A method for optimizing microstructure of neodymium-iron-boron magnet rapid solidified flakes using ultrasound

Abstract

The application provides a method for optimizing microstructure of a neodymium-iron-boron magnet rapid solidification sheet by using ultrasonic waves, and belongs to the technical field of neodymium-iron-boron alloy rapid solidification casting sheet. The application applies ultrasonic vibration on a copper roller by using an ultrasonic wave introduction device while the copper roller is rotating, then neodymium-iron-boron alloy melt is cast onto the surface of the copper roller to obtain a neodymium-iron-boron magnet rapid solidification sheet; the initial driving frequency of the copper roller is accurately designed and the amplitude is limited during the casting process, so that the nucleation rate of the magnetic phase grains near the roller surface of the rapid solidification sheet is increased, the growth of the magnetic phase grains in the direction from the near roller surface to the far roller surface is promoted, the magnetic phase columnar crystals are effectively refined, and the uniformity of the microstructure and the thickness consistency of the rapid solidification sheet are significantly improved, so that the effects of improving the nucleation rate and inhibiting the growth of coarse crystals are achieved, and finally the rapid solidification sheet with refined columnar crystals and good orientation is obtained.

Description

Technical Field

[0001] This invention belongs to the field of neodymium iron boron alloy rapid solidification casting technology, specifically relating to a method for optimizing the microstructure of neodymium iron boron magnet rapid solidification sheets using ultrasound. Background Technology

[0002] As a typical representative of third-generation rare-earth permanent magnets, neodymium iron boron (NdFeB) permanent magnets have become the most widely used and extensively applied permanent magnet material due to their superior magnetic properties. The microstructure of the rapidly solidified sheet, the alloy precursor (first process) for NdFeB permanent magnets, significantly influences the magnetic properties of the subsequent magnets. It is generally believed in the industry that an ideal rapidly solidified sheet should possess a uniform, fine, penetrating columnar crystal structure, and Nd2Fe... 14 The B magnetic principal phase exhibits preferential orientation along the heat flow direction.

[0003] Rapid solidification and ribbon casting is a key technology for preparing rapid solidification sheets of rare earth alloys. This technology involves casting molten rare earth alloy liquid onto the surface of a high-speed rotating cooling copper roller, allowing the alloy liquid to solidify in a very short time and fly out in the form of a thin ribbon. This effectively suppresses the formation of soft magnetic phases and rare earth impurities, resulting in Nd2Fe alloy sheets. 14 Rapidly solidified flakes, dominated by the magnetic phase and with a uniform microstructure, provide a good microstructural basis for subsequent hydrogen crushing and air jet milling. However, existing rapid solidification casting technology has many problems in practical applications: First, rapid solidification flakes often exhibit defects such as coarse dendrites and uneven distribution of the second phase; secondly, in conventional strip casting processes, the nucleation rate of the alloy melt on the roller surface is low, easily forming a dense equiaxed crystal region; and thirdly, due to the uneven distribution of nucleation points, rapid solidification flakes are prone to developing coarse dendrites, making it difficult to achieve uniform and refined columnar crystal growth.

[0004] Therefore, how to improve the microstructure of the quick-setting tablets has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for optimizing the microstructure of rapidly solidified neodymium iron boron magnets using ultrasound. The method provided by this invention can improve the nucleation rate, inhibit coarse grain growth, and obtain rapidly solidified sheets with refined columnar crystals and good orientation.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for optimizing the microstructure of a neodymium iron boron magnet rapid coagulation sheet using ultrasound, comprising the following steps: (1) Perform resonance state simulation on the copper roller to obtain the mode shapes corresponding to different frequencies, and then select the mode shape and corresponding frequency of the pitch circle vibration. f 1 , the frequency f 1 The point of maximum amplitude is taken as the excitation point; (2) Install the ultrasonic wave introduction device and the copper roller, and at the frequency f 1 and f 2 Adjust the driving frequency of the ultrasonic wave introduction device to find the mode shape of the nodal circle vibration that matches the mode shape in step (1) and the corresponding initial driving frequency. f 0 The initial driving frequency f 0 The point of maximum amplitude is taken as the excitation point; the frequency f 2 and f 1 The difference is ≤10kHz; (3) Using the initial driving frequency f 0 Ultrasonic waves are applied to the copper roller at the excitation point obtained in step (2), and then the NdFeB alloy melt is cast onto the surface of the rotating copper roller to obtain a NdFeB magnet rapid solidification sheet; the amplitude A of the roller surface corresponding to the excitation point is < A max , A max The calculation formula is shown in Equation I: Formula I; In formula I, ρ This refers to the density of neodymium iron boron magnet rapid solidification sheets, in g / cm³. 3 ; h The thickness of the neodymium iron boron magnet rapid solidification sheet is given in μm; g is the acceleration due to gravity in m / s². 2 ; θ The angle between the line connecting the casting point on the surface of the copper roller and the center of the copper roller and the horizontal direction is expressed in degrees. f 0 The initial driving frequency is expressed in Hz. P The unit is the adsorption pressure of NdFeB alloy melt without ultrasound, expressed in Pa. ω The angular velocity of the copper roller is expressed in rad / s. R The radius of the copper roller is in meters (m).

[0007] Preferably, in step (3), the operating frequency of the ultrasonic introduction device is adjusted in real time during the casting of the NdFeB alloy melt. f ( t ), f ( t The calculation formula for ) is shown in Equation II: Formula II; In formula II, f(t)The real-time operating frequency of the ultrasonic wave introduction device corresponding to the application time t (s); f 0 The initial driving frequency is expressed in Hz. α f Temperature drift coefficient of the piezoelectric ceramic used in the ultrasonic wave introduction device, expressed in Kelvin. -1 , which is a negative value; T t The ambient temperature is in real-time, expressed in Kelvin (K). T 0 The initial ambient temperature, expressed in Kelvin (K). T max The thermal equilibrium temperature of the ultrasonic wave introduction device is expressed in K. τ th The thermal equilibrium time of the ultrasonic wave introduction device is expressed in seconds.

[0008] Preferably, the composition of the NdFeB alloy melt in step (3) is: RE x Fe y M z B n x, y, z and n are all mass percentages, where RE is one or more of Nd, Pr, Dy and Tb, M is one or more of Cu, Al, Co, Zr, Ga and Nb, x is 25~35, y is 65~75, z is 0~2 and n is 0.8~1.2.

[0009] Preferably, in step (3) A max Maximum driving voltage U max The driving voltage U of the ultrasonic wave introduction device is obtained below. max U max Initial driving frequency f 0 The corresponding maximum driving voltage.

[0010] Preferably, the driving voltage U of the ultrasonic wave introduction device is less than 0.9U. max .

[0011] Preferably, the excitation point in step (3) is the end face or roller surface of the copper roller.

[0012] Preferably, the linear velocity of the copper roller in step (3) is 1~2m / s.

[0013] Preferably, the solidification time of the NdFeB alloy melt in step (3) is 10 minutes. -6 ~10 -3 s.

[0014] ​Preferably, the drift of the working frequency during the casting process in step (3) is ≤10%.

[0015] Preferably, in step (3), the initial output power P0 of the ultrasonic wave is 10~2000W, and the output power of the ultrasonic wave introduction device is monitored in real time during the casting process of the NdFeB alloy melt, and the drift of the real-time output power is ≤10%.

[0016] This invention applies ultrasonic vibration to a rotating copper roller using an ultrasonic induction device, then casts molten NdFeB alloy onto the roller surface to obtain NdFeB magnet-based rapid-solidified sheets. During casting, precise design of the initial driving frequency of the copper roller and reasonable adjustment and compensation of the ultrasonic operating frequency based on changes in ambient temperature increase the nucleation rate of magnetic phase grains near the roller surface, promoting the growth of magnetic phase grains along the direction from the near-roller surface to the far-roller surface. This effectively refines the columnar crystals of the magnetic phase and significantly improves the uniformity and thickness consistency of the rapid-solidified sheet, achieving the effects of increasing the nucleation rate and suppressing coarse grain growth, ultimately obtaining rapid-solidified sheets with refined columnar crystals and good orientation. Experimental results show that the average width of the columnar crystals in the rapid-solidified sheets obtained by the method provided in this invention is 3.5~4.3μm, and the coercivity of the rapid-solidified sheets is 10.0~11.7kOe. Attached Figure Description

[0017] Figure 1 The image shown is a simulation of the resonant state at 19.8 kHz in Example 1. Figure 2 The image shown is a simulation of the resonant state at 20.2 kHz in Example 1. Figure 3 The image shown is a simulation of the resonant state at 21 kHz in Example 1. Figure 4 Backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Example 1; Figure 5 Backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Comparative Example 1; Figure 6 The image shows the backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Example 2. Figure 7 Backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Comparative Example 2; Figure 8 Backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Example 3; Figure 9 The image shows the backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Comparative Example 3. Detailed Implementation

[0018] This invention provides a method for optimizing the microstructure of a neodymium iron boron magnet rapid coagulation sheet using ultrasound, comprising the following steps: (1) Perform resonance state simulation on the copper roller to obtain the vibration modes corresponding to different frequencies, and then select the vibration mode and corresponding frequency of the pitch circle vibration. f 1 , the frequency f 1 The point of maximum amplitude is taken as the excitation point; (2) Install the ultrasonic wave introduction device and the copper roller, and set the frequency... f 1 and f 2 Adjust the driving frequency of the ultrasonic wave introduction device to find the mode shape of the nodal circle vibration that matches the mode shape in step (1) and the corresponding initial driving frequency. f 0 The initial driving frequency f 0 The point of maximum amplitude is taken as the excitation point; the frequency f 2 and f 1 The difference is ≤10kHz; (3) Using the initial driving frequency f 0 Ultrasonic waves are applied to the copper roller at the excitation point obtained in step (2), and then the NdFeB alloy melt is cast onto the surface of the rotating copper roller to obtain a NdFeB magnet rapid solidification sheet; the amplitude A of the roller surface corresponding to the excitation point is < A max , A max The calculation formula is shown in Equation I: Formula I; In formula I, ρ This refers to the density of neodymium iron boron magnet rapid solidification sheets, in g / cm³. 3 ; h The thickness of the neodymium iron boron magnet rapid solidification sheet is given in μm; g is the acceleration due to gravity in m / s². 2 ; θ The angle between the line connecting the casting point on the surface of the copper roller and the center of the copper roller and the horizontal direction is expressed in degrees. f 0 The initial driving frequency is expressed in Hz. P The unit is the adsorption pressure of NdFeB alloy melt without ultrasound, expressed in Pa. ω The angular velocity of the copper roller is expressed in rad / s. R The radius of the copper roller is in meters (m).

[0019] Unless otherwise specified, the present invention does not impose any special restrictions on the source of the raw materials, and commercially available products well known to those skilled in the art can be used.

[0020] This invention simulates the resonant state of a copper roller to obtain the mode shapes corresponding to different frequencies, and then selects the mode shape and corresponding frequency of the pitch circle vibration. f 1 The frequency f 1 The point of maximum amplitude is taken as the excitation point. This invention first performs simulation to obtain the desired frequency. f 1 And the excitation point, so as to facilitate the exploration of the initial driving frequency during subsequent actual operation.

[0021] This invention performs resonance state simulation on the copper roller to obtain the vibration modes corresponding to different frequencies, and then selects the vibration mode and corresponding frequency of the pitch circle vibration. f 1 There are no special limitations on the operation; any operation familiar to those skilled in the art can be used.

[0022] In one implementation, the present invention can construct a geometric model of a copper roller in the simulation software COMSOL, and then set the density, Young's modulus and Poisson's ratio of the copper roller material; then select the solid mechanics module, and then set the boundary conditions of unilateral fixation; then mesh the geometric model, and set appropriate characteristic frequency reference values ​​and required characteristic frequencies in the solver to obtain the characteristic frequency mode shapes and modal distribution of the geometric model.

[0023] In this invention, the excitation point is the installation location of the ultrasonic wave introduction device.

[0024] This invention integrates an ultrasonic wave introduction device and a copper roller, at a frequency... f 1 and f 2 Adjust the driving frequency of the ultrasonic wave introduction device to find the vibration mode of the pitch circle vibration that matches the aforementioned vibration mode and the corresponding initial driving frequency. f 0 The initial driving frequency f 0 The point of maximum amplitude is taken as the excitation point.

[0025] In this invention, the ultrasonic wave introduction device preferably includes an ultrasonic power supply and an ultrasonic transducer. The ultrasonic transducer of this invention ensures proper contact between the transducer and the copper roller at the excitation point, guaranteeing effective ultrasonic wave introduction.

[0026] The present invention does not have any special limitations on the operation of installing the ultrasonic wave introduction device and the copper roller; any operation known to those skilled in the art can be used.

[0027] In this invention, the frequency f 2 and f 1 The difference is ≤10kHz.

[0028] In this invention, a vibration measuring device is preferably used to perform surface scanning mode shape verification to find the mode shape of the pitch circle vibration that is consistent with the aforementioned mode shape. As one embodiment, the vibration measuring device can be a laser vibrometer.

[0029] In this invention, when f 1 and f 2 When no mode shape matching the aforementioned mode shape can be found, it is preferable to […]. f 1 , f 2 The search continues at frequencies near the design mode until the test mode matches the design mode. This invention addresses the issue of frequencies near the design mode. f 1 , f 2 There are no specific limitations on the specific frequencies in the vicinity, as long as the test mode shape matches the design mode shape.

[0030] In this invention, the excitation point is preferably the end face or roller surface of the copper roller, and more preferably the roller surface or side surface farthest from the center of the copper roller surface.

[0031] Obtain the initial driving frequency f 0 After reaching the excitation point, the present invention uses an initial driving frequency. f 0 Ultrasonic waves are applied to the copper roller at the excitation point, and then the NdFeB alloy melt is poured onto the surface of the rotating copper roller to obtain a NdFeB magnet rapid solidification sheet.

[0032] In this invention, the amplitude A of the roller surface corresponding to the excitation point is < A max , A max The calculation formula is shown in Equation I: Formula I; In formula I, ρ This refers to the density of neodymium iron boron magnet rapid solidification sheets, in g / cm³. 3 ; h The thickness of the neodymium iron boron magnet rapid solidification sheet is given in μm; g is the acceleration due to gravity in m / s². 2 ; θ The angle between the line connecting the casting point on the surface of the copper roller and the center of the copper roller and the horizontal direction is expressed in degrees. f0 The initial driving frequency is expressed in Hz. P The unit is the adsorption pressure of NdFeB alloy melt without ultrasound, expressed in Pa. ω The angular velocity of the copper roller is expressed in rad / s. R The radius of the copper roller is in meters (m).

[0033] This invention limits the amplitude A of the roller surface corresponding to the excitation point. A max This can prevent the ultrasonic amplitude from being too large, causing the quick-setting sheet to detach from the roller surface before solidification is complete, thus weakening the ultrasonic effect.

[0034] In one implementation, the amplitude A of the roller surface corresponding to the excitation point can be <0.5μm, or it can be 0.02μm. <A≤0.3μm。

[0035] In this invention, the P Preferably, the result is obtained through a liquid peeling test on a solid surface. This invention relates to the method used in the liquid peeling test on a solid surface. P The operation is not particularly limited and can be performed using methods familiar to those skilled in the art. In this invention, the... P This represents the interfacial dynamic adsorption strength of the alloy during solidification.

[0036] In this invention, the P The value is preferably a fixed value; the fixed value is preferably 15400 Pa.

[0037] In this invention, the preferred composition of the NdFeB alloy melt is: RE x Fe y M z B n The values ​​of x, y, z, and n are all mass percentages; the RE is preferably one or more of Nd, Pr, Dy, and Tb; the M is preferably one or more of Cu, Al, Co, Zr, Ga, and Nb; the x is preferably 25-35; the y is preferably 65-75; the z is preferably 0-2; and the n is preferably 0.8-1.2. As one embodiment, the M can be Co, Cu, and Al; the mass ratio of Co, Cu, and Al can be 0.1:0.4:0.4; the x can be 33; the y can be 65; the z can be 0.9; and the n can be 1.1.

[0038] The present invention does not impose any special limitations on the preparation method of the NdFeB alloy melt, as long as the above-mentioned composition requirements are met.

[0039] As one embodiment, the method for preparing the NdFeB alloy melt can be to melt the NdFeB alloy raw material in an inert atmosphere to a molten state, and then hold it at a certain temperature; the holding time can be 10~20 min, or 10~15 min; the pressure of the inert atmosphere can be >0.2 atm.

[0040] In this invention, the linear velocity of the copper roller is preferably 1~2 m / s. As one embodiment, the linear velocity of the copper roller can be 1.5 m / s.

[0041] The present invention does not impose any particular limitation on the cooling water temperature used for cooling the copper roller; any cooling water temperature well known to those skilled in the art can be used. As one embodiment, the cooling water temperature can be 17°C.

[0042] In this invention, it is preferable to adjust the operating frequency of the ultrasonic wave introduction device in real time during the casting process of the NdFeB alloy melt. f ( t ), f ( t The calculation formula for ) is shown in Equation II: Formula II; In formula II, f(t) The real-time operating frequency of the ultrasonic wave introduction device corresponding to the application time t (s); f 0 The initial driving frequency is expressed in Hz. α f Temperature drift coefficient of the piezoelectric ceramic used in the ultrasonic wave introduction device, expressed in Kelvin. -1 , which is a negative value; T t The ambient temperature is in real-time, expressed in Kelvin (K). T 0 The initial ambient temperature, in Kelvin (K). T max The thermal equilibrium temperature of the ultrasonic wave introduction device is expressed in K. τ th The thermal equilibrium time of the ultrasonic wave introduction device is expressed in seconds.

[0043] In this invention, in order to ensure that the amplitude of the roller surface corresponding to the excitation point remains unchanged during the casting process, it is necessary to adjust the working frequency in real time. The amplitude of the roller surface remains unchanged by changing the working frequency.

[0044] In this invention, it is preferable to determine whether the amplitude of the roller surface corresponding to the excitation point is stable based on the real-time output power displayed by the power supply of the ultrasonic introduction device.

[0045] In this invention, when the deviation of the real-time output power displayed by the power supply of the ultrasonic introduction device is preferably >10%, the amplitude of the roller surface corresponding to the excitation point is unstable.

[0046] In this invention, the α f Determined by the inherent properties of the material, the impedance is measured using an impedance analyzer at different ambient temperatures. As one implementation method, the... α f It can be -150×10 -6 K -1 .

[0047] In this invention, the T max and τ th Preferably, the temperature-time curve of the ultrasonic transducer measured at room temperature is fitted. As one embodiment, the... T max and τ th The testing method can be as follows: When the ultrasonic transducer is working, the working time corresponding to the temperature of the piezoelectric ceramic rising from room temperature to no significant change (heat dissipation equilibrium) is measured. The real-time temperature of the piezoelectric ceramic corresponding to the working time is recorded and a curve is plotted. The result is obtained by fitting an exponential function. T max and τ th .

[0048] In this invention, the T max Preferably 333K; the τ th The preferred value is 342s.

[0049] In this invention, the drift of the working frequency during the casting process is preferably ≤10%. As one embodiment, the working frequency can be 10~100kHz, or it can be 15kHz, 30kHz or 60kHz.

[0050] In this invention, the A max Maximum driving voltage U max The preferred driving voltage U of the ultrasonic wave introduction device is obtained below. max More preferably <0.9U max U max Initial driving frequency f 0 The corresponding maximum driving voltage.​

[0051] As one implementation method, the U max It can be 2000V.

[0052] In this invention, the casting is preferably carried out in an inert atmosphere; the pressure of the inert atmosphere is preferably >0.2 atm.

[0053] In this invention, the initial output power P0 of the ultrasonic wave is preferably 10~2000W; the output power of the ultrasonic wave introduction device is preferably monitored in real time during the casting process of the NdFeB alloy melt; the drift of the real-time output power is preferably ≤10%. As one embodiment, the initial output power P0 of the ultrasonic wave can be 500W, 1000W, 1200W or 1500W; the offset of the real-time output power can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%.

[0054] In this invention, the preferred solidification time for the NdFeB alloy melt is 10 minutes. -6 ~10 -3 s.

[0055] In this invention, the thickness of the neodymium iron boron magnet rapid solidification sheet is preferably 200~350μm.

[0056] The core mechanism of the method provided by this invention is universal, and the optimization effect of the superfluid effect on the solidification process of alloy melt is applicable to the preparation of NdFeB permanent magnet rapid solidification sheets of various compositions.

[0057] This invention, through ultrasonic optimization treatment, produces the following effects in the preparation of rapidly solidified sheets: ultrasound significantly improves the wettability of the alloy liquid and the copper roller, increasing the effective heterogeneous nucleation sites on the copper roller surface, thereby improving the nucleation rate; in the final microstructure, columnar crystals are significantly refined, the number of penetrating crystals increases, and the uniformity of grain orientation is greatly improved; undesirable phase regions are significantly reduced or eliminated, the second phase is evenly distributed, and local agglomeration is significantly reduced; thickness uniformity is improved. The microstructure of the rapidly solidified sheets is comprehensively and significantly optimized, which is of great significance for improving magnet performance.

[0058] Compared with NdFeB alloy rapid solidification sheets treated without power ultrasonication, the ultrasonically optimized NdFeB alloy rapid solidification sheets of this invention exhibit significantly refined columnar crystals and greatly improved orientation; the phenomenon of second-phase agglomeration is greatly reduced; and the magnets made from the ultrasonically optimized rapid solidification sheets are expected to possess superior comprehensive magnetic properties, which is beneficial for advancing the preparation of high-performance NdFeB permanent magnets.

[0059] Currently, although there are operations that apply ultrasound to the quick-setting sheet casting process, such as CN114121473B: applying ultrasound to the flow channel can break up the large crystal embryos formed in the flow channel of the alloy liquid, and assisting electromagnetic stirring to achieve uniform distribution of the crystal embryos, thereby achieving the effect of microstructure optimization; another example is applying ultrasound to the tundish (CN118073079A) in order to break up the crystal nuclei that have already formed in the tundish, and to promote the uniformity of the alloy liquid composition by applying pulse stirring. The shortcomings of the above two schemes are: (1) During the solidification process of the quick-setting sheet, only a small number of nuclei are present in the tundish or flow channel in the early stage of casting. As the casting time increases, the number of nuclei on the roller surface will gradually decrease, and a large number of nuclei will appear when the alloy melt is cast to the roller surface; (2) Under the superheated state, the difference in superheat of alloy melts with different compositions will affect the actual nucleation effect, so there is a certain limitation on the alloy composition ratio; For example, CN114535519A: By combining the control of copper roller surface roughness, control of alloy liquid flow rate, and application of ultrasound to copper roller, the grain size can be optimized, the product qualification rate and performance stability can be improved. However, this scheme implements the three processes at the same time, and the applied ultrasound frequency is a constant value. The ultrasound parameters are not optimized in real time during the casting process, and it is not feasible to implement in practice. Applying multiple methods at the same time makes the scheme complex and difficult to operate.

[0060] This invention identifies the excitation point on the copper roller through copper roller vibration mode design and amplitude testing. An ultrasonic transducer is then placed at the excitation point to generate ultrasonic vibration waves that act on the roller surface. When the NdFeB alloy melt passes over the roller surface, it is subjected to ultrasonic waves, achieving an optimized power ultrasonic effect. When applying ultrasound, the ultrasonic parameters need to be monitored throughout the casting process. If ultrasonic power and ultrasonic amplitude drift occur during the casting process, the ultrasonic frequency needs to be adjusted in real time to ensure that the ultrasonic power and ultrasonic amplitude remain within the effective range.

[0061] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0062] Example 1 A method for optimizing the tissue of a neodymium iron boron magnet rapid coagulation sheet using ultrasound comprises the following steps: (1) Construct a geometric model of the copper roller (800mm in length and 600mm in diameter) in the simulation software COMSOL, and then set the density of the copper roller material (8.92g / cm³). 3 Young's modulus (13.5 × 10⁻⁶) 3MPa) and Poisson's ratio (0.33); select the solid mechanics module and set the boundary conditions of one-sided fixation; then mesh the geometric model (25mm), and set the characteristic frequency reference value (20.5kHz) and the required number of characteristic frequencies in the solver (20 characteristic frequencies between 19 and 22kHz, in the following order: 19.15kHz, 19.30kHz, 19.42kHz, 19.58kHz, 19.73kHz, 19.8kHz, 20.04kHz, 20.2kHz, 20.31kHz, 20.50kHz, 20.62kHz, 20.75kHz, 20.91kHz, 21kHz, 21.22kHz, 21.37kHz, 21.53kHz, 21.68kHz, 21.84kHz and 22kHz), to obtain a series of copper roller resonance simulation modes, select the mode with circumferential isofrontal planes and the corresponding frequencies. f 1 (21kHz), the frequency f 1 The point of maximum amplitude is taken as the excitation point; (2) Selecting the frequency f 2 Matching and installing a 20kHz ultrasonic transducer and copper roller at the frequency... f 1 and f 2 Adjust the driving frequency of the ultrasonic transducer (20kHz / 2000W standard stepped transducer, piezoelectric ceramic material is PZT-8) to find the vibration mode and corresponding initial driving frequency that are consistent with the vibration mode in step (1). f 0 20.8kHz, the initial driving frequency f 0 The maximum amplitude is taken as the excitation point, and the maximum driving voltage is 2000V, and the maximum output power is 1800W. (3) Under the protection of high-purity argon gas at a pressure of 0.25 atm, the Nd component ratio is... 33 Fe 65 Co 0.1 Al 0.4 Cu 0.4 B 1.1 (wt.%) of alloy raw materials are placed in a melting crucible and heated to a molten state at a melting temperature of 1350℃ and held for 15 minutes to obtain NdFeB alloy melt; (4) Turn on the ultrasonic power supply and set the initial drive frequency. f 0The frequency was 20.8 kHz, the driving voltage was 1200 V, and the initial output power P0 was 1000 W. Ultrasonic waves were applied to the copper roller at the excitation point, and then neodymium iron boron alloy melt was cast onto the surface of the rotating copper roller. The cooling water temperature of the copper roller was 17 °C, and the temperature was 3.5 × 10⁻⁶ W. -5 Rapid solidification within s yields neodymium iron boron magnet fast-solidification sheets; The amplitude A of the roller surface corresponding to the excitation point < A max , A max The calculation formula is shown in Equation I: Formula I; In formula I, ρ This refers to the density of neodymium iron boron magnet rapid solidification sheets, in g / cm³. 3 ; h The thickness of the neodymium iron boron magnet rapid solidification sheet is given in μm; g is the acceleration due to gravity in m / s². 2 ; θ The angle between the line connecting the casting point on the surface of the copper roller and the center of the copper roller and the horizontal direction is expressed in degrees. f 0 This is the initial driving frequency, in Hz. P The adsorption pressure of NdFeB alloy melt without ultrasound is expressed in Pa. ω The angular velocity of the copper roller is expressed in rad / s. R The radius of the copper roller is in meters (m). In formula I, ρ 7.5 g / cm 3 ; h It is 240μm; θ It is 23°; R It is 0.3m; ω It is 5 rad / s. f 0 It is 20.8kHz. P The Pa is 15400; A max It is 0.501 μm; The amplitude A of the roller surface corresponding to the excitation point is 0.11 μm; The linear speed of the copper roller is 1.5 m / s, and the casting time is 15 min. During the casting process, it is necessary to adjust the working frequency in real time to keep the amplitude A of the roller surface constant. The operating frequency of the ultrasonic transducer is adjusted in real time during the casting process of the neodymium iron boron alloy melt. f ( t ), f ( t The calculation formula for ) is shown in Equation II: Formula II; In formula II, f(t) The real-time operating frequency of the ultrasonic transducer corresponds to the application time t (s); f 0 This is the initial driving frequency, in Hz. α f Temperature drift coefficient of the piezoelectric ceramic used in ultrasonic transducers at the operating frequency, in Kelvin. -1 , which is a negative value; T t The ambient temperature is in real-time, expressed in Kelvin (K). T 0 The initial ambient temperature is 25℃, and the unit is K. T max The thermal equilibrium temperature of the ultrasonic wave introduction device is expressed in K. τ th The thermal equilibrium time of the ultrasonic wave introduction device is expressed in seconds. After casting, the ambient temperature in real time T t The value is 313K, and the time is 900s. α f =-150×10 -6 K -1 , T max It is 333K. τ th The time was 342 seconds, which yielded that the operating frequency of the ultrasonic transducer at the end of the casting process was 19.79 kHz; the real-time output power fluctuated with frequency by 980 W, with a power deviation of 2%. The quick-setting flakes then rapidly detach from the roller surface and are automatically collected into the receiving cylinder; after casting is completed, the ultrasonic vibration device is turned off and the copper roller rotation switch is turned off.

[0063] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that ultrasound is not introduced during the casting process; otherwise, they are the same as Example 1.

[0064] Example 2 The only difference between Example 2 and Example 1 is that the driving voltage of the ultrasonic transducer during the casting process is 1800V, the initial output power P0 is 1500W, and the amplitude A is 0.3μm. The rest is the same as Example 1.

[0065] Comparative Example 2 The only difference between Comparative Example 2 and Example 2 is that ultrasound is not introduced during the casting process; otherwise, they are the same as Example 2.

[0066] Example 3 The only difference between Example 3 and Example 1 is that the driving voltage of the ultrasonic transducer during the casting process is 1500V, the initial output power P0 is 1300W, and the amplitude A is 0.15μm. Everything else is the same as in Example 1.

[0067] Comparative Example 3 The only difference between Comparative Example 3 and Example 3 is that ultrasound is not introduced during the casting process; otherwise, they are the same as Example 3.

[0068] Figure 1 The image shown is a simulation of the resonant state at 19.8 kHz in Example 1. Figure 2 The image shown is a simulation of the resonant state at 20.2 kHz in Example 1. Figure 3 The image is a simulation of the resonant state at 21 kHz in Example 1.

[0069] from Figures 1-3 It can be seen that, Figure 3 To achieve a mode shape with circumferential isoplanets, i.e., a superior toroidal resonance mode shape, the excitation point location is selected... Figure 3 The raised area in the middle is where the arrow points.

[0070] Figure 4 Backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Example 1; Figure 5 Backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Comparative Example 1; Figure 6 The image shows the backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Example 2. Figure 7 Backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Comparative Example 2; Figure 8 Backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Example 3; Figure 9 The image shows the backscattered electron image of the neodymium iron boron magnet rapid solidification sheet prepared in Comparative Example 3.

[0071] from Figures 4-9 It can be seen that the microstructure of the rapidly solidified sheet without ultrasonic optimization treatment exhibits more coarse dendritic crystals and unoriented grains. After ultrasonic optimization treatment, the grains are significantly transformed into uniform and fine columnar crystals across the entire cross-section, exhibiting a straighter and more uniform growth pattern. This refinement and homogenization of the microstructure indicates that ultrasound not only inhibits the growth of coarse dendrites but also improves the consistency of grain orientation. This result lays a reliable microstructural foundation for the preparation of high-performance NdFeB magnets.

[0072] Table 1. Statistical table of ultrasound parameters and indices for Examples 1-3 and Comparative Examples 1-3

[0073] As can be seen from Table 1, the average width of the columnar crystals in Example 1 was refined to 3.5 μm, and a coercivity increment (ΔHcj) of 2.3 kOe was obtained.

[0074] Based on the performance indicators of the above embodiments and comparative examples, it can be found that the rapidly solidified sheets prepared by ultrasonic optimization have well-oriented and uniformly arranged refined columnar crystals. In subsequent hydrogen crushing and air jet milling processes, alloys with this structure are more likely to produce uniformly distributed powder. This invention effectively improves the overall performance of rapidly solidified sheets of NdFeB rare earth permanent magnets, and will effectively improve the overall magnetic properties of sintered NdFeB magnets.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for optimizing the microstructure of a neodymium iron boron magnet rapid coagulation sheet using ultrasound, characterized in that, Includes the following steps: (1) Perform resonance state simulation on the copper roller to obtain the mode shapes corresponding to different frequencies, and then select the mode shape and corresponding frequency of the pitch circle vibration. f 1 , the frequency f 1 The point of maximum amplitude is taken as the excitation point; (2) Install the ultrasonic wave introduction device and the copper roller, and at the frequency f 1 and f 2 Adjust the driving frequency of the ultrasonic wave introduction device to find the mode shape of the nodal circle vibration that matches the mode shape in step (1) and the corresponding initial driving frequency. f 0 The initial driving frequency f 0 The point of maximum amplitude is taken as the excitation point; the frequency f 2 and f 1 The difference is ≤10kHz; (3) Using the initial driving frequency f 0 Ultrasonic waves are applied to the copper roller at the excitation point obtained in step (2), and then the NdFeB alloy melt is cast onto the surface of the rotating copper roller to obtain a NdFeB magnet rapid solidification sheet; the amplitude A of the roller surface corresponding to the excitation point is < A max , A max The calculation formula is shown in Equation I: Equation I; In formula I, ρ This refers to the density of neodymium iron boron magnet rapid solidification sheets, in g / cm³. 3 ; h The thickness of the neodymium iron boron magnet rapid solidification sheet is given in μm; g is the acceleration due to gravity in m / s². 2 ; θ The angle between the line connecting the casting point on the surface of the copper roller and the center of the copper roller and the horizontal direction is expressed in degrees. f 0 The initial driving frequency is expressed in Hz. P The unit is the adsorption pressure of NdFeB alloy melt without ultrasound, expressed in Pa. ω The angular velocity of the copper roller is expressed in rad / s. R The radius of the copper roller is in meters (m). In step (3), the working frequency of the ultrasonic introduction device is adjusted in real time during the casting process of the NdFeB alloy melt. f ( t ), f ( t The calculation formula for ) is shown in Equation II: Formula II; In formula II, f(t) The real-time operating frequency of the ultrasonic wave introduction device corresponding to the application time t (s); f 0 The initial driving frequency is expressed in Hz. α f Temperature drift coefficient of the piezoelectric ceramic used in the ultrasonic wave introduction device, expressed in Kelvin. -1 , which is a negative value; T t The ambient temperature is in real-time, expressed in Kelvin (K). T 0 The initial ambient temperature, in Kelvin (K). T max The thermal equilibrium temperature of the ultrasonic wave introduction device is expressed in K. τ th The thermal equilibrium time of the ultrasonic wave introduction device is expressed in seconds. In step (3) A max Maximum driving voltage U max The driving voltage U of the ultrasonic wave introduction device is obtained below. max U max Initial driving frequency f 0 The corresponding maximum driving voltage;​ In step (3), the initial output power P0 of the ultrasonic wave is 10~2000W. During the casting of the NdFeB alloy melt, the output power of the ultrasonic wave introduction device is monitored in real time. The drift of the real-time output power is ≤10%. When the offset of the real-time output power displayed by the power supply of the ultrasonic wave introduction device is >10%, the amplitude of the roller surface corresponding to the excitation point is unstable. It is necessary to correct the working frequency in real time and ensure that the amplitude of the roller surface remains unchanged by changing the working frequency.

2. The method according to claim 1, characterized in that, The composition of the NdFeB alloy melt in step (3) is: RE x Fe y M z B n x, y, z and n are all mass percentages, where RE is one or more of Nd, Pr, Dy and Tb, M is one or more of Cu, Al, Co, Zr, Ga and Nb, x is 25~35, y is 65~75, z is 0~2 and n is 0.8~1.

2.

3. The method according to claim 1, characterized in that, The driving voltage U of the ultrasonic wave introduction device is less than 0.9U. max .

4. The method according to claim 1, characterized in that, The excitation point in step (3) is the end face or roller surface of the copper roller.

5. The method according to claim 1, characterized in that, In step (3), the linear velocity of the copper roller is 1~2m / s.

6. The method according to claim 1, characterized in that, In step (3), the solidification time of the NdFeB alloy melt is 10 minutes. -6 ~10 -3 s.

7. The method according to claim 1, characterized in that, The drift of the working frequency during the casting process in step (3) is ≤10%.

Images