Neodymium-iron-boron magnet, preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a neodymium-iron-boron magnet, a preparation method therefor and a use thereof. The neodymium-iron-boron magnet comprises an easy demagnetization area, a non-easy demagnetization area and a bonding area, wherein the volume of the easy demagnetization area accounts for 15-50% of the total volume of the neodymium-iron-boron magnet, the volume of the bonding area accounts for 0.5-4.0% of the total volume of the neodymium-iron-boron magnet, and the ratio of the coercive force of the non-easy demagnetization area to the coercive force of the easy demagnetization area is 0.7-1. According to the neodymium-iron-boron magnet provided by the present invention, good demagnetization resistance can be maintained while the cost is greatly reduced.

Description

Neodymium iron boron magnet and its preparation method and application Technical Field

[0001] The present invention particularly relates to a neodymium iron boron magnet and a preparation method and application thereof. Background Art

[0002] Since its introduction, neodymium iron boron (NdFeB) permanent magnets have been widely used in automotive, wind power, home appliances, industrial robots, and other fields. Due to the varying operating conditions in each field, the performance requirements for magnetic steel used in these fields also vary. In recent years, with the booming development of new energy vehicles, the demand for magnetic steel in the main drive motor has increased dramatically. Since the normal operating temperature of the main drive motor is mainly concentrated in the range of 120-180°C, NdFeB requires higher coercivity and thermal stability. To improve the temperature resistance of rare earth permanent magnets, large amounts of heavy rare earths Dy and Tb are usually added to increase the main phase magnetocrystalline anisotropy field. However, the scarcity and high price of heavy rare earth resources have severely restricted the application of NdFeB magnets in various industries.

[0003] With the increasing demand for high-performance magnets, grain boundary diffusion (GBD) technology has gradually become well-known and accepted. Conventional GBD technology uses a physical vapor deposition method to deposit a diffusion source on the magnet surface. The source is then infiltrated into the magnet's interior along the grain boundaries under high temperature and pressure. The greatest advantage of this technology is that it significantly increases coercivity while maintaining virtually unchanged remanence, using only a small amount of heavy rare earth elements. In terms of effective heavy rare earth utilization, conventional GBD products significantly improve over non-GBD products.

[0004] However, since the reverse magnetic field generated after the coil in the motor is energized is not a uniform magnetic field, the position of the magnet close to the coil is most susceptible to demagnetization and is called the easy demagnetization zone, while the position far from the coil is not easily demagnetized and is called the non-easy demagnetization zone. In NdFeB magnets, in addition to being subjected to the demagnetization field of the magnetic circuit during operation, the magnets are also subjected to demagnetization caused by rising temperature. In the magnetic circuit, the demagnetization of the magnets starts from the corners, while the demagnetization caused by the rise in operating temperature starts from the core. In order to solve the demagnetization of the core at high temperatures, Chinese patent CN111653407A discloses a gradient-distributed NdFeB magnet, which performs different grain boundary diffusion treatments on different areas of the NdFeB magnet, which can reduce the demagnetization rate at high temperatures. However, since it is processed in different areas of the entire magnet, the operation is extremely difficult, and the anti-demagnetization performance is still not ideal.

[0005] Summary of the Invention

[0006] To overcome the demagnetization defect of NdFeB magnets in the prior art, the present invention provides NdFeB magnets, their preparation method, and applications. The NdFeB magnets provided by the present invention can achieve good anti-demagnetization performance while significantly reducing costs.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The present invention provides a neodymium iron boron magnet, which comprises an easily demagnetized area, a non-easily demagnetized area and a bonding area, wherein the volume of the easily demagnetized area accounts for 15%-50% of the total volume of the neodymium iron boron magnet;

[0009] Wherein, the volume of the bonding area accounts for 0.5%-4.0% of the total volume of the NdFeB magnet;

[0010] Wherein, the ratio of the coercive force of the non-easily demagnetized region to the coercive force of the easily demagnetized region is 0.7-1.

[0011] In the present invention, the volume of the easily demagnetized region accounts for 25%-50% of the total volume of the NdFeB magnet, for example, 32% or 50%. This easily demagnetized region, within the volume range of the present invention, is more conducive to stable performance of the NdFeB magnet, precise utilization of the heavy rare earth elements Dy and Tb, and also reduces eddy current losses to a certain extent.

[0012] In the present invention, the ratio of the coercive force of the non-easily demagnetized region to the coercive force of the easily demagnetized region may be 0.87-0.96, preferably 0.90-0.95, such as 0.90, 0.92 or 0.93.

[0013] In the present invention, the material of the bonding area can be a substance that can bond the easily demagnetized area and the non-easily demagnetized area without affecting the performance of the NdFeB magnet, preferably glue, and the glue is more preferably one or more of resin glue, polyester glue and hot melt glue.

[0014] Since the magnets are usually located inside the motor slots, the heat dissipation conditions are not good. During the operation of the motor, relatively high eddy current losses are easily generated on the magnetic material, resulting in an increase in the surface temperature of the magnets. When the temperature exceeds its operating temperature, the magnets are easily demagnetized. The magnets of the present invention are bonded together with glue to insulate the magnets, which increases the resistance between the magnets to a certain extent. Moreover, the glue does not have magnetic properties, so there is no demagnetization, which is beneficial for reducing eddy current losses of the magnets at high temperatures and enhancing the temperature resistance and anti-demagnetization ability of the magnets. The present invention is different from a whole magnet or a conventional bonded magnet. On the one hand, the magnetic properties of the magnets can be flexibly customized and strengthened according to the easily demagnetized area in the motor. On the other hand, since the reverse field and temperature of the non-easy demagnetization area are smaller than those of the easy demagnetization area during use, the actual coercive force performance requirement of the non-easy demagnetization area is less than that of the easy demagnetization area. Therefore, the amount of heavy rare earth can be saved by lowering the coercive force, ultimately achieving the purpose of reducing costs. In addition, the anti-demagnetization ability of the whole non-bonded magnet in the motor is comparable to that of the whole non-bonded magnet.

[0015] In the present invention, the volume of the bonding area may be 1%-4%, where the percentage is the percentage of the volume of the bonding area to the total volume of the NdFeB magnet.

[0016] In the present invention, the width of the bonding area can be 0-0.12mm, but not 0; it is preferably 0.05mm-0.12mm. The width of the bonding area primarily affects the magnetic flux of the magnet. The wider the width, the greater the volume of the bonding area. At the same volume, the proportion of the magnetic steel decreases, resulting in a decrease in the overall magnetic flux. Therefore, the width of the bonding area should be within the range of the present invention to achieve a good overall magnet effect.

[0017] In the present invention, the bonding area preferably has a porosity of 0%. If the glue is applied unevenly or bubbles form in the gaps, resulting in direct contact between the magnets, the anti-eddy current loss effect and bonding strength will be reduced, affecting the anti-demagnetization effect. In some specific implementations, fully automatic equipment is used for magnet bonding. The glue is evenly applied to the magnet bonding surface using a nozzle. The bonding is then automatically performed on the same marble reference surface. The glue application area is scanned by infrared light to automatically identify magnets that have not been fully coated, ensuring that the magnet bonding area is free of pores and has good consistency.

[0018] In the present invention, the remanence of the easily demagnetized area and the non-easily demagnetized area may be the same. The same remanence should be understood as the remanence being the same within a certain deviation range, and the deviation may be ±0.5 kGs.

[0019] In the present invention, the difference ΔHcj between the coercivity of the non-easily demagnetized region and the coercivity of the easily demagnetized region may be 1 kOe-7.5 kOe, preferably 1 kOe-3 kOe, such as 1.8 kOe, 2.2 kOe, 2.4 kOe or 2.6 kOe.

[0020] The present invention also provides a method for preparing a NdFeB magnet, the method comprising bonding a first magnet and a second magnet to obtain the NdFeB magnet;

[0021] Wherein, the first magnet forms an easily demagnetized area; the second magnet forms a non-easy demagnetized area; and the bonding forms a bonding area;

[0022] Wherein, the volume of the easily demagnetized area accounts for 15%-50% of the total volume of the NdFeB magnet;

[0023] Wherein, the volume of the bonding area accounts for 0.5%-4.0% of the total volume of the NdFeB magnet;

[0024] Wherein, the ratio of the coercive force of the non-easily demagnetized region to the coercive force of the easily demagnetized region is 0.7-1.

[0025] In the present invention, the first magnets are preferably symmetrically distributed on both sides of the second magnet.

[0026] In the present invention, the easily demagnetized region may include at least two first magnets, for example, two magnets.

[0027] In the present invention, the percentage of the volume of the bonding area to the volume of the easily demagnetized area may be 1-5%, preferably 1.58%-3.79%.

[0028] In the present invention, the non-demagnetizable region may include 1-3 second magnets, for example, 1 or 2.

[0029] In the present invention, the percentage of the volume of the bonding area to the volume of the non-easily demagnetized area may be 1-4%, preferably 1.58%-3.79%.

[0030] In the present invention, the volume of the bonding area refers to the sum of the volumes of the bonding area between the first magnet and the bonding area between the first magnet and the second magnet. In the present invention, the width of the bonding area can be 0-0.12 mm, but not 0; preferably, it is 0.05 mm-0.12 mm.

[0031] In the present invention, the preparation methods of the first and second magnets can be conventional methods in the art, preferably, by treating a NdFeB substrate; the treatment methods include one or more of a single alloy method, a dual alloy method, and a diffusion method. The NdFeB substrate can be commercially available or prepared according to conventional methods in the art, such as by smelting, hydrogen crushing, jet milling, pressing, and sintering a raw material composition to obtain a green body, and then machining and cleaning the green body to obtain the NdFeB substrate; the green body is preferably 52H.

[0032] The raw material composition includes an R element, which may be Nd or "Nd and Pr". The content of the R element is preferably 27.5 wt%-31.5 wt%, for example 28 wt%, where the percentage refers to the weight percentage in the raw material composition.

[0033] The raw material composition includes element B, and the content of element B is preferably 0.87 wt%-0.99 wt%, more preferably 0.94 wt%-0.99 wt%, where the percentage refers to the weight percentage in the raw material composition.

[0034] The raw material composition may contain Co element, and the content of the Co element is preferably 0-2.5 wt %, for example, 1 wt %. The percentage refers to the weight percentage in the raw material composition.

[0035] The raw material composition may contain Cu element, and the content of the Cu element is preferably 0.1 wt%-0.3 wt%, for example, 0.2 wt%. The percentage refers to the weight percentage in the raw material composition.

[0036] The raw material composition may contain Al element, and the content of the Al element is preferably 0-0.2 wt %, for example, 0.1 wt %. The percentage refers to the weight percentage in the raw material composition.

[0037] The raw material composition may contain Ga element, and the content of the Ga element is preferably 0.1wt%-0.3wt%, more preferably 0.2-0.3wt%, and the percentage refers to the weight percentage in the raw material composition.

[0038] The raw material composition contains T element, which may be one or more of Zn, Si, Ti, V, Cr, Mn, Ni, Ge, Zr, Ti, Nb, Mo, Pd, Ag, Cd, Sb, Hf, Ta, W, O, C, N, S, F and P, preferably Ti and / or Zr; the content of the T element is preferably 0.1wt%-0.25wt%, for example, 0.2wt%, where the percentage refers to the weight percentage in the raw material composition.

[0039] The raw material composition may include M, and the mass percentage of M is preferably 0.1wt%-3.0wt%, where the percentage refers to the weight percentage in the easily demagnetized region; the M is preferably selected from at least one of Al, Co, Cu, Ga, Sn, Pb and In.

[0040] The raw material composition may contain Fe element, and the content of the Fe element is preferably 66 wt %-70 wt %, where the percentage refers to the weight percentage in the raw material composition.

[0041] Among them, the diffusion method can be conventional in the field, for example: coating the surface of the substrate of the first magnet or the substrate of the second magnet with a diffusion source, and diffusing the heavy rare earth element under heat treatment conditions; the direction of the diffusion can be parallel to the magnetization direction or perpendicular to the magnetization direction.

[0042] The coating method is preferably a vapor deposition method or a vapor diffusion method.

[0043] Among them, the heat treatment step is preferably to perform diffusion heat treatment at a temperature of 700-950°C for 24-60 hours under vacuum or argon atmosphere; then cool to 200°C, then heat to 400-600°C and keep warm for 1-6 hours, and finally cool to room temperature to obtain the first magnet or the second magnet.

[0044] The diffusion source used in the diffusion method may be a material conventional in the art, such as one or more of heavy rare earth metals, heavy rare earth oxides, heavy rare earth hydrofluorides, heavy rare earth fluorides, heavy rare earth hydrogenates, heavy rare earth oxyfluorides, and heavy rare earth-M alloys.

[0045] Preferably, the heavy rare earth in the diffusion source can be selected from at least one of Dy, Tb, Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; more preferably, Dy and / or Tb; preferably, the M element in the heavy rare earth-M alloy includes one or more of Al, Co, Cu, Ga, Sn, Pb and In elements.

[0046] In some embodiments, the Dy content of the easily demagnetized region may be 0-4.3%, such as 0, 0.85, 1.6, 2.6, or 2.9%. The percentage refers to the weight percentage of Dy relative to the weight of the easily demagnetized region. The Dy content refers to the sum of the Dy content in the base material of the first magnet and the Dy content obtained by diffusion.

[0047] In some embodiments, the Dy content of the non-demagnetizable region may be 0-4.0%, such as 0.9%, 1.5%, 1.8%, or 2.2%. The percentage refers to the weight percentage of Dy relative to the weight of the non-demagnetizable region. The Dy content refers to the sum of the Dy content in the substrate of the second magnet and the Dy content obtained by diffusion.

[0048] In some embodiments, the Tb content of the easily demagnetized region may be 0-1.5%, for example, 0 or 0.50%. The percentage refers to the weight percentage of Tb in the easily demagnetized region. The Tb content refers to the sum of the Tb content in the base material of the first magnet and the Tb content obtained by diffusion.

[0049] In some embodiments, the Tb content of the non-demagnetizable region may be 0-1.0%, such as 0, 0.4%, 0.45%, or 0.50%. The percentage refers to the weight percentage of Tb in the non-demagnetizable region or the non-demagnetizable region. The Tb content refers to the sum of the Tb content in the base material of the second magnet and the Tb content obtained by diffusion.

[0050] In some specific embodiments, the total content of Dy and Tb based on the easily demagnetized region may be ≤ 5%, for example, 0.5%, 1.35%, 2.1%, 2.6%, or 3.4%, where the percentage refers to the total weight of Dy and Tb relative to the weight of the easily demagnetized region. The Dy and Tb content refers to the sum of the Dy and Tb content in the base material of the first magnet and the Dy and Tb content obtained by diffusion.

[0051] In some specific embodiments, the total content of Dy and Tb based on the non-demagnetizable region may be ≤ 4.5%, such as 0.4%, 1.35%, 1.5%, 1.8%, or 2.7%, where the percentage refers to the total weight of Dy and Tb relative to the weight of the non-demagnetizable region. The Dy and Tb content refers to the sum of the Dy and Tb content in the base material of the second magnet and the Dy and Tb content obtained by diffusion.

[0052] In some specific embodiments, the total content of Dy and Tb in the NdFeB magnet material may be ≤ 9.5%, such as 0.9%, 2.85%, 3.45%, 4.4%, or 6.1%. The percentage refers to the total weight of Dy and Tb as a percentage of the weight of the NdFeB magnet material. The Dy and Tb content refers to the sum of the Dy and Tb content in the base materials of the first and second magnets and the Dy and Tb content obtained by diffusion.

[0053] In some embodiments, when the diffusion source is a heavy rare earth-M alloy, the content of M element is preferably 2wt%-30wt%, and the content of heavy rare earth is preferably 70wt%-98wt%, where percentage refers to the weight percentage in the diffusion source.

[0054] In the present invention, the total rare earth element content in the first magnet or the second magnet is preferably 28wt%-32.5wt%, more preferably 29.5wt%-31.5wt%, where the percentage refers to the weight percentage in the first magnet or the second magnet; the rare earth element is preferably selected from at least one of Dy, Tb, Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho.

[0055] In some specific embodiments, the easily demagnetized region includes the following components in weight proportions: 7% Nd; 21% Pr; 0.85% Dy; 0.5% Tb; 1.5% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe; and the non-easily demagnetized region includes the following components in weight proportions: 7% Nd; 21% Pr; 1.50% Dy; 1.5% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe.

[0056] In some specific embodiments, the easily demagnetized region includes the following components in weight proportions: 6.45% Nd; 19.35% Pr; 2.9% Dy; 0.5% Tb; 1.5% Gd; 0.2% Cu; 0.10% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe; the non-easily demagnetized region includes the following components in weight proportions: 6.45% Nd; 19.35% Pr; 2.2% Dy; 0.5% Tb; 2.2% Gd; 0.2% Cu; 0.10% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe.

[0057] In some specific embodiments, the easily demagnetized region includes the following components in weight proportions: 7% Nd; 21% Pr; 1.6% Dy; 0.5% Tb; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe; the non-easily demagnetized region includes the following components in weight proportions: 7.38% Nd; 22.13% Pr; 0.9% Dy; 0.45% Tb; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe.

[0058] In some specific embodiments, the easily demagnetized region includes the following components in weight proportions: 7% Nd; 21% Pr; 0.5% Tb; 3% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe; the non-easily demagnetized region includes the following components in weight proportions: 7% Nd; 21% Pr; 0.4% Tb; 3% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe.

[0059] In some specific embodiments, the easily demagnetized region includes the following components in weight proportions: 6.75% Nd; 20.25% Pr; 2.6% Dy; 1.5% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe; the non-easily demagnetized region includes the following components in weight proportions: 6.75% Nd; 21% Pr; 1.8% Dy; 2.3% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the remainder Fe.

[0060] The present invention also provides a neodymium iron boron magnet prepared by the above-mentioned preparation method.

[0061] The present invention also provides a use of the above-mentioned NdFeB magnet in magnetic steel.

[0062] In some specific embodiments, when the mass of a single piece of the magnetic steel is 5-30 g, the width of the bonding area may be 0.05-0.12 mm; and the volume of the bonding area may be 0.5-2% of the total volume of the magnetic steel.

[0063] In the present invention, when the NdFeB magnet is used in magnetic steel, in order to prevent the high temperature of the easy demagnetization area and the coverage of the reverse magnetic field from affecting the non-easy demagnetization area, the width of the theoretical easy demagnetization area can be increased by 0.5 mm.

[0064] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0065] The reagents and raw materials used in the present invention are commercially available.

[0066] The positive progress effect of the present invention is:

[0067] The NdFeB magnet material provided by the present invention has an anti-demagnetization capability comparable to that of the prior art at a lower heavy rare earth cost.

[0068] In a preferred embodiment, when the volume of the easily demagnetized area accounts for 32% and is close to the demagnetization rate of the entire magnetic steel, no obvious demagnetization occurs, but the cost is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 is a schematic structural diagram of the NdFeB magnets obtained in Examples 1-10 (1 is the easily demagnetized area, where a = 3-4 mm; b = 17.25 mm; c = 3.8 mm; 2 is the non-easily demagnetized area, where d = 11 mm; 3 is the bonding area, whose width is 0.05-0.12 mm).

[0070] FIG2 is a schematic diagram of the structure of the NdFeB magnet of the present invention (1 is the easily demagnetized area, where a = 3-4 mm; b = 17.25 mm; c = 3.8 mm; 2 is the non-easy demagnetized area, where d1 = 5.5 mm, d2 = 5.5 mm; 3 is the bonding area, whose width is 0.05-0.12 mm) DETAILED DESCRIPTION

[0071] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0072] The NdFeB magnet described in the present invention is made by bonding a first magnet and a second magnet with different coercive forces. The non-demagnetized region can consist of a single magnet, as shown in Figure 1; the non-demagnetized region can also consist of two second magnets, as shown in Figure 2. The coercive force of the non-demagnetized region is 87%-96% of that of the easily demagnetized region.

[0073] In the structure of the NdFeB magnet material obtained in Example 1-10, the easily demagnetized region includes two first magnets, and the non-easily demagnetized region includes one second magnet. The structural schematic diagram is shown in FIG1 .

[0074] The preparation method of NdFeB magnet material is as follows:

[0075] (1) Melting and casting process: According to the formula shown in Table 1, the prepared raw materials were placed in an alumina crucible and heated in a high-frequency vacuum induction melting furnace at 5×10 -2 Vacuum melting is performed at a temperature below 1550°C in a vacuum of 1000 Pa. Ar gas is introduced into the melting furnace after vacuum melting to a pressure of 30 kPa, and casting is performed. 2 ℃ / second~10 4 The rapidly cooled alloy was obtained at a cooling rate of 1.5 °C / s.

[0076] (2) Hydrogen pulverization process: The melting furnace containing the rapidly cooled alloy is evacuated at room temperature, and then 99.9% pure hydrogen is introduced into the hydrogen pulverization furnace, and the hydrogen pressure is maintained at 0.56-0.9 MPa. After sufficient hydrogen absorption, the temperature is raised while evacuating the furnace to fully dehydrogenate, and then the furnace is cooled and the powder after hydrogen pulverization is taken out.

[0077] (3) Fine pulverization step: The powder after hydrogen pulverization is subjected to jet milling for 3 hours in a nitrogen atmosphere with an oxidizing gas content of 150 ppm or less and a mill chamber pressure of 0.60 MPa to obtain a fine powder. The oxidizing gas refers to oxygen or water.

[0078] (4) Add zinc stearate to the powder after the air flow mill, the amount of zinc stearate added is 0.08% of the weight of the mixed powder, and then fully mix it using a three-dimensional mixer.

[0079] (5) Magnetic field forming process: Using a right-angle orientation magnetic field forming machine, in an orientation magnetic field of 1.6T, at 0.35ton / cm 2 The powder with zinc stearate added was formed into a cube with a side length of 25 mm under a molding pressure of 1.3 ton / cm. After the primary molding, it was demagnetized in a magnetic field of 0.2 T. In order to prevent the molded body from contacting the air after the primary molding, it was sealed and then a secondary molding machine (isostatic pressing machine) was used to press the molded body at a pressure of 1.3 ton / cm. 2 Secondary forming is performed under pressure.

[0080] (6) Sintering process: Each formed body is moved to the sintering furnace for sintering. -3 Pa, after maintaining at 300℃, 600℃ and 920℃ for 1 hour respectively, sintering at 1050-1095℃ for 4 hours, then introducing Ar gas to make the gas pressure reach 0.1MPa, cooling to room temperature and taking out.

[0081] (7) Grain boundary diffusion: The sintered body is processed into corresponding square sheets with a sheet thickness of less than 6mm. The thickness direction is the magnetic field orientation direction. After the surface is cleaned, the raw material prepared with the diffusion source is spray-coated on the magnet. The coated magnet is dried and a coating with the diffusion source is sprayed on the magnet surface in a high-purity Ar gas atmosphere. The magnet is then subjected to a diffusion heat treatment at a temperature of 700-950°C for 24-60 hours. The magnet is cooled to 200°C, then heated to 400-600°C and kept at this temperature for 1-6 hours. Finally, the magnet is cooled to room temperature to obtain the desired magnet.

[0082] The raw material compositions of the NdFeB magnet materials in Examples 1-5 and Comparative Examples 1-5 are shown in Table 1 below; the process conditions of the grain boundary diffusion treatment are shown in Table 2.

[0083] Table 1 Magnet components in each corresponding area

[0084] Table 2

[0085] The only difference between Example 6 and Example 1 is that the volume proportion of the easily demagnetized region is 50%.

[0086] The only difference between Example 7 and Example 2 is that the volume proportion of the easily demagnetized region is 50%.

[0087] The only difference between Example 8 and Example 3 is that the volume proportion of the easily demagnetized region is 50%.

[0088] The only difference between Example 9 and Example 4 is that the volume proportion of the easily demagnetized region is 50%.

[0089] The only difference between Example 10 and Example 5 is that the volume proportion of the easily demagnetized region is 50%.

[0090] The only difference between Comparative Example 6 and Example 1 is that the volume proportion of the easily demagnetized region is 5%.

[0091] The only difference between Comparative Example 7 and Example 2 is that the volume proportion of the easily demagnetized region is 5%.

[0092] The only difference between Comparative Example 8 and Example 3 is that the volume proportion of the easily demagnetized region is 5%.

[0093] The only difference between Comparative Example 9 and Example 4 is that the volume proportion of the easily demagnetized region is 5%.

[0094] The only difference between Comparative Example 10 and Example 5 is that the volume proportion of the easily demagnetized region is 5%.

[0095] Table 3

[0096] Effect embodiment

[0097] 1. Test method of demagnetization rate

[0098] Demagnetization rate test is performed by measuring the no-load back electromotive force before and after demagnetization at 13000rpm@160℃ or 180℃:

[0099] Using a certain electromagnetic simulation software, the input speed is 13000 rpm, and then the temperature is adjusted to 160℃ or 180℃. At the same time, the back electromotive force data of the motor is collected and the changes in the magnetic steel cloud map are observed to determine whether the magnetic steel has demagnetized.

[0100] Among them, Examples 1, 3-6, 8-10 and Comparative Examples 1, 3-6, 8-10 were bonded as shown in Figure 1 and tested at 160°C;

[0101] Example 2, Example 7 and Comparative Example 2, Comparative Example 7 were bonded as shown in FIG1 and tested at 180° C. The test results are shown in Table 3.

[0102] 2. Test methods for remanence and coercivity

[0103] The magnetic properties of the NdFeB magnets of Examples 1-5 and Comparative Examples 1-5 were tested using the NIM-10000H BH bulk rare earth permanent magnet non-destructive measurement system of the China National Institute of Metrology.

[0104] Demagnetization-prone area: Sample preparation specifications are W2~3±0.1*L17.25±0.1*T3.8±0.1mm, two pieces are stacked for testing, and coils with dimensions of W3*L19~20*T2.7mm are used in the permanent magnet precision measurement system NIM-62000 for normal and high temperature testing (temperature ≤200℃);

[0105] Non-demagnetization zone: Sample preparation specifications are W7±0.1*L7±0.1*T4±0.1mm, two pieces are stacked for testing, and a coil with a diameter of 12*T4.2mm is used on the permanent magnet precision measurement system NIM-62000 for normal and high temperature testing (temperature ≤ 200℃);

[0106] The test results are shown in Table 2.

[0107] The NdFeB magnet material of the present invention has an easily demagnetized area and a non-easily demagnetized area connected in a bonding manner, and the coercive force and proportion of each area are specially designed to achieve remanence, coercive force and anti-demagnetization properties comparable to those of the prior art, and can significantly reduce the use of rare earths and reduce costs.

[0108] It can be seen from Table 3 that when the volume of the easily demagnetized region increases to a certain extent, the effect of further increase on the improvement of the demagnetization rate becomes smaller. It can be seen from Example 1, Example 6 and Comparative Example 6 that when the volume of the easily demagnetized region increases from 5% to 32%, its demagnetization rate decreases from 12.2% to 1.5%, the volume increases by 27%, and the demagnetization rate decreases by 10.7%; when it increases from 32% to 50%, its demagnetization rate decreases from 1.5% to 1.45%, the volume of the easily demagnetized region increases by 18%, but the demagnetization rate only decreases by 0.5%; other embodiments and comparative examples can also obtain corresponding rules. It can be seen that the coercive force of the easily demagnetized region is high, and the content of Dy and Tb is high, and their volume share increases, and the cost also increases; when the volume of the easily demagnetized region is within the scope of the present invention, it can ensure a demagnetization rate equivalent to that of the prior art while effectively reducing the use of heavy rare earths and saving costs.

[0109] Table 4

[0110] The NdFeB magnet material provided by the present invention has a coercive force setting suitable for actual application scenarios and a remanence equivalent to that of the prior art. More importantly, it achieves a demagnetization rate equivalent to that of the prior art, which is lower than 1.8% and can be lower than 1.5% in some preferred embodiments, while using lower amounts of rare earth metals or at lower costs.

[0111] It can be seen from Table 4 that the demagnetization rates of Example 1 and Comparative Example 1 are comparable. However, since the unit price of Dy is RMB 2.55 million / ton and the unit price of Tb metal is RMB 9.05 million / ton, the cost of Tb metal is approximately 3.55 times or more of the cost of Dy. Under the condition that the total mass of the NdFeB magnet is the same, the Tb content used in Comparative Example 1 is 0.5% of the total mass of the NdFeB magnet, while the Tb content in Example 1 is only 0.5% of the mass of the easily demagnetized area in the NdFeB magnet. It can be seen that the amount of Tb used in Example 1 is much lower than that in Comparative Example 1, and its cost is also lower. Therefore, it can be explained that the present invention achieves an effect comparable to that of the prior art at a lower cost. Compared with Comparative Example 2, Example 2 has the same contents of all components except Dy and Tb. The Dy+Tb content of Example 2 is 6.1%, while the Dy+Tb content of Comparative Example 2 is 6.8%. Although the Dy+Tb content of Example 2 is less than that of Comparative Example 2, the demagnetization rate is comparable to that of Comparative Example 2. This demonstrates that the present invention achieves a demagnetization rate comparable to that of the prior art using less rare earth metal, effectively reducing costs. Comparing Example 3 with Comparative Example 3, Example 4 with Comparative Example 4, and Example 5 with Comparative Example 5, the situation is the same as above. The NdFeB magnet material of the present invention achieves good anti-demagnetization effect by using less rare earth metal.

Claims

1. A neodymium iron boron magnet, characterized in that: It includes an easy demagnetization area, a non-easy demagnetization area and a bonding area, wherein the volume of the easy demagnetization area accounts for 15%-50% of the total volume of the NdFeB magnet; Wherein, the volume of the bonding area accounts for 0.5%-4.0% of the total volume of the NdFeB magnet; Wherein, the ratio of the coercive force of the non-demagnetizable region to the coercive force of the demagnetizable region is 0.7-1.

2. The NdFeB magnet according to claim 1, wherein: The volume of the easily demagnetized area accounts for 25%-50% of the total volume of the NdFeB magnet, for example, 32% or 50%; and / or, the ratio of the coercivity of the non-demagnetizable region to the coercivity of the demagnetizable region is 0.87-0.96, preferably 0.90-0.95, for example 0.90, 0.92 or 0.93; And / or, the difference ΔHcj between the coercivity of the non-demagnetizable region and the coercivity of the demagnetizable region is 1 kOe-7.5 kOe, preferably 1 kOe-3 kOe, for example, 1.8 kOe, 2.2 kOe, 2.4 kOe or 2.6 kOe.

3. The NdFeB magnet according to claim 1, wherein: The material of the bonding area is glue, preferably one or more of resin glue, polyester glue and hot melt glue; And / or, the volume of the bonding area is 1%-4%, where the percentage is the percentage of the volume of the bonding area to the total volume of the NdFeB magnet; And / or, the width of the bonding area is 0-0.12 mm, but not 0; preferably 0.05 mm-0.12 mm; And / or, the porosity of the bonding area is 0.

4. A method for preparing a neodymium iron boron magnet, characterized in that: The steps include bonding a first magnet and a second magnet to obtain the NdFeB magnet; Wherein, the first magnet forms an easily demagnetized area; the second magnet forms a non-easy demagnetized area; and the bonding forms a bonding area; Wherein, the volume of the easily demagnetized area accounts for 15%-50% of the total volume of the NdFeB magnet; Wherein, the volume of the bonding area accounts for 0.5%-4.0% of the total volume of the NdFeB magnet; Wherein, the ratio of the coercive force of the non-demagnetization region to the coercive force of the demagnetization region is 0.7-1.

5. The method for preparing a NdFeB magnet according to claim 4, wherein: The width of the bonding area is 0-0.12 mm, but not 0; preferably 0.05 mm-0.12 mm; And / or, the easily demagnetized area includes at least two first magnets, for example, two pieces; And / or, the non-demagnetizable region includes 1-3 pieces of second magnets, such as 1 piece or 2 pieces; and / or, the first magnets are symmetrically distributed on both sides of the second magnet; and / or, the volume of the bonding area accounts for 1-5% of the volume of the easily demagnetized area, preferably 1.58%-3.79%; And / or, the volume of the bonding area accounts for 1-4% of the volume of the non-demagnetizable area, preferably 1.58%-3.79%.

6. The method for preparing a NdFeB magnet according to claim 4, wherein: The preparation method of the first magnet and the second magnet comprises the following steps: treating the NdFeB substrate; the treatment method comprises one or more of a single alloy method, a dual alloy method and a diffusion method; The method for preparing the NdFeB substrate is preferably to obtain a green body by subjecting the raw material composition to smelting, hydrogen cracking, jet milling, pressing and sintering, and then subjecting the green body to mechanical processing and cleaning to obtain the NdFeB substrate; the green body is preferably 52H; Among them, the diffusion method preferably includes the following steps: coating a diffusion source on the surface of the substrate of the first magnet or the substrate of the second magnet respectively, and diffusing the heavy rare earth element under heat treatment conditions; the diffusion direction is parallel to the magnetization direction or perpendicular to the magnetization direction.

7. The method for preparing a NdFeB magnet according to claim 6, wherein: The raw material composition includes an R element, wherein the R element is Nd or "Nd and Pr", and the content of the R element is preferably 27.5wt%-31.5wt%, for example, 28wt%, where the percentage refers to the weight percentage in the raw material composition; And / or, the raw material composition includes element B, the content of element B is preferably 0.87wt%-0.99wt%, more preferably 0.94wt%-0.99wt%, and the percentage refers to the weight percentage in the raw material composition; And / or, the raw material composition includes Co element, and the content of the Co element is preferably 0-2.5wt%, for example, 1wt%, and the percentage refers to the weight percentage in the raw material composition; And / or, the raw material composition includes Cu element, and the content of Cu element is preferably 0.1wt%-0.3wt%, for example 0.2wt%, and the percentage refers to the weight percentage in the raw material composition; And / or, the raw material composition includes Al element, and the content of Al element is preferably 0-0.2wt%, for example 0.1wt%, the percentage refers to the weight percentage in the raw material composition; And / or, the raw material composition includes Ga element, and the content of Ga element is preferably 0.1wt%-0.3wt%, more preferably 0.2-0.3wt%, and the percentage refers to the weight percentage in the raw material composition; And / or, the raw material composition includes T element, and the T element is one or more of Zn, Si, Ti, V, Cr, Mn, Ni, Ge, Zr, Ti, Nb, Mo, Pd, Ag, Cd, Sb, Hf, Ta, W, O, C, N, S, F and P, preferably Ti and / or Zr; the content of the T element is preferably 0.1wt%-0.25wt%, for example, 0.2wt%, and the percentage refers to the weight percentage in the raw material composition; And / or, the raw material composition includes Fe element, and the content of the Fe element is preferably 66wt%-70wt%, and the percentage refers to the weight percentage in the raw material composition; And / or, the raw material composition includes M, the mass percentage of M is preferably 0.1wt%-3.0wt%, and the percentage refers to the weight percentage in the easily demagnetized area; M is preferably selected from at least one of Al, Co, Cu, Ga, Sn, Pb and In; And / or, the coating method is a vapor deposition method or a vapor diffusion method; And / or, the heat treatment step is to perform diffusion heat treatment at a temperature of 700-950° C. for 24-60 hours under vacuum or argon atmosphere; then cool to 200° C., then heat to 400-600° C., and keep warm for 1-6 hours, and finally cool to room temperature to obtain the first magnet or the second magnet; And / or, the diffusion source is one or more of heavy rare earth metals, heavy rare earth oxides, heavy rare earth hydrofluorides, heavy rare earth fluorides, heavy rare earth hydrogenates, heavy rare earth fluorides, and heavy rare earth-M alloys; Preferably, the heavy rare earth in the diffusion source is selected from at least one of Dy, Tb, Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; more preferably, Dy and / or Tb; Preferably, the M element in the heavy rare earth-M alloy includes one or more of Al, Co, Cu, Ga, Sn, Pb and In elements; the content of the M element is preferably 2wt%-30wt%, and the content of the heavy rare earth is preferably 70wt%-98wt%, and the percentage refers to the weight percentage in the heavy rare earth-M alloy.

8. The method for preparing a NdFeB magnet according to claim 6, wherein: The content of Dy in the easily demagnetized area is 0-4.3%; for example, 0, 0.85%, 1.6%, 2.6% or 2.9%; the percentage refers to the weight percentage of Dy in the easily demagnetized area; And / or, the Dy content of the non-demagnetizable region is 0-4.0%; for example, 0.9%, 1.5%, 1.8% or 2.2%; the percentage refers to the weight percentage of Dy in the non-demagnetizable region; And / or, the Tb content of the easily demagnetized region is 0-1.5%; for example, 0 or 0.50%; the percentage refers to the weight percentage of Tb in the easily demagnetized region; And / or, the content of Tb in the non-easily demagnetized region is 0-1.0%; for example, 0, 0.4%, 0.45% or 0.50%; the percentage refers to the weight percentage of Tb in the non-easily demagnetized region or the non-easily demagnetized region; And / or, based on the easily demagnetized region, the total content of Dy and Tb is ≤5%; for example, 0.5%, 1.35%, 2.1%, 2.6% or 3.4%, where the percentage refers to the total weight of Dy and Tb as a percentage of the weight of the easily demagnetized region; And / or, based on the non-demagnetizable region, the total content of Dy and Tb is ≤4.5%; for example, 0.4%, 1.35%, 1.5%, 1.8% or 2.7%, where the percentage refers to the total weight of Dy and Tb as a percentage of the weight of the non-demagnetizable region; And / or, based on the NdFeB magnet material, the total content of Dy and Tb is ≤9.5%; for example, 0.9%, 2.85%, 3.45%, 4.4% or 6.1%; the percentage refers to the total weight of Dy and Tb as a percentage of the weight of the NdFeB magnet material; Alternatively, the easily demagnetized region comprises the following components in weight fractions: 7% Nd; 21% Pr; 0.85% Dy; 0.5% Tb; 1.5% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; the non-easily demagnetized region comprises the following components in weight fractions: 7% Nd; 21% Pr; 1.50% Dy; 1.5% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; Alternatively, the easily demagnetized region comprises the following components in weight fractions: 6.45% Nd; 19.35% Pr; 2.9% Dy; 0.5% Tb; 1.5% Gd; 0.2% Cu; 0.10% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; the non-easily demagnetized region comprises the following components in weight fractions: 6.45% Nd; 19.35% Pr; 2.2% Dy; 0.5% Tb; 2.2% Gd; 0.2% Cu; 0.10% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; Alternatively, the easily demagnetized region comprises the following components in weight fractions: 7% Nd; 21% Pr; 1.6% Dy; 0.5% Tb; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; the non-easily demagnetized region comprises the following components in weight fractions: 7.38% Nd; 22.13% Pr; 0.9% Dy; 0.45% Tb; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; Alternatively, the easily demagnetized region comprises the following components in weight fractions: 7% Nd; 21% Pr; 0.5% Tb; 3% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; the non-easily demagnetized region comprises the following components in weight fractions: 7% Nd; 21% Pr; 0.4% Tb; 3% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; Alternatively, the easily demagnetized region comprises the following components in weight fractions: 6.75% Nd; 20.25% Pr; 2.6% Dy; 1.5% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe; the non-easily demagnetized region comprises the following components in weight fractions: 6.75% Nd; 21% Pr; 1.8% Dy; 2.3% Gd; 0.2% Cu; 0.03% Al; 0.3% Ga; 0.2% Ti; 0.98% B and the balance Fe.

9. A neodymium iron boron magnet obtained by the preparation method according to any one of claims 4 to 8.

10. Use of the NdFeB magnet according to any one of claims 1 to 4 or 9 in magnetic steel; Preferably, when the mass of a single piece of the magnetic steel is 5-30 g, the width of the bonding area is 0.05-0.12 mm; and the volume of the bonding area is 0.5-2% of the total volume of the magnetic steel.

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