Preparation method of heavy-rare-earth-free high-coercivity neodymium iron boron

Abstract

The invention relates to the technical field of magnetic materials, in particular to a preparation method of heavy-rare-earth-free high-coercivity neodymium iron boron. The preparation method of the heavy-rare-earth-free high-coercivity neodymium iron boron comprises the following steps: preparing a main-phase alloy rapid-hardening sheet and an auxiliary-phase alloy steel ingot, mixing, then carrying out hydrogen decrepitation treatment, adding an antioxidant and a lubricant, carrying out airflow grinding to obtain fine powder, and then carrying out magnetic field forming, isostatic cool pressing, vacuum sintering and segmented tempering treatment, thereby obtaining the heavy-rare-earth-free high-coercivity neodymium iron boron. The magnet is composed of a main phase alloy and an auxiliary phase alloy, and the main phase alloy is composed of, by mass, 30.5 wt.% of Pr25Nd75, 0.91 wt.% of B, 0.4 wt.% of Al, 0.25 wt.% of Zr, 0.7 wt.% of Co, 0.35 wt.% of Cu, 0.5 wt.% of Ga and the balance Fe; the auxiliary phase alloy is prepared from the following components in percentage by mass: 18 to 23 wt.% of Cu, 23 to 26 wt.% of Ga, 4 to 6 wt.% of Mo, 0.5 to 0.8 wt.% of Ag and the balance of Nd; the neodymium iron boron prepared by the method has the magnet performance of high coercive force and high residual magnetism, and the quality and the performance of the neodymium iron boron are effectively ensured.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, specifically to a method for preparing heavy rare earth-free, high-coercivity neodymium iron boron. Background Technology

[0002] Neodymium magnets, also known as neodymium iron boron magnets, are tetragonal crystals composed of neodymium, iron, and boron. These magnets have a higher magnetic energy product than samarium cobalt magnets. They are currently the second strongest permanent magnets after holmium magnets at absolute zero, and are the most commonly used rare-earth magnets. Neodymium iron boron magnets are widely used in electronic products such as hard drives, mobile phones, headphones, and battery-powered tools.

[0003] Currently, the high coercivity NdFeB magnets prepared using traditional sintering processes often require the addition of heavy rare earth elements Dy and Tb. However, Dy and Tb are low in content in the Earth's crust, are key strategic elements, and are very expensive, which cannot meet the current production capacity demand. Without the addition of Dy and Tb, the magnets have lower coercivity, which is difficult to meet the requirements for high-performance magnets.

[0004] Therefore, the present invention provides a method for preparing heavy rare earth-free high coercivity neodymium iron boron to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing heavy rare earth-free high coercivity neodymium iron boron. The prepared neodymium iron boron has high coercivity and high remanence, effectively ensuring its quality and performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing heavy rare earth-free, high-coercivity neodymium iron boron includes the following steps: Step 1: Preparation of the main phase alloy: The main phase alloy is prepared according to its composition and added to a vacuum rapid solidification sintering furnace. It is first melted at 1400-1500℃, and then cast and cooled by copper rollers to obtain rapid solidification sheets. The thickness of the rapid solidification sheets is 0.1-0.45mm. Step 2: Preparation of secondary phase alloy: The raw materials are batched according to the composition of the secondary phase alloy. After batching, the raw materials are added to a vacuum melting furnace and melted and cast at a temperature of 950-1050℃ to obtain secondary phase alloy steel ingots. Step 3, Powdering: The rapidly solidified flakes are mixed with the secondary phase alloy steel ingot. The resulting mixture is fed into a hydrogen crushing furnace for hydrogen crushing. After hydrogen crushing is completed, antioxidants and lubricants are added to the resulting coarse powder. After uniform mixing, the resulting coarse powder is processed by an air jet mill to produce fine powder. The proportion of the secondary phase alloy steel ingot in the mixture is 3-6 wt.%. Step 4, Magnetic Field Molding: The fine mixed powder obtained in Step 3 is placed in a magnetic field press and pressed into shape in an environment with an oxygen content of less than 100 ppm to obtain a pressed blank. Step 5, Cold Isostatic Pressing: The obtained compact is placed in a cold isostatic pressing equipment under vacuum sealing and subjected to a second pressing at a pressure of 150-280MPa, which increases the density of the compact by 8-18% to obtain an isostatic compact. Step 6, Sintering: The isostatic pressing blank obtained in step 5 is transferred into a vacuum sintering furnace. After sintering and tempering, heavy rare earth-free high coercivity NdFeB is obtained.

[0007] Furthermore, the main phase alloy is composed of the following components by mass percentage: 30.5 wt.% Pr25Nd75, 0.91 wt.% B, 0.4 wt.% Al, 0.25 wt.% Zr, 0.7 wt.% Co, 0.35 wt.% Cu, 0.5 wt.% Ga, with the balance being Fe.

[0008] Furthermore, the secondary phase alloy is composed of the following mass percentage components: 18-23 wt.% Cu, 23-26 wt.% Ga, 4-6 wt.% Mo, 0.5-0.8 wt.% Ag, with the balance being Nd.

[0009] Furthermore, the amount of antioxidant used is 0.08-0.15 wt.% of the hydrogen-crushed coarse powder; the antioxidant is any one of tert-butylhydroquinone, 4-hexylresorcinol, butylated hydroxytoluene, and antimony dialkyldithiocarbamate.

[0010] Furthermore, the amount of the lubricant used is 0.06-0.1 wt.% of the hydrogen-crushed coarse powder; and the lubricant is selected from any one of oxidized polyethylene wax, butyl oleate, zinc stearate, and sodium stearate.

[0011] Furthermore, the magnetic induction intensity during the magnetic field forming is 1.8-2.3T, and the forming pressure is set to 3-6MPa.

[0012] Furthermore, the hydrogen dehydrogenation process includes hydrogen absorption treatment, a first dehydrogenation treatment, and a second dehydrogenation treatment. The hydrogen absorption treatment is carried out at a temperature of 330-360℃ for 45-60 minutes. The first dehydrogenation treatment is carried out at a temperature of 435-465℃ for 2-3 hours. The second dehydrogenation treatment is carried out at a temperature of 570-590℃ for 6-8 hours.

[0013] Furthermore, the sintering includes a first sintering and a second sintering; the conditions for the first sintering include: a vacuum degree of less than 5 × 10⁻⁶. -2 The conditions for the second sintering include: a vacuum degree of less than 5 × 10⁻⁶ Pa, a temperature of 1020-1050℃, and a holding time of 2-4 hours;-2 Pa, temperature 1060-1100℃, heat preservation time 8-10h.

[0014] Furthermore, the tempering process includes a first-stage tempering and a second-stage tempering; the conditions for the first-stage tempering are: vacuum degree less than 5 Pa, temperature 890-920℃, and time 3-5 h; the conditions for the second-stage tempering are: vacuum degree less than 8 Pa, temperature 490-520℃, and time 5-7 h.

[0015] Furthermore, the grinding pressure of the air jet mill is 5.9-6.1 MPa, and the powder output speed is 130-160 kg / h; the average particle size of the fine mixed powder obtained after air jet milling is 1-4 μm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: The high coercivity magnet prepared by this invention still exhibits high coercivity and remanence without using heavy rare earth elements Dy and Tb, reaching the highest level of mass-producible magnets currently available. Traditional magnets achieve high coercivity mainly by adding heavy rare earth elements Dy and Tb to form hard magnetic (Nd,Tb)₂Fe around the main phase grains. 14 The B-shell layer is prone to problems such as uneven shell structure and poor grain boundary phase distribution during sintering, which greatly wastes heavy rare earth resources. The reason why high coercivity can be achieved in heavy rare earth-free magnets is mainly due to the preparation of NdFeB powder with an average particle size of 2-4 μm through process control. In the subsequent sintering process, the synergistic effect of elements such as B, Ga, and Cu forms a thin and continuous nonferromagnetic RE6Fe. 13 The formation of the M grain boundary phase, a thin non-ferromagnetic grain boundary phase, is beneficial for isolating the main phase grains and reducing the magnetic coupling between the main phase grains, thereby improving the coercivity. In addition, the addition of Al element is beneficial for further improving the coercivity.

[0017] The secondary phase alloy of this invention contains Cu, Ga, Mo, Ag, and Nd elements. These elements effectively promote the wetting and diffusion of the grain boundary phase during sintering, contributing to the formation of a thin and continuous non-ferromagnetic grain boundary layer. This better isolates the main phase grains, reduces magnetic coupling effects, and enhances coercivity. Secondly, Mo and Ag elements refine the grain boundary structure and inhibit abnormal grain growth, further improving the microstructure uniformity and thermal stability of the magnet. Furthermore, the addition of the secondary phase alloy optimizes the composition and distribution of the grain boundary phase without significantly affecting the magnetic properties of the main phase. This overcomes the limitations of relying solely on the main phase alloy for adjustment, enabling the magnet to achieve a significant improvement in coercivity while maintaining high remanence. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 A method for preparing heavy rare earth-free, high-coercivity neodymium iron boron includes the following steps: Step 1: Preparation of the main phase alloy: The main phase alloy is prepared according to its composition and added to a vacuum rapid solidification flake furnace. It is first melted at 1400℃, and then cast and cooled by copper rollers to obtain rapid solidification flakes with a thickness of 0.1 mm. The main phase alloy is composed of the following components by mass percentage: 30.5 wt.% Pr25Nd75, 0.91 wt.% B, 0.4 wt.% Al, 0.25 wt.% Zr, 0.7 wt.% Co, 0.35 wt.% Cu, 0.5 wt.% Ga, with the balance being Fe. Step 2: Preparation of the secondary phase alloy: The raw materials are batched according to the composition of the secondary phase alloy. After batching, the raw materials are added to a vacuum melting furnace and melted at 950℃. After casting, a secondary phase alloy steel ingot is obtained. The secondary phase alloy consists of the following mass percentage components: 18-23 wt.% Cu, 23-26 wt.% Ga, 4-6 wt.% Mo, 0.5-0.8 wt.% Ag, with the balance being Nd. Step 3, Powdering: The rapidly solidified flakes are mixed with the secondary phase alloy steel ingot. The resulting mixture is fed into a hydrogen crushing furnace for hydrogen crushing. After hydrogen crushing is complete, antioxidants and lubricants are added to the resulting coarse powder. After uniform mixing, the resulting coarse powder is processed by an air jet mill to produce fine powder. The proportion of secondary phase alloy steel ingot in the mixture is 3 wt.%. The hydrogen decomposition process includes hydrogen absorption treatment, first dehydrogenation treatment, and second dehydrogenation treatment. The temperature of the hydrogen absorption treatment is 330℃, and the holding time is 60 min. The temperature of the first dehydrogenation treatment is 435℃, and the holding time is 3 h. The temperature of the second dehydrogenation treatment is 570℃, and the holding time is 8 h. The grinding pressure of the air jet mill was 5.9 MPa, and the powder output speed was 130 kg / h; the average particle size of the fine mixed powder obtained after air jet milling was 1 μm. The amount of antioxidant used is 0.08 wt.% of the hydrogen-crushed coarse powder; the antioxidant is tert-butylhydroquinone. The amount of lubricant used is 0.06 wt.% of the hydrogen-crushed coarse powder; and the lubricant used is oxidized polyethylene wax. Step 4, Magnetic Field Molding: The fine mixed powder obtained in Step 3 is placed in a magnetic field press and pressed into shape in an environment with an oxygen content of less than 100 ppm to obtain a compact; wherein, the magnetic induction intensity during magnetic field molding is 1.8T and the molding pressure is set to 3MPa. Step 5, Cold Isostatic Pressing: The obtained compact is placed in a cold isostatic pressing equipment under vacuum sealing and subjected to a second pressing at a pressure of 150 MPa, thereby increasing the compact density by 8% to obtain an isostatic compact. Step 6, Sintering: The isostatic pressing billet obtained in step 5 is transferred into a vacuum sintering furnace. After sintering and tempering, heavy rare earth-free high coercivity NdFeB is obtained. The sintering process includes a first sintering and a second sintering; the conditions for the first sintering include: a vacuum degree of less than 5 × 10⁻⁶. - 2 The conditions for the second sintering include: a vacuum degree of less than 5 × 10⁻⁶ Pa, a temperature of 1020℃, and a holding time of 4 hours; -2 Pa, temperature is 1060℃, heat preservation time is 10h; The tempering process includes a first-stage tempering and a second-stage tempering. The conditions for the first-stage tempering are: vacuum degree less than 5 Pa, temperature 890℃, and time 5 h. The conditions for the second-stage tempering are: vacuum degree less than 8 Pa, temperature 490℃, and time 7 h.

[0020] Example 2 A method for preparing heavy rare earth-free, high-coercivity neodymium iron boron includes the following steps: Step 1: Preparation of the main phase alloy: The main phase alloy is prepared according to its composition and added to a vacuum rapid solidification flake furnace. It is first melted at 1450℃, and then cast and cooled by copper rollers to obtain rapid solidification flakes with a thickness of 0.3 mm. The main phase alloy is composed of the following components by mass percentage: 30.5 wt.% Pr25Nd75, 0.91 wt.% B, 0.4 wt.% Al, 0.25 wt.% Zr, 0.7 wt.% Co, 0.35 wt.% Cu, 0.5 wt.% Ga, with the balance being Fe. Step 2: Preparation of the secondary phase alloy: The raw materials are batched according to the composition of the secondary phase alloy. After batching, the raw materials are added to a vacuum melting furnace and melted and cast at a temperature of 1000℃ to obtain a secondary phase alloy steel ingot. The secondary phase alloy is composed of the following mass percentage components: 20wt.%Cu, 25wt.%Ga, 5wt.%Mo, 0.6wt.%Ag, with the balance being Nd. Step 3, Powdering: The rapidly solidified flakes are mixed with the secondary phase alloy steel ingot. The resulting mixture is fed into a hydrogen crushing furnace for hydrogen crushing. After hydrogen crushing is complete, antioxidants and lubricants are added to the resulting coarse powder. After uniform mixing, the resulting coarse powder is processed by an air jet mill to produce fine powder. The proportion of secondary phase alloy steel ingot in the mixture is 5 wt.%. The hydrogen decomposition process includes hydrogen absorption treatment, first dehydrogenation treatment, and second dehydrogenation treatment. The temperature of the hydrogen absorption treatment is 350℃, and the holding time is 50 min. The temperature of the first dehydrogenation treatment is 455℃, and the holding time is 3 h. The temperature of the second dehydrogenation treatment is 580℃, and the holding time is 7 h. The grinding pressure of the air jet mill is 6.0 MPa, and the powder output speed is 150 kg / h; the average particle size of the fine mixed powder obtained after air jet milling is 2 μm. The amount of antioxidant used is 0.1 wt.% of the hydrogen-crushed coarse powder; the antioxidant is 4-hexylresorcinol. The amount of lubricant used is 0.08 wt.% of the hydrogen-crushed coarse powder; and the lubricant used is butyl oleate. Step 4, Magnetic Field Molding: The fine mixed powder obtained in Step 3 is placed in a magnetic field press and pressed into shape in an environment with an oxygen content of less than 100 ppm to obtain a compact; wherein, the magnetic induction intensity during magnetic field molding is 2.0T and the molding pressure is set to 5MPa. Step 5, Cold Isostatic Pressing: The obtained compact is placed in a cold isostatic pressing equipment under vacuum sealing and subjected to a second pressing at a pressure of 200 MPa, which increases the density of the compact by 12% to obtain an isostatic compact. Step 6, Sintering: The isostatic pressing billet obtained in step 5 is transferred into a vacuum sintering furnace. After sintering and tempering, heavy rare earth-free high coercivity NdFeB is obtained. The sintering process includes a first sintering and a second sintering; the conditions for the first sintering include: a vacuum degree of less than 5 × 10⁻⁶. - 2 The conditions for the second sintering include: a vacuum degree of less than 5 × 10⁻⁶ Pa, a temperature of 1030 °C, and a holding time of 4 h; -2 Pa, temperature 1080℃, heat preservation time 9h; The tempering process includes a first-stage tempering and a second-stage tempering. The conditions for the first-stage tempering are: vacuum degree less than 5 Pa, temperature 900℃, and time 4 h. The conditions for the second-stage tempering are: vacuum degree less than 8 Pa, temperature 500℃, and time 6 h.

[0021] Example 3 A method for preparing heavy rare earth-free, high-coercivity neodymium iron boron includes the following steps: Step 1: Preparation of the main phase alloy: The main phase alloy is prepared according to its composition and added to a vacuum rapid solidification flake furnace. It is first melted at 1500℃, and then cast and cooled by copper rollers to obtain rapid solidification flakes with a thickness of 0.45 mm. The main phase alloy is composed of the following components by mass percentage: 30.5 wt.% Pr25Nd75, 0.91 wt.% B, 0.4 wt.% Al, 0.25 wt.% Zr, 0.7 wt.% Co, 0.35 wt.% Cu, 0.5 wt.% Ga, with the balance being Fe. Step 2: Preparation of the secondary phase alloy: The raw materials are batched according to the composition of the secondary phase alloy. After batching, the raw materials are added to a vacuum melting furnace and melted and cast at a temperature of 1050℃ to obtain a secondary phase alloy steel ingot. The secondary phase alloy is composed of the following mass percentage components: 23wt.%Cu, 26wt.%Ga, 6wt.%Mo, 0.8wt.%Ag, with the balance being Nd. Step 3, Powdering: The rapidly solidified flakes are mixed with the secondary phase alloy steel ingot. The resulting mixture is fed into a hydrogen crushing furnace for hydrogen crushing. After hydrogen crushing is complete, antioxidants and lubricants are added to the resulting coarse powder. After uniform mixing, the resulting coarse powder is processed by an air jet mill to produce fine powder. The proportion of secondary phase alloy steel ingot in the mixture is 6 wt.%. The hydrogen decomposition process includes hydrogen absorption treatment, a first dehydrogenation treatment, and a second dehydrogenation treatment. The hydrogen absorption treatment is performed at a temperature of 360°C for 45 minutes; the first dehydrogenation treatment is performed at a temperature of 465°C for 2 hours; and the second dehydrogenation treatment is performed at a temperature of 590°C for 6 hours. The grinding pressure of the air jet mill was 6.1 MPa, and the powder output speed was 160 kg / h; the average particle size of the fine mixed powder obtained after air jet milling was 4 μm. The amount of antioxidant used is 0.15 wt.% of the hydrogen-crushed coarse powder; the antioxidant is butylated hydroxytoluene. The amount of lubricant used is 0.1 wt.% of the hydrogen-crushed coarse powder; and the lubricant used is zinc stearate. Step 4, Magnetic Field Molding: The fine mixed powder obtained in Step 3 is placed in a magnetic field press and pressed into shape in an environment with an oxygen content of less than 100 ppm to obtain a compact; wherein, the magnetic induction intensity during magnetic field molding is 2.3T and the molding pressure is set to 6 MPa. Step 5, Cold Isostatic Pressing: The obtained compact is placed in a cold isostatic pressing equipment under vacuum sealing and subjected to a second pressing at a pressure of 280MPa, which increases the density of the compact by 18% to obtain an isostatic compact. Step 6, Sintering: The isostatic pressing billet obtained in step 5 is transferred into a vacuum sintering furnace. After sintering and tempering, heavy rare earth-free high coercivity NdFeB is obtained. The sintering process includes a first sintering and a second sintering; the conditions for the first sintering include: a vacuum degree of less than 5 × 10⁻⁶. - 2 The conditions for the second sintering include: a vacuum degree of less than 5 × 10⁻⁶ Pa, a temperature of 1050℃, and a holding time of 2 hours; -2 Pa, temperature is 1100℃, heat preservation time is 8h; The tempering process includes a first-stage tempering and a second-stage tempering. The conditions for the first-stage tempering are: vacuum degree less than 5 Pa, temperature 920℃, and time 3 h. The conditions for the second-stage tempering are: vacuum degree less than 8 Pa, temperature 520℃, and time 5 h.

[0022] Comparative Example 1: The difference from Example 1 is that no secondary phase alloy was used in the preparation of heavy rare earth-free high coercivity NdFeB in this comparative example.

[0023] Comparative Example 2: The difference from Example 1 is that the neodymium iron boron magnet prepared in Example 4 of the invention patent with application number "CN202411572827.X" and title "A method for preparing a high coercivity and high thickness neodymium iron boron magnet".

[0024] Comparative Example 3: The difference from Example 1 is that the main phase alloy used in the preparation of heavy rare earth-free high coercivity NdFeB in this comparative example does not contain Al.

[0025] Performance Testing: The NdFeB samples prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to relevant performance tests according to GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials", and the test data are recorded in the table below: By comparing and analyzing the relevant data in the table, it can be seen that the NdFeB prepared by this invention possesses high coercivity and high remanence, effectively ensuring its quality and performance. This indicates that the method for preparing heavy rare-earth-free, high-coercivity NdFeB provided by this invention has a broader market prospect and is more suitable for widespread application.

[0026] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0027] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing heavy rare earth-free, high-coercivity neodymium iron boron, characterized in that, Includes the following steps: Step 1: Preparation of the main phase alloy: The main phase alloy is prepared according to its composition and added to a vacuum rapid solidification sintering furnace. It is first melted at 1400-1500℃, and then cast and cooled by copper rollers to obtain rapid solidification sheets. The thickness of the rapid solidification sheets is 0.1-0.45mm. Step 2: Preparation of secondary phase alloy: The raw materials are batched according to the composition of the secondary phase alloy. After batching, the raw materials are added to a vacuum melting furnace and melted and cast at a temperature of 950-1050℃ to obtain secondary phase alloy steel ingots. Step 3, Powdering: The rapidly solidified flakes are mixed with the secondary phase alloy steel ingot. The resulting mixture is fed into a hydrogen crushing furnace for hydrogen crushing. After hydrogen crushing is completed, antioxidants and lubricants are added to the resulting coarse powder. After uniform mixing, the resulting coarse powder is processed by an air jet mill to produce fine powder. The proportion of the secondary phase alloy steel ingot in the mixture is 3-6 wt.%. Step 4, Magnetic Field Molding: The fine mixed powder obtained in Step 3 is placed in a magnetic field press and pressed into shape in an environment with an oxygen content of less than 100 ppm to obtain a pressed blank. Step 5, Cold Isostatic Pressing: The obtained compact is placed in a cold isostatic pressing equipment under vacuum sealing and subjected to a second pressing at a pressure of 150-280MPa, which increases the density of the compact by 8-18% to obtain an isostatic compact. Step 6, Sintering: The isostatic pressing blank obtained in step 5 is transferred into a vacuum sintering furnace. After sintering and tempering, heavy rare earth-free high coercivity NdFeB is obtained.

2. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that, The main phase alloy is composed of the following components by mass percentage: 30.5 wt.% Pr25Nd75, 0.91 wt.% B, 0.4 wt.% Al, 0.25 wt.% Zr, 0.7 wt.% Co, 0.35 wt.% Cu, 0.5 wt.% Ga, with the balance being Fe.

3. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that, The secondary phase alloy is composed of the following mass percentage components: 18-23 wt.% Cu, 23-26 wt.% Ga, 4-6 wt.% Mo, 0.5-0.8 wt.% Ag, with the balance being Nd.

4. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that: The amount of antioxidant used is 0.08-0.15 wt.% of the hydrogen-crushed coarse powder; the antioxidant is any one of tert-butylhydroquinone, 4-hexylresorcinol, butylated hydroxytoluene, and antimony dialkyldithiocarbamate.

5. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that: The amount of the lubricant used is 0.06-0.1 wt.% of the hydrogen-crushed coarse powder; and the lubricant is selected from any one of oxidized polyethylene wax, butyl oleate, zinc stearate, and sodium stearate.

6. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that: The magnetic induction intensity during the magnetic field forming process is 1.8-2.3T, and the forming pressure is set to 3-6MPa.

7. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that, The hydrogen dehydrogenation process includes hydrogen absorption treatment, first dehydrogenation treatment, and second dehydrogenation treatment. The temperature of the hydrogen absorption treatment is 330-360℃, and the holding time is 45-60 min. The temperature of the first dehydrogenation treatment is 435-465℃, and the holding time is 2-3 h. The temperature of the second dehydrogenation treatment is 570-590℃, and the holding time is 6-8 h.

8. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that: Sintering includes a first sintering and a second sintering; the conditions for the first sintering include: a vacuum degree of less than 5 × 10⁻⁶. -2 The conditions for the second sintering include: a vacuum degree of less than 5 × 10⁻⁶ Pa, a temperature of 1020-1050℃, and a holding time of 2-4 hours; -2 Pa, temperature 1060-1100℃, heat preservation time 8-10h.

9. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that: Tempering treatment includes one-stage tempering and two-stage tempering; the conditions for one-stage tempering are: vacuum degree less than 5 Pa, temperature 890-920℃, and time 3-5 h; the conditions for two-stage tempering are: vacuum degree less than 8 Pa, temperature 490-520℃, and time 5-7 h.

10. The method for preparing heavy rare earth-free, high-coercivity NdFeB according to claim 1, characterized in that: The grinding pressure of the air jet mill is 5.9-6.1 MPa, and the powder output speed is 130-160 kg / h; the average particle size of the fine mixed powder obtained after air jet milling is 1-4 μm.

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