Anti-oxidation powder mixing method of neodymium-iron-boron permanent magnet material and application of anti-oxidation powder mixing method

Abstract

The invention discloses an anti-oxidation powder mixing method of a neodymium-iron-boron permanent magnet material and application of the anti-oxidation powder mixing method, and belongs to the technical field of preparation of neodymium-iron-boron permanent magnet materials. The powder mixing method comprises the steps of coarse powder anti-oxidation powder mixing, cooling aging, nitrogen protection airflow powder grinding, fine powder anti-oxidation powder mixing and cooling, an antioxidant is added through coarse powder and fine powder two stages, and anti-oxidation is achieved in combination with inert atmosphere protection and precise process control. Blank preparation is completed by taking the magnetic powder as a raw material through aging treatment, nitrogen protection orientation molding and waste anti-oxidation recovery; the neodymium iron boron permanent magnet material is prepared from the blank. The limitation of traditional single-stage anti-oxidation is broken through, the oxidation risk of the magnetic powder is reduced and the dispersity and forming performance of the magnetic powder are improved through full-process protection and process cooperation, and the prepared permanent magnet material is excellent in magnetic performance, easy to industrialize in process and high in practicability.

Description

Technical Field

[0001] This invention relates to the field of neodymium iron boron permanent magnet material preparation technology, specifically to an anti-oxidation powder mixing method for neodymium iron boron permanent magnet materials and its application. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnets, due to their superior magnetic properties, are widely used in strategic emerging industries such as new energy vehicles, wind power generation, and consumer electronics, making them an indispensable key material in modern industrial systems. In the preparation process of sintered NdFeB permanent magnets, the powder preparation and mixing processes directly determine the degree of oxidation, compositional uniformity, and subsequent forming performance of the magnetic powder, thus decisively influencing the intrinsic coercivity, remanence, and other core indicators of the final permanent magnet. However, neodymium in NdFeB alloys has extremely high chemical reactivity and readily reacts with oxygen in the air during powder processing to form neodymium oxide. This not only leads to a significant decrease in magnetic properties but may also trigger a chain reaction of problems such as powder agglomeration and insufficient forming density, becoming a core technological bottleneck restricting the development of the high-performance NdFeB industry.

[0003] In existing technologies, the industry has recognized the importance of oxidation prevention and has taken a series of measures. For example, nitrogen protective atmosphere is used in the air jet milling process to reduce the oxygen content inside the equipment; some processes add antioxidants in the fine powder stage to form a surface coating layer in an attempt to block the oxidation path. However, these measures still have significant technical shortcomings and are difficult to meet the stringent requirements of high-end NdFeB magnets for low oxygen content.

[0004] From the perspective of anti-oxidation timing, existing technologies generally focus on anti-oxidation measures during the fine powder stage, neglecting the oxidation risks during coarse powder processing. After hydrogen explosion treatment, coarse powder has a large number of active sites on its surface, which easily react with oxygen in the air during transportation and premixing to form an initial oxide layer. This oxide layer is further broken down and dispersed during subsequent air jet milling, resulting in the uniform distribution of oxidized impurities in the fine powder, ultimately reducing the coercivity of the magnet. Although some existing technologies mention coarse powder treatment, they only use simple vacuum sealing methods and do not form a systematic protection of anti-oxidant coating and aging stability, resulting in limited oxidation control effects.

[0005] Regarding atmosphere control, existing technologies mostly employ a single nitrogen protection mode, but this presents two major problems: first, the equipment's sealing performance deteriorates during the feeding stage of the air jet mill, allowing air infiltration and causing fluctuations in oxygen content; second, there is a lack of targeted oxygen content regulation mechanisms. Appropriate micro-oxygen supplementation can form a dense oxide film on the surface of fine powder, while excessive deoxidation can lead to excessively high powder activity, increasing the risk of oxidation in subsequent molding stages. Furthermore, atmosphere replacement before fine powder mixing often relies on experience-based judgment, without clearly defined venting time and pressure parameters, frequently resulting in incomplete replacement.

[0006] In terms of additive usage and process matching, existing technologies suffer from vague parameters and insufficient synergy. The amount of antioxidant added is either too low, leading to incomplete coating, or too high, resulting in increased carbon residue after sintering and affecting magnetic properties. Furthermore, the combined use of molding agents and antioxidants lacks theoretical guidance, often resulting in powder agglomeration or difficulties in demolding. The mixing time settings are also relatively simplistic, failing to differentiate based on the complexity of the fine powder composition. This leads to over-mixing of single-component fine powders causing particle breakage, or insufficient mixing of multi-component fine powders resulting in uneven composition.

[0007] In the application of magnetic powder, existing technologies lack sufficient control over the state of the magnetic powder before molding. After mixing, the magnetic powder carries a certain amount of processing stress, and direct molding can lead to uneven density within the magnet. Furthermore, the lack of timely regulations for waste disposal means that recyclable waste exposed to air for more than 30 minutes will have an increased oxygen content, severely impacting product consistency when used as backfill material. These issues collectively result in neodymium iron boron magnets produced using existing processes failing to simultaneously meet the dual requirements of high magnetic energy product and high-temperature stability in high-end applications such as new energy vehicle drive motors.

[0008] In summary, current NdFeB mixed powder anti-oxidation technology suffers from systemic defects such as "delayed anti-oxidation timing, crude atmosphere control, poor additive synergy, and disconnect between application processes." How to construct a complete anti-oxidation system from coarse powder pretreatment to magnetic powder forming and application, achieving precise control of oxidation levels and synergistic improvement of magnetic properties, has become a pressing technical challenge in this field. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides a method for anti-oxidation mixing of neodymium iron boron permanent magnet materials and its application. This invention solves problems such as delayed anti-oxidation and crude atmosphere control by using a two-stage anti-oxidation process involving both coarse and fine powders and precise oxygen control, thereby improving the performance of the magnetic powder.

[0010] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0011] A method for anti-oxidation mixing of neodymium iron boron permanent magnet materials includes the following steps:

[0012] (1) Coarse powder anti-oxidation mixing: The NdFeB alloy coarse powder is mixed with an anti-oxidant for the first time;

[0013] (2) First cooling and aging: The mixed coarse powder obtained in step (1) is cooled and then allowed to stand under a protective atmosphere or an inert atmosphere;

[0014] (3) Airflow milling: The coarse powder after step (2) is subjected to airflow milling under a nitrogen protective atmosphere. The oxygen content can be dynamically supplemented or adjusted according to at least one process parameter in the mill chamber, such as particle size, pressure or milling stage, to obtain fine powder.

[0015] (4) Fine powder anti-oxidation mixing and cooling: The fine powder obtained in step (3) is transferred to a sealed mixing equipment. After the air in the equipment is replaced by an inert gas, an anti-oxidant and a molding agent are added for the second mixing. After the second mixing is completed, the mixed fine powder is cooled and left to stand to obtain magnetic powder for NdFeB molding.

[0016] Preferably, in step (1), the amount of antioxidant added to the first mixed powder is 0.05% to 0.5% of the weight of the coarse powder.

[0017] Preferably, in step (2), the settling time is 4 to 24 hours.

[0018] Preferably, in step (3), the material is fed to the air jet mill by vibration feeding, and the amount of material fed at one time is 2~8kg.

[0019] Preferably, in step (3), during the air jet milling process, the oxygen content in the mill is supplemented or adjusted according to at least one process parameter in the mill chamber, such as particle size, pressure, or milling stage.

[0020] Preferably, in step (4), the air purging time of the inert gas replacement device is 10 to 30 minutes.

[0021] Preferably, in step (4), the amount of antioxidant added is 0.05% to 0.5% of the weight of fine powder, and the amount of molding agent added is 0.05% to 0.5% of the weight of fine powder.

[0022] Preferably, in step (4), the second mixing time is 60 to 180 minutes; the cooling and settling time is 1 to 6 hours.

[0023] A method for preparing a neodymium iron boron permanent magnet blank, using neodymium iron boron molding magnetic powder prepared by the method as raw material, includes the following steps:

[0024] S1. Aging treatment: The magnetic powder is left to stand in an inert or protective atmosphere for 12 to 48 hours before molding;

[0025] S2. Nitrogen-protected molding: The magnetic powder is oriented and pressed in a sealed molding equipment filled with an inert atmosphere, wherein the magnetizing current corresponding to the orientation magnetic field strength is not less than 60A.

[0026] S3. Waste disposal: Recyclable waste generated during the compression molding process is collected and vacuum-sealed within 30 minutes for use as repressed material.

[0027] Compared with the prior art, the present invention has the following advantages and technical effects:

[0028] The core innovation of this invention lies in overcoming the limitations of traditional powder mixing processes' "single-stage anti-oxidation" approach by proposing a two-stage anti-oxidation strategy involving coarse powder pretreatment and precise protection of fine powder. Traditional processes typically focus anti-oxidation measures after fine powder preparation, neglecting the oxidation risk of coarse powder during cooling aging and air jet milling. Neodymium in NdFeB alloys has extremely high chemical reactivity; even brief contact with air in an exposed environment can cause surface oxidation of the coarse powder. The resulting oxide layer breaks down and mixes with the fine powder during subsequent air jet milling, leading to a decrease in the overall magnetic properties of the magnetic powder. This invention introduces an antioxidant during the coarse powder stage for pre-protection, forming a dense chemical adsorption layer on the coarse powder surface, thus blocking the oxidation reaction at its source. Combined with inert atmosphere replacement and secondary anti-oxidation treatment during the fine powder stage, this creates a "double protective barrier."

[0029] The technical advantages of this invention are mainly reflected in the precise solution to the pain points of existing technologies. Its creativity lies not only in the breakthrough of technical concept, but also in the collaborative design of process details, which enables the technical solution to be directly adapted to the needs of industrial production and solves many practical problems that have long plagued the industry.

[0030] Firstly, this invention effectively solves the problem of "delayed oxidation prevention" in traditional processes, achieving full-process control of oxidation risks. In existing technologies, most anti-oxidation measures begin after the fine powder preparation is completed, while the long-term static setting during the cooling and aging of coarse powder and the atmospheric fluctuations during the air jet milling process can become "windows" for potential oxidation risks. This invention moves the anti-oxidation intervention point forward to the coarse powder stage. Through the full combination of the anti-oxidant and coarse powder during the first powder mixing process, the anti-oxidant molecules are uniformly attached to the surface of the coarse powder particles, continuously exerting a protective effect during the subsequent cooling and aging process. In the air jet milling stage, a combination of nitrogen protective atmosphere and dynamic oxygen content adjustment is used, which not only avoids the problem of low efficiency of air jet milling under a purely inert atmosphere, but also prevents excessive oxidation of fine powder through precise oxygen control, achieving a balance between protection and efficiency. This full-process risk control mechanism ensures that the magnetic powder is in a stable anti-oxidation environment at each process stage, completely solving the industry pain point of "the transmission of potential oxidation risks from the preceding process to subsequent processes" in traditional processes, and improving the batch stability of magnetic powder.

[0031] Secondly, this invention solves the problem of poor compatibility between anti-oxidation and molding in traditional processes, achieving synergistic optimization of anti-oxidation effect and molding performance. In traditional processes, the addition of antioxidants and molding agents often interferes with each other—some antioxidants affect the dispersibility of the molding agent, leading to decreased magnetic powder flowability during pressing and molding, resulting in uneven blank density and cracking; while prioritizing molding performance sacrifices anti-oxidation effect. This invention clarifies the differentiated application logic of antioxidants in the coarse and fine powder stages. In the coarse powder stage, the antioxidant focuses on "long-term protection," while in the fine powder stage, it balances anti-oxidation and molding synergy. With the precise addition of the molding agent, the antioxidant and molding agent are uniformly dispersed in an inert atmosphere, ensuring the antioxidant capacity of the fine powder before storage and molding, while also improving the flowability and molding density of the magnetic powder. This solves the long-standing technical contradiction of difficulty in balancing anti-oxidation and easy molding, providing a stable raw material guarantee for the subsequent preparation of permanent magnet blanks.

[0032] Thirdly, the process design of this invention has high industrial adaptability, solving the problems of "poor versatility and difficulty in waste recycling" in traditional processes. Existing anti-oxidation processes are often designed for specific specifications of magnetic powder, lacking adaptability to multi-component mixed fine powders, and the waste generated during the pressing process is difficult to recycle effectively due to the high risk of oxidation. This invention, through a differentiated design of the second mixing time, formulates mixing strategies for single-component and multi-component fine powders respectively, ensuring that fine powders of different systems can achieve uniform coating of anti-oxidant; at the same time, in the magnetic powder application stage, a timely vacuum sealing process for waste is clearly defined, preventing waste oxidation by isolating it from air, so that the returned material can still maintain stable performance, which reduces production costs and improves resource utilization, adapting to the needs of large-scale industrial production.

[0033] From a technical perspective, the dual-stage anti-oxidation system of this invention effectively reduces the oxygen content of the magnetic powder, preventing the formation of oxide phases and thus improving the magnetic properties of the final permanent magnet blank. Simultaneously, the atmosphere control and anti-oxidation design throughout the process reduce particle agglomeration, improve powder dispersibility, and result in a more uniform density in the pressed blank, reducing the risk of cracking during subsequent sintering. Furthermore, the process steps of this invention are clear and controllable, requiring no large-scale modification of existing production equipment, enabling industrial application and demonstrating significant economic value and promising prospects for technological promotion. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0035] A method for anti-oxidation mixing of neodymium iron boron permanent magnet materials includes the following steps:

[0036] (1) Coarse powder anti-oxidation mixing: The NdFeB alloy coarse powder is mixed with an anti-oxidant for the first time;

[0037] (2) First cooling and aging: The mixed coarse powder obtained in step (1) is cooled and then allowed to stand under a protective atmosphere or an inert atmosphere;

[0038] (3) Air jet milling: The coarse powder processed in step (2) is subjected to air jet milling under a nitrogen protective atmosphere to obtain fine powder;

[0039] (4) Fine powder anti-oxidation mixing and cooling: The fine powder obtained in step (3) is transferred to a sealed mixing equipment. After the air in the equipment is replaced by an inert gas, an anti-oxidant and a molding agent are added for the second mixing. After the second mixing is completed, the mixed fine powder is cooled and left to stand to obtain magnetic powder for NdFeB molding.

[0040] The mechanisms of action of each preparation step are as follows:

[0041] The synergistic effect of each preparation step and raw material in this invention constructs an anti-oxidation and performance optimization system that blocks oxidation at the source, controls the process, and enhances the final stage. The precise selection of process parameters at each stage enables the raw material effect and process advantages to form a superimposed effect, achieving technical effects beyond the expected timeframe.

[0042] The coarse powder mixing step is the primary line of defense against oxidation, with its core function being the pre-adsorption of the antioxidant. The highly reactive neodymium element in NdFeB coarse powder readily reacts with oxygen. The antioxidant forms a chemical adsorption layer on the surface of the coarse powder through intermolecular forces. This adsorption layer fills the micropores and defects on the surface of the coarse powder, spatially blocking oxygen molecules from contacting the metal matrix. The key to the process design of this step is early intervention for protection, avoiding the accumulation of oxidation risks in the coarse powder stage of traditional processes, and laying a low-oxidation foundation for subsequent processes.

[0043] The first cooling and aging step serves a "protective stabilization" function. The cooling process lowers the temperature of the coarse powder to room temperature, preventing high temperatures from accelerating the oxidation reaction; the static aging provides sufficient time for the antioxidant to interact with the surface of the coarse powder, promoting the transformation of the adsorption layer from physical adsorption to chemical adsorption, forming a denser and more stable protective film. The core logic for selecting parameters in this step is to balance cooling efficiency and adsorption stability, ensuring the protective film is fully formed through a reasonable static aging time, providing "conformal protection" against particle breakage during the air jet milling process.

[0044] The core of air jet milling is the synergy between protection and efficiency. A nitrogen protective atmosphere creates an inert environment, inhibiting oxidation of the newly formed surfaces of fine powder. Vibration feeding ensures uniform feeding, preventing localized increases in oxygen concentration caused by material accumulation within the mill chamber. Dynamic oxygen content adjustment is a key innovation. By precisely controlling the oxygen content, trace amounts of oxygen are used to promote particle surface passivation while avoiding excessive oxidation, achieving a balance between air jet mill efficiency and anti-oxidation effects. This solves the problem of low grinding efficiency under traditional purely inert atmospheres.

[0045] The fine powder mixing and the second cooling step form a final enhanced protection. Inert atmosphere replacement thoroughly removes air from the equipment, eliminating oxidizing agents. The secondary addition of antioxidants forms a double barrier with the protective layer from the coarse powder stage, while also working synergistically with the forming agent—the antioxidant improves the dispersibility of the forming agent on the surface of the fine powder, while the forming agent reduces fine powder agglomeration through lubrication, ensuring uniform coating of the particles by the antioxidant. Cooling and settling further stabilize the protective film structure, ensuring stable performance during magnetic powder storage and forming processes.

[0046] Each step in the application process achieves "performance maintenance and resource optimization." Aging treatment releases internal stress in the magnetic powder, ensuring molding consistency; nitrogen protection during molding prevents oxidation; and vacuum encapsulation of waste materials preserves their reusability by isolating them from air, forming a closed-loop process. The synergy between raw materials and process steps creates a positive interaction between oxidation prevention, molding performance, and resource utilization.

[0047] To make the present invention more fully disclosed, more specific embodiments are described below.

[0048] Example 1

[0049] (1) Coarse powder mixing: Take NdFeB alloy coarse powder, add 0.2% of the weight of the coarse powder as an antioxidant, and place it in a mixer for the first mixing. The mixing speed is 300 r / min.

[0050] (2) First cooling and aging: The mixed coarse powder was naturally cooled to room temperature and then allowed to stand for 12 hours under a nitrogen atmosphere;

[0051] (3) Airflow milling: The coarse powder after cooling and aging is fed into the airflow mill by vibration feeding. The single feeding amount is 5kg. Nitrogen is used as the protective atmosphere. During the airflow milling process, when the particle size in the mill chamber drops to 5μm, a trace amount of oxygen is added to adjust the oxygen content. After the particle size stabilizes, oxygen supplementation is stopped to obtain fine powder.

[0052] (4) Fine powder mixing and second cooling: The fine powder is transferred into a sealed mixing equipment, and nitrogen is introduced to purge the air in the equipment for 20 minutes; then, 0.3% of the weight of the fine powder is added as an antioxidant and 0.3% as a molding agent, and the second mixing is carried out (mixing time is 90 minutes); after the mixing is completed, the powder is cooled and left to stand for 3 hours to obtain the magnetic powder for NdFeB molding.

[0053] (5) Magnetic powder application: The magnetic powder is left to stand in a nitrogen atmosphere for 24 hours to complete the aging treatment; it is then transferred to a sealing molding equipment, nitrogen is introduced until the oxygen content in the equipment is less than 0.1%, and a 70A magnetizing current is used to provide an orientation magnetic field for orientation pressing molding; the recyclable waste generated during the molding process is collected and vacuum sealing is completed within 30 minutes.

[0054] Example 2

[0055] (1) Coarse powder mixing: Take two different NdFeB alloy coarse powders (weight ratio 1:1) and mix them. Add an antioxidant accounting for 0.5% of the weight of the mixed coarse powder and place it in a mixer for the first mixing. The mixing speed is 350 r / min.

[0056] (2) First cooling and aging: The mixed coarse powder was forced to cool to room temperature and then allowed to stand for 24 hours under a nitrogen atmosphere;

[0057] (3) Airflow milling: The coarse powder after cooling and aging is fed into the airflow mill by vibration feeding. The single feeding amount is 8kg. Nitrogen is used as the protective atmosphere. The oxygen content in the mill chamber is monitored throughout the airflow milling process. The oxygen supply is dynamically adjusted according to the degree of particle refinement to obtain fine powder.

[0058] (4) Fine powder mixing and second cooling: The fine powder is transferred into a sealed mixing equipment, and nitrogen is introduced to purge the air in the equipment for 30 minutes; then, 0.5% of the weight of the fine powder is added as an antioxidant and 0.5% as a molding agent, and the second mixing is carried out (mixing time is 150 minutes); after the mixing is completed, the powder is cooled and left to stand for 6 hours to obtain the magnetic powder for NdFeB molding.

[0059] (5) Magnetic powder application: The magnetic powder is left to stand for 48 hours under an argon atmosphere to complete the aging treatment; it is then transferred to a sealing molding equipment, nitrogen is introduced until the oxygen content in the equipment is less than 0.1%, and an orientation magnetic field is provided with an 80A magnetizing current to perform orientation pressing molding; the recyclable waste generated during the molding process is collected and vacuum sealing is completed within 20 minutes.

[0060] Example 3

[0061] (1) Coarse powder mixing: Take NdFeB alloy coarse powder, add 0.05% of antioxidant by weight of coarse powder, and place it in a mixer for the first mixing. The mixing speed is 280 r / min.

[0062] (2) First cooling and aging: The mixed coarse powder was naturally cooled to room temperature and then allowed to stand for 4 hours under a nitrogen atmosphere;

[0063] (3) Airflow milling: The cooled and aged coarse powder is fed into the airflow mill by vibration feeding. The single feeding amount is 2kg. Nitrogen is used as the protective atmosphere. During the airflow milling process, only a trace amount of oxygen is added in the initial crushing stage of the particles to obtain fine powder.

[0064] (4) Fine powder mixing and second cooling: Transfer the fine powder into a sealed mixing equipment, purge the air in the equipment with nitrogen for 10 minutes; then add 0.05% antioxidant and 0.05% molding agent by weight of fine powder, and carry out the second mixing (mixing time 60 minutes); after the mixing is completed, cool and let stand for 1 hour to obtain NdFeB molding magnetic powder;

[0065] (5) Magnetic powder application: The magnetic powder is left to stand for 12 hours in a nitrogen atmosphere to complete the aging treatment; it is then transferred to a sealing molding equipment, nitrogen is introduced until the oxygen content in the equipment is less than 0.1%, and a 60A magnetizing current is used to provide an orientation magnetic field for orientation pressing molding; the recyclable waste generated during the molding process is collected and vacuum sealing is completed within 15 minutes.

[0066] Example 4

[0067] (1) Coarse powder pretreatment: Take the coarse powder from the NdFeB waste and sieve it through a 200-mesh screen to remove impurities;

[0068] (2) Coarse powder mixing: Add 0.3% of the weight of antioxidant to the sieved coarse powder and place it in a mixer for the first mixing. The mixing speed is 320 r / min.

[0069] (3) First cooling and aging: The mixed coarse powder was naturally cooled to room temperature and then allowed to stand for 18 hours under a nitrogen atmosphere;

[0070] (4) Airflow milling: The coarse powder after cooling and aging is fed into the airflow mill by vibration feeding. The single feeding amount is 6 kg. Nitrogen is used as the protective atmosphere. During the airflow milling process, the oxygen supply is adjusted according to the pressure change in the mill chamber to obtain fine powder.

[0071] (5) Fine powder mixing and second cooling: The fine powder is transferred into a sealed mixing equipment, and nitrogen is introduced to purge the air in the equipment for 25 minutes; then, 0.4% of the weight of the fine powder is added as an antioxidant and 0.4% as a molding agent, and the second mixing is carried out (mixing time is 120 minutes); after the mixing is completed, the powder is cooled and left to stand for 4 hours to obtain the magnetic powder for NdFeB molding.

[0072] (6) Magnetic powder application: The magnetic powder is left to stand in a nitrogen atmosphere for 36 hours to complete the aging treatment; it is then transferred to a sealing molding equipment, nitrogen is introduced until the oxygen content in the equipment is less than 0.1%, and a 75A magnetizing current is used to provide an orientation magnetic field for orientation pressing molding; the recyclable waste generated during the molding process is collected and vacuum sealing is completed within 25 minutes.

[0073] Example 5

[0074] (1) Coarse powder mixing: Take high neodymium content (neodymium element content ≥30%) neodymium iron boron alloy coarse powder, add 0.4% of antioxidant by weight of coarse powder, place it in a mixer for the first mixing, and mix at a speed of 400 r / min;

[0075] (2) First cooling and aging: The mixed coarse powder is forced to cool to below 50°C and then allowed to stand for 20 hours under a nitrogen atmosphere;

[0076] (3) Airflow milling: The coarse powder after cooling and aging is fed into the airflow mill by vibration feeding. The single feeding amount is 4kg. Nitrogen is used as the protective atmosphere. During the airflow milling process, a segmented oxygen supplementation strategy is adopted. The oxygen content is adjusted three times according to the particle size change to obtain fine powder.

[0077] (4) Fine powder mixing and second cooling: The fine powder is transferred into a sealed mixing equipment, and nitrogen is introduced to purge the air in the equipment for 25 minutes; then, 0.4% of the weight of the fine powder is added as an antioxidant and 0.2% as a molding agent, and the second mixing is carried out (mixing time is 180 minutes); after the mixing is completed, the powder is cooled and left to stand for 5 hours to obtain the magnetic powder for NdFeB molding.

[0078] (5) Magnetic powder application: The magnetic powder is placed in a nitrogen and argon mixed atmosphere (volume ratio 1:1) for 30 hours to complete the aging treatment; it is then transferred to a sealing molding equipment, nitrogen is introduced until the oxygen content in the equipment is less than 0.05%, and a 90A magnetizing current is used to provide an orientation magnetic field for orientation pressing molding; the recyclable waste generated during the molding process is collected and vacuum sealing is completed within 20 minutes.

[0079] Comparative Example 1

[0080] Step (1) Coarse powder mixing: Take the same NdFeB alloy coarse powder as in Example 1, without adding an antioxidant, and directly perform air mixing; the process parameters for the remaining steps are the same as in Example 1.

[0081] Comparative Example 2

[0082] Step (3) Airflow milling: Pure nitrogen is used as the protective atmosphere, and no oxygen content is replenished or adjusted throughout the process. The process parameters for the remaining steps are the same as in Example 1.

[0083] Comparative Example 3

[0084] Step (5) Magnetic powder application: Magnetic powder is directly molded without aging treatment; molding waste is naturally piled up without vacuum sealing, and the process parameters of the remaining steps are the same as in Example 1.

[0085] Examples, comparative data results, and theoretical analysis

[0086] (a) Test Results

[0087] The test data results of Examples 1-5 and Comparative Examples 1-3 of the present invention are shown in Table 1.

[0088]

[0089] Note: 1. The oxygen content of the magnetic powder was determined by pulsed infrared absorption method, and the unit is % .

[0090] 2. Remanence (Br) was measured using a permanent magnet material measuring instrument, and the unit is T;

[0091] 3. Compressive strength was determined using a universal testing machine, and the unit is MPa;

[0092] 4. The dispersibility of magnetic powder is determined by a laser particle size analyzer and expressed as a uniformity coefficient (the closer the coefficient is to 1, the better the dispersibility).

[0093] (II) Theoretical Analysis

[0094] 1. Analysis of Antioxidant Performance

[0095] The oxygen content of the magnetic powder in Examples 1-5 ranged from 0.14% to 0.19%, with Example 1 having an oxygen content as low as 0.14%, while the lowest oxygen content in Comparative Examples 1-3 was 0.32%. The oxygen content of Example 1 was reduced by 82.9% compared to Comparative Example 1, 74.5% compared to Comparative Example 2, and 56.25% compared to Comparative Example 3. This advantage stems from the synergistic mechanism of the present invention's two-stage anti-oxidation and full-process atmosphere control: the anti-oxidant added in the coarse powder stage forms an initial protective film on the particle surface through chemical adsorption, filling surface defects of the coarse powder and blocking oxygen molecule contact; the cooling and aging process promotes the transformation of the protective film from physical adsorption to chemical adsorption, forming a more stable and dense structure. In the fine powder stage, the inert atmosphere is first replaced to thoroughly remove the oxidizing medium, and the second-added anti-oxidant targets the newly active surface generated by the air jet mill for targeted protection. When working synergistically with the forming agent, the lubricating and dispersing effect of the forming agent ensures that the anti-oxidant uniformly coats each fine powder particle, avoiding local protection blind spots.

[0096] In contrast, Comparative Example 1, because antioxidants were only added in the fine powder stage, the oxidation risks accumulated in the coarse powder stage could not be eliminated, and the newly formed surface of the fine powder was not protected in time, resulting in a sharp increase in oxygen content; Comparative Example 2, without dynamic oxygen control in the air jet mill stage, the active surface generated by the crushing of fine powder under a pure nitrogen atmosphere was prone to oxidation, and at the same time, the lack of passivation effect promoted by trace oxygen greatly reduced the protective effect; Comparative Example 3 omitted the aging before magnetic powder forming and the vacuum sealing of waste materials, and the magnetic powder was in continuous contact with oxygen before forming and during waste material storage, further increasing the overall oxygen content.

[0097] 2. Magnetic properties (remanence Br) analysis

[0098] The remanence of the permanent magnet blanks in Examples 1-5 ranged from 1.35T to 1.43T. Example 5, due to its optimized process for high NdFeB coarse powder, achieved a remanence as high as 1.43T, while the highest remanence in Comparative Examples 1-3 was only 1.28T. The remanence of Example 5 was 27.68% higher than Comparative Example 1, 17.21% higher than Comparative Example 2, and 11.72% higher than Comparative Example 3. The key to this improved remanence lies in the precise control of the oxidation degree and particle uniformity of the magnetic powder: low oxygen content prevents the NdFeB main phase from being oxidized into a non-magnetic oxide phase, ensuring the integrity of the magnetic domain structure and reducing magnetic performance loss; premixing in the coarse powder stage and targeted mixing in the fine powder stage result in a uniform particle size distribution, more regular particle arrangement during molding, and improved orientation, thereby enhancing remanence. The synergistic effect of antioxidants and forming agents is crucial. Antioxidants maintain the intrinsic magnetic properties of magnetic powder, while forming agents improve particle flowability, making it easier for magnetic powder to align along the direction of the magnetic field in the orientation magnetic field, thus avoiding orientation disorder caused by particle agglomeration.

[0099] In contrast, the high oxygen content in Comparative Example 1 caused a large amount of the main phase to be oxidized, reducing the number of magnetic domains and significantly decreasing remanence. In Comparative Example 2, the lack of controlled oxygen in the air jet mill led to localized oxidation of the fine powder, while the uneven particle refinement and poor orientation consistency limited the improvement of remanence. In Comparative Example 3, the magnetic powder was not aged before molding, and the internal stress of the particles caused disordered magnetic domain orientation. Furthermore, the secondary oxidation caused by the lack of vacuum sealing of the waste further weakened the magnetic properties, resulting in a lower improvement in remanence than in the examples.

[0100] 3. Molding performance analysis

[0101] The compressive strength of the permanent magnet blanks in Examples 1-5 ranged from 202 MPa to 219 MPa, and the uniformity coefficient of magnetic powder dispersion was all below 1.15. In contrast, the highest compressive strength of Comparative Examples 1-3 was only 181 MPa, and the lowest uniformity coefficient was 1.25. The compressive strength of Example 1 was increased by 50.34% compared to Comparative Example 1, 29.76% compared to Comparative Example 2, and 20.44% compared to Comparative Example 3. The uniformity coefficient of dispersion was decreased by 28.9% compared to Comparative Example 1, 21.74% compared to Comparative Example 2, and 13.6% compared to Comparative Example 3. The advantages in compressive strength and dispersibility stem from the synergistic optimization of the process and raw materials: the addition of forming agents reduces the friction coefficient between particles, resulting in more uniform dispersion of the magnetic powder, optimized uniformity coefficient, and tighter contact between particles during molding, reducing voids and defects; dual-stage anti-oxidation prevents oxidation products from forming brittle interfaces between particles, enhancing the bonding force between particles; aging treatment before magnetic powder molding releases internal stress in the particles, reducing stress concentration in the molded blank and lowering the risk of crack initiation. Vibration feeding and dynamic powder mixing time control further ensure uniform particle size and composition distribution, making stress transmission more uniform when the blank is under stress, avoiding damage caused by local stress concentration.

[0102] In contrast, Comparative Example 1 suffered from severe oxidation of the magnetic powder, resulting in a large number of brittle oxides between particles, weak bonding force, and poor dispersibility, leading to numerous molding voids and extremely low compressive strength. Comparative Example 2, with its uncontrolled oxygenation in the air jet mill, resulted in uneven oxidation of the fine powder, affecting dispersibility and bonding force, and insufficient improvement in compressive strength. Comparative Example 3, by omitting the aging treatment, resulted in high internal stress in the blank, and the impurities introduced by the improperly treated waste further damaged the structural integrity, making its compressive strength and dispersibility inferior to the examples.

[0103] The above description, in conjunction with preferred embodiments, provides a further detailed explanation of the present invention and should not be construed as limiting the specific implementation of the invention to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the inventive concept, and all such substitutions or modifications should be considered within the scope of protection of the present invention.

[0104] Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention. Furthermore, the scope of the invention is not limited to the specific embodiments of the processes, manufactures, compositions of matter, methods, and steps described in the specification. From the disclosure of this invention, those skilled in the art will readily utilize existing or future processes, manufactures, compositions of matter, methods, or steps that substantially perform the same function or achieve the same results as the corresponding embodiments described herein. Therefore, the appended claims are intended to encompass such processes, manufactures, compositions of matter, methods, or steps.

Claims

1. A method for anti-oxidation mixing of neodymium iron boron permanent magnet materials, characterized in that, Includes the following steps: (1) Coarse powder anti-oxidation mixing: The NdFeB alloy coarse powder is mixed with an anti-oxidant for the first time; (2) First cooling and aging: The mixed coarse powder obtained in step (1) is cooled and then allowed to stand under a protective atmosphere or an inert atmosphere; (3) Air jet milling: The coarse powder processed in step (2) is subjected to air jet milling under a nitrogen protective atmosphere to obtain fine powder; (4) Fine powder anti-oxidation mixing and cooling: The fine powder obtained in step (3) is transferred to a sealed mixing equipment. After the air in the equipment is replaced by an inert gas, an anti-oxidant and a molding agent are added for the second mixing. After the second mixing is completed, the mixed fine powder is cooled and left to stand to obtain magnetic powder for NdFeB molding.

2. The method for anti-oxidation mixing of neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step (1), the amount of antioxidant added to the first mixed powder is 0.05% to 0.5% of the weight of the coarse powder.

3. The method for anti-oxidation mixing of neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step (2), the settling time is 4 to 24 hours.

4. The method for anti-oxidation mixing of neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step (3), the material is fed to the air jet mill by vibration feeding, and the amount of material fed at one time is 2~8kg.

5. The method for anti-oxidation mixing of neodymium iron boron permanent magnet material according to claim 4, characterized in that, In step (3), during the air jet milling process, the oxygen content in the mill is supplemented or adjusted according to at least one process parameter in the mill chamber, such as particle size, pressure, or milling stage.

6. The method for anti-oxidation mixing of neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step (4), the air purging time of the inert gas replacement equipment is 10 to 30 minutes.

7. The method for anti-oxidation mixing of neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step (4), the amount of antioxidant added is 0.05% to 0.5% of the weight of fine powder, and the amount of molding agent added is 0.05% to 0.5% of the weight of fine powder.

8. The method for anti-oxidation mixing of neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step (4), the second mixing time is 60 to 180 minutes; the cooling and settling time is 1 to 6 hours.

9. A method for preparing a neodymium iron boron permanent magnet material blank, characterized in that, Using the NdFeB molding magnetic powder prepared by the method according to any one of claims 1-8 as a raw material, the process includes the following steps: S1. Aging treatment: The magnetic powder is left to stand in an inert or protective atmosphere for 12 to 48 hours before molding; S2. Nitrogen-protected molding: The magnetic powder is oriented and pressed in a sealed molding equipment filled with an inert atmosphere, wherein the magnetizing current corresponding to the orientation magnetic field strength is not less than 60A. S3. Waste disposal: Recyclable waste generated during the compression molding process is collected and vacuum-sealed within 30 minutes for use as repressed material.

10. The application of a neodymium iron boron molding magnetic powder prepared by any one of claims 1-8 in the preparation of neodymium iron boron permanent magnet materials.

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