CN104269238A - High-performance sintered neodymium-iron-boron magnet and preparation method - Google Patents

Abstract

A high-performance sintered NdFeB magnet, including 85-97wt% main phase alloy RE _x Fe _residual M _z B _y and 3-15 wt% grain boundary rare earth-rich phase alloy RE _S N _J Fe _residual , RE in the main phase alloy _x is one or two of light rare earth elements Nd and Pr, RE _S in grain boundary rare earth rich phase alloy contains one or more of Nd, Dy, Tb, and at least contains heavy rare earth elements Dy and Tb One or two of them, the preparation method includes: according to the composition of the main phase alloy and the grain boundary rare earth phase alloy, respectively batching, smelting, casting, hydrogen crushing, and the grain boundary rare earth phase alloy powder screened by hydrogen crushing Airflow milling into 2.5-3.5μm fine powder, mixing the jet-milled grain boundary-rich rare earth with the main phase alloy hydrogen powder in proportion, and then airflow grinding into 2.8-3.0μm powder, and then weighing into the mold, Magnetic field orientation press molding, and then sintering the green compact in a vacuum furnace. The invention can distribute the heavy rare earths Dy and Tb to the grain boundary of the main phase alloy to prepare a high-performance magnet with lower cost.

Description

A high-performance sintered NdFeB magnet and its preparation method

technical field

The invention relates to a high-performance sintered magnet and a preparation method.

Background technique

Since the advent of sintered Nd-Fe-B in 1983, it has been widely used in IT, medical, new energy, aerospace and other fields due to its excellent magnetic properties. Sintered Nd-Fe-B magnets generally consist of Nd ₂ Fe ₁₄ B matrix phase, grain boundary Nd-rich phase and Nd _1+ε Fe ₄ B ₄ boron-rich phase. Among them, the grain boundary Nd-rich phase plays a role in accelerating the densification of liquid phase sintering, and its composition, structure and distribution also have an important impact on the performance of the magnet. The coercive force mechanism of sintered NdFeB magnets is a nucleation mechanism, which is easy to form reverse magnetization domains at the grain boundaries and reduce the coercive force of the magnet. Studies have shown that if the heavy rare earth elements such as Dy and Tb can be diffused to the grain boundary and the anisotropy of the grain boundary can be improved, the coercive force of the magnet can be greatly improved, and the remanence Br of the magnet can be reduced very little, and can Effectively reduce the amount of Dy added. In response to this situation, domestic and foreign scientific research institutions and related enterprises have carried out research on infiltration Dy and Tb technology. However, there are still many problems in the industrial application of infiltration Dy technology, such as: limited diffusion depth is not suitable for large-scale products; poor performance controllability in mass production, poor product stability and consistency; professional equipment for grain boundary diffusion Immature and needs further research. Therefore, at present, domestic enterprises still use conventional preparation methods to prepare sintered NdFeB magnets: single alloy method or general double alloy method. Conventional preparation methods cannot effectively utilize heavy rare earth elements, and at the same time, the controllability of grain boundaries is poor. The preparation of high-performance magnets not only requires higher costs, but it is also difficult to prepare ultra-high-performance magnets.

Contents of the invention

The invention provides a high-performance magnet and a preparation method of the high-performance magnet. The method of the invention can not only better distribute Dy and Tb elements to grain boundaries, obtain low-cost high-performance magnets, and do not need to modify original production equipment for industrial production, but also can prepare ultra-high-performance magnets.

The technical solution of the present invention is: a high-performance sintered NdFeB magnet, which is characterized by comprising 85-97wt% main phase alloy RE _x Fe _remaining M _z B _y and 3-15wt% grain boundary rare earth-rich phase alloy RE _S N _{J The remainder of} Fe, of which:

RE _x in the main phase alloy composition is one or two of light rare earth elements Nd and Pr, RE _x is 28 to 29 wt%, and M _z is one or one of the added metal elements Ga, Cu, Al, Co More than one species, M _z is 0.2-2wt%, B element _By is 0.95-1.02wt%, and the balance is Fe;

RE _S in the grain boundary rare earth-rich phase alloy composition contains one or more of Nd, Dy, and Tb, and at least one or two of heavy rare earth elements Dy and Tb, and RE _S is 40 to 80 wt% , and the proportion of (Dy+Tb) is 15%~ _RES , N _J is one or more of the added metal elements Ga, Cu, Al, Co, Nb, Zr, N _J is 4~10 wt%, and the rest The amount is Fe.

A method for preparing a high-performance sintered NdFeB magnet, comprising the following steps:

1) According to the composition ratio of the main phase alloy, the ingredients are weighed, put into a vacuum intermediate frequency melting furnace for melting, and the casting is cast by the quick-setting process. The main phase alloy casting sheet is obtained; the main phase alloy casting sheet is subjected to hydrogen crushing, and the oxygen content of the crushed powder is controlled to be ≤400PPm;

2) According to the composition ratio of rare earth-rich phase alloy at the grain boundary, the batching and weighing are carried out, put into the vacuum intermediate frequency melting furnace for melting, adopt the conventional quick-setting process to cast the sheet, set the copper roller speed to 1.2-1.5m/s, and the casting temperature to 1440 ℃～1450℃, to prepare the grain boundary rare earth-rich phase alloy cast piece; carry out hydrogen crushing on the grain boundary rare earth-rich alloy cast piece, and screen the powder with a particle size of ≤380μm in the hydrogen broken powder;

3) The grain boundary rare earth-rich phase alloy powder screened by hydrogen blasting is jet milled under an inert gas atmosphere, the oxygen content is controlled below 5 PPm, and the particle size of the fine powder after jet milling is controlled at 2.5-3.5 μm;

4) Mix the grain boundary rare earth-rich phase alloy fine powder and the main phase alloy hydrogen broken powder in proportion after jet milling, and the addition ratio of the grain boundary rare earth Jet milling is carried out under an inert gas atmosphere, and the oxygen content in the milling chamber is controlled to be ≤10 ppm, and the powder particle size is 2.8-3.0 μm;

5) Weigh the uniformly mixed powder, fill it into the forming mold, add ≥ 2.0T magnetic field orientation and press molding, after the green body is vacuum-packed, put it into the press and pressurize 150-200Mpa, keep the pressure and let it stand for 1-3 minute;

6) Put the green body that has been kept under pressure into a vacuum sintering furnace with a vacuum degree of ≤4.0×10 ^-2 Pa, sinter at a temperature of 1020°C to 1060°C for 3.5 to 5.5 hours, and then sinter at a temperature of 450°C ~600°C for 4~6h aging treatment, take out the finished NdFeB magnet from the sintering furnace.

In the above, Nd and Pr are selected for RE in the main phase alloy, and heavy rare earths such as Dy and Tb are not added to ensure that they do not diffuse into the main phase. X is selected to be 28-29wt% because the composition of the main phase alloy must be close to NdFe The main phase composition of boron; the main phase alloy is easy to produce soft magnetic phase a-Fe during the smelting process due to the low rare earth content, and the formation of a-Fe during smelting can be suppressed by adding M element; too high B addition will lead to Nd _1+ε The proportion of Fe ₄ B ₄ phase is too high to reduce the proportion of the main phase, thus affecting the performance of the magnet;

In the above, a large proportion of heavy rare earth elements must be added to the grain boundary rare earth-rich phase alloy, because the purpose of the present invention is to better distribute heavy rare earth elements such as Dy and Tb on the boundary; The grain boundary of the magnet forms a grain boundary phase and refines the grains of the main phase;

If the grain boundary rare earth-rich phase fine powder is added in a ratio of <3wt%, it will lead to too little grain boundary phase of the magnet, and the performance will deteriorate; if the addition ratio is >15wt%, it will cause too much grain boundary phase and a large amount of grain boundary phase agglomeration lead to performance degradation.

Among the above, the main phase alloy is only ground once, and the grain boundary rare earth-rich phase alloy is equal to two grinding times; the advantage of adopting this method is that it further refines the particle size of the grain boundary rare earth-rich phase powder to make it more effective. Encapsulation of the main alloy phase can prevent the risk of powder oxidation when the grain boundary rare earth-rich phase is milled separately twice; moreover, the powder can be mixed more uniformly through the jet milling process.

Using this method to prepare magnets 1) In the case of the same composition, a dense magnet can be obtained at a lower sintering temperature, so the abnormal grain growth of the magnet due to high temperature sintering can be controlled; 2) The heavy rare earth can be more effectively Dy and Tb are distributed to the grain boundaries to prepare low-cost high-performance magnets; 3) ultra-high-performance magnets can be prepared. 4) The present invention can be industrialized on the existing production line without special heavy rare earth grain boundary diffusion equipment.

patent drawings

The following 3 figures are the distribution of heavy rare earth elements in the magnet prepared by the present invention, and the test method is EMPA;

Figure 1 is a picture of the microstructure of the magnet. In the figure, the white is the rare earth-rich phase at the grain boundary of the magnet, and the black is the main phase;

Figure 2 is the distribution of the heavy rare earth element Dy corresponding to Figure 1, mainly distributed in the grain boundary;

Fig. 3 is the distribution of the heavy rare earth element Tb corresponding to Fig. 1, which is mainly distributed in the grain boundary.

Note: The color-changing scale on the right side of Figure 2 and Figure 3 indicates the distribution abundance of the corresponding element in each area in Figure 1, and the distribution corresponds to the value in the scale.

Detailed ways

Example 1:

1) The main phase alloy is smelted according to the _proportion of Nd _29.0 Co _1.0 Ga _0.2 B _1.0 Fe (wt%), and the cast sheet is cast by quick-setting technology, the copper roll speed is 1.5m/s, and the pouring temperature is 1430°C; The tablets are crushed by hydrogen, and the oxygen content of the crushed powder is controlled to be ≤400PPm;

2) The grain boundary rare earth-rich phase alloy is smelted according to the _proportion of Nd ₂₅ Dy ₁₅ Cu _2.0 Al _2.0 Co _3.0 Fe (wt%), and the cast piece is cast by the rapid solidification technology, the copper roll speed is 1.2m/s, and the casting temperature is 1450 ℃; casting sheet hydrogen crushing, the hydrogen crushing powder is sieved in an Ar protection environment (O ₂ ≤10PPm), the sieve opening is 40 mesh, and the rare earth-rich phase hydrogen crushing powder with a particle size of ≤380 μm is screened;

3) The grain boundary rare earth-rich phase alloy powder screened by hydrogen blasting is jet-milled in an Ar gas atmosphere, and the oxygen content in the milling chamber is controlled to be ≤5PPm, and the particle size of the powder is 3-3.5μm;

4) Mix the jet-milled grain boundary rare earth-rich phase alloy powder with the hydrogen-breaking powder of the main phase alloy (that is, mix the above 1) and 2), and the addition ratio of the grain boundary rare earth-rich phase alloy powder is 8wt%, The main phase alloy powder is 92 wt%. The composition content of the mixed alloy _powder is: Nd _28.68 Dy _1.20 Co _1.16 Cu _0.16 Al _0.16 Ga _0.18 B _0.92 Fe (wt%). Jet mill the mixed powder under Ar gas atmosphere, control the oxygen content in the mill chamber to be ≤10PPm, and the powder particle size to be 3.0μm;

5) Fill the uniformly mixed powder into the mold, add 2.0T magnetic field orientation and press molding, vacuum seal the green body and put it into the press, pressurize at 220Mpa, and oil-cool isostatic pressing for 1min;

6) The blank after isostatic pressing is sintered and aged in a vacuum furnace of ≤4.0×10 ^-2 Pa, the sintering temperature is 1020℃～1060℃, and the sintering time is 3.5h; aging process: 500℃×4h. After aging, sintered NdFeB magnets were obtained.

Comparative Example 1A:

1) Using conventional preparation methods, the composition is Nd _28.68 Dy _1.2 Co _1.16 Cu _0.16 Al _0.16 Ga _0.18 B _0.92 Fe ( _that is, the composition of the mixed alloy powder in Example 1), using conventional rapid-setting technology: copper roll speed 1.2～ 1.5m/s, casting temperature 1440℃～1460℃; cast sheet hydrogen broken, hydrogen broken powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled to control the fine powder particle size to 3.0-3.5 μm;

3) Put the air-milled powder into the mold, shape it in a magnetic field of 2.0T, and vacuum-pack the green body. The packaged blank is subjected to oil-cooled isostatic pressing at 200-250MPa for 1-3 minutes;

4) The blank after isostatic pressing is sintered and aged under the vacuum condition of ≤4.0×10 ^-2 Pa, the sintering temperature is 1020℃～1060℃, the sintering time is 3.5h; the aging process is 500℃×4h. After aging, the sintered NdFeB magnet was prepared.

Comparative Example 1B:

1) The conventional preparation method is adopted, the composition is Nd ₂₈ Dy _1.6 Co _1.2 Cu _0.2 Al _0.2 Ga _0.2 B _0.95 Fe, _and the conventional quick-setting technology is adopted: the copper roller speed is 1.2-1.5m/s, the casting temperature is 1440℃～1460℃; Hydrogen flakes, hydrogen powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled to control the particle size of the fine powder to 3.0-3.5 μm;

3) Put the jet-milled powder into the mold, shape it in a 2.0T magnetic field, and vacuum-pack the formed green body. The packaged blank is oil-cooled and isostatically pressed at 200-250MPa for 1-3 minutes;

4) The isostatic pressing blank is sintered at 1045°C for 3.5h under the vacuum condition of ≤4.0×10 ^-2 Pa; aging process, 500°C×4h. After aging, the sintered NdFeB magnet was prepared.

Table 1A Density comparison table at different sintering temperatures

It can be seen from the comparison table above that the density of NdFeB magnets prepared by the method of the present invention at a sintering temperature of 1020° C. to 1050° C. is significantly higher than that of magnets prepared by conventional methods. Although the NdFeB magnets produced at the sintering temperature of 1060°C have the same density, the grains of the NdFeB magnets produced by the traditional method grow abnormally, which affects the performance of the magnet. Therefore, with the present invention, under the condition of the same composition, a dense magnet can be obtained at a lower sintering temperature, so that the abnormal grain growth of the magnet due to high temperature sintering can be controlled.

Table 1B Comparison table of magnetic properties and Dy content

It can be seen from the comparison table above that the NdFeB magnets with similar magnetic properties obtained by the method of the present invention and the conventional method have a 0.4wt% reduction in the content of heavy rare earth Dy, which reduces the cost. Therefore, the present method enables the preparation of lower-cost high-performance magnets.

Example 2:

1) The main phase alloy is smelted according to the ratio of Nd _28.5 Fe _to Cu _0.2 Ga _0.2 B _1.0 (wt%), and the cast sheet is cast by quick-setting technology, the copper roll speed is 1.8m/s, and the pouring temperature is 1425°C; Hydrogen crushing is carried out, and the oxygen content of the crushed powder is controlled to be ≤400PPm;

2) Rare-earth-rich phase alloys at grain boundaries were smelted according to the _ratio of Nd ₄₅ Dy ₂₅ Tb ₁₀ Nb _1.0 Al _2.0 Co _3.0 Fe (wt%), and the casting was cast using rapid solidification technology. The copper roll speed was 1.2m/s, and the casting temperature was The temperature is 1450°C; cast hydrogen powder, the hydrogen powder is sieved in an Ar protection environment (O ₂ ≤10PPm), the sieve is 40 mesh, and the rare earth-rich phase hydrogen powder with a particle size of ≤380μm is screened;

3) The grain boundary rare earth-rich phase alloy powder screened by hydrogen breaking is jet-milled in an Ar gas atmosphere, and the oxygen content in the milling chamber is controlled to be ≤5PPm, and the powder particle size is 3.0-3.5μm;

4) Mix the grain boundary rare earth-rich phase alloy powder after jet milling with the main phase alloy hydrogen powder (that is, mix the above 1) and 2), the addition ratio of the grain boundary rare earth phase alloy is 5wt%, the main phase The alloy is 95 wt%; the composition content of the mixed alloy powder is: Nd _29.33 Dy _1.25 Tb _0.50 Co _0.50 Cu _0.19 Al _0.10 Ga _0.19 Nb _0.05 B _0.95 Fe (wt%), the _mixed alloy powder in the Ar gas atmosphere Then carry out jet milling, control the oxygen content in the milling chamber ≤10PPm, and the powder particle size is 2.8～3.0μm;

5) Put the uniformly mixed powder into the mold and apply 2.0T magnetic field orientation to press molding. After the green body is vacuum packaged, put it into the press, pressurize at 220MPa, and oil-cool isostatic pressing for 1min;

6) The blank after isostatic pressing is sintered and aged under the vacuum condition of ≤4.0×10 ^-2 Pa, the sintering temperature is 1020℃～1050℃, and the sintering time is 4.5h; aging process: 480℃×4h. After aging, sintered NdFeB magnets were obtained.

Comparative Example 2A:

1) Using a conventional preparation method, the composition is Nd _29.33 Dy _1.25 Tb _0.5 Co _0.5 Cu _0.19 Al _0.1 Ga _0.19 Nb _0.05 B _0.95 Fe (wt%) (that is, the _composition of the mixed alloy powder in Example 2); Coagulation technology: Copper roller speed 1.2~1.5m/s, casting temperature 1440℃~1460℃; cast sheet hydrogen broken, hydrogen broken powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled to control the particle size of the fine powder to 3.0-3.5 μm;

3) Put the jet-milled powder into the mold, shape it in a 2.0T magnetic field, and vacuum-pack the formed green body. The packaged blank is oil-cooled and isostatically pressed at 200-250MPa for 1-3 minutes;

4) The isostatic pressing blank is sintered and aged under the vacuum condition of ≤4.0×10 ^-2 Pa, the sintering temperature is 1020℃～1050℃, the sintering time is 4.5h; the aging process is 480℃×4h. After aging, the sintered NdFeB magnet was prepared.

Comparative Example 2B:

1) Using conventional preparation methods, the composition is Nd _29.5 Dy _1.8 Tb _0.5 Co _0.5 Cu _0.19 Al _0.10 Ga _0.19 Nb _0.05 B _0.95 Fe (wt%); _using conventional quick-setting technology: copper roller speed 1.2 ~ 1.5m/s, Casting temperature is 1440℃～1460℃; casting sheet hydrogen broken, hydrogen broken powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled, and the fine powder particle size is 3.0-3.5 μm;

3) Put the jet mill powder into the mold, shape it in a 2.0T magnetic field, and vacuum-pack the formed green body. The packaged blank is subjected to oil-cooled isostatic pressing at 200-250MPa for 1-3 minutes;

The isostatic pressing blank is sintered at 1040°C for 4.5h under the vacuum condition of ≤4.0×10 ^-2 Pa; the aging process is 480°C for 4h. After aging, the sintered NdFeB magnet was prepared.

Table 2A Density comparison table at different sintering temperatures

It can be seen from the comparison table above that the density of NdFeB magnets prepared by the method of the present invention at a sintering temperature of 1020° C. to 1040° C. is higher than that of magnets prepared by conventional methods. Although the NdFeB magnets produced at the sintering temperature of 1050°C have the same density, the grains of the NdFeB magnets produced by conventional methods grow abnormally, which affects the performance of the magnets. Therefore, with the present invention, under the condition of the same composition, a dense magnet can be obtained at a lower sintering temperature, so that the abnormal grain growth of the magnet due to high temperature sintering can be controlled.

Table 2B Comparison table of magnetic properties and Dy content

It can be seen from the comparison table above that the NdFeB magnets with similar magnetic properties are produced by the method of the present invention and the conventional method, and the content of the heavy rare earth Dy is reduced by 0.55%, which reduces the cost. Therefore, the present method enables the preparation of lower-cost high-performance magnets.

Example 3:

1) The main phase alloy is smelted according to the proportion of Pr ₇ Nd ₂₁ Fe _remaining Al _0.2 Co _1.0 B _1.0 (wt%), using the quick-setting technology to cast the sheet, the copper roll speed is 2.0m/s, and the pouring temperature is 1425°C; The casting is crushed by hydrogen, and the oxygen content of the crushed powder is controlled to be ≤400PPm;

2) The grain boundary rare earth-rich phase alloy is smelted according to the _ratio of Nd ₃₀ Dy ₂₀ Zr _1.0 Ga ₂ Cu ₂ Fe (wt%), and the casting is cast using the rapid solidification technology. The copper roll speed is 1.4m/s, and the casting temperature is 1450 ℃; casting sheet hydrogen crushing, the hydrogen crushing powder is sieved in an Ar protection environment (O ₂ ≤10PPm), the sieve opening is 40 mesh, and the rare earth-rich phase hydrogen crushing powder with a particle size of ≤380 μm is screened;

3) The grain boundary rare earth-rich phase alloy powder screened by hydrogen blasting is jet-milled in an Ar gas atmosphere, and the oxygen content in the milling chamber is controlled to be ≤5PPm, and the particle size of the powder is 3.0μm;

4) Mix the grain boundary rare earth-rich phase alloy powder after jet milling with the main phase alloy hydrogen breaking powder (that is, mix the above 1) and 2), the addition ratio of the rare earth-rich phase alloy powder is 15wt%, and the main phase alloy is ₈₅ wt%; the mixed alloy powder composition content is: Nd _22.35 Pr _5.95 Dy _3.0 Co _0.85 Cu _0.3 Al _0.17 Ga _0.3 Zr _0.15 B _0.85 Fe (wt%). Under the Ar gas atmosphere, the mixed alloy powder is jet milled again, and the oxygen content in the milling chamber is controlled to be ≤10PPm, and the powder particle size is 2.8μm;

5) Fill the uniformly mixed powder into the mold and apply 2.0T magnetic field orientation to press molding. After the green body is vacuum packaged, put it into the press, pressurize at 220MPa, and oil-cool isostatic pressing for 1min;

6) The blank after isostatic pressing is sintered and aged under the vacuum condition of ≤4.0×10 ^-2 Pa, the sintering temperature is 1020℃～1050℃, and the sintering time is 4.5h; aging process: 520℃×4h. After aging, sintered NdFeB magnets were obtained.

Comparative Example 3A:

1) Using a conventional preparation method, the composition is Nd _22.35 Pr _5.95 Dy _3.0 Co _0.85 Cu _0.3 Al _0.17 Ga _0.3 Zr _0.15 B _0.85 Fe (wt.%) (that is, the _composition of the mixed alloy powder in Example 3); Accelerated setting technology: copper roll speed 1.2~1.5m/s, casting temperature 1440℃~1460℃; cast sheet hydrogen broken, hydrogen broken powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled to control the particle size of the fine powder to 3.0-3.5 μm;

3) Put the jet-milled powder into the mold, shape it in a 2.0T magnetic field, and vacuum-pack the formed green body. The packaged blank is oil-cooled and isostatically pressed at 200-250MPa for 1-3 minutes;

4) The isostatic pressing billet is sintered and aged under the vacuum condition of ≤4.0×10 ^-2 Pa, the sintering temperature is 1020℃～1050℃, and the sintering time is 4.5h; the aging process is 520℃×4h. After aging, the sintered NdFeB magnet was prepared.

Comparative Example 3B:

1) Using conventional preparation methods, the composition is Nd _22.4 Pr _5.6 Dy _4.0 Co _1.0 Cu _0.3 Al _0.2 Ga _0.3 Zr _0.15 B _0.85 Fe (wt.%); _using conventional quick-setting technology: copper roller speed 1.2 ~ 1.5m/s , the casting temperature is 1440℃～1460℃; cast sheet hydrogen broken, hydrogen broken powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled to control the particle size of the fine powder to 3.0-3.5 μm;

3) Put the jet-milled powder into the mold, shape it in a 2.0T magnetic field, and vacuum-pack the formed green body. The packaged blank is oil-cooled and isostatically pressed at 200-250MPa for 1-3 minutes;

The isostatic pressing blank is sintered at 1045°C for 3.5h under the vacuum condition of ≤4.0×10 ^-2 Pa; the aging process is at 480°C for 4h. After aging, the sintered NdFeB magnet was prepared.

Table 3A Density comparison table at different sintering temperatures

It can be seen from the comparison table above that the density of NdFeB magnets prepared by the method of the present invention at a sintering temperature of 1020° C. to 1050° C. is higher than that of magnets prepared by conventional methods. Therefore, with the present invention, under the condition of the same composition, a dense magnet can be obtained at a lower sintering temperature, so that the abnormal grain growth of the magnet due to high temperature sintering can be controlled.

Table 3B Magnetic properties and Dy content comparison table

It can be seen from the comparison table above that the NdFeB magnets with similar magnetic properties are produced by the method of the present invention and the conventional method, and the content of the heavy rare earth Dy is reduced by 0.5%, which reduces the cost. Therefore, the present method enables the preparation of lower-cost high-performance magnets.

Example 4:

1) The main phase alloy is smelted according to the ratio of Nd _28.5 Fe _to Co _1.0 B _1.0 (wt%), using the rapid solidification technology to cast the sheet, the copper roll speed is 1.8m/s, and the pouring temperature is 1420°C; Broken, crushed powder oxygen content control ≤ 400PPm;

2) The grain boundary rare earth-rich phase alloy is smelted according to the _ratio of Nd ₃₅ Dy ₂₀ Nb _1.0 Ga ₂ Cu ₂ Fe (wt%), and the casting is cast by quick-setting technology, the copper roll speed is 1.5m/s, and the casting temperature is 1450 ℃; casting sheet hydrogen crushing, the hydrogen crushing powder is sieved in an Ar protection environment (O ₂ ≤10PPm), the sieve opening is 40 mesh, and the rare earth-rich phase hydrogen crushing powder with a particle size of ≤380 μm is screened;

3) The grain boundary rare-earth-rich phase alloy powder screened by hydrogen blasting is jet-milled in an Ar gas atmosphere, and the O ₂ in the milling chamber is controlled to be ≤5PPm, and the particle size of the powder is 3.0μm;

4) Mix the grain boundary rare earth-rich phase alloy powder after jet milling with the main phase alloy hydrogen breaking powder (that is, mix the above 1) and 2), the addition ratio of the rare earth-rich phase alloy powder is 3wt%, and the main phase alloy is 97wt%; the mixed alloy powder composition content is: Nd _{28.83 Dy 1.00} Co _0.95 Cu _0.10 Ga _0.10 Nb _0.05 B _0.95 Fe (wt%), the mixed alloy powder is then jet milled under the Ar gas atmosphere to control Oxygen content in the mill chamber ≤10PPm, powder particle size 2.8μm;

5) Fill the uniformly mixed powder into the mold and apply 2.0T magnetic field orientation to press molding. After the green body is vacuum-packaged, put it into the press, pressurize at 220MPa, and press oil-cooled isostatically for 3 minutes;

6) The blank after isostatic pressing is sintered and aged under the vacuum condition of ≤4.0×10 ^-2 Pa, the sintering temperature is 1045°C, and the sintering time is 5.5h; aging process: 485°C×4h. After aging, a sintered NdFeB magnet was prepared. The magnet has ultra-high remanence and magnetic energy product, and its performance is shown in Table 4.

Table 4 Magnet performance table

Comparative example 4

1) Using conventional preparation methods, the composition is Nd _28.83 Dy _1.0 Co _0.95 Cu _0.1 Ga _0.1 Nb _0.05 B _0.95 Fe (wt%); _using conventional quick-setting technology: copper roller speed 1.2-1.5m/s, casting temperature 1440°C ～1460℃; cast sheet hydrogen broken, hydrogen broken powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled to control the particle size of the fine powder to 3.0-3.5 μm;

3) Put the jet-milled powder into the mold, shape it in a 2.0T magnetic field, and vacuum-pack the formed green body. The packaged blank is oil-cooled and isostatically pressed at 200-250MPa for 1-3 minutes;

The isostatic pressing blank is sintered at 1045°C for 3.5h under the vacuum condition of ≤4.0×10 ^-2 Pa; the aging process is at 480°C for 4h. After aging, the sintered NdFeB magnet was prepared. The magnet is difficult to be sintered densely, the density of the magnet is less than 7.0g/cm ³ , and it has no magnetic performance.

It can be seen from the above comparison that with the same formula, a magnet with ultra-high remanence and magnetic energy product can be produced by the method of the present invention, while the NdFeB magnet prepared by the conventional method has no magnetic properties. The reason is: to prepare ultra-high remanence and energy product magnets, it is necessary to ensure that the rare earth content in the magnet composition is close to the main phase composition content (26.8wt%) to obtain a high proportion of the main phase, while the grain boundary rare earth-rich phase content is less. With the conventional preparation method, the rare earth-rich phase at the grain boundary is freely distributed, and the distribution will be uneven, which leads to insufficient liquid phase sintering during the sintering process and low magnet density. However, with the present invention, the rare earth-rich phase at the grain boundary can be very uniformly distributed in the grain boundary, thereby improving the sintering compact behavior, and a high-density magnet can be obtained even when the ratio of the rare earth-rich phase at the grain boundary is small. Therefore, the method of the present invention can be used to prepare an ultra-high magnetic performance magnet with both high remanence and high magnetic energy product.

Example 5:

1) The main phase alloy is smelted according to the ratio of Nd _28.5 Fe _to Co _1.0 B _1.0 (wt%), using the rapid solidification technology to cast the sheet, the copper roll speed is 1.8m/s, and the pouring temperature is 1420°C; Broken, crushed powder oxygen content control ≤ 400PPm;

2) The grain boundary rare earth-rich phase alloy is smelted according to the _proportion of Dy ₂₅ Tb ₂₀ Co _2.0 Ga _2.0 Cu _2.0 Al _4.0 Fe (wt%), using the rapid solidification technology to cast the sheet, the copper roll speed is 1.3m/s, and the casting temperature is The temperature is 1445°C; the cast hydrogen powder is sieved in an Ar protection environment (O ₂ ≤10PPm), the sieve hole is 40 mesh, and the rare earth-rich phase alloy hydrogen powder with a particle size of ≤380 μm is screened;

3) The grain boundary rare-earth-rich phase alloy powder screened by hydrogen blasting is jet-milled under the protection of Ar gas, the O ₂ in the milling chamber is ≤5PPm, and the particle size of the powder is 3.5μm;

4) Mix the grain boundary rare earth-rich phase alloy powder after jet milling with the main phase alloy hydrogen breaking powder (that is, mix the above 1) and 2), the addition ratio of the rare earth-rich phase alloy powder is 10wt%, and the main phase alloy 90wt%; the composition of the alloy powder after mixing is: Nd _25.65 Dy _2.50 Tb _2.00 Co _1.10 Cu _0.20 Ga _0.20 Al _0.40 B _0.95 Fe (wt%), the mixed alloy powder is jet _milled under the Ar gas atmosphere , control the oxygen content in the mill room ≤ 10PPm, powder particle size 3.0μm;

5) Fill the uniformly mixed powder into the mold and apply 2.0T magnetic field orientation to press molding. After the green body is vacuum packaged, put it into the press, pressurize at 220MPa, and press oil-cooled isostatically for 2 minutes;

6) The blank after isostatic pressing is sintered and aged under a vacuum condition of ≤4.0×10 ^-2 Pa, the sintering temperature is 1045°C, and the sintering time is 3.5h; aging process: 485°C×4h. After aging, a sintered NdFeB magnet was prepared. The magnet has high remanence and high coercive force, and its performance is shown in Table 5.

Comparative Example 5

1) Using conventional preparation methods, the composition is Nd _25.65 Dy _2.5 Tb _2.0 Co _1.1 Cu _0.2 Ga _0.2 Al _0.4 B _0.95 Fe (wt%); _using conventional quick-setting technology: copper roller speed 1.2-1.5m/s, casting temperature 1440℃～1460℃; cast sheet hydrogen broken, hydrogen broken powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled to control the particle size of the fine powder to 3.0-3.5 μm;

3) Put the jet-milled powder into the mold, shape it in a 2.0T magnetic field, and vacuum-pack the formed green body. The packaged blank is oil-cooled and isostatically pressed at 200-250MPa for 1-3 minutes;

The isostatic pressing blank is sintered at 1045°C for 3.5h under the vacuum condition of ≤4.0×10 ^-2 Pa; the aging process is at 480°C for 4h. After aging, the sintered NdFeB magnet was prepared. The magnet properties are shown in Table 5

Table 5 Magnet performance comparison table

As can be seen from the above comparison table, the NdFeB magnets prepared by the method of the present invention using the same material formula have an increased remanence of 0.15kGs and a higher coercive force than the NdFeB magnets prepared by the conventional method. 2.3kOe. With the conventional preparation method, since Dy and Tb heavy rare earth elements enter into the main phase more, if the coercive force of the magnet is increased by adding heavy rare earth, the remanence will be sacrificed; if the remanence is increased by increasing the proportion of the main phase , the coercive force level will drop. Therefore, for the formulation of this example, if the conventional method is used to prepare a magnet with a coercive force level of 20.5kOe, the content of heavy rare earth Dy or Tb must be increased in the ingredients, and the increase of Dy or Tb will lead to a decrease in remanence. The remanence can't reach the level of 13.75kGs, and it is impossible to make a magnet with both high remanence and high coercive force. With the present invention, since Dy and Tb heavy rare earths can be evenly distributed in the grain boundaries and rarely enter the main phase, a magnet with ultra-high magnetic properties with high remanence and high coercive force can be produced.

Embodiment 6:

1) The main phase alloy is smelted according to the ratio of Nd _29.0 Fe _to Co _1.0 B _1.0 (wt%), using the rapid solidification technology to cast the sheet, the copper roll speed is 1.8m/s, and the pouring temperature is 1420°C; Broken, crushed powder oxygen content control ≤ 400PPm;

2) The grain boundary rare earth-rich phase alloy is smelted according to the _proportion of Dy ₂₀ Tb ₃₀ Co _3.0 Ga _2.0 Cu _2.0 Al _4.0 Fe (wt%), using the rapid solidification technology to cast the sheet, the copper roll speed is 1.3m/s, and the casting temperature is The temperature is 1445°C; the cast hydrogen powder is sieved in an Ar protection environment (O ₂ ≤10PPm), and the sieve opening is 40 mesh, and the rare earth-rich phase hydrogen powder with a particle size of ≤380 μm is screened;

3) The grain boundary rare-earth-rich phase alloy powder screened by hydrogen blasting is jet milled under the protection of Ar gas, and the O ₂ in the milling chamber is controlled to be ≤5PPm, and the particle size of the powder is 3.5μm;

4) Mix the grain boundary rare earth-rich phase alloy powder after jet milling with the main phase alloy hydrogen breaking powder (that is, mix the above 1) and 2), the addition ratio of the rare earth-rich phase alloy powder is 12wt%, and the main phase alloy 88wt%; the composition of the alloy powder after mixing is: Nd _25.52 Dy _2.40 Tb _3.60 Co _1.24 Cu _0.24 Ga _0.24 Al _0.48 B _0.88 Fe (wt%), the mixed alloy powder is jet _milled under the Ar gas atmosphere , control the oxygen content in the mill room ≤ 10PPm, powder particle size 3.0μm;

5) Fill the uniformly mixed powder into the mold and apply 2.0T magnetic field orientation to press molding. After the green body is vacuum-packaged, put it into the press, pressurize at 220MPa, and press oil-cooled isostatically for 3 minutes;

6) The blank after isostatic pressing is sintered and aged under a vacuum condition of ≤4.0×10 ^-2 Pa, the sintering temperature is 1045°C, and the sintering time is 3.5h; aging process: 485°C×4h. After aging, a sintered NdFeB magnet was prepared. The magnet has high remanence and ultra-high coercive force, and its performance is shown in Table 6. The structure of the magnet is shown in Figure 1, the distribution of Dy is shown in Figure 2, and the distribution of Tb is shown in Figure 3.

Comparative example 6

1) Using conventional preparation methods, the composition is Nd _25.52 Dy _2.40 Tb _3.60 Co _1.24 Cu _0.24 Ga _0.24 Al _0.48 B _0.88 Fe (wt.%); _using conventional quick-setting technology: copper roller speed 1.2 ~ 1.5m/s, casting Temperature 1440℃～1460℃; cast sheet hydrogen broken, hydrogen broken powder O ₂ ≤800PPm, H ₂ ≤800PPm;

2) The hydrogen broken powder is jet milled to control the particle size of the fine powder to 3.0-3.5 μm;

3) Put the jet-milled powder into the mold, shape it in a 2.0T magnetic field, and vacuum-pack the formed green body. The packaged blank is oil-cooled and isostatically pressed at 200-250MPa for 1-3 minutes;

The isostatic pressing blank is sintered at 1045°C for 3.5h under the vacuum condition of ≤4.0×10 ^-2 Pa; the aging process is at 480°C for 4h. After aging, the sintered NdFeB magnet was prepared. The magnet properties are shown in Table 6.

Table 6 Magnet performance comparison table

As can be seen from the above comparison table, using the same material formula, the NdFeB magnets prepared by the method of the present invention have a remanence of 0.25kGs and a coercive force of Increased by 2.5kOe. With the conventional preparation method, since Dy and Tb heavy rare earth elements enter into the main phase more, if the coercive force of the magnet is increased by adding heavy rare earth, the remanence will be sacrificed; if the remanence is increased by increasing the proportion of the main phase , the coercive force level will drop. Therefore, for the formulation of this example, if a magnet with a coercive force level of 30.5kOe is to be prepared by a common method, the content of heavy rare earth Dy or Tb must be increased in the ingredients, and the increase of Dy or Tb will lead to remanence Decrease, the level of 12.85kGs cannot be reached, and it is impossible to make a magnet with both high remanence and high coercive force. The method of the invention can be used to prepare a magnet with high remanence and high coercive force and ultra-high magnetic performance.

Claims (10)

1. A high-performance sintered NdFeB magnet, characterized in comprising 85-97wt% main phase alloy RE _x Fe _surplus M _z B _y and 3-15wt% grain boundary rare earth-rich phase alloy RE _S N _J Fe _surplus , wherein: RE _x in the main phase alloy composition is one or two of light rare earth elements Nd and Pr, RE _x is 28 to 29 wt%, and M _z is one or one of the added metal elements Ga, Cu, Al, Co More than one species, M _z is 0.2-2wt%, B element _By is 0.95-1.02wt%, and the balance is Fe; RE _S in the grain boundary rare earth-rich phase alloy composition contains one or more of Nd, Dy, and Tb, and at least one or two of heavy rare earth elements Dy and Tb, and RE _S is 40 to 80 wt% , and the proportion of (Dy+Tb) is 15%~ _RES , N _J is one or more of the added metal elements Ga, Cu, Al, Co, Nb, Zr, N _J is 4~10 wt%, and the rest The amount is Fe. 2. A kind of high performance sintered NdFeB magnet according to claim 1, characterized in that the composition content of the high performance NdFeB magnet, Nd is 28.68wt%, Dy is 1.20wt%, Co is 1.16wt%, Cu is 0.16wt%, Al is 0.16wt%, Ga is 0.18wt%, B is 0.92wt%, and the balance is Fe. 3. a kind of high performance sintered NdFeB magnet according to claim 1 is characterized in that the composition content of high performance NdFeB magnet, Nd is 28.83 wt%, Dy is 1.00wt%, Co is 0.95wt%, Cu is 0.10wt%, Ga is 0.10wt%, Nb is 0.05wt%, B is 0.95wt%, and the balance is Fe. 4. A kind of high performance sintered NdFeB magnet according to claim 1, characterized in that the composition content of the high performance NdFeB magnet, Nd is 25.65 wt%, Dy is 2.50 wt%, Tb is 2.00 wt%, Co is 1.10 wt%, Cu is 0.20 wt%, Ga is 0.20 wt%, Al is 0.40 wt%, B is 0.95 wt%, and the balance is Fe. 5. A kind of high-performance sintered NdFeB magnet according to claim 1, characterized in that the composition content of the high-performance NdFeB magnet, Nd is 25.52 wt%, Dy is 2.40 wt%, Co is 1.14 wt%, Cu is 0.24 wt%, Ga is 0.24 wt%, Al is 0.48 wt%, B is 0.88 wt%, and the balance is Fe. 6. A method for preparing a high-performance sintered NdFeB magnet, comprising the following steps: 1) According to the composition ratio of the main phase alloy, the ingredients are weighed, put into a vacuum intermediate frequency melting furnace for melting, and the casting is cast by the quick-setting process. The main phase alloy casting sheet is obtained; the main phase alloy casting sheet is subjected to hydrogen crushing, and the oxygen content of the crushed powder is controlled to be ≤400PPm; 2) According to the composition ratio of rare earth-rich phase alloy at the grain boundary, the batching and weighing are carried out, put into the vacuum intermediate frequency melting furnace for melting, adopt the conventional quick-setting process to cast the sheet, set the copper roller speed to 1.2-1.5m/s, and the casting temperature to 1440 ℃～1450℃, to prepare the grain boundary rare earth-rich phase alloy cast piece; carry out hydrogen crushing on the grain boundary rare earth-rich alloy cast piece, and screen the powder with a particle size of ≤380μm in the hydrogen broken powder; 3) The grain boundary rare earth-rich phase alloy powder screened by hydrogen blasting is jet milled under an inert gas atmosphere, the oxygen content is controlled below 5 PPm, and the particle size of the fine powder after jet milling is controlled at 2.5-3.5 μm; 4) Mix the grain boundary rare earth-rich phase alloy fine powder and the main phase alloy hydrogen broken powder in proportion after jet milling, and the addition ratio of the grain boundary rare earth Jet milling is carried out under an inert gas atmosphere, and the oxygen content in the milling chamber is controlled to be ≤10 ppm, and the powder particle size is 2.8-3.0 μm; 5) Weigh the uniformly mixed powder, fill it into the forming mold, add a magnetic field ≥ 2.0T to orientate it, and press it into shape. After the green body is evacuated and packaged, put it into a press and pressurize it at 150-200Mpa, and keep the pressure for 1-3 minute; 6) Put the green body that has been kept under pressure into a vacuum sintering furnace with a vacuum degree of ≤4.0×10 ^-2 Pa, sinter at a temperature of 1020°C to 1060°C for 3.5 to 5.5 hours, and then sinter at a temperature of 450°C ~600°C for 4~6h aging treatment, take out the finished NdFeB magnet from the sintering furnace. 7. A method for preparing a high-performance sintered NdFeB magnet according to claim 6, characterized in that in step 1), the main phase alloy composition suppresses smelting by adding at least one of the elements Ga, Cu, Al, and Co In the generation of a-Fe. 8. A method for preparing a high-performance sintered NdFeB magnet according to claim 6, characterized in that in step 1), the speed of the copper roller is set to be 1.8m/s, and the casting temperature is 1420°C. 9. A method for preparing a high-performance sintered NdFeB magnet according to claim 6, characterized in that in step 2), the screening of the rare earth-rich phase hydrogen powder at the grain boundary is under the protection of an inert gas, and the O ₂ ≤ 10PPm, sieved through a 40-mesh sieve. 10. The method for preparing a high-performance sintered NdFeB magnet according to claim 6, characterized in that the sintering temperature in a vacuum furnace in step 6) is 1020°C-1040°C, and the sintering is 3.5-4.5 hours.