Method for reducing magnetic declination of sintered neodymium-iron-boron magnet

Abstract

The invention belongs to the technical field of neodymium-iron-boron magnets, and relates to a method for reducing magnetic declination of a sintered neodymium-iron-boron magnet. The invention discloses a method for reducing magnetic declination of a sintered neodymium-iron-boron magnet, which comprises the following steps: placing neodymium-iron-boron alloy powder in a mold, and adjusting the saturation magnetization Ms value of the neodymium-iron-boron alloy powder to be the same as the saturation magnetization Ms value of a magnetic conductive female mold of the mold; and carrying out orientation pressing, sintering and tempering heat treatment on the neodymium-iron-boron alloy powder to obtain the low-magnetic-declination sintered neodymium-iron-boron magnet. The magnetic declination of the low-magnetic-declination sintered neodymium-iron-boron magnet is smaller than 3 degrees. The saturation magnetization Ms value of the neodymium-iron-boron alloy powder is kept consistent with the Ms value of the magnetic conductive female die, so that the magnetic field bending phenomenon of the edge of the forming die is effectively improved, and the technical problem that the magnetic declination angle of a magnet is too large is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of NdFeB magnets and relates to a method for reducing the magnetic deflection angle of a sintered NdFeB magnet. Background Art

[0002] The magnetic declination of sintered NdFeB material refers to the angle between the magnetic pole axis of the physical shape of the permanent magnet and the actual magnetic pole direction after magnetization. Theoretically, these two axes should completely coincide, but in the actual preparation process, due to multiple factors such as molding process and mechanical processing, there is often an angle deviation between the two, which is defined as the magnetic declination. The existence of this angle will cause the magnet to generate a stray magnetic field in the non-polarized direction, thereby reducing the effective magnetic properties of the permanent magnet.

[0003] With the in-depth application of sintered NdFeB materials in the field of precision magnetic devices, magnetic declination has become a key parameter affecting product performance. Especially in high-end applications such as consumer electronic micro devices and precision motors, excessive magnetic declination not only significantly reduces product quality, but also causes safety hazards. Specifically, in the field of consumer electronic products, excessive magnetic declination directly leads to a sharp drop in the qualified rate of micro magnets; in motor applications, it will cause problems such as increased vibration, increased noise and deterioration of positioning accuracy, which will not only cause a waste of permanent magnet magnetic properties, but also cause a chain reaction of deterioration in the performance of the entire machine. The current industry standard has clearly required that the magnetic declination of permanent magnet materials for high-precision motors must be strictly controlled within 3°.

[0004] In order to meet this stringent standard, the production end faces severe challenges: for consumer electronic products that need to be magnetized before shipment, manufacturers have to adopt a full inspection and screening method, retaining only products with uniform magnetic field lines and up-to-standard magnetic declination for subsequent processing. This causes the material utilization rate to drop sharply to 30-40%, which is significantly lower than the 60% utilization rate of conventional products, and the production cost increases exponentially. For non-magnetized products, the existing process system cannot stably control the magnetic declination within the 3° threshold, which seriously restricts the market expansion in high-end application fields. Breaking through this technical bottleneck has become a core issue that the industry needs to solve urgently. Summary of the invention

[0005] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and propose a method for reducing the magnetic deflection angle of a sintered NdFeB magnet. By adjusting the saturation magnetization intensity Ms value of the NdFeB alloy powder to be the same as the saturation magnetization intensity Ms value of the magnetic conductive female mold of the mold, the magnetic field bending occurring at the edge of the molding mold is improved so that the magnetic deflection angle of the sintered NdFeB magnet meets the requirements.

[0006] One object of the present invention is achieved by the following technical solutions:

[0007] A method for reducing the magnetic deflection of a sintered NdFeB magnet, the method comprising:

[0008] Place the neodymium-iron-boron alloy powder in a mold, and adjust the saturation magnetization Ms value of the neodymium-iron-boron alloy powder to be the same as the saturation magnetization Ms value of the magnetic conductive female mold of the mold; then subject the neodymium-iron-boron alloy powder to orientation pressing, sintering and tempering heat treatment to obtain a low magnetic declination sintered neodymium-iron-boron magnet; the magnetic declination of the low magnetic declination sintered neodymium-iron-boron magnet < 3°.

[0009] Preferably, the magnetic declination of the low magnetic declination sintered neodymium-iron-boron magnet < 1°.

[0010] Preferably, the average particle size of the neodymium-iron-boron alloy powder is 2.5 - 3.6 μm.

[0011] More preferably, the average particle size of the neodymium-iron-boron alloy powder is 2.5 - 3.3 μm.

[0012] Preferably, the neodymium-iron-boron alloy powder further includes 0.01 - 0.5 wt% of a lubricant.

[0013] More preferably, the lubricant is ethanol, zinc stearate, and n-hexane with a mass ratio of (90 - 98):(1 - 5):(1 - 5).

[0014] Even more preferably, the zinc content in the zinc stearate is 11.2 - 11.7 wt%, and the particle size SMD value is 2.2 - 2.5 μm.

[0015] Preferably, the neodymium-iron-boron alloy powder is obtained by batching, melting, rapid solidification by spinning, hydrogen crushing, grinding with a jet mill, and powder mixing.

[0016] More preferably, the batching includes: batching the neodymium-iron-boron alloy according to the grade of the target sintered neodymium-iron-boron magnet in proportion.

[0017] More preferably, the melting includes: melting the neodymium-iron-boron alloy batch to form an alloy ingot.

[0018] More preferably, the rapid solidification by spinning includes: remelting the alloy ingot and spraying it onto a high-speed rotating copper roller through a nozzle to form a rapidly solidified sheet.

[0019] More preferably, the hydrogen crushing includes: putting the rapidly solidified sheet into a hydrogen crushing furnace, filling the hydrogen crushing furnace with hydrogen and heating it to the hydrogen absorption temperature to make the rapidly solidified sheet hydrogen absorption saturated; rotating the hydrogen crushing furnace and dehydrogenating the rapidly solidified sheet to obtain neodymium-iron-boron alloy coarse powder.

[0020] More preferably, the grinding with a jet mill includes: grinding the neodymium-iron-boron alloy coarse powder in a jet mill to obtain neodymium-iron-boron alloy fine powder, and the average particle size of the neodymium-iron-boron alloy fine powder is 2.1 - 3.6 μm.

[0021] Further preferably, the mixed powder comprises: mixing neodymium iron boron alloy fine powder and a lubricant evenly to obtain neodymium iron boron alloy powder.

[0022] Preferably, the method for reducing the magnetic declination angle of the sintered neodymium iron boron magnet comprises: placing neodymium iron boron alloy powder containing 0.01 - 0.5 wt% of a lubricant into a mold, wherein the lubricant is ethanol, zinc stearate, and n-hexane with a mass ratio of (90 - 98):(1 - 5):(1 - 5); adjusting the saturation magnetization intensity Ms value of the neodymium iron boron alloy powder to be the same as the saturation magnetization intensity Ms value of the magnetic conductive female mold of the mold; then subjecting the neodymium iron boron alloy powder to orientation pressing, sintering, and tempering heat treatment to obtain a sintered neodymium iron boron magnet with a low magnetic declination angle; the magnetic declination angle of the sintered neodymium iron boron magnet with a low magnetic declination angle < 1°.

[0023] Preferably, the density of the neodymium iron boron alloy powder is 1.0 - 3.0 g / cm 3 .

[0024] Further preferably, the density of the neodymium iron boron alloy powder is 1.5 - 2.5 g / cm 3 .

[0025] Preferably, the process of adjusting the saturation magnetization intensity Ms value of the neodymium iron boron alloy powder to be the same as the saturation magnetization intensity Ms value of the magnetic conductive female mold of the mold comprises:

[0026] (1) Testing the magnetization intensity M value of the neodymium iron boron alloy powder corresponding to different densities, fitting the M-H curve, and obtaining the saturation magnetization intensity Ms value;

[0027] (2) Testing the magnetization intensity M value of the magnetic conductive female mold of the mold, fitting the M-H curve, and obtaining the saturation magnetization intensity Ms value;

[0028] (3) Determining the theoretical density of the neodymium iron boron alloy powder when it has the same saturation magnetization intensity Ms value according to the saturation magnetization intensity Ms value of the magnetic conductive female mold of the mold;

[0029] (4) Adjusting the weight of the neodymium iron boron alloy powder in the mold according to the theoretical density so that the density of the neodymium iron boron alloy powder is the same as the theoretical density.

[0030] Further preferably, the density of the neodymium iron boron alloy powder is the ratio of the weight of the neodymium iron boron alloy powder to the total volume before orientation pressing in the mold.

[0031] Preferably, the mold comprises an upper punch, a lower punch, and a magnetic conductive female mold, and the neodymium iron boron alloy powder is orientation pressed into a neodymium iron boron green body in the magnetic conductive female mold by pressing of the upper punch and the lower punch.

[0032] Further preferably, the density of the neodymium iron boron green body is 4.0 - 4.2 g / cm 3。

[0033] Preferably, the magnetic field strength for the orientation pressing is 1.4 - 2.6 T, and the pressure is 40 - 60 MPa;

[0034] Preferably, the sintering temperature is 960 - 1150 °C, and the sintering time is 4 - 20 h.

[0035] More preferably, the sintering temperature is 1000 - 1100 °C, and the sintering time is 6 - 10 h.

[0036] Preferably, the temper heat treatment includes primary tempering and secondary tempering. The primary tempering temperature is 650 - 960 °C, and the primary tempering time is 1 - 10 h; the secondary tempering temperature is 300 - 640 °C, and the secondary tempering time is 1 - 10 h.

[0037] More preferably, the temper heat treatment includes primary tempering and secondary tempering. The primary tempering temperature is 850 - 950 °C, and the primary tempering time is 1 - 5 h; the secondary tempering temperature is 460 - 560 °C, and the secondary tempering time is 1 - 5 h.

[0038] More preferably, the sintering temperature > the primary tempering temperature.

[0039] The second object of the present invention is achieved by the following technical solutions:

[0040] A low magnetic declination sintered NdFeB magnet, with its magnetic declination < 1°.

[0041] Preferably, the low magnetic declination sintered NdFeB magnet is obtained by placing NdFeB alloy powder containing 0.01 - 0.5 wt% of lubricant in a mold. The lubricant is ethanol, zinc stearate, and n - hexane with a mass ratio of (90 - 98):(1 - 5):(1 - 5); adjusting the saturation magnetization Ms value of the NdFeB alloy powder to be the same as the saturation magnetization Ms value of the magnetic - conducting female mold of the mold; and then performing orientation pressing, sintering, and temper heat treatment on the NdFeB alloy powder.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. By making the saturation magnetization Ms value of the NdFeB alloy powder consistent with the Ms value of the magnetic - conducting female mold, the present invention effectively improves the magnetic field bending phenomenon at the edge of the forming mold, and fundamentally solves the technical problem of excessive magnetic declination of the magnet.

[0044] 2. The method for reducing the magnetic declination angle of sintered Nd-Fe-B magnets according to the present invention, while retaining the existing mold structure, controls the density of the Nd-Fe-B alloy powder before orientation pressing by matching the composition of the Nd-Fe-B alloy powder, and achieves precise control of the magnetic declination angle by means of a simple and feasible process.

[0045] 3. The present invention adds a lubricant to the Nd-Fe-B alloy powder, significantly improving the powder fluidity and forming performance, ensuring that the magnetic powder is fully aligned along the magnetic field direction during the magnetization orientation process, thereby further reducing the magnetic declination angle.

[0046] 4. The method for reducing the magnetic declination angle of sintered Nd-Fe-B magnets according to the present invention successfully improves the qualified rate of magnet products, and at the same time makes a substantial breakthrough in the application performance of sintered Nd-Fe-B materials in fields such as high-precision motors, significantly reducing the equipment vibration and noise levels.

[0047] 5. The sintered Nd-Fe-B magnet with a low magnetic declination angle according to the present invention breaks through the application limitations of traditional materials, providing a new solution for expanding the applications in fields such as high-end precision equipment and new drive systems. Description of the Drawings

[0048] Figure 1 It is the fitting Y-H curve graph of the Nd-Fe-B alloy powder and the magnetic conduction female mold of the mold at different densities in Example 1 of the present invention. Detailed Embodiments

[0049] The technical solutions of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only used to help understand the present invention and are not intended to limit the present invention specifically.

[0050] If there is no special description, the raw materials used in the embodiments of the present invention are all common raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0051] In this article, the method for reducing the magnetic declination angle of sintered Nd-Fe-B magnets includes:

[0052] (1) After proportioning according to the Nd-Fe-B alloy ratio, a rapid solidification strip is made by the rapid solidification and strip casting process, and then the rapid solidification strip is ground into Nd-Fe-B alloy fine powder through hydrogen crushing and powder making. 0.01-0.5 wt% of lubricant is added to the Nd-Fe-B alloy fine powder, and after stirring and mixing the powder, Nd-Fe-B alloy powder is obtained;

[0053] The average particle size of the Nd-Fe-B alloy powder is 2.5-3.3 μm;

[0054] The lubricant is ethanol, zinc stearate, and n-hexane with a mass ratio of (90-98):(1-5):(1-5);

[0055] (2) Test the saturation magnetization Ms values corresponding to NdFeB alloy powders at different densities, and test the saturation magnetization Ms value of the magnetic conductive female die of the test mold;

[0056] (3) Place the NdFeB alloy powder in the mold, and adjust the saturation magnetization Ms value of the NdFeB alloy powder to be the same as the saturation magnetization Ms value of the magnetic conductive female die of the mold;

[0057] (4) Orient and press the NdFeB alloy powder to obtain a NdFeB green compact; the magnetic field strength of the orientation pressing is 1.4 - 2.6 T, and the pressure is 40 - 60 MPa;

[0058] (5) Sinter and perform tempering heat treatment on the NdFeB green compact to obtain a low magnetic declination sintered NdFeB magnet; the sintering temperature is 900 - 1600 °C, and the sintering time is 1 - 20 h; the tempering heat treatment includes primary tempering and secondary tempering, the primary tempering temperature is 650 - 1000 °C, and the primary tempering time is 1 - 10 h; the secondary tempering temperature is 300 - 640 °C, and the secondary tempering time is 1 - 10 h; the magnetic declination of the low magnetic declination sintered NdFeB magnet < 1°.

[0059] In this article, the mold includes an upper punch, a lower punch, and a magnetic conductive female die. The NdFeB alloy powder is oriented and pressed into a NdFeB green body in the magnetic conductive female die by the pressing of the upper punch and the lower punch.

[0060] In this article, there are no special restrictions on the specific grade (ratio) of the NdFeB alloy. Adjusting the saturation magnetization Ms value of the iron-boron alloy powder to be the same as the saturation magnetization Ms value of the magnetic conductive female die of the mold can achieve a magnetic declination of the low magnetic declination sintered NdFeB magnet < 1°.

[0061] In this article, the saturation magnetization Ms value of the iron-boron alloy powder changes correspondingly with the change of the magnetic conductive female die of the mold.

[0062] In this article, the density of the NdFeB alloy powder is the ratio of the weight of the NdFeB alloy powder to the total volume before orientation pressing in the mold.

[0063] Example 1

[0064] (1) After proportioning according to the ratio of NdFeB alloy 50H, use the rapid solidification and strip casting process to make a rapid solidification sheet, and then grind the rapid solidification sheet into fine NdFeB alloy powder through hydrogen crushing and powder making. 0.1 wt% of lubricant is added to the NdFeB alloy fine powder. The lubricant is ethanol, zinc stearate, and n-hexane with a mass ratio of 98:1:1. The zinc content in zinc stearate is 11.5 wt%, and the particle size SMD value is 2.3 μm; after stirring and mixing the powder, NdFeB alloy powder is obtained; the average particle size of the NdFeB alloy powder is 2.8 μm;

[0065] (2) The saturation magnetization Ms values of neodymium-iron-boron alloy powders at test densities of 1.5 g / cm 3 、2.0 g / cm 3 、2.5 g / cm 3 are 0.27 T, 0.32 T, and 0.39 T respectively; the saturation magnetization Ms value of the magnetic conductive female die YG12 of the test die is 0.32 T; the fitted Y-H curves of the two are shown in Figure 1 .

[0066] (3) Place the neodymium-iron-boron alloy powder in the die and adjust the densities of the neodymium-iron-boron alloy powder to 1.5 g / cm 3 、2.0 g / cm 3 、2.5 g / cm 3 respectively;

[0067] (4) Orient and press the neodymium-iron-boron alloy powder under a magnetic field strength of 2.0 T and a pressure of 60 MPa to obtain a neodymium-iron-boron green compact with a density of 4.0 g / cm 3 ;

[0068] (5) Sinter and perform tempering heat treatment on the neodymium-iron-boron green compact to obtain a sintered neodymium-iron-boron magnet with a low magnetic declination angle; the sintering temperature is 1045 °C and the sintering time is 8 h; the tempering heat treatment includes primary tempering and secondary tempering, the primary tempering temperature is 900 °C and the primary tempering time is 3 h; the secondary tempering temperature is 500 °C and the secondary tempering time is 4 h, to obtain a sintered neodymium-iron-boron magnet of 82 mm * 35 mm * 46 mm.

[0069] Cut the sintered neodymium-iron-boron magnet into sample columns with a diameter of 10 mm and a height of 10 mm for magnetic property testing, and the test results are shown in Table 1.

[0070] Example 2

[0071] (1) After proportioning according to the ratio of neodymium-iron-boron alloy 38UH, use the rapid solidification and strip casting process to make a rapid solidification sheet, and then grind the rapid solidification sheet into neodymium-iron-boron alloy fine powder through hydrogenation and powder making. Add 0.1 wt% of lubricant to the neodymium-iron-boron alloy fine powder. The lubricant is ethanol, zinc stearate, and n-hexane with a mass ratio of 97:2:1. The zinc content in zinc stearate is 11.5 wt%, and the particle size SMD value is 2.3 μm; after stirring and mixing the powder, obtain neodymium-iron-boron alloy powder; the average particle size of the neodymium-iron-boron alloy powder is 3.0 μm;

[0072] (2) Test the saturation magnetization Ms values of neodymium-iron-boron alloy powders at test densities of 1.5 g / cm 3 、1.8 g / cm 3 、2.7 g / cm 3The saturation magnetization Ms values corresponding to the neodymium-iron-boron alloy powders are 0.22 T, 0.32 T, and 0.45 T respectively; the saturation magnetization Ms value of the magnetic conductive female die YG12 of the test die is 0.32 T;

[0073] (3) Place the neodymium-iron-boron alloy powder in the die and adjust the density of the neodymium-iron-boron alloy powder to be 1.5 g / cm 3 , 1.8 g / cm 3 , 2.7 g / cm 3 ;

[0074] (4) Orient and press the neodymium-iron-boron alloy powder under a magnetic field strength of 2.0 T and a pressure of 60 MPa to obtain a neodymium-iron-boron green compact with a density of 4.1 g / cm 3 ;

[0075] (5) Sinter and perform tempering heat treatment on the neodymium-iron-boron green compact to obtain a sintered neodymium-iron-boron magnet with a low magnetic declination angle; the sintering temperature is 1045 °C and the sintering time is 8 h; the tempering heat treatment includes primary tempering and secondary tempering, the primary tempering temperature is 900 °C and the primary tempering time is 3 h; the secondary tempering temperature is 500 °C and the secondary tempering time is 4 h to obtain a sintered neodymium-iron-boron magnet.

[0076] Cut the sintered neodymium-iron-boron magnet into a sample column with a diameter of 10 mm and a height of 10 mm for magnetic property testing, and the test results are shown in Table 1.

[0077] Example 3

[0078] (1) After proportioning according to the ratio of neodymium-iron-boron alloy N52, use the rapid solidification and strip casting process to make a rapid solidification sheet, and then grind the rapid solidification sheet into neodymium-iron-boron alloy fine powder through hydrogenation crushing and powder making. Add 0.1 wt% of lubricant to the neodymium-iron-boron alloy fine powder. The lubricant is ethanol, zinc stearate, and n-hexane with a mass ratio of 96:1:3. The zinc content in zinc stearate is 11.5 wt%, and the particle size SMD value is 2.3 μm; after stirring and mixing the powder, obtain neodymium-iron-boron alloy powder; the average particle size of the neodymium-iron-boron alloy powder is 2.5 μm;

[0079] (2) Test the saturation magnetization Ms values corresponding to the neodymium-iron-boron alloy powders with densities of 1.6 g / cm 3 , 2.2 g / cm 3 , 2.6 g / cm 3 respectively, which are 0.26 T, 0.32 T, and 0.40 T; the saturation magnetization Ms value of the magnetic conductive female die YG12 of the test die is 0.32 T;

[0080] (3) Place the neodymium-iron-boron alloy powder in the die and adjust the density of the neodymium-iron-boron alloy powder to be 1.6 g / cm 3 , 2.2 g / cm3 , 2.6 g / cm 3 ;

[0081] (4) The neodymium-iron-boron alloy powder is subjected to orientation pressing under a magnetic field strength of 2.0 T and a pressure of 60 MPa to obtain a neodymium-iron-boron green compact with a density of 4.0 g / cm 3 ;

[0082] (5) The neodymium-iron-boron green compact is subjected to sintering and tempering heat treatment to obtain a sintered neodymium-iron-boron magnet with a low magnetic declination angle; the sintering temperature is 1055 °C and the sintering time is 8 h; the tempering heat treatment includes primary tempering and secondary tempering, the primary tempering temperature is 900 °C and the primary tempering time is 3 h; the secondary tempering temperature is 500 °C and the secondary tempering time is 4 h, to obtain a sintered neodymium-iron-boron magnet.

[0083] The sintered neodymium-iron-boron magnet is cut into a sample column with a diameter of 10 mm and a height of 10 mm for magnetic property testing, and the test results are shown in Table 1.

[0084] Example 4

[0085] Compared with Example 1, the difference is that

[0086] (1) After proportioning according to the ratio of neodymium-iron-boron alloy 50H, a rapidly solidified sheet is made by the rapid solidification and strip casting process, and then the rapidly solidified sheet is hydrogenated, pulverized and ground into neodymium-iron-boron alloy fine powder. 0.1 wt% of lubricant is added to the neodymium-iron-boron alloy fine powder, and the lubricant is ethanol and n-hexane with a mass ratio of 98:1, and the zinc content in zinc stearate is 11.5 wt%, and the particle size SMD value is 2.3 μm; after stirring and mixing the powder, neodymium-iron-boron alloy powder is obtained; the average particle size of the neodymium-iron-boron alloy powder is 2.8 μm.

[0087] (2 - 5) The steps are the same as those in (2 - 5) of Example 1.

[0088] The sintered neodymium-iron-boron magnet is cut into a sample column with a diameter of 10 mm and a height of 10 mm for magnetic property testing, and the test results are shown in Table 1.

[0089] Example 5

[0090] (1) After proportioning according to the ratio of neodymium-iron-boron alloy 50H, a rapidly solidified sheet is made by the rapid solidification and strip casting process, and then the rapidly solidified sheet is hydrogenated, pulverized and ground into neodymium-iron-boron alloy fine powder. 0.1 wt% of lubricant is added to the neodymium-iron-boron alloy fine powder, and the lubricant is ethanol, zinc stearate and n-hexane with a mass ratio of 98:1:1, and the zinc content in zinc stearate is 11.5 wt%, and the particle size SMD value is 2.3 μm; after stirring and mixing the powder, neodymium-iron-boron alloy powder is obtained; the average particle size of the neodymium-iron-boron alloy powder is 2.0 μm.

[0091] (2 - 5) are the same as steps (2 - 5) in Example 1.

[0092] The sintered NdFeB magnet was cut into sample columns with a diameter of 10 mm and a height of 10 mm for magnetic property testing, and the test results are shown in Table 1.

[0093] Example 6

[0094] (1) After proportioning according to the ratio of NdFeB alloy 50H, a rapidly solidified ribbon was made by the rapid solidification and melt spinning process. Then the rapidly solidified ribbon was hydrogenated and pulverized and ground into NdFeB alloy fine powder. 0.1 wt% of a lubricant was added to the NdFeB alloy fine powder. The lubricant was ethanol, zinc stearate, and n - hexane with a mass ratio of 98:1:1. The zinc content in zinc stearate was 11.5 wt%, and the SMD value of the particle size was 2.3 μm. After stirring and mixing the powder, NdFeB alloy powder was obtained. The average particle size of the NdFeB alloy powder was 3.4 μm.

[0095] (2 - 5) are the same as steps (2 - 5) in Example 1.

[0096] The sintered NdFeB magnet was cut into sample columns with a diameter of 10 mm and a height of 10 mm for magnetic property testing, and the test results are shown in Table 1.

[0097] Example 7

[0098] (1) After proportioning according to the ratio of NdFeB alloy 50H, a rapidly solidified ribbon was made by the rapid solidification and melt spinning process. Then the rapidly solidified ribbon was hydrogenated and pulverized and ground into NdFeB alloy fine powder. 0.1 wt% of a lubricant was added to the NdFeB alloy fine powder. The lubricant was ethanol, zinc stearate, and n - hexane with a mass ratio of 98:1:1. The zinc content in zinc stearate was 11.5 wt%, and the SMD value of the particle size was 2.3 μm. After stirring and mixing the powder, NdFeB alloy powder was obtained. The average particle size of the NdFeB alloy powder was 4.0 μm.

[0099] (2 - 5) are the same as steps (2 - 5) in Example 1.

[0100] The sintered NdFeB magnet was cut into sample columns with a diameter of 10 mm and a height of 10 mm for magnetic property testing, and the test results are shown in Table 1.

[0101] Example 8

[0102] (1) After proportioning according to the ratio of neodymium-iron-boron alloy 50H, a rapidly solidified sheet is made by the rapid solidification and strip casting process. Then, the rapidly solidified sheet is hydrogenated and pulverized, and then ground into fine neodymium-iron-boron alloy powder. 0.1 wt% of a lubricant is added to the neodymium-iron-boron alloy fine powder. The lubricant is ethanol, zinc stearate, and n-hexane with a mass ratio of 98:1:1. The zinc content in zinc stearate is 11.5 wt%, and the SMD value of the particle size is 2.3 μm. After stirring and mixing the powder, neodymium-iron-boron alloy powder is obtained. The average particle size of the neodymium-iron-boron alloy powder is 1.5 μm.

[0103] (2 - 5) are the same as steps (2 - 5) in Example 1.

[0104] The sintered neodymium-iron-boron magnet is cut into a sample column with a diameter of 10 mm and a height of 10 mm for magnetic property testing. The test results are shown in Table 1.

[0105] Table 1. Magnetic properties of sintered neodymium-iron-boron magnets

[0106]

[0107] As can be seen from the above table, in the present invention, the saturation magnetization intensity Ms value of the neodymium-iron-boron alloy powder is adjusted to be the same as the saturation magnetization intensity Ms value of the magnetic conductive female die of the mold. While improving the magnetic properties of the sintered neodymium-iron-boron magnet, the magnetic declination is reduced to <1°. Zinc stearate was not added to the neodymium-iron-boron alloy powder in Example 4, resulting in a significant increase in the magnetic declination; however, excessive zinc stearate will instead cause deterioration of the magnetic properties of the magnet. The average particle size of the neodymium-iron-boron alloy powder in Examples 5 and 6 is too small or too large, which has a certain impact on the magnetic properties.

[0108] In summary, on the premise of retaining the existing mold structure, the present invention adjusts the saturation magnetization intensity Ms value of the neodymium-iron-boron alloy powder to be consistent with the Ms value of the magnetic conductive female die by matching the components of the neodymium-iron-boron alloy powder, effectively improving the magnetic field bending phenomenon at the edge of the forming mold, and fundamentally solving the technical problem of excessive magnetic declination of the magnet; at the same time, adding a lubricant to the neodymium-iron-boron alloy powder significantly improves the powder fluidity and forming performance, ensuring that the magnetic powder is fully oriented during the magnetization and orientation process, thereby further reducing the magnetic declination.

[0109] All aspects, embodiments, and features of the present invention should be considered illustrative in all respects and do not limit the present invention. The scope of the present invention is only defined by the claims. Without departing from the spirit and scope of the claimed invention, those skilled in the art will be aware of other embodiments, modifications, and uses.

[0110] In the preparation method of the present invention, the order of each step is not limited to the listed order. For those of ordinary skill in the art, without creative efforts, the sequence changes of each step are also within the protection scope of the present invention. In addition, two or more steps or actions can be carried out simultaneously.

[0111] Finally, it should be noted that the specific embodiments described herein are merely examples of the present invention and do not limit the implementation manner of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. It is not necessary and impossible to list all implementation manners here. And these obvious changes or variations derived from the essential spirit of the present invention still belong to the protection scope of the present invention. Interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A method for reducing the magnetic deflection of a sintered NdFeB magnet, characterized in that: The method comprises: placing NdFeB alloy powder in a mold, adjusting the saturation magnetization Ms value of the NdFeB alloy powder to be the same as the saturation magnetization Ms value of a magnetic conductive negative mold of the mold; then subjecting the NdFeB alloy powder to orientation pressing, sintering and tempering heat treatment to obtain a low magnetic declination sintered NdFeB magnet; the magnetic declination of the low magnetic declination sintered NdFeB magnet is less than 3°.

2. The method for reducing the magnetic deflection of a sintered NdFeB magnet according to claim 1, characterized in that: The NdFeB alloy powder also includes 0.01-0.5wt% of lubricant.

3. The method for reducing the magnetic deflection of a sintered NdFeB magnet according to claim 2, characterized in that: The lubricant is ethanol, zinc stearate and n-hexane in a mass ratio of (90-98):(1-5):(1-5).

4. The method for reducing the magnetic deflection of a sintered NdFeB magnet according to claim 2, characterized in that: The low magnetic deflection sintered NdFeB magnet has a magnetic deflection angle of less than 1°.

5. The method for reducing the magnetic deflection of a sintered NdFeB magnet according to claim 1, characterized in that: The NdFeB alloy powder is obtained through batching, smelting, rapid solidification belt spinning, hydrogen crushing, air flow grinding and powder mixing.

6. The method for reducing magnetic deflection of sintered NdFeB magnets according to claim 1, characterized in that: The process of adjusting the saturation magnetization Ms value of the NdFeB alloy powder to be the same as the saturation magnetization Ms value of the magnetic conductive female mold of the mold comprises: (1) Test the magnetization intensity M value corresponding to NdFeB alloy powder at different densities, and fit the MH curve to obtain the saturation magnetization intensity Ms value; (2) Testing the magnetization intensity M value of the magnetic conductive negative mold of the mold and fitting the MH curve to obtain the saturation magnetization intensity Ms value; (3) Determine the theoretical density of the NdFeB alloy powder when it has the same saturation magnetization Ms value according to the saturation magnetization Ms value of the magnetic conductive female mold of the mold; (4) The weight of the NdFeB alloy powder in the mold is adjusted according to the theoretical density so that the density of the NdFeB alloy powder is the same as the theoretical density.

7. The method for reducing the magnetic deflection of a sintered NdFeB magnet according to claim 1 or 6, characterized in that: The density of the NdFeB alloy powder is the ratio of the weight of the NdFeB alloy powder to the total volume before orientation pressing in the mold.

8. The method for reducing magnetic deflection of sintered NdFeB magnets according to claim 1, characterized in that: The sintering temperature is 960-1150° C., and the sintering time is 4-20 hours.

9. The method for reducing magnetic deflection of sintered NdFeB magnets according to claim 1, characterized in that: The tempering heat treatment includes primary tempering and secondary tempering. The primary tempering temperature is 650-960° C. and the primary tempering time is 1-10 hours. The secondary tempering temperature is 300-640° C. and the secondary tempering time is 1-10 hours.

10. A low magnetic deflection sintered NdFeB magnet, characterized in that: The magnet is obtained by the method for reducing the magnetic deflection angle of a sintered NdFeB magnet as described in any one of claims 1 to 9.

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