R-t-b rare earth permanent magnet alloy flake and rare earth permanent magnet

Abstract

Disclosed in the present invention are an R-T-B rare earth permanent magnet alloy flake and a rare earth permanent magnet. Columnar grains of the alloy flake satisfy: 0.9≤B1 / B2≤1.1; the roughness of a quenching roller satisfies: 0.9≤R1 / R2≤1.1. In the present invention, by performing laser grinding on the quenching roller, the surface of the quenching roller is treated in a smelting and casting process, so that the roughness of the quenching roller is kept within a relatively stable range, thereby ensuring that the thickness and the cooling rate of the rare earth alloy flake remain basically consistent in the casting process, and thus maintaining the stability of the crystallization time and the grain production time of the rare earth alloy flake and reducing generation of coarse grains and a small amount of impurity phases such as Fe-rich phases in the later stage of casting.

Description

A type of RTB-based rare-earth permanent magnet alloy flakes and rare-earth permanent magnets

[0001] This application claims priority to an earlier application filed on August 27, 2024, with patent application number 2024111782519 entitled "An RTB-based Rare Earth Permanent Magnet Alloy Flake and a Rare Earth Permanent Magnet". The entire contents of the earlier application are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of RTB-based rare earth material preparation, and relates to an RTB-based rare earth permanent magnet alloy flake and a rare earth permanent magnet, particularly to an RTB-based rare earth permanent magnet alloy flake and an RTB-based rare earth permanent magnet prepared from the RTB-based rare earth permanent magnet alloy flake. Background Technology

[0003] RTB-based rare-earth permanent magnets are typical high-performance permanent magnets, where R represents at least one rare-earth element, T represents at least one transition metal element, and B represents boron. In recent years, high-performance new energy vehicles have been continuously developing, and high-performance permanent magnet motors are a key component of these vehicles.

[0004] RTB-based rare-earth permanent magnets with R2T 14 The RTB-based rare earth permanent magnet is predominantly boron (B) phase, and possesses a rare earth element-rich, low-melting-point R phase structure and a B-rich phase. RTB-based rare earth permanent magnets are typically prepared as follows: First, RTB-based rare earth permanent magnet alloy raw materials are mixed and melted according to a specified ratio to obtain alloy steel liquid. Rare earth alloy flakes are then obtained through strip spinning, a process generally carried out in a vacuum or inert gas atmosphere. The cast rare earth alloy flakes are then treated with hydrogen explosion and air jet milling to produce alloy powder, which is subsequently pressed into shape in a magnetic field and sintered at approximately 1000℃~1100℃ to obtain the RTB-based rare earth permanent magnet. Further, the obtained RTB-based rare earth permanent magnet undergoes heat treatment and machining, and may even be subjected to surface treatments such as plating to improve corrosion resistance, depending on actual application requirements.

[0005] In RTB-based rare-earth permanent magnets, the R-rich phase is the fundamental structure and significantly impacts magnet performance. It increases magnet density and strength, eliminates inhomogeneous grain boundaries, reduces antimagnetic domain nucleation sites, and isolates the main phase, thereby enhancing coercivity. If the R-rich phase is unevenly dispersed in the green body before sintering, the magnetization and coercivity of the magnet will decrease. Therefore, ensuring uniform dispersion of the R-rich phase and controlling the consistency of its dispersion during production are crucial for obtaining high-performance permanent magnets.

[0006] To ensure consistency in the magnet production process, the industry often uses sandblasting to blast the outer periphery of the quenching roller. However, sandblasting has the potential to introduce external impurities. Furthermore, the surface condition of the quenching roller changes as the casting time progresses, leading to a change in the cooling rate of the strip compared to the early stage of casting. This results in variations in crystal structure deviation and uniformity, which in turn leads to differences in the distribution of R-rich phase between the early and late stages of casting. Consequently, the uniformity and consistency of R-rich phase dispersion deteriorates during the production of RTB-based rare earth alloy flakes.

[0007] In summary, simply using sandblasting to ensure the uniformity of R-rich phase dispersion to improve magnet performance still has some problems. Summary of the Invention

[0008] To address the problems of existing technologies, this invention provides an RTB-based rare-earth permanent magnet alloy flake and an RTB-based rare-earth permanent magnet. During the production process, the RTB-based rare-earth permanent magnet alloy flake of this invention exhibits better stability in the distribution of the R-rich phase and a more uniform dispersion of the R-rich phase. This results in more stable shrinkage ratios and better performance of the RTB-based rare-earth permanent magnet prepared from the rare-earth permanent magnet alloy flake across different melting furnaces during production. The RTB-based rare-earth permanent magnet also has a more uniform crystal structure, reducing the formation of ultrafine grains during melting and the occurrence of transgranular fracture during powder preparation, leading to higher performance in the RTB-based rare-earth permanent magnet.

[0009] The technical solution of the present invention is as follows:

[0010] An RTB-based rare earth permanent magnet alloy flake, the RTB-based rare earth permanent magnet alloy flake comprising two main surfaces and a plurality of columnar crystals extending radially from one main surface to the other main surface in the thickness direction.

[0011] The two main surfaces are the contact end face of the quenching roller and the free end face opposite to the contact end face of the quenching roller; the thickness refers to the cross-section perpendicular to the two main surfaces.

[0012] The columnar crystals satisfy the following condition: 0.9 ≤ B1 / B2 ≤ 1.1;

[0013] Wherein, B1 is the average short axis length of columnar crystals located in the section perpendicular to the two main surfaces during the early stage of casting, in μm; B2 is the average short axis length of columnar crystals located in the section perpendicular to the two main surfaces during the later stage of casting, in μm.

[0014] The surface roughness of the quenching rollers must satisfy: 0.9 ≤ R1 / R2 ≤ 1.1;

[0015] Where R1 is the surface roughness of the quenching roller in the early stage of casting, in μm; and R2 is the surface roughness of the quenching roller in the later stage of casting, in μm.

[0016] The first third of the casting time is the early stage of casting, and the second third is the late stage of casting.

[0017] For example, if the casting time is 30 minutes, then the first 10 minutes are the early stage of casting, and the last 10 minutes are the late stage of casting.

[0018] In this invention, the two main surfaces refer to the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions, respectively, which are the contact end face of the quenching roller and the free end face opposite to the contact end face of the quenching roller.

[0019] According to an embodiment of the present invention, the contact end face of the quenching roller of the RTB-based rare earth alloy flake is the lower surface of the rare earth permanent magnet alloy flake along the length and width directions. Conversely, the surface that does not contact the quenching roller is the free end face, that is, the free end face opposite to the contact end face of the quenching roller. The contact end face of the quenching roller is also called the roller-attached surface, and the surface opposite to the contact end face of the quenching roller is called the free end face.

[0020] According to an embodiment of the present invention, the cross section is the cross section of the upper and lower surfaces of the rare earth permanent magnet alloy flake along the length and width directions; that is, the end face perpendicular to the roller surface and the free surface of the rare earth alloy flake is the cross section.

[0021] According to an embodiment of the present invention, B1 / B2 is 0.9, 0.95, 1.0, 1.05 or 1.1.

[0022] According to an embodiment of the present invention, R1 / R2 is 0.9, 0.95, 1.0, 1.05 or 1.1.

[0023] When the columnar crystals and roughness meet the above conditions, the present invention has a relatively stable quenching roller roughness in the early and late stages of casting, resulting in a stable cooling rate and a more uniform crystal structure for rare earth permanent magnet alloy flakes.

[0024] This invention employs laser-assisted continuous grinding of the quenching rollers during the casting process, maintaining the rollers' roughness within a relatively stable range throughout the entire casting process. This ensures a consistent cooling rate for the rare earth alloy flakes, thereby stabilizing the crystallization and grain formation time of the flakes and reducing the formation of coarse grains and small amounts of Fe-rich impurities in the later stages of casting. This facilitates the breakage of rare earth permanent magnet alloy flakes, enhances the stability of the powder preparation process, reduces fluctuations in the shrinkage ratio of the green blank during sintering, and is beneficial for controlling the dimensions and properties of the rare earth permanent magnet alloy during production.

[0025] According to an embodiment of the present invention, the plurality of columnar crystals satisfy: 2.0μm≤B1≤5μm; wherein, B1 is the average minor axis length of the plurality of columnar crystals in the cross-section of the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions during the early stage of casting, in μm. For example, B1 can be 2.0μm, 2.3μm, 2.5μm, 2.8μm, 3.0μm, 3.3μm, 3.5μm, 3.8μm, 4.0μm, 4.3μm, 4.5μm, 4.8μm, or 5.0μm. B1 is obtained, for example, by testing as follows: during the early stage of casting, on the contact end face of the quench roll, the number of columnar crystals per unit area is N, and the sum of the minor axis lengths of adjacent columnar crystals along the minor axis direction is ∑B1. Then, the average minor axis length B1 of the columnar crystals on the contact end face of the quench roll is B1=∑B1 / N.

[0026] According to an embodiment of the present invention, the plurality of columnar crystals satisfy: 2.0 μm ≤ B1' ≤ 5 μm; wherein, B1' is the minor axis length of any columnar crystal in the cross-section of the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions during the early stage of casting, in μm. Exemplarily, B1' is 2.0 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.3 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.3 μm, 4.5 μm, 4.8 μm, or 5.0 μm.

[0027] According to an embodiment of the present invention, the plurality of columnar crystals satisfy: 2.0μm≤B2≤5μm; wherein, B2 is the average minor axis length of the plurality of columnar crystals in the cross-section of the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions in the later stage of casting, in μm. Exemplarily, B2 is 2.0μm, 2.3μm, 2.5μm, 2.8μm, 3.0μm, 3.3μm, 3.5μm, 3.8μm, 4.0μm, 4.3μm, 4.5μm, 4.8μm, or 5.0μm. B2 is obtained, for example, by testing as follows: in the later stage of casting, on the contact end face of the quench roll, the number of columnar crystals per unit area is N, and the sum of the minor axis lengths of adjacent columnar crystals along the minor axis direction is ∑B2, then the average minor axis length of the columnar crystals on the contact end face of the quench roll is B2=∑B2 / N.

[0028] According to an embodiment of the present invention, the plurality of columnar crystals satisfy: 2.0 μm ≤ B2' ≤ 5 μm; wherein, B2' is the minor axis length of any columnar crystal in the cross-section of the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions after casting, in μm. Exemplarily, B2' is 2.0 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.3 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.3 μm, 4.5 μm, 4.8 μm, or 5.0 μm.

[0029] According to an embodiment of the present invention, the arbitrary columnar crystals satisfy the following conditions: 2.0 μm ≤ B1' ≤ 5 μm and 2.0 μm ≤ B2' ≤ 5 μm. Studies have found that within this range, the R-rich phase distribution becomes more uniform, easier to pulverize, easier to break during the air jet milling process, and the probability of transgranular fracture during pulverization is reduced, crystal defects are decreased, and the performance of RTB-based rare-earth permanent magnets is improved. When the short axis length of the columnar crystals is greater than 5.0 μm, transgranular fracture increases during the pulverization process of the rare-earth permanent magnet alloy flakes, severely damaging the crystal structure of the RTB-based rare-earth permanent magnets, resulting in poor magnet performance or even performance below market demand; simultaneously, it negatively impacts the pulverization process of the rare-earth permanent magnet alloy flakes, for example, increasing the difficulty of hydrogen explosion, reducing air jet mill output, and significantly affecting production efficiency and magnet quality. When the short axis length of columnar crystals is less than 2.0 μm, a large number of ultrafine crystals will be generated in the rare earth permanent magnet alloy flakes. During the crushing process of the rare earth permanent magnet alloy flakes through an air jet mill, the ultrafine crystals will be converted into ultrafine powder and filtered out. However, the ultrafine powder is usually discarded, resulting in material waste. Furthermore, the ultrafine crystals will also affect the mechanical strength and magnetic properties of the magnet.

[0030] According to an embodiment of the present invention, the roughness of the quenching roller satisfies: 1μm≤R1≤20μm; where R1 is the surface roughness of the quenching roller in the early stage of casting, in μm. For example, R1 can be 1μm, 3μm, 5μm, 8μm, 10μm, 13μm, 15μm, 18μm, or 20μm. R1 is obtained, for example, by testing the roughness of the quenching roller at N locations using a roughness meter in the early stage of casting, and summing the roughness at each point to obtain ∑R1. Therefore, the roughness in the early stage of casting, R1 = ∑R1 / N.

[0031] According to an embodiment of the present invention, the roughness of the quenching roller satisfies: 1μm≤R2≤20μm; where R2 is the surface roughness of the quenching roller in the later stage of casting, in μm. For example, R2 can be 1μm, 3μm, 5μm, 8μm, 10μm, 13μm, 15μm, 18μm, or 20μm. R2 is obtained, for example, by testing the roughness at N locations on the quenching roller in the later stage of casting using a roughness meter, and summing the roughness at each point to obtain ∑R2. Therefore, the roughness in the later stage of casting is R2=∑R2 / N.

[0032] According to an embodiment of the present invention, the roughness of the quenching roller satisfies: 1μm≤R1≤20μm and 1μm≤R2≤20μm. Studies have found that within this range, the cooling effect of the alloy steel liquid is better and more stable during the casting of rare earth permanent magnet alloy flakes, resulting in columnar crystals with short axis lengths that meet requirements and exhibit better consistency. This ensures that after the powder preparation process, the particle size distribution of the magnetic powder is more concentrated, the sintering process has a wider range of applications, and the final magnet has a concentrated grain size and more uniform grain boundary phase composition, which is beneficial for improving the shrinkage ratio and stability of the permanent magnet and enhancing its magnetic properties.

[0033] According to an embodiment of the present invention, in the RTB-based rare-earth permanent magnet alloy flakes, R is selected from at least one of Sm, La, Ce, Y, Nd, Pr, Ho, Gd, Dy, and Tb. In the raw materials used for preparation, the mass content of R is not less than 28 wt% and not more than 35 wt%; preferably not less than 29 wt% and not more than 33 wt%.

[0034] According to an embodiment of the present invention, in the RTB-based rare-earth permanent magnet alloy flakes, T is selected from at least one of Co, Ga, Cu, Al, Nb, Zr, and Ti. In the raw materials used for preparation, the mass content of T is not less than 0.5 wt% and not more than 5 wt%; preferably not less than 1 wt% and not more than 3 wt%.

[0035] According to an embodiment of the present invention, the content of B in the raw materials for preparing the RTB-based rare earth permanent magnet alloy flakes is not less than 0.93 wt% and not more than 1.3 wt%; preferably not less than 0.95 wt% and not more than 1.1 wt%.

[0036] The remainder consists of Fe and unavoidable impurity elements.

[0037] This invention also provides a method for preparing RTB-based rare-earth permanent magnet alloy flakes, the method comprising:

[0038] (1) The raw materials for preparing RTB-based rare earth permanent magnet alloy flakes are mixed and melted according to the proportion to obtain alloy steel liquid;

[0039] (2) The alloy steel liquid from step (1) is poured onto the surface of a rotating quenching roller for a first cooling treatment, and the surface of the quenching roller is laser treated at the same time; then the steel liquid poured onto the surface of the quenching roller is cooled and falls into a water-cooled roller for a second cooling treatment, and finally enters a cooling trolley for a third cooling treatment to prepare the RTB-based rare earth permanent magnet alloy flakes.

[0040] According to an embodiment of the present invention, in step (1), the raw materials for preparing rare earth permanent magnet alloy flakes are not specifically defined, and can be any raw materials known in the art for preparing rare earth permanent magnet alloy flakes. Specifically, the raw materials for preparing rare earth permanent magnet alloy flakes can be selected according to the composition of the target RTB system rare earth permanent magnet.

[0041] According to an embodiment of the present invention, in step (1), the melting temperature is 1200-1500℃, and the melting time (the holding time after the raw material is completely melted) is 5-60 min.

[0042] According to an embodiment of the present invention, in step (2), the rotational speed of the quenching roller is ≥1.0 m / s, for example, 1.0-20 m / s; after the alloy steel liquid is poured onto the surface of the rotating quenching roller, the alloy steel liquid will undergo a cooling process on the surface of the quenching roller.

[0043] According to an embodiment of the present invention, in step (2), the temperature of the surface of the quenching roller is maintained at 10 to 50°C by circulating cooling water into the quenching roller.

[0044] According to an embodiment of the present invention, in step (2), a laser is used to roughen the surface of the quenching roller so that the roughness R of the quenching roller is 1 to 20, in μm, and 0.9≤R1 / R2≤1.1, where R1 is the surface roughness of the quenching roller in the early stage of casting and R2 is the surface roughness of the quenching roller in the later stage of casting.

[0045] According to an embodiment of the present invention, in step (2), the irradiation angle of the laser treatment is 20 to 80 degrees.

[0046] According to an embodiment of the present invention, in step (2), the irradiation speed of the laser treatment is 50 to 900 mm / sec.

[0047] According to an embodiment of the present invention, in step (2), the power energy density of the laser treatment is 0.5 to 50 GW / cm². 2 .

[0048] According to an embodiment of the present invention, in step (2), the laser treatment is repeated 10 to 25 times.

[0049] According to an embodiment of the present invention, in step (2), the temperature of the cooling water in the water-cooled drum is 10 to 40°C.

[0050] According to an embodiment of the present invention, in step (2), the temperature of the cooling water on the cooling trolley is 10 to 60°C.

[0051] This invention provides a rare earth permanent magnet alloy flake, which is prepared by the above method.

[0052] The present invention also provides an RTB-based rare earth permanent magnet, which is prepared using the above-mentioned rare earth permanent magnet alloy flakes as raw materials.

[0053] This invention also provides a method for preparing the above-mentioned RTB-based rare-earth permanent magnet, the method comprising the following steps:

[0054] (a) The above rare earth permanent magnet alloy flakes were hydrogen-exploded and then ground by air jet mill to obtain magnetic powder with a particle size range of 1-10 μm and an average particle size of 2.0-3.5 μm; an antioxidant was added to the magnetic powder and mixed evenly.

[0055] (b) The magnetic powder from step (a) is pressed into a green body under a nitrogen atmosphere and a magnetic field greater than 1.8T.

[0056] (c) Place the green blank from step (b) into a vacuum sintering furnace for sintering treatment;

[0057] (d) The green body after sintering in step (c) is subjected to a first-stage aging treatment and a second-stage aging treatment to obtain the RTB-based rare earth permanent magnet.

[0058] According to an embodiment of the present invention, in step (a), an antioxidant (such as a fatty acid ester) accounting for 0.02-5 wt% of the total mass of the magnetic powder is added to the magnetic powder, and the mixture is continuously mechanically stirred for 3-6 hours until it is uniformly dispersed.

[0059] According to an embodiment of the present invention, in step (b), the magnetic powder from step (a) is pressed into shape under a nitrogen atmosphere and a magnetic field strength of 2-5T, with the magnetic field orientation direction.

[0060] According to an embodiment of the present invention, in step (b), the content of impurity elements in the green body satisfies the following: 100ppm≤N content≤1400ppm, 200ppm≤H content≤3700ppm.

[0061] Preferably, the nitrogen content is 120ppm, 200ppm, 300ppm, 400ppm, 500ppm, 800ppm, 1000ppm, 1200ppm, 1300ppm or 1400ppm.

[0062] Preferably, the content of H element is 200ppm, 300ppm, 400ppm, 500ppm, 800ppm, 1000ppm, 1200ppm, 1500ppm, 1800ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm or 3700ppm.

[0063] According to an embodiment of the present invention, in step (c), the sintering treatment involves heating to 260-400℃ (e.g., 260℃, 280℃, 300℃, 320℃, 350℃, 360℃, 380℃, or 400℃) at a heating rate of 3-9℃ / min, holding at 260-400℃ for 40-70min (e.g., 40min, 50min, 60min, or 70min), and then heating to 680-730℃ (e.g., 680℃, 690℃, or 400℃) at a heating rate of 3-7℃ / min. 700℃, 710℃, 720℃ or 730℃), hold at 680-730℃ for 60-100min (e.g. 60min, 70min, 80min, 90min or 100min), then raise the temperature to 1050-1100℃ at a rate of 5-8℃ / min (e.g. 1050℃, 1060℃, 1070℃, 1080℃, 1090℃ or 1100℃), and hold at 1050-1100℃ for 3-6h (e.g. 3h, 4h, 5h or 6h).

[0064] According to an embodiment of the present invention, in step (c), the sintering process is carried out in a vacuum environment.

[0065] According to an embodiment of the present invention, in step (c), the sintering process is followed by cooling to room temperature.

[0066] According to an embodiment of the present invention, in step (d), the temperature of the first-stage aging treatment is 790-920℃ (e.g., 790℃, 800℃, 820℃, 850℃, 860℃, 880℃, 900℃ or 920℃), and the time of the first-stage aging treatment is 3-6h (e.g., 3h, 4h, 5h or 6h); the temperature of the second-stage aging treatment is 500-540℃ (e.g., 500℃, 510℃, 520℃, 530℃ or 540℃), and the time of the second-stage aging treatment is 2-4h (e.g., 2h, 3h or 4h).

[0067] According to an embodiment of the present invention, in step (d), after the first-stage aging treatment, the temperature is cooled to room temperature, and then the temperature is increased to perform the second-stage aging treatment.

[0068] The present invention also provides an RTB-based rare-earth permanent magnet prepared by the above method.

[0069] The beneficial effects of this invention are:

[0070] This invention provides an RTB-based rare-earth permanent magnet alloy flake, whose columnar crystals satisfy the following condition: 0.9 ≤ B1 / B2 ≤ 1.1, and the roughness of the quenching roller satisfies the following condition: 0.9 ≤ R1 / R2 ≤ 1.1. When the columnar crystals and roughness respectively meet the above conditions, the rare-earth permanent magnet alloy flake of this invention exhibits relatively stable quenching roller roughness, cooling rate, and a more uniform crystal structure in the early and late stages of casting. Specifically, during the production process, the RTB-based rare-earth permanent magnet alloy flake of this invention exhibits better stability in the distribution of the R-rich phase and more uniform dispersion of the R-rich phase. This results in more stable shrinkage ratios and better performance of the RTB-based rare-earth permanent magnets prepared using the rare-earth permanent magnet alloy flakes across different melting furnaces. The more uniform crystal structure of the RTB-based rare-earth permanent magnets reduces the formation of ultrafine crystals during melting and the occurrence of transgranular fracture during powder preparation, leading to higher performance of the RTB-based rare-earth permanent magnets.

[0071] This invention employs laser grinding of the quench roll surface during the smelting and casting process. This treatment maintains the quench roll's roughness within a relatively stable range, ensuring consistent thickness and cooling rate of the rare earth alloy flakes during casting. This, in turn, stabilizes the crystallization and grain formation time of the rare earth alloy flakes, reducing the formation of coarse grains and small amounts of Fe-rich impurities in the later stages of casting. It also facilitates the breakage of rare earth permanent magnet alloy flakes, enhances the stability of the powder preparation process, reduces fluctuations in the shrinkage ratio of the green blank during sintering, and is beneficial for controlling the size and performance of RTB-based rare earth permanent magnets during production. Detailed Implementation

[0072] The technical solution 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 merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection 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.

[0073] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0074] The neodymium iron boron magnet raw materials used in all embodiments and comparative examples of this invention use the same formula.

[0075] Example 1

[0076] (1) The raw materials for preparing RTB-based rare earth permanent magnet alloy flakes were mixed and melted according to the specified ratio to obtain alloy steel liquid. The raw material ratio was: NdPr 31.1wt%, B 0.99wt%, Zr 0.18wt%, Ga 0.15wt%, Al 0.4wt%, Cu 0.15wt%, Co 1.52wt%, with the remainder being Fe and unavoidable impurities, wherein the purity of each raw material was ≥99%. The melting temperature was 1450℃, and the melting time (the holding time after the raw materials were completely melted) was 30min.

[0077] (2) The molten steel from step (1) is poured onto the surface of the rotating quenching roller for a first cooling treatment, while the surface of the quenching roller is continuously laser-polished; then the molten steel poured onto the surface of the quenching roller is cooled and falls into the water-cooled roller for a second cooling treatment, and finally enters the cooling trolley for a third cooling treatment. (3) In step (2), the rotation speed of the quenching roller is 1.5 m / s.

[0078] In step (2), the temperature of the cooling water for the quenching roller is 15°C.

[0079] In step (2), the surface roughness R1 of the quenching roller is 8, in μm, and R1 / R2 = 0.98, where R1 is the surface roughness of the quenching roller in the early stage of casting and R2 is the surface roughness of the quenching roller in the later stage of casting.

[0080] In step (2), the laser treatment irradiation angle is 25 degrees.

[0081] In step (2), the irradiation speed of the laser treatment is 100 mm / sec.

[0082] In step (2), the power energy density of the laser treatment is 10 GW / cm². 2 .

[0083] In step (2), the laser treatment is repeated 10 times.

[0084] Example 2

[0085] (1) Same as step (1) in Example 1.

[0086] (2) The molten steel from step (1) is poured onto the surface of the rotating quench roller for a first cooling treatment, while the surface of the quench roller is continuously laser polished. Then the molten steel poured onto the surface of the quench roller is cooled and falls into the water-cooled roller for a second cooling treatment, and finally enters the cooling trolley for a third cooling treatment.

[0087] (3) In step (2), the rotation speed of the quenching roller is 1.5 m / s.

[0088] In step (2), the cooling water temperature of the quench roller is 15℃.

[0089] In step (2), the surface roughness R1 of the quench roll is 10, in μm, and R1 / R2 = 1.02, where R1 is the surface roughness of the quench roll in the early stage of casting and R2 is the surface roughness of the quench roll in the later stage of casting.

[0090] In step (2), the laser treatment irradiation angle is 50 degrees.

[0091] In step (2), the irradiation speed of the laser treatment is 400 mm / sec.

[0092] In step (2), the power energy density of the laser treatment is 25 GW / cm². 2 .

[0093] In step (2), the laser treatment is repeated 15 times.

[0094] Example 3

[0095] (1) Same as step (1) in Example 1.

[0096] (2) The molten steel from step (1) is poured onto the surface of the rotating quench roller for a first cooling treatment, while the surface of the quench roller is continuously laser polished. Then the molten steel poured onto the surface of the quench roller is cooled and falls into the water-cooled roller for a second cooling treatment, and finally enters the cooling trolley for a third cooling treatment.

[0097] (3) In step (2), the rotation speed of the quenching roller is 1.5 m / s.

[0098] And / or, in step (2), the temperature of the cooling water for the quenching roller is 15°C.

[0099] And / or, in step (2), the roughness R1 of the quench roll is 15, in μm, and R1 / R2 = 1, where R1 is the surface roughness of the quench roll in the early stage of casting and R2 is the roughness of the quench roll in the later stage of casting.

[0100] And / or, in step (2), the irradiation angle of the laser treatment is 75 degrees.

[0101] And / or, in step (2), the irradiation speed of the laser treatment is 800 mm / sec.

[0102] And / or, in step (2), the power energy density of the laser treatment is 42 GW / cm². 2 .

[0103] And / or, in step (2), the laser treatment is repeated 25 times.

[0104] Comparative Example 1

[0105] (1) Polish the cooling copper roller with 80-grit sandpaper. The roughness R1 of the quench roller is 2, and R1 / R2 = 1.38.

[0106] (2) The raw material was melted and refined at a constant power of 550kW; the raw material was the same as that in step (1) of Example 1.

[0107] (3) The molten and refined steel is poured into the polished cooling copper roller. The steel poured onto the surface of the quench roller is then cooled once and falls into the water-cooled roller for secondary cooling. Finally, it enters the cooling trolley for tertiary cooling.

[0108] Comparative Example 2

[0109] (1) Use sandblasting equipment to sandblast and polish the cooling copper roller. The abrasive used in sandblasting is 10-mesh quartz sand. The roughness R1 of the quenching roller is 15, and R1 / R2 = 1.25.

[0110] (2) The raw material was melted and refined at a constant power of 550kW; the raw material was the same as that in step (1) of Example 1.

[0111] (3) The molten and refined steel liquid is poured into the polished cooling copper roller. The steel liquid cast onto the surface of the quench roller is cooled once and falls into the water-cooled roller for secondary cooling. Finally, it enters the cooling trolley for tertiary cooling.

[0112] Comparative Example 3

[0113] (1) Use sandblasting equipment to sandblast and polish the cooling copper roller. The abrasive used in sandblasting is 50-mesh steel grit. The roughness R1 of the quenching roller is 10, and R1 / R2 = 1.42.

[0114] (2) The raw materials are melted and refined at a constant power of 550kW;

[0115] (3) The molten and refined steel liquid is poured into the polished cooling copper roller. The steel liquid cast onto the surface of the quench roller is cooled once and falls into the water-cooled roller for secondary cooling. Finally, it enters the cooling trolley for tertiary cooling.

[0116] Rare earth permanent magnets were prepared from the flakes prepared in Examples 1-3 and Comparative Examples 1-3. The specific preparation process of the rare earth permanent magnets was described in paragraphs 74-77 of the specification of patent CN117174420A, and the blank size and magnetic properties were tested.

[0117] After polishing and etching, the cross-sections of the rare earth permanent magnet alloy flakes prepared in Examples 1-3 and Comparative Examples 1-3 were observed using a scanning electron microscope to examine their internal structure; the width and length of the columnar crystals were measured using a 400x scanning electron microscope image field of view combined with a scale.

[0118] The shrinkage ratio is calculated as blank size / pressed size. The ratio of blank size to pressed size in the three directions of product length, height, and orientation is the shrinkage ratio.

[0119] The test results are shown in Table 1.

[0120] Table 1

[0121] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An RTB-based rare-earth permanent magnet alloy scale, characterized in that, The RTB-based rare-earth permanent magnet alloy flakes include two main surfaces and several columnar crystals that extend radially from one main surface to the other in the thickness direction. The two main surfaces are the contact end face of the quenching roller and the free end face opposite to the contact end face of the quenching roller; the thickness refers to the cross-section perpendicular to the two main surfaces. The columnar crystals satisfy the following condition: 0.9 ≤ B1 / B2 ≤ 1.1; Wherein, B1 is the average short axis length of columnar crystals located in the section perpendicular to the two main surfaces during the early stage of casting, in μm; B2 is the average short axis length of columnar crystals located in the section perpendicular to the two main surfaces during the later stage of casting, in μm. The surface roughness of the quenching rollers must satisfy: 0.9 ≤ R1 / R2 ≤ 1.1; Where R1 is the surface roughness of the quenching roller in the early stage of casting, in μm; and R2 is the surface roughness of the quenching roller in the later stage of casting, in μm. The first third of the casting time is the early stage of casting, and the second third is the late stage of casting.

2. The alloy flakes according to claim 1, characterized in that, The columnar crystals satisfy the following condition: 2.0μm≤B1≤5μm; where B1 is the average short axis length of the columnar crystals in the cross-section of the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions in the early stage of casting, in μm. And / or, the plurality of columnar crystals satisfy: 2.0μm≤B1'≤5μm; wherein, B1' is the short axis length of any columnar crystal in the cross-section of the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions in the early stage of casting, in μm.

3. The alloy flakes according to claim 1, characterized in that, The columnar crystals satisfy the following condition: 2.0μm≤B2≤5μm; where B2 is the average short axis length of the columnar crystals in the cross-section of the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions in the later stage of casting, in μm. And / or, the plurality of columnar crystals satisfy: 2.0μm≤B2'≤5μm; wherein, B2' is the short axis length of any columnar crystal in the cross-section of the upper and lower surfaces of the rare earth permanent magnet alloy flakes along the length and width directions in the later stage of casting, in μm.

4. The alloy flakes according to claim 1, characterized in that, The surface roughness of the quenching roller satisfies: 1μm≤R1≤20μm; where R1 is the surface roughness of the quenching roller in the early stage of casting, in μm. And / or, the roughness of the quenching roller satisfies: 1μm≤R2≤20μm; where R2 is the surface roughness of the quenching roller in the later stage of casting, in μm.

5. The method for preparing RTB-based rare-earth permanent magnet alloy flakes according to any one of claims 1-4, characterized in that, The method includes: (1) The raw materials for preparing RTB-based rare earth permanent magnet alloy flakes are mixed and melted according to the proportion to obtain alloy steel liquid; (2) The alloy steel liquid from step (1) is poured onto the surface of a rotating quenching roller for a first cooling treatment, and the surface of the quenching roller is laser treated at the same time; then the steel liquid poured onto the surface of the quenching roller is cooled and falls into a water-cooled roller for a second cooling treatment, and finally enters a cooling trolley for a third cooling treatment to prepare the RTB-based rare earth permanent magnet alloy flakes.

6. The method according to claim 5, characterized in that, In step (2), the rotational speed of the quenching roller is ≥1.0m / s.

7. The method according to claim 5, characterized in that, In step (2), the surface of the quenching roller is roughened by laser so that the roughness R of the quenching roller is 1 to 20, in μm, and 0.9≤R1 / R2≤1.1, where R1 is the surface roughness of the quenching roller in the early stage of casting and R2 is the surface roughness of the quenching roller in the later stage of casting. And / or, in step (2), the irradiation angle of the laser treatment is 20 degrees to 80 degrees; And / or, in step (2), the irradiation speed of the laser treatment is 50 to 900 mm / sec; And / or, in step (2), the power energy density of the laser treatment is 0.5–50 GW / cm². 2 ; And / or, in step (2), the laser treatment is repeated 10 to 25 times.

8. An RTB-based rare-earth permanent magnet, characterized in that, The RTB-based rare earth permanent magnet is prepared using rare earth permanent magnet alloy flakes obtained by the method described in any one of claims 1-4 or any one of claims 5-7 as raw materials.

9. The method for preparing the RTB-based rare-earth permanent magnet according to claim 8, the method comprising the following steps: (a) The above rare earth permanent magnet alloy flakes were hydrogen-exploded and then ground by air jet mill to obtain magnetic powder with a particle size range of 1-10 μm and an average particle size of 2.0-3.5 μm; an antioxidant was added to the magnetic powder and mixed evenly. (b) The magnetic powder from step (a) is pressed into a green body under a nitrogen atmosphere and a magnetic field greater than 1.8T. (c) Place the green blank from step (b) into a vacuum sintering furnace for sintering treatment; (d) The green body after sintering in step (c) is subjected to a first-stage aging treatment and a second-stage aging treatment to obtain the RTB-based rare earth permanent magnet.

10. The RTB-based rare-earth permanent magnet prepared by the method of claim 9.

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