Neodymium-iron-boron magnet with non-uniform performance distribution and preparation method and application thereof

Abstract

The invention provides a neodymium-iron-boron magnet with non-uniform performance distribution as well as a preparation method and application of the neodymium-iron-boron magnet. The preparation method of the neodymium-iron-boron magnet with the non-uniform performance distribution comprises the steps that S1, neodymium-iron-boron magnetic steel with the Pc value smaller than or equal to 0.5 is provided, the magnetization face of the neodymium-iron-boron magnetic steel is divided into an easy-to-demagnetize area and a difficult-to-demagnetize area, and the difficult-to-demagnetize area is arranged on the outer edge of the easy-to-demagnetize area in a surrounding mode; s2, coating the surface of the easy demagnetization area with heavy rare earth slurry to obtain neodymium iron boron magnetic steel coated with the slurry; and S3, the neodymium-iron-boron magnetic steel coated with the slurry is sequentially subjected to drying, diffusion and aging treatment, and the neodymium-iron-boron magnet with the non-uniform performance distribution is obtained. According to the application, the center area of the magnetized surface is divided into the easy-to-demagnetize area especially for the neodymium-iron-boron magnetic steel with a small height-diameter ratio and a Pc value less than or equal to 0.5, and then the neodymium-iron-boron magnet with excellent demagnetization resistance is prepared by coating the surface of the easy-to-demagnetize area with the heavy rare earth.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and in particular, to a neodymium iron boron magnet with non-uniform property distribution, a preparation method thereof, and an application thereof. Background Art

[0002] Permanent magnetic materials are one of the most important functional materials in modern life, and they are widely used in various fields such as motors, electronic products, medical devices, and construction machinery. Permanent magnetic materials mainly include neodymium iron boron, samarium cobalt, ferrite, alnico, etc. Demagnetization is one of the main failure modes of permanent magnetic materials. According to different demagnetization reasons, it can be divided into high-temperature demagnetization, low-temperature demagnetization, demagnetization by demagnetizing field, and vibration demagnetization, etc. The demagnetization modes of different types of magnets and different application fields also vary.

[0003] Neodymium iron boron is the permanent magnetic material with the highest magnetic performance discovered so far. In practical applications, the main demagnetization mode of neodymium iron boron magnets is high-temperature demagnetization, and the main demagnetization mode of neodymium iron boron magnets used in motors is high-temperature + demagnetizing field demagnetization. The working conditions of different parts of the magnet are different, and the demagnetization risks are also different. In order to balance the efficient use of rare earth resources and reduce costs, people have tried to prepare neodymium iron boron magnets with gradient property distribution. For example, in ZL202110238620.9 and 202010698191.9, the main technical feature is that in the grain boundary diffusion process, more heavy rare earths are coated in the regions where demagnetization is likely to occur at the corners and edges, and less is coated in the regions where demagnetization is not likely to occur in the center, so as to finally achieve the use of less heavy rare earths and obtain good demagnetization resistance at the same time. However, not all neodymium iron boron magnets with different height-to-diameter ratios processed by this method have excellent demagnetization resistance.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The main object of the present invention is to provide a neodymium iron boron magnet with non-uniform property distribution, a preparation method thereof, and an application thereof, so as to solve the problem that neodymium iron boron magnets with a small height-to-diameter ratio obtained by coating more heavy rare earths in the regions where demagnetization is likely to occur at the corners and edges and less heavy rare earths in the regions where demagnetization is not likely to occur in the center in the prior art do not have excellent demagnetization resistance.

[0006] To achieve the above object, according to one aspect of the present invention, a preparation method of a neodymium iron boron magnet with non-uniform property distribution includes: Step S1, providing a neodymium iron boron magnetic steel with a Pc value ≤ 0.5, and dividing the magnetization surface of the neodymium iron boron magnetic steel into an easily demagnetized region and a region not easily demagnetized, wherein the region not easily demagnetized surrounds the outer edge of the easily demagnetized region; Step S2, coating a heavy rare earth slurry on the surface of the easily demagnetized region to obtain a neodymium iron boron magnetic steel coated with the slurry; Step S3, sequentially performing drying, diffusion, and aging treatments on the neodymium iron boron magnetic steel coated with the slurry to obtain a neodymium iron boron magnet with non-uniform property distribution.

[0007] Further, in step S1, the Pc value of the neodymium iron boron magnet is ≤ 0.4, preferably Pc ≤ 0.3.

[0008] Further, the neodymium iron boron magnet steel is in the shape of a cuboid, with its length being a, width being b, and thickness being c. The easily demagnetized region is in the shape of a cuboid coaxial with the neodymium iron boron magnet steel, with its length being a1 and width being b1. In the length direction of the neodymium iron boron magnet steel, the distances from the easily demagnetized region to the first side and the third side, which are opposite to the length direction of the neodymium iron boron magnet steel, are both x. In the width direction of the neodymium iron boron magnet steel, the distances from the easily demagnetized region to the second surface and the fourth surface, which are opposite to the length direction of the neodymium iron boron magnet steel, are both y. Among them, 2x + a1 = a, 2y + b1 = b, and 0.1a / c ≤ x ≤ 0.5a / c, 0.1b / c ≤ y ≤ 0.5b / c.

[0009] Further, 0.2a / c ≤ x ≤ 0.5a / c, 0.2b / c ≤ y ≤ 0.5b / c.

[0010] Further, the neodymium iron boron magnet steel is in the shape of a cylinder, with its diameter being d and height being h. The diameter of the easily demagnetized region is d1, and the non - easily demagnetized region is in the shape of an annular ring, with its width being z. 2z + d1 = d, and 0.1d / h ≤ z ≤ 0.5d / h.

[0011] Further, 0.2d / h ≤ z ≤ 0.5d / h.

[0012] Further, the heavy rare - earth slurry includes heavy rare - earth substances, thickeners, and solvents. The heavy rare - earth substances are selected from at least one of heavy rare - earth metal simple substances, heavy rare - earth alloys, or heavy metal hydrides; the thickeners are selected from at least one of industrial glue, polyurethane resin, bismaleimide resin, silicone - modified epoxy resin, oleic acid amide, PVA (polyvinyl alcohol), PVB (polyvinyl butyral), PVC (polyvinyl chloride), nylon 66; the solvents include at least one of aromatic solvents, alcohol solvents, cellosolves, and ketone solvents.

[0013] Further, in the heavy rare - earth slurry, the content of the heavy rare - earth substances is 40 - 90 wt%.

[0014] Further, the heavy rare - earth simple substance in the heavy rare - earth slurry accounts for 0.2 - 0.5% of the mass of the easily demagnetized region; and / or, the heavy rare - earth substances in the heavy rare - earth slurry are in granular form, with a particle size of 2 - 50 μm. To achieve the above object, according to another aspect of the present invention, there is provided a neodymium iron boron magnet with non - uniform performance distribution, which is obtained according to the preparation method provided in the above first aspect.

[0015] According to the third aspect of the present invention, there is provided the application of the non - uniformly distributed neodymium iron boron magnet provided in the second aspect in the fields of motors, electronics, medical devices, and construction machinery.

[0016] Applying the technical solution of the present application, the applicant found that in many application scenarios, the most easily demagnetized area of the neodymium iron boron magnet is often not the edge of the magnet. Especially for magnets with a small height-to-diameter ratio and Pc value ≤ 0.5, the self-demagnetizing field in the center of the magnet is larger, and the risk of thermal demagnetization is also greater. The preparation method of the neodymium iron boron magnet with non-uniform performance distribution provided by the present application is specifically aimed at neodymium iron boron magnets with a small height-to-diameter ratio and Pc value ≤ 0.5. The edge area of the magnetization surface is divided into a non-easily demagnetized area, and the central area is divided into an easily demagnetized area. Then, a neodymium iron boron magnet with excellent demagnetization resistance performance is prepared by coating the surface of the easily demagnetized area with heavy rare earth.

[0017] In addition, the preparation method of the neodymium iron boron magnet with non-uniform performance distribution provided by the present application coats the heavy rare earth slurry in the easily demagnetized area and does not coat the heavy rare earth slurry in the non-easily demagnetized area. This not only makes the coating process simple and fast, but also reduces the usage amount of the heavy rare earth slurry, which is more conducive to reducing the preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0019] Figure 1 The structural schematic diagram of a cuboid-shaped neodymium iron boron magnet provided by the present invention is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0021] As analyzed in the background art of the present application, people in the prior art have tried to prepare a neodymium iron boron magnet with a gradient performance distribution and excellent demagnetization resistance performance by coating more heavy rare earth in the easily demagnetized area at the edge and less heavy metal in the non-easily demagnetized area in the center. However, the applicant found in actual applications that not all neodymium iron boron magnets with different height-to-diameter ratios have excellent demagnetization resistance after being treated by this method. Especially for neodymium iron boron magnets with a small height-to-diameter ratio and Pc ≤ 0.5, the demagnetization resistance performance of the magnets obtained after being treated by this method has not been significantly improved. To solve this problem, the present application provides a neodymium iron boron magnet with non-uniform performance distribution, its preparation method and application.

[0022] It should be noted that Pc is calculated according to the following formula: Pc = 1.43 × AR × (SQRT(1 + AR^2) + AR^0.25);

[0023] Among them, the aspect ratio AR = L / D; L is the length in the magnet orientation direction; D is the equivalent diameter. For a magnet with a cylindrical cross-section in the orientation direction, D is the diameter of the circular cross-section; for a block magnet, D = 2×SQRT(cross-section length a × cross-section width b / π).

[0024] In the first typical embodiment provided by the present application, a method for preparing a neodymium iron boron magnet with non-uniform performance distribution is provided. The preparation method includes: Step S1, providing a neodymium iron boron magnetic steel with a Pc value ≤ 0.5, and dividing the magnetization surface of the neodymium iron boron magnetic steel into an easily demagnetized region and a not easily demagnetized region, wherein the not easily demagnetized region surrounds the outer edge of the easily demagnetized region; Step S2, coating a heavy rare earth slurry on the surface of the easily demagnetized region to obtain a magnet coated with the slurry; Step S3, sequentially drying, diffusing, and aging the magnet coated with the slurry to obtain the neodymium iron boron magnet with non-uniform performance distribution.

[0025] Applying the technical solution of the present application, the applicant found that the most easily demagnetized region of the neodymium iron boron magnet in many application scenarios is often not the corner of the magnet. Especially for a magnet with a small aspect ratio and a Pc value ≤ 0.5, the self-demagnetizing field in the center of the magnet is larger, and the risk of thermal demagnetization is also greater. The preparation method of the neodymium iron boron magnet with non-uniform performance distribution provided by the present application is specifically for a neodymium iron boron magnetic steel with a small aspect ratio and a Pc value ≤ 0.5. The edge region of the magnetization surface is divided into a not easily demagnetized region, and the central region is divided into an easily demagnetized region. Then, a neodymium iron boron magnet with excellent demagnetization resistance performance is prepared by coating a heavy rare earth on the surface of the easily demagnetized region.

[0026] In addition, the preparation method of the neodymium iron boron magnet with non-uniform performance distribution provided by the present application coats the heavy rare earth slurry in the easily demagnetized region and does not coat the heavy rare earth slurry in the not easily demagnetized region. Not only is the coating process simple and fast, but also the amount of the heavy rare earth slurry is reduced, which is more conducive to reducing the preparation cost.

[0027] In some embodiments of the present application, when the Pc value of the neodymium iron boron magnet ≤ 0.4, especially when its Pc value ≤ 0.3, it is more conducive to preparing a neodymium iron boron material with excellent permanent magnet performance by the above method.

[0028] Typical but non-limiting, the Pc values of the neodymium iron boron magnetic steels applicable to the preparation method provided by the present application are, for example, 0.01, 0.02, 0.05, 0.08, 0.1, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5 or a range value composed of any two numerical values.

[0029] The specific shape of the above-mentioned neodymium iron boron magnet is not specifically limited, and it can be in the shape of a cuboid or a cylinder. If it is in an irregular shape, it can be converted according to the cuboid or cylinder shape disclosed in this application.

[0030] In some embodiments of the present application, as Figure 1 shown, the neodymium iron boron magnet is in the shape of a cuboid, its length is a, its width is b, its thickness is c, and the easy demagnetization region is in the shape of a rectangle coaxial with the neodymium iron boron magnet, its length is a1, its width is b1. In the length direction of the neodymium iron boron magnet, the distances between the easy demagnetization region and the first side and the third side opposite to the length direction of the neodymium iron boron magnet are both x. In the width direction of the neodymium iron boron magnet, the distances between the easy demagnetization region and the second surface and the fourth surface opposite to the length direction of the neodymium iron boron magnet are both y. Among them, 2x + a1 = a, 2y + b1 = b, and 0.1a / c ≤ x ≤ 0.5a / c, 0.1b / c ≤ y ≤ 0.5b / c. By the above method, the division of the easy demagnetization region and the non - easy demagnetization region of the cuboid shape is determined, and then the prepared cuboid - shaped neodymium iron boron magnet with non - uniform performance distribution has excellent anti - demagnetization performance.

[0031] Especially when dividing the easy demagnetization region and the non - easy demagnetization region, when 0.2a / c ≤ x ≤ 0.5a / c, 0.2b / c ≤ y ≤ 0.5b / c, it is more beneficial to improve the anti - demagnetization performance of the cuboid - shaped neodymium iron boron magnet with non - uniform performance distribution while reducing the consumption of heavy rare earths, and thus has more excellent high - temperature stability.

[0032] In some other embodiments of the present application, the neodymium iron boron magnet is cylindrical, its diameter is d, its height is h, the diameter of the easy demagnetization region is d1, and the non - easy demagnetization region is an annular shape, its width is z, 2z + d1 = d, and 0.1d / h ≤ z ≤ 0.5d / h. By the above method, the division of the easy demagnetization region and the non - easy demagnetization region of the cylindrical shape is determined, and then the prepared cylindrical - shaped neodymium iron boron magnet with non - uniform performance distribution has excellent anti - demagnetization performance. Especially when 0.2d / h ≤ z ≤ 0.5d / h, it is more beneficial to improve the anti - demagnetization performance of the cylindrical - shaped neodymium iron boron magnet with non - uniform performance distribution while reducing the consumption of heavy rare earths, and thus has more excellent high - temperature stability.

[0033] The heavy rare earth slurry used in the above step S2 includes heavy rare earth substances and solvents. The heavy rare earth substances are selected from any one or a mixture of multiple kinds of heavy rare earth metal simple substances, heavy rare earth alloys or heavy metal hydrides. The solvents include, but are not limited to, any one or a mixed solvent formed by a combination of gasoline, ethanol, acrylic acid or oleic acid amide. It should be noted that the heavy rare earths in the heavy rare earth substances include, but are not limited to, Dy, Tb, Gd, etc.

[0034] In order to further improve the coating efficiency of the heavy rare earth slurry, it is preferred that in the heavy rare earth slurry, the mass content of the heavy rare earth substance is 40-95%, such as 40%, 50%, 60%, 70%, 80%, 90% or a range value composed of any two numerical values.

[0035] In order to improve the demagnetization resistance of the NdFeB magnet while reducing the preparation cost, it is preferred that the heavy rare earth simple substance in the heavy rare earth slurry (if the heavy rare earth substance in the heavy rare earth slurry is not a heavy rare earth simple substance, it is calculated according to the content of the heavy rare earth element in the heavy rare earth substance) accounts for 0.2-0.5% of the mass of the easily demagnetized region, such as 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5% or a range value composed of any two numerical values.

[0036] In order to further improve the coating uniformity of the heavy rare earth slurry, it is preferred that the heavy rare earth substance in the heavy rare earth slurry is granular, and its particle size is 2-50 μm, such as 2 μm, 2.5 μm, 3 μm, 4 μm, 4.5 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm or a range value composed of any two numerical values.

[0037] In the second typical embodiment of the present application, a NdFeB magnet with non-uniform performance distribution is further provided, which is obtained according to the preparation method provided in the above first typical embodiment.

[0038] The NdFeB magnet with non-uniform performance distribution provided by the present application and having a small aspect ratio and a Pc≤0.5 value is not only low in cost, but also has excellent demagnetization resistance and excellent high-temperature stability, and has broad application prospects in the field of permanent magnetic materials.

[0039] In the third typical embodiment of the present application, the application of the non-uniformly distributed NdFeB magnet provided in the above second typical embodiment in the fields of motors, electronics, medical devices, and construction machinery is further provided.

[0040] Hereinafter, the technical effects of the application will be further described in combination with examples and comparative examples.

[0041] Example A-1

[0042] The present application provides a preparation method of a NdFeB magnet with non-uniform performance distribution and a Pc value of 0.169, which includes the following steps:

[0043] (1) Provide a N55 NdFeB magnetic steel blank, and process the magnetic steel blank into a rectangular magnetic steel sheet with a length a of 70 mm, a width b of 30 mm, and a thickness c of 4 mm;

[0044] (2) Mix oleic acid amide and ethanol in a mass ratio of 1:10, stir evenly to obtain a glue solution, and mix evenly the metallic terbium powder with an average particle size of 3 μm in a glove box under nitrogen protection to obtain a Tb slurry. Among them, the mass ratio of the metallic terbium powder to the glue solution is 4:1;

[0045] (3) As Figure 1 shown, divide the magnetization surface of the magnetic steel sheet into an easily demagnetized area and a not easily demagnetized area. Among them, the not easily demagnetized area is enclosed by x and y. x takes 0.1×a / c = 1.75 mm, and y takes 0.1×b / c = 0.75 mm. Coat the Tb slurry on the easily demagnetized area. The coating amount of the Tb slurry is coated according to the mass ratio of 0.4:100 of the magnetic steel in the coating area. Among them, Tb accounts for 0.29% of the total mass of the magnetic steel to obtain the neodymium iron boron magnetic steel coated with the slurry;

[0046] (4) Dry the neodymium iron boron magnetic steel coated with the slurry in sequence, put it into a vacuum diffusion furnace, keep it at 450 °C for 2 hours to remove organic substances, then raise the temperature to 900 ± 3 °C for grain boundary diffusion treatment, the diffusion time is 24 hours. After the diffusion is completed, quickly cool it to below 85 °C, then raise the temperature to 510 °C for aging treatment, the aging time is 4 hours. After the aging is completed, quickly cool it to below 80 °C and take it out of the furnace to obtain a neodymium iron boron magnet with non-uniform property distribution.

[0047] Example A-2

[0048] The difference between this example and Example A-1 is that x takes 0.2a / c, y takes 0.2a / c, and the coating amount of the Tb slurry is coated according to the mass ratio of 0.4:100 of the mass of Tb to the magnetic steel in the coating area. Among them, Tb accounts for 0.26% of the total mass of the magnetic steel.

[0049] Example A-3

[0050] The difference between this example and Example A-1 is that x takes 0.3a / c, y takes 0.3b / c, and the coating amount of the Tb slurry is coated according to the mass ratio of 0.4:100 of the mass of Tb to the magnetic steel in the coating area. Among them, Tb accounts for 0.23% of the total mass of the magnetic steel.

[0051] Example A-4

[0052] The difference between this example and Example A-1 is that x takes 0.4a / c, y takes 0.4b / c, and the coating amount of the Tb slurry is coated according to the mass ratio of 0.4:100 of the mass of Tb to the magnetic steel in the coating area. Among them, Tb accounts for 0.2% of the total mass of the magnetic steel.

[0053] Example A-5

[0054] The difference between this embodiment and Embodiment A-1 is that x is taken as 0.5a / c, y is taken as 0.5b / c, and the coating amount of the Tb slurry is coated according to the mass ratio of Tb to the magnet steel in the coating area being 0.4:100, where Tb accounts for 0.18% of the total mass of the magnet steel.

[0055] Embodiment A-6

[0056] The difference between this embodiment and Embodiment A-1 is that x is taken as 0.05a / c, y is taken as 0.05b / c, and the coating amount of the Tb slurry is coated according to the mass ratio of Tb to the magnet steel in the coating area being 0.4:100.

[0057] Embodiment A-7

[0058] The difference between this embodiment and Embodiment A-1 is that x is taken as 1.5a / c, y is taken as 1.5b / c, and the coating amount of the Tb slurry is coated according to the mass ratio of Tb to the magnet steel in the coating area being 0.4:100, where Tb accounts for 0.02% of the total mass of the magnet steel.

[0059] Embodiment A-8

[0060] The difference between this embodiment and Embodiment A-1 is that the coating amount of the Tb slurry is coated according to the mass ratio of Tb to the magnet steel in the easily coated area being 0.2:100.

[0061] Embodiment A-9

[0062] The difference between this embodiment and Embodiment A-1 is that the coating amount of the Tb slurry is coated according to the mass ratio of Tb to the magnet steel in the easily coated area being 0.5:100.

[0063] Embodiment A-10

[0064] The difference between this embodiment and Embodiment A-1 is that the coating amount of the Tb slurry is coated according to the mass ratio of Tb to the magnet steel in the easily coated area being 0.05:100.

[0065] Embodiment A-11

[0066] The difference between this embodiment and Embodiment A-1 is that the coating amount of the Tb slurry is coated according to the mass ratio of Tb to the magnet steel in the easily coated area being 0.6:100.

[0067] Comparative Example A-1

[0068] The difference between this comparative example and Embodiment A-1 is that the rectangular magnet steel sheet provided in step (1) is not coated with the Tb slurry and directly proceeds to the subsequent step (4).

[0069] Comparative Example A-2

[0070] The difference between this comparative example and Example A-1 lies in that, in step (3), the easily demagnetizable region and the not-easily demagnetizable region are not divided, and the Tb slurry is directly and evenly coated on the two magnetization surfaces of the neodymium-iron-boron permanent magnet. The dosage of terbium is 0.5% of the total weight of the permanent magnet sheet.

[0071] Comparative Example A-3

[0072] The difference between this comparative example and Example A-1 lies in that, in step (3), an area of 32×13 (mm) at the center of the two 70×30 (mm) surfaces is divided into the not-easily demagnetizable region, and the remaining part is divided into the easily demagnetizable region. The Tb powder slurry is coated on the easily demagnetizable region. The dosage of terbium is 0.4% of the total weight of the permanent magnet sheet.

[0073] Comparative Example A-4

[0074] The difference between this comparative example and Example A-1 lies in that, in step (3), the 70×30 (mm) surface is divided into three parts along the 70 mm direction. The sizes of all three regions are 70×10 (mm). The terbium dosage in the two 70×10 (mm) magnetic regions on both sides is coated at 0.5% of the sample mass of this region, and the coating amount in the middle 70×10 (mm) region is 0.2%. The terbium amount used in the fourth group of samples is 80% of that in the second group. The total dosage of terbium is 0.4% of the total weight of the permanent magnet sheet.

[0075] Test Example 1

[0076] The magnetic properties of the neodymium-iron-boron magnets with non-uniform distribution of performance with Pc value of 0.169 provided in the above examples and comparative examples were measured respectively, and the results are shown in Table 1 below.

[0077] Among them, (1) Demagnetization curve test: The magnetic properties were measured using the NIM-62000T permanent magnet material precision measurement system of the National Institute of Metrology, China. The test sample was of the test sample specification, without cutting and processing. The thickness direction was tested with two pieces stacked. Br and Hcj were obtained by testing the demagnetization curve of the permanent magnet material.

[0078] (2) The measurement method of the semi-open circuit magnetic loss at 120 °C is as follows: The sample was magnetized, and the magnetic moment of the sample was measured and recorded as M1 using the EF5 magnetic moment tester of Magnet Physic Company, Germany; the high-precision high-temperature oven was heated to the measurement temperature (120 °C), and then the N or S pole of the sample was attracted to an iron plate with a thickness of 2 mm. The iron plate together with the magnet was placed in the oven and kept warm for 2 hours; the sample was taken out and cooled to room temperature, and the magnetic moment M2 of the sample was measured again. The semi-open circuit magnetic loss was (M1 - M2) / M1×100%.

[0079] Table 1

[0080]

[0081]

[0082] Note: The dosage of Tb refers to the ratio of the mass of Tb in the Tb slurry to the mass of the magnetic steel sheet.

[0083] Example B-1

[0084] The present application provides a method for preparing a neodymium iron boron magnet with a non-uniform performance distribution and a Pc value of 0.496, which includes the following steps:

[0085] (1) Provide a neodymium iron boron magnetic steel blank of N50M, and process the magnetic steel blank into a rectangular magnetic steel sheet with a length a of 30 mm, a width b of 10 mm, and a thickness c of 4 mm;

[0086] (2) Mix oleic acid amide and ethanol in a mass ratio of 1:10, stir evenly to obtain a glue solution, and mix evenly the metal terbium powder with an average particle size of 3 μm in a glove box under nitrogen protection to obtain a Tb slurry. Among them, the mass ratio of the metal terbium powder to the glue solution is 4:1;

[0087] (3) As Figure 1 shown, divide the magnetization surface of the magnetic steel sheet into an easy demagnetization region and a non-easy demagnetization region. Among them, the non-easy demagnetization region is enclosed by x and y. x takes 0.2×a / c = 1.5 mm, and y takes 0.2×b / c = 0.75 mm. Coat the Tb slurry on the easy demagnetization region, and coat the Tb slurry according to a mass ratio of 0.4:100 of the magnetic steel in the coating region to obtain a neodymium iron boron magnetic steel coated with the slurry;

[0088] (4) Dry the neodymium iron boron magnetic steel coated with the slurry in sequence, put it into a vacuum diffusion furnace, keep it at 450 °C for 2 hours to remove organic substances, then raise the temperature to 900 ± 3 °C for grain boundary diffusion treatment, the diffusion time is 24 hours, after the diffusion is completed, quickly cool it to below 85 °C, then raise the temperature to 510 °C for aging treatment, the aging time is 4 hours, after the aging is completed, quickly cool it to below 80 °C and then take it out of the furnace to obtain a neodymium iron boron magnet with a non-uniform performance distribution.

[0089] Example B-2

[0090] The difference between this example and Example B-1 is that in step (3), x is 0.5a / c and y is 0.5b / c.

[0091] Comparative Example B-1

[0092] The difference between this comparative example and Example B-1 is that the rectangular magnetic steel sheet provided in step (1) is not coated with the Tb slurry and directly proceeds to the subsequent step (4).

[0093] Comparative Example B-2

[0094] The difference between this comparative example and Example B-1 is that in step (3), the Tb slurry is evenly coated on the two magnetization surfaces of the neodymium iron boron magnet, and the dosage of terbium is 0.5% of the total weight of the magnet sheet.

[0095] Test Example 2

[0096] The magnetic properties of the neodymium iron boron magnets with non-uniform performance and a Pc value of 0.496 provided in the above examples and comparative examples were measured respectively, and the results are shown in Table 2 below. Among them, the test methods for each property are the same as those in Test Example 1, and will not be elaborated here.

[0097] Table 2

[0098]

[0099] Example C-1

[0100] The present application provides a method for preparing a neodymium iron boron magnet with non-uniform performance and a Pc value of 0.031, which includes the following steps:

[0101] (1) Provide a neodymium iron boron magnet blank of N40, and process the magnet blank into a rectangular magnet sheet with a diameter a of 100 mm, a width b of 100 mm, and a thickness c of 1.8 mm;

[0102] (2) Mix oleic acid amide and ethanol according to a mass ratio of 1:10, stir evenly to obtain a glue solution, and mix the metal terbium powder with an average particle size of 3 μm evenly in a glove box under nitrogen protection to obtain a Tb slurry. Among them, the mass ratio of the metal terbium powder to the glue solution is 4:1;

[0103] (3) As Figure 1 shown, divide the magnetization surface of the magnet sheet into an easily demagnetized area and a not easily demagnetized area. The not easily demagnetized area is enclosed by x and y, where x is taken as 0.1×a / c = 11.1 mm, and y is taken as 0.1×b / c = 11.1 mm. Coat the Tb slurry on the easily demagnetized area, and the coating amount of the Tb slurry is coated according to the mass ratio of Tb to the magnet in the easily coated area of 0.4:100 to obtain a neodymium iron boron magnet coated with the slurry;

[0104] (4) The neodymium iron boron magnet coated with the slurry is dried in sequence, put into a vacuum diffusion furnace, and kept at 450 °C for 2 hours to remove organic substances, then heated to 900 ± 3 °C for grain boundary diffusion treatment, the diffusion time is 24 hours, after the diffusion is completed, it is quickly cooled to below 85 °C, then heated to 510 °C for aging treatment, the aging time is 4 hours, after the aging is completed, it is quickly cooled to below 80 °C and taken out of the furnace to obtain a neodymium iron boron magnet with non-uniform performance.

[0105] Example C-2

[0106] The present application provides a method for preparing a neodymium-iron-boron magnet with a non-uniform performance distribution and a Pc value of 0.031, which comprises the following steps:

[0107] (1) Provide a neodymium-iron-boron magnet steel blank of N40, and process the magnet steel blank into a rectangular magnet steel sheet with a diameter a of 100 mm, a width b of 100 mm, and a thickness c of 1.8 mm;

[0108] (2) Mix oleic acid amide and ethanol according to a mass ratio of 1:10, stir evenly to obtain a glue solution, and mix evenly the metal dysprosium Dy powder with an average particle size of 50 μm in a glove box under nitrogen protection to obtain a Dy slurry. Among them, the mass ratio of the metal dysprosium powder to the glue solution is 4:1;

[0109] (3) As shown in Figure 1 , divide the magnetization surface of the magnet steel sheet into an easily demagnetized area and a not easily demagnetized area. Among them, the not easily demagnetized area is enclosed by x and y. x is taken as 0.5×a / c = 27.8 mm, and y is taken as 0.5×b / c = 27.8 mm. Coat the Dy slurry on the easily demagnetized area, and the coating amount of the Dy slurry is coated according to the mass ratio of Dy to the magnet steel in the easily coated area of 1:100 to obtain a neodymium-iron-boron magnet steel coated with the slurry;

[0110] (4) Dry the neodymium-iron-boron magnet steel coated with the slurry in sequence, put it into a vacuum diffusion furnace, keep it at 450 °C for 2 hours to remove organic substances, then raise the temperature to 900 ± 3 °C for grain boundary diffusion treatment, the diffusion time is 24 hours, after the diffusion is completed, quickly cool it to below 85 °C, then raise the temperature to 510 °C for aging treatment, the aging time is 4 hours. After the aging is completed, quickly cool it to below 80 °C and take it out of the furnace to obtain a neodymium-iron-boron magnet with a non-uniform performance distribution.

[0111] Comparative Example C-1

[0112] The difference between this comparative example and Example C-1 is that the rectangular magnet steel sheet provided in step (1) is not coated with the Dy slurry, and the subsequent step (4) is directly carried out.

[0113] Comparative Example C-2

[0114] The difference between this comparative example and Example C-1 is that in step (3), the easily demagnetized area and the not easily demagnetized area are not divided, and the Dy slurry is directly and evenly coated on the two magnetization surfaces of the neodymium-iron-boron magnet steel. In the coating amount of the dysprosium slurry, Dy is 0.5% of the total weight of the magnet steel sheet.

[0115] Test Example 3

[0116] The magnetic properties of the NdFeB magnets with non-uniform performance distribution and a Pc value of 0.031 provided in the above-mentioned examples and comparative examples were measured respectively, and the results are shown in Table 3 below. Among them, the test methods for each property are the same as those in Test Example 1, and will not be elaborated here.

[0117] Table 3

[0118]

[0119] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: The preparation method of the NdFeB magnet with non-uniform performance distribution provided in this application is especially for NdFeB magnetic steel with a small height-to-diameter ratio and a Pc value ≤ 0.5. The edge area of the magnetization surface is divided into a non-easy-to-demagnetize area, and the central area is divided into an easy-to-demagnetize area. Then, by coating the surface of the easy-to-demagnetize area with heavy rare earths, an NdFeB magnet with excellent demagnetization resistance performance is prepared.

[0120] In addition, the preparation method of the NdFeB magnet with non-uniform performance distribution provided in this application coats the heavy rare earth slurry in the easy-to-demagnetize area and does not coat the heavy rare earth slurry in the non-easy-to-demagnetize area. Not only is the coating process simple and fast, but also the amount of heavy rare earth slurry used is reduced, which is more conducive to reducing the preparation cost.

[0121] The preparation method of the NdFeB magnet with non-uniform performance distribution provided in this application has a high cost performance, that is, with the same amount of heavy rare earth used, the high-temperature irreversible magnetic loss is lower, or with the same irreversible magnetic loss, the amount of heavy rare earth used is lower. Generally speaking, the lower the Pc, the more obvious the effect.

[0122] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a neodymium iron boron magnet with non-uniform property distribution, characterized in that, the preparation method comprises: Step S1, providing a neodymium iron boron magnetic steel with Pc value ≤ 0.5, dividing the magnetization surface of the neodymium iron boron magnetic steel into an easily demagnetized area and a not easily demagnetized area, wherein the not easily demagnetized area surrounds the outer edge of the easily demagnetized area; Step S2, coating a heavy rare earth slurry on the surface of the easily demagnetized area to obtain a neodymium iron boron magnetic steel coated with the slurry; Step S3, successively drying, diffusing and aging the neodymium iron boron magnetic steel coated with the slurry to obtain the neodymium iron boron magnet with non-uniform property distribution.

2. The preparation method according to claim 1, characterized in that, in step S1, the Pc value of the neodymium iron boron magnet is ≤ 0.4, preferably Pc ≤ 0.

3.

3. The preparation method according to claim 1, characterized in that, the neodymium iron boron magnetic steel is rectangular parallelepiped-shaped, with length a, width b and thickness c, the easily demagnetized area is rectangular parallelepiped-shaped and coaxial with the neodymium iron boron magnetic steel, with length a1 and width b1, in the length direction of the neodymium iron boron magnetic steel, the distances between the easily demagnetized area and the first side and the third side opposite to the length direction of the neodymium iron boron magnetic steel are both x, in the width direction of the neodymium iron boron magnetic steel, the distances between the easily demagnetized area and the second surface and the fourth surface opposite to the length direction of the neodymium iron boron magnetic steel are both y, wherein 2x + a1 = a, 2y + b1 = b, and 0.1a / c ≤ x ≤ 0.5a / c, 0.1b / c ≤ y ≤ 0.5b / c.

4. The preparation method according to claim 3, characterized in that, 0.2a / c ≤ x ≤ 0.5a / c, 0.2b / c ≤ y ≤ 0.5b / c.

5. The preparation method according to claim 1, characterized in that, the neodymium iron boron magnetic steel is cylindrical, with diameter d and height h, the diameter of the easily demagnetized area is d1, the not easily demagnetized area is annular, with width z, 2z + d1 = d, and 0.1d / h ≤ z ≤ 0.5d / h.

6. The preparation method according to claim 5, characterized in that, 0.2d / h ≤ z ≤ 0.5d / h.

7. The preparation method according to any one of claims 1 to 5, characterized in that, the heavy rare earth slurry comprises a heavy rare earth substance, a thickening agent and a solvent, the heavy rare earth substance is selected from at least one of heavy rare earth metal simple substances, heavy rare earth alloys or heavy metal hydrides; the thickening agent comprises at least one of industrial glue, polyurethane resin, bismaleimide resin, organosilicon modified epoxy resin, oleic acid amide, PVA, PVB, PVC, nylon 66; the solvent comprises at least one of aromatic solvents, alcohol solvents, cellosolves, ketone solvents; preferably, in the heavy rare earth slurry, the content of the heavy rare earth substance is 40 - 90 wt%.

8. The preparation method according to any one of claims 1 to 5, characterized in that, the heavy rare earth elements in the heavy rare earth slurry account for 0.2 - 0.5% of the mass of the easily demagnetized area; And / or, the heavy rare earth substance in the heavy rare earth slurry is granular, and its particle size is 2 to 50 μm.

9. A neodymium iron boron magnet with non-uniform property distribution, characterized in that, the neodymium iron boron magnet with non-uniform property distribution is obtained by the preparation method according to any one of claims 1 to 8.

10. Application of the neodymium iron boron magnet with non-uniform distribution according to claim 9 in the fields of motors, electronics, medical devices, and construction machinery.

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