Sintered neodymium iron boron thin-wall radiation ring and preparation method thereof
By optimizing the formula and process, adopting low-temperature sintering and slow cooling technology, and combining grain boundary diffusion, the cracking problem of sintered NdFeB radiation rings during high-temperature sintering was solved, and the yield and magnet performance were improved.
Patent Information
- Application Number
- CN202511102297.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-07
- Publication Date
- 2025-10-17
AI Technical Summary
In the prior art, sintered NdFeB radiation rings are prone to cracking due to high shrinkage and thermal stress during high-temperature sintering, especially thin-walled rings, which affects the yield and consistency of the product.
By optimizing the formula composition, adopting low-temperature sintering and slow cooling technology, combining with grain boundary diffusion process, using high melting point elements and heavy rare earth elements to form a heavy rare earth shell, shrinkage stress is reduced and the density of the magnet is improved.
The cracking rate of sintered NdFeB radiation rings is significantly reduced, the yield rate and the coercive force of the magnet are improved, and the density and consistency of the magnet are enhanced.
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Figure CN120809408A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of radiation ring manufacturing, in particular to a sintered neodymium-iron-boron thin-wall radiation ring and a preparation method thereof. BACKGROUND
[0002] As the third generation of permanent magnet material, sintered neodymium-iron-boron is widely used in various fields such as motors, wind power, new energy vehicles, aerospace, industrial robots, etc., and has become an indispensable key functional material in national life and industrial production. At present, the residual magnetism and magnetic energy product of neodymium-iron-boron magnet have approached the theoretical value, but the coercive force is only 30% of the theoretical value. Current research confirms that by heavy rare earth grain boundary diffusion, a heavy rare earth shell layer is formed at the grain boundary of the main phase, the coercive force of the magnet is greatly improved, and the residual magnetism is slightly reduced. However, the grain boundary diffusion method is only suitable for magnets with a thickness of less than 10 mm.
[0003] In recent years, sintered neodymium-iron-boron radiation magnetic rings have very broad application prospects in the fields of navigation, magnetic transmission, magnetic fluid bearing, medical treatment, magnetic levitation, super capacitor, etc. Compared with the currently commonly used tile-shaped magnet bonding ring of motor, the tile-shaped magnet has strict requirements on the processing precision, the dynamic balance of the spliced magnetic ring is poor, and the transition zone between the magnetic poles is large, which can cause noise and vibration of the motor. The installed permanent magnet rotor is in a magnetized state, and manual polishing is difficult to increase the installation cost. The sintered neodymium-iron-boron radiation ring magnet has the advantages of simple assembly, higher mechanical precision, stable magnetic circuit, and reduced air resistance of the motor, thereby improving the efficiency of the motor. However, the current sintered neodymium-iron-boron radiation magnetic ring has the disadvantages of high production process requirement, complex process, and relatively high price. In particular, the cracking of thin-wall (wall thickness of 3-10 mm) neodymium-iron-boron radiation ring magnets during the sintering process is a problem that needs to be solved urgently. The reason is that the material shrinkage rate of the neodymium-iron-boron radiation ring magnet during sintering is as high as 15%~20%, which easily leads to deformation (ovality, size deviation) of the ring body, especially for large-diameter (outer diameter of 100mm-300mm) thin-wall radiation rings. Secondly, it is easily affected by thermal stress in a high-temperature environment. When it is rapidly cooled from a high-temperature environment to room temperature, due to the difference in temperature between the inside and outside of the magnet, cooling shrinkage stress is generated, which easily leads to cracking of the magnet, resulting in poor yield and consistency of the sintered neodymium-iron-boron radiation ring magnet.
[0004] Therefore, how to reduce the cracking phenomenon of ultra-thin neodymium-iron-boron radiation ring magnets caused by high shrinkage rate, thermal stress, etc. during high-temperature sintering process is a problem that needs to be solved urgently in the preparation process of neodymium-iron-boron radiation ring magnets. SUMMARY
[0005] The present application aims at making up for the above-mentioned deficiencies and providing a sintered neodymium-iron-boron thin-wall radiation ring and a preparation method thereof, which can reduce the cracking caused by the shrinkage stress formed in the high-temperature sintering, grain boundary diffusion and aging cooling stages of the neodymium-iron-boron, improve the coercivity of the radiation ring magnet and greatly improve the yield of the ultra-thin neodymium-iron-boron radiation ring magnet.
[0006] The technical solution of the present application is as follows: A sintered neodymium-iron-boron thin-wall radiation ring, the material of the thin-wall radiation ring comprises, by weight percentage, R x Fe bal B y M z , R is one or a mixture of several of rare earth Pr, Nd, Gd, Tb, Dy and Ho, and at least one element of Pr or Nd, B is boron, M is one or a mixture of several of Co, Cu, Al, Ga, Ti, Zr, Nb, W and Mo, and at least contains two of high melting point elements Ti, Zr, Nb, W and Mo, wherein the range of x is 28-35 wt.%, the range of y is 0.85-1.2 wt.%, the range of z is 0.01-5.0 wt.%, and the rest is Fe.
[0007] The further optimization measures of the technical solution are as follows: Further, the R contains one or more of Gd, Tb, Dy and Ho, the addition content of Gd is controlled to be 0%-5%, the addition content of Tb is controlled to be 0-2%, the addition content of Dy is controlled to be 0-4%, and the addition content of Ho is controlled to be 0-5%, and the addition content is the weight percentage of the corresponding element in the total element content.
[0008] A preparation method of a sintered neodymium-iron-boron thin-wall radiation ring, comprising the following steps: Step one, batching; Step two, rapid solidification spinning; Step three, hydrogen crushing; Step four, airflow grinding, different particle sizes and distributions of magnetic powders are obtained by adjusting the airflow grinding speed, and the different particle sizes at least include a basic particle size and a coarse particle size, in the basic particle size, X50=4.5-6.0 μm, in the coarse particle size, X50=6.0-7.5 μm, wherein X50 is the particle size corresponding to the cumulative distribution of 50% of the particle size ratio, and the magnetic powders of different particle sizes are mixed, and the weight ratio of the basic particle size to the coarse particle size is 2.5-5.5; Step five, radiation orientation molding: the forming pressure is controlled to be 6-7.5 MPa, and the green density is controlled to be 3.5-3.8 g / cm 3 ; Step six, isostatic pressing; Step seven, sintering, aging, to obtain a sintered thin-walled neodymium-iron-boron radiation ring magnet.
[0009] The X90 / X10 of the base particle size is controlled to be 4.5-5.0, and the X90 / X10 of the coarse particle size is controlled to be 5.5-6.5; wherein X10 is the particle size corresponding to the cumulative distribution of 10% of the particle size distribution of the magnetic powder, and X90 is the particle size corresponding to the cumulative distribution of 90% of the particle size distribution of the particle.
[0010] The oxygen content of the base particle size magnetic powder is controlled to be O≤200p.p.m, and the oxygen content of the coarse particle size magnetic powder is controlled to be 300p.p.m≤O≤600p.p.m.
[0011] Further, the wall thickness of the radiation ring magnet is 3mm-10mm, and the outer diameter of the radiation ring magnet is 100mm-300mm.
[0012] Further, in step seven, the sintering temperature is 930-1050℃, the holding time is 1-10 hours, the slow cooling is to 500-750℃, then argon is filled to slowly cool to 250-350℃, the holding time is 0.5-5 hours, the furnace is cooled out, and the density of the sintered radiation ring magnet is controlled to be 6.5-7.2g / cm 3 .
[0013] Further, the cooling rate of the slow cooling is 0.1-5℃ / min.
[0014] Further, a diffusion source with Dy / Tb heavy rare earth elements is uniformly covered on the surface of the sintered thin-walled neodymium-iron-boron radiation ring magnet, the proportion of the heavy rare earth diffusion source is 0.2%-1.5% of the weight of the radiation ring magnet, then the grain boundary diffusion is carried out at 650-950℃, the holding time is 0.5-100 hours, the cooling rate is 0.1-5℃ / min, then the aging process is carried out at 400-600℃, the holding time is 0.5-10 hours, and the cooling rate is 0.1-5℃ / min.
[0015] Further, the diffusion source is covered by dipping, spraying or coating.
[0016] Compared with the prior art, the present application has the following advantages: (1) By optimizing the formula components, reducing the main phase lattice distortion, reducing the sintering shrinkage, strengthening the grain boundary and the main phase binding force, and inhibiting the crack propagation.
[0017] (2) The particle size of the magnetic powder is controlled, different particle sizes of the magnetic powder are mixed, the particle size distribution width is increased, the forming pressure in the subsequent compression process is reduced, and the forming performance of the magnet is finally improved.
[0018] (3) Low-temperature sintering process, appropriately reducing the sintering temperature and sintering time, appropriately reducing the magnet density, reducing the shrinkage rate of the magnet sintering process, and reducing the shrinkage stress through slow cooling.
[0019] (4) Grain boundary diffusion technology, the wall thickness of the ultra-thin neodymium iron boron radiation ring sintered magnet is 3-10 mm, the heavy rare earth is diffused into the magnet through the grain boundary diffusion process, the grain boundary defect problem caused by low-temperature sintering is made up, the density and coercive force of the magnet are improved, the cracking of the magnet is reduced, and the yield of the radiation ring magnet is significantly improved. BRIEF DESCRIPTION OF DRAWINGS
[0020] Figure 1 is the fracture structure diagram of the magnetic ring after sintering at 1030 DEG C for 8 hours of the embodiment 7 of the present application; Figure 2 is the fracture structure diagram of the magnetic ring after diffusion at 950 DEG C for 30 hours of the embodiment 7 of the present application. DETAILED DESCRIPTION
[0021] The present application will be further described in detail below with reference to the accompanying drawings: A sintered neodymium iron boron thin-wall radiation ring, the material of the thin-wall radiation ring is mainly R x Fe bal B y M z , R is one or a mixture of several of rare earth Pr, Nd, Gd, Tb, Dy and Ho, and at least one element of Pr or Nd, B is boron, M is one or a mixture of several of Co, Cu, Al, Ga, Ti, Zr, Nb, W and Mo, and at least contains two of high melting point elements Ti, Zr, Nb, W and Mo; wherein the range of x is 28-35 wt.%, the range of y is 0.85-1.2 wt.%, the range of z is 0.01-5.0 wt.%, and the rest is Fe.
[0022] To improve the sintered Nd2Fe 14 B main phase crystal symmetry, reduce the main phase lattice distortion, reduce the shrinkage difference of the magnetization and non-magnetization direction in the radiation ring sintering process, the R contains one or more of Gd, Tb, Dy and Ho, the addition content of Gd is controlled in 0%-5%, the addition content of Tb is controlled in 0-2%, the addition content of Dy is controlled in 0-4%, and the addition content of Ho is controlled in 0-5%, and the addition content is the weight percentage of the corresponding element in the total element content.
[0023] The addition of trace elements M is to enhance the grain boundary bonding force, and especially the addition of high melting point elements Ti, Zr, Nb, W and Mo can inhibit crack propagation.
[0024] A preparation method of a sintered neodymium-iron-boron thin-wall radiation ring, comprising the following steps: Step one, ingredient preparation.
[0025] Step two, rapid solidification and tape casting.
[0026] Step three, hydrogen crushing.
[0027] Step four, jet mill, different particle sizes and distributions of magnetic powders are obtained by adjusting the rotation speed of the jet mill, wherein the different particle sizes at least include a basic particle size and a coarse particle size, in the basic particle size, X50 = 4.5-6.0 μm, in the coarse particle size, X50 = 6.0-7.5 μm, wherein X50 is the particle size corresponding to the cumulative distribution of 50% of the particle size ratio, and the magnetic powders of different particle sizes are mixed, wherein the weight ratio of the basic particle size to the coarse particle size is 2.5-5.5, in the basic particle size, X90 / X10 = 4.5-5.0, in the coarse particle size, X90 / X10 = 5.5-6.5, wherein X10 is the particle size corresponding to the cumulative distribution of 10% of the particle size ratio, and X90 is the particle size corresponding to the cumulative distribution of 90% of the particle size ratio, X90 / X10 refers to the range of the particle size distribution, the larger the value, the wider the particle size distribution, and the smaller the value, the more concentrated the distribution, the oxygen content of the basic particle size magnetic powder is controlled to be O≤200 p.p.m, and the oxygen content of the coarse particle size magnetic powder is controlled to be 300 p.p.m≤O≤600 p.p.m.
[0028] Step five, radiation orientation and molding: the forming pressure is controlled to be 6-7.5 MPa, and the green density is controlled to be 3.5-3.8 g / cm 3 Reducing the forming pressure is beneficial to reducing the stress concentration caused by the particle accumulation in the green body and improving the forming performance of the magnet.
[0029] Step six, isostatic pressing.
[0030] Step seven, sintering and aging, specifically, the sintering temperature is 930-1050℃, the holding time is 1-10 hours, slow cooling to 500-750℃, then slow cooling to 250-350℃ under argon atmosphere, the holding time is 0.5-5 hours, and the sintered radiation ring magnet density is controlled to be 6.5-7.2 g / cm 3cooling rate is 0.1-5 ℃ / min; a sintered thin-wall neodymium-iron-boron radiation ring magnet is obtained. The wall thickness of the obtained radiation ring magnet is 3-10 mm, and the outer diameter of the radiation ring magnet is 100-300 mm. A diffusion source with Dy / Tb heavy rare earth elements is uniformly coated on the surface of the sintered thin-wall neodymium-iron-boron radiation ring magnet, and the proportion of the heavy rare earth diffusion source is 0.2%-1.5% of the weight of the radiation ring magnet. Then, the grain boundary diffusion is carried out at 650-950 ℃, the holding time is 0.5-100 hours, and the cooling rate is 0.1-5 ℃ / min. Then, the aging process is carried out at 400-600 ℃, the holding time is 0.5-10 hours, and the cooling rate is 0.1-5 ℃ / min. The diffusion source is coated by dipping, spraying or coating, and the spraying is preferred.
[0031] The low-temperature sintering technology (sintering temperature is 930-1050 ℃) is used to reduce the shrinkage rate of the magnet and obtain a low-density radiation ring magnet. The sintered radiation ring magnet obtained by the preparation method has a density of 6.5 g / cm 3 ~7.2 g / cm 3 , which is 85%-95% of the theoretical density of the same formula, i.e., 85%-95% relative density (relative density refers to the percentage of actual density to theoretical density); and the slow cooling technology reduces the stress difference between the inner and outer diameters and reduces the cracking caused by shrinkage stress.
[0032] In addition, the grain boundary diffusion and aging process of the low-density magnet in the preparation method can compensate for the problems of discontinuous grain boundary phase and low-density of the low-temperature sintered magnet. The heavy rare earth elements Dy / Tb diffuse into the magnet along the grain boundary to form a heavy rare earth shell layer. Finally, a high-density ultra-thin neodymium-iron-boron radiation ring magnet is obtained, and the coercive force and yield of the magnet are also significantly improved.
[0033] The following will be further described through specific examples and comparative examples: 1) The neodymium-iron-boron formula (all in weight percentage, wt.%) in the following Table 1 is prepared, argon is filled in a vacuum melting furnace, electromagnetic heating is carried out, the melting temperature is heated to 1440-1500 ℃, more preferably 1450-1490 ℃, the molten liquid is refined and then cast into a rotating cooling copper roll through a tundish to obtain a neodymium-iron-boron strip casting piece.
[0034] Table 1 Element formula of Example 1-Example 7 and Comparative Example 8 2) The casting piece obtained in Example 1-Example 7 and Comparative Example 8 is subjected to hydrogen decrepitation treatment, and then subjected to air jet milling.
[0035] 3) Obtain different particle size airflow mill powder by adjusting the airflow mill rotation speed, obtain two particle size airflow mill powders: ① basic particle size X50=4.63~4.85μm (X90 / X10=4.81~4.92) and ② coarse particle size X50=6.22~6.95μm (X90 / X10=5.60~6.03), and the coarse particle size is subjected to pre-oxidation treatment. Then, the two particle size powders are mixed, wherein the coarse particle size powder accounts for 20%, and a lubricant with a weight of 0.5‰ of the powder is added during the mixing process to obtain mixed airflow mill fine powder. The particle size parameters and oxygen content data of the airflow mill powder of the above-mentioned examples 1-7 and comparative example 8 are shown in Table 2: Table 2: 4) The above-mentioned mixed airflow mill fine powder is subjected to radiation orientation and compression in a radiation ring forming die. The upper compression head is just attached to the magnetic powder, and then radiation orientation is performed, the radiation orientation magnetic field is 20000Gs, and then compression is performed after orientation, the compression pressure is 7MPa, and the green body density is 3.5-3.8g / cm 3 The compressed green body is subjected to isostatic pressing at a pressure of 180MPa to obtain a neodymium-iron-boron radiation magnetic ring green body with a forming density of 4.0~4.2g / cm 3 .
[0036] 5) The above-mentioned green body is subjected to low-temperature sintering treatment in a vacuum sintering furnace, the sintering temperature is 1030℃, the holding time is 8h, after the holding time ends, furnace cooling is performed at a cooling rate of 0.5℃ / min to 510℃, then argon is filled to cool to 300℃ at a rate of 5℃ / min, holding for 3h, then argon is filled again to cool to 50℃ at a rate of 5℃ / min, and the furnace is discharged to obtain a sintered state radiation ring magnet.
[0037] 6) The cracking rate and magnetic properties of the neodymium-iron-boron radiation magnetic rings prepared by the above-mentioned different formulations are counted, and the data are shown in Table 3: Table 3: It can be seen that the addition of high-melting-point elements Nb, Zr, Ti, W, Mo can improve the coercive force of the neodymium-iron-boron radiation ring magnet prepared by the preparation method of the present application, and the low-temperature sintering can reduce the cracking of the oriented radiation ring green body during the sintering process, but the low-temperature sintering leads to a low density of the radiation magnetic ring, as shown in Figure 1 the fracture structure of the magnetic ring of example 7 after sintering at 1030℃ for 8h, wherein there are a large number of voids, so the residual magnetism is lower than the theoretical residual magnetism.
[0038] Further, the formulation of example 7 in table 1 is subjected to electromagnetic heating in a vacuum melting furnace filled with argon, heated to a melting temperature of 1450~1490℃, the molten liquid is refined and then cast onto a rotating cooling copper roller through a tundish to obtain a neodymium-iron-boron strip casting piece.
[0039] The castings obtained by melting the formulation of Example 7 above were subjected to hydrogen decrepitation treatment, and then subjected to jet milling.
[0040] Jet milled powders of different particle sizes were obtained by adjusting the jet milling speed, and two particle size jet milled powders were obtained: ① base particle size X50 = 4.76 μm (X90 / X10 = 4.94) and ② coarse particle size X50 = 6.26 μm (X90 / X10 = 5.68), with the oxygen content of the base particle size magnetic powder controlled at 136 p.p.m. and the oxygen content of the coarse particle size magnetic powder controlled at 437 p.p.m.
[0041] Example 7a The two particle size powders were mixed, with the coarse particle size powder accounting for 15%, and a lubricant was added to the mixed jet milled powders in an amount of 0.5‰ of the weight of the powders.
[0042] The mixed jet milled powders were subjected to radiation orientation and pressing in a radiation ring forming mold. The upper punch was just attached to the magnetic powders, and then radiation orientation was performed at a magnetic field of 20000 Gs. After orientation, the green compact was pressed at a pressure of 7 MPa, and the green compact density was 3.5-3.8 g / cm 3 The pressed green compact was subjected to isostatic pressing at a pressure of 180 MPa, and a neodymium-iron-boron radiation magnetic ring green body with a forming density of 4.0-4.2 g / cm 3 was obtained.
[0043] The green body was subjected to low temperature sintering in a vacuum sintering furnace, and the sintering temperature was 1030℃ for 8h. After the holding period, the furnace was slowly cooled at a rate of 0.5℃ / min to 510℃, and then argon was introduced to cool the furnace at a rate of 5℃ / min to 300℃ for 3h. Argon was again introduced to cool the furnace at a rate of 5℃ / min to 50℃, and the sintered radiation ring magnet was obtained.
[0044] Example 7b The two particle size powders were mixed, with the coarse particle size powder accounting for 30%, and a lubricant was added to the mixed jet milled powders in an amount of 0.5‰ of the weight of the powders. The remaining process was the same as that of Example 7a.
[0045] Comparative Example 7c The difference from Example 7a was that no coarse particle size powder was mixed, and the base particle size X50 = 4.80 μm (X90 / X10 = 4.90) accounted for 100%. Only a lubricant was added in an amount of 0.5‰ of the weight of the powders. The remaining process was the same as that of Example 7a.
[0046] Comparative Example 7d The difference from Example 7a was that the coarse particle size powder accounted for 10% when mixed. The remaining process was the same as that of Example 7a.
[0047] Comparative Example 7e The difference between Example 7a and Comparative Example 7e is that the ratio of coarse particle size powder is 35% when mixing the powder. The rest of the process is exactly the same as Example 7a.
[0048] Comparative Example 7f The difference between Example 7a and Comparative Example 7f is that the ratio of coarse particle size powder is 40% when mixing the powder. The rest of the process is exactly the same as Example 7a.
[0049] Comparative Example 7g The difference between Example 7a and Comparative Example 7g is that the ratio of coarse particle size powder is 20% when mixing the powder. After orientation, the pressure is 8 MPa, and the green body is isostatic pressed at 180 MPa to obtain a sintered Nd-Fe-B radiation ring with a density of 4.2-4.4 g / cm 3 . The rest of the process is exactly the same as Example 7a.
[0050] Comparative Example 7h The difference between Example 7a and Comparative Example 7h is that the ratio of coarse particle size powder is 20% when mixing the powder. After orientation, the pressure is 8 MPa, and the green body density is 3.8-4.0 g / cm 3 . The green body is isostatic pressed at 180 MPa to obtain a sintered Nd-Fe-B radiation ring with a density of 4.2-4.5 g / cm 3 . After sintering, the slow cooling is not performed, and the furnace is cooled to 900℃ at 1℃ / min, and then the furnace is filled with argon and cooled to 50℃ at 5℃ / min to obtain a sintered radiation ring. The rest of the process is exactly the same as Example 7a.
[0051] Comparative Example 7i The difference between Example 7a and Comparative Example 7i is that the ratio of coarse particle size powder is 20% when mixing the powder. After sintering, the slow cooling is not performed, and the furnace is cooled to 900℃ at 1℃ / min, and then the furnace is filled with argon and cooled to 50℃ at 5℃ / min to obtain a sintered radiation ring. The rest of the process is exactly the same as Example 7a.
[0052] Comparative Example 7j The difference between Example 7a and Comparative Example 7j is that the oxygen content of the basic particle size magnetic powder is controlled to be 136 p.p.m, and the oxygen content of the coarse particle size magnetic powder is controlled to be 106 p.p.m. The rest of the process is exactly the same as Example 7a.
[0053] The process parameters of the preparation process of Example 7a-Example 7b and Comparative Example 7c-Comparative Example 7i are shown in Table 4: Table 4 Process parameters of Example 7a-Example 7b and Comparative Example 7c-Comparative Example 7i The cracking rate and magnetic properties of the sintered radiation ring magnets prepared in the above Example 7a-Example 7b and Comparative Example 7c-Comparative Example 7j are statistically analyzed, and the data are shown in Table 5: Table 5: It can be seen from the comparison that, without adopting the slow cooling process, the cracking rate of the sintered Nd-Fe-B oriented radiation ring is as high as 70%-80%, and the cracking rate of the sintered Nd-Fe-B radiation ring with a mixed powder ratio of the basic particle size and the coarse particle size deviating from the basic particle size of the present application is 10%-20% higher than that of the examples. In addition, when the oxygen content of the coarse particle size is too low, the cracking rate of the sintered Nd-Fe-B oriented radiation ring is also close to 50%. Further analysis shows that the introduction of appropriate oxygen in the coarse particle size can increase the proportion of rare earth oxide, which is beneficial to the adhesion between the magnetic powders during the sintering process, thereby realizing the reduction of the cracking rate of the radiation magnetic ring. When the forming pressure is lower than 6 MPa, the oriented radiation ring is basically impossible to be formed, and even after isostatic pressing, it is directly broken. When the forming pressure is ≥8 MPa, the higher forming pressure causes greater internal stress between the particles, and after isostatic pressing, the inner and outer diameters of the blank body rebound to different sizes, the internal stress is unevenly distributed, and the internal stress is released after sintering, resulting in an increase in the cracking rate.
[0054] The sintered Nd-Fe-B radiation ring with a low cracking rate in Example 7, Example 7a, and Example 7b is polished on the thickness surface, and further a layer of heavy rare earth or heavy rare earth alloy diffusion source is sprayed, coated, deposited, or printed on the surface of the magnetic ring. The heavy rare earth or heavy rare earth alloy diffusion source is Tb, the proportion of the heavy rare earth diffusion source coated on the surface of the magnetic ring is 0.7% of the weight of the magnetic ring, and further crystal boundary diffusion treatment and aging heat treatment are performed. The diffusion heat treatment is at 950℃ for 30h, and after the heat preservation is completed, it is cooled to 510℃ at a speed of 0.5℃ / min, and then argon is filled to cool to 300℃ at a speed of 5℃ / min for 2h, and then argon is filled again to cool to 70℃ at a speed of 5℃ / min. Then, aging heat treatment is performed at an aging temperature of 480℃ for 5h, and then argon is filled again to cool to 50℃ at a speed of 5℃ / min. Thus, a high-performance sintered Nd-Fe-B thin-wall radiation ring can be obtained.
[0055] The Nd-Fe-B thin-wall radiation ring after the above diffusion-aging heat treatment is further tested for density and magnetic properties, and the test data are shown in Table 6: Table 6: The above diffusion source Tb can also be replaced by diffusion source Dy.
[0056] It can be seen that the low-density sintered Nd-Fe-B radiation ring has a density close to the dense state after 950℃ diffusion for 30h, such as Figure 2The fracture structure of the example 7 after diffusion at 950℃ for 30h, that is, the voids caused by low density can be repaired to reach a dense state after coating with heavy rare earth and long time diffusion heat treatment, and the magnetic properties, especially the coercivity, are greatly improved after aging treatment.
[0057] The above merely describes the preferred embodiments of the present application, but does not limit the embodiments and protection scope of the present application. It should be understood by those skilled in the art that any equivalent replacement and obvious change made according to the content of the present application should be included in the protection scope of the present application.
Claims
1. A sintered NdFeB thin-walled radiation ring, characterized by: The material of the thin-walled radiation ring is mainly composed of R x Fe bal B y M z , R is a mixture of one or more of the rare earth elements Pr, Nd, Gd, Tb, Dy, and Ho, and contains at least one element of Pr or Nd, B is boron, M is a mixture of one or more of the rare earth elements Co, Cu, Al, Ga, Ti, Zr, Nb, W, and Mo, and contains at least two of the high melting point elements Ti, Zr, Nb, W, and Mo, wherein the range of x is 28~35 wt.%, the range of y is 0.85~1.2 wt.%, the range of z is 0.01~5.0 wt.%, and the rest is Fe.
2. The sintered NdFeB thin-walled radiation ring according to claim 1, characterized in that: The R contains one or more of Gd, Tb, Dy, and Ho, with the added content of Gd controlled at 0% to 5%, the added content of Tb controlled at 0% to 2%, the added content of Dy controlled at 0% to 4%, and the added content of Ho controlled at 0% to 5%. The added content is the weight percentage of the corresponding element in the total element content.
3. The method for preparing a sintered NdFeB thin-walled radiation ring according to claim 1, characterized in that: The following steps are involved: Step 1: Ingredients; Step 2: Quick setting and throwing belt; Step 3: hydrogen crushing; Step 4, jet milling, by adjusting the speed of the jet mill to obtain magnetic powders of different particle sizes and distributions, the different particle sizes of the magnetic powders include at least a basic particle size and a coarse particle size, in the basic particle size, X50 = 4.5~6.0μm, in the coarse particle size, X50 = 6.0~7.5μm, wherein X50 is the particle size corresponding to the cumulative distribution of particle size ratio to 50%; and mixing the magnetic powders of different particle sizes, wherein the weight ratio of the mixed powder is basic particle size: coarse particle size = 2.5~5.5; Step 5: Radiation Oriented Pressing: The molding pressure is controlled at 6~7.5MPa and the green density is controlled at 3.5~3.8 g / cm 3 ; Step 6: isostatic pressing; Step seven: sintering and aging to obtain a sintered thin-walled NdFeB radiation ring magnet.
4. The method for preparing a sintered NdFeB thin-walled radiation ring according to claim 3, wherein: In the basic particle size, X90 / X10 is controlled to be 4.5~5.0; in the coarse particle size, X90 / X10 is controlled to be 5.5~6.5; wherein X10 is the particle size corresponding to the cumulative distribution of the magnetic powder particle size ratio to 10% in the magnetic powder particle size distribution, and X90 is the particle size corresponding to the cumulative distribution of the particle size ratio to 90%.
5. The method for preparing a sintered NdFeB thin-walled radiation ring according to claim 3, wherein: The oxygen content weight ratio of the basic particle size magnetic powder is controlled to be 0≤200p.pm, and the oxygen content weight ratio of the coarse particle size magnetic powder is controlled to be 300p.pm≤O≤600p.pm.
6. The method for preparing a sintered NdFeB thin-walled radiation ring according to claim 3, wherein: The wall thickness of the radiation ring magnet is 3 mm to 10 mm, and the outer diameter of the radiation ring magnet is 100 mm to 300 mm.
7. The method for preparing a sintered NdFeB thin-walled radiation ring according to claim 3, characterized in that: In the step 7, the sintering temperature is 930-1050°C, the holding time is 1-10 hours, and then slowly cooled to 500-750°C. Then, argon is filled and the temperature is slowly lowered to 250-350°C. The holding time is 0.5-5 hours, and the magnet is slowly cooled out of the furnace. The density of the sintered radiation ring magnet is controlled to be 6.5-7.2 g / cm 3 .
8. The method for preparing a sintered NdFeB thin-walled radiation ring according to claim 7, wherein: The cooling rate of the slow cooling is 0.1-5°C / min.
9. The method for preparing a sintered NdFeB thin-walled radiation ring according to claim 3, characterized in that: The surface of the sintered thin-walled NdFeB radiation ring magnet is uniformly covered with a diffusion source of Dy / Tb heavy rare earth elements, with the proportion of the heavy rare earth diffusion source being 0.2%~1.5% of the weight of the radiation ring magnet. The magnet then undergoes grain boundary diffusion at 650~950℃, holding time 0.5~100 hours, cooling rate 0.1~5℃ / min, and then undergoes an aging process at 400~600℃, holding time 0.5~10 hours, and cooling rate 0.1~5℃ / min.
10. The method for preparing a sintered NdFeB thin-walled radiation ring according to claim 9, characterized in that: The diffusion source is covered by dipping, spraying or coating.