Hot-rolled rare earth permanent magnet and method of manufacturing

Abstract

The present invention relates to a hot-rolled rare earth permanent magnet and a preparation method thereof, belonging to the field of vacuum hot rolling technology of rare earth permanent magnet materials. A method is proposed in which a hot-pressed full-density RE-Ga-M-Fe-B permanent magnet is vacuum hot-rolled without a coating to allow the grains to flow, and the magnet is finally oriented parallel to the rolling direction. This method solves the problem that the existing thermorheological method for preparing Nd-Fe-B permanent magnets cannot be mass-produced. A hot-rolled rare earth permanent magnet, the composition formula of which is RE a Ga b M c Fe d B e , where RE is one or more of Nd, Pr, Ce, La, or Dy; M is one or more of Co, Cu, Al, Zr, Ti, or Nb; and the mass fractions (in percentage) are: 28.0 ≤ a ≤ 32.0; 0.2 ≤ b ≤ 0.8; 3.0 ≤ c ≤ 6.0; 0.8 ≤ e ≤ 1.1; and d = 100-a-b-c-e. This results in high-performance plate-, tile-, and tube-shaped rolled permanent magnets with high density, high orientation, good corrosion resistance, and excellent temperature stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum hot rolling of rare earth permanent magnet materials, and particularly relates to a hot-rolled rare earth permanent magnet and a preparation method. BACKGROUND

[0002] As a functional material, the rare earth iron-based permanent magnet is widely used in high-tech and emerging industries such as wind power generation, propulsion motor, artificial intelligence micro motor, and has become an important material basis indispensable to social progress. At present, the commercial production of Nd-Fe-B permanent magnets mainly has three preparation methods of powder metallurgy sintering, powder bonding and rapid quenching powder hot extrusion rheology.

[0003] The sintering technology is the main method for producing Nd-Fe-B permanent magnets, and the annual production in China is about 200,000 tons, but the sintering technology produces 20% to 50% of processing waste; the rapid quenching powder bonding technology is the second, and the annual production is about 12,000 tons, and the bonded magnets will mix with the adhesive, and the magnetic properties are low; and the rapid quenching powder hot extrusion rheology technology can only produce ring-shaped magnets due to the limitation of the pressing process conditions, and the annual production is about 1,000 tons. With the development of market demand, the demand for hot extrusion magnets is also increasing, and the pressing process in hot extrusion greatly limits the industrial production of this technology.

[0004] The hot rolling process is very mature in Daye metallurgy industry, which can significantly reduce energy consumption and cost, and can improve the processing performance of metals and alloys, that is, the coarse grains in the casting state are broken, the cracks are significantly healed, the casting defects are reduced or eliminated, the casting structure is changed into a deformed structure, and the processing performance of the alloy is improved. Therefore, the hot rolling process is used for the hot rheological forming of magnetic powder, but based on the particularity that the neodymium iron boron material is easily oxidized, the existing technology adopts the method of coating the alloy powder for hot rolling. In this method, the alloy powder or cold pressed powder blank is coated with metal, vacuumized, heat sealed, and then the vacuum sealed magnet is heated and rolled in the atmosphere. The highest magnetic performance obtained by this method is 30.1 MGOe. Since the vacuum coating process of this method is complicated and can only be prepared in the laboratory, it is difficult to form large-scale industrial production, and the heating of the blank in the sleeve is difficult to control, resulting in low performance of the magnet after hot rolling. SUMMARY

[0005] In view of the above analysis, the embodiments of the present application aim to provide a hot-rolled rare earth permanent magnet and a preparation method, to solve at least one of the problems of the existing hot rheological method for preparing rare earth iron-based permanent magnets, such as large-scale production, low magnet performance, and complex processing process.

[0006] In one aspect, the embodiments of the present application provide a hot-rolled rare earth permanent magnet, and the composition of the permanent magnet has a general formula of RE a Ga b Mc Fe d B e , wherein RE is one or more of Nd, Pr, Ce, La or Dy; M is one or more of Co, Cu, Al, Zr, Ti, Nb; the mass fraction is expressed in percentage as follows: 28.0≤a≤32.0; 0.2≤b≤0.8; 3.0≤c≤6.0; 0.8≤e≤1.1; d=100-abce.

[0007] On the other hand, an embodiment of the present invention further provides a method for preparing a hot-rolled rare earth permanent magnet, which is prepared according to the above-mentioned permanent magnet composition formula, comprising the following steps:

[0008] Step 1, preparation of RE-Ga-M-Fe-B rapid quenching magnetic powder;

[0009] Step 2, cold molding: the rapid quenching magnetic powder prepared in step 1 is evenly loaded into a cold press mold for cold molding at a pressure greater than 100 MPa to obtain a blank with a density of more than 60%;

[0010] Step 3, hot isostatic pressing: under vacuum or argon protection, the blank of step 2 is subjected to hot isostatic pressing to obtain an isotropic full-density blank with a density of 100%;

[0011] Step 4, uncoated vacuum hot rolling: The full-density blank obtained in step 3 is continuously vacuum hot rolled without coating at a temperature of 800-900° C. to obtain a hot-rolled permanent magnet product.

[0012] Preferably, the method for preparing the RE-Ga-M-Fe-B rapid quenching magnetic powder in step 1 comprises the following steps:

[0013] S1-1. According to the designed composition ratio, the alloy raw materials are subjected to vacuum induction melting at a melting temperature of 1400° C. to 1500° C. to obtain an alloy ingot;

[0014] S1-2, rapidly quenching the alloy ingot obtained in S1 to obtain a rapidly quenched thin strip, wherein the roller surface linear speed of the rapidly quenching roller is 25-50 m / s, and the average grain size of the rapidly quenched thin strip is 30-300 nm;

[0015] S1-3, mechanically crushing the rapidly quenched thin strip obtained in S2 into rapidly quenched magnetic powder with an average particle size of 100-200 mesh.

[0016] Specifically, the full-density blank in step 3 is in the shape of a plate, a tile or a tube.

[0017] Furthermore, the hot isostatic pressing process parameters in step 3 are: temperature 700-750° C., and pressure 60-70 MPa.

[0018] Furthermore, the unclad vacuum hot rolling in step 4 comprises the following steps:

[0019] S4-1, heating: the full density blank obtained in step 3 is placed in a continuous hot rolling equipment, and vacuumed to 10 -3 Pa and filled with argon, then quickly heated to 800 °C;

[0020] S4-2, hot rolling: the heated full density blank enters the vacuum rolling mill chamber and is hot rolled at 800-850°C to obtain the rolled permanent magnet;

[0021] S4-3, leveling and bending: After rolling, the permanent magnet enters the leveling roller and the bending roller for leveling and bending;

[0022] S4-4. Cooling: After flattening and flat bending, the magnet enters a cooling chamber and is cooled to room temperature at a rate of 5-10°C / min to obtain anisotropic hot-rolled permanent magnet products with the required shape and size and orientation parallel to the rolling direction.

[0023] It should be noted that the heating method in step S4-1 is vacuum induction heating.

[0024] Preferably, during the hot rolling process in step S4-2, the rolling force of the roller is 2 to 5 tons and the roller speed is 2 to 5 meters per minute.

[0025] Specifically, during the hot rolling process of step S4-2, the reduction ratio of the full-density blank is between 60% and 75%.

[0026] For example, the process conditions of the leveling and bending process in step S4-3 are: roller speed 2 to 10 m / min, roller spacing size is the same as the hot rolling roller spacing size, and temperature is 800 to 850°C.

[0027] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0028] 1. The present invention optimizes the design of rare earth permanent magnet components to improve the high-temperature thermal deformation ability of the permanent magnet, enabling continuous hot rolling operations and ensuring the performance and quality of the permanent magnet during the continuous hot rolling process.

[0029] 2. The method provided by the present invention for preparing permanent magnets by vacuum hot rolling RE-Ga-M-Fe-B full-density blanks without coating has a simple process, and the blank temperature is easy to control and heated evenly, thereby solving the problem that grain rheology permanent magnets cannot be produced on an industrial scale, and obtaining high-performance permanent magnets in the form of plates, tiles, and tubes with high density, high orientation, good corrosion resistance, and good temperature stability.

[0030] 3. This invention utilizes a vacuum and inert gas atmosphere, eliminating the need for a coating process. The hot rolling process, encompassing heating, rolling, leveling and bending correction, and cooling, can be performed continuously and rapidly, enabling large-scale industrial production. Compared to traditional sintering processes, this method offers a shorter process, faster magnet production, near-net-shape formation, and lower costs. Due to the near-net-shape size and shape achieved with this vacuum hot rolling technology and its reasonable price-performance ratio, it is highly competitive compared to traditional bonded magnet production. The vacuum hot-rolled RE-Ga-M-Fe-B rheological permanent magnets produced using this method have a maximum magnetic energy product of ≥38 MGOe.

[0031] 4. The present invention optimizes and precisely controls parameters such as vacuum hot rolling temperature, speed, and roll reduction force to control the full-density blank reduction shrinkage ratio between 60% and 75%. The entire hot rolling process is carried out continuously and rapidly, ultimately obtaining high-performance hot-rolled permanent magnets with grain rheological orientation.

[0032] 5. The present invention continuously performs cold molding and hot isostatic pressing, and precisely controls the temperature and pressure of the hot isostatic pressing process to press the magnetic powder into an isotropic blank with qualified composition and high density (>99%), so as to meet the billet density requirement required by the subsequent hot rolling process.

[0033] 6. The present invention adopts induction heating in the hot rolling process to quickly heat the blank to the required temperature, effectively avoiding the long thermal diffusion time that causes the magnet grains to grow and affects the magnetic properties.

[0034] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages may become obvious from the description or be understood through practice of the present invention. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention are described in detail below. Together with the embodiments of the present invention, they are used to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0036] On the one hand, a specific embodiment of the present invention discloses a hot-rolled rare earth permanent magnet, wherein the composition formula of the permanent magnet is RE a Ga b M c Fe d B e , wherein RE is one or more of Nd, Pr, Ce, La or Dy; M is one or more of Co, Cu, Al, Zr, Ti, Nb; the mass fraction is expressed in percentage as follows: 28.0≤a≤32.0; 0.2≤b≤0.8; 3.0≤c≤6.0; 0.8≤e≤1.1; d=100-abce.

[0037] Optimizing the design of rare earth permanent magnet composition fully utilizes the combined properties of rare earth and ferromagnetic elements to enhance the high-temperature thermal deformation capability of the permanent magnet, enabling continuous hot rolling operations and ensuring the performance and quality of the permanent magnet during the continuous hot rolling process. In particular, precise control of the Ga content can significantly improve the alloy's rolling characteristics.

[0038] On the other hand, a specific embodiment of the present invention further discloses a method for preparing a hot-rolled rare earth permanent magnet, which is prepared according to the above-mentioned permanent magnet composition formula, comprising the following steps:

[0039] Step 1, preparation of RE-Ga-M-Fe-B rapid quenching magnetic powder;

[0040] Step 2, cold molding: the rapid quenching magnetic powder prepared in step 1 is evenly loaded into a cold press mold for cold molding at a pressure greater than 100 MPa to obtain a blank with a density of more than 60%;

[0041] Step 3, hot isostatic pressing: Under vacuum or argon protection, the blank obtained in step 2 is subjected to hot isostatic pressing to obtain an isotropic full-density blank;

[0042] Step 4, uncoated vacuum hot rolling: The full-density blank obtained in step 3 is continuously vacuum hot rolled without coating at a temperature of 800-900° C. to obtain a hot-rolled permanent magnet product.

[0043] Specifically, in step 1, the method for preparing the RE-Ga-M-Fe-B rapid quenching magnetic powder comprises the following steps:

[0044] S1-1. According to the designed composition ratio, the alloy raw materials are subjected to vacuum induction melting at a melting temperature of 1400° C. to 1500° C. to obtain an alloy ingot;

[0045] S1-2, rapidly quenching the alloy ingot obtained in S1 to obtain a rapidly quenched thin strip, wherein the roller surface linear speed of the rapidly quenching roller is 25-50 m / s, and the average grain size of the rapidly quenched thin strip is 30-300 nm;

[0046] S1-3, mechanically crushing the rapidly quenched thin strip obtained in S2 into rapidly quenched magnetic powder with an average particle size of 100-200 mesh.

[0047] For example, the full-density blank in step 3 is in the shape of a plate, tile or tube. The permanent magnet preparation method of the present invention can be used to prepare tile-shaped or tube-shaped permanent magnets with complex grain orientations and difficult to coat, while still achieving good magnetic properties.

[0048] Furthermore, the hot isostatic pressing process parameters in step 3 are: temperature 700-750°C, pressure 60-70 MPa. Preferably, the hot isostatic pressing temperature is 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, and the pressure is 60 MPa, 65 MPa, or 70 MPa.

[0049] To obtain the desired final size and shape of hot-rolled permanent magnet products, it is first necessary to obtain a cold-molded blank of the corresponding shape and size, and to achieve a blank density of at least 60%, preparing for the next hot isostatic pressing process to further increase the blank density to >99%. The blank density required for the hot rolling process must reach 100% to ensure high magnetic properties. The cold-molded blank density can only reach 60-70%, so hot isostatic pressing of the cold-molded blank is required to further improve the density. If the temperature and pressure during the hot isostatic pressing process are too low, the required density will not be achieved. If the temperature and pressure are too high, the rare earth liquid phase will overflow, affecting the magnetic properties.

[0050] Furthermore, the unclad vacuum hot rolling in step 4 comprises the following steps:

[0051] S4-1, heating: the full density blank obtained in step 3 is placed in a continuous hot rolling equipment, and vacuumed to 10 -3 Pa and filled with argon, then quickly heated to 800 °C;

[0052] S4-2, hot rolling: the heated full density blank enters the vacuum rolling mill chamber and is hot rolled at 800-850°C to obtain the rolled permanent magnet;

[0053] S4-3, leveling and bending: After rolling, the permanent magnet enters the leveling roller and the bending roller for leveling and bending;

[0054] S4-4. Cooling: After flattening and flat bending, the magnet enters a cooling chamber and is cooled to room temperature at a rate of 5-10°C / min to obtain anisotropic hot-rolled permanent magnet products with the required shape and size and orientation parallel to the rolling direction.

[0055] It is worth noting that the heating method in step S4-1 is vacuum induction heating. Vacuum induction heating has a fast heating speed, which prevents the magnet grains from growing during the heating process and affecting the magnetic properties.

[0056] Furthermore, during the hot rolling process in step S4-2, the roll reduction force is 2 to 5 tons, and the roll speed is 2 to 5 meters per minute. Preferably, the roll reduction force is 2 tons, 3 tons, 4 tons, or 5 tons, the roll speed is 2, 3, 4, or 5 meters per minute, and the hot rolling temperature is 800, 810, 820, 830, 840, or 850°C.

[0057] Specifically, during the hot rolling process of step S4-2, the reduction ratio of the full-density blank is between 60% and 75%. Preferably, the reduction ratio of the full-density blank is 60%, 65%, 70%, or 75%.

[0058] In step S4-2, during the hot rolling process, the hot rolling temperature, roller pressure, and hot rolling speed must be properly controlled. Excessively high temperatures will cause rapid grain growth, affecting coercivity, while lower temperatures will affect grain rotation and orientation. This is especially true for tile-shaped and tubular permanent magnet blanks, which are constrained by the rolling force and have complex grain orientation, resulting in low remanent magnetic properties. Excessively high hot rolling speeds, i.e., excessive deformation rates, prevent some grains from having time to orient themselves, affecting magnetic properties. Excessively low roller pressure will prevent the permanent magnet from achieving a reduction ratio of 60-75%, affecting magnetic properties.

[0059] It should be noted that the process conditions of the leveling and bending process in step S4-3 are: roller speed 2 to 10 m / min, roller spacing size is the same as the hot rolling roller spacing size, and temperature is 800 to 850°C; the permanent magnet after hot rolling will be deformed due to the rolling pressure, and after rolling, the permanent magnet enters the leveling roller and the bending roller for leveling and bending.

[0060] Exemplarily, the cooling rate in step S4-4 is controlled at 5-10°C / min. A too slow cooling rate will prolong the cooling time and affect the squareness of the demagnetization curve, while a too fast cooling rate will easily cause cracking of the permanent magnet. Preferably, the cooling rate is 5, 7, 8, 9, or 10°C / min.

[0061] The hot-rolled permanent magnet of the required shape and size described in step S4-4 is obtained by changing the shape of the rolling roller.

[0062] Preferably, the hot-rolled permanent magnet can be prepared into a plate shape, a tile shape, or a tube shape. The size requirements of hot-rolled permanent magnets of different shapes are: plate shape, length 50-200 mm × width 50-100 mm × height 2-10 mm; tile shape, radius R10-50 mm × height 50-200 mm × wall thickness 2-10 mm; tube shape, diameter Ф20-100 mm × height 50-200 mm × wall thickness 2-10 mm.

[0063] It is worth noting that the entire hot rolling process is carried out continuously in a hot rolling equipment in a vacuum environment, and finally anisotropic high-performance RE-Ga-M-Fe-B hot-rolled permanent magnet with grain rheological orientation is obtained, and the maximum magnetic energy product of the magnet is greater than 38MGOe.

[0064] In summary, the present invention optimizes the design of the rare earth permanent magnet composition to improve the high-temperature thermal deformation ability of the permanent magnet, enables continuous hot rolling operations, and ensures the performance and quality of the permanent magnet during the continuous hot rolling process; the method for preparing permanent magnets by vacuum hot rolling RE-Ga-M-Fe-B full-density blanks without coating is simple in process, easy to control the blank temperature, and uniformly heated, which solves the problem that grain rheology permanent magnets cannot be produced on an industrial scale; optimizes parameters such as vacuum hot rolling temperature, speed, and roll pressure and accurately controls them to obtain plate-shaped, tile-shaped, and tubular high-performance permanent magnets with high density, high orientation, good corrosion resistance, and good temperature stability.

[0065] The hot-rolled rare earth permanent magnet and its preparation method of the present invention are described below with reference to specific embodiments.

[0066] Example 1 and Comparative Examples 1 to 6 are plate-shaped hot-rolled rare earth permanent magnets, Example 2 and Comparative Examples 7 to 12 are tile-shaped hot-rolled rare earth permanent magnets, and Example 3 and Comparative Examples 13 to 18 are tubular hot-rolled rare earth permanent magnets.

[0067] Examples 1-1 and 1-2

[0068] This embodiment provides a hot-rolled rare earth permanent magnet and a preparation method thereof.

[0069] The composition of permanent magnets in mass percentage is: Nd 28 Pr3Ga 0.6 Co4Cu 0.5 Fe 63 B 0.9

[0070] The specific preparation process is as follows:

[0071] Step 1: Prepare magnetic powder that meets the composition requirements: Prepare rapid quenching magnetic powder with a particle size of 100-200 mesh according to the designed composition ratio.

[0072] Step 2, cold molding: The rapidly quenched magnetic powder is evenly loaded into the cold press mold for cold molding, and pressed into a plate-shaped blank at a pressure greater than 100 MPa. The blank size is: 76×46×26 mm, and the density of the blank reaches 65%.

[0073] Step 3, hot isostatic pressing: The molded Nd-Fe-B plate blank is placed on a grid support and placed in a hot isostatic pressing device; the process parameters are: temperature set at 750°C, pressure set at 70 MPa, and argon gas is used for hot isostatic pressing to obtain a shrunken plate blank with a size of 50×30×17 mm and a blank density of 100%.

[0074] Step 4: Vacuum continuous hot rolling:

[0075] S4-1, place the full density blank after hot isostatic pressing in a continuous professional hot rolling equipment and pre-evacuate to 10 -3 Pa is filled with argon, and then the temperature is rapidly raised to 800°C using vacuum induction heating;

[0076] S4-2. The heated blank enters a vacuum rolling mill chamber and is subjected to a rolling process with the temperature controlled at 800° C. (Example 1-2) and 830° C. (Example 1-1), respectively. During the rolling process, the blank does not require coating protection. The rolling force is controlled at 3 tons and the roller speed is controlled at 4 m / min for hot rolling operation to obtain a 100×50×5 mm plate-shaped magnet with a reduction ratio of about 70%.

[0077] S4-3, the plate-shaped magnet after rolling enters the leveling roller for leveling process, with the roller speed of 5 m / min, the roller spacing size being the same as the hot rolling roller spacing size, and the temperature being 800-850°C to complete the leveling process;

[0078] S4-4. The flattened magnet enters a cooling chamber and is cooled to room temperature at a cooling rate of 5°C / min (Example 1-1) and 10°C / min (Example 1-2), respectively, to obtain a plate-shaped hot-rolled permanent magnet.

[0079] The magnetic properties of the hot-rolled magnets obtained in Example 1-1 and Example 1-2 and the results of adjustment of relevant process parameters are shown in Table 1.

[0080] It can be seen from Examples 1-1 and 1-2 that plate-shaped hot-rolled permanent magnets with excellent magnetic properties can be obtained by vacuum hot rolling using the method of the present invention.

[0081] Comparative Examples 1 to 6

[0082] The permanent magnets and preparation methods provided in Comparative Examples 1 to 6 have the same composition and shape as those in Examples 1-1 and 1-2.

[0083] The difference between Comparative Example 1 and Example 1 is that the hot rolling process in step 4 is different, a metal outer layer is used for coating, and a muffle furnace is used for heating.

[0084] The difference between Comparative Example 2 and Example 1 is that the heating method in step 4 (1) is different, and a vacuum molybdenum belt furnace is used for heating.

[0085] The difference between Comparative Example 3 and Example 1 is that the hot rolling temperature in step 4 (2) is different;

[0086] Comparative Example 3-1 adopts a hot rolling temperature of 900°C;

[0087] Comparative Example 3-2 used a hot rolling temperature of 750°C.

[0088] The difference between Comparative Example 4 and Example 1 is that the rolling speed and rolling pressure in step 4 (2) are different;

[0089] Comparative Example 4-1 uses a rolling speed of 10 m / min and a rolling reduction force of 3 tons;

[0090] Comparative Example 4-2 adopts a rolling speed of 4 m / min and a rolling reduction force of 1 ton.

[0091] The difference between Comparative Example 5 and Example 1 is that the pressure and temperature of hot isostatic pressing in step 3 are different;

[0092] Comparative Example 5-1 adopts a hot isostatic pressing process at 100 MPa and 750°C;

[0093] Comparative Example 5-2 adopts a hot isostatic pressing process at 70 MPa and 650°C.

[0094] The difference between Comparative Example 6 and Example 1 is that the hot isostatic pressing process in step 3 is not performed.

[0095] The obtained magnetic properties of the magnet and the related process parameter adjustment results are shown in Table 1.

[0096] As can be seen from Table 1, the outer layer coating used in Comparative Example 1 requires processes such as metal shape processing, welding sealing, and vacuum coating sealing in order to be hot-rolled in the atmosphere. The coated permanent magnet requires a long period of temperature diffusion to be evenly heated, resulting in grain growth that affects performance. The heated coated sample needs to be manually clamped out and then fed into the rolling mill, resulting in a rapid cooling rate that affects performance. Therefore, the metal outer layer coating process is complicated and cannot be continuously rolled. It can only be used for laboratory research and is not suitable for large-scale industrial production.

[0097] In Comparative Example 2, a vacuum molybdenum strip furnace is used for heating. Although hot rolling can be performed continuously, this heating method requires a long thermal diffusion time to heat the permanent magnet blank evenly, which will cause grain growth and affect the magnetic properties.

[0098] Comparative Examples 3-1 and 3-2 use hot rolling temperatures of 900°C and 750°C, respectively, which exceed the optimal rolling temperature range required by the present invention. Too high a temperature will cause rapid grain growth and affect the coercive force performance, while too low a temperature will affect the rotational orientation of the grains and the remanent magnetic properties will be low.

[0099] Comparative Example 4-1 uses a rolling process of 10 meters per minute, and its rolling speed exceeds the hot rolling speed range of the present invention. The hot rolling speed is too fast, that is, the deformation rate is too fast, so that some grains do not have time to orient themselves, thereby affecting the magnetic properties. In addition, Comparative Example 4-2 uses a rolling roller pressure of 1 ton, as a result, the permanent magnet cannot reach the reduction shrinkage ratio of the present invention, thereby affecting the magnetic properties.

[0100] In Comparative Example 5-1, a hot isostatic pressing process of 100 MPa was used. Due to the excessive pressure, some liquid phase of the magnet overflowed, resulting in changes in composition and affecting the magnetic properties. In Comparative Example 5-2, a hot isostatic pressing process of 650°C was used. Due to the low temperature, the density of the pressed blank was low, which affected the magnetic properties.

[0101] In Comparative Example 6, the cold-molded blank was directly heated and then hot-rolled without hot isostatic pressing. Similarly, the initial density of the blank was low, which ultimately affected the magnetic properties of the permanent magnet after hot rolling.

[0102] The above comparative examples further illustrate that the vacuum hot-rolling method of the present invention enables continuous and rapid hot-rolling operations, ultimately producing high-performance, plate-shaped hot-rolled permanent magnets with rheologically oriented grains, while also enabling large-scale industrial production. Regarding the cooling rates of the magnets after hot rolling, Examples 1-1 and 1-2 set them at 5 and 10°C / min, respectively, both achieving ideal magnetic properties. However, a slower cooling rate would prolong the cooling time and affect the squareness of the demagnetization curve, while a faster rate would easily cause the magnets to crack.

[0103] Table 1 Magnetic properties of hot-rolled permanent magnets and main adjustment process parameters

[0104]

[0105] Examples 2-1 and 2-2

[0106] This embodiment provides a hot-rolled rare earth permanent magnet and a preparation method thereof.

[0107] The composition of permanent magnets in mass percentage is: Nd 28 Dy2G 0.4 Co 5.5 Al 0.5 Fe 62.7 B 0.9 ; Step 1, prepare magnetic powder that meets the composition requirements: according to the designed composition ratio, prepare rapid quenching magnetic powder with a particle size of 100-200 mesh.

[0108] Step 2, cold molding: the rapid quenching magnetic powder is evenly loaded into the cold press mold for cold molding, and pressed into a tile-shaped blank at a pressure greater than 100 MPa. The blank size is: R30 (depth: 28) × height 110 × wall thickness 22 mm, and the density of the blank reaches 65%.

[0109] Step 3, Hot Isostatic Pressing: The molded Nd-Fe-B blank was placed on a grid support and placed in a hot isostatic pressing machine. The process parameters were: temperature set at 750°C, pressure set at 70 MPa, and argon gas. The hot isostatic pressing process produced a shrinkage tile-shaped blank with dimensions of R30 (18mm long) x 70mm high x 14mm thick. The blank achieved 100% density.

[0110] Step 4: Vacuum continuous hot rolling:

[0111] S4-1, place the full density blank after hot isostatic pressing in a continuous professional hot rolling equipment and pre-evacuate to 10 -3 Pa is filled with argon, and then the temperature is rapidly raised to 800°C using vacuum induction heating;

[0112] S4-2. The heated blank enters a vacuum rolling mill chamber and is subjected to a rolling process with the temperature controlled at 800° C. (Example 2-2) and 830° C. (Example 2-1), respectively. During the rolling process, the blank does not require coating protection. The roller pressure is controlled at 3 tons and the roller speed is controlled at 4 m / min for hot rolling operation, obtaining a magnet with a reduction ratio of about 70% and a size of R30×100×4 mm.

[0113] S4-3. After rolling, the magnet enters the leveling roller for leveling. The leveling process is completed at a roller speed of 5 m / min, a roller spacing size that is the same as the hot rolling roller spacing size, and a temperature of 800-850°C.

[0114] S4-4. The flattened magnet enters a cooling chamber and is cooled to room temperature at a cooling rate of 5°C / min (Example 2-1) and 10°C / min (Example 2-2).

[0115] The magnetic properties of the hot-rolled permanent magnets obtained in Example 2-1 and Example 2-2 and the results of adjustment of relevant process parameters are shown in Table 2.

[0116] It can be seen from Examples 2-1 and 2-2 that tile-shaped hot-rolled permanent magnets with excellent magnetic properties can be obtained by vacuum hot rolling using the method of the present invention.

[0117] Comparative Examples 7 to 12

[0118] The permanent magnets and preparation methods provided in Comparative Examples 7 to 12 have the same composition and shape as those in Examples 2-1 and 2-2.

[0119] The difference between Comparative Example 7 and Example 2 is that the hot rolling process in step 4 is different, a metal outer layer is used for coating, and a muffle furnace is used for heating.

[0120] The difference between Comparative Example 8 and Example 2 is that the heating method in step 4 (1) is different, and a vacuum molybdenum belt furnace is used for heating.

[0121] The difference between Comparative Example 9 and Example 2 is that the hot rolling temperature in step 4 (2) is different;

[0122] Comparative Example 9-1 used a hot rolling temperature of 900°C;

[0123] Comparative Example 9-2 used a hot rolling temperature of 750°C.

[0124] Comparative Example 10 differs from Example 2 in the rolling speed and rolling reduction force of Step 4(2);

[0125] Comparative Example 10-1 uses a rolling speed of 10 meters / minute and a rolling reduction force of 3 tons;

[0126] Comparative Example 10-2 uses a rolling speed of 4 meters / minute and a rolling reduction force of 1 ton.

[0127] Comparative Example 11 differs from Example 2 in the pressure and temperature of the hot isostatic pressing of Step 3;

[0128] Comparative Example 11-1 uses a hot isostatic pressing process of 100 MPa and 750°C;

[0129] Comparative Example 11-2 uses a hot isostatic pressing process of 70 MPa and 650°C.

[0130] Comparative Example 12 differs from Example 2 in that the hot isostatic pressing process of Step 3 is not performed.

[0131] The magnetic performance results of the magnets obtained and the related process parameter adjustment results are shown in Table 2.

[0132] As can be seen from Table 2, Comparative Example 7 uses an outer layer cladding that requires metal shaping, welding sealing, and vacuum cladding sealing processes, so that the cladding permanent magnet needs a long time temperature diffusion to be uniformly heated, which leads to grain growth affecting the performance; the cladded sample after heating needs to be manually clamped out and then sent into the rolling mill, which has a fast cooling speed, affecting the performance, and therefore the metal outer layer cladding process is complicated and cannot be continuously rolled, but can only be used for laboratory research, and is not suitable for large-scale industrial production.

[0133] In Comparative Example 8, a vacuum molybdenum belt furnace is used for heating, which can continuously perform hot rolling operation, but this heating method needs a long heat diffusion time to uniformly heat the permanent magnet blank, which leads to grain growth, affecting the magnetic performance.

[0134] Comparative Examples 9-1 and 9-2 respectively use hot rolling temperatures of 900°C and 750°C, which are outside the optimal rolling temperature range required by the present application; a temperature that is too high can cause rapid grain growth affecting the coercive force performance, and a lower temperature can affect the grain rotation orientation, resulting in a low remanence performance, especially for the W-shaped permanent magnet blank which is constrained by the rolling force, the grain orientation is more complicated, resulting in a low remanence performance.

[0135] In comparative example 10-1, a rolling process of 10 m / min is adopted, and its rolling speed exceeds the hot rolling speed range of the present invention. The hot rolling speed is too fast, that is, the deformation rate is too fast, so that some grains do not have time to orient themselves and thus affect the magnetic properties. In addition, a rolling roller pressure of 1 ton is adopted in comparative example 10-2, as a result, the magnet cannot reach the reduction shrinkage ratio in the present invention and thus affects the magnetic properties.

[0136] In comparative example 11-1, a hot isostatic pressing process of 100 MPa was adopted. Due to the excessive pressure, some liquid phase of the magnet overflowed, resulting in changes in composition and affecting the magnetic properties. In comparative example 11-2, a hot isostatic pressing process of 650°C was adopted. Due to the low temperature, the density of the blank after pressing was low, which affected the magnetic properties.

[0137] In Comparative Example 12, the cold molded blank was directly heated and then hot rolled without hot isostatic pressing. Similarly, the initial density of the blank was low, which ultimately affected the magnetic properties of the magnet after hot rolling.

[0138] The above comparative examples further demonstrate that the vacuum hot-rolling method of the present invention allows for continuous and rapid hot-rolling operations, ultimately yielding high-performance tile-shaped hot-rolled permanent magnets with rheologically oriented grains, while also enabling large-scale industrial production. The cooling rates for the hot-rolled magnets in Examples 2-1 and 2-2 were set at 5°C / min and 10°C / min, respectively, both achieving ideal magnetic properties. However, a slower cooling rate would prolong the cooling time and affect the squareness of the demagnetization curve, while a faster cooling rate could easily lead to cracking of the magnets.

[0139] Table 2 Magnetic properties of tile-shaped hot-rolled permanent magnets and main adjustment process parameters

[0140]

[0141] Examples 3-1 and 3-2

[0142] This embodiment provides a hot-rolled rare earth permanent magnet and a preparation method thereof.

[0143] The composition of permanent magnets in mass percentage is: Nd 25 Ce3Dy4Ga 0.8 Co 5.8 Ti 0.2 Fe 60.3 B 0.9

[0144] Step 1: Prepare magnetic powder that meets the composition requirements: Prepare rapid quenching magnetic powder with a particle size of 100-200 mesh according to the designed composition ratio.

[0145] Step 2, cold molding: The rapidly quenched magnetic powder is evenly loaded into the cold press mold for cold molding, and pressed into a tubular blank at a pressure greater than 100 MPa. The blank size is: 98mm × height 110mm × wall thickness 22mm, and the density of the blank reaches 65%.

[0146] Step 3: Hot Isostatic Pressing (HIPP): The molded Nd-Fe-B blank was placed on a grid support and placed in a hot isostatic pressing (HIPP) machine. The process parameters were: temperature set at 750°C, pressure set at 70 MPa, and argon gas. The HIP process produced a tubular blank with dimensions of 64 mm (Ø) x 70 mm (H) x 14 mm (W) thickness, achieving 100% density.

[0147] Step 4: Vacuum continuous hot rolling:

[0148] S4-1, place the full density blank after hot isostatic pressing in a continuous professional hot rolling equipment and pre-evacuate to 10 -3 Pa is filled with argon, and then the temperature is rapidly raised to 800°C using vacuum induction heating;

[0149] S4-2. The heated blank enters a vacuum rolling mill chamber and is subjected to a rolling process with the temperature controlled at 800° C. (Example 3-2) and 830° C. (Example 3-1), respectively. During the rolling process, the blank does not require coating protection. The roller pressure is controlled at 3 tons and the roller speed is controlled at 4 m / min for hot rolling operation, obtaining a magnet with a diameter of 50 mm, a height of 100 mm, and a wall thickness of 4 mm, and a reduction ratio of about 70%.

[0150] S4-3. After rolling, the magnet enters the leveling roller for leveling. The leveling process is completed at a roller speed of 5 m / min, a roller spacing size that is the same as the hot rolling roller spacing size, and a temperature of 800-850°C.

[0151] S4-4. The flattened magnet enters a cooling chamber and is cooled to room temperature at a cooling rate of 5°C / min (Example 3-1) and 10°C / min (Example 3-2).

[0152] The magnetic properties of the hot-rolled permanent magnets obtained in Example 3-1 and Example 3-2 and the results of adjustment of relevant process parameters are shown in Table 3.

[0153] It can be seen from Examples 3-1 and 3-2 that tubular hot-rolled permanent magnets with excellent magnetic properties can be obtained by vacuum hot rolling using the method of the present invention.

[0154] Comparative Examples 13 to 18

[0155] The permanent magnets and preparation methods provided in Comparative Examples 13 to 18 have the same composition and shape as those in Examples 3-1 and 3-2.

[0156] The difference between Comparative Example 13 and Example 3 is that the hot rolling process in step 4 is different, a metal outer layer is used for coating, and a muffle furnace is used for heating.

[0157] The difference between Comparative Example 14 and Example 3 is that the heating method in step 4 (1) is different, and a vacuum molybdenum belt furnace is used for heating.

[0158] The difference between Comparative Example 15 and Example 3 is that the hot rolling temperature in step 4 (2) is different;

[0159] Comparative Example 15-1 adopts a hot rolling temperature of 900°C;

[0160] Comparative Example 15-2 used a hot rolling temperature of 750°C.

[0161] The difference between Comparative Example 16 and Example 3 is that the rolling speed and rolling pressure in step 4 (2) are different;

[0162] Comparative Example 16-1 uses a rolling speed of 10 m / min and a rolling reduction force of 3 tons;

[0163] Comparative Example 16-2 uses a rolling speed of 4 m / min and a rolling reduction force of 1 ton.

[0164] The difference between Comparative Example 17 and Example 3 is that the pressure and temperature of the hot isostatic pressing in step 3 are different;

[0165] Comparative Example 17-1 adopts a hot isostatic pressing process at 100 MPa and 750°C;

[0166] Comparative Example 17-2 adopts a hot isostatic pressing process at 70 MPa and 650°C.

[0167] The difference between Comparative Example 19 and Example 3 is that the hot isostatic pressing process in step 3 is not performed.

[0168] The obtained magnetic properties of the magnet and the related process parameter adjustment results are shown in Table 2.

[0169] As can be seen from Table 2, the outer layer coating used in Comparative Example 13 requires processes such as metal shape processing, welding sealing, and vacuum coating sealing in order to be hot-rolled in the atmosphere. The coated magnets require a long period of temperature diffusion to be evenly heated, resulting in grain growth that affects performance. The heated coated samples need to be manually clamped out and then fed into the rolling mill, resulting in a rapid cooling rate that affects performance. Therefore, the metal outer layer coating process is complicated and cannot be continuously rolled. It can only be used for laboratory research and is not suitable for large-scale industrial production.

[0170] In Comparative Example 14, a vacuum molybdenum strip furnace is used for heating. Although hot rolling can be performed continuously, this heating method requires a long thermal diffusion time to heat the magnet blank evenly, which will cause grain growth and affect the magnetic properties.

[0171] Comparative Examples 15-1 and 15-2 use hot rolling temperatures of 900°C and 750°C, respectively, which exceed the optimal rolling temperature range required by the present invention. Excessively high temperatures will cause rapid grain growth, affecting coercivity performance, while lower temperatures will affect grain rotation orientation, resulting in low remanent magnetic properties. In particular, the tubular permanent magnet blank is constrained by the rolling force, and the grain orientation is complex, resulting in low remanent magnetic properties.

[0172] In comparative example 16-1, a rolling process of 10 m / min is adopted, and its rolling speed exceeds the hot rolling speed range of the present invention. The hot rolling speed is too fast, that is, the deformation rate is too fast, so that some grains do not have time to orient themselves and thus affect the magnetic properties. In addition, a rolling roller pressure of 1 ton is adopted in comparative example 16-2, as a result, the magnet cannot reach the reduction shrinkage ratio in the present invention and thus affects the magnetic properties.

[0173] In Comparative Example 17-1, a hot isostatic pressing process of 100 MPa was used. Due to the excessive pressure, some liquid phase of the magnet overflowed, resulting in changes in composition and affecting the magnetic properties. In Comparative Example 17-2, a hot isostatic pressing process of 650°C was used. Due to the low temperature, the density of the blank after pressing was low, which affected the magnetic properties.

[0174] In Comparative Example 18, the cold molded blank was directly heated and then hot rolled without hot isostatic pressing. Similarly, due to the low density of the initial blank, the magnetic properties of the magnet after hot rolling were ultimately affected.

[0175] The above comparative examples further demonstrate that the vacuum hot-rolling method of the present invention allows for continuous and rapid hot-rolling operations, ultimately yielding high-performance tubular hot-rolled permanent magnets with rheologically oriented grains, while also enabling large-scale industrial production. The cooling rates for the hot-rolled magnets in Examples 3-1 and 3-2 were set at 5°C / min and 10°C / min, respectively, both achieving ideal magnetic properties. However, a slower cooling rate would prolong the cooling time and affect the squareness of the demagnetization curve, while a faster cooling rate would predispose the magnets to cracking.

[0176] Table 3 Magnetic properties of tubular hot-rolled permanent magnets and main adjustment process parameters

[0177]

[0178] In summary, the present invention optimizes the design of the rare earth permanent magnet composition to improve the high-temperature thermal deformation ability of the permanent magnet, enables continuous hot rolling operations, and ensures the performance and quality of the permanent magnet during the continuous hot rolling process; the method for preparing permanent magnets by vacuum hot rolling RE-Ga-M-Fe-B full-density blanks without coating is simple in process, easy to control the blank temperature, and uniformly heated, which solves the problem that grain rheology permanent magnets cannot be produced on an industrial scale; optimizes parameters such as vacuum hot rolling temperature, speed, and roll pressure and accurately controls them to obtain plate-shaped, tile-shaped, and tubular high-performance permanent magnets with high density, high orientation, good corrosion resistance, and good temperature stability.

[0179] The above description is only the preferred embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for preparing a hot-rolled rare earth permanent magnet, characterized in that: The steps include: Step 1, preparing RE-Ga-M-Fe-B rapid quenching magnetic powder; wherein RE is one or more of Nd, Pr, Ce, La or Dy; M is one or more of Co, Cu, Al, Zr, Ti, Nb; Step 2, cold molding: the rapid quenching magnetic powder prepared in step 1 is evenly loaded into a cold press mold for cold molding at a pressure greater than 100 MPa to obtain a blank with a density of more than 60%; Step 3, hot isostatic pressing: Under vacuum or argon protection, the blank obtained in step 2 is hot isostatically pressed to obtain an isotropic full-density blank; the hot isostatic pressing process parameters are: temperature 710-750°C, pressure 60-70 MPa; Step 4, uncoated vacuum hot rolling: the full-density blank of step 3 is continuously vacuum hot rolled without coating to directly form the hot-rolled permanent magnet product into the desired shape; The unclad vacuum hot rolling process does not use a cladding process, and the blank does not need cladding protection during the rolling process, and includes the following steps: S4-1, heating: the full density blank obtained in step 3 is placed in a continuous hot rolling equipment, and vacuumed to 10 -3 Pa and filled with argon, then quickly heated to 800 ° C; the heating method adopts vacuum induction heating; S4-2, hot rolling: the heated full-density blank is put into a vacuum rolling mill and hot rolled at 830-850°C to obtain the rolled permanent magnet; during the hot rolling process, the roller pressure is 2-5 tons and the roller speed is 2-5 m / min; the full-density blank reduction shrinkage ratio is between 70-75%; S4-3, leveling and bending: After rolling, the permanent magnet enters the leveling roller and the bending roller for leveling and bending; S4-4, cooling: After flattening and flat bending, the magnet enters the cooling chamber and is cooled to room temperature at 5-10°C / min to obtain anisotropic hot-rolled permanent magnet products with the required shape and size and orientation parallel to the rolling direction, achieving near-net forming; The entire hot rolling process is carried out continuously in a hot rolling equipment in a vacuum environment. The blank does not need to be covered for protection during the rolling process, and finally anisotropic RE-Ga-M-Fe-B hot-rolled permanent magnet with rheological grain orientation is obtained.

2. The preparation method according to claim 1, characterized in that The preparation method of the RE-Ga-M-Fe-B rapid quenching magnetic powder described in step 1 comprises the following steps: S1-1. According to the designed composition ratio, the alloy raw materials are subjected to vacuum induction melting at a melting temperature of 1400° C. to 1500° C. to obtain an alloy ingot; S1-2, rapidly quenching the alloy ingot obtained in S1 to obtain a rapidly quenched thin strip, wherein the roller surface linear speed of the rapidly quenching roller is 25-50 m / s, and the average grain size of the rapidly quenched thin strip is 30-300 nm; S1-3, mechanically crushing the rapidly quenched thin strip obtained in S2 into rapidly quenched magnetic powder with an average particle size of 100-200 mesh.

3. The preparation method according to claim 1, characterized in that The full-density blank described in step 3 is in the shape of a plate, tile or tube.

4. The preparation method according to claim 1, characterized in that The hot isostatic pressing process parameters in step 3 are: temperature 710~750℃, pressure 65~70MPa.

5. The preparation method according to claim 1, characterized in that The unclad vacuum hot rolling in step 4 comprises the following steps: S4-1, heating: the full density blank obtained in step 3 is placed in a continuous hot rolling equipment, and vacuumed to 10 -3 Pa and filled with argon, then quickly heated to 800 °C; S4-2, hot rolling: the heated full density blank enters the vacuum rolling mill chamber and is hot rolled at 840-850°C to obtain the rolled permanent magnet; S4-3, leveling and bending: After rolling, the permanent magnet enters the leveling roller and the bending roller for leveling and bending; S4-4. Cooling: After flattening and flat bending, the magnet enters the cooling chamber and is cooled to room temperature at 7-10°C / min to obtain anisotropic hot-rolled permanent magnet products with the required shape and size and orientation parallel to the rolling direction.

6. The preparation method according to claim 5, characterized in that During the hot rolling process in step S4-2, the rolling force of the rollers is 3 to 5 tons and the roller speed is 3 to 5 meters per minute.

7. The preparation method according to claim 5, characterized in that The process conditions of the leveling and bending process in step S4-3 are: roller speed 2-10 m / min, roller spacing size is the same as the hot rolling roller spacing size, and temperature is 800-850°C.

8. A hot-rolled rare earth permanent magnet, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7, the permanent magnet has the general formula RE a Ga b M c Fe d B e ,in, RE is one or more of Nd, Pr, Ce, La or Dy; M is one or more of Co, Cu, Al, Zr, Ti and Nb; the mass fractions expressed in percentage are: 28.0≤a≤32.0; 0.2≤b≤0.8; 3.0≤c≤6.0; 0.8≤e≤1.1; d=100-abce.

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