Sintered re-fe-b permanent magnet with grain size gradient and preparation method and application thereof

Abstract

The application discloses a sintered Re-Fe-B permanent magnet with a grain size gradient and a preparation method and application thereof. The sintered Re-Fe-B permanent magnet has structure one and structure two, and the structure one and the structure two are symmetrical. The structure one refers to a region from an outer surface to a core of the sintered Re-Fe-B permanent magnet in a pressing direction, and the region is divided into n regions, a region close to the outer surface is recorded as a first region, 2 <= n <= 5. The average size of complete grains from the first region to the n-th region is D1 to Dn, and D1 < D2 <... < Dn. n The average size of complete grains from the first region to the n-th region is D1 to Dn, and D1 < D2 <... < Dn. n The thickness of each region is independently selected from H*10% to H*40%, and the thickness of each region is added to H*50%. The sintered neodymium-iron-boron permanent magnet has a gradient structure of grain size, and realizes a gradient distribution of the performance of the sintered neodymium-iron-boron permanent magnet. The fine-grained structure of the sintered neodymium-iron-boron permanent magnet at the corners helps to improve the coercive force, has higher temperature resistance, and is more in line with the phenomenon that the demagnetization of the sintered neodymium-iron-boron permanent magnet at the corners is more serious than that of the core in the operation of the motor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rare earth permanent magnet material preparation, and particularly relates to a sintered Re-Fe-B permanent magnet with a grain size gradient and a preparation method thereof. BACKGROUND

[0002] As one of the important components of new energy technology, the core material of permanent magnet motor technology is permanent magnet. Neodymium iron boron is widely used in permanent magnet motors due to its high residual magnetic density, high coercivity, high magnetic energy product and other characteristics. In recent years, due to the wide application of new energy technology, permanent magnet motors have higher requirements for the working temperature of permanent magnets, which requires the magnets to have higher temperature resistance.

[0003] In order to meet the normal work of the magnet under high temperature conditions, during the manufacture of neodymium iron boron, on the one hand, more heavy rare earth elements such as Dy / Tb are added in the magnet through substrate addition or grain boundary diffusion, and on the other hand, the grain size is refined and the microstructure is optimized to improve the overall coercivity of neodymium iron boron. During the operation of the motor, the temperature distribution of the permanent magnet is uneven, and due to the influence of eddy current, the edge angle position of the magnet will bear higher temperature than the center position. Therefore, under the condition of reducing cost, the scheme of only strengthening the coercivity of the edge angle of the magnet instead of improving the overall coercivity has been recognized by more and more motor designers. At present, the high coercivity of the edge angle is mainly obtained by increasing the content of heavy rare earth elements at the edge angle. With the rising price of heavy rare earth elements, there is an urgent need for a lower-cost solution to reduce the use of heavy rare earth elements and improve the edge angle coercivity of the magnet. SUMMARY

[0004] To solve the above problems of the prior art, the technical scheme of the present application is as follows:

[0005] A sintered Re-Fe-B permanent magnet, the sintered Re-Fe-B permanent magnet has structure one and structure two, structure one and structure two are symmetrical;

[0006] The structure one refers to the direction of pressing from the outer surface to the core of the sintered Re-Fe-B permanent magnet, which is divided into n regions, the region close to the outer surface is recorded as the first region, 2≤n≤5;

[0007] Among them, the average size D1 to Dn of the complete grain from the first region to the nth region gradually increases, that is, D1 n < D2 < … < Dn n ; preferably Dn n ≥ 1.1 * D1;

[0008] The thickness of each region is independently selected from H*10% to H*40%, and the sum of the thicknesses of each region is H*50%;

[0009] H represents the length of the sintered Re-Fe-B permanent magnet along the pressing direction, and the total thickness of structure one and structure two is H, and the thickness of structure one and structure two is equal, and is H*50%;

[0010] The core refers to the position along the pressing direction which is H*50% away from the outer surface of the sintered Re-Fe-B permanent magnet.

[0011] According to the embodiment of the present application, the sintered Re-Fe-B permanent magnet has a grain size gradient distribution substantially as shown in the following table. Figure 1

[0012] According to the embodiment of the present application, n is for example selected from 2, 3, 4, 5.

[0013] According to the embodiment of the present application, the D n may be 1.1~2 times of D1, for example, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 times. The inventors found that when D n particle size <1.1D1, the difference δHcj of Hcj of the first region and the n-th region of the sintered Re-Fe-B permanent magnet is <15kA / m, and the magnetic property of the first region of the sintered Re-Fe-B permanent magnet, i.e. the edge region, cannot be improved.

[0014] According to the embodiment of the present application, in the sintered Re-Fe-B permanent magnet, the thickness of each region is for example H*10%, H*20%, H*30%, H*40%.

[0015] According to the preferred embodiment of the present application, when n=3, structure one of the sintered Re-Fe-B permanent magnet along the pressing direction comprises three regions, which are the first region, the second region and the third region from the outer surface to the core, and the thickness of the three regions is independently selected from H*10%~H*30%, and the sum of the thickness of the three regions is H*50%; the average size of all complete grains in the first region is D1, the average size of all complete grains in the second region is D2, and the average size of all complete grains in the third region is D3, and D1<D2<D3; for example, the thickness of the first region is H*10%, the thickness of the second region is H*20%, and the thickness of the third region is H*20%.

[0016] ​According to a preferred scheme of the present application, when n=2, in the pressing direction, the structure one of the sintered Re-Fe-B permanent magnet comprises two regions, a first region and a second region in turn from the outer surface to the core, the thickness of the two regions is independently selected from H*10% to H*40%, and the sum of the thickness of the two regions is H*50%; the average size of all complete grains in the first region is D1, the average size of all complete grains in the second region is D2, and D1

[0017] According to a preferred scheme of the present application, when n=5, in the pressing direction, the structure one of the sintered Re-Fe-B permanent magnet comprises five regions, a first region, a second region, a third region, a fourth region, and a fifth region in turn from the outer surface to the core, the thickness of the five regions is independently selected from H*10%, and the sum of the thickness of the five regions is H*50%; the average size of all complete grains in the first region is D1, the average size of all complete grains in the second region is D2, the average size of all complete grains in the third region is D3, the average size of all complete grains in the fourth region is D4, the average size of all complete grains in the fifth region is D5, and D1

[0018] According to an embodiment of the present application, the sintered Re-Fe-B permanent magnet is (Nd 1-x R x ) a Fe 1-a-b-c M b B c , wherein,

[0019] R is selected from one or more of Sm, La, Ce, Y, Pr, Ho, Gd, Dy, and Tb, 0≤x≤1, 28 wt%≤a≤35 wt%;

[0020] M is selected from one or more of Al, Ga, Zr, Ti, Cu, and Co, 0 wt%≤b≤5 wt%;

[0021] The content of B is 0.8 wt%≤c≤1.2 wt%; the rest is Fe.

[0022] The present application also provides a preparation method of the above sintered Re-Fe-B permanent magnet, which comprises the following steps:

[0023] (1) preparing Re-Fe-B alloy rapid quenching flakes, and crushing the Re-Fe-B alloy rapid quenching flakes to obtain magnetic powders with different particle sizes;

[0024] (2) compression molding: along the compression direction, different particle sizes of magnetic powders are filled in sequence, and a green body with different particle sizes of powders in the compression direction is obtained after magnetic field orientation and molding;

[0025] (3) the green body of step (2) is densified by two-step sintering in a vacuum environment and then tempered to obtain the sintered Re-Fe-B permanent magnet.

[0026] According to the embodiment of the present application, in step (1), the raw material for preparing the rapid solidification flake includes:

[0027] Nd and R, R is selected from one or more of Sm, La, Ce, Y, Pr, Ho, Gd, Dy and Tb;

[0028] M is selected from one or more of Al, Ga, Zr, Ti, Cu and Co;

[0029] B;

[0030] the rest is Fe.

[0031] According to the embodiment of the present application, the amount of each element in the raw material for preparing the rapid solidification flake is referred to the mass percentage described above.

[0032] According to the embodiment of the present application, in step (1), the rapid solidification flake is prepared by a method known in the art, for example, by using rapid solidification spinning technology. Illustratively, the preparation method of the rapid solidification flake is as follows: the raw material is heated to melting by electromagnetic induction in vacuum or inert gas, then kept for 10-60 min, and then poured on the surface of a quenching roller, and then enters a cooling cylinder for further cooling to obtain Re-Fe-B alloy rapid solidification flake.

[0033] According to the embodiment of the present application, in step (1), the crushing step specifically includes: the Re-Fe-B alloy rapid solidification flake is coarsely crushed by hydrogen explosion, then stirred and mixed, and then ball milled and air-jet milled to obtain magnetic powder. Illustratively, the crushing step is as follows: the Re-Fe-B alloy rapid solidification flake is coarsely crushed by hydrogen explosion, then the powder is stirred and mixed for 1-5 h, then ball milled for 1-5 h, then air-jet milled, and then stirred and mixed for 1-5 h to obtain magnetic powder with different particle size central values. Preferably, the particle size central value D50 of the magnetic powder is 1.5 μm-5 μm.

[0034] According to the embodiment of the present application, in step (1), the magnetic powder is prepared into n groups of powders with different particle sizes according to the size of the particle size central value, and is respectively denoted as A powder, B powder, C powder, …, N powder, wherein the particle size central values of the A powder, B powder, C powder, …, N powder are Ra, Rb, Rc, …, Rn, and satisfy 5 μm≥Rn>…>Rc>Rb>Ra≥1.5 μm.

[0035] According to the embodiment of the present application, in the airflow milling process, the oxygen content in the powders of different particle sizes in the n groups is regulated respectively by adding 0-800 ppm of O2, and the smaller the particle size, the higher the oxygen content. Preferably, the oxygen contents of the first group of powders to the n group of powders are O(A), O(B), O(C)…O(N) respectively, 1500 ppm≥O(A)>O(B)>O(C)>…>O(N)≥50 ppm. The inventors found that the smaller the particle size of the powder, the higher the sintering activity, and therefore the fine particle size powder is more prone to grow during sintering. Therefore, in order to coordinate the grain growth process in different regions and inhibit the grain growth tendency in the fine particle size powder region, O2 is added during the airflow milling to regulate the oxygen content in the powders of different particle sizes, especially to increase the oxygen content of the powder of smaller particle size (for example, the oxygen content of the A powder).

[0036] According to the embodiment of the present application, in step (2), the magnetic powders of different particle sizes are filled in sequence, specifically, the n groups of powders of different particle sizes are filled in the order of particle size from small to large and then from large to small along the pressing direction to obtain green bodies with different particle sizes in the pressing direction. Preferably, A powder to N powder is added in sequence from bottom to top along the pressing direction, and when the half of the thickness of the green body in the pressing direction is reached, N powder to A powder is added in sequence, and the amount of different powders added corresponds to the thickness of the n regions of the sintered Re-Fe-B permanent magnet.

[0037] According to the preferred embodiment of the present application, when the sintered Re-Fe-B permanent magnet has 3 regions in the pressing direction from the outer surface of the sintered Re-Fe-B permanent magnet to the core part, the first region is selected from A powder, the second region is selected from B powder, and the third region is selected from C powder; the particle size center value of A powder is Ra', the particle size center value of B powder is Rb', and the particle size center value of C powder is Rc', 5 μm≥Rc'>Rb'>Ra'>1.5 μm; in step (2), the magnetic powders of different particle sizes are filled in sequence, including: A powder, B powder, C powder, C powder, B powder and A powder are filled in sequence, and the filling amount is 10%, 20%, 20%, 20%, 20% and 10% of the volume of the green body, respectively.

[0038] According to the embodiment of the present application, in step (2), the magnetic field orientation forming specifically includes: orientation forming in a field strength of 2T, and then cold isostatic pressing to obtain the green body.

[0039] According to the embodiment of the present application, in step (3), to inhibit the tendency of grain growth in the fine-grained region, a two-step sintering method is used for sintering densification, i.e., first sintering at a high temperature for a short time, then rapidly reducing to a low temperature for long time sintering, during which the grain growth is inhibited. The green body obtained is heated to T1 in a vacuum environment for 0-10 min, then rapidly cooled to T2, and sintered at T2 for 2-10 h for densification, and after cooling, two-stage aging heat treatment is performed, i.e., the first stage is aging at 750-950℃ for 2-6 h, and the second stage is aging at 450-650℃ for 2-6 h, to obtain the target product or target diffusion substrate. Wherein, T1 = T2 + ΔT, T2 = 900-1050℃, and ΔT = 20-100℃.

[0040] According to the embodiment of the present application, the sintered Re-Fe-B permanent magnet prepared in steps (1)-(3) has a Br difference δBr between the first region and the n-th region of ≤0.01T (e.g., 0.005T), and a Hcj difference δHcj of ≥15kA / m (e.g., 20kA / m, 30kA / m, 40kA / m).

[0041] According to the embodiment of the present application, the preparation method further comprises: (4) performing grain boundary diffusion treatment on the sintered Re-Fe-B permanent magnet.

[0042] According to the embodiment of the present application, the grain boundary diffusion treatment comprises: uniformly arranging the prepared diffusion source on the outer surface of the sintered Re-Fe-B permanent magnet, and infiltrating in a vacuum environment at 720-900℃ for 5-30 h, and then vacuum aging at 400-600℃ for 2-10 h.

[0043] Preferably, the diffusion source comprises at least one of Tb, Dy, Ho, Pr, Nd, La, Ce, and other rare earth elements.

[0044] Preferably, the sintered Re-Fe-B permanent magnet is optionally processed into a sheet before the grain boundary diffusion treatment.

[0045] The present application also provides a sintered Re-Fe-B permanent magnet prepared by the above preparation method, which has the meanings as described above.

[0046] The present application also provides the application of the above sintered Re-Fe-B permanent magnet, which is preferably used in a motor.

[0047] The present application has the following beneficial effects:

[0048] The sintered Nd-Fe-B permanent magnet has a gradient structure of grain size, and realizes the gradient distribution of the performance of the sintered Nd-Fe-B permanent magnet. The fine-grained structure at the corners of the sintered Nd-Fe-B permanent magnet helps to improve the coercivity, has higher temperature resistance, and is more in line with the phenomenon that the demagnetization of the sintered Nd-Fe-B permanent magnet at the corners is more serious than that of the core in the operation of the motor. In order to coordinate the growth process of powders with different particle sizes, the oxygen content of fine-grained powder is increased by adjusting the oxygen content of magnetic powders with different particle sizes in the airflow milling process, and a two-step sintering method is used in the sintering process, that is, the temperature is first raised to a higher temperature to activate the grain boundary, and then cooled to a lower temperature for long-time low-temperature sintering densification, so as to inhibit the grain growth of fine-grained powder in the edge region in the sintering process. Compared with the prior art, the use of rare earth is saved, and the material cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 It is a structural schematic diagram of the sintered Re-Fe-B permanent magnet with a gradient distribution of grain size.

[0050] Figure 2 It is a schematic diagram of the sintering schedule of the two-step sintering method.

[0051] Figure 3 It is an EPMA image of different regions of the permanent magnet after grain boundary diffusion in Example 7.

[0052] Figure 4 It is a grain size distribution diagram of different regions of the product of Example 7.

[0053] Figure 5 It is a partitioning schematic diagram of the blank product in Example 1. DETAILED DESCRIPTION

[0054] The technical solutions of the present application will be further described in detail below in combination with specific embodiments. It should be understood that the following examples are only illustratively described and explained, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope of protection intended by the present application.

[0055] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0056] In the following examples, the test method of the average grain size of the sintered Re-Fe-B permanent magnet grains is as follows: taking the cross section of the nth region of the sintered Re-Fe-B permanent magnet as an observation surface, polishing the observation surface and placing it under a scanning electron microscope (SEM) at 10000 times magnification, randomly selecting 10 observation positions on each observation surface for sampling; image analysis is performed on the sampling images at different observation positions respectively, the cross-sectional area of each grain is measured and converted into the equivalent diameter of each grain, then the grain size distribution graph at different observation positions is drawn, and the median diameter (i.e. the particle size central value) D50 of the grains at different observation positions is calculated; the median diameters D50 of the grains at the 10 observation positions in the observation surface are averaged, and the average grain size of the grains in the observation surface is obtained.

[0057] Example 1

[0058] A preparation method of a sintered neodymium-iron-boron magnet, the steps are as follows:

[0059] (1) The raw materials are proportioned according to the following ratio, Pr 20 Nd 80 31.0wt%, Ga 0.2wt%, Al 0.3wt%, Co 1.0wt%, B 1.0wt%, and the rest is Fe and impurities. The proportioned materials are vacuum melted at 1420℃ for 15min, and then poured onto the surface of a quenching roller, and then dropped into a water cooling bucket to obtain neodymium-iron-boron flakes;

[0060] (2) The neodymium-iron-boron flakes of step (1) are divided into three parts, each of which is subjected to hydrogen explosion and ball milling coarse crushing, and then subjected to air jet milling. In the air jet milling process, the rotating speed of the classification wheel is adjusted, and A powder with a particle size central value D50 of 3μm, B powder with a particle size central value D50 of 3.5μm and C powder with a particle size central value D50 of 4μm are obtained respectively. In the A powder milling process, 350ppm of O2 is introduced into the milling chamber, and the oxygen content of the A powder O(A)=800~1000ppm; in the B powder milling process, 150ppm of O2 is introduced into the milling chamber, and the oxygen content of the B powder O(B)=600~800ppm; in the C powder milling process, no additional O2 is introduced, and the oxygen content of the C powder O(C)≤600ppm;

[0061] (3) The magnetic powders of step (2) are sequentially filled into a vacuum press mold in the order and proportion of A powder / 10%-B powder / 20%-C powder / 40%-B powder / 20%-A powder / 10% under a magnetic field strength of 2T, and oriented and pressed to form a green body;

[0062] (4) Put the green body of step (3) into a vacuum sintering furnace, and heat at a rate of 5°C / min from room temperature to 250°C, keep at 250°C for 30 min; heat at a rate of 3°C / min from 250°C to 400°C, keep at 400°C for 30 min; heat at a rate of 5°C / min from 400°C to 700°C, keep at 700°C for 90 min, and then heat at a rate of 8°C / min to 1050°C and sinter for 4 h. Then, perform first-stage aging treatment at 900°C for 4 h and second-stage aging treatment at 550°C for 4 h to obtain the Nd-Fe-B blank, a structural schematic diagram of which is shown in Figure 5 FIG. 1, wherein the A particle size region is the first region, the B particle size region is the second region, and the C particle size region is the third region; the size of the Nd-Fe-B blank is 45 mm-60 mm-35 mm, wherein the 45 mm direction is the pressing direction, and the 35 mm direction is the orientation direction.

[0063] Performance test:

[0064] After uniformly removing the material skin, the Nd-Fe-B blank is sampled and processed into 10 sample pieces of 1 mm-1 mm-1 mm in each of the A particle size region, the B particle size region, and the C particle size region for magnetic property testing, and the average value of the results at different positions is taken. The test results are shown in Table 1.

[0065] Example 2

[0066] Example 2 has the same preparation method as Example 1, except that the material ratio of Example 2 is that Nd accounts for 32.0wt%, Zr accounts for 0.3wt%, Al accounts for 0.15wt%, Co accounts for 1.0wt%, B accounts for 0.96wt%, and the rest is Fe and impurities, and an Nd-Fe-B blank is prepared.

[0067] The performance test of the Nd-Fe-B blank is the same as that of Example 1, and the test results are shown in Table 1.

[0068] Example 3

[0069] Example 3 has the same preparation method as Example 1, except that the A powder with a particle size center value D50 of 2.5 μm, the B powder with a particle size center value D50 of 3 μm, and the C powder with a particle size center value D50 of 4 μm are obtained in step (2), and the filling powder in the pressing process of step (3) is A powder / 10%-B powder / 20%-C powder / 40%-B powder / 20%-A powder / 10% in sequence, and an Nd-Fe-B blank is prepared.

[0070] The performance test of the Nd-Fe-B blank is the same as that of Example 1, and the test results are shown in Table 1.

[0071] Example 4

[0072] Example 4 is prepared in the same way as Example 1, except that the Nd-Fe-B magnet prepared in Example 1 is processed into an oriented direction 8mm Nd-Fe-B blank, i.e. the size of the Nd-Fe-B blank is 45mm-60mm-8mm.

[0073] Diffusion: The slurry containing 50wt% of Dy is uniformly coated on the two sides of the 45mm-60mm large surface of the blank prepared above, and after drying, the coating amount is 0.7% of the mass of the sheet. The coated Nd-Fe-B sheet is first heat treated at 850℃ for 4h, and then heat treated at 550℃ for 3h to obtain a Dy-diffused permanent magnet.

[0074] The performance test of the Dy-diffused permanent magnet is the same as that of Example 1, and the test results are shown in Table 1.

[0075] Example 5

[0076] Example 5 is prepared in the same way as Example 1, except that in step (2), A powder with a particle size center value D50 of 3μm and B powder with a particle size center value D50 of 4μm are obtained, and in step (3), the powder filled in the molding process is A powder / 20%-B powder / 60%-A powder / 20% in turn, to prepare a Nd-Fe-B blank; the obtained blank includes an A particle size zone (i.e. a first zone) and a B particle size zone (i.e. a second zone).

[0077] The performance test of the Nd-Fe-B blank is the same as that of Example 1.

[0078] Example 6

[0079] Example 6 is prepared in the same way as Example 1, except that in the airflow milling process of Example 6, the rotational speed of the classification wheel is adjusted to obtain A powder with a particle size center value D50 of 2.5μm, B powder with a particle size center value D50 of 3μm, C powder with a particle size center value D50 of 3.5μm, D powder with a particle size center value D50 of 4μm, and E powder with a particle size center value D50 of 4.5μm. Measurement shows that the oxygen content of each group of powder is: oxygen content O(A)=1000~1200ppm, O(B)=800~1000ppm, O(C)=600~800ppm, O(D)≤600ppm, and O(E)≤600ppm.

[0080] In the molding process, the powder filled in is A powder / 10%-B powder / 10%-C powder / 10%-D powder / 10%-E powder / 20%-D powder / 10%-C powder / 10%-B powder / 10%-A powder / 10% in turn; the obtained blank product includes an A particle size zone (i.e. a first zone), a B particle size zone (i.e. a second zone), a C particle size zone (i.e. a third zone), a D particle size zone (i.e. a fourth zone), and an E particle size zone (i.e. a fifth zone), to prepare a Nd-Fe-B blank.

[0081] Nd-Fe-B blank A particle size region E particle size region sampling processing 10 sample pieces of 1mm-1mm-1mm respectively for magnetic property test, average value of different position results, test results refer to table 1.

[0082] Example 7

[0083] Example 7 is the same as the preparation method of example 1, the difference is that in the airflow mill process of step (2) of example 7, the classification wheel rotating speed is adjusted, A powder with a particle size center value D50 of 3.0μm, B powder with a particle size center value D50 of 4.1μm, C powder with a particle size center value D50 of 4.8μm are obtained, O(A)=800~1000ppm, O(B)≤600ppm, O(C)≤600ppm. In step (3), the magnetic powder of step (2) is sequentially filled in the vacuum press mold according to the order and proportion of A powder / 20%-B powder / 20%-C powder / 20%-B powder / 20%-A powder / 20%, and oriented and pressed into a green compact under a magnetic field strength of 2T. After cold isostatic pressing, a green compact is obtained. The green compact is sintered to obtain a Nd-Fe-B blank, and the size of the blank is 10mm-40mm-20mm, wherein the 10mm direction is the pressing direction, and the 20mm direction is the orientation direction. The blank is processed into a product with a size of 10mm-20mm-4mm, wherein the 4mm direction is the orientation direction, to obtain a Nd-Fe-B blank, wherein the grain size of each region is as shown in Figure 4 The grain size of the powder in the above different regions increases slightly after sintering.

[0084] Diffusion: The slurry containing 50wt% of Tb is uniformly coated on both sides of the Nd-Fe-B blank, 20mm-4mm side, after drying, the coating amount is 0.5% of the mass of the sheet. The coated neodymium iron boron sheet is first heat treated at 850℃ for 4h, and then heat treated at 550℃ for 3h, to obtain a Tb-diffused permanent magnet, and the EPMA images of different regions of the Tb-diffused permanent magnet are as shown in Figure 3 .

[0085] The performance test of the Tb-diffused permanent magnet is the same as that of example 1, and the test results are shown in table 1.

[0086] Table 1 Magnetic properties of different products in examples

[0087]

[0088] From table 1, it can be found that the gradient change of the grain size leads to the gradient change of the coercivity, and the grain refinement stabilizes Br(D1 and D n The difference of Br in the D1 and D nThe Hcj difference of the region is greater than 15 kA / m, and the finer the grain of the edge region D1 of the magnet, the higher the Hcj. Without additional rare earth elements, the temperature resistance of the product corners is improved. And examples 4 and 7 also verify that the grain refined magnet in the edge region can also be used as a diffusion substrate to further improve the coercivity by grain boundary diffusion technology, and the coercivity of the fine grain position regions A and B at the corners is still greater than that of the center region C.

[0089] Comparative Example 1

[0090] Comparative Example 1 has the same preparation method as Example 1, except that in step (2), A powder with a particle size center value D50 of 3.0 μm and B powder with a particle size center value D50 of 3.2 μm are obtained, and in step (3), the powder filled in the molding process is A powder / 20%-B powder / 60%-A powder / 20% in turn, to obtain a Nd-Fe-B blank.

[0091] The performance test of the Nd-Fe-B blank is the same as that of Example 1, and the test results are shown in Table 2.

[0092] Comparative Example 2

[0093] Comparative Example 2 has the same preparation method as Example 4, except that in step (2), A powder with a particle size center value D50 of 4.0 μm is obtained, and in step (3), the powder filled in the molding process is A powder / 100%, to obtain a Nd-Fe-B blank.

[0094] The performance test of the Nd-Fe-B blank is the same as that of Example 1, and the test results are shown in Table 2.

[0095] Comparative Example 3

[0096] Comparative Example 3 has the same preparation method as Example 4, except that in step (2), A powder with a particle size center value D50 of 4.0 μm is obtained, and in step (3), the powder filled in the molding process is A powder / 100%. A Nd-Fe-B blank with an orientation direction of 8 mm is prepared.

[0097] Diffusion: A slurry containing 50wt% of Dy is uniformly coated on both sides of the above Nd-Fe-B blank, and after drying, the coating amount is 0.9% of the mass of the flake. The remaining steps are the same as those of Example 4, to obtain a diffused permanent magnet.

[0098] The performance test of the diffused permanent magnet is the same as that of Example 1, and the test results are shown in Table 2.

[0099] Table 2 Magnetic properties of different products in the comparative examples

[0100]

[0101] From Tables 1 and 2, it can be seen that:

[0102] Since the particle size D2 of the B powder is slightly larger than the particle size of the B powder, i.e. D2 < D1*1.1, the difference in particle size of different regions of the magnet is small, the difference in magnetic properties of each region of the magnet of Comparative Example 1 is small (the difference in Hcj of the A particle size region and the B particle size region is only 5 kA / m), and the grain gradient scheme does not achieve obvious improvement in performance.

[0103] Comparing the magnetic properties of Comparative Example 2 and Example 4, it can be seen that Comparative Example 2 only uses one kind of magnetic powder, and the magnetic properties of different regions of the magnet are basically the same as the magnetic properties of the C particle size region (core region) of Example 4; but since Example 4 uses the grain gradient of the application to improve the coercive force of the edge region (A particle size region) of the magnet, further improves the demagnetization resistance of the edge region of the magnet, and is more in line with the situation that the edge region of the magnet is more prone to demagnetization than the core region when the magnet works in the motor.

[0104] Comparing the magnetic properties of Comparative Example 3 and Example 4, it can be seen that Comparative Example 3 only uses one kind of magnetic powder, and the magnetic properties of different regions of the magnet are basically the same as the magnetic properties of the edge region A particle size region of Example 4, but 0.9% of Dy needs to be added in Comparative Example 3, while only 0.7% is needed in Example 4, and the grain gradient scheme used in Example 4 can save 0.2% of Dy, greatly reducing the use of heavy rare earth elements and significantly reducing the cost of using rare earth.

[0105] The above describes exemplary embodiments of the application. However, the protection scope of the present application is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A sintered Re-Fe-B permanent magnet, characterized in that, The sintered Re-Fe-B permanent magnet has structure one and structure two, and structure one and structure two are symmetrical. The structure refers to the structure extending from the outer surface of the sintered Re-Fe-B permanent magnet to the core in the pressing direction, which is divided into n regions. The region closest to the outer surface is denoted as the first region, and 2≤n≤5. Among them, the average size D1 of the complete grain from the first region to the nth region is D n Gradually increase, i.e., D1 < D2 < ... < D n The D n It is 1.1 to 2 times that of D1; The thickness of each region is independently selected from H*10% to H*40%, and the sum of the thicknesses of all regions is H*50%; H represents the length of the sintered Re-Fe-B permanent magnet along the pressing direction, and the total thickness of Structure 1 and Structure 2 is H. The thicknesses of Structure 1 and Structure 2 are equal, each being H*50%. The core refers to the position along the pressing direction at a distance of H*50% from the outer surface of the sintered Re-Fe-B permanent magnet; The sintered Re-Fe-B permanent magnet is (Nd) 1-x R x ) a Fe 1-a-b-c M b B c ,in, R is selected from one or more of Sm, La, Ce, Y, Pr, Ho, Gd, Dy, and Tb, where 0 ≤ x ≤ 1 and 28 wt% ≤ a ≤ 35 wt%. M is selected from one or more of Al, Ga, Zr, Ti, Cu, and Co, and 0 wt% ≤ b ≤ 5 wt%; The content of B is 0.8 wt% ≤ c ≤ 1.2 wt%; the remainder is Fe.

2. The sintered Re-Fe-B permanent magnet according to claim 1, characterized in that, When n=3, the structure of the sintered Re-Fe-B permanent magnet in the pressing direction includes three regions, namely the first region, the second region, and the third region from the outer surface to the core. The thickness of the three regions is independently selected from H*10% to H*30%, and the sum of the thicknesses of the three regions is H*50%. The average size D1 of all complete grains in the first region, the average size D2 of all complete grains in the second region, and the average size D3 of all complete grains in the third region are all equal, with D1 < D2 < D3.

3. The sintered Re-Fe-B permanent magnet according to claim 1, characterized in that, When n=2, in the pressing direction, the structure of the sintered Re-Fe-B permanent magnet includes two regions, namely the first region and the second region from the outer surface to the core. The thickness of the two regions is independently selected from H*10% to H*40%, and the sum of the thicknesses of the two regions is H*50%. The average size D1 of all complete grains in the first region and the average size D2 of all complete grains in the second region are, and D1 < D2.

4. The sintered Re-Fe-B permanent magnet according to claim 1, characterized in that, When n=5, in the pressing direction, the structure of the sintered Re-Fe-B permanent magnet includes 5 regions, which are sequentially named as the first region, the second region, the third region, the fourth region, and the fifth region from the outer surface to the core. The thickness of each of the 5 regions is independently selected from H*10%, and the sum of the thicknesses of the 5 regions is H*50%. The average size of all complete grains in the first region is D1, the average size of all complete grains in the second region is D2, the average size of all complete grains in the third region is D3, the average size of all complete grains in the fourth region is D4, and the average size of all complete grains in the fifth region is D5, and D1 < D2 < D3 < D4 < D5.

5. The method for preparing the sintered Re-Fe-B permanent magnet according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: (1) Prepare Re-Fe-B alloy rapid solidification sheets, and pulverize the Re-Fe-B alloy rapid solidification sheets to obtain magnetic powders of different particle sizes; (2) Pressing and molding: Magnetic powder of different particle sizes is filled in sequentially along the pressing direction, and after being oriented by a magnetic field, a green body with different powder particle sizes in the pressing direction is obtained. (3) The green blank from step (2) is densified by two-step sintering in a vacuum environment and then tempered to obtain the sintered Re-Fe-B permanent magnet.

6. The preparation method according to claim 5, characterized in that, In step (1), the crushing step specifically includes: the Re-Fe-B alloy rapid solidification sheet is coarsely crushed by hydrogen explosion and then stirred and mixed, and then crushed by ball milling and air jet milling and stirred and mixed to obtain magnetic powder; In step (1), the magnetic powder is prepared into n groups of powders with different particle sizes according to the size of the center value of the particle size, which are respectively denoted as powder A, powder B, powder C... powder N, wherein the center values ​​of the particle size of powder A, powder B, powder C... powder N are Ra, Rb, Rc... Rn, and satisfy 5μm≥Rn>...>Rc>Rb>Ra≥1.5μm; During the air jet milling process, the oxygen content in n groups of powders with different particle sizes was adjusted by adding 0~800ppmO2, and the smaller the particle size, the higher the oxygen content. The oxygen contents of the first group of powders to the nth group of powders are O(A), O(B), O(C)...O(N), respectively, with 1500ppm≥O(A)>O(B)>O(C)>...>O(N)≥50ppm.

7. The preparation method according to claim 6, characterized in that, In step (2), filling in magnetic powder of different particle sizes in sequence specifically means: along the pressing direction, filling in n groups of powder of different particle sizes in the order of particle size from small to large and then from large to small, so as to obtain powder particles of different sizes in the pressing direction.

8. The preparation method according to claim 5, characterized in that, In step (2), the magnetic field orientation molding specifically includes: orientation pressing in a field with a magnetic field strength of 2T, followed by cold isostatic pressing to obtain the green blank.

9. The preparation method according to claim 7, characterized in that, When the sintered Re-Fe-B permanent magnet is divided into a first region, a second region, and a third region in the pressing direction from the outer surface of the sintered Re-Fe-B permanent magnet to the core, the first region uses powder A, the second region uses powder B, and the third region uses powder C; wherein the center particle size of powder A is Ra', the center particle size of powder B is Rb', and the center particle size of powder C is Rc', and 5μm≥Rc'>Rb'>Ra'≥1.5μm; in step (2), the magnetic powders of different particle sizes are filled in sequentially, including: filling in powder A, powder B, powder C, powder C, powder B, and powder A in sequence, with the filling amounts being 10%, 20%, 20%, 20%, 20%, and 10% of the green body volume, respectively.

10. The preparation method according to claim 5, characterized in that, The sintered Re-Fe-B permanent magnets prepared in steps (1)-(3) have a Br difference δBr≤0.01T and an Hcj difference δHcj≥15kA / m between the first region and the nth region.

11. The preparation method according to claim 5, characterized in that, The preparation method further includes: (4) subjecting the sintered Re-Fe-B permanent magnet to grain boundary diffusion treatment; The grain boundary diffusion treatment includes: uniformly arranging the configured diffusion source on the outer surface of the sintered Re-Fe-B permanent magnet, permeating it in a vacuum environment at 720~900℃ for 5~30h, and aging it in a vacuum at 400~600℃ for 2~10h. The sintered Re-Fe-B permanent magnet is optionally processed into thin sheets and then subjected to grain boundary diffusion treatment.

12. The preparation method according to claim 11, characterized in that, The diffusion source includes at least one of the rare earth elements Tb, Dy, Ho, Pr, Nd, La, and Ce.

13. The application of the sintered Re-Fe-B permanent magnet according to any one of claims 1-4 in an electric motor.

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