High-performance sintered neodymium-iron-boron magnet without heavy rare earth and preparation method thereof

Abstract

The application belongs to the technical field of rare earth permanent magnet material preparation, and relates to a heavy rare earth-free high-performance sintered neodymium-iron-boron magnet and a preparation method thereof. 13 The formation and uniform distribution of the M phase effectively promote the stable obtaining of high coercivity and excellent demagnetization stability without containing heavy rare earth.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet material preparation technology, and relates to a high-performance sintered NdFeB magnet without heavy rare earth and its preparation method. Background Technology

[0002] In recent years, the high-performance NdFeB permanent magnet material industry has faced fierce market competition due to overcapacity, while also being strongly driven by emerging industries such as new energy vehicles and humanoid robots, resulting in continuous growth in market demand and further intensifying industry competition. On the other hand, with the country implementing stricter controls on the mining and export of heavy rare earth elements, the traditional technological path relying on heavy rare earth elements to prepare high-performance NdFeB magnets faces significant constraints. Therefore, how to achieve high comprehensive performance of magnets without heavy rare earth elements has become a key technical problem that the industry urgently needs to overcome.

[0003] Currently, research on the preparation of high-performance NdFeB magnets without heavy rare earth elements mainly focuses on the following directions: first, developing low-melting-point alloys without heavy rare earth elements as grain boundary penetration sources; second, exploring grain boundary doping modification processes for heavy rare earth-free alloy powders; and third, conducting composite addition and composition ratio optimization of elements such as titanium (Ti), copper (Cu), and gallium (Ga). Among these technical approaches, the composite addition method of elements such as titanium, copper, and gallium is considered to be more suitable for actual production conditions and has better industrialization prospects due to its high process compatibility and ease of integration into existing production lines.

[0004] Existing Ti, Cu, and Ga composite addition technologies for high-performance NdFeB magnets without heavy rare earth elements still have significant shortcomings in terms of synergistic optimization of elemental ratios, precise control of the key second phase (R6Fe13Ga phase), and "composition-process" matching. This makes it difficult to consistently obtain magnet products with high energy product, high coercivity, and high demagnetization stability. Therefore, it is necessary to further optimize the synergistic ratio design of key elements based on existing technologies and develop a matching refined preparation process to achieve optimal control of R6Fe13Ga phase. 13 Precise control of the formation and distribution of the Ga phase effectively solves the shortcomings in the above-mentioned composition design and process control, and stably obtains high-performance magnets. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, the present invention aims to provide a high-performance sintered NdFeB magnet without heavy rare earth elements and its preparation method, thereby overcoming the above deficiencies.

[0006] One objective of this invention is achieved through the following technical solution:

[0007] A high-performance sintered NdFeB magnet without heavy rare earth elements, the composition of which includes R, B, Zr, Cu, Ga, Fe, and Co, where R is one or two of Pr and Nd, and does not include heavy rare earth elements (heavy rare earth elements are gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium);

[0008] In 100 parts of sintered NdFeB magnets, the weight parts of R are 29–33 parts, the weight parts of B are 0.88–0.95 parts, and the weight parts of Zr, Cu, Ga, Fe, and Co satisfy the following conditions:

[0009] a = (weight parts of B) / 10.811 - 2 × (weight parts of Zr) / 91.224

[0010] b = (parts by weight of Fe) / 55.845 + (parts by weight of Co) / 59

[0011] c = (Nd weight parts / 144.242) + (Pr weight parts / 140.908)

[0012] d = (weight parts of Cu) / 63.546 + (weight parts of Ga) / 69.723

[0013] f = (parts by weight of Zr / 91.224) / c

[0014] 0.1 ≤ b - 14a ≤ 0.15

[0015] 1.7≤c / (b-14a)≤2.3

[0016] 0.08≤d / (b-14a)≤0.13,

[0017] 0.01≤f≤0.02.

[0018] Preferably, in 100 parts of sintered NdFeB magnets, R is 29.5 to 32 parts by weight and B is 0.89 to 0.93 parts by weight.

[0019] Preferably, in 100 parts of sintered NdFeB magnets, the weight parts of Fe are 62-72 parts and the weight parts of Co are 0.1-2 parts. More preferably, the weight parts of Fe are 64-70 parts and the weight parts of Co are 0.2-1.8 parts.

[0020] The composition of the sintered NdFeB magnet may or may not include Al. Preferably, the composition of the sintered NdFeB magnet further includes Al, and the weight percentage of Al satisfies the following conditions:

[0021] e = (weight parts of Al / 26.981) / c,

[0022] 0 < e ≤ 0.07.

[0023] When the composition of sintered NdFeB magnets does not include Al, then e is 0.

[0024] Preferably, the crystal phase of the sintered NdFeB magnet includes a main phase, a first grain boundary phase, and a second grain boundary phase.

[0025] Preferably, the composition of the first grain boundary phase includes:

[0026] The total content of Pr and Nd is 60–90 wt%, the total content of Fe and Co is 0–35 wt%, and the total content of Cu and Ga is 0–1.0 wt%.

[0027] Preferably, the composition of the second grain boundary phase includes:

[0028] The total content of Pr and Nd is 35-50 wt%, the total content of Fe and Co is 45-55 wt%, the total content of Cu and Ga is 2-5 wt%, and the Zr content satisfies: 0.2 ≤ Zr / (Cu+Ga) ≤ 0.8.

[0029] The second objective of this invention is achieved through the following technical solution:

[0030] A method for preparing a high-performance sintered NdFeB magnet without heavy rare earth elements includes batching, melting to obtain a casting, hydrogen breaking of the casting to obtain coarse powder, air jet milling to obtain fine powder, orientation molding, sintering, and aging.

[0031] Optionally, in the step of obtaining the casting sheet through melting, the melting temperature is 1420–1460℃, the casting temperature is 1410–1440℃, the copper roller linear speed is 1.15–1.25 m / s, the casting sheet thickness ranges from 0.18 to 0.34 mm, the average thickness is 0.2–0.25 mm, and the casting sheet thickness variance is 8 × 10⁻⁶. -4 ~10×10 -4 .

[0032] Optionally, in the step of obtaining coarse powder by hydrogen pulverization of cast iron, the particle size of the coarse powder obtained by hydrogen pulverization is 200-400 μm, the dehydrogenation treatment temperature is 300-600℃, and the time is 50-300 min.

[0033] Optionally, before performing air jet milling, 0.01–0.08 wt% of antioxidant and 0.01–0.08 wt% of gasoline by weight of the coarse powder are added to the coarse powder and stirred for 1–3 hours.

[0034] Optionally, in the step of obtaining fine powder by air jet milling, 20 to 60 ppm of oxygen is introduced during air jet milling, and the average particle size of the obtained fine powder is 2.0 to 4.0 μm.

[0035] Optionally, 0.02–0.09 wt% of an antioxidant and 0.02–0.09 wt% of gasoline by weight of the fine powder are further added to the fine powder, stirred for 1–5 hours, and then oriented molding is performed. Optionally, the orientation molding is carried out under an inert atmosphere with a magnetic field strength of 1.0–2.0 T.

[0036] Optionally, sintering is carried out in an inert atmosphere at a temperature of 1020–1200°C for 3–10 hours. After the holding time, the temperature is then reduced to 800–920°C under vacuum and then cooled to room temperature by inert gas.

[0037] Preferably, the aging process employs a three-stage aging process: the first stage has a holding temperature of 860–880℃ and a holding time of 2–4 hours; the second stage has a holding temperature of 500–520℃ and a holding time of 20–40 minutes; and the third stage has a holding temperature of 450–470℃ and a holding time of 4–6 hours.

[0038] More preferably, after the first stage of heat preservation is completed, inert gas is introduced and the temperature is cooled to 450-550°C at a cooling rate of 25-30°C / min, and then cooled to 20-80°C at a cooling rate of 10-15°C / min; after the second and third stages of heat preservation are completed, inert gas is introduced and the temperature is cooled to 20-80°C at a cooling rate of 10-15°C / min.

[0039] The inert gas used in this article is argon or nitrogen.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) Optimized composition design and strong process compatibility: By synergistically controlling the total amount of rare earth elements and the content and ratio of key elements such as boron, zirconium, copper, and gallium, the coercivity of the magnet is significantly improved without drastically changing the existing process flow. This formulation system does not require the introduction of additional processing steps, is seamlessly integrated with existing production processes, and has excellent industrial applicability.

[0042] (2) Controllable microstructure and high performance consistency: By adopting a specific three-stage aging process and precisely controlling the sintering cooling rate, the aging of R6FeCo is effectively promoted. 13 The formation and uniform distribution of the M phase optimizes the microstructure of the magnet, laying a reliable technological foundation for the preparation of NdFeB magnets with high performance and high consistency.

[0043] (3) Excellent overall performance and reduced production cost: The magnet prepared by this invention has a significantly optimized microstructure compared to conventional magnets, effectively compensating for the decline in service performance such as thermal demagnetization and corrosion resistance that may be caused by reducing the addition of heavy rare earth elements. While maintaining or even improving the overall performance of the magnet, the production cost is greatly reduced, demonstrating significant economic and technological value.

[0044] In summary, this invention achieves high coercivity and excellent demagnetization stability without containing any heavy rare earth elements by controlling the total amount of rare earth elements, the content and ratio of key elements such as boron, zirconium, copper, and gallium, and by combining it with a specific three-stage aging process. Attached Figure Description

[0045] Figure 1 The images shown are SEM images and EPMA point scan diagrams of the magnets in Examples 1-3, where (a) is the SEM image and EPMA point scan diagram of the magnet in Example 1, (b) is the SEM image and EPMA point scan diagram of the magnet in Example 2, and (c) is the SEM image and EPMA point scan diagram of the magnet in Example 3.

[0046] Figure 2 The images show SEM images and EPMA point scan diagrams of the magnets in Examples 6 and 8, where (a) is the SEM image and EPMA point scan diagram of the magnet in Example 6, and (b) is the SEM image and EPMA point scan diagram of the magnet in Example 8.

[0047] Figure 3 Here are the SEM images and EPMA point scan diagrams of the magnet in Example 12;

[0048] Figure 4 The image shows the SEM image and EPMA point scan diagram of the magnet in Example 14. Detailed Implementation

[0049] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, and includes both a and b. "Multiple" includes two, three, four, five, or more.

[0050] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0051] Example 1

[0052] The chemical composition of the sintered NdFeB magnet in this embodiment is expressed as follows (percentages are by weight): (Pr 20％ Nd 80％ ) 30％ Cu 0.25％ Ga 0.35％ Zr 0.25％ Al 0％ Co 0.5％ B 0.915％ Fe 67.735％ b-14a is 0.11, c / (b-14a) is 1.85, d / (b-14a) is 0.08, e is 0, and f is 0.013.

[0053] The sintered NdFeB magnet in this embodiment is obtained by the following preparation method:

[0054] S1: The ingredients were proportioned according to their respective weight percentages. The melting temperature was 1440℃, the casting temperature was 1430℃, the copper roller linear speed was 1.17m / s, and casting was performed according to the system program. The final product was an alloy sheet with an average thickness of 0.22mm and a thickness variance of 9.1×10⁻⁶. -4 The prepared castings were subjected to hydrogen pyrolysis treatment. The coarse powder obtained by hydrogen pyrolysis had a particle size of 300 μm. The dehydrogenation treatment temperature was 500℃ and the time was 100 min.

[0055] S2: After hydrogenation, add 0.05 wt% of zinc stearate (an antioxidant) and 0.04 wt% of gasoline (by weight of the coarse powder) to the coarse powder and stir for 2 hours. Then, perform air jet milling, introducing 40 ppm oxygen during the process, and grind the coarse powder to 3.1 μm. Add 0.06 wt% of zinc stearate (an antioxidant) and 0.05 wt% of gasoline (by weight of the fine powder) to the fine powder obtained after milling and stir for 3 hours.

[0056] S3: Under nitrogen protection, the fine powder is oriented and shaped in a 1.8T magnetic field and then stripped of oil before being fed into the furnace;

[0057] S4: The high-temperature sintering temperature during the sintering process is 1085℃, the holding time is 5h, after the holding time is completed, the temperature is vacuum-cooled to 900℃, and then argon-filled air-cooled, with a cooling rate of 8℃ / min as usual.

[0058] S5: The first stage aging temperature is 880℃, the holding time is 2.5h, and after the holding time is completed, nitrogen is purged and air-cooled. The cooling rate from 880℃ to 500℃ is 28℃ / min, and the cooling rate from 500℃ to 70℃ is 12℃ / min. The second stage aging temperature is 515℃, the holding time is 0.5h, and after the holding time is completed, nitrogen is purged and air-cooled to 70℃, with a cooling rate of 12℃ / min. The third stage aging temperature is 460℃, the holding time is 4.5h, and after the holding time is completed, nitrogen is purged and air-cooled to 70℃, with a cooling rate of 12℃ / min.

[0059] Examples 2-15

[0060] The weight percentages of each component in Examples 2-15 are shown in Table 1, and the preparation methods are the same as in Example 1.

[0061] Table 1. Composition of sintered NdFeB magnets in Examples 1-15

[0062]

[0063] Comparative Example 1

[0064] The chemical composition of the sintered NdFeB magnet in Comparative Example 1 is expressed as follows (percentages are by weight): (Pr 20％ Nd 80％ ) 30％ Cu 0.1％ Ga 0.3％ Zr 0.15％ Al 0％ Co 0.7％ B 0.915％ Fe 67.835％ b-14a is 0.09, c / (b-14a) is 2.38, d / (b-14a) is 0.07, e is 0, and f is 0.008.

[0065] The sintered NdFeB magnet in this embodiment is obtained by the following preparation method:

[0066] S1: The ingredients were proportioned according to their respective weight percentages. The melting temperature was 1440℃, the casting temperature was 1430℃, the copper roller linear speed was 1.17m / s, and casting was performed according to the system program. The final product was an alloy sheet with an average thickness of 0.22mm and a thickness variance of 9.3×10⁻⁶. -4 The prepared castings were subjected to hydrogen pyrolysis treatment. The coarse powder obtained by hydrogen pyrolysis had a particle size of 300 μm. The dehydrogenation treatment temperature was 500℃ and the time was 100 min.

[0067] S2: After hydrogenation, add 0.05 wt% of zinc stearate (an antioxidant) and 0.04 wt% of gasoline (by weight of the coarse powder) to the coarse powder and stir for 2 hours. Then, perform air jet milling, introducing 40 ppm oxygen during the process, and grind the coarse powder to 3.1 μm. Add 0.06 wt% of zinc stearate (an antioxidant) and 0.05 wt% of gasoline (by weight of the fine powder) to the fine powder obtained after milling and stir for 3 hours.

[0068] S3: Under nitrogen protection, the fine powder is oriented and shaped in a 1.8T magnetic field and then stripped of oil before being fed into the furnace;

[0069] S4: The high-temperature sintering temperature during the sintering process is 1085℃, the holding time is 5h, after the holding time is completed, the temperature is vacuum-cooled to 900℃, and then argon-filled air-cooled, with a cooling rate of 6℃ / min as usual.

[0070] S5: The first stage of aging is at a temperature of 900℃ and a holding time of 2.5h. After the holding time is completed, the temperature is purged with argon and cooled to 70℃ at a cooling rate of 10℃ / min. The second stage of aging is at a temperature of 485℃ and a holding time of 4.5h. After the holding time is completed, the temperature is purged with argon and cooled to 70℃ at a cooling rate of 8℃ / min.

[0071] Comparative Example 2

[0072] The only difference between Comparative Example 2 and Comparative Example 1 is the formulation composition. The preparation method is the same as Comparative Example 1. The chemical composition of the sintered NdFeB magnet in Comparative Example 2 is expressed as (percentages are by weight): (Pr 20％ Nd 80％ ) 30.5％ Cu 0.1％ Ga 0.2％ Zr 0.1％ Al 0.1％ Co 0.5％ B 0.915％ Fe 67.585％ b-14a is 0.06, c / (b-14a) is 3.29, d / (b-14a) is 0.07, e is 0.02, and f is 0.005.

[0073] Comparative Example 3

[0074] The only difference between Comparative Example 3 and Comparative Example 1 is the formulation composition. The preparation method is the same as Comparative Example 1. The chemical composition of the sintered NdFeB magnet in Comparative Example 3 is expressed as follows:

[0075] (Pr 20％ Nd 80％ ) 31.5％ Cu 0.15％ Ga 0.3％ Zr 0.1％ Al 0.3％ Co 1.5％ B0.915％ Fe 65.235％ b-14a is 0.04, c / (b-14a) is 5.57, d / (b-14a) is 0.17, e is 0.05, and f is 0.005.

[0076] Comparative Example 4

[0077] The only difference between Comparative Example 4 and Example 1 is that S5 only uses a two-stage sintering process. The first stage aging temperature is 880℃, the holding time is 2.5h, and after the holding time is completed, nitrogen is purged and air-cooled. The cooling rate from 880℃ to 500℃ is 28℃ / min, and the cooling rate from 500℃ to 70℃ is 12℃ / min. The second stage aging temperature is 460℃, the holding time is 4.5h, and after the holding time is completed, nitrogen is purged and air-cooled to 70℃ at a cooling rate of 12℃ / min.

[0078] Comparative Example 5

[0079] The only difference between Comparative Example 5 and Example 1 is that, in step S5, the aging temperature of the third stage is 485°C.

[0080] Comparative Example 6

[0081] The only difference between Comparative Example 6 and Example 1 is that, in step S5, the aging temperature of the third stage is 420°C.

[0082] Comparative Example 7

[0083] The only difference between Comparative Example 7 and Example 1 is that, in step S5, the first aging temperature is 820°C.

[0084] Comparative Example 8

[0085] The only difference between Comparative Example 8 and Example 1 is that, in step S5, the first aging temperature is 900°C.

[0086] Comparative Example 9

[0087] The only difference between Comparative Example 9 and Example 1 is that, in step S5, the second aging temperature is 490°C.

[0088] Comparative Example 10

[0089] The only difference between Comparative Example 10 and Example 1 is that, in step S5, the second aging temperature is 530°C.

[0090] Comparative Example 11

[0091] The only difference between Comparative Example 11 and Example 1 is that, in step S5, the second stage of aging and heat preservation time is 1.5h.

[0092] Comparative Example 12

[0093] The only difference between Comparative Example 12 and Example 1 is that, in step S5, the second stage of aging and heat preservation time is 0.2h.

[0094] Comparative Example 13

[0095] The only difference between Comparative Example 13 and Example 1 is that, in step S5, after the first stage of aging and heat preservation, the cooling rate of nitrogen-filled air cooling to 500°C is 10°C / min.

[0096] Comparative Example 14

[0097] The only difference between Comparative Example 14 and Example 1 is that, in step S5, after the first stage of aging and heat preservation, the cooling rate of nitrogen-filled air cooling to 500°C is 34°C / min.

[0098] Comparative Example 15

[0099] The only difference between Comparative Example 15 and Example 1 is that, in step S5, after the first stage of aging and heat preservation, the nitrogen-filled air cooling rate from 500°C to 70°C is 5°C / min.

[0100] Comparative Example 16

[0101] The only difference between Comparative Example 16 and Example 1 is that, in step S5, after the first stage of aging and heat preservation, the nitrogen-filled air cooling rate from 500°C to 70°C is 17°C / min.

[0102] Comparative Example 17

[0103] The only difference between Comparative Example 17 and Example 1 is that, in step S5, after the second and third stages of aging and heat preservation, the nitrogen-filled air-cooled cooling rate to 70°C is 5°C / min.

[0104] Comparative Example 18

[0105] The only difference between Comparative Example 18 and Example 1 is that, in step S5, after the second and third stages of aging and heat preservation, the nitrogen-filled air-cooled cooling rate to 70°C is 17°C / min.

[0106] Magnetic performance samples were prepared by wire cutting, coreless grinding, and end face grinding. The samples were φ10mm×10mm cylinders. The samples were tested at room temperature (20℃) using a NIM-62000 demagnetization curve testing device. The magnetic properties of the sintered NdFeB magnets prepared in Examples 1-15 and Comparative Examples 1-18 were obtained. The test results are shown in Table 2.

[0107] Table 2 Magnetic properties of sintered NdFeB magnets in Examples 1-15 and Comparative Examples 1-18

[0108]

[0109]

[0110] *R6(FeCo) 13 M in M ​​stands for Cu and Ga.

[0111] Comparing Example 1 with Comparative Example 1, Example 4 with Comparative Example 2, and Example 10 with Comparative Example 3, it can be seen that under the same total rare earth content, the formation of the second grain boundary phase can be effectively promoted by adjusting the content of elements such as Cu, Ga, and Zr, as well as by controlling the process. Although the remanence decreases slightly, the coercivity of the magnet can be significantly enhanced.

[0112] Comparative studies of Examples 1-3 revealed that excessively low Cu and Ga addition ratios resulted in a small d / (b-14a) ratio, which failed to effectively form the second grain boundary phase, leading to a significant reduction in coercivity. Conversely, excessively high addition ratios resulted in an excessively large d / (b-14a) ratio, which not only caused local aggregation of the first and second grain boundary phases but also resulted in a slight decrease in coercivity and a significant deterioration in the squareness of the demagnetization curve.

[0113] The microstructure of the sintered NdFeB magnets obtained in Examples 1 to 3 was characterized by scanning electron microscopy (SEM), and the results are shown in... Figure 1 (a) Figure 1 (b) and Figure 1 (c). The characteristics of the grain boundary phases in each embodiment are compared as follows: Compared with embodiment 2, the magnet of embodiment 1 has a more continuous and clearer distribution of grain boundary phases and a greater thickness of grain boundary phases; compared with embodiment 3, the magnet of embodiment 1 has a more uniform distribution of grain boundary phases.

[0114] right Figure 1 (a) to Figure 1 Compositional analysis was performed at the scanned locations indicated in (c), and the resulting mass fractions are shown in Table 3. From the grain boundary phase composition data shown in Table 3, it can be seen that: Example 2 only formed the first grain boundary phase; while Examples 1 and 3 simultaneously formed a conventional first grain boundary phase and a Cu- and Ga-rich second grain boundary phase. The typical characteristics of this second grain boundary phase are that the total content of Cu and Ga is 2–5%, and its atomic ratio Zr / (Cu+Ga) is between 0.2 and 0.8.

[0115] Table 3. Grain boundary phase composition (wt%) of Examples 1-3

[0116]

[0117] The comparative results of Examples 4-6 and Examples 7-9 confirm that when the total rare earth content or boron content is too high (Examples 5 and 9), the b-14a value is too low, resulting in insufficient Fe remaining after the formation of the main phase, which prevents the formation of a sufficient amount of the second grain boundary phase, thus causing a significant decrease in coercivity. When the total rare earth content or boron content is too low (Examples 6 and 8), the b-14a value is too high, resulting in excessive Fe content in the grain boundary phase, which forms a magnetic phase, ultimately causing a deterioration in both coercivity and squareness.

[0118] The sintered NdFeB magnets obtained in Examples 6 and 8 were observed using SEM to examine their microstructure. The results are as follows: Figure 2 (a) Figure 2 As shown in (b), the grain boundary phases of the NdFeB magnets obtained in Examples 6 and 8 are not sufficiently continuous and clear, and their characteristics are similar to those of Comparative Examples 1-3. Figure 2 (a) to Figure 2 Compositional analysis was performed on the scanned locations indicated in (b), and the resulting mass fractions are shown in Table 4. As can be seen from the data in Table 4, neither formed a second grain boundary phase; instead, a magnetic phase with high Fe content and low Cu+Ga content was present at the grain boundaries. This magnetic phase distribution at the grain boundaries weakens the magnetic isolation effect, directly leading to a decrease in the coercivity of the magnet.

[0119] Table 4. Grain boundary phase composition (wt%) of Examples 6 and 8

[0120]

[0121] Comparative studies of Examples 10-12 show that the Zr content and the corresponding f value have a crucial impact on the formation and distribution of the second grain boundary phase. When the Zr content is too high and the f value is too large, the distribution of the second grain boundary phase tends to be uneven, resulting in a decrease in the coercivity of the magnet and a worsening of the squareness of the demagnetization curve; while when the Zr content is too low and the f value is too small, the second grain boundary phase cannot be effectively formed, resulting in a significant decrease in coercivity.

[0122] The sintered NdFeB magnet prepared in Example 12 was analyzed by SEM microstructure, and the results are as follows: Figure 3 As shown, the grain boundary phase exhibits a distinct aggregated morphology. Figure 3Compositional analysis was performed on the marked scanning locations, and the resulting mass fractions are shown in Table 5. Based on the grain boundary phase composition data in Table 5, the total Cu+Ga proportion in this region exceeds 5%, and the Zr / (Cu+Ga) ratio is higher than the upper limit of 0.8. The excessive addition of Zr reduces the fluidity of the grain boundary phase, causing Zr segregation at the grain boundaries. This leads to differences in the distribution and proportion of the formed Zr-B2 phase, ultimately interfering with the uniform formation of the second grain boundary phase. Specifically, in regions with low Zr content, the second grain boundary phase is difficult to form; while in regions with high Zr content, Zr, Cu, Ga, and other elements are excessively enriched, resulting in an overall decrease in magnet performance and structural consistency.

[0123] Table 5. Grain boundary phase composition (wt%) of Example 12

[0124]

[0125] The comparative results and analysis of Comparative Examples 13-15 show that the c / (b-14a) ratio needs to be controlled within a reasonable range. If the ratio is too low, it will lead to the formation of a magnetic phase; if the ratio is too high, it will lead to a low proportion of the formation of the second grain boundary phase.

[0126] The sintered NdFeB magnet prepared in Example 14 was analyzed by SEM microstructure, and the results are as follows: Figure 4 As shown, the thickness of the grain boundary phase is significantly reduced. Figure 4 Compositional analysis was performed on the marked point scanning locations, and the resulting mass fractions are shown in Table 6. Based on the grain boundary phase composition data in Table 6, although the grain boundary phase composition of the magnet prepared in Example 14 conforms to the characteristics of a second grain boundary phase, the proportion of this phase is significantly lower than that in Example 1. This indicates that an excessively high c / (b-14a) ratio inhibits the effective formation of the second grain boundary phase.

[0127] Table 6. Grain boundary phase composition (wt%) of Example 14

[0128]

[0129] The aging processes of Comparative Examples 4-18 differ from those of Example 1. Comparing Example 1 and Comparative Example 4, it can be seen that the three-stage aging process of the present invention is more conducive to promoting the formation of the second grain boundary phase and significantly improving its distribution uniformity and consistency compared to the traditional two-stage aging process.

[0130] Comparing Example 1 with Comparative Examples 5-8, it can be seen that the holding temperatures of the first and third aging stages have a crucial impact on the formation of the second grain boundary phase. Excessively high temperatures will inhibit the formation of this phase, leading to a significant decrease in coercivity; excessively low temperatures will reduce the proportion of this phase formed and worsen its distribution, thereby causing a decrease in coercivity and a deterioration in the squareness of the demagnetization curve.

[0131] Compared to conventional two-stage aging processes, the second-stage aging introduced in this invention aims to achieve a more uniform distribution of the grain boundary phase before the precipitation of the second grain boundary phase in the third-stage aging process, thereby ultimately promoting the uniform precipitation of the second grain boundary phase. Comparative Examples 1 and 9-12 show that if the holding temperature in this stage is too high or the time is too long, it will not be able to effectively achieve grain boundary phase homogenization and subsequent uniform precipitation of the second grain boundary phase, because high temperature and long duration will cause the grain boundaries to directly generate the conventional first grain boundary phase, resulting in a significant reduction in coercivity; if the temperature in this stage is too low or the time is too short, the grain boundary phase homogenization effect is insufficient, although the reduction in coercivity is small, the squareness will be significantly deteriorated.

[0132] Comparing Example 1 with Comparative Examples 13-18, it can be seen that the cooling rate after the three-stage aging process has a direct impact on the magnet performance and the precipitation behavior of the second grain boundary phase. When the cooling rate is slow, the magnet cannot effectively form the second grain boundary phase, and the coercivity decreases significantly. The cooling rate during the first stage of aging, from 880°C to 500°C, has the most significant impact on the magnetic properties. However, once the cooling rate reaches a certain threshold, further increasing the cooling rate has a diminishing or even decreasing effect on improving the magnetic properties.

[0133] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0134] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0135] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A high-performance sintered NdFeB magnet without heavy rare earth elements, characterized in that, Its components include R, B, Zr, Cu, Ga, Fe, and Co, where R is two of Pr and Nd, and it does not include heavy rare earth elements; In 100 parts of sintered NdFeB magnets, the weight parts of R are 29-33 parts, the weight parts of B are 0.88-0.95 parts, and the weight parts of Zr, Cu, Ga, Fe, and Co meet the following conditions: a = (weight parts of B) / 10.811 - 2 × (weight parts of Zr) / 91.224 b = (parts by weight of Fe) / 55.845 + (parts by weight of Co) / 59 c = (Nd weight parts) / 144.242 + (Pr weight parts) / 140.908 d = (weight parts of Cu) / 63.546 + (weight parts of Ga) / 69.723 f = (parts by weight of Zr / 91.224) / c 0.1 ≤ b - 14a ≤ 0.15 1.7 ≤ c / (b-14a) ≤ 2.3 0.08≤d / (b-14a)≤0.13, 0.01≤f≤0.02； The crystal phases of the sintered NdFeB magnet include a main phase, a first grain boundary phase, and a second grain boundary phase; The composition of the first grain boundary phase includes: The total content of Pr and Nd is 60-90 wt%, the total content of Fe and Co is ≤35 wt%, and the total content of Cu and Ga is 0-1.0 wt%. The composition of the second grain boundary phase includes: The total content of Pr and Nd is 35~50wt%, the total content of Fe and Co is 45~55wt%, the total content of Cu and Ga is 2~5wt%, and the content of Zr satisfies: 0.2≤Zr / (Cu+Ga)≤0.

8.

2. The heavy rare earth-free high-performance sintered NdFeB magnet according to claim 1, characterized in that, In 100 parts of sintered NdFeB magnets, the weight parts of R are 29.5 to 32 parts and the weight parts of B are 0.89 to 0.93 parts.

3. The heavy rare earth-free high-performance sintered NdFeB magnet according to claim 1, characterized in that, The sintered NdFeB magnet also includes Al, and the weight percentage of Al satisfies the following conditions: e = (weight parts of Al / 26.981) / c, 0＜e≤0.07。 4. A method for preparing a high-performance sintered NdFeB magnet without heavy rare earth elements as described in any one of claims 1 to 3, characterized in that, The preparation method includes batching, melting to obtain a casting, hydrogen breaking of the casting to obtain coarse powder, air jet milling to obtain fine powder, orientation molding, sintering and aging; The aging process adopts a three-stage aging process: the first stage has a heat preservation temperature of 860~880℃ and a heat preservation time of 2~4h; The second stage of heat preservation temperature is 500~520℃, and the heat preservation time is 20~40min; the third stage of heat preservation temperature is 450~470℃, and the heat preservation time is 4~6h. After the first stage of heat preservation is completed, inert gas is introduced and the temperature is cooled to 450-550°C at a cooling rate of 25-30°C / min, and then cooled to 20-80°C at a cooling rate of 10-15°C / min. After the second and third stages of heat preservation are completed, inert gas is introduced and the temperature is cooled to 20-80°C at a cooling rate of 10-15°C / min.

5. The preparation method according to claim 4, characterized in that, In the process of obtaining the casting sheet through melting, the melting temperature is 1420~1460℃, the casting temperature is 1410~1440℃, the copper roller linear speed is 1.15~1.25m / s, the casting sheet thickness ranges from 0.18~0.34mm, the average thickness is 0.2~0.25mm, and the casting sheet thickness variance is 8×10⁻⁶. -4 ~10×10 -4 .

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