A sintered neodymium iron boron magnet, its preparation method and application

Abstract

The present invention discloses a sintered neodymium iron boron magnet, its preparation method and application. The sintered neodymium iron boron magnet, calculated based on 100% by mass percentage, comprises: Re: 28 - 32%, where Re is selected from at least one of Pr, Nd, Dy, Tb, Ho; B: 1.000% - 1.080%; M: 0 - 5%, M includes at least Zr and / or Ti, and 0.1% < Zr + Ti ≤ 0.2%. The magnet of the present invention increases the content of element B, ensures the presence of an appropriate amount of boron-rich phase, and during the diffusion process of the thin magnet, it can delay the diffusion of heavy rare earth elements dysprosium or terbium into the magnet, preventing the decrease of Hcj and Hk / Hcj caused by excessive diffusion.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth permanent magnet materials and their preparation, and particularly relates to a sintered NdFeB magnet, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its ultra-high magnetic strength, only a small number of sintered NdFeB magnets are required to generate the same magnetic field as a large number of other magnetic materials during application. Therefore, using NdFeB magnetic steel in the shape of a thin sheet can significantly reduce the product volume and weight, meeting the requirements of the motor industry for miniaturization and light weight.

[0003] The coercivity of NdFeB magnets can be improved by using the grain boundary diffusion technology while avoiding a significant decrease in the remanence. This technology utilizes the diffusion of heavy rare earth elements (such as Dy or Tb) along the grain boundaries of NdFeB magnets at high temperatures, thereby forming a high-coercivity shell structure at the edges of the main phase grains. This structure can effectively improve the coercivity of NdFeB magnets while avoiding a significant decrease in the remanence. This process is widely applied to sintered NdFeB magnets with a thickness of 2 - 8 mm, and magnets with high comprehensive magnetic properties that are difficult to achieve by traditional processes can be prepared. However, for thin sheet products, especially those with an oriented thickness less than 1.3 mm, excessive diffusion is likely to occur. A large amount of heavy rare earth diffuses into the main phase, and an inverse core-shell structure will form in the main phase grains, resulting in a significant decrease in both Hcj and Hk / Hcj. Summary of the Invention

[0004] To address the above technical problems, the present invention provides a sintered NdFeB magnet, which, based on 100% by mass percentage, comprises:

[0005] Re: 28 - 32%, where Re is selected from at least one of Pr, Nd, Dy, Tb, and Ho;

[0006] B: 1.000% - 1.080%;

[0007] M: 0 - 5% and not zero, M includes at least Zr and / or Ti, and 0.1% < Zr + Ti ≤ 0.2%.

[0008] According to an embodiment of the present invention, the thickness T of the NdFeB magnet in the oriented direction is T ≤ 1.3 mm, preferably, 0.6 mm ≤ T ≤ 1.3 mm; examples are 0.6 mm, 0.8 mm, 1 mm, and 1.3 mm.

[0009] According to an embodiment of the present invention, 1.065% - T / 2000 ≤ [B] ≤ 1.065% - T / 3000; where [B] refers to the mass content of B, and T is the thickness of the NdFeB magnet in the oriented direction.

[0010] Preferably, when the magnet thickness is 0.6 mm, the B content is 1.035% - 1.045%;

[0011] when the magnet thickness is 0.8 mm, the B content is 1.025% - 1.038%;

[0012] when the magnet thickness is 1.0 mm, the B content is 1.015% - 1.031%;

[0013] when the magnet thickness is 1.3 mm, the B content is 1.000% - 1.021%;

[0014] According to an embodiment of the present invention, M may further include at least one of Co, Ni, Al, Cu, and Ga.

[0015] According to an embodiment of the present invention, the total content of Zr and Ti is 0.15 - 0.2%, for example, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, or 0.2%.

[0016] According to an embodiment of the present invention, in the neodymium iron boron magnet, the balance is Fe and impurities. Among them, the impurities are inevitable impurities, such as at least one of elements such as C, N, O, S, Si, and Mn.

[0017] According to an embodiment of the present invention, based on 100% by mass percentage of the composition of the neodymium iron boron magnet, Re is 29.0 - 31.5 wt%, for example, 29.0%, 29.5%, 30.0%, 30.3%, 30.5%, 31.0%, 31.5%.

[0018] According to an embodiment of the present invention, in the neodymium iron boron magnet, Re at least includes Nd, and may further include at least one of Pr, Dy, Tb, and Ho.

[0019] According to an embodiment of the present invention, based on 100% by mass percentage of the composition of the neodymium iron boron magnet, the content of B is, for example, 1 wt%, 1.02 wt%, 1.04 wt%, 1.05 wt%, 1.06 wt%, 1.07 wt%, or 1.08 wt%.

[0020] It is found that when the grain boundary diffusion is carried out on the magnet of the present invention, a high content of B element can ensure the existence of an appropriate amount of boron-rich phase. During the process of grain boundary diffusion of the magnet of the present invention, the diffusion of heavy rare earth elements dysprosium or terbium into the magnet interior can be delayed, thereby effectively preventing the decrease of Hcj and Hk / Hcj caused by excessive diffusion.

[0021] According to an embodiment of the present invention, based on 100% by mass of the composition of the magnet, the content of M is, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, 4 wt% or 5 wt%.

[0022] According to an embodiment of the present invention, the difference between the content on the surface and the central distribution content of the heavy rare earth metals (such as Dy and / or Tb) in the magnet is 0.1 - 0.2%.

[0023] The present invention also provides a method for manufacturing the above-mentioned sintered neodymium iron boron magnet, and the method includes:

[0024] Processing the preparation raw materials of the above-mentioned sintered neodymium iron boron magnet through a melting process, a powder-making process, a molding process, a heat treatment process and a diffusion process to prepare the sintered neodymium iron boron magnet.

[0025] According to an embodiment of the present invention, in the melting process, the raw materials are proportioned according to the respective component ratios of the magnet, and the prepared raw materials are melted at 1300 - 1450 °C and rapidly cooled to form alloy sheets.

[0026] According to an embodiment of the present invention, in the powder-making process, the melted alloy sheets are made into alloy powders through HD hydrogen crushing, coarse grinding, medium grinding, first air jet milling and second air jet milling processes in sequence. In the present invention, the HD hydrogen crushing, coarse grinding, medium grinding and air jet milling can all adopt methods known in the art.

[0027] Preferably, the hydrogen absorption pressure of the HD hydrogen crushing is 200 MPa.

[0028] Preferably, the particle size of the first air jet milled powder ≥ 5.0 μm, preferably, the particle size of the first air jet milled powder ≥ 5.0 μm and < 7.0 μm.

[0029] Preferably, the particle size of the second air jet milled powder ≥ 3.0 μm, preferably, the particle size of the second air jet milled powder ≥ 5.0 μm and ≤ 4.0 μm.

[0030] Preferably, the difference between the particle size of the first airflow milling and the particle size of the second airflow milling is ≥ 2.0 μm. The alloy powder of the present invention passes through two airflow mills, making the particle size of the first airflow milling and the particle size of the second airflow milling differ by more than 2.0 μm, so that the powder ground in the second time is more easily broken, the shape is closer to spherical, and the massive impurity grain boundary phases at the grain boundary coupling are removed, preventing the agglomeration and uneven diffusion of heavy rare earths during diffusion, facilitating the thin layer distribution of the neodymium-rich phase, thus ensuring the diffusion consistency and uniformity at different positions of the magnet product, and the Hcj is also improved. At the same time, the neodymium-rich phase is fully nitrided, and the nitrogen content in the magnet is 600 - 1000 ppm, which can slow down the diffusion rate and prevent the heavy rare earths from entering the main phase during diffusion.

[0031] According to an embodiment of the present invention, the powder ground in the first airflow milling is sent into a cyclone separator for separation. Preferably, the powder ground in the first airflow milling is sent into the first cyclone separator for separation.

[0032] According to an embodiment of the present invention, the powder ground in the second airflow milling is sent into a cyclone separator for separation. Preferably, the powder ground in the second airflow milling is sent into the second cyclone separator for separation.

[0033] According to an embodiment of the present invention, the cyclone separator comprises a cylinder and a cone barrel from top to bottom, and the cylinder and the cone barrel are connected.

[0034] Above the cylinder, there are a cylinder inlet and a cylinder outlet. The cylinder inlet is used to feed the powder ground by airflow milling (including the powder ground in the first airflow milling or the powder ground in the second airflow milling), and the cylinder outlet is used to discharge the gas, and the gas contains a small amount of ultrafine powder.

[0035] Below the cone barrel, there is a cone barrel outlet, and the cone barrel outlet is used to collect the powder with the required particle size.

[0036] Preferably, the first airflow milling and the second airflow milling processes in the powder making process are carried out in an airflow milling device, and the airflow milling device includes a first cyclone separator, a second grinding chamber and a second cyclone separator.

[0037] Preferably, the diameter of the cylinder of the cyclone separator is between 0.55 - 0.75 m, and the height of the cylinder is 0.8 - 1.2 m.

[0038] Preferably, the height of the cone barrel of the cyclone separator is 1.0 - 1.4 m.

[0039] In the present invention, by controlling the recovery amount of the ultrafine powder after the second airflow milling to be between 1.5 - 3%, where the ultrafine powder is the powder discharged above the second cyclone separator, the massive impurity grain boundary phases at the grain boundary coupling can be separated out, which is beneficial to the thin layer distribution of the neodymium-rich phase, and can slow down the diffusion rate of the thin sheet product, thus avoiding over-diffusion.

[0040] According to an embodiment of the present invention, in the compacting process, magnetic powder is oriented and compacted under an external magnetic field, and then demagnetized to obtain a massive green compact. Preferably, before compacting and forming, orientation magnetization and forming are required under a magnetic field strength of 1.5 - 2T. After compacting and forming, a reverse magnetic field of 1.8 - 2T is applied for demagnetization. Preferably, the density of the massive green compact is 4 - 4.5 g / cm 3 .

[0041] According to an embodiment of the present invention, after the compacting process and before the heat treatment process, isostatic pressing treatment can also be performed on the massive green compact. Through isostatic pressing treatment, the density of the green compact is increased, and the qualified rate of the subsequent sintered product is improved.

[0042] Preferably, the pressure and time of isostatic pressing treatment can adopt the techniques well-known in the art. For example, isostatic pressing treatment is performed at 170 MPa.

[0043] According to an embodiment of the present invention, in the heat treatment process, the green compact obtained from the compacting process is sintered and aged in an inert gas atmosphere to obtain a neodymium iron boron blank. Preferably, the inert gas is selected from nitrogen, argon, helium, etc.

[0044] According to an embodiment of the present invention, the sintering temperature is 1000 - 1100 °C, and the sintering time is 4 - 10 h.

[0045] According to an embodiment of the present invention, the aging treatment includes a first aging process and / or a second aging process;

[0046] The first aging process includes: the treatment temperature is 600 - 750 °C; the treatment time is 4 - 10 h;

[0047] The second aging process includes: the treatment temperature is 500 - 650 °C; the treatment time is 4 - 10 h.

[0048] According to an embodiment of the present invention, after the heat treatment process, the sintered product can first be processed into a thin sheet with a thickness T of ≤ 1.3 mm.

[0049] Preferably, after multi-wire cutting, the thin sheet is not subjected to double-sided grinding, but only washed and then directly subjected to the diffusion process. The washing is, for example, water washing and / or alcohol washing, etc. In the present invention, the surface grains and neodymium-rich phase after multi-wire cutting are damaged, preventing heavy rare earth from quickly entering the grain boundary phase, which is beneficial to the diffusion of the thin sheet.

[0050] Preferably, before the diffusion process, the prepared neodymium iron boron magnet substrate is processed into a block with dimensions of 45 - 20 - T mm (length - width - thickness, where T is the thickness of the neodymium iron boron magnet in the orientation direction).

[0051] Preferably, the thickness T of the neodymium iron boron magnet in the orientation direction is T ≤ 1.3 mm.

[0052] According to an embodiment of the present invention, the diffusion process adopts the processes and equipment commonly used in the art.

[0053] According to an embodiment of the present invention, the diffusion source adopts heavy rare earth metals, such as Dy and / or Tb powders. Preferably, the content of heavy rare earth metals on the surface of the product is 0.08-2 wt%, for example, 0.08 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt% or 2 wt%.

[0054] According to an embodiment of the present invention, the diffusion process is as follows:

[0055] Cover the diffusion source on the surface of the NdFeB magnet substrate and perform heat treatment.

[0056] According to an embodiment of the present invention, in the diffusion process, first diffusion and second diffusion treatments are adopted. After the second diffusion treatment, it is cooled to room temperature, and then the third diffusion treatment is carried out;

[0057] Among them, the temperature of the first diffusion is 700-800 °C, and the diffusion time is 5-10 h. Preferably, the diffusion temperature is, for example, 700 °C, 720 °C, 740 °C, 750 °C, 760 °C, 780 °C or 800 °C;

[0058] The temperature of the second diffusion is 800-900 °C, and the diffusion time is 5-10 h. Preferably, the diffusion temperature is, for example, 800 °C, 820 °C, 840 °C, 850 °C, 860 °C, 880 °C or 900 °C;

[0059] The temperature of the third diffusion is 450-660 °C, and the diffusion time is 5-10 h. Preferably, the diffusion temperature is, for example, 450 °C, 480 °C, 500 °C, 550 °C, 560 °C, 580 °C, 600 °C, 620 °C or 660 °C.

[0060] The present invention adopts multiple low-temperature diffusions, which can allow heavy rare earths to slowly enter the thin-film product, and can be more uniform, preventing diffusion into the main phase.

[0061] In the magnet of the present invention, the difference in coercivity before and after diffusion is ≥900 kA / m, and the difference in the surface content and the central distribution content of heavy rare earth metals (such as Dy and / or Tb) after diffusion is 0.1-0.2%.

[0062] The present invention also provides the application of the above magnet in the fields of motors, speakers, magnetic separators, computer disk drives, magnetic resonance imaging equipment, etc.

[0063] Preferably, the application of the magnet as a motor rotor magnet steel in a motor.

[0064] Advantages of the present invention:

[0065] Compared with the diffusion of conventional thin magnetic products, the magnet of the present invention increases the content of element B, ensures the existence of an appropriate amount of boron-rich phase. During the diffusion process of the thin magnetic sheet, it can delay the diffusion rate of heavy rare earth elements dysprosium or terbium into the magnet, preventing the decrease of Hcj and Hk / Hcj caused by the excessive diffusion of heavy rare earths. In addition, the secondary air jet milling process is adopted, with a particle size difference of more than 0.2 μm between the two grindings, making the powder of the second grinding easier to break, with a shape closer to a sphere, and removing the massive impurity grain boundary phase at the grain boundary coupling, preventing the agglomeration of heavy rare earths and uneven diffusion during diffusion, being conducive to the thin layer distribution of the neodymium-rich phase, ensuring the diffusion consistency and uniformity at different positions of the magnet product, and also improving Hcj. At the same time, the neodymium-rich phase is fully nitrided, which can slow down the diffusion rate and avoid the entry of heavy rare earths into the main phase during diffusion. The method of the present invention adopts multiple low-temperature diffusions, which can allow heavy rare earths to slowly enter the thin sheet product more uniformly and prevent diffusion into the main phase. Brief Description of the Drawings

[0066] Figure 1 It is a schematic structural diagram of the cyclone separator of the present invention. Detailed Embodiments

[0067] The technical solutions of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only for illustrative and explanatory purposes of the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0068] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products or can be prepared by known methods.

[0069] The raw materials were respectively configured according to the composition table of the neodymium-iron-boron magnet in Table 1 (unit: wt%), and the sintered neodymium-iron-boron magnet was prepared by the following preparation method:

[0070] The raw material mass ratio in Table 1 was put into a vacuum melting furnace and melted by electromagnetic induction heating to 1450 °C in an Ar atmosphere. The alloy melt was poured onto a polished chill roll, and after cooling, a neodymium-iron-boron rapid solidification thin sheet was obtained.

[0071] Table 1

[0072]

[0073] The obtained quick-setting scales are subjected to hydrogen explosion treatment with a hydrogen absorption pressure of 200 MPa. Then, rough grinding by ball milling is carried out, followed by the first airflow milling and the second airflow milling processes. The target particle size D50 of the first airflow milling is 5.0 μm, and the target particle size D50 of the second airflow milling is 3.0 μm.

[0074] The first airflow milling and the second airflow milling processes of the powder preparation process are carried out in an airflow milling device, and the airflow milling device includes a first cyclone separator (i.e., Figure 1 separator 1 in Figure 1 grinding 2), and a second cyclone separator (i.e., Figure 1 separator 2 in

[0075] The first airflow milled powder obtained from the first grinding chamber (i.e., Figure 1 grinding 1) is sent into the first cyclone separator (or cyclone separator 1) for separation;

[0076] The second airflow milled powder is sent into the second cyclone separator (or cyclone separator 2 or Figure 1 separator 2 in

[0077] The cyclone separator consists of a cylinder and a cone barrel from top to bottom. The cylinder and the cone barrel are connected. The upper part of the cylinder includes a cylinder inlet and a cylinder outlet. The cylinder inlet is used to feed the airflow milled powder, and the cylinder outlet is used to discharge the gas, which contains a small amount of ultrafine powder;

[0078] The lower part of the cone barrel has a cone barrel outlet, and the cone barrel outlet is used to collect the powder with the required particle size.

[0079] The powder collected from the cone barrel outlet of the cyclone separator 1 (i.e., Figure 1 separator 1 in Figure 1 grinding 2) is ground in the second grinding chamber (i.e.,

[0080] By controlling the diameter of the cylinder of the cyclone separator to be 0.6 m, the height of the cylinder to be 0.9 m, and the height of the cone barrel to be 1.1 m, the recovery amount of the ultrafine powder after the second airflow milling is controlled at 2%. The above-mentioned airflow milled powder is filled into a vacuum press mold and subjected to orientation pressing in a magnetic field with a magnetic field strength of 2 T, and then an isostatic pressing of 170 MPa is carried out to obtain a green compact. The above-mentioned green compact is placed in a vacuum sintering furnace and heated to 1070 °C at a rate of 5 °C / min. The sintering temperature is controlled at 1070 °C and sintered for 5 h. After aging at a temperature of 510 °C for 5 h, the neodymium iron boron magnet blank of this embodiment is obtained.

[0081] Among them, the neodymium iron boron magnet blanks of Examples 1-5 and Comparative Examples 1-6 were processed into neodymium iron boron magnet black sheets with a length of 45 mm, a width of 20 mm, and a thickness as shown in Table 1, denoted as M1~M11. The heavy rare earth content of the neodymium iron boron magnet black sheets M1-M11 was measured, denoted as RH1~RH11.

[0082] The magnetic properties / squareness of the neodymium iron boron magnet black sheets of Examples 1-5 and Comparative Examples 1-6 were detected, denoted as H1 / F1, H2 / F2……H111 / F11.

[0083] Without any grinding treatment, the above-mentioned neodymium iron boron magnet black sheets were only treated by water washing. After a treatment time of 10 min, diffusion treatment was carried out. The specific method of diffusion treatment was as follows: after attaching 0.9 wt% of Tb (in this example, the coating method was used for treatment), secondary grain boundary diffusion treatment at 750 °C for 10 h + 880 °C for 10 h was carried out, cooled to room temperature, and then heated to 550 °C and held for 5 h for diffusion aging treatment (i.e., the third diffusion) to obtain the magnet M1’~M11’ with high remanence and high coercivity after diffusion treatment. The heavy rare earth content of the neodymium iron boron magnets M1’~M11’ was measured, denoted as RH1’~RH11’.

[0084] The magnetic properties / squareness of the neodymium iron boron magnet black sheets of Examples 1-5 and Comparative Examples 1-6 were detected, denoted as H’1 / F’ 1, H’2 / F’ 2……H’11 / F’ 11.

[0085] The test method

[0086] (1) Measurement method of heavy rare earth difference: First, grind 0.03 mm in the thickness direction of the product after diffusion, and then process 3 adjacent sample columns of 2&2&T in the length, width, and thickness directions of the product, where T is the thickness of the product, and they are respectively labeled as sample columns A, B, and C. Grind sample column A along the T direction to 0.3 mm, grind 0.15 mm on both sides of sample column B along the T direction, and sample column C is not processed. The heavy rare earth content RH(A), RH(B), and RH(C) is measured by full dissolution using a spectrometer. The heavy rare earth difference △RH=(RH(C)×T - RH(B×(T - 0.3))) / 0.3 - RH(A), and the heavy rare earth difference refers to the difference in heavy rare earth content between the 0.15 mm surface layer on both sides along the T direction of the product and the 0.3 mm heavy rare earth content in the center.

[0087] (2) Measurement method of magnetic energy: First, grind 0.03 mm in the thickness direction of the product after diffusion, and then process n adjacent sample columns of 7&7&T in the length, width, and thickness directions of the product, where 3.8 / T < n < 4.4 / T. The n sample columns are stacked and aligned along the thickness direction to test the magnetic properties.

[0088] (3)Method for measuring squareness: The method is the same as (2). First, grind 0.03 mm in the thickness direction of the product after diffusion, and then process n adjacent sample columns of 7&7&T in the length, width, and thickness directions of the product, where 3.8 / T < n < 4.4 / T. The n sample columns are stacked and aligned in the thickness direction to measure squareness.

[0089] The test results are shown in Table 2 below.

[0090] Table 2

[0091]

[0092] Conclusion:

[0093] The differences between Examples 1 and 2 and Comparative Example 6 are that Examples 1 and 2 contain Ti and Zr, and 0.1% < Zr + Ti ≤ 0.2%, while the contents of Ti and Zr in Comparative Example 6 are 0.1%. The test results show that both △H and △F of Examples 1 and 2 are higher than those of Comparative Example 6. It can be seen that the Ti and / or Zr elements can improve the Hcj and squareness of the magnet within the scope of the present invention.

[0094] Research shows that when adding Ti element to the magnet, the Ti element is mainly uniformly dispersed in the grain boundary triple points in the form of Ti compounds, which plays a role in preventing grain growth. When adding Zr element to the magnet, the Zr element is mainly distributed in the intergranular position, and inhibits grain growth by forming non-magnetic particles. The content of Ti and / or Zr in the magnet of the present invention is greater than 0.1% to effectively prevent over-diffusion during the diffusion process of the thin magnetic sheet, that is, diffusion materials such as Dy and Tb enter the main phase to form an anti-core-shell structure, preventing a significant decrease in Hcj and Hk / Hcj. At the same time, the content of Ti or Zr in the magnet cannot be greater than 0.2%. Only within the range of 0.1 - 0.2% (not 0.1%) can the squareness of the magnet be significantly improved.

[0095] The differences between Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, Example 4 and Comparative Example 4, and Example 5 and Comparative Example 5 are all that the B content is different. The change amount of B in the examples satisfies 1.065% - T / 2000 ≤ [B] ≤ 1.065% - T / 3000. The test results show that both △Hcj and △F of the examples are higher than those of the comparative examples. It can be seen that a high content of B element can ensure the existence of an appropriate amount of boron-rich phase, which can play a role in delaying the diffusion of heavy rare earth elements such as dysprosium or terbium into the magnet during the diffusion process of the thin magnetic sheet, preventing a decrease in Hcj and Hk / Hcj caused by excessive diffusion.

[0096] Example 6 and Comparative Examples 7 - 8

[0097] Example 6 and Comparative Examples 7-8: Raw materials were configured according to the composition table of the neodymium iron boron material in Example 1 in Table 1 (units are all wt%), and sintered neodymium iron boron magnets were prepared using the preparation method of Example 1, the difference being that:

[0098] In the jet milling stage,

[0099] In Example 6, the particle size of the first jet milling was 6.0 μm, the particle size of the second jet milling was 3.5 μm, and the difference between the two jet millings was 2.5 μm.

[0100] In Comparative Example 7, only one jet milling was performed, and the particle size of the jet milling was 3.5 μm.

[0101] In Comparative Example 8, the particle size of the first jet milling was 4.0 μm, the particle size of the second jet milling was 3.5 μm, and the difference between the two jet millings was less than 2.0 μm.

[0102] The process differences between Example 6 and Comparative Examples 7-8 are shown in Table 3 below.

[0103] Table 3

[0104]

[0105] The magnetic property test results of the magnets prepared in Example 6 and Comparative Examples 7-8 are shown in Table 4 below.

[0106] Table 4

[0107]

[0108] Conclusion:

[0109] By comparing Example 1, 6 and Comparative Examples 7-8, it can be seen that the present invention uses two jet millings and the difference between the particle size of the first jet milling and the particle size of the second jet milling is more than 2.0 μm, making the powder in the second grinding easier to break, the shape closer to spherical, and removing part of the massive impurity grain boundary phase at the grain boundary coupling, preventing the agglomeration and uneven diffusion of heavy rare earths during diffusion, which is beneficial to the thin layer distribution of the neodymium-rich phase, thus ensuring the diffusion consistency and uniformity at different positions of the thin film product, and the Hcj is also improved. At the same time, the neodymium-rich phase is fully nitrided, and the nitrogen content in the magnet is 600-1000 ppm, which can slow down the diffusion rate and avoid the entry of heavy rare earths into the main phase during diffusion.

[0110] Raw materials were configured according to the composition table of the neodymium iron boron material in Example 1 in Table 1 (units are all wt%), and sintered neodymium iron boron magnets were prepared using the preparation method of Example 1. The difference is that the height and diameter of the cyclone separator in the second jet milling are different, resulting in different final ultra-fine powder recovery amounts, as shown in Table 5 below. The performance of the prepared magnets is shown in Table 6 below.

[0111] Table 5

[0112]

[0113] Table 6

[0114]

[0115] Conclusion:

[0116] By comparing Example 1, Example 7 and Comparative Examples 9 - 10, it can be seen that the diameter of the cyclone separator of the secondary air jet mill is between 0.55 - 0.75 m, the height of the cylinder is between 0.8 - 1.2 m, and the height of the cone is between 1.0 - 1.4 m. The recovery amount of ultrafine powder after the second air jet mill can be controlled between 1.5 - 3%. It can separate the massive impurity grain boundary phases at the grain boundary coupling, which is beneficial to the thin layer distribution of the neodymium-rich phase, and can slow down the diffusion rate of the thin sheet product, thus avoiding over-diffusion.

[0117] Example 8 and Comparative Examples 11 - 12

[0118] The raw materials were respectively configured according to the composition table of the neodymium iron boron material in Example 1 in Table 1 (the units are all wt%), and the sintered neodymium iron boron magnet was prepared by the preparation method as in Example 1, the difference is shown in Table 7; the performance of the prepared magnet is shown in Table 8 below.

[0119] Table 7

[0120]

[0121] Table 8

[0122]

[0123] Conclusion:

[0124] By comparing Example 1, Example 8 and Comparative Examples 11 - 12, it can be seen that two low-temperature diffusions can allow the heavy rare earth to slowly enter the thin sheet product more uniformly, preventing the decrease of coercivity and squareness caused by over-diffusion.

[0125] Above, the embodiments of the present invention have been described exemplarily. However, the protection scope of the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A sintered NdFeB magnet, characterized in that: Taking mass percentage as 100%, it comprises: Re: 28-32%, Re is selected from at least one of Pr, Nd, Dy, Tb, and Ho; B:1.000%-1.080%； M: 0-5% and not 0, M at least includes Zr and / or Ti, and 0.1%<Zr+Ti≤0.2%; The thickness of the NdFeB magnet in the orientation direction is 0.6 mm ≤ T ≤ 1.3 mm; 065%-T / 2000≤[B]≤1.065%-T / 3000; wherein [B] refers to the mass content of B, and T is the thickness of the NdFeB magnet in the orientation direction; When the magnet thickness is 0.6mm, the B content is 1.035%-1.045%; When the magnet thickness is 0.8mm, the B content is 1.025%-1.038%; When the magnet thickness is 1.0mm, the B content is 1.015%-1.031%; When the magnet thickness is 1.3mm, the B content is 1.000%-1.021%.

2. The magnet according to claim 1, characterized in that The M further comprises at least one of Co, Ni, Al, Cu and Ga; In the magnet, the remainder is Fe and impurities.

3. The method for preparing a magnet according to claim 1 or 2, characterized in that: The method comprises: The raw materials for preparing the sintered NdFeB magnet are processed through a smelting process, a powder making process, a pressing process, a heat treatment process and a diffusion process to prepare the sintered NdFeB magnet; In the powder making process, the smelted alloy flakes are made into alloy powder through HD hydrogen crushing, coarse grinding, medium grinding, first jet milling and second jet milling processes in sequence; The particle size of the first air jet milling is ≥5.0 μm, the particle size of the second air jet milling is ≥3.0 μm, and the difference between the particle size of the first air jet milling and the particle size of the second air jet milling is ≥2.0 μm.

4. The method according to claim 3, characterized in that The first jet milling powder is sent to a cyclone separator for separation; and / or, sending the second air flow milling powder into a cyclone separator for separation; And / or, the cyclone separator is a cylinder and a conical barrel from top to bottom, and the cylinder and the conical barrel are connected; The top of the cylinder includes a cylinder inlet and a cylinder outlet, the cylinder inlet is used to feed airflow grinding powder, and the cylinder outlet is used to discharge gas; The bottom of the cone barrel is provided with a cone barrel outlet, and the cone barrel outlet is used to collect powder of required particle size; and / or, the diameter of the cylinder of the cyclone separator is between 0.55-0.75 m, and the height of the cylinder is between 0.8-1.2 m; And / or, the height of the cone barrel of the cyclone separator is 1.0-1.4m; And / or, the recovery of ultrafine powder after air jet milling is 1.5-3%.

5. The method according to claim 3, characterized in that: The diffusion process is as follows: The diffusion source is covered on the surface of the NdFeB magnet substrate and heat treated.

6. The method according to claim 5, characterized in that In the diffusion process, the first diffusion and the second diffusion treatment are adopted, and after the second diffusion treatment is completed, the temperature is cooled to room temperature, and then the third diffusion treatment is carried out; The temperature of the first diffusion is 700-800°C and the diffusion time is 5-10h; The temperature of the second diffusion is 800-900°C and the diffusion time is 5-10h; The temperature of the third diffusion is 450-660°C and the diffusion time is 5-10h.

7. Application of the magnet according to claim 1 or 2 in the fields of motors, loudspeakers, magnetic separators, computer disk drives or magnetic resonance imaging equipment.

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