A preparation method for improving the penetration and diffusion depth and coercivity of NdFeB

Abstract

The present invention relates to a preparation method for improving the penetration diffusion depth and coercive force of NdFeB, belongs to the technical field of permanent magnetic materials, and is used to solve the problem of insufficient penetration depth of diffusion sources of existing permanent magnetic materials. The method comprises: preparing a green body of NdFeB permanent magnet, sintering the green body into a low-density NdFeB blank with a density of 65%-80%; processing the low-density NdFeB blank according to product requirements, and performing diffusion and densification treatment on the magnet: S201, forming a diffusion source layer on the surface of the magnet; S202, then heating the magnet to 750-930℃ and holding it, and quenching it; S203, holding the magnet at 800-950℃ under high pressure and quenching it; S204, holding the magnet at 450-550℃ and quenching it to obtain the NdFeB permanent magnet. The method for improving the penetration diffusion depth of NdFeB of the present invention can increase the diffusion depth and coercive force value.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnetic materials, and in particular to a preparation method for improving the penetration and diffusion depth and coercive force of neodymium iron boron. Background Art

[0002] In recent years, rare earth permanent magnet materials have been widely used in electronics, automobiles, sensors, petrochemicals, magnetic transmission and other fields. However, due to their low coercivity and poor thermal stability, the application of NdFeB permanent magnets in many areas is limited. In order to enable the wider application of NdFeB permanent magnets, improving their coercivity has been a research topic. Currently, various diffusion methods are widely used, which can increase the coercivity of NdFeB permanent magnets while not significantly reducing or even reducing the remanence of NdFeB permanent magnets. However, this method also has certain problems and limits the size of NdFeB permanent magnets. Diffusion sources are infiltrated into NdFeB magnets through ordinary pressure sintering, but the driving force of ordinary sintering is not sufficient to increase the diffusion depth of the diffusion sources.

[0003] CN110911150A discloses a method for improving the coercive force of sintered NdFeB permanent magnets. This method involves coating a granular liquid film on the surface of the sintered NdFeB permanent magnet, and then subjecting the magnet to an aging treatment to effectively improve the coercive force. CN113808839A discloses a method for preparing high-coercive force NdFeB magnets using macroscopically inhomogeneous diffusion. This method simultaneously uses two different grain boundary diffusion agents to perform grain boundary diffusion treatment on the NdFeB magnet, followed by diffusion heat treatment to improve the magnet's coercive force. CN104766717B discloses a method for improving the magnetic properties of sintered NdFeB permanent magnets. This method involves subjecting the sintered magnet to induced eddy current heating, utilizing the electromagnetic stirring effect of the induced eddy current to enhance the flow of the neodymium-rich liquid phase, thereby optimizing the magnet's microstructure and improving the magnet's magnetic properties.

[0004] However, the above-mentioned existing technologies all face the problem of insufficient penetration depth. Therefore, it is urgent to find a method to solve the current problem of insufficient penetration depth. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a preparation method for improving the penetration diffusion depth and coercive force of NdFeB, so as to solve the problem of insufficient penetration depth of diffusion source in existing permanent magnet materials.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] The present invention provides a method for increasing the penetration and diffusion depth of NdFeB, comprising:

[0008] Step 1: preparing a green body of NdFeB permanent magnet, and sintering the green body into a low-density NdFeB blank with a density of 65%-80%;

[0009] Step 2: Process the low-density NdFeB blank according to product requirements and perform diffusion and densification treatment on the magnet:

[0010] S201, forming a diffusion source layer on the surface of the magnet;

[0011] S202, then heating the magnet to 750-930°C, keeping the temperature, and rapidly cooling;

[0012] S203, keeping the magnet at 800-950° C. under high pressure, and rapidly cooling;

[0013] S204, keeping the magnet at 450-550°C, and rapidly cooling it to obtain a NdFeB permanent magnet.

[0014] Furthermore, in S202 , a staged heating-keeping mode is adopted for the mixed diffusion source containing an organic solvent. The staged heating-keeping mode includes a low-temperature volatilization process and a high-temperature diffusion process.

[0015] Furthermore, in S202, the temperature of low-temperature volatilization is 300-500°C, and the time is greater than 1 hour; after the low-temperature volatilization process is completed, the temperature is continued to rise to the high-temperature diffusion process; the temperature of the high-temperature diffusion process is 750-930°C, and the temperature is kept for 5-20 hours.

[0016] Furthermore, in S202, for the diffusion source that does not contain an organic solvent, the magnet is directly heated to 750-930°C and kept at this temperature for 5-20 hours.

[0017] Furthermore, in step 2, a vacuum treatment mode is adopted throughout the process of diffusion and densification of the magnet.

[0018] Furthermore, in S202 and S203, during the rapid cooling process, the temperature is controlled to be lowered to below 500° C. within 10 minutes.

[0019] Furthermore, in S202 and S203, the temperature is rapidly cooled to below 90°C.

[0020] Furthermore, in S203, the temperature is kept at 2-5 hours.

[0021] Furthermore, in S201 , a diffusion source layer is formed on the surface of the magnet by coating, magnetron sputtering, screen printing, physical vapor deposition, electrophoretic deposition or reduction diffusion method.

[0022] Furthermore, in S204, the temperature is kept at 3-7 hours.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] (1) The present invention provides a method for increasing the penetration and diffusion depth of NdFeB by first sintering the green body into a low-density NdFeB blank with a density of 65%-80%. This process is then combined with a specific diffusion, densification sintering, and tempering heat treatment process to increase the diffusion depth through the partially enclosed diffusion channels, thereby increasing the magnitude of the coercive force increase. Ultimately, this method improves the penetration and diffusion depth and coercive force of NdFeB.

[0025] (2) Since the diffusion depth of the present invention is increased, the thickness of the traditional diffusion substrate is increased, and the application range of the infiltration diffusion NdFeB magnet is expanded.

[0026] (3) In the method of the present invention, different temperature rising modes are used for heat treatment according to different diffusion sources, which not only increases the diffusion depth and coercive force value, but also avoids the carbon contamination problem of the magnet.

[0027] (4) The increase in the diffusion depth of the present invention increases the utilization rate of the diffusion source, which can reduce the amount of diffusion source used and reduce costs.

[0028] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the subsequent description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the contents particularly pointed out in the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a process flow chart of the present invention;

[0030] Figure 2 is the heat treatment curve in Example 1;

[0031] Figure 3 is the heat treatment curve in Comparative Example 1;

[0032] Figure 4 This is the heat treatment curve in Example 2. DETAILED DESCRIPTION

[0033] The present invention provides a method for increasing the penetration and diffusion depth of NdFeB. The process flow chart is as follows: Figure 1 As shown, including:

[0034] Step 1: Prepare a green body of NdFeB permanent magnet through a series of processes including batching, rapid solidification belt spinning, hydrogen crushing, air flow grinding, and molding (which may include isostatic pressing), and sinter the green body into a low-density NdFeB blank with a density of 65%-80%;

[0035] Step 2: Process the low-density NdFeB blank according to product requirements. According to the performance requirements of the magnet, find the appropriate diffusion source and diffusion means to diffuse and densify the magnet:

[0036] S201, forming a diffusion source layer on the surface of the magnet;

[0037] S202, diffusion: heat the magnet to 750-930℃ and keep it at this temperature for 5-20h, then cool it to below 90℃;

[0038] S203, densification sintering: the magnet is kept at 800-950℃ for 2-5h under high pressure, and then rapidly cooled to below 90℃; rapid cooling can fix the microstructure and increase the coercive force of the magnet, wherein rapid cooling is achieved by air cooling;

[0039] S204, Low-Tempering: Maintain the magnet at 450-550°C for 3-7 hours, then rapidly cool it to below 90°C to produce a NdFeB permanent magnet. Rapid cooling stabilizes the magnet's microstructure and increases its coercivity. Rapid cooling can be achieved by air cooling or water quenching.

[0040] Specifically, in the above step 1, the chemical formula of the green material is (Re x1 (Pr x2 Nd x3 )) x Fe( 100-x-y-z-x1-y1-y2-y3-y4-y5-y6 )B y Co Z Cu y1 Nb y2 Zr y3 Al y4 Ga y5 M y6 , wherein x: 29.5-32.5; y: 0.9-1; z: 0-0.4; y1: 0-0.3; y2: 0-1; y3: 0-0.3; y4: 0-2; y5: 0-1; y6: 0-1; x1: 0-15; x2: 0-25; x3: 75-100; Re is one or more combinations of Dy, Tb, Ho, Gd, La, Ce and Y, and M is one or more combinations of Si, Cr, Mo, Ti and W.

[0041] Specifically, in step 1, the green body is sintered into a low-density NdFeB blank with a density of 65%-80% by shortening the sintering time or lowering the sintering temperature. It should be noted that if the density is too low, the magnet cannot be processed properly, while if it is too high, the porosity will be too low, making it impossible to achieve uniform deep diffusion. Therefore, the density is controlled to 65%-80%.

[0042] Specifically, in the above step 2, during the diffusion and densification process of the magnet, a vacuum treatment mode is adopted throughout the process to improve the temperature uniformity of the furnace body and enhance the coercive force value.

[0043] Specifically, in the above S201, the diffusion source includes alloys or compounds composed of medium and heavy rare earth elements, light rare earth elements, and some metal elements and non-metal elements.

[0044] Specifically, in the above S201 , a diffusion source layer is formed on the surface of the magnet by coating, magnetron sputtering, screen printing, physical vapor deposition, electrophoretic deposition or reduction diffusion method.

[0045] Specifically, in the above S202, different heating modes are used for heat treatment for different diffusion sources:

[0046] 1) For mixed diffusion sources containing organic solvents (such as ethanol, ethylene glycol, propylene glycol, polyvinyl alcohol, etc.), the temperature is raised in a staged insulation mode, that is, during the heating process, insulation treatment is carried out according to the volatility characteristics of the substances in different diffusion sources to ensure that the volatile substances are fully removed. The heat treatment process includes two steps: low-temperature volatilization step and high-temperature diffusion process. The temperature of low-temperature volatilization is 300-500℃ and the time is greater than 1h. After the low-temperature volatilization process is completed, the vacuum degree reaches 10 again. -3 Pa, continue to heat up to high temperature diffusion process.

[0047] 2) For diffusion sources that do not contain organic solvents, only high-temperature diffusion processes are included.

[0048] Specifically, in the above S202, the purpose of heating the magnet to 750-930℃ and keeping it warm for 5-20 hours is to fully dissolve the diffusion source and the rare earth-rich phase together, and diffuse into the interior of the magnet through the surface of the magnet, ensuring that the diffusion source fully penetrates and diffuses in the magnet; at the same time, the penetration diffusion of the diffusion source can be used to seal the through holes in the magnet due to the low density of the blank, ensuring the smooth progress of the hot isostatic pressing process.

[0049] Specifically, in the above S202 , in order to keep the magnet in a high-temperature phase state and increase the coercive force value, during the rapid cooling process, the temperature is controlled to be lowered to below 500° C. within 10 minutes.

[0050] Specifically, in the above S203, the density of the NdFeB magnet is increased by high pressure treatment, and the microstructure of the magnet in a high temperature state is fixed by rapid cooling, thereby increasing the coercive force value of the magnet;

[0051] Specifically, in the above S203, the applied pressure is ≥30 MPa. Preferably, the applied pressure is ≥80 MPa to ensure that the magnet obtains high density at low temperature.

[0052] Specifically, in the above S203 , in order to keep the magnet in a high-temperature phase state and increase the coercive force value, during the rapid cooling process, the temperature is controlled to drop to 500° C. within 10 minutes.

[0053] Specifically, in the above S203, the density of the obtained NdFeB permanent magnet is ≥98%.

[0054] Specifically, the function of the above S204 is mainly to wet and modify the main phase boundary, thereby further improving the coercive force of the magnet.

[0055] Specifically, in the above S204, the diffusion depth of the NdFeB permanent magnet obtained is increased by 0.5-1.5 times compared with the conventional diffusion process depth. For example, the diffusion depth can be increased from 60-100 microns to 130-170 microns.

[0056] Specifically, in the above S204, the coercive force of the NdFeB permanent magnet obtained is improved by ≥1 kOe compared with the coercive force of the conventional diffusion process; for example, the coercive force can be improved to 21-29 kOe.

[0057] Compared with the prior art, the method of the present invention for improving the penetration and diffusion depth of NdFeB is to first sinter the green body into a low-density NdFeB blank with a density of 65%-80%, and then combine it with a specific heat treatment process to increase the diffusion depth through the diffusion channel that is not completely closed. At the same time, through the pressure sintering process, a high-density magnet is formed under the premise of effectively suppressing the deep diffusion of high-temperature diffusion sources in the main phase, thereby increasing the improvement range of the remanence and coercive force of the magnet.

[0058] Since the diffusion depth of the present invention is increased, the thickness of the traditional diffusion substrate is increased, and the application range of the infiltration diffusion NdFeB magnet is expanded.

[0059] The increase in diffusion depth of the present invention improves the utilization rate of the diffusion source, can reduce the amount of diffusion source used, and lower the cost.

[0060] The preferred embodiments of the present invention are described in detail below to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0061] The applicant conducted a lot of research during the research process and used some cases with poor results as comparison.

[0062] Example 1

[0063] A specific embodiment of the present invention discloses a method for increasing the penetration and diffusion depth of NdFeB. The method comprises:

[0064] (1) Use 52M powder (component is Nd 30.5 Cu 0.1 Ga 0.2 Zr 0.15Co 0.3 Al 0.1 Fe 67.69 B 0.96 ) Prepare NdFeB permanent magnets, which are formed into 30mm×30mm×15mm (magnetization direction) magnets and pressed into a density of 3.7-4.1g / cm 3 The billet is then further pressed into a density of 4.3-4.7 g / cm by cold isostatic pressing. 3 The green body was sintered at 930℃ for 5 hours to form a magnet blank with a density of 75%.

[0065] (2) Use dry grinding to remove the oxide scale on the surface of the magnet;

[0066] (3) Using a coating process, a TbF3+ethylene glycol mixture is evenly coated on the surface of the magnet in the vertical orientation direction, and the thickness of the coated diffusion source layer is 15 microns;

[0067] (4) Place the magnet into the GBD diffusion furnace for the first heat treatment: First, heat the coated magnet to 300°C in a vacuum state and keep it warm for 3 hours. Then, the ethylene glycol is discharged from the diffusion furnace through the vacuum system. When the vacuum is reduced to 1*10 -3 After Pa, the temperature was raised to 890℃ and kept at this temperature for 11h for sufficient grain boundary diffusion treatment. After the diffusion treatment, the temperature was rapidly cooled to 80℃.

[0068] (5) The second step of heat treatment is carried out in a hot isostatic pressing furnace with a sintering temperature of 800°C, a holding time of 3 hours, and a heat treatment pressure of 100 MPa; after the high temperature and high pressure treatment, the steel is rapidly cooled to 80°C;

[0069] (6) The third step of aging heat treatment: temperature 480℃, keep warm for 5h, and cool to 80℃ after the treatment. Figure 2 shown.

[0070] The measurable diffusion depth of the NdFeB permanent magnet of this embodiment is 150 microns.

[0071] The NdFeB permanent magnet was cut into sample columns of Φ10mm×15mm, and the surface of the sample column was centerless ground to remove rust spots. The magnet performance was measured using NIM-6500C. The remanent magnetism of the magnet was reduced from the original 14.35kGs to 14.21kGs. According to the national standard, the change in the remanent magnetism of the magnet did not cause a change in the magnet brand. The coercive force of the magnet increased from the previous 14.2kOe to 21.8kOe, an increase of 7.6kOe. The magnet was also changed from 52M to 52SH, which increased the utilization value of the magnet.

[0072] Comparative Example 1

[0073] This comparative example provides a preparation method for improving the coercivity of NdFeB. It includes:

[0074] (1) NdFeB permanent magnets were prepared using 52M powder with the same composition as in Example 1. The magnets were formed into 30 mm × 30 mm × 15 mm (magnetization direction) and the density was 3.7-4.1 g / cm 3 The green body is further pressed into a density of 4.3-4.7 g / cm by cold isostatic pressing. 3 The green body was sintered in a vacuum furnace at a temperature of 1050°C for 5 hours and the density was 7.55g / cm 3 The magnet has reached the theoretical density;

[0075] (2) Use dry grinding to remove the oxide scale on the surface of the magnet;

[0076] (3) Using a coating process, a TbF3+ethylene glycol mixture is evenly coated on the surface of the magnet in the vertical orientation direction, and the thickness of the coated diffusion source layer is 15 microns;

[0077] (4) Using the traditional diffusion process, the diffusion magnet was infiltrated in a GBD diffusion furnace at a temperature of 890°C for 14 hours. After cooling, the magnet was tempered at 480°C for 5 hours to obtain a NdFeB permanent magnet. The heat treatment curve of Comparative Example 1 is shown in FIG. Figure 3 shown.

[0078] The measurable diffusion depth of the NdFeB permanent magnet of this comparative example is 70 microns.

[0079] The NdFeB permanent magnet was cut into sample columns of Φ10mm×15mm, and the surface of the sample column was centerless ground to make the surface of the sample column free of rust. The magnet performance was measured using NIM-6500C. The remanence of the magnet was reduced from the original 14.35kGs to 14.26kGs, and the remanence of the magnet was almost unchanged; the coercive force of the magnet increased from the previous 14.2kOe to 17.3kOe, and the coercive force of the magnet increased by 3.1kOe. Through the traditional diffusion process, the magnet was diffused from 52M to 52H.

[0080] Compared with Comparative Example 1, Example 1 shows that the preparation method of the present invention can not only increase the diffusion depth, but also greatly improve the coercive force.

[0081] Comparative Example 2

[0082] This comparative example provides a preparation method for improving the coercivity and diffusion depth of NdFeB. It includes:

[0083] (1) NdFeB permanent magnets were prepared using 52M powder with the same composition as in Example 1. The magnets were formed into 30 mm × 30 mm × 15 mm (magnetization direction) and the density was 3.7-4.1 g / cm 3 The green body is further pressed into a density of 4.3-4.7 g / cm by cold isostatic pressing. 3 The green body was sintered in a vacuum furnace at a sintering temperature of 1000°C for 5 hours to a density of 90% of the theoretical density;

[0084] (2) Use dry grinding to remove the oxide scale on the surface of the magnet;

[0085] (3) Using a coating process, a TbF3+ethylene glycol mixed solution is evenly coated on the surface of the magnet in the vertical orientation direction, and the thickness of the coated diffusion source layer is 1 mm;

[0086] (4) The coated sintered NdFeB magnet is vacuum sealed in a glass tube and treated at 800°C and 100 MPa for 3 hours, then cooled to 480°C and aged for 5 hours. After the treatment is completed, it is slowly cooled to 80°C and taken out of the furnace.

[0087] The measurable diffusion depth of the NdFeB permanent magnet of this comparative example is 100 microns.

[0088] The NdFeB permanent magnet was cut into a sample column of Φ10mm×15mm. The sample column surface was centerless ground to leave no cutting marks on the sample column surface. The magnet performance was measured using NIM-6500C. The magnet remanence was reduced from the original 14.35kGs to 13.20kGs, which was a significant decrease in magnet remanence. The magnet coercive force increased from the previous 14.2kOe to 19.4kOe, an increase of 5.2kOe. The magnet was diffused from 52M to 42HT through a diffusion-free hot isostatic pressing process. At the same time, a large amount of black carbide was found on the surface of the magnetic sheet of Comparative Example 2, and it penetrated into the interior of the magnet. This is because the organic solvent was coated with softened glass and could not fully volatilize, and then deposited on the magnet surface. Excessive carbon penetrated into the interior of the magnet, which would damage the remanence and coercive force of the magnet.

[0089] Compared with Comparative Example 2, Example 1 shows that the preparation method of the present invention can not only increase the diffusion depth and coercive force value, but also avoid the carbon contamination problem of the magnet.

[0090] Example 2

[0091] A specific embodiment of the present invention discloses a method for increasing the penetration and diffusion depth of NdFeB. The method comprises:

[0092] (1) Using 48H (component Nd 30.3 Dy 0.7 Cu 0.1 Ga0.2 Co 0.5 Fe 67.11 Zr 0.15 B 0.94 ) powder to prepare NdFeB permanent magnets, which are then pressed into 40mm×40mm×22mm (magnetization direction) magnets with a density of 4.2g / cm 3 The blank is sintered in a vacuum sintering furnace at a temperature of 1060°C and kept warm for 30 minutes to form a magnet blank with a density of 70%.

[0093] (2) Using a cutting process to process the magnet into 40 mm × 40 mm × 10 mm magnetic sheets;

[0094] (3) using physical vapor deposition technology to diffuse Tb, with a diffusion source layer thickness of 10 μm;

[0095] (4) The magnet is placed in a GBD diffusion furnace for the first step of heat treatment. First, the coated magnet is heated to 890°C in a vacuum state and kept at this temperature for 11 hours for sufficient grain boundary diffusion treatment. After the diffusion treatment is completed, it is rapidly cooled to 80°C.

[0096] (5) The second step of heat treatment is carried out in a hot isostatic pressing furnace, with a sintering temperature of 900°C, a holding time of 2 hours, and a heat treatment pressure of 50 MPa; after the high temperature and high pressure treatment, the sintering temperature is rapidly cooled to 80°C;

[0097] (6) The third step of heat treatment: the temperature is 500℃, and the temperature is kept for 5 hours to obtain the NdFeB permanent magnet. After the treatment is completed, it is quickly cooled to 80℃ and then taken out of the furnace. The heat treatment curve of Example 2 is as follows: Figure 4 shown.

[0098] The measurable diffusion depth of the NdFeB permanent magnet of this embodiment is 170 microns.

[0099] The NdFeB permanent magnet was cut into Φ10mm×10mm standard sample columns, and the surface of the standard sample column was centerless ground to make the sample column surface free of rust. The magnet performance was measured using NIM-6500C. The remanence of the magnet was reduced from the original 13.89kGs to 13.8kGs; the remanence of the magnet was almost unchanged, and the coercive force of the magnet increased from the previous 17.5kOe to 28.6kOe, an increase of 11.1kOe; the magnet also changed from 48H to 48UH-T.

[0100] Comparative Example 3

[0101] This comparative example provides a preparation method for improving the coercive force of NdFeB.

[0102] (1) NdFeB permanent magnets were prepared using 48H powder with the same composition as in Example 2. The magnets were shaped into 40 mm × 40 mm × 22 mm (magnetization direction) and the density was 4.2 g / cm 3 The sintering temperature was 1060℃ in a vacuum sintering furnace for 5 hours, and the density was 7.57g / cm 3 The magnet has reached the theoretical density;

[0103] (2) Using a cutting process to process the magnet into 40 mm × 40 mm × 10 mm magnetic sheets;

[0104] (3) Using physical vapor deposition, Tb is sputtered on the surface of the magnet in the vertical orientation direction, and the thickness of the diffusion source layer is 10 μm;

[0105] (4) Infiltration diffusion magnets were prepared in a GBD diffusion furnace at a temperature of 900°C for 13 hours. After cooling, the magnets were tempered at 480°C for 5 hours to obtain NdFeB permanent magnets.

[0106] The measurable diffusion depth of the NdFeB permanent magnet of this comparative example is 80 μm.

[0107] The NdFeB permanent magnet was cut into sample columns of Φ10mm×10mm, and the surface of the sample column was centerless ground to make the surface of the sample column free of rust. The magnet performance was measured using NIM-6500C. The remanence of the magnet was reduced from the original 13.89kGs to 13.81kGs, and the remanence of the magnet was almost unchanged. The coercive force of the magnet increased from the previous 17.5kOe to 20.8kOe, and the coercive force of the magnet increased by 3.3kOe. Through the traditional diffusion process, the magnet was diffused from 48H to 48SH.

[0108] Compared with Comparative Example 3, Example 2 shows that the process method of the present invention can not only increase the diffusion depth, but also greatly improve the coercive force.

[0109] Comparative Example 4

[0110] This comparative example provides a preparation method for improving the coercivity and diffusion depth of NdFeB. It includes:

[0111] (1) NdFeB permanent magnets were prepared using 48H powder with the same composition as in Example 2. The magnets were shaped into 40 mm × 40 mm × 22 mm (magnetization direction) and the density was 4.2 g / cm 3 , use a vacuum sintering furnace at a sintering temperature of 1000℃, keep warm for 5 hours, and sinter to a density of 90% of the theoretical density;

[0112] (2) Using a cutting process to process the magnet into 40 mm × 40 mm × 10 mm magnetic sheets;

[0113] (3) Using physical vapor deposition, Tb is uniformly sputtered on the surface of the magnet in the vertical orientation direction, and the thickness of the diffusion source layer is 10 μm;

[0114] (4) The coated sintered NdFeB magnet is vacuum sealed in a glass tube and treated at 900°C and 50 MPa for 3 hours, then cooled to 480°C and aged for 5 hours. After the treatment is completed, it is slowly cooled to 80°C and taken out of the furnace.

[0115] The measurable diffusion depth of the NdFeB permanent magnet of this comparative example is 90 μm.

[0116] The NdFeB permanent magnet was cut into sample columns of Φ10mm×10mm, and the surface of the sample column was centerless ground so that there were no cutting marks on the surface of the sample column. The magnet performance was measured using NIM-6500C. The remanence of the magnet was reduced by 13.8kGs from the original 13.85kGs, and the remanence of the magnet was almost unchanged. The coercive force of the magnet increased from the previous 17.5kOe to 20.8kOe, and the coercive force of the magnet increased by 3.3kOe. Through the diffusionless hot isostatic pressing process, the magnet was diffused from 48H to 48SH.

[0117] Compared with Comparative Example 4, Example 2 shows that the diffusion depth and coercive force value can be increased by adopting the preparation method of the present invention.

[0118] The magnetic properties of the embodiments and comparative examples are shown in Table 1 below.

[0119] Table 1: Magnetic properties of Examples and Comparative Examples

[0120] Br(kGs) Hcj(kOe) ΔBr(kGs) ΔHcj(kOe) Substrate 1 14.35 14.2 Example 1 14.21 21.8 -0.14 7.6 Comparative Example 1 14.26 17.3 -0.09 3.1 Comparative Example 2 13.2 19.4 -1.15 5.2 Substrate 2 13.89 17.5 Example 2 13.8 28.6 -0.09 11.1 Comparative Example 3 13.81 20.8 -0.08 3.3 Comparative Example 4 13.8 20.8 -0.09 3.3

[0121] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for increasing the penetration and diffusion depth of NdFeB, characterized in that: include: Step 1: preparing a green body of NdFeB permanent magnet, and sintering the green body into a low-density NdFeB blank with a density of 65%-80%; Step 2: Process the low-density NdFeB blank according to product requirements and perform diffusion and densification treatment on the magnet: S201, forming a diffusion source layer on the surface of the magnet; S202, then heating the magnet to 750-930°C, keeping the temperature, and rapidly cooling; S203, keeping the magnet at 800-950° C. under high pressure, and rapidly cooling; S204, keeping the magnet at 450-550° C. and rapidly cooling it to obtain a NdFeB permanent magnet; In said S201, a diffusion source layer is formed on the surface of the magnet by coating, magnetron sputtering, screen printing, physical vapor deposition, electrophoretic deposition or reduction diffusion method; In the S202 and S203, during the rapid cooling process, the temperature is controlled to be lowered to below 500° C. within 10 minutes; In said S203, applying a pressure of ≥30 MPa and keeping the temperature for 2-5 hours; the pressure sintering process forms a high-density magnet under the premise of effectively suppressing the deep diffusion of high-temperature diffusion sources in the main phase; In S203, the density of the obtained NdFeB permanent magnet is ≥98%; In S204, the diffusion depth of the obtained NdFeB permanent magnet is increased by 0.5-1.5 times compared with the conventional diffusion process depth.

2. The method according to claim 1, characterized in that In S202 , a staged heating-keeping mode is adopted for the mixed diffusion source containing an organic solvent, and the staged heating-keeping mode includes a low-temperature volatilization process and a high-temperature diffusion process.

3. The method according to claim 2, characterized in that In the S202, the temperature of low-temperature volatilization is 300-500°C, and the time is greater than 1 hour. After the low-temperature volatilization process is completed, the temperature is continued to rise to the high-temperature diffusion process. The temperature of the high-temperature diffusion process is 750-930°C, and the temperature is kept for 5-20 hours.

4. The method according to claim 1, wherein In the above S202, for the diffusion source that does not contain an organic solvent, the magnet is directly heated to 750-930° C. and kept at this temperature for 5-20 hours.

5. The method according to claim 1, wherein In the step 2, the magnet is diffused and densified in a vacuum process.

6. The method according to claim 1, characterized in that In S202 and S203, the temperature is rapidly cooled to below 90°C.

7. The method according to any one of claims 1 to 6, characterized in that In the S204, the temperature is kept at 3-7 hours.

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