Sintered neodymium-iron-boron magnet and method for producing and use thereof

Abstract

The application belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a sintered neodymium-iron-boron magnet and a preparation method and application thereof. A heavy rare earth-free neodymium-iron-boron blank used in the application is composed of the following components in percentage by mass: PrNd 29.5-31.5%, B 0.88-0.96%, Al 0.05-0.15%, Cu 0.10-0.30%, Zr 0.20-0.30%, Ga 0.20-0.40%, Co 0.65-0.75%, Ti 0.01-0.10%, Nb 0.01-0.15%, V 0.05-0.15%, and the balance of Fe. The application obtains a product with higher remanence and coercive force under the condition of no heavy rare earth, while maintaining high magnetic energy product and good squareness.

Description

Technical Field

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

[0002] Sintered NdFeB permanent magnets are widely used in new energy vehicles, wind power generation, and consumer electronics due to their excellent magnetic properties. Key performance indicators for NdFeB magnets include remanence, intrinsic coercivity, maximum energy product, and squareness. Traditional high-coercivity sintered NdFeB magnets typically require the addition of heavy rare earth elements such as dysprosium or terbium. While heavy rare earth elements effectively enhance the intrinsic coercivity of magnets, they are scarce, expensive, and their addition reduces remanence and energy product.

[0003] Currently, heavy rare earth-free sintered NdFeB magnets have become a hot topic. For example, patent CN113851320B discloses a method for preparing a light rare earth alloy grain boundary diffusion-enhanced heavy rare earth-free sintered NdFeB magnet. Using a Pr-Fe alloy diffusion source, the intrinsic coercivity of the magnet is increased from 17.93 kOe to 21.94 kOe, but the remanence decreases from 13.65 kGs to 12.83 kGs, and the energy product also decreases from 45.37 MGOe to 40.26 MGOe, while the squareness remains basically maintained at around 96%. Although this method achieves an increase in coercivity, it comes at the cost of sacrificing remanence and energy product. Patent CN121839343A discloses a neodymium iron gallium dual alloy sintered neodymium iron boron magnet without heavy rare earth 54H and its preparation method. By mixing the main alloy and the auxiliary alloy, a magnet with a remanence of 14.42-14.46 kGs and an intrinsic coercivity of 17.36-17.69 kOe was obtained. However, its coercivity is still at a low level, which is difficult to meet the application requirements under high temperature or high reverse magnetic field conditions.

[0004] In summary, existing heavy rare earth-free sintered NdFeB magnets exhibit a trade-off between key performance indicators such as remanence, coercivity, energy product, and squareness: improvements in coercivity are often accompanied by significant decreases in remanence and energy product, or the absolute value of coercivity remains low. Therefore, how to obtain products with higher and more balanced remanence and coercivity while maintaining high energy product and good squareness under heavy rare earth conditions remains a pressing technical challenge to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a sintered NdFeB magnet, its preparation method and application, which obtains products with higher remanence and coercivity under heavy rare earth conditions, while maintaining high magnetic energy product and good squareness.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a sintered NdFeB magnet includes the following steps: (1) Preparation of weightless NdFeB blanks: The matrix is ​​prepared according to the following mass percentage composition: PrNd 29.5-31.5%, B 0.88-0.96%, Al 0.05-0.15%, Cu 0.10-0.30%, Zr 0.20-0.30%, Ga 0.20-0.40%, Co 0.65-0.75%, Ti 0.01-0.10%, Nb 0.01-0.15%, V 0.05-0.15%, with the balance being Fe; after preparation, the blanks are smelted, hydrogenated, air-jet milled, and shaped to obtain green blanks; the green blanks are sintered and subjected to two-stage tempering treatment; after cooling, sintered NdFeB blanks are obtained; (2) Preparation of multi-element alloy dispersants; (3) Preparation of multi-element alloy diffusion slurry: Mix the multi-element alloy diffuser with additives; (4) Preparation of NdFeB thin sheets: The sintered NdFeB blanks are processed into thin sheets, and the thin sheets are coated with multi-element alloy diffusion paste; (5) Grain boundary diffusion heat treatment: The coated NdFeB sheet is sintered and air-cooled to obtain sintered NdFeB magnet.

[0007] Preferably, the mass ratio of Ti, Nb, and V is 1:(0.8-1.2):(2.5-3.5), and the total mass percentage of the three is 0.15-0.26%.

[0008] The inventors discovered that when the mass ratio of Ti, Nb, and V is in the range of 1:(0.8-1.2):(2.5-3.5), the remanence of the magnet can be increased. Analysis shows that Ti, Nb, and V are all high-melting-point transition metal elements, which can partially dissolve in the main phase Nd₂Fe during sintering. 14 In the B lattice, refractory boride or carbide particles tend to form dispersedly at grain boundaries. At this proportion, these particles can refine the main phase grains and optimize the grain boundary structure, reducing pinning losses of magnetic domain walls and thus improving remanence. Furthermore, the inventors discovered that the coercivity can only be maintained above 20 kOe when the total mass percentage of the three components is controlled between 0.15-0.26%. This is because when the total amount is too low, the refining effect is not significant, the grain size is too large, and the antimagnetic domains are prone to nucleation; when the total amount is too high, excessive nonmagnetic phase dilutes the volume fraction of the main phase, thus reducing the coercivity.

[0009] Preferably, the mass ratio of Cu to Ga is 1:(1.3-1.6).

[0010] The inventors discovered that when the mass ratio of Cu to Ga is 1:(1.3-1.6), the squareness of the magnet is improved. Analysis shows that both Cu and Ga are low-melting-point elements, preferentially enriching in the grain boundary phase during sintering and tempering. An appropriate amount of Cu can lower the melting point of the rare-earth-rich grain boundary phase, improve its wettability to the main phase grains, and promote the uniform spreading of the grain boundary phase. Ga, on the other hand, can enhance the non-magnetic characteristics of the grain boundary phase and form a continuous, thin, and clear grain boundary layer. When the Cu to Ga ratio is within this range, their synergistic effect ensures the fluidity of the grain boundary phase while avoiding excessive coarsening, thus effectively isolating adjacent main phase grains, weakening exchange coupling, and making the demagnetization curve steeper.

[0011] More preferably, the matrix is ​​composed of the following components by mass percentage: PrNd 30.00%, B 0.92%, Al 0.10%, Cu 0.20%, Zr 0.25%, Ga 0.30%, Co 0.70%, Ti 0.045%, Nb 0.045%, V 0.135%, with the balance being Fe.

[0012] More preferably, the matrix is ​​composed of the following components by mass percentage: 29.50% PrNd, 0.96% B, 0.15% Al, 0.30% Cu, 0.20% Zr, 0.40% Ga, 0.75% Co, 0.060% Ti, 0.048% Nb, 0.15% V, with the balance being Fe.

[0013] Preferably, the multi-element alloy diffusing agent is selected from alloys with the following mass percentage composition: Pr 70 Cu 30 Pr 70 Al 15 Cu 15 、Nd 80 Ga 10 Cu 10 Pr 70 Al 15 Cu 15 and Nd 80 Ga 10 Cu 10 The mixture of Nd 70 Ce 10 Cu 10 Ga 10 .

[0014] Preferably, the multi-element alloy diffusing agent is selected from alloys with the following mass percentage composition: Pr 70 Al 15 Cu 15 and Nd 80 Ga 10 Cu 10 A mixture.

[0015] Preferably, the mass ratio of the multi-element alloy diffusing agent to the additive is (18-19):(1-2).

[0016] Preferably, the additive consists of polyvinyl alcohol, ethanol and polyethyleneimine in a mass ratio of (0.8-1.2):(1.6-2.3):(0.5-0.8).

[0017] Preferably, the sintering conditions in step (1) are: sintering at 1000-1100℃ for 5-8 hours.

[0018] Preferably, the conditions for the two-stage tempering treatment are as follows: the first-stage tempering temperature is 900-920℃, and the holding time is 2-4 hours; the second-stage tempering temperature is 480-520℃, and the holding time is 5-6 hours.

[0019] Preferably, the melting temperature is 1480°C.

[0020] More preferably, the sintering temperature in step (1) is 1100℃ and the holding time is 6h.

[0021] Further preferred, the first-stage tempering temperature is 910℃, and the holding time is 3 hours; the second-stage tempering temperature is 500℃, and the holding time is 5.5 hours.

[0022] More preferably, the conditions for the grain boundary diffusion heat treatment are: a first-stage heat treatment temperature of 880°C and a holding time of 10 hours; and a second-stage heat treatment temperature of 490°C and a holding time of 5 hours.

[0023] The inventors discovered that the conditions of the two-stage tempering process have a significant impact on coercivity. Under the two-stage tempering conditions of this invention, a coercivity of over 20 kOe can be guaranteed. This is because the first-stage high-temperature tempering allows the metastable grain boundary phase formed during sintering cooling to redissolve and distribute uniformly, eliminating compositional segregation and internal stress at the grain boundaries; the second-stage low-temperature tempering promotes the transformation of the grain boundary phase from an amorphous state to a crystalline state, forming a stable, continuous, and highly pinning rare-earth-rich grain boundary layer.

[0024] This invention provides a sintered NdFeB magnet prepared by a method thereof.

[0025] Preferably, the sintered NdFeB magnet has a remanence of 14.78-14.84 kGs, an intrinsic coercivity of 20.65-20.72 kOe, a maximum energy product of 50.21-50.54 MGOe, and a squareness of 94.5%-94.7%.

[0026] This invention provides the application of sintered NdFeB magnets prepared by the method in the preparation of rare earth permanent magnet materials.

[0027] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention utilizes a low-melting-point multi-element alloy synergistic diffusion method. Light rare-earth elements in the diffusion source form a light rare-earth shell on the outer layer of the main phase grains, suppressing demagnetizing domain nucleation, strengthening demagnetizing coupling, and improving coercivity. The Ce-containing diffusion source leverages the low melting point of the CeFe2 soft magnetic phase to improve wettability and broaden diffusion channels; Al, Ga, and Cu enhance the wettability of the rare-earth-rich phase, promote uniform diffusion of light rare-earth elements, form a continuous grain boundary phase, and weaken exchange coupling. Based on this, a carefully selected formula is used to further synergistically improve the overall performance of the magnet.

[0028] 2. This invention improves magnet performance through the synthesis of carefully selected matrix alloys. At the same time, when the mass ratio of Ti, Nb, and V is in the range of 1:(0.8-1.2):(2.5-3.5), the remanence of the magnet can be increased. And only when the total mass percentage of the three is controlled at 0.15-0.26% can the coercivity be maintained above 20kOe.

[0029] 3. In the system of the present invention, when the mass ratio of Cu to Ga is 1:(1.3-1.6), the squareness of the magnet is improved.

[0030] 4. The conditions of the two-stage tempering treatment in the preparation method of the present invention have an important influence on the coercivity. Under the two-stage tempering treatment conditions of the present invention, the coercivity of the magnet can be guaranteed to be above 20kOe, while other properties are optimized. Attached Figure Description

[0031] Figure 1 SEM image of the magnet prepared in Example 1 without using a diffusing agent.

[0032] Figure 2 SEM image of the magnet prepared in Example 1 using a Pr-Cu diffusion source.

[0033] Figure 3 for Figure 2 Enlarged diagram of point A in the middle.

[0034] Figure 4 for Figure 2 Enlarged diagram of point B in the middle.

[0035] Figure 5 SEM image of the sintered NdFeB magnet prepared in Example 4.

[0036] Figure 6 for Figure 5 Enlarged diagram of point C in the middle.

[0037] Figure 7 for Figure 5 Enlarged diagram of point D in the middle. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] The specific composition of PrNd used in the following embodiments is: Pr accounts for 25wt% and Nd accounts for 75wt%.

[0040] Performance testing was conducted in accordance with GB / T3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnet) Materials".

[0041] Example 1 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The raw materials are prepared according to the matrix composition. The matrix is ​​composed of the following components by mass percentage: 30.2% PrNd, 0.92% B, 0.10% Al, 0.20% Cu, 0.05% Ti, 0.25% Zr, 0.30% Ga, 0.70% Co, and balance Fe; Following this formulation, the raw materials undergo smelting, hydrogen crushing, air jet milling, forming, and sintering heat treatment. Specifically: the prepared raw materials are added to a vacuum induction melting furnace and heated to 1480℃ for melting. After refining, the mixture is poured onto a rotating copper roller with a linear speed of 3 m / s to obtain a rapidly solidified casting sheet with a thickness of 0.45 mm. The rapidly solidified casting sheet is then placed in a hydrogen crushing furnace with a hydrogen absorption pressure of 0.20 MPa for 2 hours. After hydrogen saturation, the temperature is raised to 550℃ for dehydrogenation treatment for 6 hours, followed by cooling to room temperature to obtain coarse hydrogen-crushed powder. This coarse hydrogen-crushed powder is then pulverized by an air jet mill under nitrogen protection at a grinding pressure of 0.50 MPa. The sorting wheel rotates at 5000 rpm to obtain fine powder with an average particle size of 2.80 μm. The fine powder is then subjected to magnetic field orientation pressing under nitrogen protection. The orientation magnetic field strength is 2T, and the pressing pressure is 10 MPa. Cold isostatic pressing is then performed at 200 MPa for 10 minutes to obtain a green compact. The green compact is placed in a vacuum sintering furnace and sintered at 1100℃ for 6 hours. After sintering, it is cooled to room temperature. A two-stage tempering process is then performed: the first stage tempering temperature is 910℃, held for 3 hours; the second stage tempering temperature is 500℃, held for 5.5 hours. After cooling, a sintered NdFeB blank is obtained. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Cu 30 ,Pr 70 Al 15 Cu 15Nd 80 Ga 10 Cu 10 ,Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 Mixed (mass ratio 1:1), Nd 70 Ce 10 Cu 10 Ga 10 Different dispersants were separately prepared and added to a vacuum melting furnace, and then hydrogen crushed and air-jet milled to obtain alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: The multi-element alloy diffusion agent and additives are mixed at a mass ratio of 19:1 for 8 hours. The additives are composed of polyvinyl alcohol, ethanol and polyethyleneimine in a mass ratio of 1:2:0.6.

[0042] (4) Preparation of NdFeB thin film: The sintered NdFeB blank is processed into a thin film with an orientation thickness of 3mm. After degreasing and rust prevention, it is rinsed with anhydrous ethanol, dried, and coated with multi-element alloy diffusion slurry. The coating weight gain ratio is 0.7%wt.

[0043] (5) Grain boundary diffusion heat treatment: The coated NdFeB sheet is placed in a vacuum sintering furnace. The first heat treatment temperature is 880℃ and the holding time is 10h; the second heat treatment temperature is 490℃ and the holding time is 5h; after the treatment, argon air cooling is performed to obtain sintered NdFeB magnets.

[0044] The grain boundary diffusion results of different multi-element alloy diffusion sources in Example 1 were tested, and their magnetic properties are shown in Table 1: Table 1. Magnetic properties of NdFeB magnets with different alloy diffusion sources in Example 1

[0045] From Table 1 and Figures 1-4 It can be seen that the coercivity of the matrix was further improved after diffusion. In terms of the magnitude of the improvement, the Pr-Al-Cu+Nd-Ga-Cu mixed diffusing agent showed the greatest increase, demonstrating the synergistic effect of multiple elements. Furthermore, the diffusion effect of the cerium-containing diffusion source Nd-Ce-Ga-Cu was comparable to that of the cerium-free diffusion source Nd-Ga-Cu, reflecting the relative influence of CeFe2 on the diffusion process. Combined with... Figure 2 and Figure 3 It can be seen that the magnet prepared in Example 1 using a Pr-Cu diffusion source exhibits a morphology of main phase particle contact; combined with Figure 2 and Figure 4It can be seen that the magnet prepared in Example 1 using a Pr-Cu diffusion source exhibits a grain boundary phase aggregation morphology.

[0046] Example 2 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: Preparation of weightless NdFeB blanks: Same as in Example 1; Preparation of multi-component alloy dispersant: The materials are prepared according to the alloy composition, which consists of the following components by mass percentage: Nd... 80 Ga 10 Cu 10 ,Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 Mixing, Nd 70 Ce 10 Cu 10 Ga 10 After being mixed, the materials are added to a vacuum melting furnace and then hydrogen-crushed and air-jet milled to obtain alloy diffusion powders with laser particle sizes of 2.75μm, 2.90μm, 3.05μm and 3.2μm, respectively.

[0047] Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0048] Preparation of NdFeB thin films: Same as in Example 1.

[0049] Grain boundary diffusion heat treatment: Same as in Example 1.

[0050] The grain boundary diffusion results of different multi-element alloy diffusion sources in Example 2 above were detected, and their magnetic properties are shown in Table 2: Table 2. Magnet properties of Nd-Ga-Cu diffusion sources at different particle sizes

[0051] Table 3. Magnet properties of Pr-Al-Cu+Nd-Ga-Cu diffusion sources with different particle sizes

[0052] Table 4. Magnet properties of Nd-Ce-Ga-Cu diffusion sources with different particle sizes

[0053] As shown in Tables 2-4, as the particle size of the alloy diffusion source decreases, the coercivity of the magnet is further improved, while the remanence of the magnet decreases slightly. This indicates that fine grains can reduce the stray magnetic field around the grains, improve the nucleation field of the antimagnetization domains, and thus improve the coercivity.

[0054] Example 3 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: Preparation of weightless NdFeB blanks: Same as in Example 1.

[0055] Preparation of multi-component alloy dispersant: The materials are prepared according to the alloy composition, which consists of the following components by mass percentage: Nd... 80 Ga 10 Cu 10 ,Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 Mixed (mass ratio 1:1), Nd 70 Ce 10 Cu 10 Ga 10 After being mixed, the materials are added to a vacuum melting furnace and then hydrogen-crushed and air-jet milled to obtain an alloy diffusion powder with a laser particle size of 2.75μm.

[0056] Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0057] Preparation of NdFeB thin films: Same as in Example 1 Grain boundary diffusion heat treatment: The coated NdFeB sheet is placed in a vacuum sintering furnace. The first heat treatment temperature is 880℃ and the holding time is 10h. The second heat treatment temperatures are 430℃, 460℃, 490℃, 520℃ and 550℃ respectively, and the holding time is 5h for each stage. Argon air cooling is performed after the treatment.

[0058] The grain boundary diffusion results of different multi-element alloy diffusion sources in Example 3 above were tested, and their magnetic properties are shown in Tables 5-7: Table 5. Magnet properties of Nd-Ga-Cu diffusion sources at different heat treatment temperatures.

[0059] Table 6. Magnet properties of Pr-Al-Cu+Nd-Ga-Cu diffusion sources at different heat treatment temperatures.

[0060] Table 7. Magnet properties of Nd-Ce-Ga-Cu diffusion sources at different heat treatment temperatures.

[0061] As shown in Tables 5-7, the coercivity of the magnet is at a relatively high level when the laser particle size is around 2.75 μm and the secondary tempering temperature is between 490-520℃. The diffusion effects of the cerium-free Nd-Ga-Cu diffusion source and the cerium-containing Nd-Ce-Ga-Cu diffusion source are comparable. In summary, the synergistic diffusion effect of multi-element alloys is better, which can significantly improve the coercivity of heavy rare earth-free magnets. Its process equipment is simple, the operation is convenient, and it is suitable for mass industrial production.

[0062] Example 4 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The matrix is ​​prepared according to the following composition by mass percentage: PrNd 30.00%, B 0.92%, Al 0.10%, Cu 0.20%, Zr 0.25%, Ga 0.30%, Co 0.70%, Ti 0.045%, Nb 0.045%, V 0.135%, with the balance being Fe. The remaining steps are the same as in Example 1. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0063] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0064] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0065] Example 5 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The matrix is ​​prepared according to the matrix composition. The matrix is ​​composed of the following components by mass percentage: PrNd 29.50%, B 0.96%, Al 0.15%, Cu 0.30%, Zr 0.20%, Ga 0.40%, Co 0.75%, Ti 0.060%, Nb 0.048%, V 0.15%, with the balance being Fe. The remaining steps are the same as in Example 1. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0066] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0067] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0068] Example 6 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: PrNd 30.00%, B 0.92%, Al 0.10%, Cu 0.20%, Zr 0.25%, Ga 0.10%, Co 0.70%, Ti 0.005%, Nb 0.005%, V 0.02%, with the balance being Fe. The remaining steps are the same as in Example 1. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0069] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0070] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0071] Example 7 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The matrix is ​​prepared according to the following composition by mass percentage: PrNd 30.00%, B 0.92%, Al 0.10%, Cu 0.20%, Zr 0.25%, Ga 0.30%, Co 0.70%, Ti 0.075%, Nb 0.1%, V 0.05%, with the balance being Fe. The remaining steps are the same as in Example 1. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0072] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0073] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0074] Example 8 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The matrix is ​​prepared according to the following mass percentage composition: PrNd 30.00%, B 0.92%, Al 0.10%, Cu 0.20%, Zr 0.25%, Ga 0.30%, Co 0.70%, Ti 0.03%, Nb 0.02%, V 0.05%, with the balance being Fe. The remaining steps are the same as in Example 1. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0075] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0076] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0077] Example 9 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The matrix is ​​prepared according to the matrix composition. The matrix is ​​composed of the following components by mass percentage: PrNd 30.00%, B 0.92%, Al 0.10%, Cu 0.20%, Zr 0.25%, Ga 0.30%, Co 0.70%, Ti 0.10%, Nb 0.10%, V 0.10%, with the balance being Fe. The remaining steps are the same as in Example 1. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0078] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0079] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0080] Example 10 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The matrix is ​​prepared according to the matrix composition. The matrix is ​​composed of the following components by mass percentage: PrNd 30.00%, B 0.92%, Al 0.10%, Cu 0.25%, Zr 0.25%, Ga 0.25%, Co 0.70%, Ti 0.045%, Nb 0.045%, V 0.135%, with the balance being Fe. The remaining steps are the same as in Example 1. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0081] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0082] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0083] Example 11 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The matrix is ​​prepared according to the following composition by mass percentage: PrNd 30.00%, B 0.92%, Al 0.10%, Cu 0.30%, Zr 0.25%, Ga 0.20%, Co 0.70%, Ti 0.045%, Nb 0.045%, V 0.135%, with the balance being Fe. The remaining steps are the same as in Example 1. (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0084] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0085] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0086] Example 12 This embodiment provides a sintered NdFeB magnet, the preparation method of which includes the following steps: (1) Preparation of weightless NdFeB blank: The difference between this step and Example 1 is that: two-stage tempering treatment: the first stage tempering temperature is 870℃ and the holding time is 2h; the second stage tempering temperature is 550℃ and the holding time is 8h, and the rest is the same as Example 1; (2) Preparation of multi-component alloy dispersant: The alloy is prepared according to the alloy composition, and the alloy is composed of the following components by mass percentage: Pr 70 Al 15 Cu 15 +Nd 80 Ga 10 Cu 10 The mixture (mass ratio 1:1) and the dispersant were separately added to a vacuum melting furnace, and then hydrogen crushed and air jet milled to obtain an alloy powder with a laser particle size of 3.0 μm. (3) Preparation of multi-element alloy diffusion slurry: Same as in Example 1.

[0087] (4) Preparation of neodymium iron boron thin film: Same as in Example 1.

[0088] (5) Grain boundary diffusion heat treatment: Same as in Example 1.

[0089] Table 8 Performance test results of neodymium iron boron magnets in Examples 1, 4-12, and CN113851320B Example 7A6-1

[0090] Through Table 8, Figures 5-7 It can be seen that the products of Examples 4 and 5 have the best overall performance, with a remanence Br of 14.78-14.84 kGs, intrinsic coercivity Hcj of 20.65-20.72 kOe, maximum energy product (BH)max of 50.21-50.54 MGOe, and squareness Hk / Hcj of 94.5%-94.7%. Their overall performance is superior to the products of patents CN113851320B and CN121839343A. (Combined with...) Figure 5 and Figure 6 It can be seen that the sintered NdFeB magnet prepared in Example 4 exhibits a morphology with distinct spacing between the main phase particles; combined with Figure 5 and Figure 7 It can be seen that the sintered NdFeB magnet prepared in Example 4 exhibits a continuous grain boundary phase and no large-area agglomeration.

[0091] Compared with Example 4, the matrix composition changed in Example 6. In particular, the lack of Ga weakened the non-magnetic characteristics of the grain boundary phase, and reduced the grain boundary continuity and demagnetizing coupling ability. The low total amount of Ti, Nb and V could not effectively refine the grains and form a dispersed pinned phase. The coercivity of Example 6 was significantly reduced, and the remanence and magnetic energy product also decreased.

[0092] Compared to Example 4, the ratio of Ti, Nb, and V in Example 7 is changed, with the V content being relatively too low. V is one of the key elements for the formation of the pinning phase, and its insufficient proportion weakens the pinning effect, resulting in a significant decrease in coercivity; at the same time, the imbalance in the proportion also affects the uniformity of grain refinement, causing a slight decrease in remanence.

[0093] Compared with Example 4, the total amount of Ti, Nb and V in Example 8 is too low. Although the proportions of the three are still within the range, the insufficient total amount results in an insufficient number of dispersed phases, limited grain boundary pinning effect, and significantly reduced coercivity.

[0094] Compared with Example 4, the total amount of Ti, Nb and V changed in Example 9. Excessive non-magnetic phases accumulated at the grain boundaries, which not only diluted the volume fraction of the main phase, but also destroyed the continuity of the grain boundaries, resulting in a decrease in both remanence and coercivity, and a worsening of squareness.

[0095] Compared to Example 4, Example 10 shows that the mass ratio of Cu to Ga deviates to 1:1, which is lower than the preferred lower limit of 1:1.3-1.6 of this invention. The relatively high Cu ratio lowers the melting point of the grain boundary phase but does not provide enough Ga to enhance its non-magnetic characteristics, resulting in a thicker grain boundary phase with reduced continuity and pinning ability, significantly decreased squareness, and slightly reduced other properties.

[0096] Compared with Example 4, the ratio of Cu to Ga changed in Example 11. Ga was insufficient, the ferromagnetism of the grain boundary phase was enhanced, the exchange coupling between adjacent main phase grains was intensified, the demagnetization curve may show a "waist collapse" phenomenon, the squareness deteriorated, and the coercivity and magnetic energy product were also adversely affected.

[0097] Compared to Example 4, Example 12 altered the two-stage tempering temperatures. The first-stage tempering temperature was too low, resulting in insufficient homogenization of the metastable grain boundary phase formed during sintering and cooling, leaving compositional segregation and internal stress at the grain boundaries. The second-stage tempering temperature was too high, causing excessive coarsening and even partial decomposition of the grain boundary phase, weakening its pinning ability against magnetic domain walls. Therefore, the coercivity of Example 12 decreased significantly, and the remanence and energy product also decreased.

[0098] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a sintered NdFeB magnet, characterized in that, Includes the following steps: (1) Preparation of weightless NdFeB blanks: The raw materials were prepared according to the matrix composition, which consisted of the following components by mass percentage: PrNd 29.5-31.5%, B 0.88-0.96%, Al 0.05-0.15%, Cu 0.10-0.30%, Zr 0.20-0.30%, Ga 0.20-0.40%, Co 0.65-0.75%, Ti 0.01-0.10%, Nb 0.01-0. 0.15% Ti, 0.05-0.15% V, with the balance being Fe; the mass ratio of Ti, Nb, and V is 1:(0.8-1.2):(2.5-3.5), and the total mass percentage of the three is 0.15-0.26%; the mass ratio of Cu and Ga is 1:(1.3-1.6); after batching, the materials are smelted, hydrogenated, air-jet milled, and shaped to obtain a green blank; the green blank is sintered and subjected to two-stage tempering treatment; after cooling, a sintered NdFeB blank is obtained. (2) Preparation of multi-element alloy dispersants; (3) Preparation of multi-element alloy diffusion slurry: Mix the multi-element alloy diffuser with additives; (4) Preparation of NdFeB thin sheets: The sintered NdFeB blanks are processed into thin sheets, and the thin sheets are coated with multi-element alloy diffusion paste; (5) Grain boundary diffusion heat treatment: The coated NdFeB sheet is sintered and air-cooled to obtain sintered NdFeB magnet.

2. The method for preparing sintered NdFeB magnets according to claim 1, characterized in that, Multi-element alloy diffusing agents are selected from alloys with the following mass percentage composition: Pr 70 Cu 30 Pr 70 Al 15 Cu 15 、Nd 80 Ga 10 Cu 10 Pr 70 Al 15 Cu 15 and Nd 80 Ga 10 Cu 10 The mixture of Nd 70 Ce 10 Cu 10 Ga 10 .

3. The method for preparing sintered NdFeB magnets according to claim 2, characterized in that, Multi-element alloy diffusing agents are selected from alloys with the following mass percentage composition: Pr 70 Al 15 Cu 15 and Nd 80 Ga 10 Cu 10 A mixture.

4. The method for preparing sintered NdFeB magnets according to claim 1, characterized in that, The mass ratio of the multi-element alloy diffusing agent to the additive is (18-19):(1-2).

5. The method for preparing sintered NdFeB magnets according to claim 4, characterized in that, The additive consists of polyvinyl alcohol, ethanol and polyethyleneimine in a mass ratio of (0.8-1.2):(1.6-2.3):(0.5-0.8).

6. The method for preparing sintered NdFeB magnets according to claim 1, characterized in that, The sintering conditions in step (1) are: sintering at 1000-1100℃ for 5-8 hours.

7. The method for preparing sintered NdFeB magnets according to claim 6, characterized in that, The conditions for the two-stage tempering treatment are as follows: the first-stage tempering temperature is 900-920℃, and the holding time is 2-4 hours; the second-stage tempering temperature is 480-520℃, and the holding time is 5-6 hours.

8. A sintered NdFeB magnet, characterized in that, The sintered NdFeB magnet is prepared using the preparation method described in any one of claims 1-7.

9. The sintered NdFeB magnet according to claim 8, characterized in that, The remanence of the sintered NdFeB magnet is 14.78-14.84 kGs; the intrinsic coercivity is 20.65-20.72 kOe; the maximum energy product is 50.21-50.54 MGOe; and the squareness is 94.5%-94.7%.

10. An application of a sintered NdFeB magnet prepared using the preparation method of any one of claims 1-7, characterized in that, The sintered NdFeB magnet is used to prepare rare earth permanent magnet materials.

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