A grain boundary diffusion process for neodymium-iron-boron magnets

Abstract

The application discloses a grain boundary diffusion process of a neodymium-iron-boron magnet and relates to the technical field of sintered neodymium-iron-boron magnetic materials, which is used for reducing the carbon-oxygen content on the surface of a sample after diffusion by a simple method; the application is based on a traditional heavy rare earth coating and drying method, which comprises the following steps: after coating slurry containing heavy rare earth on the surface of a neodymium-iron-boron blank, the coating is placed with the surface upward and is subjected to vibration treatment, so that the heavy rare earth powder with the largest density in the slurry material is deposited on the surface of the neodymium-iron-boron blank; after the vibration, the coating is dried and subjected to a vacuum heating diffusion process; the vacuum heating diffusion process further comprises at least one process of argon filling, heat preservation, pressure preservation and vacuum extraction; the process scheme of the application is simple and easy to operate, is favorable for reducing the carbon-oxygen content on the surface of a sample, improves the coercive force of the sample relative to the traditional process, and is indirectly favorable for reducing the dosage of heavy rare earth.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sintered neodymium iron boron magnetic materials, in particular to a grain boundary diffusion process of a neodymium iron boron magnet. BACKGROUND

[0002] Rare earth permanent magnet sintered neodymium iron boron is widely used in industrial production, daily life and the like. With the proposal of energy saving and emission reduction and the double carbon strategy, the performance requirements of neodymium iron boron are becoming higher and higher. With the introduction of the grain boundary diffusion technology, the heavy rare earth content of neodymium iron boron has been greatly reduced compared with the conventional production process. However, in the current coating process, heavy rare earth carbon oxides are easily produced on the surface and near the surface of the product after grain boundary diffusion. The heavy rare earth carbon oxide has a high melting point and is relatively stable, and is difficult to diffuse into the magnet. It is a kind of material waste in the diffusion process. Carbon elements enter the magnet during diffusion, reducing the performance of the product. How to reduce the production of such carbon oxides and ensure the performance improvement of the product and further reduce the use of heavy rare earth is one of the current research directions.

[0003] The present application understands that, in the whole process of grain boundary diffusion, in order to increase the bonding force between heavy rare earth and the surface of the magnet, one or more organic resin adhesives are often added. The organic adhesives are not fully volatilized during the heating process of grain boundary diffusion, and the residual carbon and oxygen combine with heavy rare earth during the subsequent heating and holding process, resulting in the generation of a large amount of heavy rare earth carbon oxides, hindering the diffusion process, causing performance loss and heavy rare earth waste.

[0004] In the invention patent with the announcement number CN109887696B and the name of an organic slurry coated on a neodymium iron boron magnet and the preparation of a high coercivity neodymium iron boron magnet, a special slurry is disclosed. The thermoplastic resin powder used therein has good adhesion, low decomposition temperature and short curing time, which can reduce the oxygen and carbon content entering the magnet. However, it needs a special slurry, and the method has low universality. Moreover, only one or several methods are still not enough, which is not conducive to the development of process technology. Therefore, there is an urgent need for a grain boundary diffusion process of a neodymium iron boron magnet. SUMMARY

[0005] The present application aims to provide a grain boundary diffusion process of a neodymium iron boron magnet, which can reduce the carbon and oxygen content on the surface of the sample after diffusion by a simple method.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution: a grain boundary diffusion process of a neodymium iron boron magnet, comprising the following specific contents: after coating the slurry containing heavy rare earth on the surface of the neodymium iron boron blank, the coated surface is placed upward for vibration treatment, so that the heavy rare earth powder with the largest density in the slurry material is deposited on the surface of the neodymium iron boron blank. After vibration, it is dried and the vacuum heating diffusion process is continued.

[0007] Preferably, the vibration treatment is performed on a high-frequency vibration platform, at a frequency of 30-120 Hz for 1-5 min.

[0008] Preferably, the vacuum heating diffusion process further comprises at least one process of argon filling, temperature maintaining, pressure maintaining and vacuum pumping during the temperature rising.

[0009] Preferably, the vacuum heating diffusion process comprises: using a tubular vacuum sintering furnace to perform diffusion treatment at 750-950 ℃ for 10-15 h, wherein the process of argon filling, temperature maintaining, pressure maintaining and vacuum pumping is performed once at 400-500 ℃ and 750-850 ℃, respectively, and tempering treatment is performed at 465-530 ℃ for 3-6 h after the diffusion treatment.

[0010] More preferably, the vacuum heating diffusion process comprises: using a tubular vacuum sintering furnace to perform diffusion treatment at 910 ℃ for 12 h, the temperature rising rate is 4 ℃ / min, the process of argon filling, temperature maintaining, pressure maintaining and vacuum pumping is performed once at 450 ℃ and 800 ℃, respectively, and tempering treatment is performed at 510 ℃ for 4 h.

[0011] Preferably, the pressure of the argon filling is 0.01-0.06 MPa, and the temperature maintaining and pressure maintaining time is 5-20 min.

[0012] Optionally, the slurry containing heavy rare earths comprises 50-80 wt.% of rare earth or rare earth alloy, 1.5-5 wt.% of organic resin binder, and the rest is solvent.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] 1. The grain boundary diffusion process of the neodymium-iron-boron magnet adopts a simple process scheme of adding vibration treatment after coating, so that the heavy rare earth powder with a larger density in the slurry is deposited on the surface of the neodymium-iron-boron blank, and the organic binder is relatively more suspended on the upper layer of the coating film, which is relatively easier to volatilize, and is beneficial to reducing the carbon and oxygen content on the surface of the sample.

[0015] 2. The grain boundary diffusion process of the neodymium-iron-boron magnet can also adopt the process of argon filling, temperature maintaining, pressure maintaining and vacuum pumping once or multiple times during the temperature rising of the vacuum heating diffusion process; the argon filling can dilute the carbon-containing and oxygen-containing atmosphere in the furnace, and then a large amount of it is taken away by vacuum pumping, which further accelerates the volatilization of the organic binder, and is beneficial to reducing the generation of heavy rare earth carbon oxides.

[0016] 3. The grain boundary diffusion process of the NdFeB magnet is simple and easy to operate. It can be achieved by simply adding steps to the original process. Since it is beneficial to reduce the carbon and oxygen content on the sample surface, it can be directly reflected in the guarantee of product performance. Its coercive force is improved compared with the traditional process. Indirectly, while ensuring equivalent performance, the method of the present invention is conducive to reducing the amount of heavy rare earth. DETAILED DESCRIPTION

[0017] A grain boundary diffusion process for NdFeB magnets, based on the traditional heavy rare earth coating and drying method, includes the following specific contents:

[0018] After coating the surface of the NdFeB blank with a slurry containing heavy rare earths, the coated surface is placed upward for vibration treatment. For reference, commonly used slurries containing heavy rare earths generally include 50-80wt.% of rare earth or rare earth alloys (which may include one or more of Tb, Dy, Ho, Pr, Nd, Cu, Al, Ga, Co, Fe, etc.), 1.5-5wt.% of organic resin binder, and the rest is solvent (usually 19-48.5wt.%), wherein the organic resin binder can be epoxy resin, phenolic resin, etc. Due to the high density of heavy rare earth powder, vibration can make the heavy rare earth powder deposit on the surface of the NdFeB blank. After vibration, the heavy rare earth is mostly deposited in the lower layer of the coating film, and the organic binder is mostly suspended in the upper layer of the coating film, which is relatively easier to volatilize. After vibration, it is dried and the vacuum heating diffusion process is continued.

[0019] In a preferred embodiment, the vibration treatment is performed on a high-frequency vibration platform, the frequency may be 30 to 120 Hz, and the vibration time is preferably set at 1 to 5 minutes.

[0020] In addition to vibration treatment, one or more argon filling, heat preservation, pressure holding and vacuuming processes can be carried out during the temperature rise of the vacuum heating diffusion process; argon filling can dilute the carbon and oxygen-containing atmosphere in the furnace, and then vacuuming can take away a large amount of it, further accelerating the volatilization of organic binders, reducing the generation of heavy rare earth carbon oxides, ensuring product performance, and indirectly reducing the amount of heavy rare earths; further optionally, the pressure of the argon filling can be 0.01~0.06MPa, and the heat preservation and pressure holding time should be controlled at 5~20min.

[0021] For reference, the vacuum heating diffusion process may include: using a tubular vacuum sintering furnace for diffusion treatment at 750-950℃ for 10-15h, wherein the above-mentioned argon filling, heat preservation, pressure holding, and vacuuming processes are respectively carried out at 400-500℃ and 750-850℃. After the diffusion treatment time is completed, the second tempering treatment is carried out at 465-530℃ for 3-6h.

[0022] The vacuum heating diffusion process can further adopt the following preferred scheme: using a tubular vacuum sintering furnace for diffusion treatment at 910℃ x 12h, the heating rate is 4℃ / min, and the processes of increasing argon filling, holding, pressure maintaining and vacuum extraction are added once at 450℃ and 800℃, respectively, and the second tempering is performed at 510℃ x 4h.

[0023] The following is only a comparative example for comparing the effect of the present scheme, and is not all the embodiments, and the parameter range of the example should not be regarded as the limitation of the present scheme. The specific parameters such as temperature, time, slurry material, etc. should be understood in the common technical knowledge of those skilled in the art, as long as the theory of the present scheme is followed and within the scope of the claims of the present invention, it should be protected.

[0024] For example, the slurry containing heavy rare earth described above, although the present application only records the reference scheme of heavy rare earth and / or heavy rare earth alloy, organic resin binder and solvent, but is not limited to this range, especially the organic resin binder, other alternative materials that can provide similar functions can also apply the method of the present application, as long as it does not hinder the present application (specifically, vibration can make the heavy rare earth with higher density settle), it should be considered within the protection scope of the present application. Even if the slurry type does not exist at the time of application, the materials that appear in the future development process can also apply the method of the present application.

[0025] Comparative example: select 45H grade neodymium iron boron blanks, grind and slice them into several square samples with a size of 25mm*25mm*6mm, test the carbon and oxygen content of the substrate and the performance of the samples. Sample numbers A01-A10, among which A01-A08 are coated with a slurry containing heavy rare earth Tb (Tb accounts for 70%, solvent 27%, organic resin 3%), after coating, take out and dry in an oven, calculate the Tb weight gain and record it, A09 and A10 are not coated. Test the surface adhesion of A01 and A02 and record it, number A03-A10 samples, use a tubular vacuum sintering furnace for diffusion treatment at 910℃ x 12h, the second tempering is performed at 510℃ x 4h, test the surface layer 0.5mm carbon and oxygen content of A03-A10 after diffusion, and collect all the test data of the substrate and A1-A10 into Table 1:

[0026] Table 1: test results of comparative example samples

[0027]

[0028] From the above table 1, it can be seen that the surface layer carbon and oxygen content of the sample after coating and diffusion increases significantly.

[0029] Example 1: Select 45H grade Nd-Fe-B blank, after grinding, slicing into size 25mm*25mm*6mm square sample several, take sample number B01~B12, coating the same kind of slurry containing heavy rare earth Tb on the surface of B01~B12 as the comparative example, after coating, put B07~B12 on the high frequency vibration platform, set the frequency to 60Hz, vibrate for 2min, then dry B01~B12 with the oven at the same time, record the weight gain after Tb, take B01, B02, B07, B08 to test the surface bonding force and record, the rest of the samples are placed in the box neatly, use the tube type vacuum sintering furnace to diffuse at 910℃*12h, temper two uses 510℃*4h system, after diffusion, test the magnetic properties and surface carbon oxygen content of the diffusion material, all the test data are summarized in table 2:

[0030] Table 2: test results of example 1 samples

[0031]

[0032] Through the comparison of the data in table 2, it can be seen that the coating layer bonding force of the samples after coating, vibration and drying (B07~B12) has no obvious change, but the surface carbon oxygen content of the samples after diffusion has decreased obviously, and the coercive force has improved obviously.

[0033] Example 2: Select 45H grade Nd-Fe-B blank, after grinding, slicing into size 25mm*25mm*6mm square sample several, take sample number C01~C15, coating the same kind of slurry containing heavy rare earth Tb on the surface of C01~C15 as the comparative example, after coating, put C07~C15 on the high frequency vibration platform, set the frequency to 60Hz, vibrate for 2min, then dry C01~C15 with the oven at the same time, record the weight gain after Tb, put C01, C02, C03, C07, C08, C09 samples in the box neatly, use the tube type vacuum sintering furnace to diffuse at 910℃*12h; Put C04, C05, C06, C010~C15 samples in the box neatly, use the tube type vacuum sintering furnace to diffuse at 910℃*12h, and increase the argon filling process once at 450℃ and 800℃ respectively, the filling pressure is 0.03MPa, the pressure holding time is 10min, after pressure holding, vacuumize and heat up again, diffuse at 910℃*12h, temper two of C01~C15 at the same time, temper two uses 510℃*4h system, after diffusion, test the magnetic properties and surface carbon oxygen content of all the samples, all the test data are summarized in table 3:

[0034] Table 3: test results of example 2 samples

[0035]

[0036] As can be seen by comparison of the data in Table 3, compared with the conventional process (C01, C02, C03), only increasing vibration (C07, C08, C09) and only increasing the argon-filled pressure maintaining process (C04, C05, C06) can effectively reduce the carbon and oxygen content on the surface of the sample, and the performance of the product is greatly improved, and the combination of the two (C10, C11, C12) has a higher performance improvement, and after reducing the weight (C13, C14, C15), the performance is still not lower than that of the conventional process, and the usage amount of heavy rare earth is saved.

[0037] The above is only a preferred embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be limited by the protection scope defined by the claims.

[0038] The part not described in the present application is the known technology of the person skilled in the art.

Claims

1. A grain boundary diffusion process for NdFeB magnets, characterized in that: The specific contents include: after coating the surface of the NdFeB blank with a slurry containing heavy rare earth, the blank is placed with the coated surface facing upward and subjected to vibration treatment, so that the heavy rare earth powder with the highest density in the slurry material is deposited on the surface of the NdFeB blank, and then dried after vibration, and the vacuum heating diffusion process is continued; The vibration treatment is carried out on a high-frequency vibration platform with a frequency of 30 to 120 Hz and a time of 1 to 5 minutes; The vacuum heating diffusion process further includes at least one process of filling with argon gas, keeping warm, keeping pressure, and evacuating during the heating process; The heavy rare earth-containing slurry includes 50-80 wt.% of rare earth or rare earth alloy, 1.5-5 wt.% of organic resin binder, and the rest is solvent.

2. The grain boundary diffusion process of a NdFeB magnet according to claim 1, characterized in that: The vacuum heating diffusion process includes: using a tubular vacuum sintering furnace to perform diffusion treatment at 750-950°C for 10-15 hours, wherein argon filling, heat preservation, pressure maintenance, and vacuuming are performed at 400-500°C and 750-850°C respectively. After the diffusion treatment time is completed, a second tempering treatment is performed at 465-530°C for 3-6 hours.

3. The grain boundary diffusion process of a NdFeB magnet according to claim 2, characterized in that: The vacuum heating diffusion process is as follows: a tubular vacuum sintering furnace is used for diffusion treatment at 910°C for 12 hours, with a heating rate of 4°C / min. When the temperature is raised to 450°C and 800°C, argon filling, heat preservation, pressure holding, and vacuuming processes are added respectively. The second tempering adopts a 510°C for 4 hours system.

4. The grain boundary diffusion process for NdFeB magnets according to any one of claims 1 to 3, characterized in that: The pressure of the argon gas is 0.01-0.06 MPa, and the heat preservation and pressure holding time is 5-20 minutes.

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