High-squareness heavy-rare-earth-free R-T-B sintered magnet and preparation method thereof

Abstract

According to the high-squareness heavy-rare-earth-free R-T-B sintered magnet and the preparation method thereof, the jet milling process is optimized, high-rare-earth alloy B coarse powder is supplemented at the later stage of jet milling, jet milling is carried out at the same time, rare earth is timely and accurately supplemented for rear-section powder with large rare earth loss, the difficulty of later-stage material mixing is reduced, and the high-squareness heavy-rare-earth-free R-T-B sintered magnet is obtained. And the rare earth content of the powder in the post-jet milling stage is increased, so that the rare earth content of the powder in the post-jet milling stage is approximately consistent with the rare earth content of the powder in the previous stage. The particle size distribution of the powder in the later stage is further optimized, the microscopic grain size distribution of the magnet is eventually homogenized, so that the high-squareness heavy-rare-earth-free R-T-B sintered magnet is obtained, the squareness SQ of the magnet is larger than or equal to 0.95, and the intrinsic coercive force Hcj is larger than or equal to 16.5 kOe.

Description

Technical Field

[0001] This invention belongs to the field of sintered NdFeB magnet technology, and relates to a high squareness heavy rare earth RTB sintered magnet and its preparation method. Background Technology

[0002] Sintered NdFeB magnets, as the commercially available permanent magnet material with the best overall magnetic properties, have core performance indicators (energy product ((BH)max), coercivity (Hcj), and squareness) that directly determine their application value in high-end equipment. With the upgrading of new energy industries such as wind power generation equipment, electric vehicle drive motors, and industrial servo motors towards "high power density, high stability, and long lifespan," the overall demand for sintered NdFeB magnets is strongly driven, and stringent requirements are being placed on their actual working performance indicators (especially high-temperature coercivity and energy product stability).

[0003] However, the preparation of traditional high-performance sintered NdFeB magnets usually relies on heavy rare earth elements (such as Dy and Tb) to improve their coercivity. But heavy rare earth elements Dy and Tb are scarce and expensive, and their introduction will also significantly reduce the remanence of the magnets. More importantly, as strategic resources, heavy rare earth elements such as Dy and Tb are susceptible to price instability or large fluctuations due to rare earth policies.

[0004] Existing heavy rare earth-free sintered NdFeB magnets primarily rely on the demagnetizing coupling effect of non-magnetic continuous grain boundary phases to ensure high coercivity. However, due to differences in the microstructure of the wafers and the distribution of rare earth-rich phases, during the hydrogen-burst air jet milling process, the fine-sized main phase and the abundant adjacent rare earth phases are crushed to the target particle size first, while the coarse-sized main phase and the less abundant adjacent rare earth phases are more difficult to crush. This ultimately leads to variations in the rare earth content and particle size of the powder produced by the air jet mill. Using a three-dimensional mixer or a high-speed mixer, complete uniform mixing is difficult to achieve due to differences in specific gravity and particle size, as well as the influence of electrostatic adsorption forces. This results in problems such as uneven distribution of microstructure and discontinuous distribution of grain boundary phases in the final oriented and sintered magnets. Consequently, the final squareness of the magnets is low, and the coercivity fluctuates greatly. The measured squareness (SQ) value is mostly below 0.95, which is insufficient to meet the technical requirements of high-end equipment manufacturing. Therefore, how to obtain heavy rare earth-free permanent magnets with excellent squareness consistency without adding heavy rare earth elements has become a problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the issue of low measured squareness (SQ) values ​​in heavy rare-earth-free sintered NdFeB magnets, this invention aims to provide a high squareness NdFeB sintered magnet and its preparation method. This invention involves adding a high-rare-earth alloy B after the air jet milling stage. The high-rare-earth alloy B is simultaneously ground and crushed with the main alloy A, dispersing alloy B within alloy A. This increases the rare-earth content of the NdFeB powder after the air jet milling stage, achieving a rare-earth content nearly identical to that of the powder in the previous stage. Simultaneously, it improves the X... 10 The particle size distribution of the powder is reduced and optimized in the later stage, ultimately making the microcrystalline size distribution of the magnet uniform and the measured squareness SQ value ≥0.95.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high squareness, weightless rare-earth RTB sintered magnet, characterized in that the composition of the magnet comprises: Re: 29.8–34 wt.%, Re is a light rare earth element, and Re includes at least one or two of Pr and Nd; M: 0.01–0.7 wt.%, M is Cu and / or Al; X: 0.05–0.45 wt.%, X is one or more of Zr, Ti, and Nb; B: 0.86–0.93 wt.%, B is boron; Ga: 0.21–0.65 wt.%; The balance is T, where T is Fe or Fe and Co and other unavoidable impurities; wt.% represents the percentage by mass of the total mass of the raw material composition; The high squareness weightless rare earth RTB sintered magnet is based on R2T 14 The sintered NdFeB magnet, with B as the main phase particles, has a PrNd content range of less than 12.5 wt.% and a Ga content range of less than 0.5 wt.% between any two triangular grain boundary phases; the magnet has a squareness SQ ≥ 0.95 and an intrinsic coercivity Hcj ≥ 16.5 kOe.

[0007] The two triangular grain boundary phases are characterized in that the positions of the triangular grain boundary phases are at least 5 μm apart; The range of PrNd and Ga contents at different locations in the triangular grain boundary phase was measured using the following method: A combination of scanning electron microscopy and energy dispersive spectroscopy was used to measure the contents of the triangular grain boundary phase with an area of ​​not less than 100 nm. 2 Micro-area scanning elemental analysis was performed at the scanning location to determine the PrNd and Ga content at that location.

[0008] This invention also provides a method for preparing a high squareness heavy rare earth RTB sintered magnet, the method comprising the following process steps: S1: Take the raw materials of main alloy A and high rare earth alloy B according to the component ratio, and prepare the main alloy A slab and high rare earth alloy B slab respectively by vacuum rapid solidification melting. The main alloy A comprises the following components by mass percentage: RL1: 29.5~33 wt.%, RL1 is a light rare earth element, and RL includes at least one or two of Pr and Nd; M1: 0.01~0.65 wt.%, M is Cu and / or Al; X1: 0.1–0.5 wt.%, X is one or more of Zr, Ti, and Nb; B: 0.88–0.935 wt.%, B is boron; Ga: 0.2–0.6 wt.%; The balance is Fe or Fe and Co and other unavoidable impurities; The high rare earth alloy B comprises the following components by mass percentage: RL2: 70~85wt.%, RL2 is a light rare earth element, selected from one or two of Pr and Nd; N: 4~10 wt.%, N is one or more of Al, Cu, and Ga, and must contain Ga; The balance is Fe or Fe and Co and other unavoidable impurities; S2: The main alloy A and high rare earth alloy B flakes from step S1 above are subjected to hydrogen crushing treatment to obtain coarse powder of main alloy A and coarse powder of high rare earth alloy B. The particle size of the coarse powder of main alloy A and coarse powder of high rare earth alloy B is less than 200 μm, preferably less than 100 μm; more preferably, the particle size of the coarse powder is 10~100 μm.

[0009] The dehydrogenation temperature of the main alloy A is 400~580℃, preferably 480~560℃.

[0010] The dehydrogenation temperature of the high rare earth alloy B is 360~460℃, preferably 380~420℃.

[0011] The dehydrogenation temperature of the high rare earth alloy B must be less than 460°C. If the dehydrogenation temperature is higher than 460°C, the coarse powder of high rare earth alloy B will agglomerate, making it impossible for the coarse powder of high rare earth alloy B to undergo subsequent air jet milling.

[0012] S3: The main alloy A coarse powder from step S2 above is subjected to air jet milling. The air jet mill is continuously fed. When the main alloy A coarse powder is ground to the point where the mass of powder collected at the outlet of the air jet mill is A1, high rare earth alloy B coarse powder is added and ground together with the remaining main alloy A coarse powder to obtain NdFeB fine powder with an average surface area particle size (SMD) of 2.5~3.3μm. The mass of coarse powder of main alloy A is A0. When coarse powder of high rare earth alloy B is added, the mass of the powder produced is A1, and A1 satisfies the following conditions: (a) When A0≥400kg, A1= A0×(80~90%); (b) When 100kg≤A0<400kg, A1=60kg; The mass of the added high rare earth alloy B coarse powder is B. x B x =(0.01~0.02)×(A0-A1).

[0013] Furthermore, the air jet mill continuously discharges material, and the discharged NdFeB fine powder is divided into pre-stage fine powder and post-stage fine powder according to the addition time of the high rare earth alloy B coarse powder. The masses of the pre-stage fine powder and the post-stage fine powder are A1 and A0-A1+B, respectively. x The fine powder from the first stage and the fine powder from the second stage are stored in the same fine powder hopper.

[0014] Furthermore, in step S3, the air jet mill includes a main feed inlet and a secondary feed inlet. The main alloy A coarse powder is continuously fed from the main feed inlet. When the main alloy A coarse powder is ground to a powder output quality of A1, the high rare earth alloy B coarse powder is fed from the secondary feed inlet, so that the high rare earth alloy B coarse powder and the remaining alloy A coarse powder are jointly subjected to air jet milling to obtain fine powder in the post-air jet milling stage.

[0015] Furthermore, the main alloy A fine powder is stored in tank A, which is connected to the main feed port. The high rare earth alloy B coarse powder is stored in tank B, which is connected to the auxiliary feed port. During the initial stage of grinding, the auxiliary feed port is closed. The quality of the fine powder at the outlet of the air jet mill is monitored in real time. When the powder quality reaches A1, the auxiliary feed port is opened, and the high rare earth alloy B coarse powder in tank B is fed through the auxiliary feed port by gravity feeding.

[0016] S4: The NdFeB fine powder obtained in step S3 above is oriented, sintered, and subjected to two-stage aging treatment to obtain a high squareness heavy rare earth RTB sintered magnet.

[0017] In the orientation forming process, the magnetic field strength is 1.5~2.3T.

[0018] The sintering process involves holding the sinter at 1070~1100℃ for 4~8 hours.

[0019] The two-stage aging process is as follows: the first-stage aging process involves holding the temperature at 870~910℃ for 2~4 hours, and the second-stage aging process involves holding the temperature at 430~510℃ for 2~4 hours.

[0020] The high squareness of the heavy rare earth RTB sintered magnet of the present invention has an intrinsic coercivity Hcj≥16.5kOe and a squareness SQ≥0.95.

[0021] This invention, based on the principle that the high coercivity of heavy rare-earth-free RTB sintered magnets depends on the distribution and composition of grain boundary phases, discovered that due to the significant rare-earth loss in the powder during the later stages of air jet milling, large-scale mixing makes it difficult to eliminate localized grain boundary phases and differences in rare-earth content, leading to poor squareness and large fluctuations in coercivity in mass production. Therefore, this invention optimizes the air jet milling process by simultaneously replenishing powder with higher rare-earth content during the later stages of air jet milling. This timely and precise replenishment of rare-earth to the powder with high rare-earth loss reduces the difficulty of later mixing, increasing the rare-earth content of the powder in the later stages of air jet milling. This achieves a near-identical rare-earth content between the powder in the later stages and the powder in the earlier stages. Further optimization of the particle size distribution of the powder in the later stages ultimately homogenizes the microcrystalline grain size distribution of the magnet, resulting in heavy rare-earth-free RTB sintered magnets with a squareness ≥95%.

[0022] Compared with the prior art, the beneficial effects of this invention are as follows: In the later stage of the air jet milling process, this invention adds coarse powder of alloy B with a high rare earth content through the auxiliary feed port of the air jet mill. At the same time, alloy B is crushed and mixed with the remaining coarse powder of main alloy A. Alloy B is uniformly dispersed in alloy A. The high rare earth content of alloy B improves the rare earth content of the fine powder in the later stage and reduces the difficulty of the later mixing process. It also optimizes the particle size distribution of the powder in the later stage and prepares a high squareness heavy rare earth-free RTB sintered magnet. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the feed inlet structure of an air jet mill.

[0024] Figure 2 This is a schematic diagram of the test locations for microscopic composition analysis of the blank in Example 2. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0026] This invention employs vacuum induction melting, hydrogen degradation (HD), air jet milling (JM), orientation forming, and sintering aging to prepare heavy rare earth-free RTB sintered magnets. The process includes the following steps: sintering and hydrogen degradation of main alloy A and alloy B, followed by air jet milling, orientation forming, and sintering aging: Vacuum induction melting of main alloy A: S11: Ingredients. (PrNd) 30.2 B 0.92 Al 0.3 Co 0.3 Cu 0.33 Ga 0.53 Zr 0.32 Fe Bal The raw materials were weighed according to the specified ratio, and the purity of Fe was greater than 99.99%.

[0027] S12: Charging. Place the raw materials into the crucible in descending order of melting point, close the furnace door, and evacuate the furnace to a vacuum level of 10. -1 Below Pa.

[0028] S13: Preheating. Preheating time: 10~30 minutes.

[0029] S14: Argon-filled heating and melting. After preheating, argon gas is introduced into the furnace to achieve a furnace pressure of 20,000~50,000 Pa, preferably 2 kPa. After argon filling, the temperature is increased, and the alloy liquid is heated to 1480~1520℃ and then subjected to a heat holding and refining process for 1~3 minutes.

[0030] S15: Casting. After heat preservation and refining, the power is turned off and the alloy liquid is subjected to self-cooling treatment. After the alloy liquid temperature reaches 1410~1430℃, casting is performed to obtain heavy rare earth-free main alloy A flakes. The average thickness of the flakes is 0.3±0.02mm.

[0031] Hydrogen decomposition treatment of main alloy A: S21: Charging and Positive / Negative Inspection. After loading the heavy rare earth main alloy A sheet into the hydrogen crushing furnace, argon gas is introduced for a positive inspection lasting 5 minutes. During the positive inspection, the pressure change inside the furnace is less than 0.01 MPa / 5 minutes. After the positive inspection, the furnace is evacuated for ≥40 minutes. After the evacuation is completed, a negative inspection begins for 5 minutes. Before and after the negative inspection, the pressure rise inside the furnace is less than 30 Pa / 5 minutes.

[0032] S22: Hydrogen absorption. One hydrogen absorption cycle consists of a pressure of 0.068~0.098 MPa. When the furnace is full of hydrogen, the furnace pressure is 0.098 MPa. The criterion for hydrogen saturation is that the furnace pressure change is less than 0.01 MPa / 5 min.

[0033] S23: Dehydrogenation. After hydrogen absorption, heating and holding for dehydrogenation begins. The heating rate is ≥15℃ / min, the dehydrogenation temperature is 400~580℃, preferably 480~540℃, and the dehydrogenation time is 2~4h to obtain coarse powder of alloy A.

[0034] Vacuum induction melting of alloy B: S31: Ingredients. (PrNd) 80 Al2Co1Cu 1.5 Ga1Fe Bal The raw materials were weighed according to the specified ratio, and the purity of Fe was greater than 99.99%.

[0035] S32: Charging. Place the raw materials into the crucible in descending order of melting point, close the furnace door, and evacuate the furnace to a vacuum level of 10. -1 Below Pa.

[0036] S33: Preheating. Preheating time: 10-30 minutes. S34: Argon-filled heating and melting. After preheating, argon gas is introduced into the furnace to achieve a furnace pressure of 20,000~50,000 Pa, preferably 2 kPa. After argon filling, the temperature is increased, and the alloy liquid is heated to 1480~1520℃ and then subjected to a heat-holding refining process for 1~3 minutes.

[0037] S35: Casting. After heat treatment and refining, the power is turned off and the alloy liquid is subjected to self-cooling treatment. After the alloy liquid temperature reaches 1410~1430℃, casting is performed to obtain high rare earth alloy B flakes. The average thickness of the flakes is 0.3±0.02mm.

[0038] Alloy B hydrogen decomposition treatment HD: S41: Charging and Positive / Negative Inspection. After loading the high rare earth alloy B sheet into the hydrogen crushing furnace, argon gas is introduced for a positive inspection lasting 5 minutes. During the positive inspection, the pressure change inside the furnace is less than 0.01 MPa / 5 minutes. After the positive inspection, the furnace is evacuated for at least 40 minutes. After the evacuation is completed, a negative inspection begins for 5 minutes. Before and after the negative inspection, the pressure rise inside the furnace is less than 30 Pa / 5 minutes.

[0039] S42: Hydrogen absorption. One hydrogen absorption cycle consists of 0.068~0.098 MPa. When the furnace is full of hydrogen, the furnace pressure is 0.098 MPa. The criterion for hydrogen saturation is that the furnace pressure change is less than 0.01 MPa / 5 min.

[0040] S43: Dehydrogenation. After hydrogen absorption, heating and holding for dehydrogenation begins. The heating rate is ≥15℃ / min, the dehydrogenation temperature is 360~460℃, preferably 380~420℃, and the dehydrogenation time is 2~4h, yielding coarse powder of alloy B.

[0041] Airflow milling: The coarse powders of main alloy A and alloy B are subjected to airflow milling to obtain fine NdFeB powder. A schematic diagram of the airflow mill feed inlet is shown below. Figure 1As shown, the air jet mill includes a material tank A, a material tank B, a main feed inlet, a secondary feed inlet, and an intermediate chamber. Material tank A is connected to the main feed inlet via a switch, and material tank B is connected to the secondary feed inlet via a switch. The outlets of both the main feed inlet and the secondary feed inlet are connected to the intermediate chamber, which is connected to the grinding chamber via a vibrating discharge structure. Figure 1 The vibratory feeding structure and grinding chamber are not shown. The intermediate silo is used for temporary storage and simple mixing of coarse powder of main alloy A and / or coarse powder of alloy B. The fine powder of main alloy A is stored in silo A, and the coarse powder of high rare earth alloy B is stored in silo B. The coarse powder of main alloy A is continuously fed through the main feed port, while the switch of the auxiliary feed port is closed. The quality of the powder output from the air jet mill is monitored in real time. When the quality of the output powder reaches A1, the switch of the auxiliary feed port is opened, and the coarse powder of high rare earth alloy B in silo B is fed through the auxiliary feed port in one go according to the formula using gravity feeding. This allows the coarse powder of high rare earth alloy B to be mixed with the remaining coarse powder of alloy A in the intermediate silo, and then enter the grinding chamber for air jet milling to obtain NdFeB fine powder with a surface area average particle size (SMD) of 2.5~3.3μm. The NdFeB fine powder includes a pre-stage fine powder and a post-stage fine powder. The mass of alloy A coarse powder is A0, and the mass of alloy A at the outlet of the air jet mill when alloy B coarse powder is added is A1. The masses of the pre-stage fine powder and the post-stage fine powder are A1 and A0-A1+B, respectively. x And A1 satisfies: (a) When A0≥400kg, A1= A0×(80~90%); (b) When 100kg≤A0<400kg, A1=60kg; The added alloy B coarse powder has a mass of B. x B x =(0.01~0.02)×(A0-A1).

[0042] The fine powder from the first stage and the fine powder from the second stage are stored in the same fine powder container.

[0043] The coarse powder of alloy B is added through the auxiliary feed port of the air jet mill. The coarse powder of alloy B is ground together with the remaining coarse powder of alloy A in the mill chamber to obtain fine powder in the later stage of air jet milling.

[0044] The fine powder in the previous stage refers to the coarse powder of alloy A obtained at the outlet of the air jet mill before the addition of coarse powder of alloy B.

[0045] The alloy A before air jet milling and the NdFeB fine powder obtained after air jet milling need to be mixed with lubricant or antioxidant. The addition ratios are 1.5‰ and 0.8‰, respectively.

[0046] Orientation forming and sintering aging treatment: The above-mentioned NdFeB fine powder is subjected to orientation forming, sintering and two-stage aging treatment to obtain the final heavy rare earth NdFeB magnet.

[0047] The orientation forming process uses a magnetic field strength of 1.5~2.3T.

[0048] The sintering and two-stage aging treatments are performed as follows: sintering process at 1070~1100℃ for 4~8 hours, first-stage aging process at 870~910℃ for 2~4 hours, and second-stage aging process at 430~510℃ for 2~4 hours.

[0049] Comparative Example 1 The component used is (PrNd). 30.2 B 0.92 Al 0.3 Co 0.3 Cu 0.33 Ga 0.53 Zr 0.32 Fe Bal The main alloy A formula was used to smelt three furnaces of main alloy A flakes, 800 kg per furnace. After the three furnaces of flakes were mixed, they were simultaneously hydrogen-crushed to separate four portions of main alloy A coarse powder. The hydrogen-crushing temperature was 560℃ and the time was 2 hours.

[0050] The component used is (PrNd). 80 Al2Co1Cu 1.5 Ga1Fe Bal The alloy B formula was smelted and hydrogen-crushed to produce alloy B coarse powder. The hydrogen-crushing temperature was 400℃ and the time was 3 hours.

[0051] This comparative air jet milling process does not add alloy B.

[0052] The maximum mass of powder loaded in the grinding chamber of the air jet mill used in this comparative example is 65 kg.

[0053] Take 600 kg of coarse powder of main alloy A and grind it into fine powder using an air jet mill to obtain NdFeB fine powder.

[0054] This comparative example does not distinguish between the fine powder in the early stage and the fine powder in the later stage.

[0055] This comparative example of NdFeB fine powder does not contain alloy B.

[0056] The particle size and composition of NdFeB fine powder were tested, and the NdFeB fine powder was mixed after adding 1.5‰ antioxidant.

[0057] Then, the NdFeB fine powder is oriented, sintered, and aged.

[0058] The orientation forming magnetic field is 2T.

[0059] The sintering and aging process is as follows: 1080℃*6h+900℃*3h+460℃*3h.

[0060] Comparative Example 2 Unlike Comparative Example 1, 600 kg of coarse powder of main alloy A was subjected to air jet milling. When collecting the fine powder from the outlet of the air jet mill, 540 kg of the first-stage fine powder and 60 kg of the second-stage fine powder were stored in different fine powder containers.

[0061] Example 1: Take one portion of the main alloy A coarse powder from Comparative Example 1 and perform an air jet mill. When the fine powder at the outlet of the air jet mill reaches 500 kg, add 1.5 kg of alloy B coarse powder from the secondary feed inlet and grind it with the remaining 100 kg of main alloy A coarse powder, and collect it in the same fine powder hopper.

[0062] Example 2 Take one portion of the coarse powder of main alloy A from Comparative Example 1 and perform an air jet mill. When the fine powder at the outlet of the air jet mill reaches 540 kg, add 0.9 kg of coarse powder of alloy B during the air jet milling process. At the same time, grind it with the remaining 60 kg of coarse powder of main alloy A and collect it in the same fine powder hopper.

[0063] Example 3 Take one portion of the coarse powder of main alloy A from Comparative Example 1 and perform an air jet mill. When the fine powder at the outlet of the air jet mill reaches 580 kg, add 0.3 kg of coarse powder of alloy B during the air jet milling process. At the same time, grind it with the remaining 20 kg of coarse powder of main alloy A and collect it in the same fine powder hopper.

[0064] Example 4 Unlike Example 2, 540 kg of the initial stage fine powder and 60.9 kg of the subsequent stage fine powder were stored in different fine powder containers.

[0065] The particle size and composition of the powder were tested using a laser particle size analyzer and an ICP analyzer. The particle size and composition of the powder are shown in Tables 1 and 2, respectively. The fine powder was used to prepare raw magnet blanks, which were then kept in a constant temperature water bath at 20°C for 5 minutes. Their performance was then tested using a NIM15000 magnetic performance tester, and the results are shown in Table 3.

[0066] Microscopic compositional analysis of the blank cylinders in Examples 1-3 was performed using a combination of scanning electron microscopy and energy-scattering spectroscopy. The triangular grain boundary phases with an area of ​​not less than 100 nm were analyzed using this combined method. 2 Micro-surface scanning elemental analysis was performed at the scanning location to determine the PrNd and Ga contents at that location. The positions of any two triangular grain boundary phases were at least 5 μm apart; the results are shown in Table 4. A schematic diagram of the microstructure analysis test locations for the blank in Example 2 is shown below. Figure 2 .

[0067] Table 1: Particle size distribution of fine powder X10 / μm X90 / μm SMD / μm weight / kg Comparative Example 1 1.76 6.60 3.17 600 Comparative Example 2 1.74 6.59 3.10 540 Comparative Example 2 1.88 6.61 3.28 60 Example 1 1.75 6.59 3.12 601.5 Example 2 1.73 6.62 3.0 600.9 Example 3 1.75 6.57 3.11 600.3 Example 4 (before) 1.73 6.58 3.10 540 After Example 4 1.77 6.60 3.15 60.9 Table 2: Fine powder composition, by mass percentage (wt.%) PrNd B Al Co Cu Ga Zr Comparative Example 1 30.200 0.92 0.3 0.3 0.33 0.53 0.32 Comparative Example 2 30.208 0.92 0.3 0.3 0.33 0.53 0.32 Comparative Example 2 30.100 0.2 0.3 0.3 0.33 0.53 0.32 Example 1 30.319 0.92 0.3 0.3 0.33 0.53 0.32 Example 2 30.272 0.92 0.3 0.3 0.33 0.53 0.32 Example 3 30.233 0.92 0.3 0.3 0.33 0.53 0.32 Example 4 (before) 30.208 0.92 0.3 0.3 0.33 0.53 0.32 After Example 4 30.837 0.92 0.3 0.3 0.33 0.53 0.32 Table 1 shows that the particle size distribution of the fine powder in the first stage (before Comparative Example 2) and the fine powder in the second stage (after Comparative Example 2) is inconsistent. The SMD and X10 of the fine powder in the first stage are smaller than those in the second stage, while the X90 difference is not significant. High-speed airflow drives coarse powder to collide with each other, causing the coarse particles to be further broken down to obtain fine powder. The particle size distribution of the fine powder is determined by the sorting wheel and cyclone separator of the airflow mill. The sorting wheel determines the maximum particle size X90, and the cyclone separator determines the minimum particle size X10. The weight of the powder in the mill chamber affects the collision effect of coarse powder, thus affecting the particle size distribution. As the weight of the powder in the mill chamber gradually decreases, the probability of coarse powder collision decreases, and the X10 and SMD of the powder increase. Furthermore, the rare earth content after Comparative Example 2 is lower than before Comparative Example 2. This is because the main phase with smaller size and more adjacent rare earth phases are crushed to the target particle size first and enter the fine powder in the first stage, resulting in a higher rare earth content in the fine powder in the first stage. The main phase is coarse and the adjacent rare earth phase is less difficult to crush, and it is concentrated in the fine powder in the later stage, which leads to a decrease in the rare earth content in the fine powder in the later stage and a larger particle size.

[0068] Adding alloy B can improve the X10 and SMD of the fine powder in the later stage (after implementation 4). This is because the high rare earth alloy B has high hardness and brittleness, and is easier to break into powder during the air jet milling process. By using the high-speed airflow of the air jet mill, it is mixed with the fine powder of the main alloy A while being crushed, which optimizes the particle size distribution of the fine powder in the later stage of the main alloy A and supplements the rare earth content of the fine powder in the later stage of the main alloy A. The rare earth content is shown in Table 2.

[0069] Table 3: Properties of Fine Powder Formed into Blanks Br / kGs Hcj / kOe SQ / % Comparative Example 1 13.85 18.56 0.932 Comparative Example 2 13.75 19.02 0.955 Comparative Example 2 14.02 16.91 0.877 Example 1 13.79 18.95 0.959 Example 2 13.83 18.88 0.954 Example 3 13.84 18.59 0.941 Example 4 (before) 13.75 19.01 0.956 After Example 4 13.88 18.35 0.963 Table 4: Statistical analysis of the range of microstructure composition of magnets in Examples 1-3 As shown in Table 3, without the addition of alloy B, the squareness SQ of the blank in Comparative Example 1 is less than 0.95. Compared with the fine powder in the later stage of Comparative Example 2 (after Comparative Example 2), the fine powder in the earlier stage of Comparative Example 2 (before Comparative Example 2) has a higher rare earth content and better particle size distribution (X90 / X10≈3.788), resulting in a squareness SQ greater than 0.95. However, the rare earth content in Comparative Example 2 is low, resulting in low coercivity, high remanence, and low squareness.

[0070] In Example 4, after adding alloy B to the fine powder in the later stage, the rare earth content of the powder increased, and the squareness (SQ) of the magnet was greater than 0.95, but the Br content of the magnet decreased significantly. In Examples 1-3, the mass of alloy B added was 0.015 times the mass of the fine powder in the later stage. After adding alloy B, by improving the distribution of rare earth content and particle size in the magnet, the squareness of the blanks in Examples 1-3 was significantly better than that of the blank in Comparative Example 1. However, due to the higher rare earth content in Example 1, the Br content of the magnet decreased more significantly compared to Examples 2 and 3. The squareness of Example 3 is not as good as that of Examples 1 and 2 because the proportion of fine powder in the first stage of Example 3 is too high, while the fine powder in the second stage only accounts for 3.33% of the NdFeB fine powder (40 / 600*100%≈3.33%). As shown in Table 4, the magnet still contains some triangular grain boundary phases with low rare earth and Ga content. The PrNd content range is greater than 12.5wt.%, and the Ga content range is greater than 0.5wt.%, indicating that there is less fine powder in the second stage containing alloy B, and it cannot be completely and uniformly dispersed in the entire main alloy A. Therefore, the proportion of fine powder in the second stage should not be too low, and should not be less than 10%.

Claims

1. A high squareness, weightless rare-earth RTB sintered magnet, characterized in that, The magnet comprises: Re: 29.8–34 wt.%, Re is a light rare earth element, and Re includes at least one or two of Pr and Nd; M: 0.01–0.7 wt.%, M is Cu and / or Al; X: 0.05–0.45 wt.%, X is one or more of Zr, Ti, and Nb; B: 0.86–0.93 wt.%, B is boron; Ga: 0.21–0.65 wt.%; The balance is T, where T is Fe or Fe and Co and other unavoidable impurities; The squareness of the magnet is SQ≥0.95, and the intrinsic coercivity is Hcj≥16.5kOe.

2. The high squareness of the heavy rare-earth RTB sintered magnet as described in claim 1, characterized in that... The high squareness weightless rare earth RTB sintered magnet is based on R2T 14 The sintered NdFeB magnets are composed of B-based main phase particles, with the PrNd content difference between any two triangular grain boundary phases in the magnet being less than 12.5 wt.% and the Ga content difference being less than 0.5 wt.%.

3. The method for preparing a high squareness heavy rare earth-free RTB sintered magnet as described in claim 1 or 2, characterized in that... The method includes the following steps: S1: Take the raw materials of main alloy A and high rare earth alloy B according to the component ratio, and prepare the main alloy A slab and high rare earth alloy B slab respectively by vacuum rapid solidification melting. S2: The main alloy A and high rare earth alloy B flakes from step S1 above are subjected to hydrogen crushing treatment to obtain coarse powder of main alloy A and coarse powder of high rare earth alloy B. S3: The main alloy A coarse powder from step S2 above is subjected to air jet milling. The air jet mill is continuously fed. When the main alloy A coarse powder is ground to the point where the mass of powder collected at the outlet of the air jet mill is A1, high rare earth alloy B coarse powder is added and ground together with the remaining main alloy A coarse powder to obtain NdFeB fine powder with an average surface area particle size (SMD) of 2.5~3.3μm. S4: The NdFeB fine powder obtained in step S3 above is oriented, sintered, and subjected to two-stage aging treatment to obtain a high squareness heavy rare earth RTB sintered magnet.

4. The method as described in claim 3, characterized in that... In step S1, the main alloy A comprises the following components by mass percentage: RL1: 29.5~33 wt.%, RL1 is a light rare earth element, and RL includes at least one or two of Pr and Nd; M1: 0.01~0.65 wt.%, M is Cu and / or Al; X1: 0.1–0.5 wt.%, X is one or more of Zr, Ti, and Nb; B: 0.88–0.935 wt.%, B is boron; Ga: 0.2–0.6 wt.%; The balance is Fe or Fe and Co and other unavoidable impurities; The high rare earth alloy B comprises the following components by mass percentage: RL2: 70~85wt.%, RL2 is a light rare earth element, selected from one or two of Pr and Nd; N: 4~10 wt.%, N is one or more of Al, Cu, and Ga, and must contain Ga; The balance is Fe or Fe and Co and other unavoidable impurities.

5. The method as described in claim 3, characterized in that... The mass of coarse powder of main alloy A is A0. When coarse powder of high rare earth alloy B is added, the mass of the powder produced is A1, and A1 satisfies the following conditions: (a) When A0≥400kg, A1= A0×(80~90%); (b) When 100kg≤A0<400kg, A1=60kg; The mass of the added high rare earth alloy B coarse powder is B. x B x =(0.01~0.02)×(A0-A1).

6. The method as described in claim 3, characterized in that... In step S2, the dehydrogenation temperature of the high rare earth alloy B is 360~460℃; the dehydrogenation temperature of the main alloy A is 400~580℃.

7. The method as described in claim 3, characterized in that... In step S2, the particle size of the coarse powder of main alloy A and coarse powder of high rare earth alloy B is less than 200 μm.

8. The method as described in claim 5, characterized in that... In step S3, the air jet mill continuously discharges material. The discharged NdFeB fine powder is divided into pre-stage fine powder and post-stage fine powder according to the addition time of the high rare earth alloy B coarse powder. The masses of the pre-stage fine powder and the post-stage fine powder are A1 and A0-A1+B, respectively. x The fine powder from the first stage and the fine powder from the second stage are stored in the same fine powder hopper.

9. The method as described in claim 8, characterized in that... In step S3, the air jet mill includes a main feed inlet and a secondary feed inlet. The main alloy A coarse powder is continuously fed from the main feed inlet. When the main alloy A coarse powder is ground to the point where the mass of the fine powder in the first stage of powder discharge is A1, the high rare earth alloy B coarse powder is fed from the secondary feed inlet, so that the high rare earth alloy B coarse powder and the remaining alloy A coarse powder are jointly subjected to air jet milling to obtain the fine powder in the later stage of air jet milling.

10. The method as described in claim 3, characterized in that... The sintering process involves holding the sinter at 1070~1100℃ for 4~8 hours. The two-stage aging process is as follows: the first-stage aging process involves holding the temperature at 870~910℃ for 2~4 hours, and the second-stage aging process involves holding the temperature at 430~510℃ for 2~4 hours.

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