Hydrogen-crushing method for NdFeB alloys and preparation method for NdFeB magnets

Abstract

This invention discloses a method for hydrogen-crushing neodymium iron boron (NdFeB) alloys. The method includes the following steps: (1) first absorbing hydrogen into a NdFeB alloy sheet, followed by a first dehydrogenation, and cooling to obtain pre-hydrogenated NdFeB; wherein the hydrogen content of the pre-hydrogenated NdFeB is above 1800 ppm; (2) second absorbing hydrogen into the pre-hydrogenated NdFeB, followed by a second dehydrogenation, and cooling to obtain coarse NdFeB powder. This method can improve the coercivity of NdFeB magnets without affecting remanence. This invention also discloses a method for preparing NdFeB magnets.

Description

Technical Field

[0001] This invention relates to a method for hydrogen crushing of neodymium iron boron alloys, and also to a method for preparing neodymium iron boron magnets. Background Technology

[0002] Sintered NdFeB magnets not only possess outstanding magnetic properties but also exhibit high efficiency, energy saving, light weight, small size, and good speed control, leading to their widespread application since their introduction in 1983. Coercivity and remanence are two important indicators for evaluating sintered NdFeB magnets, typically improved by adjusting the composition of raw materials and the manufacturing process. Adding heavy rare earth elements to sintered NdFeB magnets increases their coercivity, but the presence of these elements simultaneously reduces their remanence.

[0003] Traditional hydrogen fragmentation methods involve a single hydrogen absorption process, primarily consisting of four stages. The first stage is surface activation during the spinning process; no hydrogen absorption reaction occurs in this stage. The second stage involves hydrogen absorption by the neodymium-rich phase on the spinning surface, where the neodymium-rich Nd phase combines with hydrogen to form NdH. x Compound. Because the NdFeB-rich phase accounts for less than 10% by volume, it releases relatively little heat. After absorbing hydrogen, the NdFeB-rich phase undergoes grain boundary fracture, an intergranular reaction process, and the main phase becomes large single-crystal particles. Third stage: Hydrogen gas travels inward along the grain boundaries to the main phase, initiating the main phase's hydrogen absorption process. This process releases a large amount of heat, forming Nd2Fe. 14 BH y The compound undergoes hydrogen absorption by the main phase, transforming large single-crystal main phase particles into smaller grains. Fourth stage: Hydrogen gas causes hydrogen fragmentation in the core of the wafer. Due to hydrogen absorption by the main phase, numerous cracks appear, decreasing in size and increasing in number from the outside in. As heat release increases and temperature rises, coupled with the increased number of cracks, hydrogen diffusion to the core of the wafer slows down, reducing hydrogen absorption. This results in some neodymium-rich phases and main phase grains not fully absorbing hydrogen, which affects the performance of the neodymium iron boron magnet.

[0004] CN103537705A discloses a hydrogen crushing process for sintered NdFeB permanent magnet materials. NdFeB castings are placed in a hydrogen crushing furnace and heated to 60–150°C. Nitric oxide is introduced into the furnace for activation. The nitrogen oxide supply is then stopped, a vacuum is created, and argon gas is introduced to replace the nitrogen oxide in the furnace. The furnace is then evacuated again until the nitrogen oxide concentration by weight ratio is less than 100 ppm. Hydrogen is then introduced into the furnace, causing the NdFeB castings to expand and break into powder. This process addresses the problem of uneven hydrogen absorption in sintered NdFeB castings by activating the castings, thereby improving their magnetic properties.

[0005] CN105405563A discloses a method for hydrogen-induced crushing of neodymium iron boron (NdFeB) magnets, comprising the following steps: placing NdFeB semi-finished products into a hydrogen crushing device and subjecting them to vacuum treatment; then introducing a protective gas and hydrogen into the hydrogen crushing device to perform a hydrogen absorption reaction, followed by vacuum treatment and heating to perform a dehydrogenation reaction, thereby obtaining fine NdFeB raw material powder. This method utilizes the pressure of the protective gas to uniformly disperse small-molecule hydrogen into the furnace cavity, ensuring that the NdFeB semi-finished products in all parts can react with hydrogen, thus ensuring that the NdFeB semi-finished products are fully crushed. However, this method cannot fully absorb hydrogen and crush the core of the NdFeB semi-finished products, resulting in a relatively small improvement in their magnetic properties.

[0006] CN111029075A discloses a method for preparing neodymium-iron-boron (NdFeB) magnetic powder. This method utilizes the different hydrogen absorption reaction temperatures of the NdFeB alloy's neodymium-rich phase and the main phase. By controlling the hydrogen absorption temperature during hydrogen treatment, the NdFeB phase and the main phase are crushed separately. After passing the powder through an air-jet milling process, magnetic powder with a uniform particle size distribution is obtained. This method allows the main phase to directly contact hydrogen gas, fully react, and undergo transgranular fracture, resulting in more uniform and thorough crushing of the main phase. However, this method cannot fully crush the NdFeB-rich phase and the main phase in the core, thus affecting the uniformity of the magnetic powder. Summary of the Invention

[0007] One object of the present invention is to provide a hydrogenation method for neodymium iron boron (NdFeB) magnets, which reduces the particle size of NdFeB coarse powder, improves the intrinsic coercivity of the NdFeB magnets, and does not significantly change the remanence. Another object of the present invention is to provide a method for preparing NdFeB magnets, which improves the coercivity of the NdFeB magnets and does not significantly change the remanence. A further object of the present invention is to provide a method for improving the coercivity of NdFeB magnets.

[0008] On one hand, the present invention provides a method for hydrogen crushing of neodymium iron boron alloys, comprising the following steps:

[0009] (1) The neodymium iron boron alloy sheet is first absorbed with hydrogen, then dehydrogenated for the first time, and cooled to obtain pre-hydrogenated crushed neodymium iron boron; wherein the hydrogen content of the pre-hydrogenated crushed neodymium iron boron is above 1800 ppm;

[0010] (2) The pre-hydrogenated NdFeB is subjected to hydrogen absorption for the second time, followed by dehydrogenation for the second time and then cooled to obtain NdFeB coarse powder.

[0011] According to the hydrogen crushing method of the present invention, preferably, the first hydrogen absorption time is 0.3 to 4 hours and the first hydrogen absorption pressure is 0.010 to 0.200 MPa.

[0012] According to the hydrogen crushing method of the present invention, preferably, the second hydrogen absorption time is 0.3 to 4 hours, and the second hydrogen absorption pressure is 0.010 to 0.200 MPa.

[0013] According to the hydrogenation method of the present invention, preferably, the first dehydrogenation temperature is 400-700°C and the first dehydrogenation time is 2-6 hours.

[0014] According to the hydrogen dehydrogenation method of the present invention, preferably, the first dehydrogenation time includes a first heating time and a first holding time, wherein the first heating time is 0.5 to 3 hours and the first holding time is 1 to 4 hours.

[0015] According to the hydrogenation method of the present invention, preferably, the second dehydrogenation temperature is 400-700°C; and the second dehydrogenation time is 7-12 hours.

[0016] According to the hydrogenation method of the present invention, preferably, the second dehydrogenation time includes a second heating time and a second holding time, wherein the second heating time is 0.5 to 3 hours and the second holding time is 5 to 10 hours.

[0017] According to the hydrogen calcination method of the present invention, preferably, the neodymium iron boron alloy sheet contains the following components: 50-70 wt% iron, 20-45 wt% praseodymium and neodymium, 0.5-2.5 wt% aluminum, 0.3-2 wt% boron, 0.5-2.5 wt% cobalt, 0.01-0.5 wt% gallium and 0.01-0.5 wt% zirconium.

[0018] On the other hand, the present invention provides a method for preparing a neodymium iron boron magnet, comprising the following steps:

[0019] (1) The above method was used to perform hydrogen crushing to obtain NdFeB coarse powder;

[0020] (2) The coarse NdFeB powder was processed by air jet milling to obtain fine NdFeB powder;

[0021] (3) Press the NdFeB fine powder into shape to obtain NdFeB blank;

[0022] (4) The neodymium iron boron blank is sintered at 1000-1200℃ for 3-7h, treated at 700-950℃ for 1-5h, and treated at 380-550℃ for 3-7h to obtain neodymium iron boron magnet.

[0023] In another aspect, the present invention provides a method for improving the coercivity of neodymium iron boron magnets, comprising the following steps:

[0024] (1) The neodymium iron boron alloy sheet is first absorbed with hydrogen, then dehydrogenated for the first time, and cooled to obtain pre-hydrogenated crushed neodymium iron boron; wherein the hydrogen content of the pre-hydrogenated crushed neodymium iron boron is above 1800 ppm;

[0025] (2) The pre-hydrogenated NdFeB is subjected to hydrogen absorption for the second time, followed by dehydrogenation for the second time and cooling to obtain NdFeB coarse powder;

[0026] (3) The coarse NdFeB powder was processed by air jet milling to obtain fine NdFeB powder;

[0027] (4) Press the NdFeB fine powder into shape to obtain NdFeB blank;

[0028] (5) The neodymium iron boron blank is sintered at 1000-1200℃ for 3-7h, treated at 700-950℃ for 1-5h, and treated at 380-550℃ for 3-7h to obtain neodymium iron boron magnet.

[0029] The hydrogen-breaking method of this invention includes two hydrogen absorption processes and two hydrogen dehydrogenation processes to promote the full absorption of hydrogen by the neodymium-rich core phase and main phase that have not fully absorbed hydrogen, and to separate adjacent main phases. Large particles of the main phase undergo transgranular fracture, transforming into smaller grains that are identical to the outer grains, thus improving the performance of the NdFeB magnet. Since the secondary hydrogen absorption only occurs on a small amount of the neodymium-rich core phase and main phase, and the large grains become smaller grains, the intrinsic coercivity of the NdFeB magnet is only improved, while the remanence does not change significantly. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] The "vacuum" referred to in this invention means an absolute vacuum degree of less than or equal to 0.1 Pa, preferably less than or equal to 0.01 Pa, and more preferably less than or equal to 0.001 Pa. In this invention, the smaller the absolute vacuum degree value, the higher the vacuum degree.

[0032] The "inert atmosphere" described in this invention refers to an atmosphere that does not react with a magnet and does not affect its magnetism. In this invention, the "inert atmosphere" includes an atmosphere formed by nitrogen or an inert gas (helium, neon, argon, krypton, xenon).

[0033] <Hydrogen Decomposition Method for Neodymium Iron Boron Alloys>

[0034] The hydrogen calcination method for NdFeB alloys of the present invention includes the following steps: (1) a primary hydrogen absorption step and (2) a secondary hydrogen absorption step. Details are described below.

[0035] One hydrogen absorption step

[0036] The neodymium iron boron alloy sheet is first absorbed with hydrogen, then dehydrogenated, and cooled to obtain pre-hydrogenated neodymium iron boron.

[0037] The thickness of the neodymium iron boron alloy sheet can be 0.05 to 3 mm; preferably 0.1 to 2 mm; more preferably 0.1 to 0.8 mm.

[0038] Neodymium iron boron (NdFeB) alloy sheets can be prepared using a rapid solidification and spinning process. NdFeB alloy sheets may contain the following components: 50–70 wt% iron, 20–45 wt% praseodymium and neodymium, 0.5–2.5 wt% aluminum, 0.3–2 wt% boron, 0.5–2.5 wt% cobalt, 0.01–0.5 wt% gallium, and 0.01–0.5 wt% zirconium. In some formulations, NdFeB alloy sheets consist of the following components: 50–70 wt% iron, 20–45 wt% praseodymium and neodymium, 0.5–2.5 wt% aluminum, 0.3–2 wt% boron, 0.5–2.5 wt% cobalt, 0.01–0.5 wt% gallium, 0.01–0.5 wt% zirconium, and unavoidable impurities.

[0039] In this invention, the iron content is 50-70 wt%; preferably 55-65 wt%; more preferably 60-65 wt%.

[0040] In this invention, the content of praseodymium and neodymium is 20-45 wt%; preferably 25-40 wt%; more preferably 28-35 wt%. The weight ratio of praseodymium to neodymium is 1:1-5; preferably 1:2-4; more preferably 1:2.5-3.5.

[0041] In this invention, the aluminum content is 0.5–2.5 wt%; preferably 0.8–2.0 wt%; more preferably 1.0–1.5 wt%.

[0042] In this invention, the boron content is 0.3–2 wt%; preferably 0.5–1.5 wt%; more preferably 0.7–1.2 wt%.

[0043] In this invention, the cobalt content is 0.5–2.5 wt%; preferably 0.8–2.0 wt%; more preferably 0.8–1.5 wt%.

[0044] In this invention, the gallium content is 0.01 to 0.5 wt%; preferably 0.05 to 0.3 wt%; more preferably 0.08 to 0.2 wt%.

[0045] In this invention, the zirconium content is 0.01–0.5 wt%; preferably 0.05–0.3 wt%; more preferably 0.08–0.2 wt%.

[0046] In this invention, the hydrogen content of the pre-hydrogenated NdFeB magnet is 1800 ppm or more; preferably, the hydrogen content is 2000 ppm or more. This ensures that secondary hydrogen absorption occurs only in a small amount of neodymium-rich phase and main phase in the core, thereby improving the intrinsic coercivity of the NdFeB magnet without affecting remanence.

[0047] In this invention, the first hydrogen absorption time can be 0.3–4 hours; preferably 0.5–3 hours; more preferably 0.8–1.5 hours. The first hydrogen absorption pressure can be 0.010–0.200 MPa; preferably 0.050–0.150 MPa; more preferably 0.070–0.120 MPa. This allows the NdFeB alloy sheet, except for a small amount of NdFeB-rich phase and main phase in the core, to fully absorb hydrogen.

[0048] In this invention, cooling is performed when the first hydrogen absorption has reached 1 / 3 to 3 / 4 of the first hydrogen absorption time; preferably, cooling is performed when the first hydrogen absorption has reached 0.4 to 0.6 of the first hydrogen absorption time. This prevents the temperature from becoming too high due to the heat released during the hydrogen absorption process.

[0049] In this invention, the first dehydrogenation is carried out under vacuum conditions. The first dehydrogenation temperature is 400–700°C; preferably 450–650°C; more preferably 500–600°C. The first dehydrogenation time is 2–6 hours; preferably 3–5 hours; more preferably 3–4 hours. The first dehydrogenation time includes a first heating time and a first holding time. The first heating time refers to the time taken to reach the first dehydrogenation temperature. The first holding time refers to the time for the dehydrogenation reaction at the first dehydrogenation temperature. The first heating time can be 0.5–3 hours; preferably 1–2.5 hours; more preferably 1–2 hours. The first holding time can be 1–4 hours; preferably 1.5–3 hours; more preferably 1.5–2.5 hours. This improves both dehydrogenation efficiency and ensures the dehydrogenation effect, keeping the hydrogen content of the pre-hydrogenated NdFeB within the range specified in this invention.

[0050] Cooling can be achieved using a combination of air and water cooling. The cooling time can be 1–8 hours; preferably 2–6 hours; more preferably 3–5 hours.

[0051] Secondary hydrogen absorption step

[0052] The pre-hydrogenated NdFeB was subjected to a second hydrogen absorption process, followed by a second dehydrogenation process and cooling to obtain NdFeB coarse powder.

[0053] In this invention, the second hydrogen absorption time can be 0.3–4 h; preferably 0.5–3 h; more preferably 0.8–1.5 h. The second hydrogen absorption pressure can be 0.010–0.200 MPa; preferably 0.050–0.150 MPa; more preferably 0.070–0.120 MPa. This allows for more thorough hydrogen absorption by both the neodymium-rich phase and the main phase in the core.

[0054] In this invention, cooling is performed when the second hydrogen absorption has reached 1 / 3 to 3 / 4 of the second hydrogen absorption time; preferably, cooling is performed when the second hydrogen absorption has reached 0.4 to 0.6 of the second hydrogen absorption time. This prevents the temperature from becoming too high due to the heat released during the hydrogen absorption process.

[0055] In this invention, the second dehydrogenation is carried out under vacuum conditions. The second dehydrogenation temperature is 400–700°C; preferably 450–650°C; more preferably 500–600°C. The second dehydrogenation time is 7–12 hours; preferably 8–11 hours; more preferably 9–10 hours. The second dehydrogenation time includes a second heating time and a second holding time. The second heating time refers to the time required to heat to the second dehydrogenation temperature. The second holding time refers to the time required for the dehydrogenation reaction at the second dehydrogenation temperature. The second heating time can be 0.5–3 hours; preferably 1–2.5 hours; more preferably 1–2 hours. The second holding time can be 5–10 hours; preferably 6–10 hours; more preferably 7–9 hours. This improves both dehydrogenation efficiency and ensures the dehydrogenation effect.

[0056] Cooling can be achieved using a combination of air and water cooling. The cooling time can be 1–8 hours; preferably 2–6 hours; more preferably 3–5 hours.

[0057] After cooling, the material can be discharged in a closed system, with inert gas introduced during the discharge process. This prevents the NdFeB coarse powder from being oxidized during discharge.

[0058] <Preparation Method of Neodymium Iron Boron Magnets>

[0059] The method for preparing the neodymium iron boron magnet of the present invention includes the following steps: hydrogen crushing, air jet milling, forming, sintering, and heat treatment. Optionally, a melting step is included before the hydrogen crushing step.

[0060] Smelting steps

[0061] In the smelting step, raw materials are provided according to the composition of the NdFeB alloy, and the raw materials are smelted to form a master alloy from the smelted magnetic raw materials. To prevent oxidation of the magnetic raw materials and the master alloy derived therefrom, smelting is preferably carried out in a vacuum or inert atmosphere. The smelting of this invention can be carried out in a high-vacuum high-frequency induction furnace. The smelting temperature can be 1100–1600°C, preferably 1450–1500°C. Smelting can be carried out in a vacuum high-frequency induction furnace. The master alloy is then processed using a rapid solidification and strip spinning process to produce NdFeB alloy sheets.

[0062] Hydrogen crushing steps

[0063] The hydrogen crushing process is as described above.

[0064] Airflow milling steps

[0065] The coarse NdFeB powder is processed by an air jet mill to obtain fine NdFeB powder. The rotation speed of the equipment can be 1500-4000 r / min; preferably 2000-3500 r / min; more preferably 2500-3000 r / min.

[0066] Molding steps

[0067] NdFeB fine powder is pressed into shape to obtain NdFeB blanks. The orientation magnetic field during molding can be greater than or equal to 1.0T; preferably greater than or equal to 1.2T; more preferably greater than or equal to 1.5T. The density of the NdFeB blanks can be 2.0–15 g / cm³. 3 Preferably 3-10 g / cm³ 3 More preferably 3.5–6 g / cm³ 3 .

[0068] Sintering and heat treatment steps

[0069] Neodymium iron boron (NdFeB) blanks are sintered and heat-treated to obtain NdFeB magnets. The sintering temperature can be 1000–1200℃, preferably 1000–1100℃. The sintering time can be 3–7 hours, preferably 4–6 hours. The heat treatment can be divided into two stages. The first stage heat treatment temperature can be 700–950℃, preferably 800–950℃, more preferably 850–950℃. The first stage heat treatment time can be 1–5 hours, preferably 1–4 hours, more preferably 2–3 hours. The second stage heat treatment temperature can be 380–550℃, preferably 450–500℃. The second stage heat treatment time can be 3–7 hours, preferably 4–6 hours. This further improves the magnetic properties of the magnet.

[0070] <Methods to improve the coercivity of neodymium iron boron magnets>

[0071] The method for improving the coercivity of NdFeB magnets according to the present invention includes the following steps: hydrogen crushing, air jet milling, forming, sintering, and heat treatment. Specifically, it includes:

[0072] (1) The neodymium iron boron alloy sheet is first absorbed with hydrogen, then dehydrogenated for the first time, and cooled to obtain pre-hydrogenated crushed neodymium iron boron; wherein the hydrogen content of the pre-hydrogenated crushed neodymium iron boron is above 1800 ppm;

[0073] (2) The pre-hydrogenated NdFeB is subjected to hydrogen absorption for the second time, followed by dehydrogenation for the second time and cooling to obtain NdFeB coarse powder;

[0074] (3) The coarse NdFeB powder was processed by air jet milling to obtain fine NdFeB powder;

[0075] (4) Press the NdFeB fine powder into shape to obtain NdFeB blank;

[0076] (5) The neodymium iron boron blank is sintered at 1000-1200℃ for 3-7 hours, treated at 700-950℃ for 1-5 hours, and treated at 380-550℃ for 3-7 hours in sequence to obtain neodymium iron boron magnets.

[0077] The details are as described above.

[0078] The testing method of this invention is described below:

[0079] Magnetic properties: tested using a NIM-10000 permanent magnet tester.

[0080] Elemental content: determined using X-ray fluorescence spectrometry.

[0081] The neodymium iron boron alloy sheets in the following examples and comparative examples have the following compositions:

[0082] The composition is 1.2 wt% aluminum, 0.95 wt% boron, 1.1 wt% cobalt, 0.1 wt% gallium, 0.1 wt% zirconium, 32 wt% praseodymium and neodymium, with the balance being iron. The mass ratio of praseodymium to neodymium is 1:3.

[0083] Preparation Example 1

[0084] According to the composition of NdFeB alloy, the raw materials are melted in a high-vacuum high-frequency induction furnace to obtain the master alloy; the master alloy is then processed into NdFeB alloy sheets using a rapid solidification and strip spinning process. The thickness of the NdFeB alloy sheets is 0.3 mm.

[0085] Example 1

[0086] The NdFeB alloy sheet obtained in Preparation Example 1 was placed in a hydrogen crushing furnace. The furnace was evacuated, and then hydrogen gas was introduced to 0.098 MPa for the first hydrogen absorption, which lasted for 1 hour. After 0.5 hours of the first hydrogen absorption, circulating water cooling was started. After the first hydrogen absorption, the reaction apparatus was heated to 550°C, and the first dehydrogenation was performed under vacuum conditions. The first heating time was 1.5 hours, and the first holding time was 2 hours. Then, air cooling and water cooling were used for 4 hours to obtain pre-hydrogenated NdFeB.

[0087] Hydrogen gas was introduced into the hydrogen crushing furnace under vacuum to a pressure of 0.098 MPa for a second hydrogen absorption period of 1 hour. After 0.5 hours of the second absorption, circulating water cooling was initiated. Following the second absorption, the reaction apparatus was heated to 550°C for a second dehydrogenation under vacuum, with a second heating time of 1.5 hours and a second holding time of 8 hours. Cooling was then performed using a combination of air and water cooling for 4 hours, yielding NdFeB coarse powder. After cooling, the powder was discharged in a closed system, with inert gas introduced during the discharge process.

[0088] Comparative Example 1

[0089] In Preparation Example 1, NdFeB alloy sheets were placed in a hydrogen decomposition furnace. The furnace was evacuated, and hydrogen gas was introduced at a pressure of 0.098 MPa for 3 hours to absorb hydrogen. After hydrogen absorption, the reaction apparatus was heated to 550°C for dehydrogenation under vacuum conditions for 1.5 hours and held at that temperature for 9.5 hours. The mixture was then cooled using a combination of air and water cooling for 4 hours to obtain NdFeB coarse powder.

[0090] Table 1

[0091]

[0092] Example 2

[0093] The NdFeB coarse powder obtained in Example 1 was processed by air jet milling to obtain NdFeB fine powder. The parameters for air jet milling were: equipment speed of 2800 r / min.

[0094] NdFeB fine powder was pressed into shape to obtain NdFeB blanks; the orientation magnetic field during molding was 1.5T. The density of the obtained NdFeB blanks was 4.15 g / cm³. 3 .

[0095] The neodymium iron boron blank was sintered at 1060℃ for 5 hours, treated at 900℃ for 3 hours, and treated at 475℃ for 5 hours in sequence to obtain neodymium iron boron magnets.

[0096] Comparative Example 2

[0097] Except for the NdFeB coarse powder, which was obtained from Comparative Example 1, the rest were the same as in Example 2.

[0098] Table 2

[0099] Example 2 Comparative Example 2 <![CDATA[D 10 (μm)]]> 1.73 1.76 <![CDATA[D 50 (μm)]]> 4.23 4.41 <![CDATA[D 90 (μm)]]> 7.28 7.42 <![CDATA[D 90 / D 10 ]]> 4.20 4.22 Br(kGs) 12.78 12.65 <![CDATA[H cj (no)]]> 19.8 19.10

[0100] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for hydrogen crushing neodymium iron boron alloy, characterized in that, Includes the following steps: (1) The neodymium iron boron alloy sheet is first absorbed with hydrogen, then dehydrogenated for the first time, and cooled to obtain pre-hydrogenated crushed neodymium iron boron; wherein the hydrogen content of the pre-hydrogenated crushed neodymium iron boron is above 2000 ppm, the first hydrogen absorption pressure is 0.010~0.200 MPa, the first hydrogen absorption time is 0.3~4 h, the first dehydrogenation temperature is 400~700℃, and the first dehydrogenation time is 2~6 h; (2) The pre-hydrogenated NdFeB is subjected to hydrogen absorption for the second time, followed by dehydrogenation for the second time and then cooled to obtain NdFeB coarse powder; wherein the second hydrogen absorption time is 0.3 to 4 hours, the second hydrogen absorption pressure is 0.010 to 0.200 MPa, the second dehydrogenation temperature is 400 to 700 °C, and the second dehydrogenation time is 7 to 12 hours.

2. The hydrogen crushing method according to claim 1, characterized in that, The first hydrogen absorption time is 0.5 to 3 hours, and the first hydrogen absorption pressure is 0.050 to 0.150 MPa.

3. The hydrogen crushing method according to claim 1, characterized in that, The second hydrogen absorption time is 0.5 to 3 hours, and the second hydrogen absorption pressure is 0.050 to 0.150 MPa.

4. The hydrogen crushing method according to claim 1, characterized in that, The first dehydrogenation temperature is 450–650℃, and the first dehydrogenation time is 3–5 hours.

5. The hydrogen crushing method according to claim 1, characterized in that, The first dehydrogenation time includes a first heating time and a first holding time, wherein the first heating time is 0.5 to 3 hours and the first holding time is 1 to 4 hours.

6. The hydrogen crushing method according to claim 1, characterized in that, The second dehydrogenation temperature is 450–650℃; the second dehydrogenation time is 8–11 hours.

7. The hydrogen crushing method according to claim 1, characterized in that, The second dehydrogenation time includes a second heating time and a second holding time, wherein the second heating time is 0.5 to 3 hours and the second holding time is 5 to 10 hours.

8. The hydrogen crushing method according to claim 1, characterized in that, The neodymium iron boron alloy sheet contains the following components: 50-70 wt% iron, 20-45 wt% praseodymium and neodymium, 0.5-2.5 wt% aluminum, 0.3-2 wt% boron, 0.5-2.5 wt% cobalt, 0.01-0.5 wt% gallium and 0.01-0.5 wt% zirconium.

9. A method for preparing a neodymium iron boron magnet, characterized in that, Includes the following steps: Neodymium iron boron (NdFeB) coarse powder is obtained by hydrogen pulverization method according to any one of claims 1 to 8; the NdFeB coarse powder is treated by air jet milling to obtain NdFeB fine powder; the NdFeB fine powder is pressed into shape to obtain NdFeB blank; the NdFeB blank is sintered at 1000–1200℃ for 3–7 h, treated at 700–950℃ for 1–5 h, and treated at 380–550℃ for 3–7 h in sequence to obtain NdFeB magnet.

10. A method for improving the coercivity of neodymium iron boron magnets, characterized in that, Includes the following steps: (1) The neodymium iron boron alloy sheet is first absorbed with hydrogen, then dehydrogenated for the first time, and cooled to obtain pre-hydrogenated crushed neodymium iron boron; wherein the hydrogen content of the pre-hydrogenated crushed neodymium iron boron is above 2000 ppm, the first hydrogen absorption pressure is 0.010~0.200 MPa, the first hydrogen absorption time is 0.3~4 h, the first dehydrogenation temperature is 400~700℃, and the first dehydrogenation time is 2~6 h; (2) The pre-hydrogenated NdFeB is subjected to hydrogen absorption for the second time, followed by dehydrogenation for the second time and cooling to obtain NdFeB coarse powder; wherein the second hydrogen absorption time is 0.3-4h, the second hydrogen absorption pressure is 0.010-0.200MPa, the second dehydrogenation temperature is 400-700℃, and the second dehydrogenation time is 7-12h; (3) The coarse NdFeB powder was processed by air jet milling to obtain fine NdFeB powder; (4) Press the NdFeB fine powder into shape to obtain NdFeB blank; (5) The neodymium iron boron blank is sintered at 1000-1200℃ for 3-7h, treated at 700-950℃ for 1-5h, and treated at 380-550℃ for 3-7h to obtain neodymium iron boron magnet.

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