A neodymium iron boron spherical micro powder and its preparation method

Abstract

This invention provides a method for preparing neodymium iron boron (NdFeB) spherical micro powder. The method involves melting alloy raw materials in a container filled with inert gas to form an alloy melt. A pulse signal with a certain voltage and frequency is input to a piezoelectric ceramic. Under the pressure difference between the inside and outside, the alloy melt is extruded from the bottom of the container and falls freely. Gas is ejected from an atomizing nozzle, impacting and breaking the molten metal extruded from the bottom of the container into small droplets. After cooling and solidification, NdFeB spherical micro powder is obtained. The NdFeB spherical micro powder comprises: Nd, Ce, La, Y, B, Pr, Cu, Hf, Ho, Zr, Gd, Al, Co, Ga, Ti, Dy, Tb, and Fe. In this invention, by preparing a NdFeB alloy melt with a certain chemical composition, the resulting NdFeB spherical micropowder has a uniform particle size distribution and good sphericity. Furthermore, the spherical micropowder prepared by the method of this invention can better meet the requirements of NdFeB bonded magnets and NdFeB magnet 3D printing for spherical micropowder. The process is controllable and suitable for promotion.

Description

Technical Field

[0001] This invention belongs to the field of metal and alloy powder preparation technology, and relates to the preparation of neodymium iron boron micro powder, and particularly to a neodymium iron boron spherical micro powder and its preparation method. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnet materials are widely used in wind power generation, electric vehicles, consumer electronics (mobile phones, audio equipment, televisions, laptops, etc.), biomedical instruments, permanent magnet motors, and other fields. Modern science and technology and the information industry are developing towards integration, thinning, miniaturization, and intelligent methods. The emergence of NdFeB permanent magnet materials has greatly promoted the progress of modern science and technology and the information industry, serving as one of its important material foundations. With the rapid development of new energy vehicles and intelligent manufacturing, the demand for NdFeB permanent magnet materials is also increasing.

[0003] CN109509628B discloses a method for preparing sintered NdFeB composite powder. The method involves preparing NdFeB coarse powder and hydrogen-containing medium alloy particles, where the hydrogen content in the hydrogen-containing medium alloy particles is 0.2-0.4% by mass. The oxide layer on the surface of the low-melting-point metal powder is activated and reduced by hydrogen released at high temperature from the hydrogen-containing medium alloy particles. The heat-treated material obtained through heat treatment is added to the NdFeB coarse powder to obtain the composite coarse powder. When the composite coarse powder is ground using an air jet mill, the surfaces of the low-melting-point metal powder and the NdFeB powder come into contact and move relative to each other during collision. The grinding debris separated from the low-melting-point metal powder, along with NdFeB micro-powder with an average particle size of 2-5 μm, is separated from the air jet mill chamber as the prepared composite powder. The advantage is that the composite powder prepared by this method has high uniformity and does not require secondary pressing during subsequent pressing and molding, making it suitable for mass production of sintered NdFeB magnets.

[0004] CN108213404A discloses a method for preparing micronized NdFeB permanent magnet materials, a target-type airflow milling method for preparing the micronized powder, and the airflow milled powder. The micronized powder has a sphericity ≥90% and a particle adhesion rate ≤10%. In the target-type airflow milling method, the relationship between the diameter A of the target center, the diameter B of the side nozzle, and the distance C between the target center and the side nozzle is: A / B=m×(C / A+B), where m ranges from 1 to 7, the jet velocity of the side nozzle is 320~580m / s, and the relationship between the diameter F of the classifying wheel and the diameter A of the target center is: F=p×A, where p ranges from 3 to 6. The airflow milled powder obtained by this method consists of ultrafine powder and the micronized powder; wherein the mass ratio of the ultrafine powder to the total mass of the airflow milled powder is ≤0.5%. The micro powder in this invention has a uniform and narrow particle size distribution and low nitrogen content, making it suitable for large-scale production of high-quality sintered NdFeB permanent magnet materials. Furthermore, the powder obtained by this target-type airflow milling method does not contain any discharge material, saving subsequent processes.

[0005] CN103990805B discloses a method and equipment for preparing neodymium iron boron rare earth permanent magnet alloy powder. First, the mixed hydrogen-crushed powder is loaded into the hopper of a feeder. The powder is then added to the grinding chamber through the feeder. High-speed airflow from the nozzle is used for grinding. The ground powder is then carried by the airflow into a centrifugal sorting wheel for powder selection. Fine powder is collected by a cyclone collector after being separated by the sorting wheel. A small amount of fine powder is discharged with the airflow from the exhaust pipe of the cyclone collector and then enters a post-cyclone collector for collection. The powder collected by the cyclone collector and the powder collected by the post-cyclone collector are introduced into a collection tank through a receiving device. The gas discharged from the post-cyclone collector is compressed by a compressor and cooled by a cooler before entering the air inlet pipe of the nozzle for recycling.

[0006] Currently, the preparation of NdFeB spherical micropowder mainly employs techniques such as hydrogen crushing-air jet milling and melt quenching. Hydrogen crushing-air jet milling relies on powder particle collision for powder preparation, which cannot effectively control the collision process, resulting in irregularly shaped powders with many sharp edges, and also generating a significant amount of ultrafine powder during the collision process. Melt quenching, using mechanical grinding, also produces irregularly shaped powders. The existing NdFeB spherical micropowder preparation techniques suffer from a series of problems, including uneven particle size distribution and low sphericity. For NdFeB bonded magnets and 3D printing of NdFeB magnets, preparing spherical micropowders with good particle size distribution, flowability, and sphericity is an effective method for obtaining high-performance NdFeB magnets. Therefore, there is an urgent need to research a novel method for preparing NdFeB spherical micropowders. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a neodymium iron boron spherical micro powder and its preparation method. In this invention, a neodymium iron boron alloy melt with a certain chemical composition is prepared, resulting in a neodymium iron boron spherical micro powder with uniform particle size distribution and good sphericity. Furthermore, the spherical micro powder prepared by the method of this invention can better meet the requirements for spherical micro powder in neodymium iron boron bonded magnets and 3D printing of neodymium iron boron magnets. The process is controllable and suitable for widespread application.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing neodymium iron boron spherical micro powder, the method comprising:

[0010] The alloy raw material is filled with inert gas in a container to melt and form an alloy melt. A pulse signal with a certain voltage and frequency is input to the piezoelectric ceramic, causing the alloy melt at the micropore at the bottom of the container to vibrate periodically. Under the action of the pressure difference between the inside and outside of the container, the alloy melt is squeezed out from the bottom of the container and falls freely. The gas is sprayed out by the atomizing nozzle. The gas impacts and breaks the molten metal squeezed out from the bottom of the container into small droplets. After cooling and solidification, NdFeB spherical micro powder is obtained.

[0011] In this invention, by preparing a NdFeB alloy melt with a certain chemical composition, the resulting NdFeB spherical micropowder has a uniform particle size distribution and good sphericity. Furthermore, the spherical micropowder prepared by the method of this invention can better meet the requirements of NdFeB bonded magnets and NdFeB magnet 3D printing for spherical micropowder. The process is controllable and suitable for promotion.

[0012] As a preferred technical solution of the present invention, the volume ratio of the alloy raw material to the container is 60 to 80:100, with a volume ratio of 100%. For example, it can be 60:100, 65:100, 70:100, 75:100, or 80:100, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] This invention specifically limits the volume ratio of alloy raw materials to container to 60-80:100. When the ratio exceeds the limit of 80:100, the melt composition will be uneven. This is because the volume ratio is too high and the electromagnetic stirring is uneven. When the ratio is lower than the limit of 60:100, the spherical powder composition will deviate from the design value. This is because the volume ratio is too low and the volatilization of rare earth elements will be aggravated during the melting process.

[0014] As a preferred technical solution of the present invention, the temperature of the melting process is 1000-1500℃, for example, it can be 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, or 1500℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] As a preferred embodiment of the present invention, the vacuum degree of the melting process is 5×10⁻⁶. -4 ~10Pa.

[0016] In a preferred embodiment of the present invention, the inert gas is argon.

[0017] As a preferred technical solution of the present invention, the angle of the inert gas ejection is 10 to 35°, for example, it can be 10°, 17°, 19°, 20°, 21°, 22°, 24°, 26°, 27°, 29°, 30°, or 35°, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the inert gas ejection velocity is 250–500 m / s, for example, it can be 250 m / s, 280 m / s, 300 m / s, 320 m / s, 340 m / s, 380 m / s, 400 m / s, 420 m / s, 440 m / s, 460 m / s, or 500 m / s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] This invention specifically limits the flow rate of the inert gas ejection to 250–500 m / s. When the flow rate exceeds the limit of 500 m / s, the sphericity of the spherical powder will deteriorate. This is because the flow rate is too high, resulting in uneven breakage of the molten metal droplets. When the flow rate is lower than the limit of 250 m / s, the particle size of the spherical powder will be too large. This is because the flow rate is too low, resulting in insufficient breakage of the molten metal.

[0020] Preferably, the gas pressure when the inert gas is ejected is 1.5 to 6 MPa, for example, it can be 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa, or 6 MPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] As a preferred technical solution of the present invention, the certain voltage is 1 to 200V, for example, it can be 1V, 10V, 50V, 60V, 80V, 100V, 160V, 170V, 180V, 190V, 200V, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] As a preferred technical solution of the present invention, the certain frequency is 10 to 300 Hz, for example, it can be 10 Hz, 30 Hz, 40 Hz, 60 Hz, 80 Hz, 100 Hz, 150 Hz, 200 Hz, 250 Hz, or 300 Hz, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] As a preferred embodiment of the present invention, the preparation method specifically includes the following steps:

[0024] (I) The alloy raw material is filled with inert gas in a container and melted at 1000-1500℃ to form an alloy melt;

[0025] (II) Input a pulse signal with a voltage of 1 to 200V and a frequency of 10 to 300Hz into the container, causing the alloy melt at the micropore at the bottom of the container to vibrate periodically. Under the action of the pressure difference between the inside and outside of the container, the alloy melt is squeezed out from the bottom of the container and falls freely.

[0026] (III) The gas is ejected from the atomizing nozzle at an angle of 10 to 35°, with a flow rate of 250 to 500 m / s and a gas pressure of 1.5 to 6 MPa. The gas impacts and breaks the molten metal liquid squeezed out of the container into small droplets, which are then cooled and solidified to obtain neodymium iron boron spherical micro powder.

[0027] In a second aspect, the present invention provides a neodymium iron boron spherical micro powder prepared by the preparation method described in the first aspect, wherein the neodymium iron boron spherical micro powder comprises the following elements: Nd, Ce, La, Y, B, Pr, Cu, Hf, Ho, Zr, Gd, Al, Co, Ga, Ti, Dy, Tb and Fe.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] In this invention, by preparing a NdFeB alloy melt with a certain chemical composition, the resulting NdFeB spherical micropowder has a uniform particle size distribution and good sphericity. Furthermore, the spherical micropowder prepared by the method of this invention can better meet the requirements of NdFeB bonded magnets and NdFeB magnet 3D printing for spherical micropowder. The process is controllable and suitable for promotion. Attached Figure Description

[0030] Figure 1 A schematic diagram of an apparatus for preparing neodymium iron boron spherical micro powder according to a specific embodiment of the present invention;

[0031] Wherein: 1-Gas inlet; 2-Piezoelectric ceramic; 3-Drive rod; 4-Alloy melt; 5-Atomizing nozzle; 6-Container. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] In one specific embodiment, the present invention provides a schematic diagram of an apparatus for preparing neodymium iron boron spherical micro powder, the apparatus being as follows: Figure 1As shown, the system includes a container 6 with a gas inlet 1 at its upper end and a transmission rod 3 inserted into the middle. A piezoelectric ceramic 2 is mounted on the side of the transmission rod 3 away from the insertion end of the container 6. An atomizing nozzle 5 is positioned between the containers 6. Inert gas is introduced into the container 6 to melt the alloy raw material, forming an alloy melt. A pulse signal with a certain voltage and frequency is then input into the container 6, causing the alloy melt at the micropores at the bottom of the container 6 to vibrate. Under the pressure difference between the inside and outside of the container 6, the alloy melt is squeezed out from the bottom of the container 6 and falls freely. Gas is ejected from the atomizing nozzle 5, which impacts and breaks the molten metal squeezed out of the container 6 into small droplets. After cooling and solidification, NdFeB spherical micropowder is obtained.

[0034] Example 1

[0035] This embodiment provides a method for preparing neodymium iron boron spherical micro powder, the preparation method specifically including the following steps:

[0036] (1) Use a shot peening machine to grind the surface of raw materials such as neodymium and iron. Put the raw materials into the crucible chamber. The total volume of the raw materials accounts for 65% of the crucible chamber. Vacuum is drawn. After the vacuum reaches 4Pa, argon gas is filled in for protection. The crucible is heated to 1340℃ to completely melt the raw materials and obtain neodymium iron boron alloy melt 4.

[0037] (2) When an inert gas is introduced into the crucible, the NdFeB alloy melt 4 is more easily squeezed out from the bottom of the crucible when the pressure difference between the inside and outside of the crucible reaches 3 kPa. A pulse signal with an input voltage of 20V and a frequency of 100Hz drives the piezoelectric ceramic 2 to produce displacement, which drives the transmission rod 3 to perform periodic reciprocating vibration. Under the action of the pressure difference between the inside and outside of the crucible and the periodic vibration of the alloy melt 4 at the bottom of the crucible, part of the alloy melt 4 is squeezed out from the bottom of the crucible and falls freely.

[0038] (3) During the free fall of the alloy melt 4, the atomizing nozzles 5 on both sides spray nitrogen gas with a gas pressure of 3.5MPa and a gas velocity of 290m / s at a 25° angle, which impacts and breaks the molten metal liquid into small droplets. After the droplets solidify, they form spheres and fall into the collection container 6, thus obtaining NdFeB spherical micro powder.

[0039] Example 2

[0040] This embodiment provides a method for preparing neodymium iron boron spherical micro powder, the preparation method specifically including the following steps:

[0041] (1) Use a shot peening machine to grind the surface of raw materials such as neodymium and iron, put the raw materials into the crucible chamber, the total volume of the raw materials occupies 60% of the crucible chamber, evacuate the vacuum, fill the vacuum with argon gas for protection after the vacuum reaches 4Pa, heat the crucible to 1400℃ to completely melt the raw materials to obtain neodymium iron boron alloy melt 4.

[0042] (2) When an inert gas is introduced into the crucible, the NdFeB alloy melt 4 is more easily squeezed out from the bottom of the crucible when the pressure difference between the inside and outside of the crucible reaches 3 kPa. A pulse signal with an input voltage of 30V and a frequency of 120Hz drives the piezoelectric ceramic 2 to produce displacement, which drives the transmission rod 3 to perform periodic reciprocating vibration. Under the action of the pressure difference between the inside and outside of the crucible and the periodic vibration of the alloy melt 4 at the bottom of the crucible, part of the alloy melt 4 is squeezed out from the bottom of the crucible and falls freely.

[0043] (3) During the free fall of the alloy melt 4, the atomizing nozzles 5 on both sides spray nitrogen gas with a gas pressure of 3.5MPa and a gas velocity of 350m / s at an angle of 15°, which impacts and breaks the molten metal liquid into small droplets. After the droplets solidify, they form spheres and fall into the collection container 6, thus obtaining neodymium iron boron spherical micro powder.

[0044] Example 3

[0045] This embodiment provides a method for preparing neodymium iron boron spherical micro powder. The difference between this embodiment and Embodiment 1 is that in step (3), the gas flow rate is 200 m / s. The remaining process parameters and operating steps are exactly the same as in Embodiment 1.

[0046] Example 4

[0047] This embodiment provides a method for preparing neodymium iron boron spherical micro powder. The difference between this embodiment and Embodiment 1 is that in step (3), the gas flow rate is 550 m / s. The remaining process parameters and operating steps are exactly the same as in Embodiment 1.

[0048] The particle size and sphericity data of the neodymium iron boron magnet micropowders prepared in each embodiment are shown in Table 1.

[0049] Table 1

[0050]

[0051] As can be seen from the data in Table 1:

[0052] (2) Compared with Example 1, the particle size of Example 3 was significantly larger than that of Example 1, and the sphericity of Example 4 was significantly lower than that of Example 1. This is because the gas flow rate in Example 3 was too low, while the gas flow rate in Example 4 was too high. A high gas flow rate affects sphericity, while a low gas flow rate affects particle size. The reason is that when the gas flow rate exceeds the limit of 500 m / s, the sphericity of the spherical powder deteriorates because the excessive flow rate leads to uneven breakage of the molten metal droplets; when the gas flow rate is below 250 m / s, the particle size of the spherical powder is too large because the insufficient flow rate prevents the molten metal from being fully broken up.

[0053] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for producing a neodymium-iron-boron spherical fine powder, characterized by, The preparation method comprises: (I) putting alloy raw materials into a container, filling inert gas, and melting to form an alloy melt at 1000-1500 ℃; the volume ratio of the alloy raw materials to the container is 60-80:100, based on 100% in volume; (II) inputting a pulse signal with a voltage of 1-200 V and a frequency of 10-300 Hz to the piezoelectric ceramic, so that the alloy melt at the micropores at the bottom of the container is periodically vibrated, and the alloy melt is extruded from the bottom of the container and freely falls under the action of the pressure difference between the inside and outside of the container; (III) spraying nitrogen gas from the atomizing nozzle, the angle of the nitrogen gas spray is 10-35°, the flow rate is 250-500 m / s, the gas flow pressure is 1.5-6 MPa, the nitrogen gas impacts and breaks the molten metal liquid extruded from the container to form small droplets, which are cooled and solidified to obtain neodymium iron boron spherical micro powder.

2. The production method according to claim 1, characterized by, The vacuum degree of the melting process is 5 x 10 -4 Pa.

3. The preparation method according to claim 1, characterized in that, The inert gas is argon.

4. The spherical Nd-Fe-B micropowder prepared by the method of any one of claims 1-3, characterized in that, The neodymium iron boron spherical micro powder comprises the following elements: Nd, Ce, La, Y, B, Pr, Cu, Hf, Ho, Zr, Gd, Al, Co, Ga, Ti, Dy, Tb and Fe.

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