Neodymium-iron-boron permanent magnet material and preparation method and application thereof

Abstract

The invention discloses a neodymium iron boron permanent magnet material and a preparation method and application thereof, and belongs to the field of magnets. The preparation method of the neodymium-iron-boron permanent magnet material comprises the following steps: S1, performing primary film coating on a neodymium-iron-boron diffusion substrate by adopting a first diffusion source to obtain a first precursor; s2, performing secondary film coating on the first precursor by adopting a second diffusion source to obtain a second precursor; and S3, performing diffusion treatment and aging treatment on the second precursor to prepare the neodymium iron boron permanent magnet material, wherein in the steps S1 and S2, the first diffusion source and the second diffusion source respectively and independently comprise heavy rare earth elements; the heavy rare earth element comprises Dy and / or Tb and exists in the form of a heavy rare earth simple substance, a heavy rare earth alloy or a heavy rare earth compound. The obtained permanent magnet material can simultaneously realize excellent performances such as high coercive force, high residual magnetism, high squareness and high diffusion depth; and the preparation method can remarkably shorten the production cycle and reduce the cost, and is especially suitable for large-thickness products.

Description

Technical Field

[0001] This invention belongs to the field of magnets, specifically relating to a neodymium iron boron permanent magnet material, its preparation method, and its application. Background Technology

[0002] With technological advancements, the market demand for large-size, high-coercivity sintered NdFeB permanent magnet materials is increasing. In recent years, orders for products with large thicknesses (above 5 mm) and high coercivity (above 25 kOe) have risen annually. However, conventional grain boundary diffusion processes often result in insufficient diffusion depth, inadequate coercivity, and poor squareness for these products. Therefore, developing a novel diffusion process for the production of such large-thickness, high-coercivity products is urgently needed.

[0003] Currently, for the preparation of such thick, high-coercivity products, when the coercivity of a single diffusion process (a continuous diffusion step performed only once) is insufficient, a two-stage diffusion process is often used (after the first diffusion, a diffusion source is applied again for a second diffusion). That is, after the sample has undergone the first diffusion, a simple surface treatment is performed before a second coating diffusion. This two-stage diffusion process can significantly improve the coercivity of thick, high-coercivity products while maintaining their original diffusion properties.

[0004] However, using existing secondary diffusion processes for the production of thick, high-coercivity products still presents several challenges. Firstly, there's the production cycle issue. Secondary diffusion involves three additional steps compared to single-stage diffusion: secondary coating, surface treatment, and secondary furnace diffusion. These steps alone add 3-4 days to the process time, significantly impacting delivery time and factory capacity. Secondly, there are product performance issues. While traditional secondary diffusion can significantly improve the coercivity of thick products, the two-stage diffusion process inevitably leads to excessively long high-temperature treatment times. During prolonged and intense grain boundary activity, significant intrusion of heavy rare earth elements into the main phase occurs, resulting in a substantial decrease in remanent magnetic induction. Thirdly, there's the cost issue. Secondary diffusion requires two heating and cooling cycles, incurring substantial costs in labor, depreciation, and energy, increasing production costs by over 30% compared to single-stage diffusion. Summary of the Invention

[0005] To overcome the shortcomings of existing conventional grain boundary diffusion processes, such as insufficient diffusion depth, inadequate coercivity, and poor product squareness, as well as the drawbacks of secondary diffusion processes, such as poor overall product performance, long production cycle, and high cost, this invention provides a neodymium iron boron permanent magnet material, its preparation method, and its applications. The permanent magnet material prepared by this method achieves coercivity comparable to that obtained by existing secondary diffusion processes, while simultaneously ensuring excellent properties such as high remanence, high squareness, and high diffusion depth. Furthermore, this preparation method significantly shortens the production cycle and reduces costs, making it particularly suitable for products with large thicknesses.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] This invention provides a method for preparing neodymium iron boron permanent magnet materials, the method comprising the following steps:

[0008] S1. The neodymium iron boron diffusion matrix is ​​coated once using a first diffusion source to obtain the first precursor;

[0009] The primary coating process is performed using magnetron sputtering.

[0010] S2. The first precursor is coated with a second diffusion source to obtain a second precursor.

[0011] S3. The second precursor is subjected to diffusion treatment and aging treatment to obtain the neodymium iron boron permanent magnet material;

[0012] In steps S1 and S2, the first diffusion source and the second diffusion source each independently include heavy rare earth elements; the heavy rare earth elements include Dy and / or Tb; the heavy rare earth elements exist in the form of heavy rare earth elements, heavy rare earth alloys or heavy rare earth compounds.

[0013] In this invention, a significant improvement in the overall performance of the obtained NdFeB permanent magnet material can be ensured by using a two-stage coating process, with the first coating process being magnetron sputtering. Specifically, the coercivity is significantly improved while maintaining high remanence and squareness. Furthermore, research has shown that some performance characteristics are superior to existing two-stage diffusion processes, greatly shortening the production cycle and reducing costs. This is particularly suitable for products with large thicknesses (e.g., products with a thickness of 5.5 mm or more for Dy diffusion and products with a thickness of 8.5 mm or more for Tb diffusion). In contrast, if other conventional coating methods such as screen printing are used in the first coating process, it is difficult to guarantee a good morphology of the final magnet material, and the performance will also be reduced accordingly.

[0014] In this invention, the terms "first coating" and "second coating" refer to sequentially applying a first coating and a second coating to two corresponding surfaces of the NdFeB diffusion substrate. Those skilled in the art will understand their specific meaning.

[0015] In some implementations, in steps S1 and S2, the heavy rare earth element also independently includes Ho.

[0016] In some preferred embodiments, in steps S1 and S2, the heavy rare earth elements in the first diffusion source and the second diffusion source are the same.

[0017] In this invention, in steps S1 and S2, the heavy rare earth elements can each exist independently in a conventional form in the art, generally including the form of heavy rare earth elements, heavy rare earth alloys, or heavy rare earth compounds.

[0018] In some implementations, in steps S1 and S2, the content of the heavy rare earth elements in the heavy rare earth alloy is independently not less than 20 wt%.

[0019] In some implementations, in steps S1 and S2, the heavy rare earth alloys each independently satisfy the following general formula: HR x HL y M z Wherein, HR is the heavy rare earth element, HL is the light rare earth element, and M is one or more of Ga, Al, Cu, Co, Ti, Zr, Nb, W, Fe and B; by mass percentage, 20wt%≤x<100wt%, 0≤y<80wt%, 0≤z<80wt%, and y and z are not both 0.

[0020] The x is preferably 65wt%-95wt%, for example 86.56wt%.

[0021] Wherein, y is preferably 5wt%-35wt%.

[0022] The HL preferably includes one or more of Ce, Pr, Nd and Y.

[0023] The z is preferably 5wt%-35wt%, for example 13.44wt%.

[0024] The M preferably includes one or more of Al, Cu, Co, Fe and B, such as B.

[0025] In some implementations, in steps S1 and S2, the heavy rare earth alloys each independently satisfy the following general formula: HR a N bWherein, HR is the heavy rare earth element and N is the non-metallic element; by mass percentage, 20wt%≤a<100wt%, 0<b≤80wt%.

[0026] Wherein, the value of a is preferably 65wt%-95wt%, for example 86.56wt%.

[0027] Wherein, b is preferably 5wt%-35wt%, for example 13.44wt%.

[0028] Preferably, N is B.

[0029] In some specific implementations, in steps S1 and S2, the heavy rare earth alloy is Dy independently. 86.56 B 13.44 .

[0030] In some embodiments, in steps S1 and S2, the heavy rare earth compounds each independently include one or more of heavy rare earth oxides, heavy rare earth hydrides, and heavy rare earth fluorides.

[0031] In some preferred embodiments, in steps S1 and S2, the first diffusion source and the second diffusion source are each independently the heavy rare earth element. The heavy rare earth element is, for example, Dy.

[0032] In some preferred embodiments, in steps S1 and S2, the first diffusion source and the second diffusion source are each independently the heavy rare earth alloy.

[0033] Preferably, the heavy rare earth alloys in the first diffusion source and the second diffusion source are the same. The heavy rare earth alloy is, for example, Dy. 86.56 B 13.44 .

[0034] In some preferred embodiments, in steps S1 and S2, the first diffusion source is the heavy rare earth element, and the second diffusion source is the heavy rare earth alloy. The heavy rare earth element is, for example, Dy, and the heavy rare earth alloy is, for example, Dy. 86.56 B 13.44 .

[0035] In some preferred embodiments, in steps S1 and S2, the first diffusion source is the heavy rare earth alloy, and the second diffusion source is the heavy rare earth element. The heavy rare earth element is, for example, Dy, and the heavy rare earth alloy is, for example, Dy. 86.56 B 13.44 .

[0036] In some preferred embodiments, in steps S1 and S2, the heavy rare earth elements do not include La and Ga, respectively.

[0037] In some implementations, in steps S1 and S2, the weight gain of heavy rare earth elements after the first coating and the second coating are each independently 0.05wt%-1wt%, for example 0.5wt%.

[0038] In some implementations, step S1 further includes a step of coating the first precursor with an oxide after the initial coating.

[0039] The oxide preferably includes one or more of Al2O3, ZrO2 and TiO2.

[0040] Preferably, the melting point of the oxide is not lower than 2000°C.

[0041] The coating is preferably applied by spraying.

[0042] The oxide membrane formed after the coating process has a thickness of 0.5-5 μm, preferably 1-3 μm.

[0043] In this invention, in step S2, the secondary coating can be performed using conventional coating methods in the art, generally including one or more of magnetron sputtering, screen printing, and spraying, with screen printing being the preferred method.

[0044] In some specific implementations, in steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth element, and the primary coating is performed by magnetron sputtering, while the secondary coating is performed by screen printing. The heavy rare earth element is, for example, Dy.

[0045] In some specific implementations, in steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth alloy, and the primary coating is performed by magnetron sputtering, while the secondary coating is performed by screen printing. The heavy rare earth alloy is, for example, Dy.

[0046] In some specific implementations, in steps S1 and S2, the first diffusion source is the heavy rare earth element, the second diffusion source is the heavy rare earth alloy, and the primary coating is performed by magnetron sputtering, while the secondary coating is performed by screen printing. The heavy rare earth element is, for example, Dy, and the heavy rare earth alloy is, for example, Dy. 86.56 B 13.44 .

[0047] In some specific implementations, in steps S1 and S2, the first diffusion source is the heavy rare earth alloy, the second diffusion source is the heavy rare earth element, and the primary coating is performed by magnetron sputtering, while the secondary coating is performed by screen printing. The heavy rare earth element is, for example, Dy, and the heavy rare earth alloy is, for example, Dy.86.56 B 13.44 .

[0048] In some implementations, in step S3, the diffusion treatment temperature is 850℃-950℃. The temperature range refers to the temperature being maintained within this range throughout the diffusion treatment process; specifically, diffusion can be carried out at a constant temperature value or at different temperature values, the specific meaning of which will be understood by those skilled in the art.

[0049] In some implementations, the diffusion treatment in step S3 takes 10-40 hours. This time range refers to the total diffusion time being kept within this range during the diffusion treatment process; those skilled in the art will understand its specific meaning.

[0050] In some implementations, in step S3, the vacuum degree of the diffusion process is not less than 5 × 10⁻⁶. -3 Pa. The vacuum level refers to the range that needs to be maintained throughout the diffusion process; those skilled in the art will understand its specific meaning.

[0051] In some preferred embodiments, in step S3, the diffusion process is carried out in a single stage or in segments. Although the segmented process involves segmented diffusion, it is still considered a complete and continuous diffusion process.

[0052] The time for the one-stage processing is preferably 15-25 hours; the temperature for the one-stage processing is preferably 850℃-950℃, for example, 900℃.

[0053] The segmented processing is preferably a three-segment processing.

[0054] In the three-stage process, the temperature of the second diffusion stage is preferably 5-20°C higher than that of the first diffusion stage, for example, 10°C higher; and the temperature of the third diffusion stage is preferably 10-20°C higher than that of the second diffusion stage, for example, 15°C higher.

[0055] In the three-stage process, the first stage of diffusion processing preferably takes 3-7 hours, for example, 5 hours; the second stage of diffusion processing preferably takes 5-10 hours, for example, 8 hours; and the third stage of diffusion processing preferably takes 15-25 hours.

[0056] In some preferred embodiments, the method for preparing the neodymium iron boron permanent magnet material includes:

[0057] In steps S1 and S2, the first diffusion source and the second diffusion source are not simultaneously the heavy rare earth elements;

[0058] In step S1, after the first coating, the process further includes coating the first precursor with an oxide film.

[0059] In step S3, the diffusion process adopts the three-stage process.

[0060] Research has shown that when the first and second diffusion sources are different and heavy rare earth elements are used, and the diffusion treatment adopts a three-stage process, the overall improvement effect is relatively optimal when oxide coating is used between the first and second coating stages. At this time, compared with the diffusion matrix, the obtained NdFeB permanent magnet material has an Hcj increase of at least 6.6 kOe (approximately 48% in relative terms), while the Br value decreases by less than 0.25 kGs (approximately 1.7% in relative terms) and the squareness decreases by less than 4.5% (approximately 0.04% in relative terms).

[0061] In some specific implementations, in steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth element, and the primary coating is performed by magnetron sputtering, while the secondary coating is performed by screen printing; in step S3, the diffusion treatment is a one-stage process, the duration of which is 15-25 hours; the temperature of the diffusion treatment is 850℃-950℃. The heavy rare earth element is, for example, Dy.

[0062] In some specific implementations, in steps S1 and S2, the first and second diffusion sources are the same heavy rare earth element, and the first coating is performed by magnetron sputtering, while the second coating is performed by screen printing. In step S3, the diffusion treatment is a three-stage process, with the temperature of the second stage diffusion treatment being 5-20°C higher than that of the first stage, and the temperature of the third stage diffusion treatment being 10-20°C higher than that of the second stage. The duration of the first stage diffusion treatment is 3-7 hours, the duration of the second stage diffusion treatment is 5-10 hours, and the duration of the third stage diffusion treatment is 15-25 hours. The heavy rare earth element is, for example, Dy.

[0063] In some specific implementations, in steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth alloy, and the first coating is performed by magnetron sputtering, while the second coating is performed by screen printing; in step S3, the diffusion treatment is a one-stage process, the duration of which is 15-25 hours; the temperature of the diffusion treatment is 850℃-950℃. The heavy rare earth alloy is, for example, Dy.

[0064] In some specific implementations, in steps S1 and S2, the first and second diffusion sources are the same heavy rare earth alloy, and the first coating is performed by magnetron sputtering, while the second coating is performed by screen printing. In step S3, the diffusion treatment is a three-stage process, with the temperature of the second stage diffusion treatment being 5-20°C higher than that of the first stage, and the temperature of the third stage diffusion treatment being 10-20°C higher than that of the second stage. The duration of the first stage diffusion treatment is 3-7 hours, the duration of the second stage diffusion treatment is 5-10 hours, and the duration of the third stage diffusion treatment is 15-25 hours. The heavy rare earth alloy is, for example, Dy.

[0065] In some specific implementations, in steps S1 and S2, the first diffusion source is the heavy rare earth element, the second diffusion source is the heavy rare earth alloy, and the primary coating is performed by magnetron sputtering, while the secondary coating is performed by screen printing. In step S3, the diffusion treatment is a one-stage process, with a treatment time of 15-25 hours; the diffusion treatment temperature is 850℃-950℃. The heavy rare earth element is, for example, Dy, and the heavy rare earth alloy is, for example, Dy. 86.56 B 13.44 .

[0066] In some specific implementations, in steps S1 and S2, the first diffusion source is the heavy rare earth element, the second diffusion source is the heavy rare earth alloy, and the first coating is performed by magnetron sputtering, while the second coating is performed by screen printing. In step S3, the diffusion treatment is a three-stage process, with the temperature of the second stage diffusion treatment being 5-20°C higher than that of the first stage, and the temperature of the third stage diffusion treatment being 10-20°C higher than that of the second stage. The duration of the first stage diffusion treatment is 3-7 hours, the duration of the second stage diffusion treatment is 5-10 hours, and the duration of the third stage diffusion treatment is 15-25 hours. The heavy rare earth element is, for example, Dy, and the heavy rare earth alloy is, for example, Dy. 86.56 B 13.44 .

[0067] In some specific implementations, in steps S1 and S2, the first diffusion source is the heavy rare earth alloy, the second diffusion source is the heavy rare earth element, and the primary coating is performed by magnetron sputtering, while the secondary coating is performed by screen printing. In step S3, the diffusion treatment is a one-stage process, with a treatment time of 15-25 hours; the diffusion treatment temperature is 850℃-950℃. The heavy rare earth element is, for example, Dy, and the heavy rare earth alloy is, for example, Dy. 86.56 B 13.44 .

[0068] In some specific implementations, in steps S1 and S2, the first diffusion source is the heavy rare earth alloy, the second diffusion source is the heavy rare earth element, and the first coating is performed by magnetron sputtering, while the second coating is performed by screen printing. In step S3, the diffusion treatment is a three-stage process, with the temperature of the second stage diffusion treatment being 5-20°C higher than that of the first stage, and the temperature of the third stage diffusion treatment being 10-20°C higher than that of the second stage. The duration of the first stage diffusion treatment is 3-7 hours, the duration of the second stage diffusion treatment is 5-10 hours, and the duration of the third stage diffusion treatment is 15-25 hours. The heavy rare earth element is, for example, Dy, and the heavy rare earth alloy is, for example, Dy. 86.56 B 13.44 .

[0069] Research has shown that if the first diffusion source uses a heavy rare earth alloy and the second diffusion source uses heavy rare earth elements, in a conventional one-stage diffusion process, the high-melting-point heavy rare earth alloy on the sample surface may hinder the diffusion channels of the outer heavy rare earth elements, resulting in a slight decrease in the diffusion efficiency of the heavy rare earth elements. However, in the case of a three-stage diffusion process, even if a heavy rare earth alloy is used first, followed by heavy rare earth elements for coating, the overall performance is still relatively superior.

[0070] In some implementations, step S3 further includes a cooling step after the diffusion treatment. The cooling can be a conventional operation in the art, preferably using air cooling, such as using argon gas for cooling.

[0071] In this invention, the aging process in step S3 is a conventional operation in the field.

[0072] In some implementations, the aging treatment temperature in step S3 is 400-600°C, for example, 500°C.

[0073] In some implementations, the aging process in step S3 takes 2-8 hours.

[0074] In some implementations, in step S3, the vacuum degree of the aging treatment is not less than 10. -1 Pa.

[0075] In this invention, in step S1, the neodymium iron boron diffusion matrix can be obtained according to the conventional sintered magnet preparation method in the art, which generally includes raw material melting, hydrogen breaking, air jet milling, forming and sintering steps.

[0076] In some specific embodiments, in step S1, the NdFeB diffusion matrix comprises the following components by mass percentage:

[0077] 28.5wt%-32.5wt% rare earth elements, 0-5wt% trace elements, 0.85wt%-1.1wt% B, the remainder being Fe;

[0078] The rare earth elements include one or more of La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, and Y; the trace elements include one or more of Ga, Al, Cu, Co, Ti, Zr, and Nb.

[0079] In some specific implementations, step S1, the method for preparing the NdFeB diffusion matrix includes the following steps:

[0080] (1) The alloy of the corresponding composition is vacuum melted and cast into a sheet; the thickness of the sheet is preferably 0.15-0.45 mm, for example 0.2-0.35 mm; the casting temperature is preferably 1450±30℃;

[0081] (2) The spun pieces are coarsely crushed by hydrogen crushing, and then dehydrogenated to obtain coarse powder; the dehydrogenation temperature is, for example, 580±20℃;

[0082] (3) The coarse powder is prepared into fine powder by air jet milling; the particle size X50 of the fine powder is 1.5-8μm, preferably 3.0-4.5μm;

[0083] (4) The fine powder is pressed into a blank using a two-person manual forming press; the blank size is, for example, 62×42×40 mm; the pressing is orientation pressing, and the orientation magnetic field of the orientation pressing is, for example, >1.75T; after pressing, a cold isostatic press is used for cold isostatic pressing, and the cold isostatic pressing is, for example, held at 200MPa for 40s.

[0084] (5) Sintering is then performed, for example, vacuum sintering at 1075°C for 8 hours, maintaining a vacuum level of 5×10⁻⁶ throughout the process. -3 Pa or above;

[0085] (6) The sintered product is cut into products with dimensions of 30×20×6mm using a multi-wire cutting machine as the NdFeB diffusion matrix.

[0086] The present invention also provides a neodymium iron boron permanent magnet material, which is prepared by the method described above for preparing neodymium iron boron permanent magnet materials.

[0087] In some embodiments, the diffusion depth of the heavy rare earth elements in the neodymium iron boron permanent magnet material is not less than 150 μm, preferably not less than 220 μm, more preferably not less than 300 μm, for example, 320-430 μm.

[0088] The present invention also provides an application of neodymium iron boron permanent magnet material as described above in an electric motor.

[0089] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0090] The reagents and raw materials used in this invention are all commercially available.

[0091] The positive and progressive effects of this invention are as follows:

[0092] This invention achieves effective diffusion of heavy rare earth elements on the surface of a thick sintered magnet through two coating processes, with the first coating using magnetron sputtering and a single diffusion process. The resulting magnet has high Hcj while also ensuring high Br, Hk and squareness. Furthermore, this preparation method can significantly shorten the overall process time and reduce production costs compared to the traditional two-stage diffusion process. Attached Figure Description

[0093] Figure 1 This is a schematic diagram illustrating the preparation principle of the neodymium iron boron permanent magnet material obtained in Example 7 of the present invention.

[0094] The attached figures are labeled as follows:

[0095] 1-Diffusion matrix; 2-First diffusion source; 3-Second diffusion source; 4-Oxide membrane. Detailed Implementation

[0096] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0097] In the following examples and comparative examples, the specific composition of the neodymium iron boron diffusion matrix used is (PrNdGdHo). 30.1 (GaAlCuCoTiZr) 1.2 Fe 67.73 B 0.97 The process involves smelting, hydrogen breaking, air jet milling, forming, and sintering the corresponding raw materials to obtain sintered NdFeB blanks. These blanks are then cut into products with dimensions of 30×20×6mm using a multi-wire cutting machine. Specifically:

[0098] (1) Vacuum melt and cast the corresponding alloy into 0.2-0.35mm thick sheets at a casting temperature of 1450±30℃;

[0099] (2) The hydrogen crusher performs coarse crushing and dehydrogenation at 580±20℃;

[0100] (3) The particle size X50 of the powder prepared by air jet mill is 3.0-4.5 μm;

[0101] (4) A two-person manual forming press is used to press a blank with a size of 62×42×40 mm. The orientation magnetic field is set to >1.75T. After forming, a cold isostatic press is used to hold the pressure at 200MPa for 40s for cold isostatic pressing.

[0102] (5) Vacuum sintering was performed at 1075℃ for 8 hours, maintaining a vacuum level of 5×10 throughout the process. -3 Pa or above.

[0103] (6) The above sintered blank is cut into products with dimensions of 30×20×6mm using a multi-wire cutting machine as NdFeB diffusion matrix.

[0104] Example 1

[0105] Based on the neodymium iron boron diffusion matrix obtained above, the neodymium iron boron permanent magnet material of this embodiment is prepared according to the following steps:

[0106] S1. A magnetron sputtering process is used to coat the two opposite surfaces of the neodymium iron boron diffusion substrate with a first diffusion source. The first diffusion source is elemental Dy with a Dy weight gain of 0.5 wt%, thus obtaining the first precursor.

[0107] S2. A second coating is performed on the two opposite surfaces (i.e., the surfaces after the first coating) of the obtained first precursor using a screen printing process and a second diffusion source. The second diffusion source is elemental Dy, and the weight gain of Dy is 0.5wt%, thus obtaining the second precursor.

[0108] S3. The obtained second precursor is placed in a high-vacuum single-unit vacuum sintering furnace for diffusion and aging treatment:

[0109] The diffusion process was carried out in a single stage: the diffusion temperature was 900±5℃, the total diffusion time was 15 hours, and the vacuum degree was maintained at 5×10 throughout the process. -3 Above Pa. After diffusion treatment, rapid cooling with argon gas is used. After cooling, a one-stage aging process is used for aging treatment at a temperature of 500±5℃ for 8 hours, with the vacuum level maintained at 10 throughout. -1 Pa or above.

[0110] Due to the special nature of the process and equipment, the temperature of the diffusion process can only be controlled within a certain range.

[0111] Example 2

[0112] Compared to Example 1, only the first diffusion source is changed to Dy. 86.56 B 13.44 After one coating, the weight gain of Dy was still controlled to 0.5wt%.

[0113] Example 3

[0114] Compared to Example 1, only the second diffusion source was changed to Dy. 86.56 B 13.44 After the second coating, the weight gain of Dy was still controlled to 0.5wt%.

[0115] Example 4

[0116] Compared to Example 1, only the first and second diffusion sources are changed to Dy. 86.56 B 13.44 In both single and double coating processes, the weight gain of Dy was controlled to be 0.5 wt%.

[0117] Example 5

[0118] Compared to Example 3, only the diffusion process in step S3 is changed, as follows:

[0119] The second precursor was subjected to a three-stage diffusion process. The first stage diffusion temperature was 900±5℃, with a holding time of 5 hours; the second stage diffusion temperature was 910±5℃, with a holding time of 8 hours; and the third stage diffusion temperature was 925±5℃, with a holding time of 20 hours. A vacuum of 5×10⁻⁶ was maintained throughout the diffusion process. -3 Above Pa, after diffusion is complete, rapid cooling with argon gas is used.

[0120] Due to the special nature of the process and equipment, the temperature of the diffusion process can only be controlled within a certain range for each stage.

[0121] Example 6

[0122] Compared to Example 2, only the diffusion process in step S3 is changed; the diffusion process is the same as in Example 5.

[0123] Example 7

[0124] Compared to Example 5, a 1 μm thick nano-alumina powder was sprayed using a spraying process only between the first and second coating processes.

[0125] The overall structure before diffusion treatment is as follows Figure 1 As shown, from the inside out, it includes a diffusion substrate 1, a first diffusion source 2, an oxide diaphragm 4, and a second diffusion source 3.

[0126] Example 8

[0127] Compared to Example 7, the only difference is that the thickness of the sprayed nano-alumina powder is changed to 2 μm.

[0128] Example 9

[0129] Compared to Example 7, the only difference is that the thickness of the sprayed nano-alumina powder is changed to 3 μm.

[0130] Example 10

[0131] Compared to Example 4, only the diffusion process in step S3 is changed; the diffusion process is the same as in Example 5.

[0132] Example 11

[0133] Compared to Example 5, a 1 μm thick nano-alumina powder was sprayed using a spraying process only between the first and second coating processes.

[0134] Example 12

[0135] Compared to Example 10, a 1 μm thick nano-alumina powder was sprayed using a spraying process only between the first and second coating processes.

[0136] Example 13

[0137] Compared to Example 7, only the position of the oxide diaphragm in the spraying process is adjusted so that the oxide diaphragm is coated on the outer layer of the second precursor.

[0138] Comparative Example 1

[0139] Compared to Example 1, diffusion and aging treatments are performed immediately after the first coating, thus eliminating the need for a second coating. Specifically, a magnetron sputtering process is used, and a first diffusion source is employed to coat the two opposing surfaces of the NdFeB diffusion substrate. The first diffusion source is elemental Dy, with a Dy weight gain of 1 wt%.

[0140] Comparative Example 2

[0141] Compared to Comparative Example 1, only the first diffusion source was changed to Dy 86.56 B 13.44 The weight gain of Dy was still controlled at 1 wt%.

[0142] Comparative Example 3

[0143] Compared to Comparative Example 1, only the lamination process was changed to screen printing.

[0144] Comparative Example 4

[0145] Compared to Comparative Example 2, only the lamination process was changed to screen printing.

[0146] Comparative Example 5

[0147] Compared to Comparative Example 3, only the weight gain of the coated Dy element was changed to 0.5%.

[0148] Comparative Example 6

[0149] Compared to Comparative Example 4, only the coated Dy 86.56 B 13.44The overall Dy weight gain was changed to 0.5%.

[0150] Comparative Example 7

[0151] The diffusion matrix was treated with a conventional secondary diffusion process.

[0152] First, a screen printing process was used to coat the two opposing surfaces of the diffusion substrate. The first diffusion source was elemental Dy, with a Dy weight gain of 0.5 wt%. A subsequent diffusion treatment was performed, using the same process as Comparative Example 1. After diffusion, the diffusion surface of the sample was sanded until exposed to light. Then, a second screen printing process was used to coat the surface of the resulting product, with elemental Dy as the second diffusion source, also with a Dy weight gain of 0.5 wt%. A second diffusion treatment and an aging treatment were then performed, both using the same processes as Comparative Example 1.

[0153] Comparative Example 8

[0154] Compared to Comparative Example 7, only the first and second diffusion sources were changed to Dy. 86.56 B 13.44 In both primary and secondary coating processes, the weight gain of Dy was controlled to be 0.5 wt%.

[0155] Comparative Example 9

[0156] Compared to Example 1, only one coating process was modified to a screen printing process.

[0157] Comparative Example 10

[0158] Compared to Comparative Example 9, only the secondary coating process was modified to a magnetron sputtering process.

[0159] Comparative Example 11

[0160] Compared to Comparative Example 3, only the diffusion process was changed; the diffusion process was the same as in Example 5.

[0161] Comparative Example 12

[0162] Compared to Comparative Example 11, only the first diffusion source was changed to Dy. 86.56 B 13.44 The weight gain of Dy was still controlled at 1 wt%.

[0163] The corresponding processes of Examples 1-13 and Comparative Examples 1-12 are summarized in Table 1 below:

[0164] Table 1

[0165]

[0166] Effect Example

[0167] The effects of the neodymium iron boron permanent magnet materials obtained in Examples 1-13 and Comparative Examples 1-12 were tested respectively. Specifically:

[0168] (1) Surface morphology:

[0169] The surface condition of the sample after diffusion is determined by visual observation and by lightly scraping it with a knife.

[0170] (2) Magnetic property test:

[0171] The magnetic properties of the neodymium iron boron permanent magnet materials obtained in each embodiment and comparative example were tested using the NIM-62000 permanent magnet precision measurement system. Specifically, after the magnetized surface of the neodymium iron boron permanent magnet material was polished to light, the sample was processed into a φ10×6 sample column by electrical discharge cutting and centerless grinding. The sample was tested by stacking two pieces, and the test temperature was constant at 20℃.

[0172] (3) Diffusion depth test of heavy rare earth elements:

[0173] For the NdFeB permanent magnet materials obtained in some representative embodiments and comparative examples, after the magnetic performance testing was completed, they were demagnetized by holding them at 380°C for 2 hours in a single-unit vacuum sintering furnace, with the vacuum degree maintained at 10 throughout the process. -1 Pa or higher. Then, the diffused magnet was cut along the diffusion direction using an inner circular slicer. The cross-section was polished with 180, 400, 800, and 1200 grit sandpaper and polishing cloth in sequence. The cross-section was then placed in a field emission scanning electron microscope and the diffusion depth of Dy element was determined by surface scanning with energy dispersive spectroscopy (SEM-EDS mapping) (the process was terminated when no characteristic peak of Dy element was detected after 30s of SEM-EDS mapping).

[0174] The test results and the surface condition of the samples after diffusion completion are shown in Table 2:

[0175] Table 2

[0176]

[0177] Wherein, Br refers to remanence, Hcj refers to intrinsic coercivity, and Hk / Hcj refers to squareness; ΔBr, ΔHcj, and ΔHk / Hcj are all relative changes in the diffusion matrix.

[0178] The results show that:

[0179] In Examples 1-4, under the premise of performing a single diffusion on the precursor obtained after two coatings using a traditional one-stage process, the resulting NdFeB permanent magnet material can simultaneously meet the requirements of Br above 14.08 kGs, Hcj above 19.12 kOe, and squareness above 88.6%. Compared with the diffusion matrix, it can ensure that Hcj is increased by more than 5.5 kOe, while the Br value is reduced by less than 0.18 kGs, the squareness is reduced by less than 10.5%, and the diffusion depth can reach up to 270 μm. It can also maintain good surface morphology and high performance stability.

[0180] Furthermore, in Examples 5-13, under the premise of performing a single diffusion on the precursor obtained after two coatings using a three-stage process, the resulting NdFeB permanent magnet material can simultaneously meet the requirements of Br exceeding 13.94 kGs, Hcj exceeding 19.88 kOe, and squareness exceeding 92.1%. Compared with the diffusion matrix, it can ensure that: Hcj is increased by more than 6.3 kOe, while the Br value decreases by less than 0.35 kGs, the squareness decreases by less than 7.0%, and the diffusion depth can reach up to 430 μm; and it can also maintain good surface morphology and high performance stability.

[0181] In Examples 7-9 and 11-13, when the first and second diffusion sources are different, heavy rare earth elements are used. The primary diffusion process employs a three-stage process, and the overall improvement effect is relatively optimal when oxide coating is used between the primary and secondary coating stages. This invention has found that the oxide membrane can effectively prevent the penetration of heavy rare earth elements between the two membranes, thereby maximizing the diffusion of heavy rare earth elements at the grain boundaries and ultimately improving the overall magnetic properties of the resulting magnet. In this case, compared to the diffusion matrix, the resulting NdFeB permanent magnet material exhibits an Hcj increase of at least 6.6 kOe (approximately 48% in relative terms), a Br reduction of less than 0.25 kGs (approximately 1.7% in relative terms), and a squareness reduction of less than 4.5% (approximately 0.04% in relative terms).

[0182] In Comparative Examples 1-6 and 11-12, when only one coating and one diffusion are involved, regardless of the adjustment of the diffusion source type, coating process, or diffusion treatment process, the Hcj increase, Br decrease, and squareness decrease of the obtained NdFeB permanent magnet materials cannot simultaneously guarantee the corresponding effects of the previous embodiments.

[0183] More obviously, in Comparative Examples 7-8, when using existing traditional secondary coating and secondary diffusion processes, compared with Examples 1 and 4 with the same type of diffusion source, the Hcj of the obtained NdFeB permanent magnet materials is improved, but the overall diffusion depth is similar, and even Br and squareness are significantly reduced; for thick products, the performance consistency is poor, the production cycle is significantly longer, and the cost is significantly higher.

[0184] Furthermore, in Comparative Examples 9-10, when using existing conventional secondary coating and primary diffusion processes, compared to Example 1 with the same diffusion source, the Hcj of the obtained NdFeB permanent magnet materials was significantly worse when the primary coating used screen printing, regardless of whether the secondary coating used screen printing or magnetron sputtering. After diffusion, this even led to surface peeling, and the situation was even worse when the secondary coating used magnetron sputtering. The main reason may be that a large number of rough particles remain on the product surface after screen printing, leading to a decrease in the adhesion between the second and first layers, resulting in peeling. Specifically, magnetron sputtering on an uneven surface can cause the magnetron sputtered film to peel off after high-temperature treatment, resulting in severe peeling after diffusion. At the same time, the rough surface causes significant fluctuations in the weight gain of the secondary coating, posing a risk of performance instability during mass production.

[0185] In summary, the preparation method of the present invention can effectively diffuse heavy rare earth elements on the surface of thick sintered magnets. The resulting magnets have excellent Hcj, as well as excellent Br, Hk and squareness. Compared with the traditional secondary diffusion process, the overall process time is significantly shortened and the production cost is reduced.

Claims

1. A method for preparing neodymium iron boron permanent magnet material, characterized in that, The preparation method of the neodymium iron boron permanent magnet material includes the following steps: S1. The neodymium iron boron diffusion matrix is ​​coated once using a first diffusion source to obtain the first precursor; S2. The first precursor is coated with a second diffusion source to obtain a second precursor. S3. The second precursor is subjected to diffusion treatment and aging treatment to obtain the neodymium iron boron permanent magnet material; In steps S1 and S2, the first diffusion source and the second diffusion source each independently include heavy rare earth elements; the heavy rare earth elements include Dy and / or Tb; the heavy rare earth elements exist in the form of heavy rare earth elements, heavy rare earth alloys or heavy rare earth compounds.

2. The method for preparing the neodymium iron boron permanent magnet material as described in claim 1, characterized in that, The preparation method of the neodymium iron boron permanent magnet material satisfies one or more of the following conditions: (1) In steps S1 and S2, in the first diffusion source and the second diffusion source, the content of the heavy rare earth element in the heavy rare earth alloy is independently not less than 20 wt%; (2) In steps S1 and S2, in the first diffusion source and the second diffusion source, the heavy rare earth alloys independently satisfy the following general formula: HR x HL y M z Wherein, HR is the heavy rare earth element, HL is the light rare earth element, and M is one or more of Ga, Al, Cu, Co, Ti, Zr, Nb, W, Fe and B; by mass percentage, 20wt%≤x<100wt%, 0≤y<80wt%, 0≤z<80wt%, and y and z are not both 0; Alternatively, in steps S1 and S2, in the first diffusion source and the second diffusion source, the heavy rare earth alloys independently satisfy the following general formula: HR a N b Wherein, HR represents the heavy rare earth element, and N represents the non-metallic element; by mass percentage, 20wt%≤a<100wt%, 0<b≤80wt%; (3) In steps S1 and S2, the heavy rare earth compounds in the first diffusion source and the second diffusion source each independently include one or more of heavy rare earth oxides, heavy rare earth hydrides and heavy rare earth fluorides. (4) In steps S1 and S2, the first diffusion source and the second diffusion source are each independently the heavy rare earth element; Alternatively, in steps S1 and S2, the first diffusion source and the second diffusion source are each independently the heavy rare earth alloy. Alternatively, in steps S1 and S2, the first diffusion source is the heavy rare earth element, and the second diffusion source is the heavy rare earth alloy; Alternatively, in steps S1 and S2, the first diffusion source is the heavy rare earth alloy, and the second diffusion source is the heavy rare earth element. (5) In steps S1 and S2, the heavy rare earth element in the first diffusion source and the second diffusion source each independently includes Ho; (6) In steps S1 and S2, the heavy rare earth elements in the first diffusion source and the second diffusion source do not include La and Ga, respectively. (7) In steps S1 and S2, the weight gain of heavy rare earth elements after the first coating and the second coating is independently 0.05wt%-1wt%; (8) In step S1, after the first coating, the first precursor is further coated with an oxide. (9) In step S2, the secondary coating is performed by one or more of magnetron sputtering, screen printing and spraying.

3. The method for preparing the neodymium iron boron permanent magnet material as described in claim 2, characterized in that, The preparation method of the neodymium iron boron permanent magnet material satisfies one or more of the following conditions: (1) In steps S1 and S2, x in the first diffusion source and the second diffusion source are each independently 65wt%-95wt%; (2) In steps S1 and S2, the y in the first diffusion source and the second diffusion source are each independently 5wt%-35wt%; (3) In steps S1 and S2, the HL in the first diffusion source and the second diffusion source are each independently one or more of Ce, Pr, Nd and Y; (4) In steps S1 and S2, the z in the first diffusion source and the second diffusion source are each independently 5wt%-35wt%; (5) In steps S1 and S2, M in the first diffusion source and the second diffusion source are each independently one or more of Al, Cu, Co, Fe and B; (6) In steps S1 and S2, the a in the first diffusion source and the second diffusion source are each independently 65wt%-95wt%; (7) In steps S1 and S2, the b in the first diffusion source and the second diffusion source are each independently 5wt%-35wt%; (8) In steps S1 and S2, N in the first diffusion source and the second diffusion source are each independently B; (9) In steps S1 and S2, the heavy rare earth elements in the first diffusion source and the second diffusion source are the same; (10) In steps S1 and S2, when the first diffusion source and the second diffusion source are each independently the heavy rare earth alloy, the heavy rare earth alloys in the first diffusion source and the second diffusion source are the same.

4. The method for preparing the neodymium iron boron permanent magnet material as described in claim 2, characterized in that, The preparation method of the neodymium iron boron permanent magnet material satisfies one or more of the following conditions: (1) In step S1, the oxide includes one or more of Al2O3, ZrO2 and TiO2; (2) In step S1, the melting point of the oxide is not lower than 2000℃; (3) In step S1, the coating is applied by spraying. (4) In step S1, the thickness of the oxide membrane formed after the coating is completed is 0.5-5 μm; (5) In steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth element, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing. (6) In steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth alloy, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing. (7) In steps S1 and S2, the first diffusion source is the heavy rare earth element, the second diffusion source is the heavy rare earth alloy, and the first coating is carried out by magnetron sputtering, and the second coating is carried out by screen printing. (8) In steps S1 and S2, the first diffusion source is the heavy rare earth alloy, the second diffusion source is the heavy rare earth element, and the first coating is carried out by magnetron sputtering, and the second coating is carried out by screen printing.

5. The method for preparing neodymium iron boron permanent magnet material as described in claim 1, characterized in that, The preparation method of the neodymium iron boron permanent magnet material satisfies one or more of the following conditions: (1) In step S3, the temperature of the diffusion treatment is 850℃-950℃; (2) In step S3, the diffusion treatment time is 10-40 hours; (3) In step S3, the vacuum degree of the diffusion process is not less than 5×10⁻⁶. -3 Pa; (4) In step S3, the diffusion process is carried out in one stage or in segments; (5) In step S3, the diffusion treatment further includes a cooling step; (6) In step S3, the aging treatment temperature is 400-600℃; (7) In step S3, the time for the aging process is 2-8 hours; (8) In step S3, the vacuum degree of the aging treatment is not less than 10. -1 Pa.

6. The method for preparing the neodymium iron boron permanent magnet material as described in claim 5, characterized in that, The preparation method of the neodymium iron boron permanent magnet material satisfies one or more of the following conditions: (1) In step S3, the time for the one-stage processing is 15-25 hours; (2) In step S3, the temperature of the one-stage processing is 850℃-950℃; (3) In step S3, the segmented processing is a three-segment processing; (4) In step S3, the cooling is achieved by air cooling.

7. The method for preparing the neodymium iron boron permanent magnet material as described in claim 6, characterized in that, The preparation method of the neodymium iron boron permanent magnet material satisfies one or more of the following conditions: (1) In step S3, in the three-stage process, the temperature of the second diffusion process is 5-20°C higher than the temperature of the first diffusion process; the temperature of the third diffusion process is 10-20°C higher than the temperature of the second diffusion process. (2) In step S3, the time for the first diffusion process is 3-7 hours; the time for the second diffusion process is 5-10 hours; and the time for the third diffusion process is 15-25 hours.

8. The method for preparing the neodymium iron boron permanent magnet material according to any one of claims 1-7, characterized in that, The preparation method of the neodymium iron boron permanent magnet material satisfies one of the following conditions: (1) In steps S1 and S2, the first diffusion source and the second diffusion source are not simultaneously heavy rare earth elements; in step S1, after the first coating, the first precursor is further coated with an oxide; in step S3, the diffusion treatment is a three-stage process. (2) In steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth elements, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing; in step S3, the diffusion treatment is carried out in one stage, and the time of the one stage treatment is 15-25h; the temperature of the diffusion treatment is 850℃-950℃. (3) In steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth elements, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing; in step S3, the diffusion treatment is carried out in three stages, the temperature of the second stage diffusion treatment is 5-20°C higher than the temperature of the first stage diffusion treatment, the temperature of the third stage diffusion treatment is 10-20°C higher than the temperature of the second stage diffusion treatment, the time of the first stage diffusion treatment is 3-7h, the time of the second stage diffusion treatment is 5-10h, and the time of the third stage diffusion treatment is 15-25h; (4) In steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth alloy, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing; in step S3, the diffusion treatment is carried out in one stage, and the time of the one stage treatment is 15-25h; the temperature of the diffusion treatment is 850℃-950℃. (5) In steps S1 and S2, the first diffusion source and the second diffusion source are the same heavy rare earth alloy, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing; in step S3, the diffusion treatment is carried out in three stages, the temperature of the second stage diffusion treatment is 5-20°C higher than the temperature of the first stage diffusion treatment, the temperature of the third stage diffusion treatment is 10-20°C higher than the temperature of the second stage diffusion treatment, the time of the first stage diffusion treatment is 3-7h, the time of the second stage diffusion treatment is 5-10h, and the time of the third stage diffusion treatment is 15-25h; (6) In steps S1 and S2, the first diffusion source is a heavy rare earth element, the second diffusion source is a heavy rare earth alloy, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing; in step S3, the diffusion treatment is carried out in one stage, the time of the one stage treatment is 15-25h; the temperature of the diffusion treatment is 850℃-950℃; (7) In steps S1 and S2, the first diffusion source is a heavy rare earth element, the second diffusion source is a heavy rare earth alloy, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing; in step S3, the diffusion treatment is carried out in three stages, the temperature of the second stage diffusion treatment is 5-20°C higher than the temperature of the first stage diffusion treatment, the temperature of the third stage diffusion treatment is 10-20°C higher than the temperature of the second stage diffusion treatment, the time of the first stage diffusion treatment is 3-7h, the time of the second stage diffusion treatment is 5-10h, and the time of the third stage diffusion treatment is 15-25h; (8) In steps S1 and S2, the first diffusion source is a heavy rare earth alloy, the second diffusion source is a heavy rare earth element, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing; in step S3, the diffusion treatment is carried out in one stage, the time of the one stage treatment is 15-25h; the temperature of the diffusion treatment is 850℃-950℃; (9) In steps S1 and S2, the first diffusion source is a heavy rare earth alloy, the second diffusion source is a heavy rare earth element, and the first coating is carried out by magnetron sputtering and the second coating is carried out by screen printing; in step S3, the diffusion treatment is carried out in three stages, the temperature of the second stage diffusion treatment is 5-20°C higher than the temperature of the first stage diffusion treatment, the temperature of the third stage diffusion treatment is 10-20°C higher than the temperature of the second stage diffusion treatment, the time of the first stage diffusion treatment is 3-7h, the time of the second stage diffusion treatment is 5-10h, and the time of the third stage diffusion treatment is 15-25h.

9. A neodymium iron boron permanent magnet material, characterized in that, The neodymium iron boron permanent magnet material is prepared by the method for preparing neodymium iron boron permanent magnet material as described in any one of claims 1-8.

10. An application of the neodymium iron boron permanent magnet material as described in claim 9 in an electric motor.

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