Diffusion source and diffusion method for increasing coercivity of sintered neodymium-iron-boron magnets

Abstract

The application discloses a diffusion source for improving the coercivity of sintered neodymium-iron-boron magnets and a diffusion method. According to atomic percentage, the diffusion source comprises 80 at.% or more of heavy rare earth elements, 10-19 at.% of low-melting-point metal elements, not more than 0.2 at.% of high-melting-point metal elements, and not more than 1 at.% of magnetic elements. The heavy rare earth elements are at least one of dysprosium and terbium; the low-melting-point metal elements are at least one of aluminum, copper, gallium, tin and zinc; the high-melting-point metal elements are at least one of zirconium, vanadium, tungsten, niobium, titanium and manganese; and the magnetic elements are at least one of iron, cobalt and nickel. By optimizing the composition, attachment mode and diffusion process of the alloy diffusion source, the diffusion effect of the diffusion source is significantly improved, and the diffusion source is mainly used for grain boundary diffusion to improve the coercivity of sintered neodymium-iron-boron magnets, and is particularly suitable for grain boundary diffusion to improve the coercivity of sintered neodymium-iron-boron magnets with a thickness of more than 10 mm.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials, specifically a diffusion source and diffusion method for improving the coercivity of sintered NdFeB magnets. Background Technology

[0002] Sintered NdFeB permanent magnets are currently the most widely used and highest-performing permanent magnet materials in industrial production, earning them the reputation of "King of Permanent Magnets." They are extensively used in new energy vehicles, energy-saving home appliances, and intelligent manufacturing. Coercivity reflects a magnet's resistance to demagnetization and is a primary consideration for its long-term stable service. Common methods for improving coercivity in the preparation of sintered NdFeB magnets include directly adding heavy rare earth elements (such as Dy and Tb) during alloy smelting, adding powder containing heavy rare earth elements to the powder through a dual-alloy process, and introducing heavy rare earth elements into the magnet interior through grain boundary diffusion. Among these, grain boundary diffusion has become a more widely adopted method due to its lower cost and higher performance improvement.

[0003] During grain boundary diffusion, the diffusion source needs to diffuse through narrow grain boundary phases into the magnet's interior, and then a small amount enters the surface of the main phase grains. The grain boundary diffusion effect is influenced by the diffusion source. Compared with previous elemental or compound diffusion sources, alloy diffusion sources have significant advantages. A well-designed composition and structure of the alloy diffusion source can promote diffusion along the grain boundary phase into the magnet's interior and inhibit excessive diffusion into the main phase grains. The spray-diffusion method is currently the main method for attaching heavy rare earth alloy diffusion sources. This involves using spray equipment to spray a diffusion source rich in heavy rare earth elements, mixed with an organic binder, onto the magnet surface, followed by diffusion heat treatment. However, during high-temperature diffusion, the organic binder reacts chemically with the diffusion source, causing some of the diffusion source to be carbonized, nitrided, or oxidized, thus reducing the diffusion efficiency and the increase in coercivity. Optimizing the composition, attachment method, and diffusion process of the alloy diffusion source is crucial for improving the diffusion effect (increasing diffusion depth, suppressing remanence reduction, and increasing coercivity). Summary of the Invention

[0004] In view of this, the present invention provides a diffusion source and diffusion method for improving the coercivity of sintered NdFeB magnets, in order to solve the problems mentioned in the background art. By optimizing the composition, attachment method and diffusion process of the alloy diffusion source, the diffusion effect of the diffusion source is significantly improved (increasing diffusion depth, suppressing the decrease in remanence, and increasing the increase in coercivity). It is mainly used for grain boundary diffusion to improve the coercivity of sintered NdFeB magnets, and is particularly suitable for grain boundary diffusion to improve the coercivity of sintered NdFeB magnets with a thickness of more than 10 mm.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention discloses a diffusion source for improving the coercivity of sintered NdFeB magnets, comprising, by atomic ratio, more than 80 at.% heavy rare earth elements, 10-19 at.% low-melting-point metal elements, no more than 0.2 at.% high-melting-point metal elements, and no more than 1 at.% magnetic elements; wherein,

[0007] The heavy rare earth element is at least one of dysprosium and terbium;

[0008] The low-melting-point metal is at least one of aluminum, copper, gallium, tin, and zinc;

[0009] The high-melting-point metal is at least one of zirconium, vanadium, tungsten, niobium, titanium, and manganese;

[0010] The magnetic element is at least one of iron, cobalt, and nickel.

[0011] As a further aspect of the present invention: the melting point of the diffusion source is 700~800℃, the oxygen content is below 400ppm, the nitrogen content is below 200ppm, and the carbon content is below 200ppm.

[0012] As a further aspect of the present invention, the diffusion source is prepared by gas atomization granulation method.

[0013] As a further aspect of the present invention: the average particle size of the diffusion source is <10μm, and the sphericity is greater than 0.9.

[0014] As a further aspect of the present invention: in the low melting point metal, the atomic ratio of aluminum, copper, gallium, tin and zinc is (3-5):(3-5):(3-5):(1-2):(1-2).

[0015] Secondly, the present invention discloses a diffusion method for improving the coercivity of sintered NdFeB magnets as described above, comprising the following steps:

[0016] The diffusion source is sprayed onto the surface of the sintered NdFeB magnet to be diffused using a thermal spraying process to obtain a semi-finished product;

[0017] After the semi-finished product is subjected to high-temperature diffusion treatment and then cooled, a high-coercivity sintered NdFeB magnet is obtained.

[0018] As a further aspect of the present invention: the high-temperature diffusion treatment is carried out in a vacuum or inert gas environment, the heat treatment temperature is between ±10°C of the melting point temperature of the diffusion source, and the holding time is 5~40h.

[0019] As a further aspect of the present invention, it also includes a heat treatment step after high-temperature thermal diffusion treatment, wherein the heat treatment temperature is 460~600℃ and the time is 3~6h.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) Rationally design the composition of the diffusion source. ① By controlling the content of high-melting-point metal elements and low-melting-point metal elements, the melting point of the diffusion source can be controlled. Higher diffusion source fluidity can be obtained at a lower diffusion heat treatment temperature, which promotes the diffusion of the diffusion source along the grain boundary phase into the magnet and inhibits the diffusion of the diffusion source into the main phase grain. ② By controlling the content of magnetic elements such as iron, cobalt, and nickel, the content of iron, cobalt, and nickel in the grain boundary phase of the magnet after diffusion is reduced, a non-magnetic grain boundary phase is constructed, and the coercivity of the magnet is improved. ③ Strictly control the content of impurity elements such as oxygen, nitrogen, and carbon to reduce the consumption of impurity elements on the diffusion source and the influence on the magnetic properties of the magnet after diffusion.

[0022] (2) The diffusion source powder can be prepared by using gas atomization granulation technology, which can improve the sphericity and flowability of the diffusion source powder. Combined with the optimization of the particle size of the diffusion source powder, the uniformity of the diffusion source on the magnet surface can be significantly improved, and the uniformity of the magnet performance after diffusion can be effectively improved.

[0023] (3) The diffusion source powder is heated and partially melted by thermal spraying and then attached to the magnet surface. Compared with traditional organic adhesives, this method uses the diffusion source itself as an adhesive, which can effectively avoid the carbonization, nitriding or oxidation of the diffusion source and magnet by the organic adhesive during the high-temperature diffusion process, thereby improving the utilization rate of the diffusion source and the increase in coercivity. Detailed Implementation

[0024] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0026] Example 1

[0027] The manufacturing component is Dy 87.1 Al 3.1 Cu 3.1 Ga 3.1 Sn 1.8 Zn 1.8A diffusion source alloy of (at.%) was used to prepare diffusion source powder with a sphericity of 0.95 and an average particle size of 9.5 μm by gas atomization granulation. The melting point of the diffusion source was measured to be 732 °C, oxygen content 260 ppm, nitrogen content 143 ppm, and carbon content 86 ppm. Using a thermal spraying process, 0.6 wt% of the diffusion source was coated onto the surface of N52 grade NdFeB magnets with thicknesses of 4 mm, 8 mm, 12 mm, and 16 mm. The thermal spraying temperature was 720 °C, the spray gun pressure was 0.5 MPa, and the medium gas was argon. The magnets coated with the diffusion source were subjected to diffusion heat treatment at 735 °C. The diffusion heat treatment times for magnets with thicknesses of 2 mm, 9 mm, and 16 mm were 5 h, 22 h, and 40 h, respectively. After cooling, high coercivity sintered NdFeB magnets were obtained and labeled as Example 1.

[0028] Comparative Example 1-1

[0029] Using a magnetron sputtering coating apparatus, 0.6 wt.% of metallic dysprosium was deposited on the surface of the magnet to be diffused, the same as in Example 1. Then, diffusion heat treatment was performed at 735°C. The diffusion heat treatment times for magnets with thicknesses of 2 mm, 9 mm, and 16 mm were 5 h, 22 h, and 40 h, respectively. After cooling, high coercivity sintered NdFeB magnets were obtained and labeled as Comparative Example 1-1.

[0030] Comparative Examples 1-2

[0031] Compared with Comparative Example 1-1, the amount of diffusion source and the temperature of diffusion heat treatment were optimized and adjusted according to the melting point of the diffusion source and the Dy content in the diffusion source alloy. Specifically, the amount of diffusion source was 0.52wt%, the temperature of diffusion heat treatment was 900℃, and other process parameters were the same as those of Comparative Example 1-1, which is marked as Comparative Example 1-2.

[0032] Comparative Examples 1-3

[0033] Compared to Example 1, the composition of the diffusion source alloy is Dy 92 Al2Cu2Ga2Sn1Zn1 (at.%), with other process parameters the same as in Example 1, are labeled as Comparative Examples 1-3.

[0034] Comparative Examples 1-4

[0035] Compared with Comparative Examples 1-3, the thermal spraying temperature, diffusion source adhesion amount, and diffusion heat treatment temperature were optimized and adjusted according to the melting point of the diffusion source alloy and the Dy content in the diffusion source alloy. Specifically, the thermal spraying temperature was 905℃, the diffusion source adhesion amount was 0.57wt%, and the diffusion heat treatment temperature was 930℃. Other process parameters were the same as those in Comparative Examples 1-3, and were marked as Comparative Examples 1-4.

[0036] Comparative Examples 1-5

[0037] Compared to Example 1, the composition of the diffusion source alloy is Dy 84.1 Al 3.1 Cu 3.1 Ga 3.1 Sn 1.8 Zn 1.8 Zr1Nb1Ti1 (at.%), with other process parameters the same as in Example 1, are labeled as Comparative Examples 1-5.

[0038] Comparative Examples 1-6

[0039] Compared with Comparative Examples 1-5, the thermal spraying temperature, diffusion source adhesion amount, and diffusion heat treatment temperature were optimized and adjusted according to the melting point of the diffusion source alloy and the Dy content in the diffusion source alloy. Specifically, the thermal spraying temperature was 960℃, the diffusion source adhesion amount was 0.62wt%, and the diffusion heat treatment temperature was 980℃. Other process parameters were the same as those in Comparative Examples 1-5, and were marked as Comparative Examples 1-6.

[0040] Comparative Examples 1-7

[0041] Compared to Example 1, the composition of the diffusion source alloy is Dy 87.1 Al 9.3 Sn 1.8 Zn 1.8 (at.%), other process parameters are the same as in Example 1, and are marked as Comparative Examples 1-7.

[0042] Using a magnetic performance tester, the coercivity of Example 1 and Comparative Examples 1-1 to 1-7 was compared and tested at room temperature (23±1℃) in accordance with the requirements of GB / T 3217-2013 Permanent Magnet (Hard Magnet) Materials - Magnetic Test Methods. The results are shown in Table 1.

[0043] Table 1. Test results of Example 1 and Comparative Examples 1-1 to 1-5

[0044]

[0045] According to the test results in Table 1, it can be seen that: (1) Compared with Comparative Examples 1-1 to 1-6, the diffusion heat treatment temperature can be significantly reduced by using the technical solution of Example 1 in this paper. Under the condition of obtaining the same increase in coercivity, the effect on remanence is significantly reduced. For magnets with a thickness of more than 10 mm, the coercivity of the magnet after diffusion is significantly higher than that of Comparative Examples 1-1 to 1-6 by using the technical solution of Example 1 in this paper. (2) Compared with Comparative Examples 1-7, the increase in coercivity is greater and the decrease in remanence is smaller by using the technical solution of Example 1 in this paper.

[0046] Example 2

[0047] The manufacturing component is Tb 80.5 Al5Cu5Ga5Sn2Zn2Co 0.5 A diffusion source alloy of (at.%) was used to prepare diffusion source powder with a sphericity of 0.93 and an average particle size of 7.6 μm by gas atomization granulation. The melting point of the diffusion source was measured to be 708 °C, oxygen content 374 ppm, nitrogen content 165 ppm, and carbon content 54 ppm. Using a thermal spraying process, 0.5 wt% of the diffusion source was coated on the surface of a 52M grade NdFeB magnet with a thickness of 3 mm. The thermal spraying temperature was 690 °C, the spray gun pressure was 0.8 MPa, and the medium gas was argon. The magnet coated with the diffusion source was subjected to diffusion heat treatment at 715 °C for 15 h. After cooling, a high coercivity sintered NdFeB magnet was obtained, labeled as Example 2.

[0048] Comparative Example 2

[0049] Compared to Example 2, the only difference lies in the method of preparing the diffusion source powder. This comparative example uses hydrogen crushing + air jet milling to prepare diffusion source powder with an average particle size of 7.6 μm and a sphericity of 0.53. After cooling, a high coercivity sintered NdFeB magnet was obtained, labeled as Comparative Example 2.

[0050] Using a magnetic performance tester, the coercivity of Example 2 and Comparative Example 2 was compared and tested at room temperature (23±1℃) according to the requirements of GB / T 3217-2013 Permanent Magnet (Hard Magnet) Materials - Magnetic Test Methods. The results are shown in Table 2. Ten samples of each type were tested, and the average value was taken. The difference between the highest and lowest coercivity was also calculated. The results are shown in Table 2.

[0051] Table 2 Test results of Example 2 and Comparative Example 2

[0052]

[0053] As can be seen from the test results in Table 2, compared with Comparative Example 2, the coercivity fluctuation of the magnet after diffusion is smaller when using the technical solution of Example 2 in this paper.

[0054] Example 3

[0055] The manufacturing component is Dy 85 Al4Cu4Ga4Sn 1.4 Zn 1.5 Zr 0.1A diffusion source alloy of (at.%) was used to prepare diffusion source powder with a sphericity of 0.9 and an average particle size of 8.3 μm by gas atomization granulation. The melting point of the diffusion source was measured to be 717 °C, oxygen content 343 ppm, nitrogen content 96 ppm, and carbon content 118 ppm. The diffusion source was coated with 0.8 wt% of the magnet weight onto the surface of a 5 mm thick N54 grade NdFeB magnet using a thermal spraying process. The thermal spraying temperature was 705 °C, the spray gun pressure was 0.3 MPa, and the medium gas was argon. The magnet coated with the diffusion source was subjected to diffusion heat treatment at 720 °C for 30 h. After cooling, a high coercivity sintered NdFeB magnet was obtained, labeled as Example 3.

[0056] Comparative Example 3

[0057] Compared to Example 3, the only difference was that an organic binder, rosin, was used in combination with cold spraying instead of direct thermal spraying to attach the diffusion source powder to the magnet surface. The spraying temperature was room temperature, and the spray gun pressure and medium were the same as in Example 3. After cooling, a high-coercivity sintered NdFeB magnet was obtained, labeled as Comparative Example 3.

[0058] Using a magnetic performance tester, the coercivity of Example 3 and Comparative Example 3 was compared and tested at room temperature (23±1℃) according to the requirements of GB / T 3217-2013 Permanent Magnet (Hard Magnet) Materials - Magnetic Test Methods. The oxygen, nitrogen and carbon contents of Example 3 and Comparative Example 3 were tested using an oxygen, nitrogen and hydrogen and carbon and sulfur tester. The results are shown in Table 3.

[0059] Table 3 Test results of Example 3 and Comparative Example 3

[0060]

[0061] According to the test results in Table 3, compared with Comparative Example 3, the technical solution of Example 3 in this paper, which uses high-temperature thermal spraying to attach the low-melting-point diffusion source to the magnet surface without the use of organic adhesives, can effectively reduce the oxygen, nitrogen and carbon content of the magnet after diffusion and improve the coercivity of the magnet after diffusion.

[0062] Example 4

[0063] The manufacturing component is Tb 40 Dy 44 Al 4.5 Cu 3.5A diffusion source alloy of Ga5Sn2Zn1 (at.%) was used to prepare diffusion source powder with a sphericity of 0.91 and an average particle size of 8.8 μm by gas atomization granulation. The melting point of the diffusion source was measured to be 785℃, oxygen content 325ppm, nitrogen content 96ppm, and carbon content 35ppm. The diffusion source was coated with 0.8wt% of the magnet weight onto the surface of a 4mm thick N48 NdFeB magnet using a thermal spraying process. The thermal spraying temperature was 770℃, the spray gun pressure was 0.6MPa, and the medium gas was argon. The magnet coated with the diffusion source was subjected to diffusion heat treatment at 785℃ for 16 hours. After cooling, a high coercivity sintered NdFeB magnet was obtained, labeled as Example 4.

[0064] Comparative Example 4-1

[0065] Compared to Example 4, the composition of the diffusion source alloy is (Tb 40 Dy 44 Al 4.5 Cu 3.5 Ga5Sn2Zn1) 94 Fe3Co3 (at.%), with other process parameters the same as in Example 4, is labeled as Comparative Example 4-1.

[0066] Comparative Example 4-2

[0067] Compared with Comparative Example 4-1, the thermal spraying temperature, diffusion source adhesion amount, and diffusion heat treatment temperature were optimized and adjusted according to the melting point of the diffusion source alloy and the DyTb content in the diffusion source alloy. Specifically, the thermal spraying temperature was 815℃, the diffusion source adhesion amount was 0.85wt%, and the diffusion heat treatment temperature was 830℃. Other process parameters were the same as those in Comparative Example 4-1, and this was marked as Comparative Example 4-2.

[0068] Using a magnetic performance tester, the coercivity of Example 4 and Comparative Examples 4-1 and 4-2 was compared and tested at room temperature (23±1℃) in accordance with the requirements of GB / T 3217-2013 Permanent Magnet (Hard Magnet) Materials - Magnetic Test Methods. The results are shown in Table 4.

[0069] Table 4. Test results of Example 4 and Comparative Examples 4-1 and 4-2

[0070]

[0071] As can be seen from the test results in Table 4, compared with Comparative Examples 4-1 and 4-2, the coercivity of the diffused magnet is higher when the technical solution of Example 4 in this paper is adopted.

[0072] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0073] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A diffusion source for improving the coercivity of sintered NdFeB magnets, characterized in that, Based on atomic ratio, it contains more than 80 at.% heavy rare earth elements, 10-19 at.% low melting point metal elements, no more than 0.2 at.% high melting point metal elements, and no more than 1 at.% magnetic elements; among which, The heavy rare earth element is at least one of dysprosium and terbium; The low-melting-point metals are aluminum, copper, gallium, tin, and zinc; the atomic ratio of aluminum, copper, gallium, tin, and zinc is (3-5):(3-5):(3-5):(1-2):(1-2). The high-melting-point metal is at least one of zirconium, vanadium, tungsten, niobium, titanium, and manganese; The magnetic element is at least one of iron, cobalt, and nickel; The diffusion source has a melting point of 700~800℃, an oxygen content of less than 400ppm, a nitrogen content of less than 200ppm, and a carbon content of less than 200ppm. The diffusion source diffusion method for improving the coercivity of sintered NdFeB magnets includes the following steps: The diffusion source is sprayed onto the surface of the sintered NdFeB magnet to be diffused using a thermal spraying process to obtain a semi-finished product; After the semi-finished product is subjected to high-temperature diffusion treatment and then cooled, a high-coercivity sintered NdFeB magnet is obtained.

2. The diffusion source for improving the coercivity of sintered NdFeB magnets according to claim 1, characterized in that, The diffusion source was prepared by gas atomization granulation method.

3. The diffusion source for improving the coercivity of sintered NdFeB magnets according to claim 1, characterized in that, The average particle size of the diffusion source is <10 μm, and the sphericity is greater than 0.

9.

4. The diffusion source for improving the coercivity of sintered NdFeB magnets according to claim 1, characterized in that, The high-temperature diffusion treatment is carried out in a vacuum or inert gas environment, with the heat treatment temperature between ±10°C of the diffusion source melting point, and the holding time is 5~40h.

5. The diffusion source for improving the coercivity of sintered NdFeB magnets according to claim 1, characterized in that, It also includes a heat treatment step following high-temperature thermal diffusion treatment, wherein the heat treatment temperature is 460~600℃ and the time is 3~6h.

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