METHOD FOR IMPROVING THE MAGNETIC PERFORMANCE OF A SINTERED NdFeB MAGNET

Abstract

Method for improving the magnetic performance of a sintered NdFeB magnet, comprising: First, the surface of a sintered NdFeB magnet is coated with a raw material consisting of elements R, H and X to form a coating. and then proceed with a diffusion treatment and an aging treatment of the sintered NdFeB magnet with the coating in a vacuum or inert gas environment, where R is at least one of the elements Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, H Element hydrogen is; X is at least one of the elements C, O, N, S, B, Cl and Si, wherein in the raw material, consisting of the elements R, H and X, the content of element H, expressed as a percentage by mass, is 0.01% to 2%, and the content of element X, expressed as a percentage mass fraction, is between 0.01% and 10%, wherein the sintered NdFeB magnet with the coating is subjected to a dehydration treatment prior to the diffusion treatment, wherein a dehydration temperature is 600 °C to 800 °C and the treatment time is 0.1 h to 30 h and the hydrogen content in the coating of the The NdFeB magnets after dehydration treatment, expressed as a percentage mass fraction, amount to 0.001% to 0.2%.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates generally to methods for producing sintered NdFeB magnets, and in particular to a method for improving the magnetic performance of the sintered NdFeB magnet. 2. Description of the related prior art

[0002] Sintered permanent magnetic NdFeB material has been extensively used in aerospace, military, and civilian applications due to its excellent magnetic performance. In recent years, energy-saving products such as energy-efficient elevators, inverter air conditioners, hybrid electric vehicles, and electric vehicles have emerged as a response to energy conservation and environmental protection, as promoted by governments. These products have generated a high market demand for NdFeB products.

[0003] The performance of sintered permanent magnet NdFeB material has been significantly improved through nearly 30 years of development. Since the experimental remanence value of Br (1.555 T) has reached 97% of the theoretical value of 1.6 T, it is very difficult to further improve the remanence of sintered permanent magnet NdFeB material. In contrast, the experimental coercivity value of 652.50 kA / m is only 12% of the theoretical value of 5333.20 kA / m, indicating room for improvement. Therefore, exploring approaches to maintain high remanence and improve coercivity has become a challenging and pressing area of ​​current research. One study found that the coercivity of a magnet can be improved by using heavy rare-earth elements such as Dy / Tb to replace Nd in the magnet, creating a new phase (Nd,Dy / Tb)₂Fe. 14B to generate anisotropy where the anisotropic field exceeds that of the main phase. However, this can lead to a significant reduction in the magnet's remanence. Meanwhile, a high-coercivity magnet produced using conventional methods requires a high content of heavy rare-earth elements and incurs high manufacturing costs. Grain boundary diffusion technology is a method that has been developed in recent years for producing high-coercivity magnets.The method for adding heavy rare earth elements to magnets using grain boundary diffusion technology aims to employ a heat treatment process to ensure the diffusion of heavy rare earth elements, as contained in the magnet's coating, along the magnet's grain boundary into the magnet, in order to cause the heavy rare earth elements to distribute themselves at the grain boundary phase and on the epitaxial layer of the main phase; this can improve coercivity while preserving remanence, resulting in limited use of heavy rare earth elements and low costs.

[0004] The coating of the sintered NdFeB magnet, as produced using grain boundary diffusion technology, is typically formed by coating the surface of the sintered NdFeB magnet with a powder such as elemental rare earth, rare earth oxide, rare earth fluoride, or rare earth hydride at the micrometer and nanometer scale. Elemental rare earth exhibits poor oxidation resistance, making it difficult to produce. While rare earth oxide and rare earth fluoride, despite their high oxidation resistance, are unlikely to produce elemental rare earth upon diffusion, the oxygen and fluorine atoms present in rare earth oxide and rare earth fluoride can, to some extent, impair the magnet's performance.Compared to elemental rare earth, a rare earth hydride exhibits higher oxidation resistance, which, through dehydration at a specific temperature, can produce elemental metal and hydrogen gas; therefore, it is an ideal compound for grain boundary diffusion.

[0005] Currently, there are three methods for improving the coercivity of sintered NdFeB magnets by using heavy rare-earth hydride as the coating material, based on grain boundary diffusion technology. The first method is the vapor deposition-condensation process, as disclosed in Chinese patent number CN 1 01 908 397 B, for obtaining heavy rare-earth hydride with a particle size of 10 to 100 nm. This method aims to coat the magnet's surface with heavy rare-earth hydride powder to cause heavy rare-earth elements to penetrate the magnet's interior through heat treatment.The second method is the method disclosed in Chinese patents CN 1 02 747 318 A and CN 1 01 542 654 B for obtaining heavy rare-earth hydride powder by hydrogen absorption and fragmentation, which aims to coat the magnet surface with heavy rare-earth hydride powder and to cause heavy rare-earth elements to enter the magnet by heat treatment. The third method is the method disclosed in Chinese patent CN 1 01 563 739 B for vapor deposition using DyH₂ or TbH₂ to cause the heavy rare-earth elements to enter the magnet by heat treatment.

[0006] According to the three methods described above, heavy rare-earth hydride powder at the micrometer or nanometer scale, as used in the first and second methods, exhibits extremely high activity, which tends to cause oxygen combustion and even explosion, and is unlikely to meet the powder protection requirements for mass production. Furthermore, after the powder oxidizes, the coercivity of the sintered NdFeB magnet will be significantly reduced, to the point of poor product consistency and extremely serious potential safety risks. Moreover, due to its susceptibility to oxidation, heavy rare-earth hydride powder at the micrometer or nanometer scale is difficult to recycle, resulting in disadvantages such as low utilization of heavy rare-earth elements and high manufacturing costs.Despite the fact that the third method offers greater safety, a rare earth hydride may be present in a random distribution inside the equipment during vapor deposition, making it unlikely to adhere to the surface of the sintered NdFeB magnet; therefore, the utilization rate of rare earth elements is extremely low; moreover, expensive vapor deposition equipment and low vapor deposition efficiency can also lead to increased manufacturing costs.

[0007] US 2010 / 0129538A1 discloses a method for manufacturing a magnet that not only allows for achieving sufficient Br and HcJ values, but also results in a magnet with a sufficiently large rectangularity ratio.

[0008] US 8 231 740 B2 discloses a manufacturing process for a rare-earth permanent magnet by covering a magnetic body of a R 1-Fe-B composition, so that coercivity is increased while a decrease in its remanence is minimized.

[0009] WO 2015 / 051756A1 discloses a surface treatment method and a manufacturing process for a sintered NdFeB magnet. The surface treatment method comprises: immersion, coating, or spraying a solution containing at least one of Dy and Tb onto the surface of the sintered NdFeB magnet, and diffusion processing of the sintered NdFeB magnet in a non-oxidizing environment. The intrinsic coercivity can be improved while maintaining the maximum energy product of the sintered NdFeB magnet based on the surface treatment and manufacturing processes. SUMMARY OF THE INVENTION

[0010] The technical problem to be solved by the present invention is to provide a method for improving the performance of sintered NdFeB magnets. Such a method should be available for a mass-produced product that exhibits features such as high efficiency, excellent product consistency, high utilization of heavy rare earth elements, low manufacturing costs, and high safety.

[0011] The technical solution used by the present invention to solve the aforementioned technical problem is as follows: a method for improving the magnetic performance of a sintered NdFeB magnet comprises the following steps: First, a surface of the sintered NdFeB magnet is coated with a raw material consisting of elements R, H, and X to form a coating; then, a diffusion and aging treatment of the coated sintered NdFeB magnet is carried out in a vacuum or inert gas environment, wherein R is at least one of the elements Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu;H is the element hydrogen, X is at least one of the elements C, O, N, S, B, Cl and Si, wherein in the raw material consisting of the elements R, H and X, the content of the element H, expressed as a percentage by mass, is 0.01% to 2%, wherein in the raw material consisting of the elements R, H and X, the content of the element X, expressed as a percentage by mass, is 0.01% to 10%, wherein the sintered NdFeB magnet with the coating is subjected to a dehydration treatment before the diffusion treatment, wherein a dehydration temperature is 600°C to 800°C and the treatment time is 0.1 h to 30 h, and the hydrogen content in the coating of the sintered NdFeB magnet after the dehydration treatment, expressed as a percentage by mass, is 0.001% to 0.2%.

[0012] According to this method, the stability of the raw material can be improved by controlling the content of element H within the range of 0.01 to 2 wt%.

[0013] According to this method, the stability of the raw material can be improved by controlling the content of element X in the raw material within the range of 0.01% to 10 wt%; meanwhile, the performance of the sintered NdFeB magnet obtained by using this method can be significantly improved.

[0014] The elements R, H, and X in the raw material are present as the product of a chemical reaction of the mixture of elements R, H, and X. According to this process, the rare earth element R reacts simultaneously with H and X to create a compound containing the elements R, H, and X; the material produced using such a compound can provide a coating with higher stability.

[0015] The elements R, H, and X in the raw material are present as products of the chemical reaction of the mixture of elements R, H, and X. According to this process, element X can effectively improve the stability of rare earth hydride, which is advantageous for mass production, improved product consistency, and material recycling.

[0016] Element R is at least one of such elements, selected from Pr, Nd, Gd, Dy, Tb, and Ho. This method can significantly improve the coercivity of the magnet.

[0017] The thickness of the sintered NdFeB magnet is less than 15 mm. According to this process, the rare earth elements have entered the magnet through uniform diffusion, significantly improving its coercivity; moreover, the demagnetization curve also exhibits excellent rectangularity.

[0018] According to this method, it is possible to effectively control the hydrogen content in the coating by dehydration in order to avoid impairments of the magnetic performance due to high hydrogen content during the subsequent diffusion treatment.

[0019] Such a process can effectively control the hydrogen content in the coating to avoid impairment of the magnetic performance by hydrogen during the subsequent diffusion treatment and to ensure optimal magnetic performance.

[0020] Diffusion treatment refers to a heat treatment lasting from 1 to 30 hours at a temperature of 700°C to 1000°C. This process aims to ensure the effective diffusion of rare earth elements in the sintered NdFeB magnet for distribution at the grain boundary of the sintered NdFeB magnet and on the grain epitaxial layer of the main phase; it can significantly improve coercivity while preserving remanence.

[0021] The aging treatment refers to heat treatment for 1 to 10 hours at a temperature of 400°C to 600°C.

[0022] Compared to the prior art, the present invention has the advantage that the surface of the sintered NdFeB magnet is coated with the raw material, consisting of the elements R, H, and X, to form a coating; where R is at least one of 17 rare-earth elements; H is hydrogen; and X is at least one of such elements as C, O, N, S, B, Cl, and Si. Due to the interaction between the elements R, H, and X, the raw material exhibits lower activity for coating formation, making it unlikely to oxidize when exposed to air. Therefore, it will not suffer from product consistency problems due to oxidation of the raw material, ensuring excellent product consistency and increased safety. It is also suitable for mass production.Meanwhile, the raw material, consisting of the elements R, H, and X, is available for recycling and reuse due to its high stability. For this reason, it can improve the utilization rate of rare earth elements and reduce production costs. DESCRIPTION OF THE EXECUTION FORMS

[0023] The present invention is described in more detail below with reference to the following examples:

[0024] Embodiment 1: A method for improving the magnetic performance of the sintered NdFeB magnet includes the following steps: 1) Processing the terbium metal in the hydrogen-oxygen mixed gas with an oxygen content of 1% to obtain a powder with a hydrogen and oxygen content of 9,416 ppm and 3,174 ppm respectively; 2) Grinding the powder for 8 h to obtain powder material with an average particle size of 1.51 µm; 3) Uniformly mix the above-mentioned powder raw material with anhydrous ethanol and spray evenly onto the surface of the sintered NdFeB magnet to form a coating of 20 µm before drying at a temperature of 80 °C; 4) Proceed with a dehydration and diffusion treatment of the sintered NdFeB magnet after drying in a vacuum environment at a pressure of up to 6.0 × 10 -4 Pa, followed by an aging treatment, with a dehydration temperature of 700 °C. The dehydration duration is 0.5 h; the temperature during the diffusion treatment is 900 °C; the duration of the diffusion treatment is 16 h; the temperature of the aging treatment is 490 °C; the duration of the aging treatment is 4 h.

[0025] In this embodiment, the sintered NdFeB magnet is produced from a solid sintered NdFeB magnet by mechanical processing (cutting); its dimensions (diameter x height) are 10 × 7 mm; the solid sintered NdFeB magnet is produced using common NdFeB manufacturing processes such as strip casting, hydrogen decrepitation, jet milling, pressing, and sintering; the sintered NdFeB magnet comprises the following components: 29.5 wt.% Nd, 0.2 wt.% Dy, 1.0 wt.% B, balance Fe and other trace elements.

[0026] Embodiment 2: A method for improving the magnetic performance of the sintered NdFeB magnet comprises the following steps: 1) Processing the dysprosium metal in hydrogen gas to obtain the first powder; 2) Introducing the first coarse powder into the nitrogen-oxygen mixed gas with an oxygen content of 1.5% for passivation for 24 h in order to obtain the second powder with a hydrogen, oxygen and nitrogen content of 9,281 ppm, 3,430 ppm, and 2,161 ppm, respectively; 3) Continue ball milling of the second powder for 8 h to obtain raw powder material with an average particle size of up to 1.45 µm; 4) Mix the above-mentioned powder material uniformly with anhydrous ethanol and spray evenly onto the surface of the sintered NdFeB magnet to form a coating of 20 µm before drying at a temperature of 80 °C; 5) Continue with dehydration and diffusion treatment of the sintered NdFeB magnet in the proper sequence in a vacuum environment at a pressure of 6.0 × 10 -4Pa before aging treatment; the dehydration temperature is 680 °C; the dehydration duration is 1 h; the diffusion treatment temperature is 850 °C; the diffusion treatment duration is 12 h; the aging treatment temperature is 500 °C; the aging treatment duration is 4 h.

[0027] In this embodiment, the sintered NdFeB magnet is produced from a solid sintered NdFeB magnet by mechanical processing (cutting); its dimensions (diameter x height) are 10 × 5 mm; the solid sintered NdFeB magnet is produced using common NdFeB manufacturing processes such as strip casting, hydrogen decrepitation, jet milling, pressing, and sintering; the sintered NdFeB magnet contains the following components: 29.5 wt.% Nd, 0.2 wt.% Dy, 1.0 wt.% B, balance Fe and other trace elements.

[0028] Embodiment 3: A method for improving the magnetic performance of the sintered NdFeB magnet includes the following steps: 1) Processing the dysprosium metal in hydrogen gas to obtain the first powder; 2) Introducing the first powder into air for deactivation for 24 h in order to obtain the second powder with a hydrogen, oxygen and nitrogen content of 5,154 ppm, 7,208 ppm and 1,140 ppm respectively; 3) Continue ball milling of the second powder for 8 h to obtain raw powder material with an average particle size of 1.49 µm; 4) Mix the above-mentioned powder material uniformly with anhydrous ethanol and spray evenly onto the surface of the sintered NdFeB magnet to form a coating of 20 µm before drying at a temperature of 80 °C; 5) Proceed with dehydration and diffusion treatment of the sintered NdFeB magnet after drying in the proper sequence in a vacuum environment at a pressure of 6.0 × 10 -4 Pa before aging treatment; the dehydration temperature is 710 °C; the dehydration duration is 2 h; the diffusion treatment temperature is 900 °C; the diffusion treatment duration is 8 h; the aging treatment temperature is 510 °C; the aging treatment duration is 4 h.

[0029] In this embodiment, the sintered NdFeB magnet is produced from a solid sintered NdFeB magnet by mechanical processing (cutting); its dimensions (diameter × height) are 10 × 7 mm; the solid sintered NdFeB magnet is produced using common NdFeB manufacturing processes such as strip casting, hydrogen decrepitation, jet milling, pressing, and sintering; the sintered NdFeB magnet contains the following components: 29.5 wt.% Nd, 0.2 wt.% Dy, 1.0 wt.% B, balance Fe and other trace elements.

[0030] Embodiment 4: A method for improving the magnetic performance of a sintered NdFeB magnet includes the following steps: 1) Processing a Dy-Fe alloy in a hydrogen-oxygen mixed gas with an oxygen content of 0.5% to obtain powders with a hydrogen and oxygen content of 9,861 ppm and 2,786 ppm respectively; 2) Continue ball milling of the powder for 8 h to obtain the raw powder material with an average particle size of 1.58 µm; 3) Mix the above-mentioned powder material uniformly with anhydrous ethanol and spray evenly onto the surface of the sintered NdFeB magnet to form a coating of 20 µm before drying at a temperature of 80 °C; 4) Proceed with dehydration and diffusion treatment of the sintered NdFeB magnet after drying in the proper sequence in a vacuum environment at a pressure of 6.0 × 10 -4 Pa before aging treatment; the dehydration temperature is 650 °C; the dehydration duration is 3 h; the diffusion treatment temperature is 950 °C; the diffusion treatment duration is 20 h; the aging treatment temperature is 480 °C; the aging treatment duration is 4 h.

[0031] In this embodiment, the sintered NdFeB magnet is produced from a solid sintered NdFeB magnet by mechanical processing (cutting); its dimensions (diameter × height) are 10 × 9 mm; the solid sintered NdFeB magnet is produced using common NdFeB manufacturing processes such as strip casting, hydrogen decrepitation, jet milling, pressing, and sintering; the sintered NdFeB magnet contains the following components: 29.5 wt.% Nd, 0.2 wt.% Dy, 1.0 wt.% B, balance Fe and other trace elements.

[0032] Embodiment 5: A method for improving the magnetic performance of a sintered NdFeB magnet includes the following steps: 1) Processing a Pr-Cu alloy in hydrogen gas to obtain a first powder; 2) Introducing the first powder into a nitrogen-oxygen mixed gas with an oxygen content of 1% for deactivation for 24 h in order to obtain a second powder with a hydrogen, oxygen and nitrogen content of 9,538 ppm, 3,269 ppm, and 3,290 ppm, respectively; 3) Continue grinding the second powder for 8 h to obtain powder material with an average particle size of up to 1.67 µm; 4) Uniformly mix the above-mentioned powder material with anhydrous ethanol and spray evenly onto the surface of the sintered NdFeB magnet to form a 20 µm coating, and then dry at 80 °C. 5) Proceed with dehydration and diffusion treatment of the sintered NdFeB magnet after drying in the proper sequence in a vacuum environment at a pressure of 6.0 × 10 -4Pa before aging treatment; the dehydration temperature is 750 °C; the dehydration duration is 0.3 h; the diffusion treatment temperature is 800 °C; the diffusion treatment duration is 6 h; the aging treatment temperature is 500 °C; the aging treatment duration is 4 h.

[0033] In this embodiment, the sintered NdFeB magnet is produced from a solid sintered NdFeB magnet by mechanical processing (cutting); its dimensions (diameter × height) are 10 × 3 mm; the solid sintered NdFeB magnet is produced using common NdFeB manufacturing processes such as strip casting, hydrogen decrepitation, jet milling, pressing, and sintering; the sintered NdFeB magnet contains the following components: 29.5 wt.% Nd, 0.2 wt.% Dy, 1.0 wt.% B, balance Fe and other trace elements.

[0034] Of the sintered NdFeB magnets obtained by the methods according to embodiments 1 to 5, two magnets are selected for each embodiment; such sintered NdFeB magnets are designated as test specimens 1-1, 1-2, 2-1, 2-2, 3-1, 3-2, 4-1, 4-2, 5-1, and 5-2, respectively. Uncoated sintered NdFeB magnets are designated as the master specimen. A BH instrument for measuring permanent magnetic material is selected to perform the magnetic performance test for the master specimen and the test specimens in the embodiments mentioned above. The test data are shown in Table 1. Table 1: Magnetic properties of original samples and test specimens according to embodiments 1 to 5 Designation Remanence(T) Coercivity (kA / m) Maximum magnetic energy product (kJ / m²) 3 ) Rectangularity original sample 1,399 1184,45 371,02 91,9 Test sample 1-1 1,375 1919,95 365,05 95,5 Test sample 1-2 1,370 1900,85 364,89 96,3 Test sample 2-1 1,369 1599,96 365,20 95,2 Test sample 2-2 1,371 1586,43 365,60 95,0 Test sample 3-1 1,370 1473,40 355,97 94,3 Test sample 3-2 1,368 1457,48 354,22 94,2 Test sample 4-1 1,370 1529,91 363,85 95,5 Test sample 4-2 1,369 1537,08 363,37 95,6 Test sample 5-1 1,367 1361,16 355,89 95,4 Test sample 5-2 1,365 1359,57 355,41 95,3

[0035] Embodiment 6 (not according to the invention): A method for improving the magnetic performance of sintered NdFeB magnets comprises the following steps: 1) Processing the terbium metal in hydrogen gas to obtain powder with a hydrogen content of 9,590 ppm; 2) Continue grinding the powder for 8 h to obtain powder material with an average particle size of up to 1.54 µm; 3) Uniformly mix the above-mentioned fine powder and terbium oxide in a mass ratio of 9:1 to obtain the fine powder raw material; uniformly mix the fine powder raw material with anhydrous ethanol and spray it onto the surface of the sintered NdFeB magnet to form a coating with a thickness of 20 µm; then proceed with a drying treatment at a temperature of 80 °C; 4) Proceed with dehydration and diffusion treatment of the sintered NdFeB magnet after drying in the proper sequence in a vacuum environment at a pressure of 6.0 × 10 -4Pa before aging treatment; the dehydration temperature is 700 °C; the dehydration duration is 1 h; the diffusion treatment temperature is 950 °C; the diffusion treatment duration is 10 h; the aging treatment temperature is 510 °C; the aging treatment duration is 4 h.

[0036] In this embodiment, the sintered NdFeB magnet is produced from a solid sintered NdFeB magnet by mechanical processing (cutting); its dimensions (diameter x height) are 10 × 7 mm; the solid sintered NdFeB magnet is produced using common NdFeB manufacturing processes such as strip casting, hydrogen decrepitation, jet milling, pressing, and sintering; the sintered NdFeB magnet contains the following components: 29.5 wt.% Nd, 0.2 wt.% Dy, 1.0 wt.% B, balance Fe and other trace elements.

[0037] Embodiment 7: A method for improving the magnetic performance of a sintered NdFeB magnet includes the following steps: 1) Processing terbium metal in hydrogen gas to obtain the first powder; 2) Introducing the first powder into a nitrogen-oxygen mixed gas with an oxygen content of 1.5% for deactivation over 24 hours in order to obtain the second powder with a hydrogen, oxygen and nitrogen content of 9,378 ppm, 3,525 ppm, and 3,417 ppm, respectively; 3) Continue grinding the second powder for 8 h to obtain fine powder material with an average particle size of 1.41 µm; 4) Uniformly mix the above-mentioned fine powder and terbium nitride in a mass ratio of 9:1 to obtain fine powder raw material; uniformly mix the fine powder raw material with anhydrous ethanol and spray it onto the surface of the sintered NdFeB magnet to form a coating with a thickness of 20 µm; then proceed with a drying treatment at a temperature of 80 °C; 5) Proceed with a dehydration and diffusion treatment of the sintered NdFeB magnet after drying in the proper sequence in a vacuum environment at a pressure of 6.0 × 10 -4 Pa before aging treatment; the dehydration temperature is 660 °C; the dehydration duration is 2 h; the diffusion treatment temperature is 890 °C; the diffusion treatment duration is 18 h; the aging treatment temperature is 500 °C; the aging treatment duration is 4 h.

[0038] In this embodiment, the sintered NdFeB magnet is produced from a solid sintered NdFeB magnet by mechanical processing (cutting); its dimensions are (diameter × height) 10 × 7 mm; the solid sintered NdFeB magnet is manufactured using common processes such as strip casting, hydrogen decrepitation, jet milling, pressing and sintering in the field of NdFeB production; the sintered NdFeB magnet contains the following components: 29.5 wt.% Nd, 0.2 wt.% Dy, 1.0 wt.% B, balance Fe and other trace elements.

[0039] Embodiment 8: A method for improving the magnetic performance of a sintered NdFeB magnet includes the following steps: 1) Processing terbium metal in a hydrogen-oxygen mixed gas with an oxygen content of 1% to obtain coarse powder with a hydrogen and oxygen content of 9,891 ppm and 3,157 ppm respectively; 2) Continue ball milling of the coarse powder for 8 h to obtain the powder material with an average particle size of 1.57 µm; 3) Uniformly mix the above-mentioned fine powder and silicon dioxide in a mass ratio of 200:1 to obtain fine powder raw material; uniformly mix the fine powder raw material with anhydrous ethanol and spray it onto the surface of the sintered NdFeB magnet to form a coating with a thickness of 20 µm; then proceed with a drying treatment at a temperature of 80 °C; 4) Proceed with a dehydration and diffusion treatment of the sintered NdFeB magnet after drying in the proper sequence in a vacuum environment at a pressure of 6.0 × 10 -4Pa before aging treatment; the dehydration temperature is 730 °C; the dehydration duration is 0.5 h; the diffusion treatment temperature is 980 °C; the diffusion treatment duration is 6 h; the aging treatment temperature is 500 °C; the aging treatment duration is 4 h.

[0040] In this embodiment, the sintered NdFeB magnet is produced from a solid sintered NdFeB magnet by mechanical processing (cutting); its dimensions (diameter × height) are 10 × 7 mm; the solid sintered NdFeB magnet is produced using common NdFeB manufacturing processes such as strip casting, hydrogen decrepitation, jet milling, pressing, and sintering; the sintered NdFeB magnet contains the following components: 29.5 wt.% Nd, 0.2 wt.% Dy, 1.0 wt.% B, balance Fe and other trace elements.

[0041] Of the sintered NdFeB magnets obtained by the methods according to embodiments 6 to 8, two magnets are selected for each embodiment; such sintered NdFeB magnets are designated as test specimens 6-1, 6-2, 7-1, 7-2, 8-1, and 8-2, respectively; the uncoated sintered NdFeB magnet is designated as the master specimen. A BH instrument for measuring permanent magnetic material is selected to perform the magnetic performance test for the master specimen and the test specimens in the embodiments mentioned above. The test data are shown in Table 2. Table 2: Magnetic performance of original specimens and test specimens according to embodiments 6 to 8. Designation Remanence(T) Coercivity (kA / m) Maximum magnetic energy product (kJ / m²) 3 ) Rectangularity original sample 1,399 1184,45 371,02 91,9 Test sample 6-1 1,369 1892,89 364,25 95,3 Test sample 6-2 1,371 1904,83 365,60 96,0 Test sample 7-1 1,372 1875,38 363,45 95,3 Test sample 7-2 1,369 1880,15 363,77 95,2 Test sample 8-1 1,370 1896,07 365,20 95,2 Test sample 8-2 1,371 1902,44 365,60 95,1

[0042] From the analysis of the above-mentioned embodiments, it can be seen that the sintered NdFeB magnet produced according to the method of the present invention has a higher coercivity and excellent rectangularity.

[0043] Embodiment 9: A method for improving the magnetic performance of a sintered NdFeB magnet includes the following steps: 1) Processing terbium metal in a hydrogen-oxygen mixed gas with an oxygen content of 1% to obtain coarse powder; detecting the hydrogen content in the coarse powder during this step; 2) Continue grinding the coarse powder for 8 h to obtain raw powder material with an average particle size of 1.51 µm; 3) Mix the above-mentioned powder material uniformly with anhydrous ethanol and spray evenly onto the surface of the sintered NdFeB magnet to form a coating of 20 µm before drying at a temperature of 80 °C; 4) Proceed with dehydration of the sintered NdFeB magnet after drying in a vacuum environment under a pressure of 6.0 × 10 -4 Pa; the dehydration temperature is 700 °C; the dehydration time is 2 h; removal of the coated magnet under vacuum protection after dehydration; detection of the hydrogen content in the coating; 5) Proceed with diffusion and aging treatment of the sintered NdFeB magnet after dehydration.

[0044] Embodiment 10: A method for improving the magnetic performance of a sintered NdFeB magnet includes the following steps: 1) Process dysprosium metal in hydrogen gas to obtain coarse powder; detect the hydrogen content in the coarse powder during this step; 2) Deactivating the coarse powder in the nitrogen-oxygen mixed gas with an oxygen content of 1.5% for 24 hours; 3) Continue grinding the coarse powder for 8 h to obtain raw powder material with an average particle size per specific area of ​​1.48 µm; 4) Mix the above-mentioned powder material uniformly with anhydrous ethanol and spray evenly onto the surface of the sintered NdFeB magnet to form a coating of 20 µm before drying at a temperature of 80 °C; 5) Proceed with dehydration of the sintered NdFeB magnet after drying in a vacuum environment at a pressure of 6.0 × 10 -4Pa; the dehydration temperature is 730 °C; the dehydration time is 1 h; removal of the coated magnet under vacuum protection after dehydration; checking the hydrogen content in the final coating; 6) Proceed with diffusion and aging treatment of the sintered NdFeB magnet after dehydration.

[0045] Marking the coating without dehydration in embodiment 9 as test sample 9-1; marking the coating that has undergone dehydration as test sample 9-2; marking the coating without dehydration in embodiment 10 as test sample 10-1; marking the coating that has undergone dehydration as test sample 10-2; using a testing device to measure the hydrogen content; the measurement data are shown in Table 3. Table 3: Hydrogen content of test samples without dehydration and of dehydrated test samples. Designation Hydrogen content (ppm) Test sample 9-1 9.851 Test sample 9-2 54 Test sample 10-1 9.328 Test sample 10-2 41

[0046] From the analysis of the above-mentioned embodiments 9 and 10, it can be seen that there is a large difference in the hydrogen content in the coating before and after dehydration; therefore, it is necessary to reduce the hydrogen content to a reasonable level by dehydration in order to avoid an adverse effect, such as that caused by extremely high hydrogen content of the magnetic coating.

Claims

[1] Method for improving the magnetic performance of a sintered NdFeB magnet, comprising: First, the surface of a sintered NdFeB magnet is coated with a raw material consisting of elements R, H and X to form a coating. and then proceed with a diffusion treatment and an aging treatment of the sintered NdFeB magnet with the coating in a vacuum or inert gas environment, where R is at least one of the elements Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, H Element hydrogen is; X is at least one of the elements C, O, N, S, B, Cl and Si, wherein in the raw material, consisting of the elements R, H and X, the content of element H, expressed as a percentage by mass, is 0.01% to 2%, and the content of element X, expressed as a percentage mass fraction, is between 0.01% and 10%, wherein the sintered NdFeB magnet with the coating is subjected to a dehydration treatment prior to the diffusion treatment, wherein a dehydration temperature is 600 °C to 800 °C and the treatment time is 0.1 h to 30 h and the hydrogen content in the coating of the The NdFeB magnets after dehydration treatment, expressed as a percentage mass fraction, amount to 0.001% to 0.2%. [2] Method for improving the performance of a sintered NdFeB magnet according to claim 1, characterized by that the elements R, H and X contained in the raw material are present as the product of a chemical reaction of the mixture of elements R, H and X. [3] Method for improving the performance of a sintered NdFeB magnet according to claim 1, characterized by that the elements R, H and X contained in the raw material are present as the product of a chemical reaction of the hydride of element R with element X. [4] Method for improving the performance of a sintered NdFeB magnet according to claim 1, characterized by , that the element R is at least one of such elements as Pr, Nd, Gd, Dy, Tb and Ho. [5] Method for improving the performance of a sintered NdFeB magnet according to claim 1, characterized by that the thickness of the sintered NdFeB magnet is less than 15 mm. [6] Method for improving the performance of a sintered NdFeB magnet according to claim 1, characterized by that the diffusion treatment is carried out for 1 h to 30 h at a temperature of 700 °C to 1,000 °C. [7] Method for improving the performance of a sintered NdFeB magnet according to claim 1, characterized by , that the aging treatment is carried out by means of a heat treatment for 1 h to 10 h at a temperature of 400 °C to 600 °C.