A sintered NdFeB magnet containing high abundance of rare earth cerium and its preparation method

Abstract

This invention belongs to the field of rare earth permanent magnet material preparation technology, specifically relating to a sintered NdFeB magnet containing high abundance of rare earth cerium and its preparation method. The method includes: weighing raw materials according to atomic ratios to prepare an alloy; obtaining magnetic powder through a melting process, a rapid solidification process, a hydrogen breaking process, and an air jet milling process; the magnetic powder being oriented under a magnetic field, molded, and cold isostatically pressed to obtain a green blank; the green blank undergoing two-stage gradient sintering, followed by three-stage heat treatment and micro-nitriding treatment to prepare a sintered NdFeB magnet containing high abundance of rare earth cerium (Ce>6 wt.%). This invention can significantly improve the coercivity and temperature stability of Ce-containing magnets, achieving the requirements of a 42H / 45H high-performance grade.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet material preparation technology, specifically relating to a sintered NdFeB magnet containing high abundance of rare earth cerium and its preparation method. Background Technology

[0002] Sintered NdFeB permanent magnets are indispensable key functional materials in modern society. To reduce dependence on expensive Pr and Nd, and strategic resources Dy and Tb, partially replacing Pr and Nd with high-abundance, low-cost Ce has become an important research direction in the industry. However, the introduction of Ce severely degrades the intrinsic coercivity (H) of the magnet. cj The fundamental reasons for the low temperature stability of high-Ce magnets are: the formation of the CeFe2 phase reduces the volume fraction of the main phase; Ce atoms tend to segregate at grain boundaries, weakening the pinning ability of grain boundaries to magnetic domain flipping; and the magnetocrystalline anisotropy field of Ce-containing main phases is lower. These factors mean that magnets with high Ce content are usually only used in low- to mid-range grades (such as N35, N38, N42, etc.), and cannot meet the requirements of 42H, 45H and above grades, which have stringent high-temperature stability requirements, such as in electric vehicle voice coil speakers and air conditioning compressors.

[0003] To improve the performance of Ce-containing magnets, existing technologies often focus on composition design (e.g., dual alloying, adding heavy rare earth elements) or powder particle size distribution, or compensate for the insufficient coercivity of Ce-containing magnets by adding heavy rare earth elements Tb / Dy. cj The problem is that the content is ≥17kOe.

[0004] The existing technology has at least the following technical problems: It employs a dual-alloy process combining Ce-rich and Pr / Nd-rich alloys, attempting to improve coercivity by forming a core-shell structure. However, this method is complex, requires extremely high mixing uniformity, and the performance improvement is still insufficient when facing the demanding specifications of grades 42H / 45H. Furthermore, although adding expensive heavy rare earth elements Tb / Dy can improve the coercivity of the magnet, it inevitably leads to a significant increase in cost, overshadowing the core price advantage of highly rare earth-rich Ce magnets.

[0005] More importantly, existing conventional one-step sintering (directly sintering at high temperature) and simple high-temperature sintering followed by two-stage tempering heat treatment methods cannot finely optimize the microstructure of high-Ce magnets, which are sensitive systems prone to forming coarse grains and non-ideal grain boundary phases, to fully tap their performance potential.

[0006] Therefore, developing a novel method for preparing magnets with high abundance of rare earth cerium, with process innovation at its core, and fundamentally optimizing the grain size, grain boundary phase distribution and composition of high Ce magnets by precisely controlling the sintering densification process and subsequent phase transformation, thereby improving the coercivity of Ce magnets, is an effective and cost-effective way to break through its performance bottleneck and achieve high-performance 42H / 45H magnets. Summary of the Invention

[0007] The technical problem to be solved by this invention is to overcome the difficulty of achieving the 42H / 45H performance level in existing Ce-containing magnets without heavy rare earth elements. This invention provides a sintered NdFeB magnet with high abundance of rare earth element cerium and its preparation method. By innovatively combining multi-stage gradient sintering, multi-level heat treatment process with micro-nitriding treatment of magnet surface / grain boundary, the grains are significantly refined, the grain boundaries are optimized, and the surface magnetism is improved. This greatly enhances the coercivity and temperature stability of the Ce-containing magnet, enabling it to meet the requirements of the 42H / 45H high-performance level.

[0008] To achieve the above objectives, the present invention provides the following technical solution: In the first aspect, a method for preparing a sintered NdFeB magnet containing high abundance of rare earth cerium is provided, comprising the following steps: (1) According to the atomic ratio (Pr, Nd, Ce) x Fe y B z M w Weigh the raw materials and prepare the main alloy; where x, y, z, and w all represent atomic percentages: 29.0≤x≤32.0, 0.90≤z≤1.05, 0.1≤w≤3.0, with a remainder of y. M is selected from at least one of Co, Cu, Al, Ga, Zr, and Nb; The prepared main alloy is processed through smelting, rapid solidification, hydrogen breaking, and air jet milling to produce magnetic powder; (2) The magnetic powder obtained in step (1) is oriented by a magnetic field, molded and cold isostatically pressed to obtain a green blank; (3) The green body obtained in step (2) is subjected to two-stage gradient sintering; (4) The material obtained in step (3) is subjected to a three-stage heat treatment; (5) The material obtained in step (4) is subjected to micro-nitriding treatment. The treatment conditions include: 480~580℃ (e.g., 500℃, 520℃, 540℃, 550℃, 560℃) and in an inert mixed atmosphere (N2+Ar) with a nitrogen partial pressure of 1~100 Pa (e.g., 2Pa, 5Pa, 10Pa, 20Pa, 40Pa, 50Pa, 80Pa) for 0.5~2h (e.g., 1h, 1.5h); to prepare sintered NdFeB magnets containing rare earth cerium.

[0009] According to the preparation method provided by the present invention, in some embodiments, in the raw material preparation of step (1), Ce accounts for 20-30 at.% of the total rare earth (i.e., the percentage of Ce atoms in the total number of rare earth atoms); for example, 22 at.%, 24 at.%, 25 at.%, 26 at.%, 28 at.%. Or it can be understood that in (Pr, Nd, Ce), Ce accounts for 20-30 at.% (atomic percentage) of the total number of rare earth atoms, and the remainder is (Pr, Nd).

[0010] In some implementations, the process conditions of the smelting process in step (1) include: a smelting temperature of 1200~1500℃ (e.g., 1250℃, 1300℃, 1350℃, 1400℃, 1450℃) and a smelting time of 0.1~0.15 h.

[0011] In some implementations, the process conditions for the rapid solidification process in step (1) include: vacuum degree < 10 -2 Pa (e.g., 0.008 Pa, 0.005 Pa), and the belt-spinning speed is 1~2 m / s (e.g., 1.5 m / s).

[0012] In some implementations, the average particle size of the magnetic powder obtained in step (1) is 2.5~4.0 μm, for example, 2.6 μm, 2.8 μm, 3.0 μm, 3.05 μm, 3.2 μm, 3.5 μm, 3.6 μm, 3.8 μm.

[0013] According to the preparation method provided by the present invention, in some embodiments, in step (2), the magnetic field strength of the magnetic field orientation and pressing is 1.5~2.0 T (e.g., 1.6T, 1.8T), the pressure of cold isostatic pressing is 200~250 MPa (e.g., 210MPa, 220MPa, 240MPa), and the holding time is 5~10 min (e.g., 6 min, 8 min).

[0014] According to the preparation method provided by the present invention, in some embodiments, in the two-stage gradient sintering of step (3), the temperature is first raised to temperature T1 and held at this temperature for a period of time to perform the first stage sintering; subsequently, the temperature is rapidly raised to temperature T2 and held at this temperature for a period of time to perform the second stage sintering; wherein, The process conditions for the first stage sintering include: a vacuum degree of 0.005 Pa to 0.008 Pa; a temperature T1 of 950 to 1000℃ (e.g., 960℃, 980℃); a heating rate of 1 to 5℃ / min (e.g., 2℃ / min, 3℃ / min, 4℃ / min); and a holding time of 3 to 10 h (e.g., 4h, 5h, 6h, 8h). The process conditions for the second stage sintering include: a vacuum degree of 0.005 Pa to 0.008 Pa; a temperature T2 of 1020 to 1040 °C (e.g., 1025 °C, 1030 °C, 1035 °C); a heating rate of 10 to 20 °C / min (e.g., 12 °C / min, 14 °C / min, 15 °C / min, 18 °C / min); and a holding time of 1 to 3 h (e.g., 1.5 h, 2 h, 2.5 h).

[0015] According to the preparation method provided by the present invention, in some embodiments, in the three-stage heat treatment of step (4), The process conditions for the first-stage heat treatment include: a treatment temperature of 880~950℃ (e.g., 900℃, 910℃, 920℃, 940℃) and a treatment time of 1~3h (rapid cooling), e.g., 1.5h, 2h, 2.5h; The process conditions for the second-stage heat treatment include: a treatment temperature of 500~600℃ (e.g., 520℃, 540℃, 550℃, 580℃) and a treatment time of 1~3h, e.g., 1.5h, 2h, 2.5h; The process conditions for the third-stage heat treatment include: a treatment temperature of 400~480℃ (e.g., 420℃, 440℃, 450℃, 460℃) and a treatment time of 2~6h (furnace cooling), e.g., 2.5h, 3h, 3.5h, 4h, 4.5h, 5h.

[0016] In a second aspect, a sintered NdFeB magnet containing high abundance of rare earth cerium is provided, prepared by the method described above.

[0017] In some embodiments, the cerium (Ce) content in the neodymium iron boron magnet is greater than or equal to 6 wt.% (e.g., 6.2 wt.%, 6.5 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 12 wt.%, 15 wt.%, 18 wt.%, 20 wt.%).

[0018] Compared with the prior art, the beneficial effects of the technical solution of this application are at least as follows: By combining a unique low-temperature long-time pre-sintering with a high-temperature short-time main sintering, heat treatment, and micro-nitriding treatment, the coercivity and temperature stability of the magnets are significantly improved. Moreover, this method does not require complex alloy design or mixing processes, the process flow is stable, has good repeatability, and is suitable for mass production. Attached Figure Description

[0019] Figure 1 The performance test curves of the 42H grade magnet obtained in Embodiment 1 of this application are shown; Figure 2The performance test curves of the 45H grade magnet obtained in Embodiment 2 of this application are shown. Figure 3 The performance test curves of the N45 grade magnet obtained in Comparative Example 1 of this application are shown. Figure 4 A micrograph of the crystal phase of the 42H grade magnet obtained in Embodiment 1 of this application is shown; Figure 5 A micrograph of the crystal phase of the 45H grade magnet obtained in Embodiment 2 of this application is shown; Figure 6 A micrograph of the crystal phase of the N45 magnet obtained in Comparative Example 1 of this application is shown. Detailed Implementation

[0020] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments of the invention are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0021] A method for preparing Ce-rich rare earth 42H and 45H magnets involves a set of precisely controlled sintering and heat treatment processes to regulate the final microstructure of the magnets. The specific steps are as follows: (1) Alloy preparation and powder making: According to atomic ratio (Pr, Nd, Ce) x Fe y B z M w Weigh each raw material and mix them to prepare the main alloy, wherein: x, y, z, and w represent atomic percentages: 29.0 ≤ x ≤ 32.0, for example, x can take the values ​​29.5, 30, 30.5, 31, and 31.5; bal.y 0.90≤z≤1.05, for example, the value of z is 0.92, 0.95, 0.98, 1.0, 1.02; 0.1≤w≤3.0, for example, the value of w is 0.2, 0.5, 0.8, 1.0, 1.5, 1.8, 2.0, 2.5; M is selected from at least one of Co, Cu, Al, Ga, Zr and Nb; for example, a mixture of Co, Cu and Al, or a mixture of Co, Ga and Zr; Ce accounts for 20-30 at.% of the total number of rare earth elements, with the remainder being Pr and Nd; among which, Pr may account for 15-25 at.% for example. In preparing magnetic powder, the main alloy can be mixed with additives (e.g., zinc stearate as a lubricant). The amount of additive used can be a conventional choice in the art; The prepared main alloy is placed in a vacuum rapid solidification casting furnace and melted at 1200~1500℃ for 0.1~0.15h, and then smelted under a vacuum degree <10. -2 The magnetic powder is rapidly solidified under conditions of pa and a belt throwing speed of 1~2 m / s, then hydrogenated in a hydrogen crushing furnace and treated by air jet milling under nitrogen protection to obtain magnetic powder with an average particle size of 3.0~4.0μm.

[0022] (2) The obtained magnetic powder is oriented and molded under a magnetic field strength of 1.5~2.0 T, and then subjected to cold isostatic pressing under a pressure of 200~250 MPa for 5~10 min to obtain a green blank.

[0023] (3) Two-stage gradient sintering process: The resulting green compact is first held at a low temperature T1 (950~1000℃, heated at a rate of 1~5℃ / min) for a long time (3~10h); this first-stage sintering process aims to eliminate porosity and homogenize the composition through sufficient solid-phase diffusion, laying a uniform substrate for subsequent densification and inhibiting abnormal grain growth in the later stage. Subsequently, the temperature is rapidly increased to a higher temperature T2 (1020~1040℃, at a rate greater than 10℃ / min) and held at this temperature for a short time (1~3h); this second-stage sintering process utilizes the already formed uniform structure to quickly complete the final densification while avoiding excessive grain coarsening.

[0024] Both stages of gradient sintering were carried out under vacuum conditions of less than or equal to 0.008 Pa.

[0025] (4) Three-stage heat treatment: The magnets obtained in step (3) are processed sequentially as follows: i) Medium-high temperature annealing (processing temperature is 880~950℃, processing time is 1~3h, rapid cooling) is used to adjust the morphology and distribution of rare earth-rich phases at grain boundaries to make them continuous. ii) Medium-temperature aging (treatment temperature of 500~600℃, treatment time of 1~3h) is used to stabilize the main phase and some grain boundary phases; iii) Low-temperature aging (treatment temperature 400~480℃, treatment time 2~6h, furnace cooling) is used to further eliminate internal stress and stabilize magnetic properties.

[0026] This multi-stage heat treatment process can gradually and precisely optimize the phase structure in different temperature ranges. The first stage heat treatment is used to adjust the morphology and distribution of the rare earth-rich phase at the grain boundaries to make it continuous; the second stage heat treatment is used to stabilize the main phase and some grain boundary phases; the third stage heat treatment is used to further eliminate internal stress and stabilize magnetic properties. This multi-stage heat treatment process can gradually and precisely optimize the phase structure in different temperature ranges.

[0027] (5) Micro-nitriding treatment: After heat treatment, a medium-temperature treatment with controllable nitrogen partial pressure is introduced to carry out micro-nitrogen infiltration treatment; the conditions for micro-nitrogenation treatment are: 480~580℃, in an inert mixed atmosphere (N2+Ar) with nitrogen (N2) partial pressure of 1~100 Pa for 0.5~2h; sintered NdFeB magnets containing rare earth cerium are prepared.

[0028] Micro-nitriding creates a small number of strongly magnetically anisotropic surfaces that pin the domain walls, further enhancing coercivity. Simultaneously, micro-nitriding achieves weather-resistant passivation of grain boundaries, significantly reduces irreversible flux loss, and dramatically improves the stability of the magnet's performance.

[0029] The superior effects of the technical solution of this invention are at least as follows: 1) Process-driven microstructure optimization: Unlike existing technologies that focus on composition design, the core of this application lies in the unique system that combines low-temperature long-time pre-sintering with high-temperature short-time main sintering, three-stage heat treatment and micro-nitriding treatment. This system effectively avoids the rapid grain coarsening and compositional segregation that easily occur when high Ce magnets are directly sintered at high temperatures, and obtains fine and uniform main phase grains. At the same time, it forms a strongly magnetic anisotropic nitrided surface, forming NdN / Fe4N nanophases, pinning grain boundaries, inhibiting grain growth, and effectively suppressing surface demagnetization. This is the structural basis for ensuring that the magnet has high coercivity.

[0030] 2) Multi-stage heat treatment achieves precise control of grain boundaries: The three-stage heat treatment process targets the adjustment of grain boundary phase morphology, stabilization of the main phase, and stress elimination, respectively, which systematically optimizes the grain boundary characteristics, resulting in good grain size uniformity and clear grain boundary structure; it eliminates grain boundary defects, improves magnet density, and in particular promotes the formation of thin, continuous, and Pr / Nd-rich grain boundary phases, enhances the pinning strength of grain boundaries to antimagnetization domains, and significantly improves the coercivity and temperature stability of the magnet.

[0031] 3) Significant performance breakthrough: The preparation method of this application can stably improve the performance of magnets with Ce content (as a percentage of total rare earth content) in the range of 20~30 at.% to 42H (B r ≥13.0 kG, H cj ≥17.0 kOe) and even 45H (B r ≥13.4 kG, H cjWith a purity of ≥17.0 kOe, it achieves a balance between high abundance, low cost, and high performance of rare earth elements.

[0032] 4) High process compatibility and reliability: This application can be implemented on mainstream sintered NdFeB production equipment without the need for complex alloy design or mixing processes. The process flow is stable, has good repeatability, and is suitable for large-scale production.

[0033] The raw materials used in each embodiment and comparative example are all industrial pure metals or alloys, which are commercially available.

[0034] Example 1: The preparation of 42H grade magnets includes the following steps: (1) According to atomic ratio (Pr 0.15 Nd 0.55 Ce 0.3 ) 30.5 Fe bal B 1.0 Co 0.5 Cu 0.2 Al 0.3 Weigh out the raw materials and prepare the alloy, with Ce accounting for 30 at.% of the total rare earth elements.

[0035] The prepared alloy material was subjected to vacuum induction melting (melting temperature 1300℃, melting time 0.1h) at a vacuum degree <10 -2 Under conditions of Pa and a belt-spinning speed of 1.2 m / s, the magnetic powder was rapidly solidified and dehydrogenated by hydrogen crushing, and then air-milled under nitrogen protection until the average particle size of the magnetic powder was 3.2 μm. When preparing the magnetic powder, 0.01 wt% (based on the mass of the magnetic powder) of zinc stearate was added to it.

[0036] (2) The magnetic powder obtained in step (1) is oriented and pressed under a magnetic field of 1.8T, and then subjected to cold isostatic pressing at 200MPa for 5 minutes to obtain a green blank.

[0037] (3) The green billet is placed in a vacuum sintering furnace for two-stage gradient sintering: first, the temperature is raised to 980℃ at a heating rate of 2℃ / min and held for 6h (first stage pre-sintering); then the temperature is rapidly raised to 1020℃ at a heating rate of 15℃ / min and held for 2h (second stage main sintering); both stages of gradient sintering are carried out under a vacuum of 0.008 Pa; the sintered billet obtained after sintering is cooled with the furnace.

[0038] (4) The obtained sintered blank is subjected to three-stage heat treatment and micro-nitriding treatment: First, a three-stage heat treatment is performed: holding at 920℃ for 2 hours (medium-high temperature annealing), holding at 580℃ for 2 hours (medium temperature annealing), and then holding at 450℃ for 4 hours (low temperature annealing). Subsequently, a surface micro-nitriding treatment was performed: a mixture of Ar + 2% N2 gas was introduced into the furnace, the furnace pressure (nitrogen partial pressure) was controlled at 50 Pa, and the treatment was carried out at 480℃ for 2 hours. The resulting magnet product was cooled with the furnace.

[0039] The Ce content in the obtained magnet was 9.15 wt%.

[0040] The obtained magnet was processed into a test sample and tested using a NIM~10000H magnetic property measuring instrument; Test result: B r =13.03 kGs, H cj =17.43 kOe, (BH) max =40.71 MGOe (see Figure 1 (As shown in the test report), the irreversible demagnetization flux loss of the magnet after heating and recovery at 80°C is 2.7%. The magnet produced in this embodiment meets the performance requirements of grade 42H.

[0041] Example 2: The preparation of 45H grade magnets (including grain boundary structure adjustment) includes the following steps: (1) According to atomic ratio (Pr 0.25 Nd 0.55 Ce 0.2 ) 31.0 Fe bal B 1.02 Co 0.8 Ga 0.2 Zr 0.05 Weigh out the raw materials and prepare the alloy, with Ce accounting for 20 at.% of the total rare earth elements.

[0042] The steps for preparing the magnetic powder are the same as in Example 1, resulting in magnetic powder with an average particle size of 3.2 μm.

[0043] (2) The operation steps are the same as in Example 1 to obtain the green blank.

[0044] (3) The green billet is placed in a vacuum sintering furnace for two-stage gradient sintering: the steps are the same as in Example 1, except that the parameters are adjusted as follows: during the first stage of pre-sintering, the temperature is raised to 1000℃ at a heating rate of 2℃ / min and held for 4h; during the second stage of main sintering, the temperature is rapidly raised to 1030℃ at a heating rate of 15℃ / min and held for 1.5h; both stages of gradient sintering are carried out under a vacuum of 0.005~0.008 Pa; the sintered billet obtained after sintering is cooled with the furnace.

[0045] (4) The obtained sintered blank is subjected to three-stage heat treatment and micro-nitriding treatment: First, a three-stage heat treatment is performed: holding at 900℃ for 2 hours (medium-high temperature annealing, rapid cooling), holding at 580℃ for 2 hours (medium temperature aging), and then holding at 460℃ for 5 hours (low temperature aging). Subsequently, a surface micro-nitriding treatment was performed: a mixture of Ar + 2% N2 gas was introduced into the furnace, the furnace pressure (nitrogen partial pressure) was controlled at 50 Pa, and the temperature was maintained at 480℃ for 2 hours. The resulting magnet was then cooled with the furnace.

[0046] The Ce content in the obtained magnet was 6.2 wt%.

[0047] The obtained magnet was processed into a test sample and tested using a NIM~10000H magnetic property measuring instrument; Test result: B r =13.44 kGs, H cj =17.12 kOe, (BH) max =43.74 MGOe (see Figure 2 (As shown in the test report), the irreversible demagnetization flux loss of the magnet after heating and recovery at 80°C is 3.0%. The magnet produced in this embodiment meets the performance requirements of grade 45H.

[0048] Example 3: The preparation of 45H grade magnets (including grain boundary structure adjustment) includes the following steps: (1) The alloy preparation and magnetic powder preparation operations are the same as in Example 2; (2) The operation steps for preparing the green body are the same as in Example 2; (3) The green billet is placed in a vacuum sintering furnace for two-stage gradient sintering, the same as in Example 2; (4) The obtained sintered billet is subjected to three-stage heat treatment and micro-nitriding treatment, wherein: The operation steps for the third-stage heat treatment are the same as in Example 2; Surface micro-nitriding treatment: After three-stage heat treatment, a mixed gas of Ar + 2% N2 is introduced into the furnace, the furnace pressure is controlled at 50 Pa, and the treatment is carried out at 580℃ for 1 hour.

[0049] The Ce content in the obtained magnet was 6.2 wt%.

[0050] The obtained magnet was processed into a test sample and tested using a NIM~10000H magnetic property measuring instrument; Test result: B r =13.96 kGs, H cj =17.10 kOe, (BH) max =45.25 MGOe, the irreversible demagnetization flux loss of the magnet after heating and recovery at 80℃ is 3.2%. The magnet produced in this embodiment meets the performance requirements of grade 45H.

[0051] Comparative Example 1 (Conventional Process): (1) Alloy preparation and magnetic powder preparation are the same as in Example 2.

[0052] (2) The operation steps for preparing the green blank are the same as in Example 2.

[0053] (3) The green body is sintered using the conventional one-step method: under a vacuum of 0.008 Pa, the temperature is directly increased to 1040℃ at a heating rate of 5℃ / min and held for 3h.

[0054] (4) Conventional two-stage tempering: The material obtained in step (3) is kept at 920°C for 2 hours (rapid cooling), and then kept at 500°C for 2 hours (furnace cooling). The resulting magnet is cooled with the furnace.

[0055] The Ce content in the obtained magnet was 6.2 wt%.

[0056] The obtained magnet was processed into a test sample and tested using a NIM~10000H magnetic property measuring instrument; Test result: B r =13.43 kGs, H cj =13.07 kOe, (BH) max =42.61 MGOe (see Figure 3 (As shown in the test report), the irreversible demagnetization flux loss of the magnet after heating and recovery at 80°C was 6.5%. The performance is only equivalent to grade N45, far below that of grade 45H, and the coercivity of the magnet is significantly lower than that of Example 2.

[0057] Effect Analysis: Comparing Example 2 with Comparative Example 1, it can be seen that under the same high Ce content, the technical solution of this application, which combines multi-stage gradient sintering, multi-level heat treatment, and surface micro-nitriding treatment (Example), results in a higher coercivity (H) of the magnet compared to the traditional sintering and tempering process (Comparative Example). cj The magnet exhibited a significant improvement (from 13.07 kOe to 17.1 kOe), sufficient to upgrade its grade from N to H. Through a combination of multi-stage heat treatment and micro-nitriding of the magnet surface, the resulting magnet exhibited more uniform grain size and a clearer grain boundary structure, effectively suppressing abnormal grain growth (see appendix). Figures 4-5 Meanwhile, the thermal stability of the magnet was also significantly improved. Comparative Example 1, using a traditional sintering and tempering process, resulted in magnets with uneven grain size, failing to effectively suppress abnormal grain growth (see Appendix). Figure 6 This fully demonstrates the remarkable, albeit non-obvious, effect of the proposed process method on unlocking the performance potential of high-Ce magnets. It is key to achieving high-performance 42H / 45H levels without adding any heavy rare earth elements.

[0058] Comparative Example 2 (without micro-nitrogen permeation treatment): (1) Alloy preparation and magnetic powder preparation are the same as in Example 2.

[0059] (2) The operation steps for preparing the green blank are the same as in Example 2.

[0060] (3) Place the green billet into a vacuum sintering furnace for two-stage gradient sintering: the same as in Example 2; (4) Three-stage heat treatment was performed without surface micro-nitriding: The material obtained in step (3) was kept at 900℃ for 2 hours (medium-high temperature annealing, rapid cooling), then kept at 580℃ for 2 hours (medium temperature aging), and then kept at 460℃ for 5 hours (low temperature aging). The resulting magnet was cooled with the furnace.

[0061] The Ce content in the obtained magnet was 6.2 wt%.

[0062] The obtained magnet was processed into a test sample and tested using a NIM~10000H magnetic property measuring instrument; Test result: B r =13.41 kGs, H cj = 15.36 kOe, (BH) max = 42.85 MGOe, the irreversible demagnetization flux loss of the magnet after heating and recovery at 80℃ is 5.1%. The performance of this magnet only meets the requirements of grade N45 but does not meet the requirements of grade 45H.

[0063] Effect Analysis: Comparing Example 2 with Comparative Example 2, it is evident that under identical conditions of alloy composition, powder preparation, forming, sintering, and three-stage heat treatment, the absence of micro-nitriding treatment leads to a significant decrease in magnet coercivity and a marked deterioration in temperature stability. Micro-nitriding treatment can form strongly magnetically anisotropic nitrided pinned phases on the magnet surface and at grain boundaries, effectively suppressing the nucleation and growth of antimagnetic domains. Simultaneously, it passivates grain boundaries and reduces irreversible magnetic flux loss, making it a key process for upgrading Ce-rich rare-earth magnets from N45 to the high-performance 45H level.

[0064] Although the present invention has been described in detail through the preferred embodiments described above, it should be understood that the above description should not be considered as a limitation of the present invention. Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a sintered NdFeB magnet containing high abundance of rare earth cerium, characterized in that, Includes the following steps: (1) According to the atomic ratio (Pr, Nd, Ce) x Fe y B z M w Weigh the raw materials and prepare the main alloy; where x, y, z, and w all represent atomic percentages: 29.0≤x≤32.0, 0.90≤z≤1.05, 0.1≤w≤3.0, with a remainder of y. M is selected from at least one of Co, Cu, Al, Ga, Zr, and Nb; The prepared main alloy is processed through smelting, rapid solidification, hydrogen breaking, and air jet milling to produce magnetic powder; (2) The magnetic powder obtained in step (1) is oriented by a magnetic field, molded and cold isostatically pressed to obtain a green blank; (3) The green body obtained in step (2) is subjected to two-stage gradient sintering; (4) The material obtained in step (3) is subjected to a three-stage heat treatment; (5) The material obtained in step (4) is subjected to micro-nitriding treatment. The treatment conditions include: 480~580℃, in an inert mixed atmosphere with nitrogen partial pressure of 1~100 Pa for 0.5~2h; and a sintered NdFeB magnet containing rare earth cerium is prepared.

2. The preparation method according to claim 1, characterized in that, In step (1), Ce accounts for 20-30 at.% of the total rare earth content in the raw material preparation.

3. The preparation method according to claim 1, characterized in that, The process conditions for the smelting process in step (1) include: smelting temperature of 1200~1500℃ and smelting time of 0.1~0.15 h.

4. The preparation method according to claim 1, wherein the process conditions for the rapid solidification process in step (1) include: Vacuum degree <10 -2 Pa, the belt-spinning speed is 1~2 m / s.

5. The preparation method according to claim 1, characterized in that, The average particle size of the magnetic powder obtained in step (1) is 2.5~4.0μm.

6. The preparation method according to claim 1, characterized in that, In step (2), the magnetic field strength for magnetic field orientation and pressing is 1.5~2.0 T, the pressure for cold isostatic pressing is 200~250 MPa, and the holding time is 5~10 min.

7. The preparation method according to claim 1, characterized in that, In step (3), the two-stage gradient sintering process involves first heating to temperature T1 and holding at this temperature for a period of time for the first stage of sintering; then rapidly heating to temperature T2 and holding at this temperature for a period of time for the second stage of sintering; wherein, The process conditions for the first stage of sintering include: vacuum degree of 0.005 Pa to 0.008 Pa; temperature T1 of 950 to 1000℃; heating rate of 1 to 5℃ / min; and holding time of 3 to 10 h. The process conditions for the second stage sintering include: vacuum degree of 0.005 Pa to 0.008 Pa; temperature T2 of 1020 to 1040℃; heating rate of 10 to 20℃ / min; and holding time of 1 to 3 h.

8. The preparation method according to any one of claims 1-7, characterized in that, In the three-stage heat treatment described in step (4), The process conditions for the first-stage heat treatment include: a treatment temperature of 880~950℃ and a treatment time of 1~3 h; The process conditions for the second-stage heat treatment include: a treatment temperature of 500~600℃ and a treatment time of 1~3 h; The process conditions for the third-stage heat treatment include: a treatment temperature of 400~480℃ and a treatment time of 2~6 h.

9. A sintered NdFeB magnet containing high abundance of rare earth cerium, prepared by any one of claims 1-8.

10. The sintered NdFeB magnet containing high abundance of rare earth cerium according to claim 9, characterized in that, The cerium (Ce) content in this neodymium iron boron magnet is greater than or equal to 6 wt.%.

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