High-coercivity neodymium-iron-boron magnet and method for producing the same

Abstract

The application belongs to the technical field of Nd-Fe-B magnets, and relates to a high-coercivity Nd-Fe-B magnet and a preparation method thereof. The grain boundary triple point of the magnet is enriched with oxides of M and / or R. R is at least one of dysprosium, terbium, holmium and praseodymium. M is at least one of zirconium, titanium, tungsten, molybdenum, ruthenium, vanadium and manganese. The Nd-Fe-B magnet is added with metal salt powder of rare earth elements, and the rare earth element metal oxides are enriched at the grain boundary triple point. Since the oxides have a large number of oxygen vacancy type point defects, the grain boundary of the magnet is thickened, the flipping of magnetic domains is hindered under an external magnetic field, the rare earth element metal oxides play a pinning role, and thus the coercivity of the Nd-Fe-B magnet is improved.

Description

Technical Field

[0001] This invention belongs to the field of neodymium iron boron magnet technology, and particularly relates to a high coercivity neodymium iron boron magnet and its preparation method. Background Technology

[0002] Rare earth permanent magnet materials have always attracted much attention. Firstly, under the major trend of energy conservation and environmental protection, high-efficiency rare earth permanent magnet motors will largely replace traditional motors. Demand for high-performance NdFeB magnets in several emerging energy-saving fields related to low carbon, such as direct-drive permanent magnet wind power generation, energy-saving home appliances, energy-saving elevators, variable frequency air conditioners, and new energy vehicles, will be released in the next few years. The explosive growth in rare earth permanent magnet high-efficiency motors for hybrid vehicles, new energy vehicles, rail transit, and small lightweight vehicles, as well as rare earth permanent magnet fuel savers for multi-stage magnetization treatment, will drive long-term demand for NdFeB permanent magnet materials, providing a foundation for stable future demand growth. Secondly, the explosive demand for high-performance sintered NdFeB magnets from traditional automotive industries, electronics industries, nuclear magnetic resonance imaging, maglev trains, and energy-saving oil pumping units is imminent. Furthermore, in terms of device miniaturization, the rigid demand for high-performance NdFeB magnets in devices such as hard drive voice coil motors (VCM), DVD drives / players, mobile phone vibration motors, and micro-electroacoustic devices cannot be replaced. Because neodymium iron boron permanent magnets operate at high ambient temperatures, this presents a new demand for high-performance neodymium iron boron magnets, requiring the development of neodymium iron boron permanent magnets with high coercivity.

[0003] Previous research published in the *Journal of Rare Earths*, titled "Microstructure and Corrosion Resistance of Intered NdFeB Magnet Modified by Intergranular Addition of MgO and ZnO," investigated the introduction of MgO and ZnO into NdFeB raw materials. This resulted in the formation of more oxygen-rich intergranular phases while maintaining almost the same volume fraction of all intergranular phases, thus improving corrosion resistance. Furthermore, the addition of MgO and ZnO refined the grain size of NdFeB, while also increasing the remanence and sintering density of the magnet. The study "The Effect of Metal Hydide Powder Blending in the Production of NdFeB-type Magnet" demonstrated how adding hydrides of Dy, Nd, Nb, and V during powder preparation increased the sintering temperature and coercivity, achieved by inhibiting grain growth and improving grain boundary phases. Given the current high market demand for high-performance NdFeB materials, further improvements are needed to enhance the magnetic properties of magnets, particularly their coercivity. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a high-coercivity neodymium iron boron magnet and its preparation method.

[0005] The specific technical solution of the present invention is as follows:

[0006] The first objective of this invention is to provide a high coercivity neodymium iron boron magnet, wherein the grain boundary triple points of the magnet are enriched with oxides of M and / or R;

[0007] R is at least one of dysprosium, terbium, holmium, and praseodymium;

[0008] M is at least one of zirconium, titanium, tungsten, molybdenum, ruthenium, vanadium, and manganese.

[0009] The high coercivity NdFeB magnet of the present invention has M and / or R oxides enriched at the triple point of the grain boundary. Due to the presence of a large number of oxygen vacancy type point defects in the oxides, the grain boundary of the magnet is thickened. Under an external magnetic field, the flipping of magnetic domains is hindered, and the M and / or R oxides play a pinning role, thereby improving the coercivity of the NdFeB magnet.

[0010] Further, the neodymium iron boron magnet comprises Re 29.5–32.5 wt%, Cu 0.05–0.3 wt%, Ga 0–0.3 wt%, Al 0–1 wt%, Co 0.05–3.5 wt%, B 0.8–1.1 wt%, M 0.05–2%, where M is at least one of zirconium, titanium, tungsten, molybdenum, ruthenium, vanadium, and manganese, and the balance is Fe and unavoidable impurities.

[0011] The rare earth element Re is one or more of Pr, Nd, Dy, Tb, and Ho, with Nd and Pr preferred.

[0012] The second objective of this invention is to provide a method for preparing high coercivity neodymium iron boron magnets, comprising: 1) smelting, 2) powdering, 3) molding, 4) sintering, and further comprising the step of adding metal salt powder.

[0013] Furthermore, metal salt powder of the rare earth element is added to the raw material being smelted.

[0014] Furthermore, metal salt powder of the rare earth element is added during the powdering process, and then the mixture is mixed for 4-8 hours.

[0015] Furthermore, the rare earth element metal salt powder added during the powdering process can be: 1) added before the rapid solidification thin strip is crushed, 2) added in the coarse powder state after the rapid solidification thin strip is hydrogen-crushed, or 3) added in the fine powder state after the air jet mill.

[0016] Furthermore, the particle size of the rare earth element metal salt powder is 50nm-100μm. If the powder particle size is too small, the preparation process becomes too complex, while if the particle size is too large, such as greater than 100 micrometers, it will result in excessively large grains, affecting performance.

[0017] Furthermore, the rare earth element metal salt powder is one, two, or more of the following: dysprosium zirconate / terbium / holmium / praseodymium, dysprosium titanate / terbium / holmium / praseodymium, dysprosium tungstate, dysprosium tungstate / terbium / holmium / praseodymium, dysprosium molybdate / terbium / holmium / praseodymium, dysprosium ruthenate / terbium / holmium / praseodymium, dysprosium vanadate / terbium / holmium / praseodymium, or dysprosium manganate / terbium / holmium / praseodymium.

[0018] More preferably, the rare earth element metal salt powder is dysprosium zirconate or dysprosium manganate.

[0019] Furthermore, a method for preparing rare earth element metal salt powders, using dysprosium zirconate as an example:

[0020] Step 1): Add butyl zirconate to anhydrous ethanol while stirring to obtain an alcoholic solution of butyl zirconate. The volume ratio of butyl zirconate to alcohol is (0.4-3.5):1.

[0021] Step 2): Add anhydrous ethanol to deionized water and stir until homogeneous to obtain an alcohol-water solution. The volume ratio of anhydrous ethanol to deionized water is 3:(1-2). Add glacial acetic acid and dysprosium nitrate to the solution and stir until completely dissolved to obtain a mixed solution with a dysprosium nitrate content of 40-65 wt%. The amount of glacial acetic acid added is 3-13 wt% of the weight of dysprosium nitrate.

[0022] Step 3): Add the mixed solution containing dysprosium nitrate from step 2) to the butyl zirconate alcohol solution from step 1) according to the molar ratio Dy:Zr=(1~2):1 to obtain the mixed sol;

[0023] Step 4: The mixed sol obtained in step 3) is aged at room temperature for 20-30 hours to obtain a gel; then the gel is dried at 50-80℃, pulverized, and passed through a 100-200 mesh sieve to obtain dysprosium zirconate precursor dry gel powder.

[0024] Step 5): The dysprosium zirconate precursor dry gel is placed in an alumina crucible and calcined at 800-1100℃ for 0.5-2 hours to obtain nano-dysprosium zirconate powder.

[0025] Furthermore, the lubricant is selected from reagents known in the art, and in amounts known in the art, to achieve thorough mixing of the powder and ease of molding. For example, the lubricant is selected from volatile organic solvents such as esters or alcohols, for example, zinc stearate.

[0026] Furthermore, the amount of lubricant added is 0.1-1 wt% of the total mass of the raw materials.

[0027] Furthermore, the smelting method involves heating the raw materials to 1300-1450°C under an inert gas atmosphere or vacuum conditions to fully melt them into alloy steel liquid. The cast steel liquid is then rapidly cooled to form alloy sheets, followed by a secondary cooling at 5-20°C / 2, with the time interval between the secondary and rapid cooling not exceeding 102°C.

[0028] Furthermore, a high-temperature melting process is carried out in a vacuum induction melting furnace by medium-frequency induction heating; the rapid cooling is carried out by rapid cooling rollers; the secondary cooling is carried out by rapid cooling discs, low-temperature inert gas spraying equipment or other forms of cooling devices; the thickness of the prepared alloy sheet is 150-450μm.

[0029] Furthermore, the powder preparation method includes two-step crushing: HD hydrogen crushing and air jet milling; in the HD hydrogen crushing, the alloy sheet is subjected to hydrogen absorption and dehydrogenation processes to obtain HD powder, the HD powder is screened by a medium mill, and the screened powder is mixed and then subjected to air jet milling; the air jet milling is carried out in an inert gas atmosphere to screen out powder of suitable particle size.

[0030] Furthermore, HD hydrogen crushing is carried out in an HD furnace; the inert gas is selected from nitrogen, argon, helium, etc.; during the air jet milling, powder of suitable particle size is screened by a cyclone separator.

[0031] Furthermore, a lubricant is added before mixing, and the mixing process needs to be carried out for 3-6 hours before the air jet mill. The mixing is performed in a mixer.

[0032] Mixing is required for 3-6 hours before air jet milling to improve powder uniformity. Adding lubricant before mixing can improve powder flowability, thereby improving mixing effect and efficiency, which is beneficial for air jet milling and subsequent molding processes.

[0033] Preferably, the particle size SMD of the alloy powder is between 2.0 and 3.4 μm, and X90 / X10 ≤ 4.5.

[0034] Wherein, SMD is the area average particle size. The smaller the SMD, the smaller the particle size of the powder; the larger the SMD, the larger the particle size of the powder. X90 represents the particle size value corresponding to a cumulative distribution percentage of 90%, that is, 90% of the particles are no larger than this particle size. X10 represents the particle size value corresponding to a cumulative distribution percentage of 10%, that is, 10% of the particles are no larger than this particle size. Therefore, the ratio of X90 / X10 represents the degree of concentration of the particle size distribution range. The smaller the ratio, the more uniform the particle size and the more concentrated the distribution. The ratio should be within 4.5 to meet the usage requirements.

[0035] Furthermore, the pressing method involves oriented pressing of a fixed amount of alloy powder in a metal mold under an external magnetic field, followed by demagnetization to obtain a block-shaped pressed blank.

[0036] Furthermore, the pressing and molding process is carried out in an inert gas atmosphere chamber, with nitrogen, helium, argon, etc., being preferred inert gases. Before pressing and molding, orientation magnetization and molding are required under a magnetic field strength of 2-2.5T. After pressing and molding, a reverse magnetic field is applied for demagnetization. To improve the compact density and subsequent sintering pass rate, the compact can be subjected to isostatic pressing treatment. Preferably, the compact density is 4-4.5 g / cm³. 3 .

[0037] Furthermore, the sintering process includes sintering, cooling, and aging; the green body is sintered in a vacuum sintering furnace, and the vacuum degree is 10 during heating. -1 The sintering temperature is below 1000-1070℃, and the holding time is 240-360min; the temperature after cooling is below 200℃; after cooling, the aging treatment is performed: the temperature is raised for the first aging treatment, the temperature of the first aging treatment is 800-950℃, and the holding time is 180-300min; the temperature is cooled to below 150℃, and then the temperature is raised for the second aging treatment, the temperature of the second aging treatment is between 450-600℃, and the holding time is 240-360min.

[0038] The present invention processes the core of the obtained blank into a size commonly used in this industry for magnetic performance testing. Preferably, it is processed into a cylinder with a diameter of 10 mm and a height of 10 mm for testing.

[0039] This invention provides a high coercivity neodymium iron boron magnet and its preparation method. During the preparation process, rare earth element metal salt powder is added. The rare earth element metal salt powder is enriched at the triple point of the grain boundary in the form of rare earth element metal oxide. Due to the presence of a large number of oxygen vacancy type point defects in the oxide, the grain boundary of the magnet is thickened. Under the external magnetic field, the flipping of magnetic domains is hindered, and the rare earth element metal oxide plays a pinning role, thereby improving the coercivity of the neodymium iron boron magnet. Attached Figure Description

[0040] Figure 1 The image shown is a microscopic image of the neodymium iron boron magnet in Example 12 of this invention.

[0041] a. Neodymium-iron-boron main phase b. Neodymium-rich phase c. Dysprosium-zirconium oxide

[0042] Figure 2 The image shows a microscopic image of the neodymium iron boron magnet of Comparative Example 3 of this invention.

[0043] a. Neodymium iron boron main phase b. Neodymium-rich phase Detailed Implementation

[0044] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0045] The preparation method of nano-dysprosium zirconate powder is as follows:

[0046] Step 1): Add butyl zirconate to anhydrous ethanol while stirring to obtain an alcoholic solution of butyl zirconate. The volume ratio of butyl zirconate to ethanol is (0.4-3.5):1.

[0047] Step 2): Add anhydrous ethanol to deionized water and stir until homogeneous to obtain an alcohol-water solution. The volume ratio of anhydrous ethanol to deionized water is 3:(1-2). Add glacial acetic acid and dysprosium nitrate to the solution and stir until completely dissolved to obtain a mixed solution with a dysprosium nitrate content of 40-65 wt%. The amount of glacial acetic acid added is 3-13 wt% of the weight of dysprosium nitrate.

[0048] Step 3): Add the mixed solution containing dysprosium nitrate from step 2) to the butyl zirconate alcohol solution from step 1) according to the molar ratio Dy:Zr=(1~2):1 to obtain the mixed sol.

[0049] Step 4): The mixed sol obtained in step 3) is aged at room temperature for 20-30 hours to obtain a gel; then the gel is dried at 50-80℃, pulverized, and passed through a 100-200 mesh sieve to obtain dysprosium zirconate precursor dry gel powder.

[0050] Step 5): The dysprosium zirconate precursor dry gel is placed in an alumina crucible and calcined at 800-1100℃ for 0.5-2 hours to obtain nano-dysprosium zirconate powder with an average particle size of 5μm.

[0051] The preparation method of nano-dysprosium manganate powder is the same as that of nano-dysprosium zirconate powder, resulting in nano-dysprosium manganate powder with an average particle size of 10 μm.

[0052] Example 1:

[0053] A method for preparing neodymium iron boron coercive magnets includes the following steps:

[0054] 1) Smelting

[0055] 300 kg of raw materials with the following mass ratios were used: Nd 24.26 wt%, Pr 6.065 wt%, Cu 0.1 wt%, Ga 0.15 wt%, Zr 0 wt%, Ti 0.12 wt%, Al 0.3 wt%, Co 1.5 wt%, B 0.98 wt%, and Fe 66.525 wt%. The raw materials were fully melted into alloy steel liquid in a vacuum melting furnace at 1400 °C. The cast steel liquid was rapidly cooled to form alloy sheets, and then subjected to a second cooling at 5-20 °C / 2, with the time interval between the second and rapid cooling not exceeding 102 seconds. 289 kg of NdFeB alloy sheets with an average thickness of 0.3 mm were obtained.

[0056] 2) Powdering

[0057] HD Hydrogen Crushing: The obtained alloy sheet is placed in a hydrogen crushing furnace for hydrogen absorption. After a full reaction, it undergoes dehydrogenation treatment, which breaks the NdFeB alloy sheet into powder with a particle size of tens to hundreds of micrometers along the grain boundaries, weighing approximately 285 kg.

[0058] Air jet milling: Add 0.3 wt% zinc stearate lubricant to the hydrogen-crushed NdFeB powder, mix the powder evenly for 4 hours using a mixer, and then perform air jet milling under a nitrogen atmosphere to grind the NdFeB alloy powder into 260 kg of fine powder with SMD = 2.9 μm, X90 / X10 = 2.4.

[0059] Add nano-dysprosium zirconate powder: Take 26 kg of powder after air jet milling, add 130.65 g of nano-dysprosium zirconate powder, that is, NdFeB air jet mill powder and dysprosium zirconate powder are mixed at a mass ratio of 99.5:0.5, and then add 0.35 wt% of zinc stearate lubricant to the total material, and mix with a mixer for 5 hours.

[0060] 3) Molding

[0061] The alloy powder was oriented and pressed under a 2T magnetic field in a press under nitrogen protection. After demagnetization, a block blank was obtained, which was then subjected to isostatic pressing before proceeding to the next step.

[0062] 4) Sintering

[0063] After isostatic pressing, the blank is sintered in a 500kg vacuum sintering furnace. After step-by-step heating and degassing, it is sintered at 1040℃ for 300 minutes, cooled to room temperature, and then tempered at 900℃ for 260 minutes. After cooling to 150℃, it is tempered at 500℃ for 300 minutes and then rapidly cooled to room temperature to obtain the required NdFeB blank.

[0064] In Examples 2-10, when adding nano-dysprosium zirconate powder, 26 kg of the powder after air jet milling in Example 1 was taken. The amount of nano-dysprosium zirconate powder added was different, that is, the mass ratio of NdFeB air jet milled powder to dysprosium zirconate powder was different. Other preparation methods were the same as in Example 1. To ensure the consistency of conditions, in 4) sintering, Examples 1-10 were carried out under the same conditions in a vacuum sintering furnace.

[0065] The amounts of nano-dysprosium zirconate powder added in Examples 2-10 are as follows:

[0066] Example 2: 261.31g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 99:1;

[0067] Example 3: 391.96g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 98.5:1.5.

[0068] Example 4: 522.61g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 98:2.

[0069] Example 5: 653.27g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 97.5:2.5.

[0070] Example 6: 783.90g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 97:3.

[0071] Example 7: 914.55g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 96.5:3.5.

[0072] Example 8: 1045.20g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 96:4.

[0073] Example 9: 1175.85g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 95.5:4.5.

[0074] Example 10: 1306.5g of nano-dysprosium zirconate powder was added, that is, neodymium iron boron air jet mill powder and dysprosium zirconate powder were mixed at a mass ratio of 95:5.

[0075] Example 11

[0076] A method for preparing neodymium iron boron coercive magnets includes the following steps:

[0077] 1) Smelting

[0078] 260 kg of raw materials with the following mass ratios were prepared: Nd 24.26 wt%, Pr 6.065 wt%, Cu 0.1 wt%, Ga 0.15 wt%, Zr 0 wt%, Ti 0.12 wt%, Al 0.3 wt%, Co 1.5 wt%, B 0.98 wt%, and Fe 66.525 wt%. Dysprosium zirconate powder at a mass ratio of 1:99 was added, resulting in 2613.3 g of nano-dysprosium zirconate powder. The mixture was fully melted into alloy steel at 1400 °C in a vacuum melting furnace. The cast steel was then rapidly cooled to form alloy sheets, followed by a secondary cooling process at 5-20 °C / 2, with the time interval between the secondary and rapid cooling cycles not exceeding 102°C. This yielded 248 kg of NdFeB alloy sheets with an average thickness of 0.32 mm.

[0079] 2) Powdering

[0080] HD Hydrogen Crushing: The obtained alloy sheet is placed in a hydrogen crushing furnace for hydrogen absorption. After a full reaction, it undergoes dehydrogenation treatment, which breaks the NdFeB alloy sheet into powder with a particle size of tens to hundreds of micrometers along the grain boundaries, weighing approximately 248 kg.

[0081] Air jet milling: Add 0.3 wt% zinc stearate lubricant to the hydrogen-crushed NdFeB powder. After mixing the powder evenly for 4 hours using a mixer, perform air jet milling under a nitrogen atmosphere to grind the NdFeB alloy powder into fine powder with SMD = 2.9 μm. Then add 0.35 wt% zinc stearate lubricant to the total material and mix with a mixer for 5 hours.

[0082] 3) Pressing and 4) Sintering are the same as in Example 1, and will not be repeated here.

[0083] Example 12

[0084] Add dysprosium zirconate powder at a mass ratio of 3:97 to the raw materials, i.e., add 7839g of nano-dysprosium zirconate powder, to obtain 251kg of NdFeB alloy sheet with an average thickness of 0.31mm. HD hydrogen crushing yields approximately 250kg of powder; other conditions and operations are exactly the same as in Example 11. To ensure consistency of conditions, during sintering in 4), Example 11 was carried out under the same conditions in a vacuum sintering furnace.

[0085] Example 13

[0086] A method for preparing neodymium iron boron coercive magnets includes the following steps:

[0087] 1) Smelting

[0088] 300 kg of raw materials with the following mass ratios were used: Nd 24.26 wt%, Pr 6.065 wt%, Cu 0.1 wt%, Ga 0.15 wt%, Zr 0 wt%, Ti 0.12 wt%, Al 0.3 wt%, Co 1.5 wt%, B 0.98 wt%, and Fe 66.525 wt%. The raw materials were fully melted into alloy steel liquid in a vacuum melting furnace at 1400 °C. The cast steel liquid was rapidly cooled to form alloy sheets, and then subjected to a second cooling at 5-20 °C / 2, with the time interval between the second and rapid cooling not exceeding 102°C. This process yielded 290 kg of NdFeB alloy sheets with an average thickness of 0.31 mm.

[0089] 2) Powdering

[0090] HD Hydrogen Crushing: The obtained alloy sheet is placed in a hydrogen crushing furnace for hydrogen absorption. After a full reaction, it undergoes dehydrogenation treatment, which breaks the NdFeB alloy sheet into powder with a particle size of tens to hundreds of micrometers along the grain boundaries, weighing approximately 287 kg.

[0091] Air jet milling: Add 0.3 wt% zinc stearate lubricant to the hydrogen-crushed NdFeB powder, mix the powder evenly for 4 hours using a mixer, and then perform air jet milling under a nitrogen atmosphere to grind the NdFeB alloy powder into 266 kg of fine powder with SMD = 2.9 μm, X90 / X10 = 2.5.

[0092] Add nano-dysprosium manganate powder: Take 26.6 kg of powder after air jet milling, add 268.69 g of nano-dysprosium manganate powder, that is, NdFeB air jet mill powder and dysprosium zirconate powder are mixed at a mass ratio of 99:1, and then add 0.35 wt% of zinc stearate lubricant to the total material, and mix with a mixer for 5 hours.

[0093] 3) Pressing and 4) Sintering are the same as in Example 1, and will not be repeated here.

[0094] In Examples 14-17, when adding nano-dysprosium manganate powder, 26.6 kg of the powder after air jet milling in Example 13 was taken. The amount of nano-dysprosium manganate powder added was different, that is, the mass ratio of NdFeB air jet milled powder to dysprosium zirconate powder was different. Other preparation methods were the same as in Example 13. To ensure the consistency of conditions, in 4) sintering, Examples 13-17 were carried out under the same conditions in a vacuum sintering furnace.

[0095] The amounts of nano-dysprosium manganate added in Examples 14-17 were:

[0096] Example 14: 537.38g of nano-dysprosium manganate powder was added, that is, neodymium iron boron air jet milling powder and nano-dysprosium manganate powder were mixed at a mass ratio of 99:2.

[0097] Example 15: 806.07g of nano-dysprosium manganate powder was added, that is, neodymium iron boron air jet milling powder and nano-dysprosium manganate powder were mixed at a mass ratio of 99:3.

[0098] Example 16: 1074.76g of nano-dysprosium manganate powder was added, that is, neodymium iron boron air jet milling powder and nano-dysprosium manganate powder were mixed at a mass ratio of 99:4.

[0099] Example 17: 1343.45g of nano-dysprosium manganate powder was added, that is, neodymium iron boron air jet milling powder and nano-dysprosium manganate powder were mixed at a mass ratio of 99:5.

[0100] Comparative Example 1

[0101] The preparation of NdFeB blanks does not include the step of adding nano-dysprosium zirconate powder, as is the case in Examples 1-10. Other conditions and operations are the same and will not be described again.

[0102] Comparative Example 2

[0103] ICP analysis of the prepared nano-dysprosium zirconate powder determined that it contained 30 wt% Dy and 50 wt% Zr. The raw materials in Example 12 contained 3 wt% dysprosium zirconate. This comparative example was designed to add metallic dysprosium and metallic zirconium with the same atomic ratios of dysprosium and zirconium. Specifically, if metallic Zr and metallic Dy are added in the same amount as the nano-dysprosium zirconate powder during the smelting stage, then 0.9% metallic dysprosium and 1.5% metallic zirconium should be added. Finally, the final mass ratio of raw materials was 300 kg: Nd 24.26 wt%, Pr 6.065 wt%, Cu 0.1 wt%, Ga 0.15 wt%, Zr 1.5 wt%, Dy 0.9 wt%, Ti 0.12 wt%, Al 0.3 wt%, Co 1.5 wt%, B 0.98 wt%, and Fe 66.525 wt%. Other conditions and operations were the same as in Example 12 and will not be repeated.

[0104] Comparative Example 3

[0105] This comparative design adds the same raw materials as in Example 12, but with the same atomic ratio of dysprosium and zirconium oxide as in 3wt% dysprosium zirconate. Calculations show that 3.44 kg of dysprosium oxide and 6.08 kg of zirconium oxide are added, while the weight of other raw materials remains unchanged, resulting in a raw material volume of 302.32 kg. Other conditions and operations are the same as in Example 12 and will not be repeated here.

[0106] Experimental results:

[0107] Using the methods described in Examples 1-10, different proportions of dysprosium zirconate powder were added after air jet milling. From a production process control perspective, increasing the amount of dysprosium zirconate added facilitates mold release from the compact, making the compact easier to form and thus improving the compact yield. The increased oxygen content also improves powder flowability, resulting in more uniform powder filling during compacting, further enhancing the compact yield.

[0108] As shown in the attached diagram, Figure 1 The image is a microscopic image of Example 12. Figure 2 As shown in the microscopic image of Comparative Example 1, it can be clearly seen that when dysprosium zirconate is added during smelting, the grain boundaries of the magnet become more continuous, and there is an enrichment of dysprosium zirconium oxide at the triple point of the grain boundary. The point defects composed of oxygen vacancies play a pinning role, which hinders the flipping of magnetic domains and improves the coercivity of the magnet.

[0109] For Examples 1-17, NdFeB blanks were prepared after sintering. Sample columns with a diameter of 10 mm and a height of 10 mm were machined and tested for magnetic properties. The properties are shown in Table 1 below:

[0110] Table 1. Magnetic properties of products from the examples and comparative examples.

[0111] name Remanence Br(T) Coercivity Hcj (kA / m) Example 1 1.382 1533 Example 2 1.360 1614 Example 3 1.345 1692 Example 4 1.326 1766 Example 5 1.308 1811 Example 6 1.289 1850 Example 7 1.277 1865 Example 8 1.261 1855 Example 9 1.240 1809 Example 10 1.221 1749 Example 11 1.351 1567 Example 12 1.278 1726 Example 13 1.369 1624 Example 14 1.342 1702 Example 15 1.321 1764 Example 16 1.315 1789 Example 17 1.287 1765 Comparative Example 1 1.396 1464 Comparative Example 2 1.291 1654 Comparative Example 3 1.202 1515

[0112] Therefore, by comparing the performance of Examples 1-10 with that of Comparative Example 1, it can be seen that the addition of 1% to 3.5 wt% nano-dysprosium zirconate powder to the powder after air jet milling in Examples 1-7 significantly improves the coercivity of the magnet compared to the standard product without added dysprosium and zirconium. As the amount added increases, the remanence decreases while the coercivity gradually increases. This is attributed to the accumulation of dysprosium-zirconium oxide at the triple point of the magnet's grain boundary, where point defects composed of oxygen vacancies act as pinning agents, hindering the flipping of magnetic domains and improving the coercivity. However, as in Examples 8-10, when the amount added reaches 4-5 wt%, both the remanence and coercivity decrease with further increases in the amount added. This is because excessive dysprosium-zirconium oxide damages the microstructure of the magnet, leading to a decrease in coercivity.

[0113] By comparing the performance of Examples 11-12 with that of Comparative Example 1, it can be seen that adding 1 wt% and 3 wt% nano-dysprosium zirconate powder during smelting reduces remanence and improves coercivity of the magnet. This is also attributed to the aggregation of dysprosium zirconium oxide at the triple point of the magnet grain boundary. The point defects composed of oxygen vacancies act as pinning agents, hindering the flipping of magnetic domains and improving coercivity. However, compared with the results of adding 1 wt% and 3 wt% dysprosium zirconate powder to the powder after air jet milling in Examples 2 and 6, the increase in coercivity is relatively small. Adding dysprosium zirconate powder to the powder after air jet milling has a more significant effect on improving the coercivity of the magnet than adding dysprosium zirconate powder during smelting, and the decrease in remanence is smaller. This is mainly due to the burn-off of dysprosium zirconate caused by smelting and the fact that some of the dysprosium zirconate elements are aggregated in the main phase during smelting, resulting in a small amount at the grain boundary.

[0114] Examples 12-17 involve adding dysprosium manganate powder during powder preparation. Compared with Comparative Example 1, the coercivity can also be improved. When the amount added exceeds 4 wt%, the coercivity begins to decrease. Compared with Example 1, the effect of dysprosium manganate on improving coercivity is lower than that of dysprosium zirconate. It is speculated that this may be related to the fact that dysprosium manganate affects the microstructure of grain boundaries.

[0115] Compared with Comparative Examples 2 and 3, Example 12 showed a significant difference in the performance improvement of magnets when dysprosium and zirconium atoms were not added or were added in the same proportion, such as dysprosium metal + zirconium metal or dysprosium oxide + zirconium oxide. Comparative Examples 2 and 3 showed a significantly smaller increase in coercivity of magnets than Example 12 precisely because they lacked dysprosium zirconium oxide at the triple point.

[0116] In summary, the high coercivity NdFeB magnet provided by this invention, due to the addition of rare earth element metal salt powder during the preparation process, the rare earth element metal salt powder is enriched at the triple point of the grain boundary in the form of rare earth element metal oxide. Due to the presence of a large number of oxygen vacancy type point defects in the oxide, the grain boundary of the magnet is thickened. Under the external magnetic field, the flipping of magnetic domains is hindered, and the rare earth element metal oxide plays a pinning role, thereby improving the coercivity of the NdFeB magnet.

[0117] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high coercivity neodymium iron boron magnet, characterized in that, The three-phase points at the grain boundaries of the magnet are enriched with oxides of zirconium and dysprosium or oxides of manganese and dysprosium. The neodymium iron boron magnet comprises Re 29.5~32.5wt%, Cu 0.05~0.3wt%, Ga 0~0.3wt%, Al 0~1wt%, Co 0.05~3.5wt%, B 0.8~1.1wt%, M 0.05-2%, where M is at least one of zirconium and manganese, and the balance is Fe and unavoidable impurities. The preparation method of the high coercivity neodymium iron boron magnet includes: 1) smelting, 2) powdering, 3) molding, 4) sintering, and also includes the step of adding metal salt powder of rare earth elements; The rare earth element metal salt powder is one or both of dysprosium zirconate or dysprosium manganate.

2. A method for preparing a high coercivity neodymium iron boron magnet as described in claim 1, characterized in that, The preparation method of the high coercivity neodymium iron boron magnet includes: 1) smelting, 2) powdering, 3) molding, 4) sintering, and also includes the step of adding metal salt powder of rare earth elements.

3. The method for preparing high coercivity neodymium iron boron magnets according to claim 2, characterized in that, The metal salt powder is added during the raw material and / or powdering stage.

4. The method for preparing high coercivity neodymium iron boron magnets according to claim 3, characterized in that, The rare earth element metal salt powder added during the powdering stage is: 1) added before the rapid solidification thin strip is crushed, 2) added in the coarse powder state after the rapid solidification thin strip is hydrogen-crushed, and 3) added in the fine powder state after the air jet mill is run.

5. The method for preparing high coercivity neodymium iron boron magnets according to claim 2, wherein the particle size of the rare earth element metal salt powder is 50nm-100μm.

6. The method for preparing high coercivity neodymium iron boron magnets according to claim 2, wherein the smelting method involves heating the raw material to 1300-1450°C under an inert gas atmosphere or vacuum conditions to fully melt it into alloy steel liquid, and rapidly cooling the cast steel liquid to form alloy sheets, followed by a secondary cooling at 5-20°C / s, with the time interval between the secondary and rapid cooling not exceeding 10s.

7. The method for preparing high coercivity NdFeB magnets according to claim 2, wherein the sintering process includes sintering, cooling, and aging; the billet is sintered in a vacuum sintering furnace, and the vacuum degree is below 10⁻¹ Pa during heating; the sintering temperature is 1000-1070℃, and the holding time is 240-360 min; the temperature after cooling is below 200℃; after cooling, the aging treatment is performed: the temperature is raised for the first aging treatment, the first aging treatment temperature is 800-950℃, and the holding time is 180-300 min; the temperature is cooled to below 150℃, and then the temperature is raised for the second aging treatment, the second aging treatment temperature is between 450-600℃, and the holding time is 240-360 min.

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