Magnetic field focusing oriented neodymium-iron-boron permanent magnet and method of making same

Abstract

The application discloses a neodymium-iron-boron permanent magnet with magnetic field focusing orientation and a preparation method thereof. The permanent magnet comprises a central region and at least one group of side regions, each group of side regions comprising two side regions symmetrically distributed on both sides of the central region; the content of RE in the permanent magnet gradually decreases from the central region to the edge region; the content of Co gradually increases; the carbon content of the permanent magnet gradually increases from the central region to the edge region; the thermal expansion coefficient of the permanent magnet perpendicular to the orientation direction gradually increases from the central region to the edge region; and the difference between the thermal expansion coefficient perpendicular to the orientation direction and the thermal expansion coefficient parallel to the orientation direction gradually decreases from the central region to the edge region. The application can improve the magnetic focusing effect of the permanent magnet, reduce the internal stress of the permanent magnet and improve the qualified rate of finished products.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth permanent magnet material manufacturing, in particular to a magnetic field focusing oriented neodymium iron boron permanent magnet and a preparation method thereof. Background Art

[0002] Sintered NdFeB permanent magnet materials are widely used in important fields such as new energy vehicles, consumer electronics, and wind power generation due to their excellent comprehensive magnetic properties. Permanent magnet motors or generators are devices that realize the conversion of electrical energy and mechanical energy, and are one of the areas where sintered NdFeB is used the most. The permanent magnets in the motor are usually installed on the rotor. There is a certain air gap between the rotor and the stator. The magnetic flux generated by the permanent magnet is divided into two parts. One part is cross-linked with the armature winding through the air gap, which is called the main magnetic flux, and the other part is not cross-linked with the armature winding, which is called the leakage flux. When designing permanent magnets, the main magnetic flux should be increased and the leakage flux should be reduced to maximize the performance of the permanent magnet material. The magnetization directions of permanent magnets are usually parallel, such as Figure 1 As shown, after the permanent magnet is magnetized, its magnetic field lines are distributed as follows Figure 2 As shown, from Figure 2 It can be seen that at a certain air gap from the permanent magnet, the magnetic lines of force diverge. This structure inevitably leads to an increase in leakage flux. The solution of the existing technology is to add two magnets on both sides of the permanent magnet to form a Haier shell structure. Figure 3 shown. Figure 4 This is the magnetic field distribution of a Halbach permanent magnet assembly. As can be seen, with this structure, the magnetic field lines form a concentrated magnetic field in the upper space of the permanent magnet, with the density of magnetic field lines in the upper portion significantly greater than in the lower portion. However, this structure introduces a new challenge: the magnet manufacturing process is complex, especially due to the significant repulsive force between the magnets on both sides and the central magnet, often requiring specialized fixtures and high-strength adhesives.

[0003] Another method involves performing focused orientation magnetization during the green compacting of the permanent magnet, causing the magnetic powder to rotate toward a specific point, and then sintering and heat treating to produce a densified magnet. This method can give a single permanent magnet the effect of a Haier shell array made up of multiple pieces. Chinese Patent CN 116761689A discloses a device and method for producing a single permanent magnet with focused and parallel magnetic flux regions. This method modifies the magnetic circuit structure in the mold, resulting in a magnetic circuit structure within the mold cavity that is parallel at the bottom and focused at the top. For example, Chinese Patent CN 218041167 U provides a focused magnetization scheme that primarily arranges mutually repelling magnetic fields on both sides of the mold, resulting in the magnetic powder within the mold cavity exhibiting a focused distribution. While this scheme provides a method for magnetic field distribution within the mold, for sintered NdFeB magnetic powder, when the orientation magnetic field is non-uniform, the magnetic powder particles vary in size, resulting in significant differences in the flipping effect within the mold cavity. Furthermore, sintered NdFeB magnets exhibit anisotropic expansion characteristics, with positive expansion parallel to the orientation direction and negative expansion perpendicular to the orientation direction. This non-parallel orientation leads to significant internal stress within the magnet, inevitably causing uneven shrinkage during cooling of the magnet blank during the sintering process, and may even cause the magnet to crack. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0005] An object of the present invention is to provide a permanent magnet with a magnetic field focusing orientation and a preparation method thereof, which can improve the magnetic field focusing effect of the permanent magnet, reduce the internal stress of the permanent magnet, and improve the qualified rate of the finished product.

[0006] In order to achieve these objects and other advantages according to the present invention, the permanent magnet includes a central region and at least one group of side regions, wherein the permanent magnet has a symmetry plane in the central region, each group of side regions includes two side regions symmetrically distributed on both sides of the central region, and the outermost group of side regions in the at least one group of side regions is a group of edge regions;

[0007] The composition and magnet properties of each set of side regions remain consistent;

[0008] The composition of the permanent magnet in the central area or the side area is calculated as follows by mass percentage: RE L a RE H b Co c Cu d M e Fe bal B f, 24≤a≤31, 0≤b≤4, 0≤c≤30, 0.1≤d≤0.8, 0.2≤e≤3, 0.86≤f≤1.2, 28≤a+b≤35, bal is the margin; RE L is one or a combination of light rare earth elements Pr, Nd, La, Ce and Y, RE H is one or a combination of heavy rare earth elements Gd, Ho, Dy, and Tb, and M is one or a combination of Al, Cr, Nb, Zr, Ga, Ti, V, Mo, and Mn;

[0009] The RE content in the permanent magnet decreases from the central region to the edge region, and the Co content gradually increases. The composition distribution of the central region is rich in RE and poor in Co, and the composition distribution of the edge region is poor in RE and rich in Co. The difference in RE content between the central region and the edge region is ≤1%, and the difference in Co content between the edge region and the central region is ≤30%. L and RE H sum;

[0010] The carbon content of the permanent magnet increases from the central region to the edge region, and the difference in carbon content between the central region and the edge region is ≥400 ppm;

[0011] The thermal expansion coefficient of the permanent magnet perpendicular to the orientation direction increases from the central region to the edge region; the thermal expansion coefficient of the permanent magnet parallel to the orientation direction has no significant difference between the central region and the at least one set of side regions; the difference between the thermal expansion coefficient perpendicular to the orientation direction and the thermal expansion coefficient parallel to the orientation direction of the permanent magnet decreases from the central region to the edge region;

[0012] The permanent magnet has a focusing plane perpendicular to the symmetry plane, and on the focusing plane, the magnetic field strength of the permanent magnet increases from the edge region to the central region.

[0013] Preferably, in the permanent magnet with magnetic field focusing orientation, the permanent magnet includes two or four side regions symmetrically distributed on both sides of the central region.

[0014] The present invention also provides a method for preparing a permanent magnet with a magnetic field focusing orientation, comprising:

[0015] Step (1) prepares RE-rich and Co-poor alloy powder I, wherein the composition of the alloy powder I is as follows by mass percentage: RE L a1 RE H b1 Co c1 Cud1 Fe bal M e1 B f1 , where 30≤a1≤33, 0≤b1≤4, 0≤c1≤3, 0≤d1≤0.3, 0.2≤e1≤3, 0.86≤f1≤1.2;

[0016] Step (2) prepares RE-poor Co-rich alloy powder II, wherein the composition of the alloy powder II is as follows by mass percentage: RE L a2 RE H b2 Co c2 Cu d2 Fe bal M e2 B f2 , where 26≤a2≤31, 0≤b2≤4, 3<c2≤40, 0≤d2≤2, 0.2≤e2≤3, 0.86≤f2≤1.2;

[0017] Step (3) Powder Proportioning: The alloy powder I and the alloy powder II are mixed in at least two proportions to prepare at least two mixed alloy powders, wherein at least one of the at least two mixed alloy powders has a composition of rich RE and poor Co, and at least one of the mixed alloy powders has a composition of poor RE and rich Co, the RE content of the at least two mixed alloy powders decreases in sequence, and the Co content increases in sequence, the difference in RE content between the mixed alloy powder with the highest RE content and the mixed alloy powder with the lowest RE content in the at least two mixed alloy powders is ≤1%, and the difference in Co content between the mixed alloy powder with the highest Co content and the mixed alloy powder with the lowest Co content in the at least two mixed alloy powders is ≤30%, wherein the RE content is RE L and RE H sum;

[0018] Step (4) adding lubricant and mixed powder: adding lubricant to the at least two mixed alloy powders respectively, so that the carbon content of the at least two mixed alloy powders increases successively, the difference in carbon content between the mixed alloy powder with the highest carbon content and the mixed alloy powder with the lowest carbon content in the at least two mixed alloy powders is ≥400 ppm, and the carbon content of each mixed alloy powder is 500 to 2000 ppm;

[0019] Step (5) magnetic field orientation molding: the internal space of the mold is divided into a central space and at least one group of side spaces, each group of side spaces includes two side spaces symmetrically distributed on both sides of the central space, and the outermost group of side spaces in the at least one group of side areas is a group of edge spaces; the at least two mixed alloy powders are respectively placed in the central space and the at least one group of side spaces, and each group of side spaces is placed with mixed alloy powders of the same composition, and the RE content of the mixed alloy powders placed from the central space to the edge space is gradually reduced, and the Co content is gradually increased. The composition distribution of the mixed alloy powder placed in the central space is rich in RE and poor in Co, and the composition distribution of the mixed alloy powder placed in the edge space is poor in RE and rich in Co. The difference in RE content between the mixed alloy powders placed in the central space and the edge space is ≤1%, and the difference in Co content between the mixed alloy powders placed in the edge space and the central space is ≤30%, wherein the RE content is RE L and RE H The RE content of the mixed alloy powder placed in each of the middle space and the edge space increases successively, and the difference in carbon content between the mixed alloy powder placed in the middle space and the edge space is ≥400ppm; thereafter, the mold is placed in a magnetic field for orientation and shaping;

[0020] Step (6) sintering and tempering heat treatment;

[0021] Step (7) machining;

[0022] Step (8) magnetization.

[0023] Preferably, in the method for preparing the magnetic field focusing oriented permanent magnet, the average particle size of the alloy powder I is 1 to 5 μm; and the average particle size of the alloy powder II is 2 to 6 μm.

[0024] Preferably, in the method for preparing the magnetic field focusing oriented permanent magnet, in the step (4), the addition ratio of the lubricant is 0.1% to 1%.

[0025] Preferably, in the method for preparing a permanent magnet with magnetic field focusing orientation, in step (5), the density of the mixed alloy powder placed in the middle space and the at least one set of side spaces in the internal space of the mold is 1.6 to 2 g / cm 3 The mold is placed in a magnetic field for orientation shaping, which is specifically achieved by the following process: orientation shaping is carried out in a non-uniform magnetic field of 1.2-2.2T, and then placed in an isostatic press for secondary pressing, the isostatic pressure is 150-300MPa, and the green density obtained is 3.9-4.5g / cm 3 .

[0026] Preferably, in the preparation method of the magnetic field focusing oriented permanent magnet, in the step (6), the sintering and tempering heat treatment is specifically achieved by the following process: placing the green body in a vacuum sintering furnace with a temperature set at 1000-1100°C for sintering and densification, and the holding time is 2-10h; after the holding is completed, heating is stopped, and after slowly cooling to 800-900°C, argon is filled and a fan is turned on to quickly cool to room temperature to obtain a sintered magnet; the sintered magnet is subjected to secondary tempering treatment, and the treatment conditions are: keeping at 800-950°C for 2-6h and then quickly cooling to room temperature, and then keeping at 400-650°C for 2-10h and then quickly cooling to room temperature; the atmosphere of the tempering heat treatment is a vacuum or argon protection state.

[0027] Preferably, in the method for preparing the permanent magnet with magnetic field focusing orientation, the magnetization is specifically achieved by the following process: the magnet machined in step (7) is placed in a magnetization coil for magnetization, the magnetization method is to magnetize in parallel with the symmetry plane of the magnet machined in step (7), and the magnetization magnetic field is 3 to 10T.

[0028] The present invention has at least the following beneficial effects:

[0029] (1) The present invention solves the problems of poor focusing and low yield caused by uneven magnetization in the prior art by regulating the composition of the magnet. Furthermore, by adjusting the composition ratio of the alloy powder and the ratio of the powder lubricant mixed at different positions in the mold, the present invention makes the magnetic powder rotate more uniformly under the non-uniform orientation field. This also solves the problem of large differences in magnet expansion characteristics at the edge of the magnet. Therefore, the magnet yield of the present invention is higher.

[0030] (2) The present invention solves the problems of complex process and low material utilization caused by focusing through the Haier shell array. The permanent magnet of the present invention is integrally formed, does not require complex processing and bonding steps, is easy to implement, has high material utilization, and is more reliable.

[0031] (3) On the one hand, the present invention achieves a higher degree of orientation under the same magnetic field conditions by zoning and controlling the composition of the mixed alloy powder, thereby increasing the remanence Br in each region and ultimately obtaining a high magnetic flux. On the other hand, under the same degree of orientation, the powder particles have better adaptability to the oriented magnetic field, the stress in the magnet is smaller, the stray magnetic field caused by grain breakage is smaller, and the entire permanent magnet can maintain a higher magnetic flux. The focused oriented permanent magnet of the present invention reduces leakage flux and increases main magnetic flux, thereby reducing the amount of permanent magnets used in the motor or increasing the motor torque.

[0032] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the magnetization direction of a conventional permanent magnet.

[0034] Figure 2 This is the magnetic field line distribution diagram of a conventional parallel magnetized permanent magnet.

[0035] Figure 3 Schematic diagram of a permanent magnet assembly with a Halbach structure.

[0036] Figure 4 This is the magnetic field line distribution diagram of the Halbach permanent magnet assembly.

[0037] Figure 5 The present invention provides a flow chart of a method for preparing a permanent magnet with magnetic field focusing orientation.

[0038] Figure 6 Schematic diagram of the distribution of mixed alloy powder in the mold in Example 1 of the present invention.

[0039] Figure 7 This is a cloud diagram of the magnetic field distribution on the focusing surface of the permanent magnet prepared in Example 1 of the present invention.

[0040] Figure 8 Schematic diagram of the distribution of mixed alloy powder in the mold in Example 2 of the present invention.

[0041] Figure 9 This is a cloud diagram of the magnetic field distribution on the focusing surface of the permanent magnet prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0043] The present invention provides a permanent magnet with a magnetic field focusing orientation, the permanent magnet comprising a central region and at least one group of side regions, the permanent magnet having a symmetric plane in the central region, each group of side regions comprising two side regions symmetrically distributed on both sides of the central region, the outermost group of side regions in the at least one group of side regions being a group of edge regions; the composition and magnet performance of each group of side regions are consistent; the composition of the permanent magnet in the central region or the side region is calculated as follows by mass percentage: RE L a RE H b Co c Cu d Me Fe bal B f , 24≤a≤31, 0≤b≤4, 0≤c≤30, 0.1≤d≤0.8, 0.2≤e≤3, 0.86≤f≤1.2, 28≤a+b≤35, bal is the margin; RE L is one or a combination of light rare earth elements Pr, Nd, La, Ce and Y, RE H is one or more of the heavy rare earth Gd, Ho, Dy and Tb, M is one or more of the heavy rare earth Al, Cr, Nb, Zr, Ga, Ti, V, Mo and Mn, the RE content in the permanent magnet decreases from the central region to the edge region, and the Co content gradually increases, the composition distribution of the central region is rich in RE and poor in Co, the composition distribution of the edge region is poor in RE and rich in Co, the difference in RE content between the central region and the edge region is ≤1%, and the difference in Co content between the edge region and the central region is ≤30%, wherein the RE content is RE L and RE H the sum of the carbon content of the permanent magnet increases from the central region to the edge region, and the difference in carbon content between the central region and the edge region is ≥400ppm; the thermal expansion coefficient perpendicular to the orientation direction in the permanent magnet increases from the central region to the edge region; the thermal expansion coefficient parallel to the orientation direction of the permanent magnet has no obvious difference between the central region and the at least one group of side regions; the difference between the thermal expansion coefficient perpendicular to the orientation direction and the thermal expansion coefficient parallel to the orientation direction of the permanent magnet decreases from the central region to the edge region; the permanent magnet has a focusing plane perpendicular to the symmetry plane, and on the focusing plane, the magnetic field strength of the permanent magnet increases from the edge region to the central region.

[0044] Due to its inherent physical properties, NdFeB material exhibits different expansion characteristics parallel to the orientation direction (C∥) and perpendicular to the orientation direction (C⊥). In the C∥ direction, the magnet has a positive thermal expansion coefficient, while in the C⊥ direction, due to the magnetostrictive effect, it has a negative thermal expansion coefficient. In traditional methods, when magnetic powder is oriented and formed in a non-uniform magnetic field with focusing characteristics, different positions within the mold have different magnetic field magnitudes, resulting in different rotation angles of the magnetic powder at corresponding positions. This situation will lead to different internal expansion characteristics of the magnet during sintering and tempering, which in turn will cause significant stress concentration problems within the magnet. As a result, the focused orientation blank is prone to cracking, and the yield rate is very low. The present invention controls the composition ratio of different regions of the permanent magnet, so that the magnetic powder rotates more uniformly in a non-uniform orientation field (that is, the mixed alloy powder filled in each space in the mold cavity can maintain consistent rotation in the non-uniform orientation field). This solves the problem of poor magnet focusing effect caused by non-uniform magnetization in the prior art, and also solves the problem of excessive differences in the expansion characteristics of the permanent magnet at the edge, thereby reducing the internal stress of the permanent magnet and improving the yield rate.

[0045] Specifically, the thermal expansion coefficient perpendicular to the orientation direction of the permanent magnet increases from the central area to the edge area, and the thermal expansion coefficient perpendicular to the orientation direction of the central area is -4 to 3×10 -6 K -1 The thermal expansion coefficient of the edge region perpendicular to the orientation direction is -1.5 to 5×10 -6 K -1 The thermal expansion coefficient of the permanent magnet parallel to the orientation direction has no significant difference between the central region and at least one set of side regions, and is 6 to 9.9×10 -6 K -1 The difference between the thermal expansion coefficient of the permanent magnet perpendicular to the orientation direction and the thermal expansion coefficient parallel to the orientation direction decreases from the center area to the edge area. As a result, the stress in the permanent magnet is reduced and the qualified rate of the finished product is higher.

[0046] In a preferred embodiment, in the permanent magnet with magnetic field focusing orientation, the permanent magnet includes two or four side regions symmetrically distributed on both sides of the central region.

[0047] like Figure 5 As shown, the present invention also provides a method for preparing a permanent magnet with a magnetic field focusing orientation, comprising:

[0048] Step (1) prepares RE-rich and Co-poor alloy powder I, wherein the composition of the alloy powder I is as follows by mass percentage: RE L a1 RE H b1 Co c1 Cu d1 Febal M e1 B f1 , where 30≤a1≤33, 0≤b1≤4, 0≤c1≤3, 0≤d1≤0.3, 0.2≤e1≤3, 0.86≤f1≤1.2;

[0049] Step (2) prepares RE-poor Co-rich alloy powder II, wherein the composition of the alloy powder II is as follows by mass percentage: RE L a2 RE H b2 Co c2 Cu d2 Fe bal M e2 B f2 , where 26≤a2≤31, 0≤b2≤4, 3<c2≤40, 0≤d2≤2, 0.2≤e2≤3, 0.86≤f2≤1.2;

[0050] Step (3) Powder Proportioning: The alloy powder I and the alloy powder II are mixed in at least two proportions to prepare at least two mixed alloy powders, wherein at least one of the at least two mixed alloy powders has a composition of rich RE and poor Co, and at least one of the mixed alloy powders has a composition of poor RE and rich Co, the RE content of the at least two mixed alloy powders decreases in sequence, and the Co content increases in sequence, the difference in RE content between the mixed alloy powder with the highest RE content and the mixed alloy powder with the lowest RE content in the at least two mixed alloy powders is ≤1%, and the difference in Co content between the mixed alloy powder with the highest Co content and the mixed alloy powder with the lowest Co content in the at least two mixed alloy powders is ≤30%, wherein the RE content is RE L and RE H sum;

[0051] Step (4) adding lubricant and mixed powder: adding lubricant to the at least two mixed alloy powders respectively, so that the carbon content of the at least two mixed alloy powders increases successively, the difference in carbon content between the mixed alloy powder with the highest carbon content and the mixed alloy powder with the lowest carbon content in the at least two mixed alloy powders is ≥400 ppm, and the carbon content of each mixed alloy powder is 500 to 2000 ppm;

[0052] Step (5) magnetic field orientation molding: the internal space of the mold is divided into a central space and at least one group of side spaces, each group of side spaces includes two side spaces symmetrically distributed on both sides of the central space, and the outermost group of side spaces in the at least one group of side areas is a group of edge spaces; the at least two mixed alloy powders are respectively placed in the central space and the at least one group of side spaces, and each group of side spaces is placed with mixed alloy powders of the same composition, and the RE content of the mixed alloy powders placed from the central space to the edge space is gradually reduced, and the Co content is gradually increased. The composition distribution of the mixed alloy powder placed in the central space is rich in RE and poor in Co, and the composition distribution of the mixed alloy powder placed in the edge space is poor in RE and rich in Co. The difference in RE content between the mixed alloy powders placed in the central space and the edge space is ≤1%, and the difference in Co content between the mixed alloy powders placed in the edge space and the central space is ≤30%, wherein the RE content is RE L and RE H The RE content of the mixed alloy powder placed in each of the middle space and the edge space increases successively, and the difference in carbon content between the mixed alloy powder placed in the middle space and the edge space is ≥400ppm; thereafter, the mold is placed in a magnetic field for orientation and shaping;

[0053] Step (6) sintering and tempering heat treatment;

[0054] Step (7) machining;

[0055] Step (8) magnetization.

[0056] When NdFeB permanent magnets are used, in order to achieve the magnetic focusing effect, a Halbach array is usually used to achieve it. However, this method requires bonding and assembly, and the manufacturing process is complicated and difficult to mass produce. Another method is to perform focused orientation magnetization when the permanent magnet is prepared. However, when focused magnetization is performed during green compaction pressing, since the orientation magnetic field is a non-uniform field, it is difficult for the magnetic powder particles to rotate in unison, resulting in inconsistent sintering shrinkage after sintering of the permanent magnet, causing problems such as internal cracks in the blank, and a very low material qualification rate. On the other hand, due to the deviation in the rotation angle of the magnetic powder, the magnetic focusing effect is poor, and it is difficult to give full play to the advantages of concentrated magnetization. Based on this, the present invention provides a method for preparing a permanent magnet with magnetic field focused orientation. The method provided by the present invention divides the internal space of the mold (mold cavity) into multiple spaces, controls the composition of the magnetic powder filled in each space, and enables the magnetic powder to rotate more consistently with the orientation magnetic field in the mold cavity, thereby improving the magnetic focusing effect of the permanent magnet and reducing the internal stress of the permanent magnet.

[0057] The traditional method achieves the effect of focused magnetization by splicing multiple magnets together, but each unit of the permanent magnet needs to be processed separately, and complex tooling and fixtures are required for bonding. In addition, when the permanent magnet is used at high temperatures or in scenarios with large centrifugal forces, the adhesive layer is prone to failure, causing the motor to be scrapped. The permanent magnet manufacturing process provided by the present invention is simple, the permanent magnet is integrally formed, and no complex processing and bonding steps are required. It is easy to implement, has high material utilization, and is more reliable.

[0058] Furthermore, the present invention achieves a higher degree of orientation of the magnetic powder under the same magnetic field conditions through powder zoning and composition control, thereby increasing the remanence Br within each region of the permanent magnet and ultimately achieving high magnetic flux. The permanent magnets produced by the present invention reduce leakage flux and increase main flux, helping to reduce permanent magnet usage or increase motor torque.

[0059] The carbon content of the magnet is low in the center and high in the edges. This is because more lubricant is added to the powder in these areas, while less is added in the center. The magnetic field within the mold is low at the edges and high in the center. Therefore, improving the lubricity of the powder in these areas ensures a high degree of orientation at the edges, resulting in a higher remanent magnetization (Br).

[0060] In step (5), when placing at least two mixed alloy powders into the interior space of the mold, a plurality of partition plates can be used to divide the interior space of the mold into a central space and at least one set of side spaces. Then, the corresponding mixed alloy powders are placed in each space according to the design, and then the partition plates are removed so that there is no physical separation between the mixed alloy powders in adjacent spaces. In this way, during subsequent processing, the mixed alloy powders in the interior of the mold are processed into a permanent magnet.

[0061] In a preferred embodiment, in the method for preparing a permanent magnet with magnetic field focusing orientation, the average particle size of the alloy powder I is 1 to 5 μm; the average particle size of the alloy powder II is 2 to 6 μm.

[0062] The present invention selects the particle size of the alloy powder so that the powder particles have better adaptability to the oriented magnetic field under the same orientation degree, thereby reducing the internal stress of the permanent magnet and the stray magnetic field caused by grain breakage, and the entire permanent magnet can maintain a higher magnetic flux.

[0063] In a preferred embodiment, in the method for preparing the magnetic field focusing oriented permanent magnet, in the step (4), the addition ratio of the lubricant is 0.1% to 1%.

[0064] Specifically, the lubricant addition ratio can be adjusted according to the composition of the mixed alloy powder. By adjusting the lubricant ratio of the mixed alloy powder in different spaces within the mold, the present invention can make the powder rotate more uniformly under the non-uniform orientation field, thereby further enhancing the focusing effect and improving the magnet yield rate, better solving the problems of poor magnet focusing effect caused by non-uniform magnetization and low magnet yield caused by uneven magnet shrinkage.

[0065] In a preferred embodiment, in the method for preparing a permanent magnet with magnetic field focusing orientation, in step (5), the density of the mixed alloy powder placed in the middle space and the at least one set of side spaces in the internal space of the mold is 1.6 to 2 g / cm 3 The mold is placed in a magnetic field for orientation shaping, which is specifically achieved by the following process: orientation shaping is carried out in a non-uniform magnetic field of 1.2-2.2T, and then placed in an isostatic press for secondary pressing, the isostatic pressure is 150-300MPa, and the green density obtained is 3.9-4.5g / cm 3 .

[0066] In a preferred embodiment, in the preparation method of the magnetic field focusing oriented permanent magnet, in the step (6), the sintering and tempering heat treatment is specifically achieved by the following process: placing the green body in a vacuum sintering furnace with a temperature set at 1000-1100°C for sintering and densification, and the holding time is 2-10h; after the holding is completed, heating is stopped, and after slowly cooling to 800-900°C, argon is filled and a fan is turned on to quickly cool to room temperature to obtain a sintered magnet; the sintered magnet is subjected to secondary tempering treatment, and the treatment conditions are: keeping at 800-950°C for 2-6h and then quickly cooling to room temperature, and then keeping at 400-650°C for 2-10h and then quickly cooling to room temperature; the atmosphere of the tempering heat treatment is a vacuum or argon protection state.

[0067] In a preferred embodiment, in the method for preparing the permanent magnet with magnetic field focusing orientation, the magnetization is specifically achieved by the following process: the magnet machined in step (7) is placed in a magnetization coil for magnetization, and the magnetization method is to magnetize parallel to the symmetry plane of the magnet machined in step (7), and the magnetization magnetic field is 3 to 10T.

[0068] In a preferred embodiment, the machining process in step (7) is as follows: the permanent magnet blank obtained in step (6) is machined into a desired shape. To ensure symmetry during machining, the blank is first marked and then ground. The machined black sheet magnet is surface treated, and the surface treatment methods include phosphating, passivation, Zn, Ni plating, or epoxy coating.

[0069] Specific examples are provided below to further illustrate the magnetic field focusing and oriented permanent magnet and its preparation method provided by the present invention.

[0070] Example 1

[0071] S1: Prepare RE-rich and Co-poor alloy powder I, the composition of the alloy powder is as follows by mass percentage: (PrNd) 30 Dy 0.5 Co 1.5 Cu 0.2 Fe bal Al 0.3 Zr 0.15 B 0.90 According to the process of batching-rapid solidification belt spinning-hydrogen crushing-air flow milling, alloy fine powder with an average particle size of 3.5μm was obtained.

[0072] S2: Prepare RE-poor Co-rich alloy powder II, the composition of the alloy powder is as follows by mass percentage: PrNd 29 Dy 0.5 Co5Cu 0.8 Fe bal Al 0.3 Zr 0.15 B 0.90 According to the process of batching - rapid solidification belt spinning or ingot casting - hydrogen crushing - air flow milling or high energy ball milling, alloy fine powder with an average particle size of 4.5μm is obtained.

[0073] S3: Powder proportioning: alloy powders I and II are mixed in a ratio of 4:6 and 1:9 respectively to obtain mixed powders of two ratios.

[0074] S4: Add 0.1% lubricant to the powders at a mixing ratio of 4:6, or 0.2% lubricant to the powders at a mixing ratio of 1:9. Mix the powders in a V-type mixer for 4 hours. Allow the powders to rest for 2 to 2.5 hours after mixing to reduce their activity.

[0075] S5: Magnetic field orientation molding: The two powders are injected into the mold. The mold is divided into three areas. The middle area is injected with powders in a ratio of 4:6, and the two side areas are injected with powders in a ratio of 1:9. The distribution of the mixed alloy powder in the mold is shown in Figure 1. Figure 6 The bulk density of the powder is 1.8g / cm 3 The magnetic powder was then oriented and formed in a non-uniform magnetic field of 1.9 T, and then placed in an isostatic press for secondary pressing. The green density obtained at an isostatic pressure of 200 MPa was 4.30 g / cm 3 .

[0076] S6: Sintering and tempering heat treatment: Place the above green body in a vacuum sintering furnace with a temperature set at 1080℃ for sintering and densification, and the holding time is 6h; after the holding is completed, stop heating, slowly cool to 850℃, fill with argon and turn on the fan to quickly cool to room temperature to obtain a sintered magnet; perform secondary tempering treatment on the sintered magnet, the treatment process is to keep at 920℃ for 6h and then quickly cool to room temperature, and then keep at 450℃ for 4h and then quickly cool to room temperature; the atmosphere of the tempering heat treatment is a vacuum state.

[0077] S7: Machining: The permanent magnet blank obtained in step S6 is machined to the desired shape and dimensions. The specific dimensions are 90*40*30↑, where 30 is the magnetization direction. The permanent magnet surface treatment is Zn plating.

[0078] S8: Magnetization and Inspection: Place the processed permanent magnet into the magnetization coil for magnetization. The magnetization method is parallel magnetization and the magnetization magnetic field is 3 T. After magnetization, a permanent magnet with focusing orientation is obtained.

[0079] Comparative Example 1

[0080] The single-component magnet powder is prepared according to conventional process. The composition of the magnet powder is (PrNd) 29.5 Dy 0.5 Co 1.5 Cu 0.2 Fe bal Al 0.3 Zr 0.15 B 0.90 According to the process of batching, rapid solidification, belt spinning, hydrogen crushing and air flow milling, alloy fine powder with an average particle size of 3.5μm was obtained. Then, 0.15% additives were added to the powder. After mixing for 4 hours, the powder was allowed to stand for 2 hours. Then, the powder was injected into the mold cavity shown in the figure above. The magnetic powder was oriented and formed in a non-uniform magnetic field of 1.2T. Then, it was placed in an isostatic press for secondary pressing. The green density obtained at an isostatic pressure of 200MPa was 4.30g / cm 3 ; Use steps S6 to S8 exactly the same as in Example 1 to obtain a permanent magnet.

[0081] Sample processing and testing: Use a surface magnetic tester to measure the surface magnetic values ​​of different positions of the magnetic steel, recorded as Bs. Use a NIM permanent magnetic property tester to test the magnetic properties of the central area and edge area of ​​the permanent magnet. The sample size is D10*10mm. Prepare a D6*20mm cylinder, test the thermal expansion coefficient of the central area and edge area of ​​the permanent magnet, and calculate the difference in thermal expansion coefficient perpendicular to the orientation direction and parallel to the orientation direction, recorded as Δα. Calculate the difference in carbon content between the edge area and the central area of ​​the permanent magnet. For the permanent magnet prepared in comparative example 1, it can be divided into 3 equal parts, corresponding to the central area and a group of edge areas on both sides of the central area. The overall qualified rate of the permanent magnets prepared by the two methods is calculated, and the qualified rate = number of good products / total number * 100%. The qualified rate includes the blank, processing and electroplating links.

[0082] Table 1 Surface magnetic intensity of permanent magnets at different measurement positions in Example 1 and Comparative Example 1

[0083]

[0084] Table 2 Magnetic performance parameters and qualified rates of each region of the permanent magnets of Example 1 and Comparative Example 1

[0085]

[0086] Table 3 Thermal expansion coefficients and differences of various regions of the permanent magnets of Example 1 and Comparative Example 1

[0087]

[0088] Table 4 Composition distribution of each region of the permanent magnet of Example 1 and Comparative Example 1

[0089]

[0090]

[0091] As can be seen from Example 1 and Comparative Example 1, the focused magnetized permanent magnet prepared by the present invention has a significant focusing effect on the focusing surface after magnetization. As shown in Table 1, within a certain distance range from the focusing surface, the magnetic field Bs of Example 1 is improved by more than 10% compared to the surface magnetic field of Comparative Example 1 at the same location. As can be seen from Table 2, the edges of the magnets in Example 1 of the present invention have a higher Br, indicating that the magnets have a higher degree of orientation. A comparison of thermal expansion data shows that the expansion difference of the magnets in Example 1 is smaller, indicating less internal stress in the magnets. The qualified rate data shows that the qualified rate of the permanent magnets prepared by the method of the present invention reached 96%, while the qualified rate of Comparative Example 1 using conventional processes only reached 82%. As can be seen from Table 3, the thermal expansion coefficients of different locations in the comparative example are the same, with a difference of 11.5. However, by adjusting the component distribution, the thermal expansion coefficients of different regions of Example 1 of the present invention are different, with a difference of 10.5 in the center region and 9.2 in the edge region. The smaller the thermal expansion difference at the edge, the lower the internal stress in the magnet. It can be seen from Table 4 that the rare earth RE content, carbon content, and cobalt content of Comparative Example 1 are uniform, while those of Example 1 are gradient distributed. This is the fundamental reason why the permanent magnet of the present invention has a better magnetic concentration effect and a higher qualified rate. Figure 7 This is a cloud diagram of the surface magnetic distribution outside the focusing surface of the permanent magnet in Example 1 of the present invention. Figure 7 It can be seen from the figure that on the focusing surface, the magnetic field presents a focused magnetization characteristic with a large center and small sides, which indicates that the method of the present invention achieves a better magnetic focusing effect.

[0092] Example 2

[0093] S1: Prepare RE-rich and Co-poor alloy powder I, the composition of the alloy powder is as follows by mass percentage: (PrNd) 30 Tb3Co 1.5 Cu 0.2 Fe bal Al 0.3 Zr 0.15 B 0.86 According to the process of batching-rapid solidification belt spinning-hydrogen crushing-air flow milling, alloy fine powder with an average particle size of 1 μm was obtained.

[0094] S2: Prepare RE-poor Co-rich alloy powder II, the composition of the alloy powder is as follows by mass percentage: PrNd 25 Tb1Co 40 Cu 1.5 Fe bal Al 0.3 Zr 0.15 B 1.00 According to the process of batching - rapid solidification belt spinning or ingot casting - hydrogen crushing - air flow milling or high energy ball milling, alloy fine powder with an average particle size of 6 μm is obtained.

[0095] S3: Powder proportioning: alloy powders I and II were mixed in proportions of 3:7, 4:6, and 5:5, respectively, to obtain mixed powders of three different proportions.

[0096] S4: Add 0.3% lubricant to a 3:7 powder mix, 0.2% lubricant to a 4:6 powder mix, and 0.1% lubricant to a 5:5 powder mix. Mix the powders in a V-type mixer for 4 hours. Allow the mixture to rest for 2 to 2.5 hours after mixing to reduce powder activity.

[0097] S5: Magnetic field orientation molding: The two powders are injected into the mold. The mold is divided into 5 areas. The powders are injected into areas A and E at a ratio of 3:7, into areas B and D at a ratio of 4:6, and into area C at a ratio of 5:5. The distribution of the mixed alloy powders in the mold is shown in Figure 2. Figure 8 The bulk density of the powder is 2g / cm 3 The magnetic powder was then oriented and formed in a non-uniform magnetic field of 2.2T, and then placed in an isostatic press for secondary pressing. The green density obtained at an isostatic pressure of 300MPa was 4.50g / cm 3 .

[0098] S6: Sintering and tempering heat treatment: Place the above green body in a vacuum sintering furnace with a temperature set at 1095℃ for sintering and densification, and the holding time is 8h; after the holding is completed, stop heating, slowly cool to 800℃, fill with argon and turn on the fan to quickly cool to room temperature to obtain a sintered magnet; the sintered magnet is subjected to secondary tempering treatment, and the treatment process is to keep it at 870℃ for 6h and then quickly cool to room temperature, and then keep it at 500℃ for 4h and then quickly cool to room temperature; the atmosphere of the tempering heat treatment is a vacuum state.

[0099] S7: Machining: The permanent magnet blank obtained in step S6 is machined to the desired shape and dimensions. Its specific dimensions are 80*40*30, where 30 is the magnetization direction. The arrow points to the focused plane, and the tail of the arrow indicates the non-focused plane. The permanent magnet surface is treated with epoxy spraying.

[0100] S8: Magnetization and Inspection: Place the processed permanent magnet into the magnetization coil for magnetization. The magnetization method is parallel magnetization and the magnetization magnetic field is 9 T. After magnetization, a permanent magnet with focusing orientation is obtained.

[0101] Detect the composition distribution of each area of ​​the permanent magnet. Test the thermal expansion coefficient and magnetic properties of each area of ​​the permanent magnet.

[0102] Table 5 Composition distribution of each region of permanent magnet

[0103]

[0104]

[0105] Table 6 Thermal expansion coefficient of each region of permanent magnet

[0106] Area A Area B Area C Area D Zone E <![CDATA[α c∥ (K -1 )]]> <![CDATA[7.5×10 -6 ]]> <![CDATA[7.4×10 -6 ]]> <![CDATA[7.5×10 -6 ]]> <![CDATA[7.4×10 -6 ]]> <![CDATA[7.4×10 -6 ]]> <![CDATA[α c⊥ (K -1 )]]> <![CDATA[4.9×10 -6 ]]> <![CDATA[3.7×10 -6 ]]> <![CDATA[1.8×10 -6 ]]> <![CDATA[3.8×10 -6 ]]> <![CDATA[4.9×10 -6 ]]> <![CDATA[Δα(K -1 )]]> <![CDATA[2.6×10 -6 ]]> <![CDATA[3.7×10 -6 ]]> <![CDATA[5.7×10 -6 ]]> <![CDATA[3.6×10 -6 ]]> <![CDATA[2.5×10 -6 ]]>

[0107] Table 7 Magnetic properties of each region of permanent magnet

[0108] Area A Area B Area C Area D Zone E Br(kGs) 12.55 12.54 12.64 12.59 12.58 Hcj(kOe) 16.89 16.74 17.31 16.90 16.87

[0109] From the data of Table 5 to Table 7 of Example 2, it can be seen that the internal composition of the magnet presents a gradient distribution, that is, the total amount of rare earth in the center area of ​​the magnet is high and the total amount at the edge is low. This distribution can ensure that the Br in the edge area remains high; the cobalt content in the center area of ​​the magnet is low and the cobalt content in the edge area is high, which can improve and reduce the thermal expansion difference, help reduce the stress in the magnet, and reduce the probability of grains being crushed by backlog, thereby improving the qualified rate. The carbon content of the magnet is low in the center area and high in the edge area. This is because more lubricant is added to the powder in the edge area, while less lubricant is added in the middle. The magnetic field in the mold is low in the edge area and high in the center area. Therefore, by improving the lubricity of the powder in the edge area, it is possible to ensure that the edge area maintains a higher degree of orientation, thereby obtaining a higher remanent magnetization Br. Figure 8 This is a cloud diagram of the magnetic field distribution on the focusing surface of the permanent magnet of Example 2. It can be seen that the magnetic field exhibits a characteristic of obviously converging toward the center line, which indicates that the present invention has achieved a better focusing magnetization effect.

[0110] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and exemplary embodiments. They can be applied to a variety of fields suitable for the present invention. Further modifications will be readily apparent to those skilled in the art. Therefore, the present invention is not limited to the specific details and illustrations shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims

1. A magnetic field focusing oriented NdFeB permanent magnet, characterized in that: The permanent magnet includes a central region and at least one group of side regions, wherein the permanent magnet has a symmetric plane in the central region, each group of side regions includes two side regions symmetrically distributed on both sides of the central region, and the outermost group of side regions in the at least one group of side regions is a group of edge regions; The composition and magnet properties of each set of side regions remain consistent; The composition of the permanent magnet in the central area or the side area is calculated as follows by mass percentage: RE L a RE H b Co c Cu d M e Fe bal B f , 24≤a≤31, 0≤b≤4, 0≤c≤30, 0.1≤d≤0.8, 0.2≤e≤3, 0.86≤f≤1.2, 28≤a+b≤35, bal is the margin; RE L is one or a combination of light rare earth elements Pr, Nd, La, Ce and Y, RE H is one or a combination of heavy rare earth elements Gd, Ho, Dy, and Tb, and M is one or a combination of Al, Cr, Nb, Zr, Ga, Ti, V, Mo, and Mn; The RE content in the permanent magnet decreases from the central region to the edge region, and the Co content gradually increases. The composition distribution of the central region is rich in RE and poor in Co, and the composition distribution of the edge region is poor in RE and rich in Co. The difference in RE content between the central region and the edge region is ≤1%, and the difference in Co content between the edge region and the central region is ≤30%. L and RE H sum; The carbon content of the permanent magnet increases from the central region to the edge region, and the difference in carbon content between the central region and the edge region is ≥400 ppm; The thermal expansion coefficient of the permanent magnet perpendicular to the orientation direction increases from the central region to the edge region; the thermal expansion coefficient of the permanent magnet parallel to the orientation direction has no significant difference between the central region and the at least one set of side regions; the difference between the thermal expansion coefficient perpendicular to the orientation direction and the thermal expansion coefficient parallel to the orientation direction of the permanent magnet decreases from the central region to the edge region; The permanent magnet has a focusing plane perpendicular to the symmetry plane, and on the focusing plane, the magnetic field strength of the permanent magnet increases from the edge region to the central region.

2. The NdFeB permanent magnet with magnetic field focusing orientation according to claim 1, characterized in that: The permanent magnet includes two or four side regions symmetrically distributed on both sides of the central region.

3. A method for preparing a magnetic field focusing oriented NdFeB permanent magnet as claimed in claim 1 or 2, characterized in that: include: Step (1) prepares RE-rich and Co-poor alloy powder I, wherein the composition of the alloy powder I is as follows by mass percentage: RE L a1 RE H b1 Co c1 Cu d1 Fe bal M e1 B f1 , where 30≤a1≤33, 0≤b1≤4, 0≤c1≤3, 0≤d1≤0.3, 0.2≤e1≤3, 0.86≤f1≤1.2; Step (2) prepares RE-poor Co-rich alloy powder II, wherein the composition of the alloy powder II is as follows by mass percentage: RE L a2 RE H b2 Co c2 Cu d2 Fe bal M e2 B f2 , where 26≤a2≤31, 0≤b2≤4, 3<c2≤40, 0≤d2≤2, 0.2≤e2≤3, 0.86≤f2≤1.2; Step (3) Powder Proportioning: The alloy powder I and the alloy powder II are mixed in at least two proportions to prepare at least two mixed alloy powders, wherein at least one of the at least two mixed alloy powders has a composition of rich RE and poor Co, and at least one of the mixed alloy powders has a composition of poor RE and rich Co, the RE content of the at least two mixed alloy powders decreases in sequence, and the Co content increases in sequence, the difference in RE content between the mixed alloy powder with the highest RE content and the mixed alloy powder with the lowest RE content in the at least two mixed alloy powders is ≤1%, and the difference in Co content between the mixed alloy powder with the highest Co content and the mixed alloy powder with the lowest Co content in the at least two mixed alloy powders is ≤30%, wherein the RE content is RE L and RE H sum; Step (4) adding lubricant and mixed powder: adding lubricant to the at least two mixed alloy powders respectively, so that the carbon content of the at least two mixed alloy powders increases successively, the difference in carbon content between the mixed alloy powder with the highest carbon content and the mixed alloy powder with the lowest carbon content in the at least two mixed alloy powders is ≥400 ppm, and the carbon content of each mixed alloy powder is 500 to 2000 ppm; Step (5) magnetic field orientation molding: dividing the internal space of the mold into a middle space and at least one group of side spaces, each group of side spaces includes two side spaces symmetrically distributed on both sides of the middle space, and the outermost group of side spaces in the at least one group of side areas is a group of edge spaces; placing the at least two mixed alloy powders into the middle space and the at least one group of side spaces respectively, placing mixed alloy powders of the same composition into each group of side spaces, and making the RE content of the mixed alloy powders placed from the middle space to the edge space decrease successively, and the Co content increase successively, the composition distribution of the mixed alloy powder placed in the middle space is rich in RE and poor in Co, the composition distribution of the mixed alloy powder placed in the edge space is poor in RE and rich in Co, the difference in RE content between the mixed alloy powders placed in the middle space and the edge space is ≤1%, and the difference in Co content between the mixed alloy powders placed in the edge space and the middle space is ≤30%, wherein the RE content is RE L and RE H The RE content of the mixed alloy powder placed in each of the middle space and the edge space increases successively, and the difference in carbon content between the mixed alloy powder placed in the middle space and the edge space is ≥400ppm; thereafter, the mold is placed in a magnetic field for orientation and shaping; Step (6) sintering and tempering heat treatment; Step (7) machining; Step (8) magnetization.

4. The method for preparing a magnetic field focusing oriented NdFeB permanent magnet according to claim 3, wherein: The average particle size of the alloy powder I is 1 to 5 μm; the average particle size of the alloy powder II is 2 to 6 μm.

5. The method for preparing a magnetic field focusing oriented NdFeB permanent magnet according to claim 3, wherein: In the step (4), the addition ratio of the lubricant is 0.1% to 1%.

6. The method for preparing a magnetic field focusing oriented NdFeB permanent magnet according to claim 3, wherein: In the step (5), the density of the mixed alloy powder placed in the middle space and the at least one set of side spaces in the internal space of the mold is 1.6 to 2 g / cm 3 The mold is placed in a magnetic field for orientation shaping, which is specifically achieved by the following process: orientation shaping is carried out in a non-uniform magnetic field of 1.2-2.2T, and then placed in an isostatic press for secondary pressing, the isostatic pressure is 150-300MPa, and the green density obtained is 3.9-4.5g / cm 3 .

7. The method for preparing a magnetic field focusing oriented NdFeB permanent magnet according to claim 6, wherein: In the step (6), the sintering and tempering heat treatment is specifically achieved by the following process: placing the green body in a vacuum sintering furnace set at a temperature of 1000-1100°C for sintering and densification, and the holding time is 2-10 hours; after the holding is completed, heating is stopped, and after slowly cooling to 800-900°C, argon is filled and a blower is turned on to quickly cool to room temperature to obtain a sintered magnet; the sintered magnet is subjected to secondary tempering treatment, and the treatment conditions are: keeping at 800-950°C for 2-6 hours and then quickly cooling to room temperature, and then keeping at 400-650°C for 2-10 hours and then quickly cooling to room temperature; the atmosphere of the tempering heat treatment is a vacuum or argon protection state.

8. The method for preparing a magnetic field focusing oriented NdFeB permanent magnet according to claim 7, wherein: The magnetization is specifically achieved through the following process: the magnet machined in step (7) is placed in a magnetization coil for magnetization, the magnetization method is parallel to the symmetry plane of the magnet machined in step (7), and the magnetization magnetic field is 3 to 10T.

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