A high-safety rare earth permanent magnet powder making method and its application

Abstract

The present invention provides a highly safe rare earth permanent magnet powder making method and its application, and relates to the technical field of rare earth permanent magnet powder making. Specifically comprising: step 1) batching and smelting raw materials according to magnet components; step 2) using a vacuum quick-setting belt-spinning furnace to prepare a casting with a length and width of less than 30 mm and a thickness between 0.2-0.5 mm; step 3) placing the casting into a vacuum microwave heating device to prepare a preformed powder; step 4) air-jet milling the preformed powder to obtain magnetic powder. The present invention abandons the traditional hydrogen-crushing powder making method, makes full use of the performance of the main phase, rare earth-rich phase and boron-rich phase of the rare earth permanent magnet, and uses the process of microwave irradiation + air-jet milling to greatly shorten the powder making time and thus improve production efficiency without affecting the magnetic properties of the original product. The preparation method avoids the use of hydrogen and can also effectively improve the safety of production. Under the premise of safety and environmental protection, it speeds up the powder making speed and obtains a more uniform particle size distribution and a more complete distribution of rare earth-rich phases. High-quality powder.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth permanent magnet powder making, and in particular relates to a high-safety rare earth permanent magnet powder making method and application thereof. Background Art

[0002] Sintered NdFeB permanent magnet materials are widely used in new energy vehicles, wind power generation, consumer digital products and other fields, and are known as the "King of Magnets". The traditional preparation of sintered NdFeB permanent magnets is roughly divided into batching, smelting, strip spinning, powder making, oriented pressing, heat treatment, and subsequent processing.

[0003] The process of powder making has undergone several evolutions. The traditional wet powder making process uses a jaw crusher with nitrogen protection to crush the ingot to 1-4mm, and then uses a ball mill to crush it to 4-6μm. The improved powder making process introduces hydrogen crushing (HD) and air flow milling (JM) after crushing in the jaw crusher, which is called dry powder making. The latest process currently used simplifies the powder making process, directly uses a vacuum rapid solidification belt furnace to prepare flaky ingots (SC), and uses hydrogen crushing + air flow milling (HD+JM) process to prepare NdFeB micropowder with a particle size of about 3μm.

[0004] There are many advantages to using hydrogen pulverization. If hydrogen pulverization is used for the same S-NdFeB alloy, the pulverization efficiency will be greatly improved. According to calculations, the efficiency of one jet mill using hydrogen pulverization is approximately equal to the production efficiency of 1.5-2 jet mills used in non-hydrogen pulverization. However, inevitably, the hydrogen pulverization method has a series of disadvantages: first, the use of hydrogen has a certain explosion risk under high temperature conditions; second, incomplete hydrogen absorption and dehydrogenation may lead to residual hydrogen, thereby reducing the mechanical properties of S-NdFeB.

[0005] Therefore, how to develop a clean, safe, efficient and low-cost milling method is a technical problem that needs to be solved urgently by technicians in this field. Summary of the invention

[0006] The purpose of the present invention is to provide a highly safe rare earth permanent magnet powder making method, abandon the traditional hydrogen crushing powder making method, make full use of the performance of the main phase, rare earth-rich phase and boron-rich phase of the rare earth permanent magnet, and accelerate the powder making speed under the premise of being safer and more environmentally friendly by microwave irradiation + air flow milling, and obtain high-quality powder with more uniform particle size distribution and more complete rare earth-rich phase distribution, thereby reducing production costs and optimizing the mechanical properties and magnetic properties of the product.

[0007] In order to design a clean, safe, efficient and low-cost milling method, the research and development concept of the present invention is as follows:

[0008] Microwaves are electromagnetic waves with frequencies between 300MHz-3000GHz and wavelengths between 0.1mm and 1m. When microwaves act on matter, three effects occur: reflection, absorption, and penetration.

[0009] The mechanism of microwave heating is that when the fine structure of the material is coupled with the electromagnetic field of a specific frequency, the various losses (including conductivity loss, dielectric loss and magnetic loss) generated by the internal microscopic particles convert the absorbed microwave energy into heat energy for heating. When microwaves are used to heat magnetic materials, dielectric loss and magnetic loss usually occur, and some conductivity loss may occur.

[0010] Therefore, the inventors used microwaves to generate different losses in different phases (main phase and rare earth-rich phase) in the rapid solidification casting of rare earth permanent magnets, so that different thermal effects lead to different heating rates between different phases. Different heating rates will produce thermal stress between different phases, which will then lead to the generation of microcracks and even cracks, thereby achieving the purpose of separating particles and making powder. In the subsequent airflow milling process, microcracks will make the powder easy to break. The characteristics of microwave volume heating make the ingot act on microwaves from the inside out, so the microcracks in the obtained powder are more evenly distributed, easier to break in the airflow, and the quality of the magnetic powder is also improved under the premise of shortening the airflow milling time.

[0011] Take the preparation of NdFeB permanent magnets as an example: in the sintered NdFeB rapid solidification casting sheet, there are main phase, rare earth-rich phase and boron-rich phase. The interaction between these three phases and microwaves is as follows:

[0012] The main phase, 2:14:1 phase, is an iron-based magnetic phase with a certain conductivity, so its dielectric constant may be small, and the main losses in the microwave field are conductivity loss and magnetic loss. In addition, the skin effect of the current in the main phase will accelerate the temperature rise of the main phase grains.

[0013] Rare earth-rich phase, the composition of the rare earth-rich phase changes with the reaction time and reaction conditions. Researchers pointed out that fcc structure NdO phase, hcp structure Nd2O3 phase, fcc-Nd phase and NdFe4B4 phase are sometimes observed at the triple grain boundary. With the increase of oxygen content in the ternary Nd-Fe-O phase, it is speculated that its conductivity is poor and has a high dielectric constant. Therefore, the dielectric loss of the rare earth-rich phase can be increased by adjusting the composition of the rare earth-rich phase, making full use of the advantages of selective heating.

[0014] The boron-rich phase is neither a magnetic phase nor a conductive phase.

[0015] In summary, the following conclusions can be drawn: NdFeB is a mixed dielectric material when it is not sintered. The phases therein can couple with microwaves and absorb microwaves for heating. Under the action of the electromagnetic field, its energy loss modes include resistance loss, dielectric loss and magnetic loss. These three losses are related to physical constants such as dielectric constant, loss tangent, and conductivity of different phases. Therefore, when different phases are irradiated with the same microwave field, differences in temperature changes are inevitable. Different temperature rises can be generated in different phases in the casting by utilizing the characteristics of microwave selective heating. The present invention designs the heating rate of microwave irradiation to be about 10-100°C / min, which will produce volume expansion and thermal stress between phases with different temperature rises. Since S-NdFeB is a brittle material, its elongation is almost 0 and its fracture strength is very low. When this volume expansion and thermal stress exceed the fracture strength between the phases, microcracks and ruptures will occur, thereby achieving the purpose of powder making.

[0016] To achieve the above object, the present invention provides a high-safety rare earth permanent magnet powder making method, which specifically comprises the following steps:

[0017] Step 1) batching and smelting raw materials according to magnet components;

[0018] Step 2) preparing a casting sheet using a vacuum rapid solidification belt spinning furnace;

[0019] Step 3) placing the cast sheet obtained in step 2) into a vacuum microwave heating device to prepare a pre-made powder;

[0020] Step 4) The preformed powder obtained in step 3) is subjected to air flow grinding to obtain magnetic powder.

[0021] In a preferred embodiment, in step 1), the magnet component is (PrNd) a RE w Fe x B y M z , wherein RE is selected from at least one of Ce, La, Dy, and Tb, and M is selected from at least one of Al, Co, Cu, Nb, Zr, and Ga;

[0022] a, w, x, y, and z are all mass percentages of the corresponding elements, 27≤a≤33, 1≤w≤3, 0.95 ≤y≤1.10, 0.15≤z≤1.2, x is the remainder and x is greater than 0.

[0023] In a preferred embodiment, in step 2), the casting sheet has a length and a width both less than 30 mm and a thickness between 0.2-0.5 mm.

[0024] In order to make the stress evenly distributed during microwave irradiation, achieve the effect of full crushing and complete the required degree of crushing in a short time, the size of the casting should not be too large, so the length and width of the casting are designed to be less than 30mm. In order to select castings with uniform cooling rate, appropriate temperature gradient between the free surface and the roller surface, no α-Fe, no fine equiaxed crystal area and rich in penetrating lamellar crystals, the casting should not be too thick, so the thickness of the casting is set between 0.2-0.5mm.

[0025] In a preferred embodiment, in step 3), before using the vacuum microwave heating device, a pretreatment step is also included: evacuating the device to 10 -2 -10 -1 Pa, preheating temperature is 50-100°C, and preheating time is 0.1-1h. The pretreatment step is only an optional operation before using the vacuum microwave heating device, which can improve the efficiency of the vacuum microwave. In addition, in order to remove oxygen as much as possible, the vacuum microwave heating device can also be filled with inert gas protection.

[0026] In a preferred embodiment, in step 3), the vacuum microwave heating conditions are: microwave frequency 2.45GHz±50Hz, microwave power 1000-5000W, heating to 400-600℃ at a heating rate of 10℃ / min-100℃ / min, and continuous heating for 10-30min after the irradiation reaches the highest temperature. Among them, setting the microwave frequency to 2.45GHz±50Hz can take into account both cost and production efficiency, and 2.45GHz is one of the most widely used frequencies internationally, making the technical solution of the present invention more universal. The microwave power is 1000-5000W, which can achieve the purpose of faster heating. In addition, the present invention makes full use of temperature gradient stress for crushing and powdering, which requires a higher heating rate; but at the same time, heating too fast will cause overburning, which is not conducive to the subsequent processing of the powder, and will produce higher energy consumption pressure. Therefore, the heating rate is set to 10℃ / min-100℃ / min. If the heating temperature is too low, it is difficult to generate large thermal stress; if it is too high, it is not conducive to powder molding and will also waste energy. According to the melting point of the rare earth-rich phase of ≈650°C, the heating temperature is set to 400°C-600°C in the present invention. In order to fully break the casting under stress, a certain breaking time needs to be given; but the heating time should not be too long to avoid grain growth and oxidation. Therefore, it is designed that the heating is continued for 10-30 minutes after the irradiation reaches the highest temperature.

[0027] More preferably, the microwave frequency is 2.45 GHz, the microwave power is 3000-5000 W, the temperature is increased to 450-550° C. at a heating rate of 50° C. / min-100° C. / min, and the heating is continued for 20 minutes after the irradiation reaches the highest temperature.

[0028] In a preferred embodiment, in step 3), the particle size of the preformed powder obtained is 30-500 μm, and micro cracks caused by thermal stress exist inside the powder. If the preformed powder is too fine, it is very easy to oxidize, which is not conducive to the subsequent processing effect. If the preformed powder is too coarse, it is easy to be ground in the air flow mill, and the crushing effect is poor.

[0029] In a preferred embodiment, in step 4), the average particle size of the magnetic powder obtained is 2-5 μm, and D 99 / D 10 =2.0-5.0. To ensure that all powders are single crystals and the powders cannot be too fine to prevent oxidation and combustion in the air, the above magnet particle size range is set. To ensure good magnetic field orientation and a relatively uniform microstructure of the fired magnet, the powder is required to have a uniform and good particle size distribution, so D is required. 99 / D 10 =2.0-5.0.

[0030] In a preferred embodiment, in step 4), in order to improve the grinding effect of the airflow mill, a modifying additive may be added, and the type and amount of the modifying additive may be the same as those conventionally used in the existing milling process.

[0031] Another object of the present invention is to provide a highly safe rare earth permanent magnet powder making method for use in the preparation of permanent magnets. The magnetic powder obtained by the powder making method provided by the present invention can be widely used in the field of preparing permanent magnets, effectively shortening the powder making time and reducing energy consumption, while also greatly improving the product density and magnetic properties of the permanent magnet, which has the beneficial effect of reducing costs and increasing efficiency.

[0032] To achieve the above object, the present invention provides a highly safe rare earth permanent magnet powder making method for use in preparing permanent magnets, which specifically comprises the following steps:

[0033] Step a) orienting and pressing the magnetic powder obtained by the above powder making method in a magnetic field to obtain a blank;

[0034] Step b) heat-treating the blank after pressing in step a) to obtain a sintered NdFeB permanent magnet.

[0035] In a preferred embodiment, the orientation magnetic field in step a) is 2T.

[0036] In a preferred embodiment, the heat treatment conditions in step b) are: sintering the green compact at 900-1100°C, primary tempering at 900-950°C, and secondary tempering at 500-650°C.

[0037] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0038] The present invention combines microwave irradiation technology with airflow milling to replace the high-risk hydrogen pulverization method in the traditional technical solution, effectively reducing the residual impurity hydrogen element and improving the mechanical properties of sintered NdFeB permanent magnet products. Specifically, hydrogen residues will be introduced into the magnetic powder after hydrogen pulverization. Even after dehydrogenation, the magnetic powder usually still has (770-970)*10 -6 Hydrogen will affect the mechanical properties of magnets. However, the process of the present invention does not require hydrogen crushing and powdering. It only uses microwaves to act on different phases at different heating rates, resulting in different expansion degrees. Combined with the high mismatch between the rare earth-rich phase and the main phase, and the fact that the material is a brittle material, thermal stress can produce microcracks and separation in the area with high mismatch, thereby achieving the purpose of activating the material and powdering. Therefore, it will not have an adverse effect on the magnetic properties of the magnet.

[0039] In addition, the volumetric heating effect of microwave irradiation can significantly accelerate the process of powder making, saving time and energy consumption. The actual scheme has been verified: in the powder making step, the traditional hydrogen rupture takes 5-7 hours, while the microwave irradiation powder making scheme only takes 0.5-2 hours, which greatly reduces the powder making time, reduces energy consumption, and improves the reaction safety.

[0040] Furthermore, the activation effect of microwave irradiation can effectively improve the density of the powder joints, improve the density and magnetic properties of the product, and thus obtain high-quality rare earth permanent magnets. The actual solution has been verified: the loose density of magnetic powder produced by airflow grinding alone is 1.5-1.8g / cm 3 The bulk density of the magnetic powder obtained by microwave irradiation and jet milling is 1.6-1.9g / cm 3 Moreover, the prepared magnetic powder is crushed evenly and finely, and the process is environmentally friendly and efficient, laying the foundation for the preparation of higher performance permanent magnetic materials. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below in conjunction with specific implementation methods, but it should be understood that the protection scope of the present invention is not limited by the specific implementation methods.

[0042] Unless otherwise specified, the technical means used in the present invention are conventional means well known to those skilled in the art, and the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods. Among them, the vacuum microwave heating device can be any device as long as it can meet the microwave power, frequency, heating rate, maximum irradiation temperature and irradiation time described in the present invention, and is not limited to a specific manufacturer.

[0043] Example 1

[0044] (I) Preparation of magnetic powder:

[0045] S1: Magnet composition (wt.%): (PrNd) 28.0 Dy 1.5 Tb 1.0 Al 0.15 Cu 0.25 Co 0.5 Ga 0.1 Fe bal B 0.98 The permanent magnet components are batched and smelted.

[0046] S2: Obtain an ingot in a vacuum rapid solidification belt-spinning furnace and crush it to obtain a rapid solidification casting sheet with a specification of 30 mm*20 mm*0.3 mm.

[0047] S3: After degreasing, cleaning and drying the rapid solidification casting sheet, place it in a vacuum microwave sintering furnace with a vacuum degree of 0.01 Pa. The vacuum microwave sintering furnace is preheated and filled with nitrogen for protection. The preheating temperature is 50°C and the preheating time is 0.1h.

[0048] S4: Microwave irradiation of the casting: The microwave frequency of the microwave heating device is set to 2.45 GHz ± 50 Hz, the microwave power is set to 2000 W, the microwave radiation temperature is set to 400 ° C, the heating rate is 50 ° C / min, and the continuous heating time is 30 min after the irradiation reaches the maximum temperature (400 ° C). Sintering is performed, the microwave source position remains unchanged, and the sample stage rotates at a speed of 60 rpm.

[0049] S5: After taking out the prefabricated powder, the powder is subjected to a jet milling treatment to obtain magnetic powder with an average particle size of 2-5 μm.

[0050] (II) Preparation of permanent magnets

[0051] The mixed powder was oriented and pressed in a 2T magnetic field. The pressed green body was sintered at 1000°C for 4h, tempered at 900°C for 3h, and tempered at 500°C for 4h to obtain a sintered green body, and its magnetic properties were tested.

[0052] Comparative Example 1

[0053] The difference from Example 1 is:

[0054] (i) Preparation of magnetic powder: After steps S1 and S2, steps S3 and S4 are replaced by: sending the rapidly solidified casting sheet into a hydrogen cracking furnace for hydrogen cracking treatment to obtain hydrogen cracked powder.

[0055] The hydrogen cracking treatment conditions are: the quick-solidified casting is sent to a vacuum hydrogen cracking furnace and evacuated to 10 -2 Pa, fill with high-purity hydrogen until the hydrogen pressure reaches 10 5 Pa for 4 hours to carry out hydrogen cracking treatment. Then the temperature is raised to 590℃ for 3 hours to obtain hydrogen cracking powder.

[0056] The rest is consistent with Example 1.

[0057] Example 2

[0058] The difference from Example 1 is:

[0059] (i) Preparation of magnetic powder: In S4, the casting was subjected to microwave irradiation: the microwave frequency of the microwave heating device was set to 2.45 GHz ± 50 Hz, the microwave power was set to 3000 W, the microwave radiation temperature was set to 500 ° C, the heating rate was set to 80 ° C / min, and the continuous heating time after the irradiation reached the maximum temperature (500 ° C) was 30 min. Sintering was performed, the microwave source position remained unchanged, and the sample stage rotated at a speed of 60 rpm;

[0060] The rest is consistent with Example 1.

[0061] Comparative Example 2

[0062] The difference from Example 2 is:

[0063] (i) Preparation of magnetic powder: After steps S1 and S2, steps S3 and S4 are replaced by: sending the rapidly solidified casting sheet into a hydrogen cracking furnace for hydrogen cracking treatment to obtain hydrogen cracked powder.

[0064] The hydrogen cracking treatment conditions are: the quick-solidified casting is sent to a vacuum hydrogen cracking furnace and evacuated to 10 -2 Pa, fill with high-purity hydrogen until the hydrogen pressure reaches 10 5 Pa for 4 hours to carry out hydrogen cracking treatment. Then the temperature is raised to 590℃ for 3 hours to obtain hydrogen cracking powder.

[0065] The rest is consistent with Example 2.

[0066] Example 3

[0067] The difference from Example 1 is:

[0068] (i) Preparation of magnetic powder: In S4, the casting was subjected to microwave irradiation: the microwave frequency of the microwave heating device was set to 2.45 GHz ± 50 Hz, the microwave power was set to 5000 W, the microwave radiation temperature was set to 600 ° C, the heating rate was set to 100 ° C / min, and the continuous heating time after the irradiation reached the maximum temperature (600 ° C) was 30 minutes. Sintering was performed, the microwave source position remained unchanged, and the sample stage rotated at a speed of 60 rpm;

[0069] The rest is consistent with Example 1.

[0070] Comparative Example 3

[0071] The difference from Example 3 is:

[0072] (i) Preparation of magnetic powder: After steps S1 and S2, steps S3 and S4 are replaced by: sending the rapidly solidified casting sheet into a hydrogen cracking furnace for hydrogen cracking treatment to obtain hydrogen cracked powder.

[0073] The hydrogen cracking treatment conditions are: the quick-solidified casting is sent to a vacuum hydrogen cracking furnace and evacuated to 10 -2 Pa, fill with high-purity hydrogen until the hydrogen pressure reaches 10 5 Pa for 4 hours to carry out hydrogen cracking treatment. Then the temperature is raised to 590℃ for 3 hours to obtain hydrogen cracking powder.

[0074] The rest is consistent with Example 3.

[0075] Example 4

[0076] The difference from embodiment (1) is that:

[0077] S1: Magnet composition (wt.%): (PrNd) 29.0 Dy 1.5 Al 0.15 Cu 0.25 Co 0.5 Ga 0.1 Fe bal B 0.98 The permanent magnet components are batched and smelted.

[0078] The rest is consistent with Example 1.

[0079] Comparative Example 4

[0080] The difference from Example 4 is:

[0081] (i) Preparation of magnetic powder: After steps S1 and S2, steps S3 and S4 are replaced by: sending the rapidly solidified casting sheet into a hydrogen cracking furnace for hydrogen cracking treatment to obtain hydrogen cracked powder.

[0082] The hydrogen cracking treatment conditions are: the quick-solidified casting is sent to a vacuum hydrogen cracking furnace and evacuated to 10 -2 Pa, fill with high-purity hydrogen until the hydrogen pressure reaches 10 5 Pa for 4 hours to carry out hydrogen cracking treatment. Then the temperature is raised to 590℃ for 3 hours to obtain hydrogen cracking powder.

[0083] The rest is consistent with Example 4.

[0084] Comparative Example 5

[0085] The difference from Example 1 is:

[0086] (i) Preparation of magnetic powder: After steps S1 and S2, steps S3 and S4 are replaced by: sending the rapidly solidified casting sheet into a jaw crusher for crushing to obtain coarse powder, that is, under nitrogen protection, crushing the casting sheet to 1-4 mm, and then crushing it to 4-6 μm by ball milling.

[0087] The rest is consistent with Example 1.

[0088] Comparative Example 6

[0089] The difference from Example 1 is:

[0090] (i) Preparation of magnetic powder: After steps S1 and S2, step S3 is replaced by: degreasing, cleaning and drying the quick-setting casting sheet and placing it in a vacuum microwave sintering furnace with a vacuum degree of 0.01 Pa. After the vacuuming is completed, the furnace body is heated with a preheating temperature of 50°C and a preheating time of 0.1 h.

[0091] The rest is consistent with Example 1.

[0092] Comparative Example 7

[0093] The difference from Example 1 is:

[0094] (i) Preparation of magnetic powder: After step S1, step S2 is replaced by: obtaining an ingot in a vacuum rapid solidification belt furnace and crushing it to obtain a rapid solidification casting sheet with a specification of 10 mm*10 mm*0.3 mm.

[0095] The rest is consistent with Example 1.

[0096] Comparative Example 8

[0097] The difference from Example 1 is:

[0098] (II) Preparation of permanent magnets

[0099] The mixed powder was oriented and pressed in a magnetic field of 1.5 T. The pressed green body was sintered at 1000°C for 4 h, tempered at 900°C for 3 h, and tempered at 500°C for 4 h to obtain a sintered green body, and its magnetic properties were tested.

[0100] The rest is consistent with Example 1.

[0101] The properties of the magnets prepared in Examples 1-5 and Comparative Examples 1-8 were statistically analyzed, and the results are shown in Table 1.

[0102] Table 1

[0103]

[0104] It can be seen from Table 1 that compared with the hydrogen crushing method of comparative examples 1-4, the magnets prepared in Examples 1-4 can greatly shorten the powder making time and thus improve production efficiency without affecting the magnetic properties of the original product; and because the preparation method eliminates the use of hydrogen, the safety hazards of the production process are reduced, and the powder making speed is accelerated under the premise of safety and environmental protection, and high-quality powder with more uniform particle size distribution and more complete rare earth-rich phase distribution is obtained. Comparative Example 5 uses a jaw crusher to replace vacuum microwave powder making, and the crushing time is longer and the efficiency is lower; the protective medium used is an organic solvent such as gasoline, which has certain dangers; its crushing effect is not sufficient compared with vacuum microwave powder making, and the distribution of rare earth-rich phase is uneven, resulting in a lower coercive force. Comparative Example 6 does not charge nitrogen protection, resulting in a slightly higher oxygen content in the sintered magnet prepared by this method, and its various magnetic properties are all reduced. The size of the rapid solidification casting sheet in Comparative Example 7 is too small, resulting in a more uniform coating of the rare earth-rich phase and an increase in its coercive force. However, due to the large amount of alloy elements entering the main phase and the decrease in the volume fraction of the main phase, the remanence and magnetic energy product are reduced. The orientation magnetic field of Comparative Example 8 is 1.5 T, which causes its orientation degree to decrease, resulting in a decrease in both remanence and magnetic energy product.

[0105] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A highly safe rare earth permanent magnet powder making method, characterized in that: The following steps are involved: Step 1) batching and smelting the raw materials according to the components of NdFeB magnets; Step 2) preparing a casting sheet using a vacuum rapid solidification belt spinning furnace; Step 3) placing the cast sheet obtained in step 2) into a vacuum microwave heating device to prepare a pre-made powder; Step 4) air-milling the preformed powder obtained in step 3) to obtain magnetic powder; Wherein, in step 3), the vacuum microwave heating conditions are: microwave frequency 2.45GHz±50Hz, microwave power 1000-5000W, heating to 400-600℃ at a heating rate of 10℃ / min-100℃ / min, and continuous heating for 10-30min after the irradiation reaches the highest temperature.

2. The high-safety rare earth permanent magnet powder making method according to claim 1, characterized in that: In step 1), the composition of the NdFeB magnet is (PrNd) a RE w Fe x B y M z , wherein RE is selected from at least one of Ce, La, Dy, and Tb, and M is selected from at least one of Al, Co, Cu, Nb, Zr, and Ga; a, w, x, y, and z are all mass percentages of the corresponding elements, 27≤a≤33, 1≤w≤3, 0.95≤y≤1.10, 0.15≤z≤1.2, and x is the remainder and x is greater than 0.

3. The high-safety rare earth permanent magnet powder making method according to claim 1, characterized in that: In step 2), the size of the casting sheet is that the length and width are both less than 30 mm, and the thickness is between 0.2-0.5 mm.

4. The high-safety rare earth permanent magnet powder making method according to claim 1, characterized in that: In step 3), before using the vacuum microwave heating device, a pretreatment step is also included: the device is evacuated to 10 -2 -10 -1 Pa, preheating temperature is 50-100℃, and preheating time is 0.1-1h.

5. The high-safety rare earth permanent magnet powder making method according to claim 1, characterized in that: In step 3), the obtained preformed powder has a particle size of 30-500 μm, and microcracks caused by thermal stress exist inside the powder.

6. The high-safety rare earth permanent magnet powder making method according to claim 1, characterized in that: In step 4), the average particle size of the magnetic powder obtained is 2-5 μm, and D 99 / D 10 =2.0-5.

0.

7. Application of the high-safety rare earth permanent magnet powder making method according to any one of claims 1 to 6 in the preparation of permanent magnets, characterized in that: The following steps are involved: Step a) orienting and pressing the magnetic powder obtained by the powder making method according to any one of claims 1 to 6 in a magnetic field to obtain a blank; Step b) heat-treating the blank after pressing in step a) to obtain a sintered NdFeB permanent magnet.

8. The use according to claim 7, characterized in that Step b) The heat treatment conditions are: sintering the green compact at 900-1100°C, first tempering at 900-950°C, and second tempering at 500-650°C.

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