A grain boundary regulated high-abundance lanthanum-cerium-iron-boron permanent magnet and a preparation method thereof

Abstract

The application relates to the technical field of rare earth permanent magnet material preparation, and discloses a grain boundary regulation type high-abundance lanthanum-cerium-iron-boron permanent magnet and a preparation method, which are prepared from lanthanum-cerium-iron-boron rapid solidification cast pieces and modified preformed powders, the modified preformed powders are obtained by premixing neodymium-iron-boron waste powder, a rare earth modifier and an organic anchoring agent. The preparation method comprises the following steps: layering raw materials, saturating hydrogen absorption, heating and dehydrogenating, powdering after inert gas purging, shaping, and finally obtaining the grain boundary regulation type high-abundance lanthanum-cerium-iron-boron permanent magnet through two-stage vacuum sintering and double-stage aging treatment. In the application, the organic anchoring agent is used to fix the rare earth modifier on the surface of the waste powder, and the layering and low-temperature solid-phase reaction process are combined, so that the organic volatile components are effectively removed, and the waste powder oxide layer is used to construct a heavy rare earth shell structure. The technology realizes high-value utilization of the neodymium-iron-boron waste powder, suppresses diffusion of heavy rare earth into a main phase, and improves the coercive force and remanence of the high-abundance lanthanum-cerium magnet.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet material preparation technology, specifically to a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet and its preparation method. Background Technology

[0002] Lanthanum and cerium, among other high-abundance rare earth elements, constitute a very large proportion of rare earth deposits and are relatively inexpensive. However, because their intrinsic magnetic properties (such as saturation magnetization and magnetocrystalline anisotropy) are lower than those of praseodymium and neodymium, permanent magnets prepared by partially replacing praseodymium and neodymium with lanthanum and cerium often suffer from a significant decrease in coercivity and remanence. To improve the magnetic properties of high-abundance rare earth magnets, current technologies typically involve adding heavy rare earth elements such as dysprosium and terbium for modification. Traditional alloying methods tend to allow heavy rare earth elements to enter the main phase lattice, not only wasting expensive heavy rare earth resources but also reducing the saturation magnetization of the magnet due to the antiferromagnetic coupling between heavy rare earth atoms and iron atoms, making it difficult to simultaneously achieve high coercivity and high remanence.

[0003] On the other hand, the production process of NdFeB magnets generates a large amount of machining waste, such as press powder. Although this waste powder contains a high proportion of rare earth elements and has recycling value, it has a large specific surface area, is severely oxidized, and usually contains organic lubricants. If this waste powder is directly recycled for the preparation of high-performance magnets, the oxygen impurities will disrupt the continuity of the grain boundary phase, leading to severe deterioration of the magnet's performance. Current recycling methods mostly employ chemical extraction or remelting and dilution, which are lengthy and costly processes, making it difficult to achieve direct, short-process utilization of the waste powder in high-value magnets.

[0004] Furthermore, when attempting to control the microstructure of magnets through powder metallurgy, the differences in particle size and density between additive powders (such as heavy rare earth powders) and matrix powders easily lead to segregation during mixing and subsequent processes, resulting in uneven component distribution. Although organic binders can be added to aid dispersion, conventional processes struggle to completely remove organic matter before sintering. Residual carbon elements readily react with rare earth elements at high temperatures to form carbides, further deteriorating the magnetic properties of the magnets. Therefore, addressing the performance bottlenecks of high-abundance rare earth magnets and resolving impurities and dispersion issues in waste powder recycling while ensuring low cost and high resource utilization remains a crucial technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet and its preparation method. This solves the problem that existing high-abundance lanthanum-cerium-iron-boron permanent magnets are limited by the intrinsic magnetic properties of lanthanum and cerium, making it difficult to improve their coercivity and squareness. At the same time, the high impurity content in NdFeB waste powder leads to magnet performance degradation when used directly, and conventional mixing processes are difficult to control the distribution of heavy rare earth elements in multiphase systems, resulting in low utilization of heavy rare earth elements and significant magnetic dilution effect of the main phase.

[0006] To achieve the above objectives, the present invention provides a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet, employing the following technical solution:

[0007] It is made from raw materials comprising the following parts by weight: 100 parts of lanthanum cerium iron boron rapid solidification casting sheet; 18-25 parts of modified pre-formed powder; wherein the modified pre-formed powder is pre-mixed from NdFeB waste powder, rare earth modifier and organic anchoring agent.

[0008] By adopting the above technical solution, the microstructure of the magnet is controlled by the physicochemical interactions between the components of the pre-made powder. The specific mechanism is as follows: First, through a premixing process, the wetting and adhesion effects of the organic anchoring agent are used to adsorb the rare earth modifier powder with a high anisotropic field onto the surface of NdFeB waste powder particles. This structure uses the waste powder particles as a physical carrier for the rare earth modifier, solving the problem of component segregation caused by density differences during the mixing and transportation of micropowders, and ensuring that the modifier is evenly distributed in the matrix.

[0009] Second, during the sintering process, the pre-formed powder structure triggers interfacial reactions and reconstruction. The oxide layer enriched on the surface of the waste powder preferentially reacts with the attached rare earth modifier to generate stable rare earth oxides, which consume the oxygen on the surface of the waste powder and reduce the diffusion of oxygen into the lanthanum-cerium main phase. At the same time, the unconsumed rare earth modifier diffuses along the surface of the waste powder particles and the adjacent lanthanum-cerium main phase grain boundaries, forming a shell phase rich in heavy rare earths around the waste powder particles and the lanthanum-cerium main phase. This shell layer increases the local magnetocrystalline anisotropy field at the grain boundaries and inhibits the nucleation of antimagnetic domains. In addition, the enriched grain boundary phase blocks the direct magnetic exchange coupling between the lanthanum-cerium main phase grains and the waste powder particles, confining the magnetic performance degradation caused by lattice defects in the waste powder particles to a local area.

[0010] Third, the rare earth modifier is pre-anchored on the surface of the waste powder, which restricts the long-range diffusion of heavy rare earth elements into the interior of the lanthanum-cerium main phase grains. This distribution characteristic reduces the number of heavy rare earth atoms entering the main phase lattice to replace iron atoms, reduces the loss of saturation magnetization caused by antiferromagnetic coupling, and enables the magnet to maintain high remanence while improving coercivity.

[0011] Preferably, the modified pre-formed powder is made from the following components in parts by weight: 100 parts of neodymium iron boron press waste powder; 8-15 parts of rare earth modifier; and 0.06-0.08 parts of organic anchoring agent.

[0012] By adopting the above technical solution, the ratio of modifier to anchoring agent is controlled to balance the flowability of the powder and the modification effect. Within this dosage range, the anchoring agent can ensure the coverage of the modifier powder on the surface of the waste powder, while avoiding the introduction of excessive organic carbon sources, thus preventing incomplete decarburization and residual carbide impurities due to excessive carbon content.

[0013] Preferably, the rare earth modifier is gadolinium-holmium alloy powder or gadolinium-holmium hydride powder; the organic anchoring agent is oleic acid or zinc stearate.

[0014] By employing the above technical solution, gadolinium and holmium, as heavy rare earth elements, form a grain boundary phase with a high magnetocrystalline anisotropy field. Oleic acid or zinc stearate, as long-chain organic molecules, have polar groups that bind to active sites on the surface of the metal powder, while the non-polar long chains create steric hindrance, reducing powder agglomeration, enhancing the physical adsorption of fine modifier particles, and maintaining the structural stability of the modified pre-formulated powder during subsequent mixing and hydrogen crushing processes.

[0015] A second aspect of this invention provides a method for preparing a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet, comprising the following steps:

[0016] Neodymium iron boron waste powder, rare earth modifier and organic anchoring agent are mixed to obtain modified pre-formed powder;

[0017] Lanthanum-cerium-iron-boron rapid solidification casting sheets and the modified pre-made powder were alternately loaded into a processing container in a layered structure. After hydrogen saturation, inert gas was purged during the heating and dehydrogenation process, followed by vacuum dehydrogenation to obtain hydrogen fragments.

[0018] The hydrogen-rich powder was then ground using an air jet mill to obtain a fine powder.

[0019] The fine powder is pressed into a green body under magnetic field orientation conditions;

[0020] The green blank is subjected to vacuum sintering and two-stage aging treatment to obtain the permanent magnet.

[0021] By employing the above technical solution, this method utilizes physical and chemical means to control the removal of organic matter and the formation of microstructures. First, the layered charging and hydrogen crushing process improve the mixing effect of oily waste powder and rapid-setting casting sheets. The lattice expansion and fragmentation effect during hydrogen crushing promotes the simultaneous refinement of modified pre-formed powder and rapid-setting casting sheets; the layered distribution structure, while ensuring the material ratio, provides an escape channel for volatile organic compounds through the gaps between the layers.

[0022] Secondly, inert gas is introduced during the heating and dehydrogenation stage to purge the environment and reduce the concentration of organic anchoring agent decomposition products in the environment by utilizing the principle of gas partial pressure. The flowing inert gas will carry the hydrocarbons released from the pre-formed powder layer away from the reaction zone, reducing the probability of carbon reacting with rare earth metals at high temperatures to form carbides. This reduces the impact on the magnetic properties of the magnet while utilizing organic matter for dispersion.

[0023] Finally, by grinding and mixing the powder with an air jet mill, the waste powder particles with the modified layer are dispersed in the lanthanum-cerium-iron-boron matrix powder, providing structural conditions for grain boundary diffusion during the sintering process.

[0024] Preferably, in preparing the modified pre-formed powder, the mixing is mechanical shear mixing under inert gas protection, with a mixing speed of 60-80 rpm and a time of 20-30 minutes; the organic anchoring agent is added by atomized spraying or direct feeding.

[0025] The above technical solution utilizes mechanical shear force to disperse waste powder agglomerates, combined with atomized dispersion or direct feeding of organic anchoring agents, to wet the surface of the waste powder particles. Liquid bridging forces and van der Waals forces are used to adsorb rare earth modifier powder onto the waste powder surface, preventing the modifier from detaching or segregating in subsequent processes.

[0026] Preferably, when loading into the processing container, the bottom and top layers of the layered structure are both lanthanum-cerium-iron-boron rapid solidification casting sheets, and the modified pre-made powder is alternately laid in the middle layer; the inert gas purging specifically involves: starting argon purging within the temperature range of 250-350℃, controlling the dynamic vacuum degree of the environment to be 300-500Pa, and the purging time to be 60 minutes.

[0027] By employing the above technical solution, larger-sized rapid-solidifying casting sheets at the bottom and top layers cover the finer pre-formed powder in the middle layer, preventing powder loss due to purging airflow. The temperature range of 250-350℃ covers the thermal decomposition temperature range of oleic acid and zinc stearate. Combined with a dynamic vacuum of 300-500Pa and a purging time of 60 minutes, the organic anchoring agent decomposes and volatilizes before the carbonization reaction occurs, controlling the carbon content of the final magnet.

[0028] Preferably, during air jet milling, the oxygen content of the air jet mill atmosphere is controlled to be 50-80 ppm, and the median particle size D50 of the fine powder is 4.2-4.4 μm; during compression molding, the compression molding only includes die molding, and the green density is controlled to be 4.15-4.25 g / cm³. 3 .

[0029] By adopting the above technical solution, a lower green density preserves interconnected pore channels within the compact. These pores facilitate the removal of residual gases and reaction byproducts during subsequent sintering heating stages, reducing internal voids and cracks in the magnet and improving sintering density.

[0030] Preferably, during vacuum sintering, the vacuum sintering includes a two-stage heating process: the first stage involves heating to 450-550°C and holding for 90 minutes; the second stage involves heating to 1030-1060°C and holding for 3-5 hours.

[0031] By employing the above technical solution, a solid-phase reaction is carried out using a first-stage low-temperature insulation platform. At this temperature (450-550℃), before the liquid phase forms, the rare earth modifier on the surface of the waste powder undergoes a reduction reaction with the surface oxides, and simultaneously diffuses along the particle surface, initially constructing a rare earth-rich shell structure. This step separates the purification and structural reconstruction process from the high-temperature densification process, avoiding excessive diffusion of the modifier due to high-temperature liquid phase flow and maintaining the grain boundary control effect.

[0032] This invention provides a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet and its preparation method. It possesses the following beneficial effects:

[0033] 1. This invention anchors rare earth modifiers onto the surface of NdFeB waste powder through a premixing process. During sintering, this promotes the formation of a shell structure rich in heavy rare earth elements at the waste powder particles and near the lanthanum-cerium main phase grain boundaries, thereby increasing the local magnetocrystalline anisotropy field in the grain boundary region and effectively suppressing the nucleation and growth of antimagnetization domains, thus enhancing the coercivity of the magnet. At the same time, this structure restricts the long-range diffusion of heavy rare earth elements into the main phase grains, reducing the decrease in saturation magnetization caused by heavy rare earth elements replacing iron atoms, enabling the magnet to maintain a high remanence level while improving coercivity.

[0034] 2. This invention achieves effective control of impurity elements by employing a layered charging process combined with an inert gas purging process during the dehydrogenation stage and a low-temperature solid-state reaction mechanism during the sintering stage. Impurities are volatilized and discharged before the organic matter is carbonized, reducing the carbon content of the magnet. Simultaneously, rare earth modifiers preferentially react with the oxide layer on the surface of the waste powder, consuming the oxygen impurities carried by the waste powder and purifying the grain boundary phase. This transforms the oxidized waste powder, which would otherwise easily lead to performance degradation, into a functional component with grain boundary strengthening properties, realizing the high-value utilization of NdFeB press waste powder in high-abundance rare earth magnets.

[0035] 3. This invention solves the segregation problem of micron-sized rare earth modifiers and waste powder particles during mixing and transportation by using organic anchoring agents, ensuring the uniform distribution of modifiers in the macroscopic matrix. Combined with high-abundance lanthanum-cerium rapid solidification casting sheets as the matrix, it significantly reduces the amount of heavy rare earth (terbium, dysprosium) used and the cost of raw materials. At the same time, it makes up for the lack of intrinsic properties of lanthanum-cerium magnets through grain boundary control technology, and obtains sintered NdFeB magnets with excellent comprehensive magnetic properties and low cost, which are suitable for industrial mass production. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] Preparation Examples 1-5:

[0038] Preparation Example 1:

[0039] This preparation example provides a modified pre-formed powder P1, comprising the following preparation steps:

[0040] 100 parts of neodymium iron boron press waste powder B1 and 10 parts of gadolinium holmium alloy powder C1 were weighed and put into a V-type mixer; then 0.07 parts of oleic acid D1 (accounting for 0.07% of the mass of component B) were uniformly sprayed into the mixer through a high-pressure atomizing nozzle; nitrogen gas with a purity of 99.99% was introduced as a protective gas, and the mixer speed was controlled at 70 rpm. Mechanical shearing and mixing were carried out at room temperature for 25 minutes to allow the oleic acid to assist the gadolinium holmium particles to be oriented and anchored on the surface of the waste powder; the material was discharged to obtain modified pre-formed powder P1.

[0041] Preparation Example 2:

[0042] This preparation example provides a modified pre-formed powder P2, which includes the following preparation steps:

[0043] 100 parts of neodymium iron boron press waste powder B2 and 15 parts of gadolinium holmium hydride powder C2 were weighed and put into a three-dimensional motion mixer; then 0.08 parts of oleic acid D1 (accounting for 0.08% of the mass of component B) were sprayed into the mixer through a high-pressure atomizing nozzle; nitrogen gas with a purity of 99.99% was introduced for protection, the mixer speed was controlled at 80 rpm, and mechanical shearing was performed at room temperature for 30 minutes; the material was discharged to obtain modified pre-formed powder P2.

[0044] Preparation Example 3:

[0045] This preparation example provides a modified pre-formed powder P3, which includes the following preparation steps:

[0046] 100 parts of neodymium iron boron press waste powder B1 and 10 parts of gadolinium holmium alloy powder C1 were weighed and put into a V-type mixer; then 0.07 parts of zinc stearate powder D2 (accounting for 0.07% of the mass of component B) were added into the mixer; nitrogen gas with a purity of 99.99% was introduced for protection, the mixer speed was controlled at 70 rpm, and mechanical shearing was performed at room temperature for 25 minutes to complete the coating by utilizing the electrostatic and mechanical interlocking force between the micro powders; the material was discharged to obtain modified pre-formed powder P3.

[0047] Preparation Example 4:

[0048] This preparation example provides a modified pre-formed powder P4, which includes the following preparation steps:

[0049] 100 parts of neodymium iron boron press waste powder B1 and 8 parts of gadolinium holmium alloy powder C1 were weighed and put into a V-type mixer; then 0.06 parts of oleic acid D1 (accounting for 0.06% of the mass of component B) were sprayed into the mixer through a high-pressure atomizing nozzle; nitrogen gas with a purity of 99.99% was introduced for protection, the mixer speed was controlled at 60 rpm, and mechanical shearing was performed at room temperature for 20 minutes; the material was discharged to obtain modified pre-formed powder P4.

[0050] Preparation Example 5:

[0051] This preparation example provides a modified pre-formed powder P5, which includes the following preparation steps:

[0052] Weigh 100 parts of neodymium iron boron press waste powder B2 and 12 parts of gadolinium holmium hydride powder C2 and put them into a three-dimensional motion mixer; then add 0.08 parts of oleic acid D1 (accounting for 0.08% of the mass of component B) into the mixer; introduce nitrogen gas with a purity of 99.99% for protection, control the speed of the mixer at 80 rpm, and perform mechanical shear mixing at room temperature for 30 minutes; discharge the material to obtain modified pre-formed powder P5.

[0053] Examples 1-5:

[0054] Example 1:

[0055] This embodiment provides a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet and its preparation method, including the following steps:

[0056] 100.0 kg of lanthanum-cerium-iron-boron rapid solidification casting A1 was prepared as the matrix skeleton, and 20.0 kg of modified pre-formed powder P1 obtained from Preparation Example 1 was prepared as the filling material. The casting A1 and modified pre-formed powder P1 were loaded into the hydrogen crushing furnace charge box in a sandwich layered structure. The loading method was as follows: a 30 mm thick layer of casting A1 was laid at the bottom, followed by an 8 mm thick layer of pre-formed powder P1, and then another 30 mm thick layer of casting A1 was laid, and this cycle was repeated to ensure that the top layer was casting A1. After loading, the vacuum was evacuated to 8 Pa, and 0.10 MPa of hydrogen gas was introduced to absorb hydrogen until saturation. Then, heating was turned on, and when the temperature reached 300 °C, the argon purging mode was turned on, and the dynamic vacuum degree in the furnace was controlled at 400 Pa. The furnace was held at this temperature and purged for 60 minutes to remove organic volatiles. After that, the argon gas was turned off, and the furnace was heated to 530 °C under a high vacuum of 5 Pa and held for 3 hours for deep dehydrogenation to obtain hydrogen crushed powder.

[0057] Hydrogen-refined powder was milled using an air jet mill under a nitrogen atmosphere and an oxygen content of 60 ppm. The milling pressure was controlled at 0.60 MPa, and the powder output was 330 kg / h. The median particle size (D50) of the sorted fine powder was 4.3 μm. The fine powder was then pressed into shape under a 1.9 T orientation magnetic field and a pressure of 20 MPa, with the green density controlled at 4.20 g / cm³. 3 The green blanks were directly loaded into a graphite sintering box without undergoing cold isostatic pressing. The sintering was carried out under a vacuum of 3×10⁻⁶. -2 Under Pa conditions, the temperature was increased to 500℃ at a rate of 2.5℃ / min and held for 90 minutes for solid-state reaction; then, the temperature was increased to 1050℃ at a rate of 6℃ / min and held for 4 hours for densification sintering; after sintering, the magnet was air-cooled to room temperature. The sintered magnet was held at 670℃ for 2.5 hours and air-cooled; then held at 420℃ for 3.5 hours and rapidly cooled to obtain the final grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet.

[0058] Example 2:

[0059] This embodiment provides a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet and its preparation method, including the following steps:

[0060] Prepare 100.0 kg of lanthanum-cerium-iron-boron rapid solidification casting A2 and 25.0 kg of modified pre-formed powder P2 obtained from Preparation Example 2. Charge the powder into the hydrogen crushing furnace using the same layered charging method as in Example 1; after hydrogen saturation, raise the temperature to 350°C and start argon purging, maintaining a dynamic vacuum of 300 Pa inside the furnace, and hold for 60 minutes; then raise the temperature to 550°C under vacuum and hold for 4 hours to remove hydrogen, obtaining hydrogen-crushed powder.

[0061] Hydrogen-containing powder was milled using an air jet mill under a nitrogen atmosphere and an oxygen content of 50 ppm. The milling pressure was controlled at 0.61 MPa, the powder output flow rate at 350 kg / h, and the fine powder D50 was controlled at 4.2 μm. The powder was then pressed into shape under a 2.0 T magnetic field and a pressure of 25 MPa, with the green body density controlled at 4.25 g / cm³. 3 No cold isostatic pressing process. Under vacuum conditions <5×10⁻⁶. -2 Under Pa conditions, the temperature was raised to 550℃ and held for 90 minutes; then the temperature was raised to 1030℃ and held for 5 hours for sintering. Finally, aging treatment was performed, with holding at 660℃ for 3 hours followed by air cooling; holding at 410℃ for 4 hours followed by rapid cooling, to obtain the final grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet.

[0062] Example 3:

[0063] This embodiment provides a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet and its preparation method, including the following steps:

[0064] Prepare 100.0 kg of lanthanum-cerium-iron-boron rapid solidification casting A3 and 25.0 kg of modified pre-formed powder P4 obtained from Preparation Example 4. The furnace was charged using a layered charging method; after hydrogen saturation, the temperature was raised to 250°C and argon gas was started for purging, maintaining a dynamic vacuum of 500 Pa inside the furnace, and purging was carried out at this temperature for 60 minutes; subsequently, the temperature was raised to 500°C under vacuum and held for 3 hours to remove hydrogen, yielding hydrogen fragments.

[0065] Hydrogen-containing powder was milled using an air jet mill under a nitrogen atmosphere and an oxygen content of 80 ppm. The milling pressure was controlled at 0.59 MPa, the powder output flow rate at 310 kg / h, and the fine powder D50 was controlled at 4.4 μm. The powder was then pressed into shape under a 1.8 T magnetic field and a pressure of 15 MPa, with the green body density controlled at 4.15 g / cm³. 3 No cold isostatic pressing process. Under vacuum conditions <5×10⁻⁶. -2 Under Pa conditions, the temperature was raised to 450℃ and held for 90 minutes; then the temperature was raised to 1060℃ and held for 3 hours for sintering. Finally, aging treatment was performed: the temperature was raised to 680℃ for 2 hours and air-cooled; then the temperature was raised to 430℃ for 3 hours and rapidly cooled to obtain the final grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet.

[0066] Example 4:

[0067] This embodiment provides a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet and its preparation method, including the following steps:

[0068] Prepare 100.0 kg of lanthanum-cerium-iron-boron rapid solidification casting A1 and 20.0 kg of modified pre-formed powder P3 (containing zinc stearate) obtained from Preparation Example 3. The furnace was charged using a layered charging method; after hydrogen saturation, the temperature was raised to 320°C and argon gas was started for purging, maintaining a dynamic vacuum of 400 Pa in the furnace, and held for 60 minutes to remove the decomposition products of zinc stearate; subsequently, the temperature was raised to 540°C for dehydrogenation to obtain hydrogen-rich powder.

[0069] Hydrogen-containing powder was milled using an air jet mill under a nitrogen atmosphere and an oxygen content of 60 ppm, with a milling pressure controlled at 0.60 MPa and a D50 controlled at 4.3 μm. During pressing and molding, the green density was controlled at 4.20 g / cm³. 3 The process involves no cold isostatic pressing. During sintering, a reaction platform is set at 520℃ and held for 90 minutes; the main sintering temperature is 1050℃ and held for 4 hours. Finally, an aging treatment is performed: 670℃ for 2.5 hours, followed by air cooling; 420℃ for 3.5 hours, followed by rapid cooling, to obtain the final grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet.

[0070] Example 5:

[0071] This embodiment provides a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet and its preparation method, including the following steps:

[0072] Prepare 100.0 kg of lanthanum-cerium-iron-boron rapid solidification casting A2 and 18.0 kg of modified pre-formed powder P5 obtained from Preparation Example 5. After hydrogen absorption, decarburize by argon purging at 300 °C; then dehydrogenate at 520 °C. The grinding pressure of the air jet mill is controlled at 0.60 MPa, and the D50 is controlled at 4.25 μm.

[0073] The green body density was controlled at 4.22 g / cm³ during pressing. 3 No cold isostatic pressing process is required. During sintering, a reaction platform is set at 480℃ and held for 90 minutes; the main sintering temperature is 1040℃ and held for 4.5 hours. Finally, aging treatment is performed: 665℃ for 2.5 hours, followed by air cooling; 415℃ for 3.5 hours, followed by rapid cooling, to obtain the final grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet.

[0074] Comparative Examples 1-5:

[0075] Comparative Example 1:

[0076] This comparative example corresponds to Example 1. The difference from Example 1 is that the modified pre-powder P1 is not prepared separately, nor is layered loading. Instead, 100.0 kg of casting A1, 10.0 kg of waste powder B1, 1.0 kg of alloy powder C1 and 7.0 g of oleic acid D1 are put into a large mixer and mixed evenly in one go. Then, they are loaded into the hydrogen crushing furnace feed box for subsequent processing. The remaining steps and parameters are the same as in Example 1.

[0077] Comparative Example 2:

[0078] This comparative example corresponds to Example 1. The difference between Example 1 and Example 1 is that when preparing the modified pre-powder P1, component D1 (oleic acid) is not added, and waste powder B1 and alloy powder C1 are only dry-mixed. The remaining steps and parameters are the same as in Example 1.

[0079] Comparative Example 3:

[0080] This comparative example corresponds to Example 1. The difference from Example 1 is that: instead of using a layered charging method, the cast sheet A1 and the modified pre-made powder P1 are simply stirred and mixed before being charged into the furnace; and during the hydrogen crushing and heating process, the argon purging and decarburization step at 300°C is eliminated, and after hydrogen absorption saturation, the temperature is directly raised to 530°C under vacuum for dehydrogenation. The remaining steps and parameters are the same as in Example 1.

[0081] Comparative Example 4:

[0082] This comparative example corresponds to Example 1. The difference between Example 1 and Example 2 is that the low-temperature solid-state reaction platform of holding at 500°C for 90 minutes is cancelled during the reaction sintering process. Instead, the temperature is directly increased from room temperature to 1050°C at a rate of 6°C / min for densification sintering. All other steps and parameters are the same as in Example 1.

[0083] Comparative Example 5:

[0084] This comparative example corresponds to Example 1 and aims to compare conventional long-process technology. The differences from Example 1 are: the grinding pressure of the air jet mill is adjusted to the conventional 0.40 MPa; a cold isostatic pressing (CIP) process with a pressure of 200 MPa is added after molding, followed by boxing and sintering; the remaining steps and parameters are the same as in Example 1.

[0085] Test Example 1-2:

[0086] Test Example 1: Process Control and Verification of Intermediate Physicochemical Properties

[0087] Intermediate products and final sintered bodies from the preparation processes of Examples 1-5 and Comparative Examples 1-3 were selected as test objects. For the fine powder samples after air jet milling, the angle between the inclined plane of the powder packing cone and the horizontal plane, i.e., the angle of repose, was measured using a powder comprehensive property tester according to ASTM D6393 standard to characterize the filling and flow characteristics of the powder in the mold. For the sintered block samples, the surface oxide layer was removed and samples were broken up and taken. The total carbon content was determined using a LECO CS844 high-frequency infrared carbon-sulfur analyzer. At the same time, the green body density was calculated by geometric measurement method, and the density of the sintered body was determined according to GB / T3850 standard using Archimedes' displacement method. The relevant test data are recorded in Table 1.

[0088] Table 1. Process parameters and physicochemical property test data

[0089]

[0090] Results and conclusions: The data in Table 1 show that the organic matter removal process and powder pretreatment method have a direct impact on the density and impurity content of the final product.

[0091] Regarding the control of carbon content, Examples 1 to 5 controlled the total carbon content of the sintered body within the range of 545 ppm to 672 ppm by introducing dynamic argon gas purging at a temperature range of 250°C to 350°C during the hydrogen decomposition stage. In contrast, Comparative Example 3 omitted the gas purging step, resulting in a carbon content that increased to 1380 ppm, and its sintering density was only 7.31 g / cm³. 3 This indicates that simple vacuum heating is insufficient to completely remove the adsorbed organic components. The residual organic matter decomposes at high temperatures to form carbides, which pin grain boundary migration and thus inhibit the sintering densification process. The dynamic gas sweeping process effectively removes the anchoring agent after ensuring its effectiveness, solving the problem of high-abundance rare-earth magnets being easily interfered with by carbon impurities.

[0092] Regarding the relationship between powder flowability and molding density, the powder in the example group maintained a stable angle of repose between 30.6° and 33.1°, demonstrating good flowability. Although Comparative Example 1 added an equal amount of oleic acid, the direct dispersion of oleic acid in all raw materials (total approximately 110 kg) resulted in extremely low lubricant coverage per unit particle surface, leading to insufficient lubrication and an increased angle of repose to 41.5°. Comparative Example 2, without any anchoring agent, exhibited the highest inter-powder friction, reaching an angle of repose of 44.2°. The poor flowability resulted in green body densities of Comparative Examples 1 and 2 below 4.0 g / cm³. 3 Furthermore, the final sintering density did not reach 7.50 g / cm³. 3 The densification standard.

[0093] The data from the examples confirm that targeted pretreatment of waste powder can improve the degassing and rearrangement capabilities of the powder with only a trace amount of organic anchoring agent. This improvement allows for the production of high-density green bodies and sintered bodies through molding alone, without the aid of cold isostatic pressing, verifying the industrial feasibility of this technical approach in simplifying molding processes and reducing equipment dependence.

[0094] Test Example 2: Comprehensive Evaluation of Magnetic Properties

[0095] The final sintered magnets prepared in Examples 1-5 and Comparative Examples 1-5 were selected as test samples. Each group of magnets was machined into cylindrical samples with dimensions of Φ10mm×10mm using an electrical discharge wire cutter, and the end faces were polished to remove the surface processing layer. Under a constant temperature environment of 20℃, a NIM-10000 high-temperature permanent magnet measuring instrument was used to perform the test according to the GB / T3217-2013 standard "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials," employing the method of demagnetization after closed-circuit saturation magnetization. Remanence (Br), intrinsic coercivity (Hcj), and maximum energy product ((BH)max) were recorded. Simultaneously, the squareness of the demagnetization curve (Hk / Hcj) was calculated, where Hk is the reverse magnetic field strength corresponding to the magnetic polarization intensity J decreasing to 0.9Br; this ratio characterizes the uniformity of the internal grain structure and composition distribution of the magnet.

[0096] Table 2. Statistical data of magnetic properties of sintered magnets

[0097]

[0098] Results and Conclusions: Table 2 shows the effects of different process routes on the microstructure and macroscopic magnetic properties of the magnet.

[0099] Data from Examples 1 to 5 show that magnets prepared using the process of this invention maintain a remanence of 13.12-13.35 kGs, an intrinsic coercivity generally reaching around 14 kOe, and a squareness consistently above 0.95. This performance improvement stems from the pre-powdering process, which effectively distributes Gd and Ho elements on the surface of oxygen-rich waste powder particles. During sintering, the surface-enriched rare earth elements preferentially react with oxides on the waste powder surface, repairing grain boundary defects, blocking the interference of oxides in the waste powder on the growth of the main phase grains, and achieving magnetic decoupling and structural homogenization of the microstructure.

[0100] Comparative Example 1, employing a direct mixing process for all raw materials, resulted in a remanence of 12.75 kGs and a coercivity of only 11.45 kOe. Gd and Ho elements diffused randomly into the LaCeFeB main phase lattice without auxiliary anchoring or stepwise processing. Due to the antiferromagnetic coupling between Gd and Ho and Fe, their entry into the main phase led to a decrease in saturation magnetization, causing a reduction in remanence. Simultaneously, the heavy rare earth elements failed to accumulate at grain boundaries, failing to effectively suppress the nucleation of antimagnetic domains, resulting in a relatively small increase in coercivity.

[0101] Comparative Example 2, without the addition of organic components, showed a decrease in squareness to 0.76. Due to the lack of physical adhesion, the modifier powder underwent component segregation during mixing and transportation, resulting in localized enrichment of heavy rare earth elements within the sintered body while other areas remained unmodified. This uneven component distribution caused a broadening of the grain inversion field distribution, macroscopically manifested as a collapsed demagnetization curve and decreased squareness.

[0102] Comparative Example 3 did not undergo effective gas-sweep decarburization, resulting in a squareness reduction to 0.62 and the lowest coercivity. The residual carbon reacted with rare earth elements at high temperatures to form carbides. These carbides consumed the rare earth elements used to form the liquid phase and became nucleation centers for antimagnetic domains, disrupting the continuity and cleanliness of the grain boundaries.

[0103] Comparative Example 4 eliminated the low-temperature reaction platform, and its coercivity and squareness were lower than those of the Example. This indicates that if there is insufficient time for the Gd and Ho hydrides to undergo a solid-phase displacement reaction with the oxide layer on the surface of the waste powder before the liquid phase appears, the residual oxide layer will hinder subsequent densification and grain boundary modification.

[0104] Comparative Example 5, using a cold isostatic pressing process, exhibited properties essentially identical to those of Example 1. This demonstrates that the powder obtained in Example 1 through air jet milling and organic modification possesses excellent filling characteristics. By omitting the cold isostatic pressing step, magnets with comparable performance can be manufactured solely through molding, validating the industrial application value of this approach in reducing manufacturing costs and simplifying processes.

Claims

1. A method for preparing a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet, characterized in that, include: The grain boundary controlled high-abundance lanthanum-cerium-iron-boron permanent magnet is made from raw materials comprising the following parts by weight: 100 parts of lanthanum-cerium-iron-boron rapid solidification casting sheets; 18-25 parts of modified pre-formed powder; The modified pre-formed powder is prepared by pre-mixing neodymium iron boron waste powder, rare earth modifier, and organic anchoring agent. The modified pre-formed powder is made from the following components in parts by weight: 100 parts of waste powder from a neodymium iron boron press; 8-15 parts of rare earth modifier; 0.06-0.08 parts of organic anchoring agent; The rare earth modifier is gadolinium-holmium alloy powder or gadolinium-holmium hydride powder, and the organic anchoring agent is oleic acid or zinc stearate powder. Neodymium iron boron waste powder, rare earth modifier and organic anchoring agent are mixed to obtain modified pre-formed powder; Lanthanum-cerium-iron-boron rapid solidification casting sheets and the modified pre-made powder are alternately loaded into a processing container in a layered structure. After hydrogen saturation, inert gas is purged during heating and dehydrogenation, followed by vacuum dehydrogenation to obtain hydrogen fragments. The hydrogen fragments are then ground by an air jet mill to obtain fine powder. The fine powder is pressed into a green blank under magnetic field orientation conditions. The green blank is then subjected to vacuum sintering and two-stage aging treatment to obtain the grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet. The layered structure is composed of alternating layers of lanthanum-cerium-iron-boron rapid-solidification cast sheets and modified pre-formed powder, with the bottom and top layers both being lanthanum-cerium-iron-boron rapid-solidification cast sheets.

2. The method for preparing a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet according to claim 1, characterized in that, The mixing is mechanical shear mixing under inert gas protection, with a mixing speed of 60-80 rpm and a time of 20-30 minutes; the organic anchoring agent is added by atomized spraying or direct feeding.

3. The method for preparing a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet according to claim 1, characterized in that, The inert gas purging process specifically involves: starting argon purging within the temperature range of 250-350℃, controlling the dynamic vacuum level of the environment at 300-500Pa, and purging for 60 minutes.

4. The method for preparing a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet according to claim 1, characterized in that, During the air jet milling process, the oxygen content of the air jet mill atmosphere is controlled to be 50-80 ppm, and the median particle size D50 of the fine powder is 4.2-4.4 μm.

5. The method for preparing a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet according to claim 1, characterized in that, The compression molding process only includes die molding, and the green density is controlled to be 4.15-4.25 g / cm³. 3 .

6. The method for preparing a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet according to claim 1, characterized in that, The vacuum sintering process includes two stages of heating: the first stage involves heating to 450-550℃ and holding for 90 minutes; the second stage involves heating to 1030-1060℃ and holding for 3-5 hours.

7. The method for preparing a grain boundary-controlled high-abundance lanthanum-cerium-iron-boron permanent magnet according to claim 1, characterized in that, The two-stage aging process is as follows: the first stage aging temperature is 660-680℃, and the holding time is 2-3 hours; the second stage aging temperature is 410-430℃, and the holding time is 3-4 hours.

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