WO2024119566A1 - High-performance low-temperature-coefficient rare earth permanent magnet material and preparation method therefor - Google Patents

Abstract

The present invention relates to the technical field of rare earth permanent magnet materials. Disclosed are a high-performance low-temperature-coefficient rare earth permanent magnet material and a preparation method therefor. The material comprises a neodymium-iron-boron base material and a rare earth cobalt alloy, wherein in percentage by weight, the chemical general formula of the neodymium-iron-boron base material is (PriNdj)aLbCocCudMeBfFe100-a-b-c-d-e-f, and the chemical general formula of the rare earth cobalt alloy is RgXhCo100-g-h, wherein 25≤a≤30, 0≤b≤5, 3≤c≤8, 0.1≤d≤0.4, 0<e≤3, 0.9≤f≤1, and i:j=(23-28):(72-77); L is a rare earth element other than Pr and Nd; M is a combination of more than two of Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V and Mo; R is one or two of Dy and Tb, and 10≤g≤90; X is one or a combination of more than two of Cu, Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, Mo, and rare earth elements other than Dy and Tb, and 0＜h≤20. The rare earth permanent magnet material is obtained by grain boundary diffusion of the rare earth cobalt alloy by the neodymium-iron-boron base material having specific components, the heavy rare earth content and the cobalt content in a grain boundary phase are higher than those in a main phase, the heavy rare earth content and the cobalt content in a surface layer are higher than those inside a magnet, and the rare earth permanent magnet material has excellent high temperature stability.

Description

A high-performance, low-temperature-coefficient rare-earth permanent magnetic material and a preparation method thereof Technical Field

The present invention relates to the technical field of rare earth permanent magnet materials, in particular to a high-performance, low-temperature-coefficient rare earth permanent magnet material and a preparation method thereof, and more particularly to a high-remanence, low-temperature-coefficient, high-temperature-stability sintered NdFeB permanent magnet and a preparation method thereof.

Background technique

Rare earth permanent magnet materials are one of the fastest-growing functional materials in recent years. They are widely used in new energy vehicles, energy-saving home appliances, energy-saving elevators and new generation mobile communications. Since the industrialization of NdFeB magnets, people's research has mainly focused on improving the magnetic energy product and improving temperature stability. So far, considerable success has been achieved in improving the magnetic energy product. The theoretical limit of the magnetic energy product is 64MGOe. In 2006, the magnetic energy product of laboratory samples reached 59.6MGOe, and industrial products also exceeded 55MGOe. In recent years, with the rapid development of new energy vehicles and rail transportation, more and more power motors have adopted the design of rare earth permanent magnet motors, which not only reduces their own weight, but also improves the efficiency of the motor. In China, Germany, Japan, France and other high-speed rail countries, permanent magnet synchronous transmission systems have been applied to high-speed EMUs, subway cars and other fields. Most of them have completed the development of prototypes and the assessment of actual routes, and are gradually being applied in small batches in some occasions. However, this kind of power motor has higher requirements for the temperature stability of the magnet. Judging from current applications, most rail transit traction motors are designed with samarium cobalt magnets with a low temperature coefficient. However, samarium cobalt magnets have complex processing, high cost, are fragile, and have a low magnetic energy product. Therefore, high-performance, low-temperature coefficient sintered NdFeB magnets are one of the important research directions at present.

In order to reduce the temperature coefficient of NdFeB (the reduction here refers to the reduction of the absolute value of the temperature coefficient, the same below) and improve temperature stability, the following measures are generally taken: 1) M. Sagawa et al. added cobalt to replace iron to increase the Curie temperature. Matsuura, Mottram et al. found that replacing 1at.% of iron with cobalt will increase the Curie temperature of NdFeB magnets by about 10.9℃; but adding cobalt will reduce the intrinsic coercive force of the magnet, and NdFeB magnets with low intrinsic coercive force cannot be used at high operating temperatures. 2) Adding heavy rare earth elements such as Dy and Tb to increase the intrinsic coercive force, but Dy and Tb do not significantly improve the residual magnetic temperature coefficient, that is, the magnetic properties of permanent magnets at room temperature and high temperature are very different, causing the torque of permanent magnet motors to decrease at high temperatures, so the ultra-high intrinsic coercive force cannot meet the requirements of rail transit for the temperature stability of permanent magnets. 3) Other existing technologies, such as patent CN111640549, solve the problems of low operating temperature and poor temperature stability of sintered NdFeB magnets. By jointly adding heavy rare earth elements, cobalt elements and trace elements, the magnetic moment and microstructure of the material are effectively regulated, the grain boundary phase and grain boundary structure of the sintered rare earth permanent magnet material are optimized, and a cobalt-containing amorphous grain boundary phase is formed. A sintered rare earth permanent magnet material with high temperature stability is obtained, but the amount of heavy rare earth and cobalt used is high, the magnetic properties are low, the remanence is about 11.9 to 12.69 kGs, and the cost is high.

Summary of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and provide a high-performance, low-temperature coefficient rare earth permanent magnet material and a preparation method thereof. The rare earth permanent magnet material is obtained by grain boundary diffusion of a rare earth cobalt alloy with a specific composition of a neodymium iron boron substrate. The heavy rare earth content and cobalt content in the grain boundary phase are higher than those in the main phase, and the heavy rare earth content and cobalt content in the surface layer are higher than those in the magnet body, and the material has excellent high-temperature stability.

To achieve the purpose of the present invention, the high-performance low temperature coefficient rare earth permanent magnet material of the present invention comprises a neodymium iron boron substrate and a rare earth cobalt alloy, wherein the chemical formula of the neodymium iron boron substrate is (Pr _i Nd _j ) _a L _b Co _c Cu _{d Me} B _f Fe _100-abcdef by weight percentage, wherein 25≤a≤30, 0≤b≤5, 3≤c≤8, 0.1≤d≤0.4, 0<e≤3, 0.9≤f≤1, i:j＝23-28:72-77; L is a rare earth element other than Pr and Nd; M is a combination of two or more of Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, and Mo; the chemical formula of the rare earth cobalt alloy is R _g X _h Co _100-gh by weight percentage. , wherein R is one or two of Dy and Tb, 10≤g≤90; X is one or a combination of two or more of Cu, Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, Mo, and rare earth elements other than Dy and Tb, 0＜h≤20.

Furthermore, in some embodiments of the present invention, when b is 0, the rare earth cobalt alloy R _g X _h Co _100-gh contains Dy.

Furthermore, in some embodiments of the present invention, the maximum operating temperature of the high-performance, low-temperature-coefficient rare earth permanent magnet material is greater than 200°C.

Furthermore, in some embodiments of the present invention, the high-performance, low-temperature-coefficient rare earth permanent magnetic material is prepared by smelting, hydrogen crushing, air flow milling, magnetic field orientation molding, sintering, processing, and diffusion process steps.

On the other hand, the present invention also provides a method for preparing the above-mentioned high-performance low temperature coefficient rare earth permanent magnetic material, the method comprising the following steps:

(1) Raw material preparation: The weight percentage of the NdFeB substrate alloy (alloy 1) according to the general chemical formula is (Pr _i Nd _j ) _a L _b Co _c Cu _{d Me} B _f Fe _100-abcdef , wherein 25≤a≤30, 0≤b≤5, 3≤c≤8, 0.1≤d≤0.4, 0<e≤3, 0.9≤f≤1, i:j＝23-28:72-77; L is a rare earth element other than Pr and Nd; M is a combination of two or more of Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, and Mo;

The rare earth cobalt alloy (alloy 2) is prepared by raw materials according to the general chemical formula of R _g X _h Co _100-gh in weight percentage, wherein R is one or two of Dy and Tb, 10≤g≤90; X is one or a combination of two or more of Cu, Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, Mo, and rare earth elements other than Dy and Tb, 0＜h≤20;

(2) Preparing a quick-setting sheet: placing a NdFeB base alloy and a rare earth cobalt alloy into a crucible of a quick-setting furnace, respectively, and performing vacuum induction melting under the protection of an inert gas. After the raw materials are fully melted, the alloy liquid is poured onto a water-cooled rotating copper roller to prepare quick-setting sheets 1 and 2.

(3) Hydrogen crushing: The quick-setting sheet 1 and the quick-setting sheet 2 are crushed by a hydrogen crushing furnace to obtain millimeter-sized hydrogen-crushed medium powder 1 and hydrogen-crushed medium powder 2;

(4) Jet mill: Under nitrogen protection, the hydrogen-broken medium powder 1 and the hydrogen-broken medium powder 2 are ground into fine powder 1 and fine powder 2 respectively;

(5) Pressing: The fine powder 1 is oriented and pressed in a magnetic field press with a pressure of 1.5 T or more to obtain a NdFeB blank, which is then isostatically pressed to obtain a green blank;

(6) Sintering: Sintering the green compact obtained by pressing;

(7) Machining: Processing the blank into a magnet with dimensions close to the product specifications;

(8) Diffusion: The fine powder 2 is coated on the surface of the magnet, and then placed in a vacuum furnace for diffusion treatment, followed by tempering treatment to obtain a sintered NdFeB magnet block.

Furthermore, in some embodiments of the present invention, when b is 0, the rare earth cobalt alloy R _g X _h Co _100-gh contains Dy.

Furthermore, in some embodiments of the present invention, in step (2), after the raw materials are fully melted, the temperature is maintained at 1350-1550° C., and the alloy liquid is poured onto a water-cooled rotating copper roller.

Furthermore, in some embodiments of the present invention, the average thickness of the quick-setting sheet 1 and the quick-setting sheet 2 in step (2) is 0.2-0.4 mm.

Furthermore, in some embodiments of the present invention, the average particle size of the fine powder 1 and the fine powder 2 in step (3) is 2 to 4 μm.

Furthermore, in some embodiments of the present invention, the density of the green body in step (5) is 3.8-5 g/cm ³ .

Furthermore, in some embodiments of the present invention, the sintering in step (6) is carried out under vacuum conditions, the sintering temperature is 1040-1100° C., and the sintering time is 5-10 h.

Furthermore, in some embodiments of the present invention, a processing allowance of 0.05 to 0.5 mm is reserved in the orientation direction in step (7).

Furthermore, in some embodiments of the present invention, the coating weight in step (8) is 0.1-2% of the weight of the magnet.

Furthermore, in some embodiments of the present invention, the diffusion treatment in step (9) is performed in a vacuum furnace at 800-950° C. for 1-48 hours.

Furthermore, in some embodiments of the present invention, the tempering treatment in step (9) is performed at 400-650° C. for 2-10 hours.

Compared with the prior art, the advantages of the present invention are as follows:

(1) The high-performance, low-temperature-coefficient sintered rare earth permanent magnet material of the present invention is a NdFeB magnet having a (DyTb)-(CoFe)-B shell structure obtained by using a NdFeB substrate with a specific composition and diffusing a rare earth cobalt alloy at the grain boundaries. The magnet has the characteristics of high performance and low temperature coefficient.

(2) The remanence Br of the high-performance, low-temperature-coefficient sintered rare earth permanent magnet material of the present invention is ≥13 kGs, Hcj ≥20 kOe; the absolute value of the temperature coefficient at 20-200°C is ≤0.1%/°C, and the absolute value of the intrinsic coercive force temperature coefficient at 20-200°C is ≤0.5%/°C.

Detailed ways

In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Additional aspects and advantages of the present invention will be partially given in the following description, and part will become obvious from the following description, or be understood through the practice of the present invention. It should be understood that the following description is only used to explain the present invention and is not intended to limit the present invention.

As used herein, the terms "comprises," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

When amount, concentration or other value or parameter is represented with range, preferred range or the range limited by a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

Singular forms include plural references unless the context clearly indicates otherwise. "Optional" or "either" means that the subsequently described event or incident may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

Approximate terms in the specification and claims are used to modify quantities, indicating that the present invention is not limited to the specific quantity, but also includes acceptable and modified parts close to the quantity without causing changes in the relevant basic functions. Accordingly, the use of "about", "approximately", etc. to modify a numerical value means that the present invention is not limited to the exact numerical value. In some examples, the approximate terms may correspond to the accuracy of the instrument for measuring the numerical value. In the specification and claims of this application, range limitations can be combined and/or interchanged, and if not otherwise stated, these ranges include all subranges contained therein.

The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

In addition, the description of the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" described below means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

If not otherwise specified, the rapid solidification process in the embodiments of the present invention and the comparative examples is as follows: placing the alloy into a rapid solidification furnace crucible, performing vacuum induction melting under argon protection, and after the raw materials are fully melted, maintaining a temperature of 1350 to 1550° C., pouring the alloy liquid onto a water-cooled rotating copper roller to obtain a rapid solidification sheet with an average thickness of 0.2 to 0.4 mm.

The hydrogen crushing process is: the quick-setting sheet is crushed in a hydrogen crushing furnace to obtain millimeter-level hydrogen-crushed medium powder.

The jet milling process is as follows: under nitrogen protection, the hydrogen-degradable powder is ground into fine powder with an average particle size of 2 to 4 μm.

The pressing process is: the fine powder is oriented and pressed in a magnetic field press above 1.5T to obtain a NdFeB blank, which is then isostatically pressed to obtain a green billet with a density of 3.8 to 5g/ ^cm3 .

The sintering process is as follows: the green body obtained by pressing is sintered under vacuum conditions, the sintering temperature is 1040-1100° C., and the sintering time is 5-10 hours.

As long as the above process is carried out within the above process parameter range, the required qualified product can be obtained. For example, in the quick-setting process, after the raw materials are fully melted, the temperature range of 1350-1550°C can be maintained. There is no special requirement for the specific temperature. The thickness of the quick-setting sheet can be 0.2-0.4mm, which will not affect the quality of the products obtained in the subsequent processes.

Example 1

The high-performance, low-temperature-coefficient rare earth permanent magnetic materials are prepared by the following material selection and method:

(1) The weight percentage of the NdFeB substrate alloy 1 is (Pr ₂₅ Nd ₇₅ ) ₂₉ Dy _0.5 Co ₅ Cu _0.2 Al _0.2 Zr _0.1 B _0.98 Fe _64.02 , and the NdFeB blank is prepared by rapid solidification, hydrogen crushing, air flow grinding, pressing and sintering processes;

(2) Alloy 2, with a weight percentage of Tb ₆₀ Cu ₅ Co ₃₅ , was prepared by rapid solidification, hydrogen crushing, and air flow grinding to obtain fine powder A;

(3) Processing the NdFeB blank into a square piece of 20 mm × 20 mm × 5 mm;

(4) Diffusion: Fine powder A is coated on the surface of the square piece. The coating amount of fine powder A is 0.8% of the weight of the magnet. Diffusion is carried out at 900°C for 20 hours; and tempering is carried out at 510°C for 4 hours.

Comparative Example 1

The difference from Example 1 is that fine powder A is not applied and diffusion treatment is not performed. Other aspects are the same as Example 1.

Comparative Example 2

The difference from Example 1 is that the weight percentage of the NdFeB base alloy 1 is (Pr ₂₅ Nd ₇₅ ) ₂₉ Dy _0.5 Tb _0.48 Co _5.28 Cu _0.2 Al _0.2 Zr _0.1 B _0.98 Fe _63.26 , the fine powder A is not coated, the diffusion treatment is not performed, and the other parts are the same.

Example 1.

Comparative Example 3

The difference from Example 1 is that 0.48% pure Tb is coated, and the rest is the same as Example 1.

Comparative Example 4

The difference from Example 1 is that the weight percentage of the NdFeB base alloy 1 is (Pr ₂₅ Nd ₇₅ ) ₂₉ Dy _0.5 Tb _0.5 Co ₁₀ Cu _0.2 Al _0.2 Zr _0.1 B _0.98 Fe _58.52 diffusion fine powder A, and the rest is the same as Example 1;

Comparative Example 5

The difference from Example 1 is that the weight percentage of the NdFeB base alloy 1 is (Pr ₂₅ Nd ₇₅ ) ₂₆ Dy ₆ Tb _0.5 Co ₅ Cu _0.2 Al _0.2 Zr _0.1 B _0.98 Fe _61.02 diffusion fine powder A, and the rest is the same as Example 1;

Example 2

The high-performance, low-temperature-coefficient rare earth permanent magnetic materials are prepared by the following material selection and method:

(1) Alloy 1 has a weight percentage of (Pr ₂₅ Nd ₇₅ ) _29.5 Co ₈ Cu _0.2 Al _0.2 Zr _0.1 B _0.98 Fe _61.02 , and is prepared by rapid solidification, hydrogen crushing, jet milling, pressing and sintering to obtain a NdFeB blank;

(2) Alloy 2 is composed of Dy ₇₀ Cu ₈ Co ₂₂ by weight, and fine powder B is obtained by rapid solidification, hydrogen pulverization, and air flow grinding;

(3) Processing the NdFeB blank into a square piece of 20 mm × 20 mm × 5 mm;

(4) Diffusion: Apply fine powder B on the surface of the square piece. The coating amount of fine powder B is 1.2% of the weight of the magnet. Diffusion is carried out at 900°C for 30 hours; and tempering is carried out at 510°C for 4 hours.

The magnetic properties of the sintered rare earth permanent magnet materials obtained in the above examples and comparative examples are shown in Table 1.

Table 1 Comparison of magnetic properties of materials obtained in Examples and Comparative Examples

As shown in Table 1, the material obtained in Example 1 has excellent comprehensive magnetic properties, with a remanence of more than 14 kGs, a temperature coefficient of less than 0.1%/°C, and an intrinsic coercive force of more than 7 kOe at 200°C. It can be determined that the magnet is a high-performance, low-temperature-coefficient, and high-stability sintered NdFeB magnet that can be used at 200°C.

Comparative Example 1 is that the substrate of Example 1 has not been subjected to coating and diffusion treatment, and the intrinsic coercivity and temperature coefficient of the magnet are far inferior to those of Example 1; Comparative Example 2 also does not undergo coating and diffusion treatment, but adds the alloy elements that are coated and diffused into the magnet into the magnet during the smelting process, and the composition of the final magnet is similar to that of Example 1, but the temperature coefficient and high-temperature stability are far different; Comparative Example 3 is a pure terbium diffusion scheme, and the temperature coefficient is not as good as that of Example 1; Comparative Example 4 shows that when the cobalt content of the magnet is high, the intrinsic coercivity of the magnet will be reduced, and the low intrinsic coercivity cannot meet the requirements of high operating temperature, and will increase the cost; Comparative Example 5 shows that when the heavy rare earth content is high, the intrinsic coercivity of the magnet is improved, but the remanence of the magnet is significantly reduced, the cost is greatly increased, and the high-temperature stability of the magnet is not significantly improved. Example 2 shows that when the operating temperature requirement is low, diffusion of dysprosium alloy is also a good choice, and the cost can be reduced.

Through the above comparison, we found that cobalt can reduce the remanent magnetism temperature coefficient of the magnet, but the higher the better. When it exceeds 8%, the intrinsic coercivity of the magnet is reduced too much, and more heavy rare earth is needed to compensate for the reduction of the intrinsic coercivity, which increases the cost, reduces the remanence, and does not significantly improve the high-temperature stability. Compared with the traditional diffusion technology, the diffusion effect of grain boundary diffusion cobalt alloy is better. Through the grain boundary diffusion cobalt alloy technology, a layer of (DyTb)-(CoFe)-B shell structure is formed on the grain boundary and grain surface of the magnet, thereby obtaining a high-performance low temperature coefficient rare earth permanent magnet material, and the magnet has excellent high temperature stability. Based on this, it can be seen that high-performance sintered NdFeB magnets with low temperature coefficient and high temperature stability can be obtained with lower heavy rare earth and cobalt, and the utilization efficiency of cobalt and heavy rare earth can be improved, which has broad application prospects.

It will be easily understood by those skilled in the art that the above descriptions are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A high-performance, low-temperature-coefficient rare-earth permanent magnetic material, characterized in that the high-performance, low-temperature-coefficient rare-earth permanent magnetic material comprises a neodymium iron boron substrate and a rare-earth cobalt alloy, wherein the chemical formula of the neodymium iron boron substrate is (Pr _i Nd _j ) _a L _b Co _c Cu _{d Me} B _f Fe _100-abcdef by weight percentage, wherein 25≤a≤30, 0≤b≤5, 3≤c≤8, 0.1≤d≤0.4, 0<e≤3, 0.9≤f≤1, i:j＝23-28:72-77; L is a rare earth element other than Pr and Nd; M is a combination of two or more of Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, and Mo; the chemical formula of the rare-earth cobalt alloy is R _g X _h Co _100-gh by weight percentage. , wherein R is one or two of Dy and Tb, 10≤g≤90; X is one or a combination of two or more of Cu, Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, Mo, and rare earth elements other than Dy and Tb, 0＜h≤20.
2. The high-performance, low-temperature-coefficient rare-earth permanent magnetic material according to claim 1, characterized in that when b is 0, the rare-earth cobalt alloy R _g X _h Co _100-gh contains Dy.
3. The high-performance, low-temperature-coefficient rare earth permanent magnetic material according to claim 1 is characterized in that the maximum operating temperature of the high-performance, low-temperature-coefficient rare earth permanent magnetic material is greater than 200°C.
4. The high-performance, low-temperature-coefficient rare earth permanent magnetic material according to claim 1 is characterized in that the high-performance, low-temperature-coefficient rare earth permanent magnetic material is prepared by smelting, hydrogen crushing, air flow milling, magnetic field orientation molding, sintering, processing, and diffusion process steps.
5. The method for preparing the high-performance, low-temperature-coefficient rare earth permanent magnetic material according to any one of claims 1 to 4 is characterized in that the method comprises the following steps:

   (1) Raw material preparation: The weight percentage of the NdFeB substrate alloy according to the general chemical formula is (Pr _i Nd _j ) _a L _b Co _c Cu _{d Me} B _f Fe _100-abcdef , wherein 25≤a≤30, 0≤b≤5, 3≤c≤8, 0.1≤d≤0.4, 0<e≤3, 0.9≤f≤1, i:j＝23-28:72-77; L is a rare earth element other than Pr and Nd; M is a combination of two or more of Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, and Mo;

   The rare earth cobalt alloy is prepared according to the chemical formula R _g X _h Co _100-gh by weight, wherein R is one or two of Dy and Tb, 10≤g≤90; X is one or a combination of two or more of Cu, Al, Cr, Nb, Zr, Ga, Ti, Mn, Zn, V, Mo, and rare earth elements other than Dy and Tb, 0＜h≤20;

   (2) Preparing a quick-setting sheet: placing a NdFeB base alloy and a rare earth cobalt alloy into a crucible of a quick-setting furnace, respectively, and performing vacuum induction melting under the protection of an inert gas. After the raw materials are fully melted, the alloy liquid is poured onto a water-cooled rotating copper roller to prepare quick-setting sheets 1 and 2.

   (3) Hydrogen crushing: The quick-setting sheet 1 and the quick-setting sheet 2 are crushed by a hydrogen crushing furnace to obtain millimeter-sized hydrogen-crushed medium powder 1 and hydrogen-crushed medium powder 2;

   (4) Jet mill: Under nitrogen protection, the hydrogen-broken medium powder 1 and the hydrogen-broken medium powder 2 are ground into fine powder 1 and fine powder 2 respectively;

   (5) Pressing: The fine powder 1 is oriented and pressed in a magnetic field press with a pressure of 1.5 T or more to obtain a NdFeB blank, which is then isostatically pressed to obtain a green blank;

   (6) Sintering: Sintering the green compact obtained by pressing;

   (7) Machining: Processing the blank into a magnet with dimensions close to the product specifications;

   (8) Diffusion: The fine powder 2 is coated on the surface of the magnet, and then placed in a vacuum furnace for diffusion treatment, followed by tempering treatment to obtain a sintered NdFeB magnet block.
6. The method for preparing a high-performance, low-temperature-coefficient rare earth permanent magnetic material according to claim 5, characterized in that when b is 0, the rare earth cobalt alloy R _g X _h Co _100-gh contains Dy.
7. The method for preparing a high-performance, low-temperature-coefficient rare earth permanent magnetic material according to claim 5 is characterized in that, in the step (2), after the raw materials are fully melted, the temperature is maintained at 1350-1550° C., and the alloy liquid is poured onto a water-cooled rotating copper roller; preferably, in the step (2), the average thickness of the quick-setting sheet 1 and the quick-setting sheet 2 is 0.2-0.4 mm; preferably, in the step (3), the average particle size of the fine powder 1 and the fine powder 2 is 2-4 μm.
8. The method for preparing a high-performance, low-temperature-coefficient rare earth permanent magnetic material according to claim 5 is characterized in that the density of the green body in step (5) is 3.8-5 g/cm ³ ; preferably, the sintering in step (6) is carried out under vacuum conditions, the sintering temperature is 1040-1100° C., and the sintering time is 5-10 h.
9. The method for preparing a high-performance, low-temperature-coefficient rare earth permanent magnetic material according to claim 5 is characterized in that a processing allowance of 0.05 to 0.5 mm is reserved in the orientation direction in step (7); preferably, the coating weight in step (8) is 0.1 to 2% of the weight of the magnet.
10. The method for preparing a high-performance, low-temperature-coefficient rare earth permanent magnetic material according to claim 5 is characterized in that, in step (9), diffusion treatment is performed in a vacuum furnace at 800-950° C. for 1-48 hours; preferably, in step (9), tempering treatment is performed at 400-650° C. for 2-10 hours.