundary continuity, it can more effectively hinder the propagation of the nucleated reverse magnetization domains, thereby significantly improving the coercive force of rare earth permanent magnet materials and improving their temperature stability and anti-demagnetization properties.

[0007] In view of this, a first aspect of the present invention provides a method for preparing a rare earth permanent magnet material with high stability and high magnetic energy product, which comprises the following steps:

[0008] S1: The main alloy powder is prepared by three processes: rapid solidification casting, hydrogen explosion and air flow grinding. The main alloy is calculated in atomic percentage and its composition is (Nd a La 1-a ) x Fe 100-w-x-y-z Co w M y B z ;

[0009] M is selected from Cr, Al and Cu;

[0010] a, w, x, y, z satisfy the following relationship:

[0011] 0.8≤a≤1, 0.5≤w≤1.5, 11≤x≤16, 0≤y≤1.5, 4.5≤z≤6.5;

[0012] S2: The grain boundary phase alloy is cast into an ingot by a casting process, and the grain boundary phase alloy powder is prepared by a mechanical ball milling process. The grain boundary phase alloy has a composition of Ho in atomic percentage. 100-u Ta u , 10≤u≤20;

[0013] S3: uniformly mixing the grain boundary phase alloy powder and the nano zinc oxide powder in a mixer under a protective medium to obtain a grain boundary phase alloy modified with nano zinc oxide, wherein the weight of the added nano zinc oxide powder accounts for 0.2 to 0.8% of the total powder weight;

[0014] S4: mixing the main alloy powder and the grain boundary phase alloy powder modified by nano-zinc oxide in a mixer under a protective medium to obtain a mixed powder;

[0015] S5: The mixed powder is oriented and pressed in a magnetic field environment, and then pressed into a green body by cold isostatic pressing;

[0016] S6: Sintering the green compact, performing primary tempering, and then secondary tempering to obtain the neodymium iron boron magnet, a rare earth permanent magnet material with high stability and high magnetic energy product.

[0017] In some embodiments, the average particle diameter of the nano zinc oxide powder is 50-100 nm, for example, 50-90 nm, 50-80 nm, 60-100 nm, 60-90 nm, 60-80 nm, 60-75 nm, 70-90 nm or 70-80 nm.

[0018] In some embodiments, the average particle diameter of the nano zinc oxide powder is 65 nm or 75 nm.

[0019] In some embodiments, the average particle diameter of the nano zinc oxide powder is 70 to 80 nm.

[0020] In some embodiments, the average particle diameter of the nano zinc oxide powder is 75 nm.

[0021] In some embodiments, the master alloy comprises, by weight percentage:

[0022] Nd 10% to 13%, La 1% to 2%, Co 0.4% to 1%, B 4% to 7%, and one or more selected from Cr, Al or Cu 0.2% to 0.4%, and the balance Fe and unavoidable impurities.

[0023] In some embodiments, the master alloy comprises, by weight percentage:

[0024] Nd 10.3% to 12.5%, La 1.2% to 1.5%, Co 0.5% to 0.7%, B 4.62% to 6.2%, and one or more selected from Cr, Al or Cu 0.25% to 0.3%, and the balance Fe and unavoidable impurities.

[0025] In some embodiments, the master alloy comprises, by weight percentage:

[0026] Nd 10.3%, La 1.2%, Co 0.5% and B 6.1%,

[0027] Nd11.6%, La1.5%, Co0.53%, B4.62% and Cr0.25%,

[0028] Nd 12.5%, La 1.2%, Co 0.7%, B 6.2% and Al 0.3%,

[0029] Nd 12.5%, La 1.2%, Co 0.7%, B 6.2% and Al 0.3%, or

[0030] Nd 12.5%, La 1.2%, Co 0.7%, B 6.2% and Al 0.3%,

[0031] And the balance of Fe and inevitable impurities.

[0032] In some embodiments, the main alloy comprises, by weight percentage, 10.3% Nd, 1.2% La, 0.5% Co, 6.1% B, and the balance Fe and inevitable impurities.

[0033] In some embodiments, the main alloy comprises, by weight percentage, 11.6% Nd, 1.5% La, 0.53% Co, 4.62% B, 0.25% Cr, and the balance Fe and inevitable impurities.

[0034] In some embodiments, the main alloy comprises, by weight percentage, 12.5% ​​Nd, 1.2% La, 0.7% Co, 6.2% B, 0.3% Al, and the balance Fe and inevitable impurities.

[0035] In some embodiments, the main alloy comprises, by weight percentage, 12.5% ​​Nd, 1.2% La, 0.7% Co, 6.2% B, 0.3% Al, and the balance Fe and inevitable impurities.

[0036] In some embodiments, the main alloy comprises, by weight percentage, 12.5% ​​Nd, 1.2% La, 0.7% Co, 6.2% B, 0.3% Al, and the balance Fe and inevitable impurities.

[0037] In some embodiments, 15≤u≤20.

[0038] In some embodiments, 15.7≤u≤18.5.

[0039] In some embodiments, 17≤u≤18.5.

[0040] In some embodiments, u is 15.7 or 18.5.

[0041] In some embodiments, in step S3, the weight of the added nano zinc oxide powder accounts for 0.4% to 0.8% of the total powder weight, for example, 0.4% to 0.7% or 0.4% to 0.6%.

[0042] In some embodiments, in step S3, the weight of the added nano zinc oxide powder accounts for 0.4% to 0.6% of the total powder weight.

[0043] In some embodiments, in step S3, the weight of the added nano zinc oxide powder accounts for 0.4%, 0.5% or 0.6% of the total powder weight.

[0044] In some embodiments, in step S4, the protective medium is petroleum ether.

[0045] In some embodiments, in step S5, the mixed powder is subjected to orientation pressing in a magnetic field of 1.5 to 3 T. In some embodiments, in step S5, the mixed powder is subjected to orientation pressing in a magnetic field of 1.5 to 2.5.

[0046] In some embodiments, in step S5, the pressure of the compression molding is 140 to 250 MPa. In some embodiments, in step S5, the pressure of the compression molding is 150 to 210 MPa.

[0047] In some embodiments, in step S5, the pressing time is 50 to 200 seconds. In some embodiments, in step S5, the pressing time is 60 to 150 seconds.

[0048] In some embodiments, in step S6, the sintering temperature is 825-1050°C. In some embodiments, in step S6, the sintering temperature is 850-1000°C.

[0049] In some embodiments, in step S6, the sintering time is 1.5 to 7.5 hours. In some embodiments, in step S6, the sintering time is 2 to 6 hours.

[0050] In some embodiments, the maximum operating temperature of the high-stability and high-magnetic-energy-product rare earth permanent magnet material is greater than or equal to 240°C, and further greater than or equal to 250°C.

[0051] In some embodiments, the maximum operating temperature of the high-stability and high-magnetic-energy-product rare earth permanent magnet material is greater than or equal to 240°C and less than 275°C; further greater than or equal to 250°C and less than 275°C.

[0052] In some embodiments, the remanent magnetic properties of the high-stability and high-energy-product rare earth permanent magnet material are greater than or equal to 14.5 kGs; further greater than or equal to 14.9 kGs.

[0053] In some embodiments, the residual magnetic properties of the high-stability and high-magnetic-energy-product rare earth permanent magnet material are greater than or equal to 14.5 kGs and less than 15.2 kGs; further, greater than or equal to 14.9 kGs and less than 15.2 kGs.

[0054] In some embodiments, the intrinsic coercive force of the high-stability and high-energy-product rare earth permanent magnet material is greater than or equal to 29 kOe; further greater than or equal to 34 kOe.

[0055] In some embodiments, the intrinsic coercive force of the high-stability and high-energy-product rare earth permanent magnet material is greater than or equal to 29 kOe and less than 36 kOe; further greater than or equal to 34 kOe and less than 36 kOe.

[0056] In some embodiments, the maximum magnetic energy product of the high-stability and high-magnetic-energy-product rare earth permanent magnet material is greater than or equal to 45 MGsOe; further greater than or equal to 55 MGsOe.

[0057] In some embodiments, the maximum magnetic energy product of the high-stability and high-magnetic-energy-product rare earth permanent magnet material is greater than or equal to 45 MGsOe and less than 58 MGsOe; further, greater than or equal to 55 MGsOe and less than 58 MGsOe.

[0058] The second aspect of the present invention provides a high-stability and high-magnetic-energy-product rare earth permanent magnet material, which is prepared by the method for preparing the high-stability and high-magnetic-energy-product rare earth permanent magnet material described in any of the aforementioned embodiments.

[0059] The third aspect of the present invention provides the use of the above-mentioned high-stability and high-energy-product rare earth permanent magnet material as a magnetic device.

[0060] In some embodiments, the NdFeB magnet material is used as a magnetic device in many fields such as rail transportation, military equipment, wind power generation, low-altitude flight, artificial intelligence, aerospace, medical equipment and precision manufacturing.

[0061] Based on the common sense in this field, the above embodiments can be combined arbitrarily to obtain preferred embodiments of the present invention.

[0062] The reagents and raw materials used in the present invention are commercially available.

[0063] In the present invention, the symbols of each element have conventional meanings in the art, specifically: "Nd" is neodymium, "La" is lanthanum, "Cr" is chromium, "Ho" is holmium, "Al" is aluminum, "Cu" is copper, "Ta" is tantalum, "Co" is cobalt, "Ti" is titanium, "Fe" is iron, and "B" is boron. DETAILED DESCRIPTION

[0064] Unless otherwise indicated, the following terms and phrases used herein are intended to have the following meanings. A particular term or phrase should not be construed as indefinite or unclear unless specifically defined, but rather should be understood in accordance with its ordinary meaning. When a trade name appears in this document, it is intended to refer to the corresponding commercial product or its active ingredient.

[0065] As used herein and unless otherwise specified, the terms "comprising", "including", and "having", including their grammatical equivalents, should generally be understood as open and non-limiting, e.g., not excluding other unrecited elements or steps.

[0066] The embodiments of the present invention will be described in detail below with reference to the examples, but those skilled in the art will appreciate that the following examples are intended only to illustrate the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0067] The present invention will be further described below with reference to specific examples, but the present invention is not limited to the following examples.

[0068] Example 1

[0069] S1: Raw materials are prepared according to the weight percentages of Nd 10.3%, La 1.2%, Co 0.5%, B 6.1%, and the balance Fe, and the raw materials are placed in a vacuum induction melting furnace and cast into ingots to obtain rare earth permanent magnet ingots; the rare earth permanent magnet ingots are heat treated and subjected to hydrogen absorption and dehydrogenation treatment in a rotary hydrogen crushing furnace for 3 hours. The rare earth permanent magnet ingots are crushed to obtain coarse powder, and the coarse powder is ground in a jet mill under inert gas protection to obtain NdFeB rare earth powder;

[0070] S2: The raw materials are mixed according to the weight percentage of Ho 84.3% and Ta 15.7%, and an ingot is made by a casting process, and a grain boundary phase alloy powder is prepared by a mechanical ball milling process;

[0071] S3: Grain boundary phase alloy powder and nano zinc oxide powder (average particle diameter of about 75 nm) are mixed in a ratio of 99.6% by weight of grain boundary phase alloy powder and 0.4% by weight of nano zinc oxide powder in a mixer under a protective medium of petroleum ether to obtain a grain boundary phase alloy powder modified with nano zinc oxide powder;

[0072] S4: taking 3% of the total mass of the NdFeB rare earth powder and a nanopowder-modified grain boundary phase alloy powder, mixing the nanopowder-modified grain boundary phase alloy powder with the NdFeB rare earth powder twice, first taking 25% of the total mass of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring with the NdFeB rare earth powder for 5 minutes, then adding the remaining 75% of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring for 20 minutes, and then standing for 30 minutes to obtain a mixed powder of the NdFeB rare earth powder and the nanopowder-modified grain boundary phase alloy powder;

[0073] S5: placing the mixed powder in a molding machine mold for pre-compression; placing the pre-compressed mixed powder in an orientation magnetic field with a magnetic induction intensity of 1.5 T for orientation, and pressing the mixed powder under a cold isostatic pressing of 150 MPa to obtain a rough blank, wherein the direction of the orientation magnetic field is perpendicular to the pressing direction;

[0074] S6: Place the rough blank in a vacuum sintering furnace, sinter at 850°C for 1.8 hours, and then perform secondary aging heat treatment. In a vacuum environment or an inert gas protection environment, perform primary heat treatment at 860°C for 1.5 hours, and then perform secondary heat treatment at 520°C for 2 hours. Cool it naturally to room temperature to finally obtain NdFeB rare earth permanent magnet material.

[0075] Example 2

[0076] S1: Raw materials are prepared according to weight percentages of Nd 11.6%, La 1.5%, Cr 0.25%, Co 0.53%, B 4.62%, and the balance Fe, and the raw materials are placed in a vacuum induction melting furnace and cast into ingots to obtain rare earth permanent magnet ingots; the rare earth permanent magnet ingots are heat treated and subjected to hydrogen absorption and dehydrogenation treatment in a rotary hydrogen crushing furnace for 3 hours, and the rare earth permanent magnet ingots are crushed to obtain coarse powder, which is then ground in a jet mill under inert gas protection to produce NdFeB rare earth powder;

[0077] S2: The raw materials are mixed according to the weight percentage of Ho 81.5% and Ta 18.5%, and an ingot is made by a casting process, and a grain boundary phase alloy powder is prepared by a mechanical ball milling process;

[0078] S3: Grain boundary phase alloy powder and nano zinc oxide powder (average particle diameter of about 75 nm) are mixed in a ratio of 99.4% by weight of grain boundary phase alloy powder and 0.6% by weight of nano zinc oxide powder in a mixer under a protective medium of petroleum ether to obtain a nanopowder-modified grain boundary phase alloy powder;

[0079] S4: taking 3% of the total mass of the NdFeB rare earth powder and a nanopowder-modified grain boundary phase alloy powder, mixing the nanopowder-modified grain boundary phase alloy powder with the NdFeB rare earth powder twice, first taking 25% of the total mass of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring with the NdFeB rare earth powder for 5 minutes, then adding the remaining 75% of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring for 25 minutes, and then standing for 30 minutes to obtain a mixed powder of the NdFeB rare earth powder and the nanopowder-modified grain boundary phase alloy powder;

[0080] S5: placing the mixed powder in a molding machine mold for pre-compression; placing the pre-compressed mixed powder in an orientation magnetic field with a magnetic induction intensity of 1.8 T for orientation, and pressing the mixed powder under a cold isostatic pressing of 190 MPa to obtain a rough blank, wherein the direction of the orientation magnetic field is perpendicular to the pressing direction;

[0081] S6: Place the rough blank in a vacuum sintering furnace, sinter at 850°C for 2.1 hours, and then perform secondary aging heat treatment. In a vacuum environment or an inert gas protection environment, perform primary heat treatment at 870°C for 2 hours, and then perform secondary heat treatment at 550°C for 2.5 hours. Cool it naturally to room temperature to finally obtain NdFeB rare earth permanent magnet material.

[0082] Example 3

[0083] S1: Raw materials are prepared according to the weight percentages of Nd 12.5%, La 1.2%, B 6.2%, Al 0.3%, Co 0.7%, and the balance Fe, and the raw materials are placed in a vacuum induction melting furnace and cast into ingots to obtain rare earth permanent magnet ingots; the rare earth permanent magnet ingots are heat treated and subjected to hydrogen absorption and dehydrogenation treatment in a rotating hydrogen crushing furnace for 3 hours. The rare earth permanent magnet ingots are crushed to obtain coarse powder, and the coarse powder is ground in a jet mill under inert gas protection to obtain NdFeB rare earth powder;

[0084] S2: The raw materials are mixed according to the weight percentage of Ho 81.5% and Ta 18.5%, and an ingot is made by a casting process, and a grain boundary phase alloy powder is prepared by a mechanical ball milling process;

[0085] S3: Grain boundary phase alloy powder and nano zinc oxide powder (average particle diameter of about 75 nm) are mixed in a ratio of 99.5% by weight of grain boundary phase alloy powder and 0.5% by weight of nano zinc oxide powder in a mixer under a protective medium of petroleum ether to obtain a nanopowder-modified grain boundary phase alloy powder;

[0086] S4: taking 3% of the total mass of the NdFeB rare earth powder into a nanopowder-modified grain boundary phase alloy powder, mixing the nanopowder-modified grain boundary phase alloy powder with the NdFeB rare earth powder twice, first taking 25% of the total mass of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring with the NdFeB rare earth powder for 10 minutes, then adding the remaining 75% of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring for 25 minutes, and then standing for 30 minutes to obtain a mixed powder of the NdFeB rare earth powder and the nanopowder-modified grain boundary phase alloy powder;

[0087] S5: placing the mixed powder in a molding machine mold for pre-compression; placing the pre-compressed mixed powder in an orientation magnetic field with a magnetic induction intensity of 2.2 T for orientation, and pressing the mixed powder under a cold isostatic pressure of 200 MPa to obtain a rough blank, wherein the direction of the orientation magnetic field is perpendicular to the pressing direction;

[0088] S6: Place the rough blank in a vacuum sintering furnace, sinter at 850°C for 2.5 hours, and then perform secondary aging heat treatment. In a vacuum environment or an inert gas protection environment, perform primary heat treatment at 900°C for 2.5 hours, and then perform secondary heat treatment at 580°C for 2 hours. Cool it naturally to room temperature to finally obtain NdFeB rare earth permanent magnet material.

[0089] Example 4

[0090] S1: Raw materials are prepared according to the weight percentages of Nd 12.5%, La 1.2%, B 6.2%, Al 0.3%, Co 0.7%, and the balance Fe, and the raw materials are placed in a vacuum induction melting furnace and cast into ingots to obtain rare earth permanent magnet ingots; the rare earth permanent magnet ingots are heat treated and subjected to hydrogen absorption and dehydrogenation treatment in a rotating hydrogen crushing furnace for 3 hours. The rare earth permanent magnet ingots are crushed to obtain coarse powder, and the coarse powder is ground in a jet mill under inert gas protection to obtain NdFeB rare earth powder;

[0091] S2: The raw materials are mixed according to the weight percentage of Ho 81.5% and Ta 18.5%, and an ingot is made by a casting process, and a grain boundary phase alloy powder is prepared by a mechanical ball milling process;

[0092] S3: Grain boundary phase alloy powder and nano zinc oxide powder (average particle diameter of about 65 nm) are mixed in a ratio of 99.5% by weight of grain boundary phase alloy powder and 0.5% by weight of nano zinc oxide powder in a mixer under a protective medium of petroleum ether to obtain a nanopowder-modified grain boundary phase alloy powder;

[0093] S4: taking 3% of the total mass of the NdFeB rare earth powder into a nanopowder-modified grain boundary phase alloy powder, mixing the nanopowder-modified grain boundary phase alloy powder with the NdFeB rare earth powder twice, first taking 25% of the total mass of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring with the NdFeB rare earth powder for 10 minutes, then adding the remaining 75% of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring for 25 minutes, and then standing for 30 minutes to obtain a mixed powder of the NdFeB rare earth powder and the nanopowder-modified grain boundary phase alloy powder;

[0094] S5: placing the mixed powder in a molding machine mold for pre-compression; placing the pre-compressed mixed powder in an orientation magnetic field with a magnetic induction intensity of 2.2 T for orientation, and pressing the mixed powder under a cold isostatic pressure of 200 MPa to obtain a rough blank, wherein the direction of the orientation magnetic field is perpendicular to the pressing direction;

[0095] S6: Place the rough blank in a vacuum sintering furnace, sinter at 850°C for 2.5 hours, and then perform secondary aging heat treatment. In a vacuum environment or an inert gas protection environment, perform primary heat treatment at 900°C for 2.5 hours, and then perform secondary heat treatment at 580°C for 2 hours. Cool it naturally to room temperature to finally obtain NdFeB rare earth permanent magnet material.

[0096] Example 5

[0097] S1: Raw materials are prepared according to the weight percentages of Nd 12.5%, La 1.2%, B 6.2%, Al 0.3%, Co 0.7%, and the balance Fe, and the raw materials are placed in a vacuum induction melting furnace and cast into ingots to obtain rare earth permanent magnet ingots; the rare earth permanent magnet ingots are heat treated and subjected to hydrogen absorption and dehydrogenation treatment in a rotating hydrogen crushing furnace for 3 hours. The rare earth permanent magnet ingots are crushed to obtain coarse powder, and the coarse powder is ground in a jet mill under inert gas protection to obtain NdFeB rare earth powder;

[0098] S2: The raw materials are mixed according to the weight percentage of Ho 81.5% and Ta 18.5%, and an ingot is made by a casting process, and a grain boundary phase alloy powder is prepared by a mechanical ball milling process;

[0099] S3: Grain boundary phase alloy powder and nano zinc oxide powder (average particle diameter of about 75 nm) are mixed in a ratio of 99.2% by weight of grain boundary phase alloy powder and 0.8% by weight of nano zinc oxide powder in a mixer under a protective medium of petroleum ether to obtain a nanopowder-modified grain boundary phase alloy powder;

[0100] S4: taking 3% of the total mass of the NdFeB rare earth powder into a nanopowder-modified grain boundary phase alloy powder, mixing the nanopowder-modified grain boundary phase alloy powder with the NdFeB rare earth powder twice, first taking 25% of the total mass of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring with the NdFeB rare earth powder for 10 minutes, then adding the remaining 75% of the nanopowder-modified grain boundary phase alloy powder, mixing and stirring for 25 minutes, and then standing for 30 minutes to obtain a mixed powder of the NdFeB rare earth powder and the nanopowder-modified grain boundary phase alloy powder;

[0101] S5: placing the mixed powder in a molding machine mold for pre-compression; placing the pre-compressed mixed powder in an orientation magnetic field with a magnetic induction intensity of 2.2 T for orientation, and pressing the mixed powder under a cold isostatic pressure of 200 MPa to obtain a rough blank, wherein the direction of the orientation magnetic field is perpendicular to the pressing direction;

[0102] S6: Place the rough blank in a vacuum sintering furnace, sinter at 850°C for 2.5 hours, and then perform secondary aging heat treatment. In a vacuum environment or an inert gas protection environment, perform primary heat treatment at 900°C for 2.5 hours, and then perform secondary heat treatment at 580°C for 2 hours. Cool it naturally to room temperature to finally obtain NdFeB rare earth permanent magnet material.

[0103] Comparative Example 1

[0104] Comparative Example 1 was prepared with reference to Example 3, except that Ta was not added to the raw materials prepared in step S2.

[0105] Comparative Example 2

[0106] Comparative Example 1 was prepared with reference to Example 3, except that the zinc oxide powder modification in step S3 was not performed.

[0107] Comparative Example 3

[0108] Comparative Example 1 was prepared with reference to Example 3, except that the raw materials in step S2 were prepared with 81.5% Ho and 18.5% Ti.

[0109] Test Example 1

[0110] The remanence (Br, in kGs), maximum energy product (BH, in MGsOe), and intrinsic coercivity (Hcj, in kOe) of the NdFeB rare earth permanent magnet materials obtained in the Examples and Comparative Examples were measured using the NIM10000H and NIM200C permanent magnet material magnetic property measurement systems from the China National Institute of Metrology. The maximum operating temperature (in °C) of these samples was tested in accordance with GB / T13560-2017, "Sintered NdFeB Permanent Magnet Materials." The results are shown in Table 1 below.

[0111] Table 1

[0112]

[0113] In Table 1, when Ta is not added in Comparative Example 1, zinc oxide is not added in Comparative Example 2, or Ho and Ti are added in Comparative Example 3, the diffusion channels of the materials are all restricted, and the coercive force increase decreases. In Examples 1 to 5, Ho, Ta, and zinc oxide are added simultaneously, and the coercive force and maximum operating temperature of the materials are simultaneously increased. It can be seen that by adopting the technical solution of the present invention, zinc oxide nanopowder and Ta element are added to the grain boundary phase at the same time, and the distribution of the grain boundary phase and the grain boundary morphology are optimized through the nano-modification method, so that the zinc oxide nanoparticles pin the grain boundaries, enhance the magnetocrystalline anisotropy field at the surface of the main alloy grains, and inhibit the irregular growth of the main alloy grains, thereby preventing the formation of reverse magnetic domains on the surface of the main alloy grains during the demagnetization process. While achieving a high magnetic energy product of the NdFeB magnet, its high-temperature stability is improved. In addition, in the alloy system of the present invention, the addition of Ho and Ta elements in a certain ratio has an unexpected synergistic effect on increasing the maximum operating temperature of the permanent magnet material.

[0114] While certain features of the present invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It should be understood, therefore, that the appended claims are intended to cover all such modifications and changes that fall within the true scope of the invention.

Claims

1. A method for preparing a high-stability and high-magnetic-energy-product rare earth permanent magnetic material, characterized in that: The following steps are involved: S1: The main alloy powder is prepared by three processes: rapid solidification casting, hydrogen explosion and air flow grinding. The main alloy is calculated in atomic percentage and its composition is (Nd a La 1-a ) x Fe 100-w-x-y-z Co w M y B z ; M is selected from Cr, Al and Cu; a, w, x, y, z satisfy the following relationship: 0.8≤a≤1, 0.5≤w≤1.5, 11≤x≤16, 0≤y≤1.5, 4.5≤z≤6.5; S2: The grain boundary phase alloy is cast into an ingot by a casting process, and the grain boundary phase alloy powder is prepared by a mechanical ball milling process. The grain boundary phase alloy has a composition of Ho in atomic percentage. 100-u Ta u , 10≤u≤20; S3: uniformly mixing the grain boundary phase alloy powder and the nano zinc oxide powder in a mixer under a protective medium to obtain a grain boundary phase alloy modified with nano zinc oxide, wherein the weight of the added nano zinc oxide powder accounts for 0.2 to 0.8% of the total powder weight; S4: mixing the main alloy powder and the grain boundary phase alloy powder modified by nano-zinc oxide in a mixer under a protective medium to obtain a mixed powder; S5: The mixed powder is oriented and pressed in a magnetic field environment, and then pressed into a green body by cold isostatic pressing; S6: Sintering the green compact, performing primary tempering, and then secondary tempering to obtain the neodymium iron boron magnet, a rare earth permanent magnet material with high stability and high magnetic energy product.

2. The method for preparing a high-stability and high-magnetic-energy-product rare earth permanent magnetic material according to claim 1, wherein: The average particle diameter of the nano zinc oxide powder is 50-100 nm.

3. The method for preparing a high-stability and high-magnetic-energy-product rare earth permanent magnetic material according to claim 1, characterized in that: The average particle diameter of the nano zinc oxide powder is 70-80 nm.

4. The method for preparing a high-stability and high-magnetic-energy-product rare earth permanent magnetic material according to any one of claims 1 to 3, characterized in that: The main alloy comprises, by weight percentage: Nd 10% to 13%, La 1% to 2%, Co 0.4% to 1%, B 4% to 7%, and one or more selected from Cr, Al or Cu 0.2% to 0.4%, and the balance Fe and unavoidable impurities.

5. The method for preparing a high-stability and high-magnetic-energy-product rare earth permanent magnetic material according to any one of claims 1 to 3, characterized in that: 15≤u≤20； In step S3, the weight of the added nano zinc oxide powder accounts for 0.4% to 0.8% of the total powder weight.

6. The method for preparing a high-stability and high-magnetic-energy-product rare earth permanent magnetic material according to claim 4, characterized in that: u＝18.5； In step S3, the weight of the added nano zinc oxide powder accounts for 0.4% to 0.6% of the total powder weight.

7. The method for preparing a high-stability and high-magnetic-energy-product rare earth permanent magnetic material according to claim 4, characterized in that: In step S5, the mixed powder is oriented and pressed in a magnetic field of 1.5 to 3 T; In step S5, the pressing pressure is 140-250 MPa; In step S5, the pressing time is 50 to 200 seconds; In step S6, the sintering temperature is 800-1050°C; In step S6, the sintering time is 1.5 to 7.5 hours; In step S6, the tempering conditions include: performing primary tempering at 850°C to 920°C and maintaining for 2.5 to 5 hours, and then performing secondary tempering at 510°C to 590°C and maintaining for 3 to 5 hours.

8. The method for preparing a high-stability and high-magnetic-energy-product rare earth permanent magnetic material according to any one of claims 1 to 3, characterized in that: The maximum operating temperature of the high-stability and high-magnetic-energy-product rare-earth permanent magnet material is greater than or equal to 240°C; The residual magnetic property of the high-stability and high-magnetic-energy-product rare earth permanent magnet material is greater than or equal to 14.5 kGs; The intrinsic coercive force of the high-stability and high-magnetic-energy-product rare earth permanent magnet material is greater than or equal to 29 kOe; The maximum magnetic energy product of the high-stability and high-magnetic-energy-product rare earth permanent magnet material is greater than or equal to 45 MGsOe.

9. A rare earth permanent magnet material with high stability and high magnetic energy product, characterized in that: The magnetic material is prepared by the method for preparing a rare earth permanent magnet material with high stability and high magnetic energy product as claimed in any one of claims 1 to 8.

10. Use of the high-stability and high-energy-product rare earth permanent magnet material according to claim 9 as a magnetic device.

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