Permanent magnet material microstructure and magnetic performance characterization method

Abstract

The invention discloses a characterization method for a microstructure and magnetic performance of a permanent magnet material, belongs to the technical field of permanent magnet materials, and solves the problems that the microstructure and the magnetic performance of an existing permanent magnet material need to be detected by adopting specific instruments respectively, and the detection time is relatively long. The characterization method comprises the following steps: collecting microscopic morphology photos of different positions of the permanent magnet material; a fractal dimension calculation method is adopted to calculate the microstructure photo to obtain fractal dimensions; the uniformity, isotropy or anisotropy and magnetic performance of the permanent magnet material are judged according to the fractal dimensions of the microtopography photos at different positions; wherein the uniformity of the permanent magnet material is judged according to the absolute value of the difference value of the fractal dimensions of the microstructure pictures at different positions of the same plane; and according to the absolute value of the difference value of the fractal dimensions in the vertical orientation direction and the parallel orientation direction of the material, the isotropy or the anisotropy and the magnetic performance of the permanent magnet material are judged. The method disclosed by the invention is few in required equipment, simple, quick and accurate in result.

Description

Technical Field

[0001] The invention relates to the technical field of permanent magnetic materials, and in particular to a method for characterizing the microstructure and magnetic properties of a permanent magnetic material. Background Art

[0002] Permanent magnetic material is of great significance as a magnetic energy storage material. After a magnetization treatment, it can continuously provide a magnetic field to the outside without the need for external energy to maintain it.

[0003] The magnetic properties of permanent magnet materials have an important influence on their performance in various applications. For example, in wind power generation, the magnetic properties of permanent magnets directly affect the efficiency and stability of the motor; in electric vehicles, the magnetic properties of permanent magnets are related to the output torque and cruising range of the motor; in magnetic resonance imaging, the magnetic properties of permanent magnets determine the clarity and accuracy of the imaging. In the preparation process of permanent magnet materials, by optimizing the manufacturing process parameters such as smelting, powder making, molding, and sintering, the influence of composition, grain size, and surface defects on the magnetic properties can be reduced. The detection of the microstructure and magnetic properties of permanent magnet materials requires the use of specific instruments for detection, which takes a long time. Therefore, how to provide a method for quickly characterizing the microstructure and magnetic properties of permanent magnet materials has important application value for the research and development and production of permanent magnet materials. Summary of the invention

[0004] In view of the above situation, the present invention aims to provide a method for characterizing the microstructure and magnetic properties of permanent magnetic materials, which is used to solve at least one of the following technical problems: the detection of the magnetic microstructure and magnetic properties of existing permanent magnetic materials requires the use of specific instruments for detection, which takes a long time.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions: In one aspect, the present invention provides a method for characterizing the microstructure and magnetic properties of a permanent magnetic material, the characterization method comprising: Collect microscopic morphology photos of permanent magnetic materials at different locations; The fractal dimension calculation method is used to calculate the fractal dimension of the microscopic morphology photos; The uniformity, isotropy or anisotropy, and magnetic properties of permanent magnetic materials are determined based on the fractal dimensions of microscopic morphology photographs at different positions; Among them, the uniformity of the permanent magnetic material is judged according to the absolute value of the difference in fractal dimensions of microscopic morphology photos at different positions on the same plane; the isotropy or anisotropy and magnetic properties of the permanent magnetic material are judged according to the absolute value of the difference in fractal dimensions in the vertical orientation direction and the parallel orientation direction of the material.

[0006] Furthermore, magnetic properties mainly include remanence and coercivity.

[0007] Furthermore, the absolute value δ of the difference in fractal dimension of microscopic topography photographs at different positions on the same plane and the method for judging uniformity include: 0≤δ≤0.02, the permanent magnetic material is uniform; δ>0.02, the permanent magnetic material is non-uniform.

[0008] Further, the method for judging the isotropy or anisotropy of the permanent magnetic material according to the absolute value Δ of the difference between the fractal dimensions of the material in the perpendicular orientation direction and the parallel orientation direction includes: Δ≥0.03, the permanent magnetic material is anisotropic; 0≤Δ≤0.03, the permanent magnetic material is isotropic.

[0009] Furthermore, the method for judging the magnetic properties of the permanent magnetic material according to the absolute value Δ of the difference between the fractal dimensions of the material in the perpendicular orientation direction and the parallel orientation direction includes: Δ≥0.05, the permanent magnet material has high remanence and low coercivity; 0.03≤Δ<0.05, the permanent magnet material has high coercivity and low remanence.

[0010] Furthermore, the permanent magnet material includes rare earth permanent magnet material, ferrite permanent magnet material or aluminum nickel cobalt permanent magnet material.

[0011] Furthermore, the microscopic morphology is the microscopic morphology of a fracture specimen, a crack and / or a plane metallographic specimen.

[0012] Furthermore, the microscopic morphology is observed using one or more of an optical microscope, a scanning electron microscope, a magnetic force microscope and a transmission electron microscope.

[0013] Furthermore, the fractal dimension calculation method is used to calculate the microscopic morphology photos, including: firstly binarizing the acquired microscopic morphology photos through a computer-aided program, and the information of the picture is converted into a matrix containing only 0 and 1; then the image is processed and analyzed using image processing technology to obtain the fractal dimension.

[0014] Furthermore, image processing techniques include direct counting method, box counting method, differential box method, and small vein method.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: The method for characterizing the microstructure and magnetic properties of the permanent magnetic material of the present invention can obtain the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnetic material by analyzing microscopic morphology photos at different positions of the permanent magnetic material. Less equipment is required, the method is simple and fast, and a comprehensive characterization of the permanent magnetic material can be quickly provided.

[0016] The method for characterizing the microstructure and magnetic properties of the permanent magnetic material of the present invention can provide accurate characterization results and strong repeatability through the selection of microscopic morphology photos and the choice of observation equipment, and can conveniently and quickly provide comprehensive characterization of the permanent magnetic material.

[0017] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components; Figure 1 The scanning electron microscope photograph of a position on the fracture surface of Example 1 parallel to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Figure 2 The scanning electron microscope photograph of the fracture surface of Example 1 at two positions parallel to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Figure 3 The scanning electron microscope photograph of a position perpendicular to the orientation direction on the fracture of Example 1, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Figure 4 The scanning electron microscope photograph of the fracture surface of Example 1 at two positions perpendicular to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Figure 5 The scanning electron microscope photograph of a position on the fracture surface of Example 2 parallel to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Figure 6 The scanning electron microscope photograph of the fracture surface of Example 2 at two positions parallel to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Figure 7 The scanning electron microscope photograph of a position perpendicular to the orientation direction on the fracture of Example 2, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Figure 8 The scanning electron microscope photograph of the fracture surface of Example 2 at two positions perpendicular to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Fig. 9 The scanning electron microscope photograph of a position on the fracture surface of Example 3 parallel to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Fig.10 The scanning electron microscope photograph of the second position parallel to the orientation direction on the fracture of Example 3, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Fig.11 The scanning electron microscope photograph of a position perpendicular to the orientation direction on the fracture of Example 3, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Fig.12 The scanning electron microscope photograph of the fracture surface of Example 3 at two positions perpendicular to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Fig.13 The EBSD photograph of position 1 perpendicular to the orientation direction of Example 4, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Fig.14 The EBSD photograph of position 2 perpendicular to the orientation direction of Example 4, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Fig.15 The EBSD photograph of Example 4 at position 1 parallel to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths; Fig.16 The EBSD photograph of Example 4 at position two parallel to the orientation direction, the processed binary image, the data fitting of different box side lengths, and the fractal dimension of different box side lengths. DETAILED DESCRIPTION

[0019] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0020] The present invention provides a method for characterizing the microstructure and magnetic properties of a permanent magnetic material, the method comprising the following steps: Collect microscopic morphology photos of permanent magnetic materials at different locations; The fractal dimension calculation method is used to calculate the fractal dimension of the microscopic morphology photos; The uniformity, isotropy or anisotropy, and magnetic properties of permanent magnetic materials are determined based on the fractal dimensions of microscopic morphology photographs at different positions; The uniformity of the permanent magnetic material is judged according to the absolute value of the difference in the fractal dimension of the microscopic morphology photographs at different positions on the same plane; The isotropy or anisotropy and magnetic properties of the permanent magnetic material are determined based on the absolute value of the difference between the fractal dimensions of the material in the perpendicular orientation direction and the parallel orientation direction.

[0021] Specifically, the above-mentioned permanent magnetic material includes rare earth permanent magnetic material, ferrite permanent magnetic material or aluminum nickel cobalt permanent magnetic material.

[0022] Specifically, the rare earth permanent magnet material includes samarium cobalt magnet, neodymium iron boron magnet or cerium magnet.

[0023] Specifically, the above-mentioned microscopic morphology may be the microscopic morphology of a fracture sample, a crack and / or a plane metallographic sample.

[0024] Specifically, the above-mentioned microscopic morphology photos can be obtained by microscopically observing the fracture sample or the plane metallographic sample using an optical microscope, a scanning electron microscope, a magnetic force microscope, a transmission electron microscope and other observation equipment. Using an optical microscope, the microstructures of the permanent magnetic material such as clear grains, grain boundaries, cellular phases, and cell wall phases can be observed. The magnification of a scanning electron microscope is much higher than that of an optical microscope, so it can form a higher resolution and a larger magnification. The magnification of an electron microscope can reach hundreds of thousands of times or even higher.

[0025] Specifically, the above-mentioned microscopic morphology may include one or more of scanning electron microscope microscopic structural morphology, magnetic force microscope magnetic domain morphology, electron backscatter diffraction microscopic morphology and transmission electron microscope morphology.

[0026] Preferably, in combination with the detection equipment and the morphological characteristics of different samples, the above-mentioned microscopic morphology can be the scanning electron microscope microstructure morphology of the fracture sample and / or the electron backscatter diffraction microstructure of the plane metallographic sample.

[0027] Specifically, the fracture specimen is obtained by stretching, compressing, bending, shearing, torsion or impacting using a universal mechanical testing machine.

[0028] Preferably, the fracture specimen is obtained by compression using a universal mechanical testing machine.

[0029] Preferably, during the process of preparing the above-mentioned fracture specimen using a universal mechanical testing machine, the sample needs to be correctly installed in the fixture of the testing machine to ensure that the sample can be evenly stressed during the test, and the tightness of the fixture is adjusted to avoid damage to the sample due to the fixture being too tight or too loose before the test.

[0030] Specifically, after the fracture surface of the fracture sample is cleaned with a cleaning agent (such as acetone, alcohol, etc.), it is observed with a scanning electron microscope to obtain the scanning electron microscope microstructure morphology of the fracture sample.

[0031] Specifically, during the cleaning process of the fracture sample, it is necessary to ensure that the microstructure of the fracture is not destroyed to facilitate subsequent observation and analysis.

[0032] Specifically, the above-mentioned plane metallographic sample can be prepared by steps such as grinding, polishing, and metallographic etching.

[0033] Specifically, the above-mentioned plane metallographic specimen needs to ensure a smooth surface to facilitate subsequent observation and analysis.

[0034] Specifically, the fractal dimension calculation method is used to calculate the microscopic morphology photos, including: firstly binarizing the acquired microscopic morphology photos through a computer-aided program, and the information of the picture is converted into a matrix containing only 0 and 1; then the image is processed and analyzed using image processing technology to obtain the fractal dimension.

[0035] Specifically, the above-mentioned computer-aided programs include but are not limited to MATLAB, for example, also include advanced technical computing languages ​​and interactive environments for algorithm development, data visualization, data analysis, and numerical calculations.

[0036] Specifically, the above-mentioned image processing technology includes but is not limited to direct counting method, box counting method, differential box method, and small vein method.

[0037] Specifically, the above image processing technology adopts a box counting method, which includes: dividing the image into boxes with a side length of δk, where k=1, 2, 4, ..., that is, the side lengths of the boxes are 1, 2, 4, ... in sequence. Count the amount of image information (0 or 1) contained in each box. If a box contains at least one 1, it is considered that the box contains image information. Record the number of boxes containing image information Nk. In a double logarithmic coordinate plane, fit the data points (logδk, logNk) with a straight line using the least squares method. The negative value D of the slope of the obtained straight line is the fractal dimension of the image.

[0038] Specifically, the above magnetic properties mainly include remanence and coercive force.

[0039] Specifically, based on the fractal structure of the self-similarity of the surface morphology of the permanent magnetic material, the magnifications may be different when collecting microscopic morphology photos of different positions of the permanent magnetic material.

[0040] Specifically, the calculation of fractal dimension is based on the self-similarity of microscopic morphology. The corresponding fractal dimension is calculated from photos of microscopic morphology at different positions. The consistency of fractal dimension at different positions on the same plane can be used as a condition for judging uniformity. The absolute value δ of the difference in fractal dimension between photos of microscopic morphology at two different positions and the judgment method of uniformity are as follows: 0≤δ≤0.02, indicating that the permanent magnetic material is uniform; δ>0.02, indicating that the permanent magnetic material is inhomogeneous.

[0041] Specifically, if the permanent magnetic material is anisotropic, the microscopic morphology in the parallel orientation direction and the vertical orientation direction is different. The isotropy or anisotropy of the permanent magnetic material is determined based on the absolute value Δ of the difference in the fractal dimension in the vertical orientation direction and the parallel orientation direction of the material. On the basis that the permanent magnetic material is anisotropic, the fractal dimensions in the two directions are used as structural factors to describe the microscopic morphology of the permanent magnetic material, combined with the empirical formula of coercive force and remanence, the magnetic properties of the permanent magnetic material can be determined. The specific determination method is as follows: Δ≥0.03 indicates that the permanent magnetic material is anisotropic; thus, the coercive force and remanence of the permanent magnetic material can be judged; 0≤Δ≤0.03, indicating that the permanent magnetic material is isotropic; Δ≥0.05, indicating that the permanent magnet material has high remanence and low coercivity; 0.03≤Δ<0.05, indicating that the permanent magnet material has high coercivity and low remanence.

[0042] Specifically, the above-mentioned high remanence refers to a remanence in the range of 14.0 kGs~15.5 kGs, and low coercivity refers to a coercivity in the range of 8.0 kOe~14.0 kOe; low remanence refers to a remanence in the range of 10.0 kGs~14.0 kGs (excluding 14.0kGs); high coercivity refers to a coercivity in the range of 14.0 kOe~45.0 kOe (excluding 14.0 kOe).

[0043] The present invention also provides a permanent magnetic material microstructure and magnetic property characterization device, including a permanent magnetic material automatic feeding device, a permanent magnetic material sample preparation and polishing component, a permanent magnetic material sample surface morphology observation device, a data acquisition device, and a fractal dimension calculation system. The device integrates the sample preparation, morphology observation, data acquisition, and fractal dimension calculation of the permanent magnetic material, and can conveniently and quickly obtain the microscopic morphology and magnetic properties.

[0044] The method for characterizing the microstructure and magnetic properties of the permanent magnetic material of the present invention can obtain the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnetic material by analyzing microscopic morphology photos at different positions of the permanent magnetic material. Less equipment is required, the method is simple and fast, and a comprehensive characterization of the permanent magnetic material can be quickly provided.

[0045] The method for characterizing the microstructure and magnetic properties of the permanent magnetic material of the present invention can provide accurate characterization results and strong repeatability through the selection of microscopic morphology photos and the choice of observation equipment, and can conveniently and quickly provide comprehensive characterization of the permanent magnetic material.

[0046] The advantages of the method of the present invention are demonstrated below with specific examples.

[0047] Example 1 This embodiment provides a method for characterizing the microstructure and magnetic properties of a permanent magnetic material. The permanent magnetic material of this embodiment is a N50 grade neodymium iron boron permanent magnet. The method of this embodiment includes the following steps: Step 1: compress the sample using a universal mechanical testing machine to obtain a fracture sample; Step 2, cleaning the fracture with acetone; Step 3, observing the fracture surface with a scanning electron microscope, collecting microscopic morphology photos at different positions parallel to the orientation direction, and microscopic morphology photos at different positions perpendicular to the orientation direction; Step 4, using a fractal dimension calculation method to calculate the microscopic morphology photograph to obtain the fractal dimension; Step 5: Evaluate the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnetic material according to the fractal dimensions of the microscopic morphology photos at different positions. The fractal dimensions at different positions in two directions are used to judge the uniformity, and the average of the fractal dimensions at different positions in two directions is used to judge the isotropy or anisotropy and the evaluation of the magnetic properties. Figure 1 and Figure 2 They are respectively the results of position one and position two randomly selected on the fracture surface of Example 1 parallel to the orientation direction, wherein (a) is a scanning electron microscope photograph, (b) is a binary image after image processing using the box counting method, (c) is the data fitting of different box side lengths after image processing using the box counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box counting method; wherein, the scanning electron microscope photograph includes a gray main phase and a bright white rare earth-rich grain boundary phase.

[0048] Figure 3 and Figure 4 They are respectively the results of position one and position two randomly selected perpendicular to the orientation direction on the fracture of Example 1, wherein (a) is a scanning electron microscope photograph, (b) is a binary image after image processing using the box counting method, (c) is the data fitting of different box side lengths after image processing using the box counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box counting method; wherein, the scanning electron microscope photograph includes a gray main phase and a bright white rare earth-rich grain boundary phase.

[0049] Depend on Figure 1 and Figure 2 It can be seen that the fractal dimensions at different positions parallel to the orientation direction are 1.7360 and 1.7476 respectively, and the difference in fractal dimensions is in the range of 0<δ≤0.02, indicating that the magnet of Example 1 is uniform parallel to the orientation direction.

[0050] Depend on Figure 3 and Figure 4It can be seen that the fractal dimensions at different positions perpendicular to the orientation direction are 1.8228 and 1.8332 respectively, and the difference in fractal dimensions is in the range of 0<δ≤0.02, indicating that the magnet of Example 1 is uniform perpendicular to the orientation direction.

[0051] The difference in fractal dimension of the magnet of Example 1 in the direction parallel to the orientation and the direction perpendicular to the orientation is greater than 0.05, indicating that the magnet is anisotropic and has high remanence and low coercive force.

[0052] After detection by using a permanent magnetic material measurement system, the test performance of the magnet of Example 1 is shown in Table 1 below. The maximum difference in remanence at different parts is 0.02 kGs, and the remanence deviation at different parts (maximum difference in remanence / average value) = 0.14% < 1% (within 1% is considered to be uniform), which shows that the magnet of this embodiment is uniform; the coercive force is greater than 8 kOe (if the coercive force is greater than 8 kOe, it is anisotropic), which shows that the magnet is anisotropic, the coercive force is 12.10~12.13kOe, and the remanence is 14.19~14.21 kGs, which shows that the magnet has high remanence and low coercive force.

[0053] It can be seen that the characterization of permanent magnetic materials using the characterization method of the present invention is consistent with the actual results.

[0054] Table 1 Test performance of the magnet of Example 1

[0055] Example 2 This embodiment provides a method for characterizing the microstructure and magnetic properties of a permanent magnetic material. The permanent magnetic material of this embodiment is 30EH. The method of this embodiment includes the following steps: Step 1: compress the sample using a universal mechanical testing machine to obtain a fracture sample; Step 2: Clean the fracture surface with acetone; Step 3, observing the fracture surface with a scanning electron microscope, collecting microscopic morphology photos at different positions parallel to the orientation direction, and microscopic morphology photos at different positions perpendicular to the orientation direction; Step 4, using a fractal dimension calculation method to calculate the microscopic morphology photograph to obtain the fractal dimension; Step 5: Evaluate the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnetic material according to the fractal dimensions of the microscopic morphology photos at different positions. The fractal dimensions at different positions in two directions are used to judge the uniformity, and the average of the fractal dimensions at different positions in two directions is used to judge the isotropy or anisotropy and the evaluation of the magnetic properties. Figure 5 and Figure 6They are respectively the results of position one and position two randomly selected on the fracture surface of Example 2 parallel to the orientation direction, where (a) is a scanning electron microscope photograph, (b) is a binary image after image processing using the box counting method, (c) is the data fitting of different box side lengths after image processing using the box counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box counting method; wherein, the scanning electron microscope photograph includes a gray main phase and a bright white rare earth-rich grain boundary phase.

[0056] Figure 7 and Figure 8 They are respectively the results of position one and position two randomly selected perpendicular to the orientation direction on the fracture of Example 2, wherein (a) is a scanning electron microscope photograph, (b) is a binary image after image processing using the box counting method, (c) is the data fitting of different box side lengths after image processing using the box counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box counting method; wherein, the scanning electron microscope photograph includes a gray main phase and a bright white rare earth-rich grain boundary phase.

[0057] Depend on Figure 5 and Figure 6 It can be seen that the fractal dimensions at different positions parallel to the orientation direction are 1.7806 and 1.7935 respectively, and the difference in fractal dimensions is in the range of 0<δ≤0.02, indicating that the magnet of Example 2 is uniform parallel to the orientation direction.

[0058] Depend on Figure 7 and Figure 8 It can be seen that the fractal dimensions at different positions perpendicular to the orientation direction are 1.8146 and 1.8246 respectively, and the difference in fractal dimensions is in the range of 0<δ≤0.02, indicating that the magnet of Example 2 is uniform perpendicular to the orientation direction.

[0059] The average difference between the fractal dimensions of the magnet of Example 2 in the direction parallel to the orientation and the direction perpendicular to the orientation is between 0.03 and 0.05, indicating that the magnet is anisotropic and has high coercive force and low remanence.

[0060] After detection by using a permanent magnetic material measurement system, the test performance of the magnet of Example 2 is shown in Table 2 below. The maximum difference in remanence at different parts is 0.02 kGs, and the remanence deviation at different parts (maximum difference in remanence / average value) = 0.18% < 1% (within 1% is considered to be uniform), which shows that the magnet of this embodiment is uniform; the coercive force is greater than 8 kOe (if the coercive force is greater than 8 kOe, it is anisotropic), which shows that the magnet is anisotropic, the coercive force is 30.10~30.20 kOe, and the remanence is 11.18~11.20 kGs, which shows that the magnet has high coercive force and low remanence.

[0061] It can be seen that the characterization of permanent magnetic materials using the characterization method of the present invention is consistent with the actual results.

[0062] Table 2 Test performance of the magnet of Example 2

[0063] Example 3 This embodiment provides a method for characterizing the microstructure and magnetic properties of a permanent magnetic material. The permanent magnetic material of this embodiment is Is20. The method of this embodiment includes the following steps: Step 1: compress the sample using a universal mechanical testing machine to obtain a fracture sample; Step 2: Clean the fracture surface with acetone; Step 3, observing the fracture surface with a scanning electron microscope, collecting microscopic morphology photos at different positions parallel to the orientation direction, and microscopic morphology photos at different positions perpendicular to the orientation direction; Step 4, using a fractal dimension calculation method to calculate the microscopic morphology photograph to obtain the fractal dimension; Step 5, evaluating the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnetic material according to the fractal dimensions of the microscopic morphology photographs at different positions; Fig. 9 and Fig.10 They are respectively the results of position one and position two randomly selected on the fracture surface of Example 3 parallel to the orientation direction, wherein (a) is a scanning electron microscope photograph, (b) is a binary image after image processing using the box counting method, (c) is the data fitting of different box side lengths after image processing using the box counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box counting method; wherein, the scanning electron microscope photograph includes a gray main phase and a bright white rare earth-rich grain boundary phase.

[0064] Fig.11 and Fig.12 They are respectively the results at position one and position two on the fracture surface perpendicular to the orientation direction of Example 2, where (a) is a scanning electron microscope photograph, (b) is a binary image after image processing using the box counting method, (c) is the data fitting of different box side lengths after image processing using the box counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box counting method; wherein, the scanning electron microscope photograph includes a gray main phase and a bright white rare earth-rich grain boundary phase.

[0065] Depend on Fig. 9 and Fig.10 It can be seen that the fractal dimensions at different positions parallel to the orientation direction are 1.7987 and 1.8111 respectively, and the difference in fractal dimensions is in the range of 0<δ≤0.02, indicating that the magnet of Example 3 is uniform parallel to the orientation direction.

[0066] Depend on Fig.11 and Fig.12 It can be seen that the fractal dimensions at different positions perpendicular to the orientation direction are 1.8040 and 1.8155 respectively, and the difference in fractal dimensions is in the range of 0<δ≤0.02, indicating that the magnet of Example 3 is uniform perpendicular to the orientation direction.

[0067] The average of the differences in the fractal dimensions of the magnet of Example 3 in the direction parallel to the orientation and the direction perpendicular to the orientation is less than 0.03, indicating that the magnet is isotropic.

[0068] After detection by using a permanent magnetic material measurement system, the test performance of the magnet of Example 3 is shown in Table 3 below. The maximum difference in remanence at different parts is 0.02 kGs, and the remanence deviation at different parts (maximum difference in remanence / average value) = 0.12% < 1% (within 1% is considered to be uniform), which shows that the magnet of this embodiment is uniform; the coercive force is less than 8 kOe (if the coercive force is greater than 8 kOe, it is anisotropic), which shows that the magnet is isotropic.

[0069] It can be seen that the characterization of permanent magnetic materials using the characterization method of the present invention is consistent with the actual results.

[0070] Table 3 Test performance of the magnet of Example 3

[0071] Example 4 This embodiment provides a method for characterizing the microstructure and magnetic properties of a permanent magnetic material. The permanent magnetic material of this embodiment is 40UH. The method of this embodiment includes the following steps: Step 1, polishing the sample surface by argon ion polishing to obtain a sample; Step 2: Use a scanning electron microscope to select a position, and use a probe to collect EBSD photos in a direction perpendicular to the orientation and EBSD photos in a direction parallel to the orientation; Step 4, using a fractal dimension calculation method to calculate the EBSD photo to obtain the fractal dimension; Step 5: Evaluate the uniformity, isotropy or anisotropy, and magnetic properties of the permanent magnetic material according to the fractal dimensions of the EBSD photos at different positions. The fractal dimensions at different positions in two directions are used to judge the uniformity, and the average of the fractal dimensions at different positions in two directions is used to judge the isotropy or anisotropy and the evaluation of the magnetic properties. Fig.13 and Fig.14They are respectively the results of position 1 and position 2 randomly selected from the EBSD photograph perpendicular to the orientation direction in Example 4, where (a) is the EBSD photograph, (b) is the binary image after image processing using the box counting method, (c) is the data fitting of different box side lengths after image processing using the box counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box counting method.

[0072] Fig.15 and Fig.16 They are respectively the results of position 1 and position 2 randomly selected from the EBSD photograph parallel to the orientation direction of Example 4, where (a) is the EBSD photograph, (b) is the binary image after image processing using the box counting method, (c) is the data fitting of different box side lengths after image processing using the box counting method, and (d) is the fractal dimension of different box side lengths after image processing using the box counting method.

[0073] Depend on Fig.13 and Fig.14 It can be seen that the fractal dimensions at different positions parallel to the orientation direction are 1.7463 and 1.7475 respectively, and the difference in fractal dimensions is in the range of 0<δ≤0.02, indicating that the magnet of Example 4 is uniform parallel to the orientation direction.

[0074] Depend on Fig.15 and Fig.16 It can be seen that the fractal dimensions at different positions perpendicular to the orientation direction are 1.7805 and 1.7826 respectively, and the difference in fractal dimensions is in the range of 0<δ≤0.02, indicating that the magnet of Example 4 is uniform perpendicular to the orientation direction.

[0075] The average of the difference between the fractal dimensions of the magnet of Example 4 in the direction parallel to the orientation and the direction perpendicular to the orientation is between 0.03 and 0.05, indicating that the magnet is anisotropic and has high coercive force and low remanence.

[0076] After detection by using a permanent magnetic material measurement system, the test performance of the magnet of the embodiment is shown in Table 4 below. The maximum difference in remanence at different parts is 0.02 kGs, and the remanence deviation at different parts (maximum difference in remanence / average value) = 0.16% < 1% (within 1% is considered to be uniform), which shows that the magnet of this embodiment is uniform; the coercive force is greater than 8 kOe (if the coercive force is greater than 8 kOe, it is anisotropic), which shows that the magnet is anisotropic, the coercive force is 25.31~25.34 kOe, and the remanence is 12.48~12.50 kGs, which shows that the magnet has high coercive force and low remanence.

[0077] It can be seen that the characterization of permanent magnetic materials using the characterization method of the present invention is consistent with the actual results.

[0078] Table 4 Test performance of the magnet of Example 4

[0079] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for characterizing the microstructure and magnetic properties of a permanent magnetic material, characterized in that: The characterization method comprises: Collect microscopic morphology photos of permanent magnetic materials at different locations; The fractal dimension calculation method is used to calculate the fractal dimension of the microscopic morphology photos; The uniformity, isotropy or anisotropy, and magnetic properties of permanent magnetic materials are determined based on the fractal dimensions of microscopic morphology photographs at different positions; Among them, the uniformity of the permanent magnetic material is judged according to the absolute value of the difference in fractal dimensions of microscopic morphology photos at different positions on the same plane; the isotropy or anisotropy and magnetic properties of the permanent magnetic material are judged according to the absolute value of the difference in fractal dimensions in the vertical orientation direction and the parallel orientation direction of the material.

2. The method for characterizing the microstructure and magnetic properties of permanent magnetic materials according to claim 1, characterized in that: The magnetic properties mainly include remanence and coercivity.

3. The method for characterizing the microstructure and magnetic properties of permanent magnetic materials according to claim 1, characterized in that: The absolute value δ of the difference in fractal dimension of microscopic topography photographs at different positions on the same plane and the method for judging uniformity include: 0≤δ≤0.02, the permanent magnetic material is uniform; δ>0.02, the permanent magnetic material is non-uniform.

4. The method for characterizing the microstructure and magnetic properties of permanent magnetic materials according to claim 1, characterized in that: The method of judging the isotropy or anisotropy of a permanent magnetic material according to the absolute value Δ of the difference between the fractal dimensions of the material in the vertical orientation direction and the parallel orientation direction includes: Δ≥0.03, the permanent magnetic material is anisotropic; 0≤Δ≤0.03, the permanent magnetic material is isotropic.

5. The method for characterizing the microstructure and magnetic properties of permanent magnetic materials according to claim 4, characterized in that: The method for judging the magnetic properties of a permanent magnetic material according to the absolute value Δ of the difference between the fractal dimensions of the material in the vertical orientation direction and the parallel orientation direction includes: Δ≥0.05, the permanent magnet material has high remanence and low coercivity; 0.03≤Δ<0.05, the permanent magnet material has high coercivity and low remanence.

6. The method for characterizing the microstructure and magnetic properties of permanent magnetic materials according to claim 1, characterized in that: The permanent magnetic material includes rare earth permanent magnetic material, ferrite permanent magnetic material or aluminum nickel cobalt permanent magnetic material.

7. The method for characterizing the microstructure and magnetic properties of permanent magnetic materials according to claim 1, characterized in that: The microscopic morphology is the microscopic morphology of a fracture sample, a crack and / or a plane metallographic sample.

8. The method for characterizing the microstructure and magnetic properties of permanent magnetic materials according to claim 1, characterized in that: The microscopic morphology is observed using one or more of an optical microscope, a scanning electron microscope, a magnetic force microscope and a transmission electron microscope.

9. The method for characterizing the microstructure and magnetic properties of a permanent magnetic material according to any one of claims 1 to 8, characterized in that: The fractal dimension calculation method is used to calculate the microscopic morphology photos, including: firstly binarizing the acquired microscopic morphology photos through a computer-aided program, and the information of the picture is converted into a matrix containing only 0 and 1; then the image is processed and analyzed using image processing technology to obtain the fractal dimension.

10. The method for characterizing the microstructure and magnetic properties of permanent magnetic materials according to claim 9, characterized in that: The image processing techniques include direct counting method, box counting method, differential box method and small vein method.

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