Method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnet by magnetic field distribution

Abstract

The application relates to the technical field of irreversible demagnetization measurement of grain boundary diffusion neodymium-iron-boron magnets, and specifically discloses a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnets through magnetic field distribution. After a reverse magnetic field is applied to the saturated and magnetized grain boundary diffusion neodymium-iron-boron magnet, the number of magnetic poles on the non-diffusion surface of the magnet changes from less to more, and the irreversible demagnetization phenomenon occurs in the grain boundary diffusion neodymium-iron-boron magnet. The operation method in the application can not only detect whether the irreversible demagnetization phenomenon occurs in the grain boundary diffusion neodymium-iron-boron magnet, but also can keep the whole grain boundary diffusion neodymium-iron-boron magnet from being damaged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of irreversible demagnetization measurement of grain boundary diffusion neodymium-iron-boron magnets, and more particularly to a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnets through magnetic field distribution. BACKGROUND

[0002] Permanent magnetic materials are important energy storage materials, and many energy conversion devices cannot be separated from rare earth permanent magnetic materials, such as loudspeakers, vibration motors, drive motors, etc.

[0003] However, due to the complex internal structure of rare earth permanent magnetic materials, especially grain boundary diffusion neodymium-iron-boron magnets, the magnetization state of the grain boundary diffusion product is easily affected by the thickness, thereby affecting the performance of the permanent magnetic material. Generally, the coercivity of the surface of the grain boundary diffusion neodymium-iron-boron magnet is higher than that of the inside. However, how to evaluate or judge the demagnetization state of the grain boundary diffusion product inside it is a greater problem at present.

[0004] The currently more commonly used method for measuring the demagnetization state of the magnet mainly cuts the rare earth permanent magnetic material into multiple layers, and detects and analyzes the coercivity of each layer. Such an operating mode can obtain the detection results of each layer of the rare earth permanent magnetic material, but the detection method has the following defects:

[0005] (1) needs to be performed in multiple times, and the size of the sample to be detected is small, which easily leads to low detection efficiency;

[0006] (2) the magnet is destroyed, the macroscopic shell effect of the product is not considered, the analysis result is not accurate, and the magnet cannot be used;

[0007] (3) such detection needs to use large-scale equipment such as VSM, PPMS, MPMS, etc., which leads to large resource consumption.

[0008] Therefore, a detection and evaluation method is needed, which does not destroy the grain boundary diffusion neodymium-iron-boron magnet, and can judge whether the rare earth permanent magnetic material has demagnetization phenomenon and whether it meets the specific requirements. SUMMARY

[0009] To solve the problem of accurately measuring whether irreversible demagnetization occurs in the grain boundary diffusion product, the present application provides a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnets through magnetic field distribution.

[0010] A method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnets through magnetic field distribution, after a reverse magnetic field is applied to the saturated and magnetized grain boundary diffusion neodymium-iron-boron magnet, the number of magnetic poles of the non-diffusion surface of the magnet changes from less to more and is layered, and the grain boundary diffusion neodymium-iron-boron magnet has irreversible demagnetization phenomenon.

[0011] By adopting the technical scheme, the sample in the application is a grain boundary diffusion neodymium-iron-boron magnet, the surface of the magnet is coated with heavy rare earth material, and the heavy rare earth material enters the grain boundary phase of the magnet, so that the neodymium-iron-boron magnet has high coercivity.

[0012] The "diffusion surface" refers to the surface of the neodymium-iron-boron magnet coated with the heavy rare earth material, and the number of the surface is generally two; and the "non-diffusion surface" refers to other surfaces except the diffusion surface.

[0013] When the reverse magnetic field is applied to the grain boundary diffusion neodymium-iron-boron magnet, it is observed by means of equipment that the number of magnetic poles of the non-diffusion surface changes from less to more, at this time, it indicates that the grain boundary diffusion neodymium-iron-boron magnet appears irreversible demagnetization phenomenon.

[0014] The method in the application is not easily affected by the size of the grain boundary diffusion neodymium-iron-boron magnet, and is not easily affected by the temperature of the grain boundary diffusion neodymium-iron-boron magnet, and the shape of the magnet during operation is generally a cylinder. The method adopted in the application is not easy to affect the integrity of the grain boundary diffusion neodymium-iron-boron magnet and subsequent application.

[0015] Preferably, the operation steps are:

[0016] First, the grain boundary diffusion neodymium-iron-boron magnet is saturated and magnetized, and then a reverse magnetic field is applied;

[0017] Under the action of the reverse magnetic field, the reverse magnetic field value, the number of magnetic poles, and the distribution of magnetic poles are analyzed.

[0018] In the application, the grain boundary diffusion neodymium-iron-boron magnet is first saturated and magnetized, so that the grain boundary diffusion neodymium-iron-boron magnet obtains magnetism and is not easy to produce demagnetization phenomenon under the condition of saturation and magnetization.

[0019] Preferably, when the diffusion direction is the same as the orientation direction of the magnet, the number of magnetic poles of the non-oriented surface changes from less to more and is layered, and the grain boundary diffusion neodymium-iron-boron magnet appears irreversible demagnetization phenomenon;

[0020] When the diffusion direction is perpendicular to the orientation direction of the magnet, the number of magnetic poles of the oriented surface changes from less to more and is layered, and the grain boundary diffusion neodymium-iron-boron magnet appears irreversible demagnetization phenomenon.

[0021] In the application, the direction of the reverse applied magnetic field is the orientation direction, the surface on the grain boundary diffusion neodymium-iron-boron magnet is the oriented surface, and the other surface is the non-oriented surface.

[0022] But no matter whether the orientation direction is the same as the diffusion direction or the orientation direction is perpendicular to the diffusion direction, the final judgment condition is based on the condition displayed by the non-diffusion surface.

[0023] Preferably, when the diffusion direction is parallel to the orientation direction, the number of magnetic poles on the non-oriented surface of the magnet increases from less to more and is layered, and the magnetic poles are arranged in an N / S / N / S alternating manner.

[0024] Preferably, in the grain boundary diffusion Nd-Fe-B magnet, the heavy rare earth is coated on the oriented surface of the Nd-Fe-B magnet, and the oriented surface is the N-pole surface and the S-pole surface.

[0025] Preferably, when the diffusion direction is perpendicular to the orientation direction of the magnet, the number of magnetic poles on the oriented surface of the magnet increases from less to more and is layered, and the magnetic poles are arranged in an N / S / N or S / N / S manner.

[0026] Preferably, in the grain boundary diffusion Nd-Fe-B magnet, the heavy rare earth is coated on the non-oriented surface of the Nd-Fe-B magnet, and the non-oriented surface is a group of parallel surfaces other than the N-pole surface and the S-pole surface.

[0027] By adopting the above technical solution, the diffusion direction is the relative direction between the two diffusion surfaces of the heavy rare earth material coated on the surface of the magnet, the direction of the reverse magnetic field is the orientation direction, the oriented surface is the surface corresponding to the orientation direction, and the non-oriented surface is the surface other than the oriented surface.

[0028] When the diffusion direction is parallel to the orientation direction of the magnet, the non-oriented surface is the non-diffusion surface; when the diffusion direction is perpendicular to the orientation direction of the magnet, the oriented surface is the non-diffusion surface.

[0029] When the diffusion direction is parallel or perpendicular to the orientation direction, the magnetic pole distribution that appears is different, but the number of magnetic poles is not less than 2.

[0030] Preferably, the equipment for identifying the magnetic field distribution characteristics includes any one of a magnetic field distribution visualization device, a spatial magnetic field distribution measuring instrument, a gauss meter, a magnetic film, and a magnetic pole identification pen.

[0031] Any one of the above equipment can be used to observe and display the number of magnetic poles and the layered distribution of the magnetic poles of the grain boundary diffusion Nd-Fe-B magnet by the method in the present application, but is not limited to the above equipment. The results of the above equipment detection can also be used to prove whether the grain boundary diffusion Nd-Fe-B magnet appears irreversible demagnetization phenomenon.

[0032] Preferably, the temperature of the grain boundary diffusion Nd-Fe-B magnet itself is not lower than 20℃; and the size of the diffusion direction of the grain boundary diffusion Nd-Fe-B magnet is not greater than 12mm.

[0033] In the present application, even the grain boundary diffusion Nd-Fe-B magnet with a higher temperature during use can be directly taken out for detection, increasing the operable space for detection. Moreover, the maximum distance between the two surfaces coated with rare earth materials can reach 12mm, reducing the requirements for the size of the grain boundary diffusion Nd-Fe-B magnet to be detected.

[0034] Preferably, the applied reverse magnetic field value is lower than the coercivity of the grain boundary diffusion Nd-Fe-B magnet.

[0035] The present application finds that the reverse magnetic field value applied to the surface of the grain boundary diffusion Nd-Fe-B magnet to be detected is less than the coercivity of the grain boundary diffusion Nd-Fe-B magnet, which provides a reference and preliminary limitation for the amount of reverse magnetic field value required during detection, facilitating the detection.

[0036] In summary, the present application has the following beneficial effects:

[0037] 1. By using the method in the present application, only the grain boundary diffusion Nd-Fe-B magnet needs to be saturated and magnetized, and then a reverse magnetic field is applied. The size of the applied reverse magnetic field is controlled, and when the reverse magnetic field value reaches a certain degree, a conclusion can be drawn as to whether the grain boundary diffusion Nd-Fe-B magnet has demagnetization phenomenon. The method in the present application is not only accurate, but also does not damage the whole grain boundary diffusion Nd-Fe-B magnet. After detection, if it is judged that there is no demagnetization phenomenon, the magnet can still be used in the corresponding field.

[0038] 2. When the method in the present application is used, the direction (orientation direction) of the applied reverse magnetic field is the same as the diffusion direction of the rare earth material, the number of magnetic poles on the non-oriented surface (non-diffusion surface) of the magnet changes from less to more, and the magnetic poles are distributed in N / S / N / S alternately. When the direction (orientation direction) of the applied reverse magnetic field is perpendicular to the diffusion direction of the rare earth material, the number of magnetic poles on the oriented surface of the magnet changes from less to more, and the magnetic poles are distributed in N / S / N or S / N / S.

[0039] 3. The operation method used in the present application is simple and effective. The size of the grain boundary diffusion Nd-Fe-B magnet to be detected is not limited and can be the size required in actual application, as long as the size of the diffusion direction of the grain boundary diffusion Nd-Fe-B magnet is not greater than 12 mm. The shape specification only needs to be a cylinder. During detection, it can be attached to the surface of the magnet or within 2 mm from the surface of the magnet, and the results can be detected. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a schematic diagram of sample 1 (grain boundary diffusion Nd-Fe-B magnet) and the orientation direction and coated surface of the magnet in example 1.

[0041] Figure 2 is a magnetic field distribution image obtained by applying different reverse magnetic field sizes to sample 1 in example 1.

[0042] Figure 3 is a magnetic field distribution image obtained by applying different reverse magnetic field sizes to sample 2 in example 2.

[0043] Figure 4is a schematic diagram of sample 3 in example 3, and the orientation direction and coated surface of the magnet.

[0044] Figure 5 is a magnetic field distribution image of sample 3 in example 3, obtained by applying different reverse magnetic field strengths.

[0045] Figure 6 is a schematic diagram of sample 3, three line-scan marker lines, and the orientation direction of the reverse magnetic field in example 3.

[0046] Figure 7 is a surface magnetic field map of sample 3 in example 3, obtained by applying different reverse magnetic field strengths at three line-scan marker lines.

[0047] Figure 8 is a magnetic field distribution image obtained by detecting at different heights from the surface of sample 3 in example 4.

[0048] Figure 9 is a schematic diagram of sample 3, four marker points, and the orientation direction of the magnet in example 5 and example 6.

[0049] Figure 10 is a magnetic field distribution image of sample 5 in example 7, obtained by applying different reverse magnetic field strengths.

[0050] Figure 11 is a magnetic field distribution image of sample 2 in example 8, obtained by detecting using a magnetic film.

[0051] Figure 12 is a magnetic field distribution image of sample 3 after high-temperature treatment in example 9, obtained by applying different reverse magnetic field strengths.

[0052] Figure 13 is a magnetic field distribution image of sample 6 (amorphous grain boundary diffusion neodymium iron boron magnet) in comparative example 1, obtained by applying different reverse magnetic field strengths. DETAILED DESCRIPTION

[0053] The specific conditions of the samples used in the examples and comparative examples are shown in Table 1.

[0054] Table 1 Specific parameters of samples used in examples and comparative examples

[0055]

[0056] EXAMPLE

[0057] Example 1 is a method for identifying irreversible demagnetization of grain boundary diffusion neodymium iron boron magnets by magnetic field distribution, using sample 1, and the size specification of sample 1 is 20*15*4mm, and its related parameters are shown in Table 1.

[0058] The specific operation steps are:

[0059] 1) Select the grain boundary diffusion sample 1, and the size of the orientation surface (i.e., the diffusion surface coated with heavy rare earth, i.e., the upper and lower surfaces of the sample 1; the arrow direction is the orientation direction, which is also the direction of applying the reverse magnetic field, and is the same as the diffusion direction) is 20*15mm, and the size of the orientation direction is 4mm; as shown in the following figure: Figure 1

[0060] 2) The sample 1 is saturated magnetized, and then placed on a magnetic field distribution visualization device (Magview is used), and the magnetic field distribution characteristics of each surface of the sample 1 in the saturated magnetization state are observed;

[0061] 3) A reverse magnetic field opposite to the saturated magnetization of the sample 1 is applied to the sample 1, and the reverse magnetic field is 1.91T, and then the product is placed on the Magview detection window to observe the magnetic field distribution characteristics of each surface of the sample 1 in this state;

[0062] 4) The sample 1 is saturated magnetized again, and then a reverse magnetic field with a size of 2.03T is applied again, and the magnetic field distribution characteristics of the sample 1 in this state are observed again;

[0063] 5) Repeat step 4), adjust the size of the reverse magnetic field to 2.09T; repeat step 4) again, adjust the size of the reverse magnetic field to 2.15T; observe the magnetic field distribution characteristics of the sample 1 after the two operations;

[0064] 6) The magnetic field distribution characteristics of all the obtained sample 1 are sorted and summarized, which are shown in the following table: Figure 2 .

[0065] Figure 2 The images of not applying a reverse magnetic field and applying a reverse magnetic field with a size of 1.91T, 2.03T, 2.09T and 2.15T are disclosed in the table, and N and S in the first column and the second column correspond to the image conditions of the orientation surface (diffusion surface, i.e., the upper and lower surfaces), side1-side4 correspond to the image conditions of the non-diffusion surface, and the third column and the fourth column are the image conditions of the two opposite surfaces (front and back surfaces), and the fifth column and the sixth column are the image conditions of the two opposite surfaces (left and right surfaces).

[0066] As shown in the table: Figure 2 ​It can be seen that when the reverse magnetic field is 2.09T, the number and distribution of magnetic poles in the images of the four sides of side1-side4 have changed significantly; further, when the applied reverse magnetic field is 2.15T, the number and distribution of magnetic poles in the images of the corresponding four sides have changed more obviously. The above phenomenon shows that when the applied reverse magnetic field is 2.09T, sample 1 has already appeared irreversible demagnetization phenomenon. And the value of the applied reverse magnetic field is smaller than the coercivity of sample 1.

[0067] In example 2, a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnet by magnetic field distribution, the difference from example 1 is that sample 2 is used, the average remanence of sample 2 is 14.74kGs, the average coercivity is 21.58kOe, and other parameters are shown in table 1.

[0068] The specific operation steps are as follows:

[0069] 1) Select grain boundary diffusion sample 2, the size specification is 20*15*6mm, the size of the orientation surface (i.e. the diffusion surface coated with heavy rare earth, the orientation direction is the same as the diffusion direction) is 20*15mm, and the orientation direction size is 6mm;

[0070] 2) Saturate the sample 2, and then place it on the Magview detection window to observe the magnetic field distribution characteristics of each surface of the sample 2 in the saturated magnetization state;

[0071] 3) Apply a reverse magnetic field opposite to the saturated magnetization to the sample 2, the reverse magnetic field is 1.43T, and then observe the magnetic field distribution characteristics of each surface of the sample 1 in this state according to the method in step 2);

[0072] 4) Saturate the sample 2 again, and then apply a reverse magnetic field again, the reverse magnetic field is 1.67T, and then observe the magnetic field distribution characteristics of the sample 1 in this state according to the method in step 2);

[0073] 5) Repeat step 4), and adjust the size of the reverse magnetic field to 1.73T, 1.79T, 1.85T, 1.91T and 2.03T respectively; observe the magnetic field distribution characteristics of the sample 2 after each operation;

[0074] 6) Collect and summarize all the magnetic field distribution characteristics of the sample 2, and the details are shown in table 2. Figure 3 .

[0075] Figure 3The image data is disclosed for the following conditions: no reverse magnetic field is applied, and reverse magnetic fields of magnitudes 1.43T, 1.67T, 1.73T, 1.79T, 1.85T, 1.91T, and 2.03T are applied. Columns 1 to 4, side1 to side4, correspond to the image data of the non-diffusion surface, while columns 5 and 6, N and S, correspond to the image data of the diffusion surface. Columns 1 and 2 show the image data of the two opposing sides (front and back), side1 and side2, respectively, while columns 3 and 4 show the image data of the two opposing sides (left and right), side3 and side4, respectively.

[0076] Depend on Figure 3 It can be seen that when the magnitude of the reverse magnetic field is 1.67T, the number and distribution of magnetic poles in the images of the four sides (side1-side4) all change. Furthermore, when the applied reverse magnetic field is 1.73T, the changes in the number and distribution of magnetic poles in the images of the corresponding four sides of sample 2 are even more pronounced. These phenomena indicate that when the applied reverse magnetic field is 1.67T, sample 2 has already undergone irreversible demagnetization.

[0077] Example 3 is a method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution. The difference from Example 1 is that sample 3 is used. The average magnetic field strength of sample 3 is 14.79 kGs, the average coercivity is 22.08 kOe, and other parameters are detailed in Table 1.

[0078] The specific operating steps are as follows:

[0079] 1) Select grain boundary diffusion sample 3, with dimensions of 20*15*6mm. The diffusion surfaces coated with heavy rare earth elements, i.e., the top and bottom surfaces of sample 3, have dimensions of 20*15mm. The orientation surface (arrow direction, also called the direction of the applied reverse magnetic field, perpendicular to the diffusion surface coated with heavy rare earth elements, i.e., perpendicular to the diffusion direction) has dimensions of 20*6mm, and the orientation direction dimension is 15mm. See details. Figure 4 .

[0080] 2) Saturate magnetize sample 3 and then place it on the Magview detection window to observe the magnetic field distribution characteristics of each surface under saturated magnetization.

[0081] 3) Apply a reverse magnetic field opposite to that of the saturated magnetization to sample 3. The magnitude of the reverse magnetic field is 1.55T. Observe the magnetic field distribution characteristics of each surface of sample 1 in this state according to the method in step 2).

[0082] 4) Saturate and magnetize sample 3 again, and then apply a reverse magnetic field with a magnitude of 1.67T. Observe the magnetic field distribution characteristics of sample 1 in this state according to the method in step 2).

[0083] 5) Repeat step 4) and adjust the size of the reverse magnetic field to 1.79T, 1.91T, 2.03T, 2.15T and 2.27T respectively; observe the magnetic field distribution characteristics of sample 3 after each operation;

[0084] 6) Collect all the magnetic field distribution characteristics of sample 3, see Figure 5 for details;

[0085] 7) Further, according to the magnetic field distribution characteristics summary chart, test sample 3 under the conditions of no reverse magnetic field, 1.67T, 1.91T by using a spatial magnetic field distribution measuring instrument, and perform line scanning on sample 3 along Figure 6 ①②③ three positions;

[0086] During the test, the distance between the probe of the spatial magnetic field distribution measuring instrument and sample 3 is 0.5mm, and the results are shown in Figure 7 ;

[0087] The images obtained from step 6) Figure 5 respectively disclose the image conditions when no reverse magnetic field is applied and the size of the applied reverse magnetic field is 1.55T, 1.67T, 1.79T, 1.91T, 2.03T, 2.27T. side1-side4 respectively correspond to the image conditions of the upper and lower (diffusion surface) and left and right surfaces of sample 3, and the fifth and sixth columns respectively correspond to the image conditions of the two orientation surfaces.

[0088] From Figure 5 , it can be seen that when the size of the applied reverse magnetic field is 1.79T, the number of magnetic poles of the four non-diffusion surfaces 1.79T-3, 1.79T-4, 1.79T-N, 1.79T-S has begun to increase, and the magnetic pole distribution has also changed in layers; when the size of the applied reverse magnetic field is 1.91T, the increase in the number of magnetic poles and the change in the magnetic pole distribution of the non-diffusion surface are very obvious. Therefore, when the reverse magnetic field of 1.79T is applied, sample 3 has already shown irreversible demagnetization phenomenon.

[0089] From the Figure 7 obtained in step 7), it can be seen that when the size of the applied reverse magnetic field is 1.67T, the results of the surface magnetism obtained by ①②③ line scanning show the same magnetic pole, but when the size of the applied reverse magnetic field increases to 1.91T, the results of the surface magnetism obtained by ①②③ line scanning show different magnetic poles, and from the curve fluctuation it can be concluded that the magnetic poles are distributed in layers. Therefore, it is shown that during the process of increasing the size of the applied reverse magnetic field from 1.67T to 1.91T, the number of magnetic poles increases and the magnetic poles are distributed in layers, which indicates that sample 3 has already shown irreversible demagnetization phenomenon during this process.

[0090] In summary, the sample 3 obtained in Example 3 was detected by the Magview and the spatial magnetic field distribution measuring instrument. Figure 5 and Figure 7 After comparison, it can be clearly seen that the Magview and the spatial magnetic field distribution measuring instrument can be used to detect whether the sample 3 has demagnetization phenomenon, and the detection results of the spatial magnetic field distribution measuring instrument in step 7) are the same as the detection results of the Magview in step 6), which proves the accuracy of the results of the two instruments for judging the sample 3.

[0091] Example 4, a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnet by magnetic field distribution, which is different from Example 3 in that in step 3), the sample 3 is applied with a reverse magnetic field opposite to the saturation magnetization, and the reverse magnetic field is 1.91T. Then the product is placed on the detection window of the Magview, and the distance between the sample 3 and the detection window is 0mm, 0.5mm, 1mm, 1.5mm, 2mm and 2.5mm respectively. The magnetic field distribution characteristics of all the obtained sample 3 are sorted and summarized, which is shown in Figure 8 .

[0092] It is shown that when the distance between the sample 3 and the detection window of the Magview is in the range of 0-2.0mm, a better detection effect can be achieved. When the distance is 2.5mm or more, the magnetic pole distribution is not clear enough.

[0093] Example 5, a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnet by magnetic field distribution, which is different from Example 3 in that a gauss meter is used for detection, and the specific detection method is as follows:

[0094] The sample 3 is equally divided at intervals and marked in the manner of Figure 9 From top to bottom, the first row of mark points are a1, a2, a3; the second row of mark points are b1, b2, b3; and the third row of mark points are c1, c2, c3.

[0095] Under the conditions of saturation magnetization, applying a reverse magnetic field of 1.67T and 1.91T, the gauss meter is used to detect all the mark points, and the corresponding test results are obtained, which are shown in Table 2.

[0096] Table 2: Changes of surface magnetism of a1-a9 in Example 5

[0097]

[0098] The detection here is on the same plane, and the result obtained is the parameter of surface magnetism.

[0099] In the saturation magnetization state, that is, without applying a reverse magnetic field, demagnetization phenomenon is not easy to occur, which is used as a comparison with the application of a reverse magnetic field.

[0100] When the reverse magnetic field size increases to 1.91T, the changes of b1, b2, b3 can be obviously found, which also indicates that the sample 3 appears demagnetization phenomenon when the reverse magnetic field is applied to 1.91T.

[0101] It can be understood from the combination of example 3 that whether Magview or Gauss meter is used, the situation that demagnetization phenomenon appears can be directly proved from the detection result.

[0102] Example 6, a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnet by magnetic field distribution, the difference from example 3 is that sample 4 is used, the size of sample 4 is 20*15*6mm, the size of the orientation surface is 20*6mm, the size of the orientation direction is 15mm, the average remanence is 12.52kGs, and the average coercive force is 45.1kOe; and the detector material is a magnetic pole discrimination pen.

[0103] The sample 4 is equally spaced and marked in the manner of Figure 9 , from top to bottom into three rows, the mark points of the first row are a1, a2, a3; the mark points of the second row are b1, b2, b3; the mark points of the third row are c1, c2, c3; then after saturation magnetization, applying reverse magnetic field size of 3.42T and 3.91T, respectively, under the condition of corresponding reverse magnetic field size, the polarity of all mark points is detected by using a magnetic pole discrimination pen, and finally the corresponding test results are obtained, which are shown in Table 3.

[0104] Table 3 magnetic pole changes of a1-a9 in example 6

[0105]

[0106] From the above table, it can be seen that under the saturation magnetization state, the detection surface of sample 4 is detected to be all S poles; when the reverse magnetic field size is applied to 3.42T, the same polarity is still maintained; but when the reverse magnetic field size is applied to 3.91T, the magnetic poles at the mark points b1, b2, b3 all become N poles, and the magnetic poles at a1, b1, c1 or three points respectively appear S / N / S changes. The results show that when the reverse magnetic field size is applied to 3.91T, the magnetic poles at b points appear demagnetization state after the reverse magnetic field is applied to a certain size, so that the magnetic poles change from the original S poles to N poles.

[0107] Example 7, a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnet by magnetic field distribution, the difference from example 3 is that sample 5 is used, the average magnetic field strength of sample 5 is 13.79kGs, the average coercive force is 28.16kOe, and the parameters in sample 5 are shown in Table 1.

[0108] The specific operation method is that in step 3), the sample 5 is applied with a reverse magnetic field opposite to the saturation magnetization, the reverse magnetic field is 2.77T, then the product is placed on the Magview detection window, and the magnetic field distribution characteristics of each face of the sample 5 in this state are observed;

[0109] In step 4), the sample 5 is saturated magnetized again, then a reverse magnetic field is applied again, the reverse magnetic field is 2.51T, and the magnetic field distribution characteristics of the sample 5 in this state are observed in the manner of step 3);

[0110] In step 5), the operation of step 4) is repeated, but the reverse magnetic field is adjusted to 2.75T;

[0111] In step 6), the magnetic field distribution characteristics of all the obtained sample 5 are sorted and summarized, which can be seen from Figure 10 .

[0112] It can be known from Figure 10 that when the reverse magnetic field applied is 2.27T, the number and distribution of magnetic poles in the two images of 2.27T-N and 2.27T-S change, and further, the number and distribution of magnetic poles shown in the corresponding images are more obvious and prominent when the reverse magnetic field is 2.51T and 2.75T. The result shows that the sample 5 has demagnetization phenomenon when the reverse magnetic field is 2.27T.

[0113] Embodiment 8, a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnet by magnetic field distribution, which is different from embodiment 2 in that a magnetic film is used. The specific operation method is as follows:

[0114] 1) The sample 2 is saturated magnetized, then a reverse magnetic field opposite to the saturation magnetization is applied to the sample 2, and the reverse magnetic field is 1.79T;

[0115] 2) The magnetic film is placed above the sample 2, and the magnetic field distribution characteristics of the six faces of the sample 2 in this state are observed, which can be seen from Figure 11 .

[0116] It can be known from Figure 11 that when the reverse magnetic field applied is 1.79T, four magnetic pole distributions are shown in the magnetic film, and only two magnetic pole distributions are shown in the case of saturation magnetization.

[0117] In combination with the figure in embodiment 2, it can be known that when the reverse magnetic field is 1.79T, the number of magnetic poles has obviously increased, and the distribution of magnetic poles has also obviously changed.

[0118] Therefore, the above results show that the demagnetization phenomenon of the sample 2 can be shown by the distribution of magnetic poles by using the magnetic film.

[0119] Example 9, a method for identifying irreversible demagnetization of grain boundary diffusion neodymium-iron-boron magnet by magnetic field distribution, which is different from example 3 in that the specific operation method is as follows: after sample 3 is saturated and magnetized, it is placed in an oven at 80°C for 10 min, and then a reverse magnetic field opposite to the saturation magnetization of sample 3 is applied to sample 3, and the size of the reverse magnetic field is 1.31T. Then the product is taken out of the oven and cooled to room temperature, and then placed on the Magview detection window to observe the magnetic field distribution characteristics of each face of sample 1 in this state;

[0120] The above steps are repeated, and the size of the reverse magnetic field is adjusted to 1.43T, 1.55T, 1.67T in turn, respectively; and the magnetic field distribution characteristics of sample 3 after each operation are observed;

[0121] The magnetic field distribution characteristics of all obtained sample 3 are collated and summarized, which is shown in Figure 12 .

[0122] In the Figure 5 of example 3, when the reverse magnetic field is applied, the temperature of sample 3 is room temperature, and the size of the reverse magnetic field is 1.67T, and only then the increase in the number of magnetic poles and the change in the distribution of magnetic poles gradually appear.

[0123] In combination with Figure 12 , it can be known that when the sample 3 is treated at a higher temperature of 80°C before the reverse magnetic field is applied, the increase in the number of magnetic poles and the change in the distribution of magnetic poles can be observed when the size of the reverse magnetic field is 1.55T; and with the gradual increase in the size of the reverse magnetic field, the number of increased magnetic poles and the effect of the distribution of magnetic poles are more obvious.

[0124] Therefore, the above results show that the method in the present application is not only suitable for grain boundary diffusion neodymium-iron-boron magnet samples at room temperature, but also suitable for grain boundary diffusion neodymium-iron-boron magnet samples treated at a higher temperature and under a high reverse magnetic field, and relatively speaking, the magnet samples treated at a higher temperature and then subjected to reverse magnetization can observe the change in the number of magnetic poles and the distribution of magnetic poles under the application of a lower reverse magnetic field, which also shows that the magnet applied in a higher temperature working condition can also be identified whether it has demagnetization phenomenon by using the method in the present application.

[0125] Comparative example

[0126] Comparative example 1, a method for detecting a magnet, which is different from example 1 in that sample 6 is used, and sample 6 is a non-grain boundary diffusion magnet, and the grade is N52SH, the size is 20*15*6mm, the size of the orientation surface is 20*15mm, and the size of the orientation direction is 6mm (the orientation direction is the same as the diffusion direction); the average value of the residual magnetism is 14.32kGs, and the average value of the coercive force is 19.03kOe.

[0127] The specific operating steps are as follows:

[0128] 1) Saturate magnetize sample 6 and then place it on the Magview detection window to observe the magnetic field distribution characteristics of each surface under saturated magnetization.

[0129] 2) Apply a reverse magnetic field opposite to that of the saturated magnetization to sample 6. The magnitude of the reverse magnetic field is 1.67T. Observe the magnetic field distribution characteristics of each surface of sample 6 in this state according to the method in step 1).

[0130] 3) Saturate and magnetize sample 6 again, and then apply a reverse magnetic field with a magnitude of 1.79T. Observe the magnetic field distribution characteristics of sample 6 in this state according to the method in step 1).

[0131] 4) Repeat step 3), adjusting the magnitude of the reverse magnetic field to 1.91T and 2.03T respectively; observe the magnetic field distribution characteristics of sample 2 after each operation;

[0132] 5) The magnetic field distribution characteristics of all obtained samples 6 were compiled and summarized, see details below. Figure 13 .

[0133] Combination Figure 13 It can be seen that although N poles and S poles coexist and the number of magnetic poles increases in 1.91TN, 1.91TS, 1.91T-1, 1.91T-2, 1.91T-3, and 1.91T-4, no stratification occurs. Furthermore, as the magnitude of the applied reverse magnetic field gradually increases, no increase in the number of magnetic poles or stratification occurs. This indicates that the method in this application is only applicable to observing whether irreversible demagnetization occurs in grain boundary diffused NdFeB magnet samples, and cannot determine whether demagnetization occurs in non-grain boundary diffused NdFeB magnet samples.

[0134] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution, characterized in that, The operating steps are as follows: First, the grain boundary diffused NdFeB magnet is saturated and magnetized, and then a reverse magnetic field is applied. Under the influence of a reverse magnetic field, the corresponding reverse magnetic field value, number of magnetic poles, and magnetic pole distribution are analyzed. When the diffusion direction is the same as the orientation direction of the magnet, the number of magnetic poles appearing on the non-oriented surface increases and becomes layered, and the grain boundary diffused NdFeB magnet exhibits irreversible demagnetization. When the diffusion direction is perpendicular to the orientation direction of the magnet, the number of magnetic poles appearing on the orientation surface increases and they are layered, and the grain boundary diffused NdFeB magnet exhibits irreversible demagnetization.

2. The method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution according to claim 1, characterized in that, When the diffusion direction is the same as the orientation direction, the number of magnetic poles on the non-oriented surface of the magnet increases and becomes layered, with the magnetic poles alternating between N / S / N / S.

3. The method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution according to claim 1 or 2, characterized in that, In the grain boundary diffused NdFeB magnet, heavy rare earth elements are coated on the orientation surfaces of the NdFeB magnet, and the orientation surfaces are the N pole surface and the S pole surface.

4. The method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution according to claim 1, characterized in that, When the diffusion direction is perpendicular to the orientation direction of the magnet, the number of magnetic poles on the orientation surface of the magnet increases and becomes layered, with the magnetic pole distribution being N / S / N or S / N / S.

5. The method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution according to claim 1 or 4, characterized in that, In the grain boundary diffused NdFeB magnet, heavy rare earth elements are coated on the non-oriented surfaces of the NdFeB magnet, which are a set of parallel surfaces other than the N-pole surface and the S-pole surface.

6. The method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution according to claim 1, characterized in that, Equipment for identifying magnetic field distribution characteristics includes any one of the following: magnetic field distribution visualization device, spatial magnetic field distribution measuring instrument, gaussmeter, magnetic display film, and magnetic pole identification pen.

7. The method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution according to claim 1, characterized in that, The temperature of the grain boundary diffused NdFeB magnet itself is not lower than 20°C; the size of the grain boundary diffused NdFeB magnet in the diffusion direction is not greater than 12 mm.

8. The method for identifying irreversible demagnetization of grain boundary diffused NdFeB magnets by magnetic field distribution according to claim 1, characterized in that, The applied reverse magnetic field value is lower than the coercivity of the grain boundary diffused NdFeB magnet.

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