JP7556038B2 - How neodymium iron boron magnets are manufactured - Google Patents

Description

Detailed Description of the Invention

This application claims priority to a prior application, bearing patent application number 202010367655.8, filed with the State Intellectual Property Office of China on April 30, 2020, and entitled "Fine-crystal, high-coercivity neodymium-iron-boron sintered magnet and manufacturing method thereof," the entire text of which is incorporated herein by reference.

[Technical field]
The present invention relates to the field of neodymium-iron-boron based sintered magnets, and more particularly to fine crystal, high coercive force neodymium-iron-boron based sintered magnets and methods for producing the same.

2. Background Art
Since its discovery, NdFeB permanent magnet material has been widely applied in the fields of communication, medicine, automobiles and electronics due to its excellent magnetic properties and high cost-effectiveness, but its relatively low coercive force and relatively poor temperature stability and corrosion resistance have seriously limited the expansion of its application range.

At present, the conventional technology generally uses the following four methods to improve the coercivity of NdFeB permanent magnet materials: (1) adding heavy rare earth to the raw alloy to improve the crystal magnetic anisotropy of the main phase; (2) a two-alloy method in which two types of alloy powder with different coercivity are mixed and sintered; (3) a method of refining the crystal grains, in which as the crystal grain size becomes smaller, the effective scattering magnetic field factor of the crystal grains becomes smaller, and the coercivity of the magnet increases; and (4) a grain boundary diffusion method, in which the heavy rare earth diffuses along the grain boundary phase, significantly improving the anisotropy constant at the grain boundary, and achieving an obvious improvement in the magnet coercivity when a small amount of heavy rare earth is used. Among these methods, method (3) is relatively superior. Compared with methods (1) and (2), this method can significantly improve the magnet coercivity without using heavy rare earth or by using a small amount of heavy rare earth, while ensuring that the remanence remains unchanged. Compared to method (4), this improves magnet performance without being affected by product size and ensures uniform performance inside and outside the magnet.

The prior art further discloses a method for controlling the grain size of magnets by hot isostatic sintering using high pressure argon. First, magnetic powder with an average grain size of 3 μm is produced, and a sintered magnet with a grain size of 5.2 μm and a density of 99.5% is finally produced by this method. The prior art further discloses that a sintered magnet is produced using magnetic powder with an average grain size of 2-5 μm, in which the heavy rare earth content is less than 0.2%, and the squareness of the product is 0.95 or more. The prior art further discloses that a 47H magnet with a grain size of about 5 μm is obtained by controlling the average grain size of the magnetic powder to 2.4 μm and sintering at a low temperature, and the coercive force of the magnet reaches 17 kOe in the absence of heavy rare earth.

As described above, various methods have been used to manufacture magnets with a crystal grain size of 5 to 6 μm, and it has been disclosed that refining the crystal grains improves the coercive force of the magnet. In the absence of heavy rare earths, the product performance can reach 47 H. To further improve product performance under conditions without heavy rare earths, it is necessary to reduce the crystal grain size to 5 μm or less.

The prior literature further discloses fine-crystalline neodymium iron boron magnets with a median grain size of 4.5 μm or less in a cross section perpendicular to the c-axis. Reducing the grain size of the magnet improves the coercive force of the magnet. The prior literature further discloses that by refining the scaly columnar crystals, magnets with grain sizes of 0.5 to 5.0 μm can be produced, thereby reducing the amount of heavy rare earth used.

As mentioned above, by controlling the size of the scale-like columnar crystals, the grain size of the magnetic powder is refined, and finally, a neodymium iron boron magnet with magnet crystal grains smaller than 5 μm is produced, thereby further improving the coercive force of the product. However, there is a limit to the performance improvement mentioned therein. This is mainly because as the crystal grains become smaller than 5 μm, the activity of the corresponding powder becomes stronger, and the contents of the elements C, O, and N in the final magnet gradually increase. The elements C, O, and N consume the rare earth elements in the grain boundaries as impurities, and also act as nucleation sites for reverse magnetization domains, affecting the structure of the grain boundaries and reducing the coercive force of the magnet.

Therefore, unless the impurity elements C, O, and N in magnets are controlled, as the particle size of the magnetic powder decreases, the magnet's crystal grains will become smaller, and the magnet's coercivity will tend to increase and then decrease. Previous literature does not mention the control or method of controlling the elements C, O, and N in products when the magnet's crystal grains become smaller, especially when they are smaller than 5 μm.

Summary of the Invention
In order to remedy the shortcomings of the prior art, the present invention provides a fine-crystal, high-coercivity NdFeB-based sintered magnet and a manufacturing method thereof, in which the grain size of the NdFeB-based sintered magnet is 5 μm or less, and the contents of the elements C, O, and N in the NdFeB-based sintered magnet can be well controlled while reducing the grain size, thereby greatly improving the coercivity of the NdFeB-based sintered magnet.

The objective of the present invention is achieved by the following technical proposals:

The neodymium iron boron magnet has the chemical formula RFeBM, where R is a rare earth element, Fe is iron, and B is boron, the R content is 26-35 wt%, the B content is 0.8-1.3 wt%, and M is multiple elements selected from Co, Ga, Cu, Al, Zr, and Ti, where the Co content is 0.5-3.0 wt%, the Ga content is 0.05-0.4 wt%, the Cu content is 0.05-0.5 wt%, the Al content is 0-1.5 wt%, the Zr or Ti content is 0-0.3 wt%, and the remainder is iron and unavoidable impurities. In addition, the magnet contains the elements C, O, and N that satisfy the following: C + O + N (ppm) ≦ [1500 + (5.0 - crystal grain size (μm)) × 600] (ppm).

According to the present invention, the content of R is, for example, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, or 35 wt%.

According to the present invention, the content of B is, for example, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, or 1.3 wt%.

According to the present invention, the Co content is, for example, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, or 3.0 wt%.

According to the present invention, the Ga content is, for example, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, or 0.4 wt%.

According to the present invention, the Cu content is, for example, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%.

According to the present invention, the Al content is, for example, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 1.2 wt%, or 1.5 wt%.

According to the present invention, the content of Zr or Ti is, for example, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, or 0.3 wt%.

According to the present invention, the rare earth element is selected from lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y) and scandium (Sc).

According to the present invention, the crystal grain size of the neodymium iron boron magnet is 5 μm or less, for example, 4.8 μm, 4.5 μm, 4.3 μm, 4 μm, 3.8 μm, 3 μm, 2 μm or 1 μm.

The present invention further provides a method for producing the neodymium-iron-boron based sintered magnet, the method comprising the steps of:
1) obtaining R-Fe-B-M alloy fine powder by stripping-hydrogen explosion method;
2) grinding the alloy fine powder of step 1) with a jet mill to obtain a magnetic powder having a particle size D50 of 4.0 μm or less, mixing the magnetic powder with a lubricant, and then pressing the magnetic powder into a green compact;
3) low-temperature sintering the green compact of step 2) at 500-900°C, injecting a mixed gas of argon and hydrogen at 10 kPa or less during the low-temperature sintering, maintaining the temperature for 0.1-2 hours, evacuating to 100 Pa or less, and performing a circulation treatment at least once, followed by high-temperature sintering at 980-1040°C, maintaining the temperature for 3-8 hours, cooling, and then performing a tempering treatment to produce the neodymium-iron-boron sintered magnet.

According to the present invention, in step 1), the stripping-hydrogen explosion method includes, for example, the following steps:
The R-Fe-B-M alloy is melted under vacuum or inert gas atmosphere at a temperature of 1200-1600°C, and the melt is poured into a quenching roll with a rotation speed of 0.3-4 m/s to produce an R-Fe-B-M alloy strip. The alloy strip is then subjected to hydrogen explosion treatment in a HD hydrogen explosion furnace, and the vacuum is drawn to a pressure of less than 100 Pa before the treatment.

The thickness of the alloy strip is 0.1 to 0.5 mm.

According to the present invention, step 2) specifically includes the following steps:
Step 1) The alloy fine powder is ground by jet mill, in which the oxygen content in the jet mill process is less than 50 ppm.

According to the present invention, in step 2), the amount of the lubricant added is 0.1 to 0.5 wt% of the mass of the magnetic powder.

According to the present invention, in step 2), the mixing time is 0.1 to 3 hours. The mixing temperature is room temperature.

According to the present invention, in step 2), the magnetic powder is pressed into a green compact in a magnetic orientation molding device with an oxygen content of less than 500 ppm and an orientation magnetic field strength of 1-2 T. The size and dimensions of the green compact are not specifically defined and can be adjusted according to the required amount of the final product.

According to the present invention, in step 3), the low-temperature sintering is carried out in a mixed atmosphere of argon and hydrogen, in which argon occupies 95-99 vol% of the total volume of the mixed atmosphere and hydrogen occupies 1-5 vol% of the total volume of the mixed atmosphere. By injecting a mixed atmosphere of argon and hydrogen into the low-temperature sintering process and performing a heat retention treatment within a specific temperature range, hydrogen is reacted with the lubricant in the magnet and the oxygen and nitrogen adsorbed on the surface of the magnetic powder through the gaps in the magnet, and the final reactant is discharged, reducing the content of carbon, oxygen, and nitrogen impurities in the magnet and improving product performance.

According to the present invention, in step 3), the temperature of the low-temperature sintering is 500°C, 600°C, 700°C, 800°C or 900°C. The temperature of the high-temperature sintering is 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C or 1040°C.

According to the present invention, the tempering process includes a primary tempering process and a secondary tempering process.

The temperature of the primary tempering treatment is 700-900°C (e.g., 700°C, 750°C, 800°C, 850°C, 900°C), and the time of the primary tempering treatment is 3-7 h. The temperature of the secondary tempering treatment is 450-600°C (e.g., 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C), and the time of the secondary tempering treatment is 3-7 h.

According to the present invention, by adopting the above method, it is possible to obtain a neodymium iron boron sintered magnet with a crystal grain size of 5.0 μm or less, and the content (ppm) of C + O + N in the neodymium iron boron magnet is ≦ [1500 + (5.0 - crystal grain size (μm)) × 600] (ppm).

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the particle size measurement results of the magnetic powder in Example 1.

[Figure 2] A photograph of the fracture surface of the magnet in Example 1, scanned with a scanning electron microscope.

[Mode for carrying out the invention]
The present invention will be described in more detail with reference to the following specific examples. It should be understood that the following examples are merely illustrative and explanatory of the present invention and do not limit the scope of the claims of the present invention. Any technology realized based on the above content of the present invention is included in the scope of the claims of the present invention.

Unless otherwise specified, all experimental methods used in the following examples are conventional methods, and all reagents, materials, etc. used in the following examples are commercially available, unless otherwise specified.

The method for calculating the grain size in the present invention is as follows: using the fracture surface diagram of the green compact scanned by a scanning electron microscope, counting the number of grains in the fracture surface diagram, and then calculating the average equivalent area of the number of grains under the area of the metallographic diagram, and calculating the grain size according to the equivalent area.

The particle size D50 of the magnetic powder in this invention is measured using a laser diffraction particle size distribution analyzer.

Example 1
(1) NdPr, Co, Al, Fe, Cu, Ga, Zr and ferroboron with a purity of at least 99% by weight are melted in an argon atmosphere by high frequency induction, and the melt is poured into a quench roll to produce an alloy with a mass percentage of 31% NdPr, 0.8% Co, 0.5% Al, 0.2% Cu, 0.15% Ga, 0.10% Zr, 0.96% B, and the rest being iron and unavoidable impurities. The alloy is hydrogenated and crushed into coarse powder, which is then polished by a jet mill, and the particle size D50 of the resulting magnetic powder is 3.5 μm. After adding 0.2 wt% lubricant to the jet mill powder, the materials are mixed for 2 h and then molded under the environment of room temperature and an orientation field with a magnetic field strength of 2 T.

(2) The green compact is placed in a vacuum sintering furnace, filled with 10 kPa of a mixed gas of argon and hydrogen with a volume ratio of 98:2 at 600°C, and kept at that temperature for 0.5 h. After the temperature is kept at 600°C, the vacuum is drawn to 0.1 kPa, the temperature is continued to rise, and the compact is sintered at 1030°C for 6 h. After the temperature is kept at 600°C, the compact is cooled and then subjected to a primary tempering treatment at 900°C for 3 h. The secondary tempering treatment is performed at 520°C for 5 h. After cooling and removing from the furnace, a fine-crystalline neodymium iron boron magnet is obtained. This magnet is called A1, and a sample column (diameter 10 mm, length 10 mm) with a diameter of D10-10 mm is processed into the A1 magnet and a performance test is performed.

Comparative Example 1
The other steps are the same as in Example 1, except for step (2):
The green compact is placed in a vacuum sintering furnace and sintered at 1030℃ for 6 hours. After the heat retention, it is cooled and then subjected to the first tempering treatment at 900℃ for 3 hours. The second tempering treatment is performed at 520℃ for 5 hours. After cooling and removing from the furnace, a fine-crystalline NdFeB magnet is obtained. This magnet is called B1, and a sample column with a diameter of D10-10 mm is processed into the B1 magnet for performance testing.

As can be seen from Table 1, according to the method of the present invention, under the conditions of no heavy rare earths and a grain size of 4.5 μm, magnet A1 of Example 1 reaches a high coercivity level of 46 H. Example 1 has a comparable Br and a higher Hcj compared to Comparative Example 1, mainly because the impurity content (C + O + N) is relatively well controlled by the method of Example 1. Comparing the impurity content of Example 1 and Comparative Example 1, Example 1 < 1500 + (5.0 - grain size) x 600 < Comparative Example 1.

Example 2
(1) NdPr, Dy, Co, Al, Fe, Cu, Ga, Ti and ferroboron with a purity of at least 99% by weight are melted in an argon atmosphere by high frequency induction, and the melt is poured into a quench roll to produce an alloy with a mass percentage of 32% NdPr, 0.3% Dy, 1.0% Co, 0.8% Al, 0.15% Cu, 0.15% Ga, 0.15% Ti, 0.98% B, and the rest being iron and unavoidable impurities. The alloy is hydrogenated and crushed into coarse powder, which is then polished by a jet mill, and the particle size D50 of the resulting magnetic powder is 3.2 μm. After adding 0.3 wt% lubricant to the jet mill powder, the materials are mixed for 2 h and molded under the environment of room temperature and an orientation field with a magnetic field strength of 2 T.

(2) The green compact is placed in a vacuum sintering furnace, filled with 8 kPa of argon and hydrogen gas with a volume ratio of 99:1 at 650 °C, and kept warm for 1 h. After the warming is completed, the vacuum is drawn to less than 100 Pa, the temperature is continued to rise to 700 °C, and the argon and hydrogen gas with a volume ratio of 99:1 is filled with 5 kPa of argon and hydrogen gas, and kept warm for 0.5 h. After the warming is completed, the vacuum is drawn to 0.1 kPa, the temperature is continued to rise, and the sintering is performed at 1020 °C for 5.5 h. After the warming is completed, the cooling process is performed, and the first tempering process is performed at 850 °C for 4 h. The second tempering process is performed at 550 °C for 5 h. After cooling and removing from the furnace, a fine-crystalline neodymium iron boron magnet is obtained. This magnet is called A2, and a sample column with a D10-10 mm is processed into the A2 magnet and a performance test is performed.

Comparative Example 2
The other steps are the same as in Example 2, except for step (2):
The green compact is placed in a vacuum sintering furnace and sintered at 1020℃ for 5.5 hours. After the heat retention, it is cooled and then subjected to the first tempering treatment at 850℃ for 4 hours. The second tempering treatment is performed at 550℃ for 5 hours. After cooling and removing from the furnace, a fine-crystalline NdFeB magnet is obtained. This magnet is called B2, and a sample column with a diameter of D10-10 mm is processed into the B2 magnet for performance testing.

As can be seen from Table 2, according to the method of the present invention, magnet A2 of Example 2 reaches a high coercivity of 42 SH level under the condition of low heavy rare earth. Example 2 has a comparable Br and a higher Hcj compared to Comparative Example 2, mainly because the impurity content (C + O + N) is relatively well controlled by the method of Example 2. Comparing the impurity content of Example 2 and Comparative Example 2, Example 2 < 1500 + (5.0 - grain size) x 600 < Comparative Example 2.

Example 3
(1) NdPr, Dy, Co, Al, Fe, Cu, Ga, Ti and ferroboron with a purity of at least 99% by weight are melted in an argon atmosphere by high frequency induction, and the melt is poured into a quench roll to produce an alloy with a mass percentage of 31.5% NdPr, 0.5% Dy, 1.0% Co, 0.6% Al, 0.2% Cu, 0.10% Ga, 0.2% Ti, 0.98% B, and the rest being iron and unavoidable impurities. The alloy is hydrogenated and crushed into coarse powder, which is then polished by a jet mill, and the particle size D50 of the resulting magnetic powder is 2.6 μm. After adding 0.15 wt% lubricant to the jet mill powder, the materials are mixed for 2 h and molded under the environment of room temperature and an orientation field with a magnetic field strength of 2 T.

(2) The green compact is placed in a vacuum sintering furnace, filled with a mixture of argon and hydrogen gas with a volume ratio of 96:4 at 800°C at 6 kPa, and kept warm for 1 h. After the warming is completed, the vacuum is drawn to less than 100 Pa, and then the mixture of argon and hydrogen gas with a volume ratio of 96:4 at 800°C at 6 kPa is filled, and kept warm for 1 h. After the warming is completed, the vacuum is drawn to 0.1 kPa and the temperature is continued to increase, and the sintering is performed at 1000°C for 7 h. After the warming is completed, the cooling process is performed, and the first tempering process is performed at 850°C for 4 h. The second tempering process is performed at 500°C for 6 h. After cooling and removing from the furnace, a fine-crystalline neodymium iron boron magnet is obtained. This magnet is called A3, and a sample column with a D10-10 mm is processed into the A3 magnet and a performance test is performed.

Comparative Example 3
The other steps are the same as in Example 3, except for step (2):
The compact is placed in a vacuum sintering furnace and sintered at 1000°C for 7 hours. After the temperature is kept constant, it is cooled and then subjected to the first tempering treatment at 850°C for 4 hours. The second tempering treatment is performed at 500°C for 6 hours. After cooling and removing from the furnace, a fine-crystalline NdFeB magnet is obtained. This magnet is called B3, and a sample column with a diameter of D10-10 mm is processed into the B3 magnet for performance testing.

As can be seen from Table 3, Example 3 has comparable Br and higher Hcj compared to Comparative Example 3, which is mainly due to the relatively good control of the impurity content (C + O + N) by the method of Example 3. As the particle size of the magnetic powder becomes smaller, theoretically, the coercive force of the magnet in Comparative Example 3 increases, but the impurity content also increases rapidly, resulting in poor performance of the final product. Comparing the impurity content of Example 3 and Comparative Example 3, Example 3 < 1500 + (5.0 - grain size) x 600 < Comparative Example 3.

Example 4
(1) Nd, Co, Al, Fe, Cu, Ga and ferroboron with a purity of at least 99% by weight are melted by high frequency in an argon atmosphere, and the melt is poured into a quench roll to produce an alloy with a mass percentage of 31% Nd, 0.8% Co, 0.3% Al, 0.2% Cu, 0.1% Ga, 1% B, and the rest being iron and unavoidable impurities. The alloy is hydrogenated and crushed into coarse powder, which is then polished by a jet mill, and the particle size D50 of the resulting magnetic powder is 3.5 μm. After adding 0.1 wt% lubricant to the jet mill powder, the materials are mixed for 2 h and molded under the environment of room temperature and an orientation field with a magnetic field strength of 2 T.

(2) The green compact is placed in a vacuum sintering furnace, filled with 10 kPa of a mixed gas of argon and hydrogen with a volume ratio of 99:1 at 600°C, and kept warm for 0.5 h. After the warming is completed, the vacuum is drawn to 0 Pa, the temperature is continued to increase, and the compact is sintered at 1030°C for 6 h. After the warming is completed, the compact is cooled and then subjected to a primary tempering treatment at 900°C for 3 h. The secondary tempering treatment is performed at 510°C for 5 h. After cooling and removing from the furnace, a fine-crystalline neodymium iron boron magnet is obtained, which is marked as substrate A4.

The magnet is processed into a square piece with a size of 20-10-5 mm, and after degreasing and pickling, the square piece is subjected to Tb grain boundary diffusion treatment, and the amount of Tb diffused is 0.4 wt%. The grain boundary diffusion in this embodiment is processed by selecting the thermal spraying method, and the product after the diffusion treatment is called A5.

Comparative Example 4
The other steps are the same as in Example 4, except for step (2):
The green compact is placed in a vacuum sintering furnace and sintered at 1030℃ for 6 h. After the heat is released, it is cooled and then subjected to the first tempering treatment at 900℃ for 3 h. The second tempering treatment is performed at 510℃ for 5 h. After cooling and removing from the furnace, a fine-grained NdFeB magnet is obtained, which is marked as Base material B4.

The magnet is processed into a square piece with a size of 20-10-5 mm, and after degreasing and pickling, the square piece is subjected to Tb grain boundary diffusion treatment, and the amount of Tb diffused is 0.4 wt%. The grain boundary diffusion in this comparative example is processed by selecting the thermal spraying method, and the product after the diffusion treatment is called B5.

As can be seen from Table 4, A4 has a comparable Br and a higher Hcj compared to B4, which is mainly due to the impurity content (C + O + N) being relatively well controlled by the method of Example 4. Comparing the impurity content of A4 and B4, A4 < 1500 + (5.0 - grain size) x 600 < B4. Furthermore, looking at the coercive force of A4 and A5, the coercive force of A5 increases by 798 kA/m. Looking at the coercive force of B4 and B5, the coercive force of B5 increases by 721 kA/m. A4 magnet has a lower content of impurities C, O, and N, which is more favorable for the diffusion of heavy rare earths, but A5 magnet has a higher coercive force.

The above describes an embodiment of the present invention. However, the present invention is not limited to the above embodiment. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

4 shows the results of measuring the particle size of the magnetic powder in Example 1. 2 is a photograph of a fracture surface of the magnet in Example 1, scanned by a scanning electron microscope.

Claims (7)

A method for producing a neodymium iron boron magnet having a chemical formula of RFeBM, in which R is a rare earth element, Fe is iron, and B is boron, the R content is 26-35 wt%, the B content is 0.8-1.3 wt%, and M is a plurality of elements selected from Co, Ga, Cu, Al, Zr, and Ti, in which the Co content is 0.5-3.0 wt%, the Ga content is 0.05-0.4 wt%, the Cu content is 0.05-0.5 wt%, the Al content is 0-1.5 wt%, the Zr or Ti content is 0-0.3 wt%, and the remainder is iron and unavoidable impurities, and the contents of the elements C, O, and N in the magnet satisfy C + O + N (ppm) ≦ [1500 + (5.0 - crystal grain size (μm)) × 600] (ppm),
1) melting an R-Fe-B-M alloy in a vacuum or inert gas atmosphere at a temperature of 1200-1600°C, pouring the melt into a quench roll rotating at a speed of 0.3-4 m/s to produce an R-Fe-B-M alloy strip, and then subjecting the alloy strip to hydrogen explosion treatment in a HD hydrogen explosion furnace, followed by evacuation to a pressure of less than 100 Pa before treatment, to obtain an R-Fe-B-M alloy fine powder by a stripping-hydrogen explosion method;
2) grinding the alloy fine powder of step 1) with a jet mill to obtain a magnetic powder having a particle size D50 of 4.0 μm or less, mixing the magnetic powder with a lubricant, and then pressing the magnetic powder into a green compact;
3) low-temperature sintering the green compact of step 2 at 500-900°C, injecting a mixed gas of argon and hydrogen at 10kPa or less during the low-temperature sintering, keeping the temperature at 100-2 hours, and then evacuating the green compact to 100Pa or less at least once, and then high-temperature sintering at 980-1040°C, keeping the temperature at 100-1200°C for 3-8 hours, cooling, and then tempering the green compact to produce the neodymium iron boron magnet.
Including,
The rare earth elements are selected from lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y), and scandium (Sc);
How to manufacture neodymium iron boron magnets . In step 2), specifically,
Step 1) grinding the alloy fine powder with a jet mill, in which the oxygen content in the jet mill process is less than 50ppm;
The method for producing the neodymium iron boron magnet according to claim 1 . 3. The method for producing a neodymium iron boron magnet according to claim 1, wherein in step 2), the amount of the lubricant added is 0.1 to 0.5 wt% of the mass of the magnetic powder. The method for producing a neodymium iron boron magnet according to any one of claims 1 to 3, wherein in step 2), the magnetic powder is pressure-molded into a green compact using a magnetic orientation molding device having an oxygen content of less than 500 ppm and an orientation magnetic field strength of 1 to 2 T. The method for producing a neodymium iron boron magnet according to any one of claims 1 to 4, wherein in step 3), the low-temperature sintering is carried out in a mixed atmosphere of argon and hydrogen, in which argon occupies 95-99 vol% of the total volume of the mixed atmosphere and hydrogen occupies 1-5 vol% of the total volume of the mixed atmosphere. The method for producing a neodymium iron boron magnet according to any one of claims 1 to 5, wherein the tempering treatment includes a primary tempering treatment and a secondary tempering treatment. The method for producing a neodymium iron boron magnet according to claim 6, wherein the temperature of the first tempering treatment is 700-900°C, the time of the first tempering treatment is 3-7h, the temperature of the second tempering treatment is 450-600° C , and the time of the second tempering treatment is 3-7h.

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