A hot deformed magnet and a method of making the same

Abstract

The application relates to the technical field of magnetic materials, in particular to a hot-deformed magnet and a preparation method thereof. The preparation method comprises the following steps: preparing a precursor by hot-pressing amorphous or nanocrystalline magnetic powder, performing steel sleeve packaging and vacuumizing treatment on the precursor, and then performing hot rolling after heat preservation treatment at 600-1000 DEG C; wherein the size of the internal grains of the precursor is less than 100 nanometers. The preparation method has the dual advantages of being beneficial to large-scale and efficient production and easy to control the shape size of the magnet. The manufacturing process is no longer limited by the vacuum degree and multi-step heating, the process is simple, the energy consumption can be reduced, the cost is reduced, the energy consumption and the cost are lower than those of the hot-pressing-hot-deformation method, and the production efficiency is improved. The prepared magnet has the characteristics of high magnetic energy product and high coercivity, has a wide application range and high application value.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a hot-deformable magnet and its preparation method. Background Technology

[0002] With the development of information technology and new energy technology, magnetic materials have become one of the essential materials for the development of a high-tech society. The application of magnetic materials has permeated all aspects of modern social development, with wide and in-depth applications in industries such as new energy technology, medical equipment, and aviation. Especially in the rapidly developing new energy vehicle industry in recent years, high-end permanent magnet materials have become a core component of high-performance electric motors. Therefore, with the improvement of scientific and technological levels, the demand for magnetic materials from social development and industrial innovation will become increasingly strong, and the application prospects of magnetic materials will be even broader. Thus, in-depth research and development of magnetic materials directly promotes social development, industrial innovation, and human progress.

[0003] In recent years, significant progress has been made in the research of preparing high-performance rare-earth permanent magnets using hot deformation technology. The main hot deformation processing methods are upsetting and back extrusion. Upsetting, due to uneven deformation, produces hot-deformed magnets with uneven magnetic properties, requiring the removal of areas with small deformation in later processing, resulting in substantial waste. Furthermore, conventional upsetting methods require two heating steps, especially the second step, which is time-consuming and high-temperature, leading to high energy consumption and complex processes. Back extrusion can also be used to prepare hot-deformed magnets, magnetic rings, or magnetic tiles, but this method also requires two high-temperature processes, and both hot pressing and hot deformation require heating, cooling, and demolding, making the process complex and time-consuming. Therefore, continuous production is difficult, resulting in low production efficiency, high energy consumption, and high manufacturing costs. Low production efficiency is the bottleneck restricting the large-scale production of this technology and hot-deformed magnetic rings.

[0004] Japanese patent JPH023905A describes a method for producing NdFeB magnets by rolling NdFeB materials from ingots and controlling the content of rare earth-rich elements. Magnetic performance tests were conducted at different locations on the cross-section, showing that the maximum energy product increased from 10 MGOe to 23 MGOe and then decreased back to 10 MGOe. Japanese patent JPH2794755B2 describes rolling NdFeB ingots at 750-1150℃ with a deformation of over 30% per pass, followed by heat treatment at 400-700℃. The final (BH)max was <30 MGOe, and Hcj ranged from 5-12 kOe. However, the NdFeB materials described in these patents are all ingots. After single-pass or multi-pass rolling, the magnets exhibit excessively low magnetic properties and poor uniformity, along with low coercivity, rendering them impractical. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention provides a method for preparing a thermally deformable magnet, comprising:

[0006] After hot pressing amorphous or nanocrystalline magnetic powder into a precursor, the precursor is encapsulated in a steel sleeve and vacuumed. Then, it is hot rolled after being kept at 600-1000℃.

[0007] The size of the internal grains of the precursor is less than 100 nanometers.

[0008] This invention provides a novel technique for preparing hot-deformable magnets using a two-step method involving hot pressing and hot deformation. By preparing the precursor through hot pressing and controlling the grain size within the precursor to be less than 100 nanometers, the magnet achieves higher magnetic properties after subsequent heat treatment and hot rolling processes.

[0009] By encapsulating the precursor with a steel sleeve, the size of the steel sleeve can be flexibly adjusted, allowing for flexible adjustment of the size of the heat-deformable magnet and enabling the production of heat-deformable magnets with different performance and size requirements.

[0010] Furthermore, this invention also found that heat treatment at 600–1000°C before hot rolling can help control the growth process of grains inside the magnet during hot rolling, resulting in the hot-rolled magnet having higher magnetic properties.

[0011] Preferably, the size of the grains inside the precursor is controlled to be less than 50 nanometers, more preferably less than 30 nanometers.

[0012] In practice, the temperature of hot rolling is the same as the temperature of heat preservation treatment.

[0013] In the specific implementation process, the precursor is a block precursor.

[0014] In a preferred embodiment of the present invention, the heat preservation time is 10 to 30 minutes.

[0015] Under the above conditions, heat preservation treatment can effectively control the growth process of grains inside the magnet during hot rolling, and further improve the magnetic properties of the hot-rolled magnet.

[0016] In a preferred embodiment of the present invention, the reduction rate of the hot rolling process is 60% or more.

[0017] In this invention, the reduction rate is the ratio of the reduction in steel sleeve thickness to its original thickness.

[0018] In this invention, a thermally deformable magnet with excellent magnetic properties can be obtained by controlling the reduction rate to 60%.

[0019] In the specific implementation process, during the hot rolling process, single-pass rolling or multi-pass rolling can be adopted, and the deformation between different passes can be flexibly adjusted.

[0020] In a preferred embodiment of the present invention, the hot pressing temperature is 300-500°C.

[0021] In a preferred embodiment of the present invention, the pressure of the hot pressing is 500-1000 MPa.

[0022] In a preferred embodiment of the present invention, the hot pressing time is 1 to 5 minutes.

[0023] When the hot pressing time is controlled within the above range, the size of the grains inside the precursor can be effectively controlled, thereby further improving the magnetic properties of the magnet after hot rolling.

[0024] In a preferred embodiment of the present invention, the density of the precursor is more than 95% of the theoretical density of the magnetic powder material.

[0025] In a preferred embodiment of the present invention, the vacuum degree of the vacuuming process is below 0.06 Pa.

[0026] As a preferred embodiment of the present invention, the preparation method further includes: cutting the steel sleeve after hot rolling to obtain a hot-deformed magnet.

[0027] In the specific implementation process, this includes, but is not limited to, using wire cutting, slicing machines or laser cutting machines to cut and separate the steel sleeve and the heat-deformed magnet.

[0028] As a preferred embodiment of the present invention, molybdenum disulfide and / or boron nitride are coated on the inner wall of the steel sleeve as a release agent before vacuuming.

[0029] Furthermore, the present invention also provides a thermally deformable magnet prepared according to any of the above embodiments.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The preparation method of this invention has the dual advantages of facilitating large-scale, efficient production and easy control of the magnet's external dimensions. The manufacturing process is no longer limited by vacuum levels and multi-step heating, simplifying the process, reducing energy consumption and costs (both energy consumption and cost are lower than the hot-pressing-hot-deformation method), and improving production efficiency. The prepared magnets exhibit high magnetic energy product and high coercivity, making them suitable for a wide range of applications and possessing high application value. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of an embodiment of the present invention.

[0033] Figure 2 This is a photograph of the neodymium iron boron hot-deformation magnet of Embodiment 1 of the present invention.

[0034] Figure 3 This is an X-ray diffraction pattern of the neodymium iron boron hot-deformation magnet of Embodiment 1 of the present invention.

[0035] Figure 4 This is a fracture morphology diagram of the neodymium iron boron hot-deformation magnet of Embodiment 1 of the present invention. Detailed Implementation

[0036] In this invention, there are no particular limitations on the amorphous or nanocrystalline magnetic powder. For example, a rapid quenching band can be obtained by melt rapid quenching, and then the rapid quenching band can be crushed to obtain rapid quenching powder. Alternatively, ultrafine powder can be obtained by high-energy ball milling. Commercially available rapid quenching powder can also be used, such as MQU series magnetic powder purchased from Magnetomagne (Tianjin) Co., Ltd. The amorphous or nanocrystalline magnetic powder used can have nanoscale grain sizes, and can also be amorphous and crystallize during hot pressing and hot deformation. There are no particular limitations on the alloy composition of the amorphous or nanocrystalline magnetic powder; for example, RE2Fe can be used. 14 B or RECo5 single-phase alloy, where RE represents Nd, Sm or other rare earth elements or combinations thereof.

[0037] In this invention, there are no special restrictions on the hot pressing process; generally, a mold of the same size as the steel sleeve is used for hot pressing. A corresponding hot-pressed block precursor is prepared according to the dimensions of the hot-rolled steel sleeve; it can be a cube, cuboid, cylinder, or a column with other cross-sections.

[0038] In this invention, the vacuuming process generally employs vacuum devices such as mechanical pumps, diffusion pumps, or molecular pumps. A vacuum steel pipe is welded to one end of the steel sleeve, and then the vacuum steel pipe is sealed to achieve the vacuum requirement.

[0039] In this invention, the steel sleeve is rolled at a temperature of 600-1000°C. The hot rolling process can be carried out in air. There are no specific requirements for the heating rate, such as 20-200°C / minute; after holding at the temperature, rolling deformation is performed, pushing the steel sleeve from one end of the roll to the other end to form the sleeve. This process can be carried out in single-pass or multi-pass rolling.

[0040] In this invention, molybdenum disulfide or boron nitride can be uniformly coated on the inner wall of the steel sleeve beforehand as a release agent. After rolling, the steel sleeve and the heat-deformed magnet can be separated by wire cutting, slicing machine, and laser cutting machine.

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] Unless otherwise specified, all methods used in the examples were conventional or performed according to techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents and instruments used without specified manufacturers were all conventional products that could be purchased from legitimate channels.

[0043] The process flow diagram of the following embodiments is as follows: Figure 1 As shown.

[0044] Example 1

[0045] This embodiment provides a heat-deformable magnet, the preparation method of which is as follows:

[0046] Using commercially available neodymium iron boron rapid-quenching magnetic powder as raw material, a precursor was prepared by hot pressing. The hot pressing temperature was 500℃, the pressing pressure was 500MPa, and the holding time was 1 minute to obtain a hot-deformed precursor material with a density of 7.52 g / cm³. 3 (98.9% of the theoretical density of the magnetic powder material), with an average grain size of 50 nanometers. The precursor was placed into a size-matched steel sleeve and a vacuum was evacuated to achieve a vacuum level of 5 × 10⁻⁶ inside the sleeve. -2 Pa. The encapsulated steel sleeve is heat-insulated at 600℃ for 10 minutes, and then hot-rolled using a single-pass rolling process with a reduction rate of 60%. Molybdenum disulfide release agent is uniformly applied to the inner wall of the steel sleeve beforehand, and then mechanically cut to obtain neodymium iron boron hot-deformable magnets (such as...). Figure 2 (As shown). The X-ray diffraction pattern of the neodymium iron boron hot-deformation magnet is shown below. Figure 3 As shown in the figure. The fracture morphology of the NdFeB hot-deformation magnet is shown in the figure. Figure 4 As shown.

[0047] Example 2

[0048] This embodiment provides a heat-deformable magnet, the preparation method of which is as follows:

[0049] Using high-energy ball-milled samarium-cobalt amorphous magnetic powder as raw material, a precursor was prepared by hot pressing. The hot pressing temperature was 300℃, the pressing pressure was 1000MPa, and the holding time was 5 minutes to obtain a heat-deformed precursor material with a density of 8.46 g / cm³. 3(99.5% of the theoretical density of the magnetic powder material), with an average grain size of 30 nanometers. The precursor was placed into a size-matched steel sleeve and a vacuum was evacuated to achieve a vacuum level of 1×10⁻⁶ inside the sleeve. -2 Pa. The encapsulated steel sleeve is heat-insulated at 1000℃ for 30 minutes, and then hot-rolled using a three-pass rolling process with a reduction rate of 90%. Boron nitride release agent is uniformly applied to the inner wall of the steel sleeve in advance, and samarium cobalt hot-deformation magnets are obtained by mechanical cutting.

[0050] Comparative Example 1

[0051] This comparative example provides a heat-deformable magnet, the preparation method of which is as follows:

[0052] Using ball-milled NdFeB cast alloy powder as raw material, a precursor was prepared by hot pressing. The hot pressing temperature was 500℃, the pressing pressure was 500MPa, and the holding time was 1 minute to obtain a hot-deformed precursor material with a density of 7.53 g / cm³. 3 (99.1% of the theoretical density of the magnetic powder material), with an average grain size of 5.5 micrometers (5500 nanometers). The precursor was fitted into a size-matched steel sleeve and a vacuum was evacuated, achieving a vacuum level of 5 × 10⁻⁶ inside the sleeve. -2 Pa. The encapsulated steel sleeve is heat-insulated at 600℃ for 10 minutes, and then hot-rolled using a single-pass rolling process with a reduction rate of 60%. Molybdenum disulfide release agent is uniformly applied to the inner wall of the steel sleeve in advance, and then the neodymium iron boron hot deformable magnet is obtained by mechanical cutting.

[0053] Comparative Example 2

[0054] This comparative example provides a hot-deformable magnet. The only difference between this and Example 2 is that after the precursor is packaged, it is directly hot-rolled without heat preservation, as detailed below:

[0055] Using high-energy ball-milled samarium-cobalt amorphous magnetic powder as raw material, a precursor was prepared by hot pressing. The hot pressing temperature was 300℃, the pressing pressure was 1000MPa, and the holding time was 5 minutes to obtain a heat-deformed precursor material with a density of 8.46 g / cm³. 3 (99.5% of the theoretical density of the magnetic powder material), with an average grain size of 30 nanometers. The precursor was placed into a size-matched steel sleeve and a vacuum was evacuated to achieve a vacuum level of 1×10⁻⁶ inside the sleeve. -2 Pa. The encapsulated steel sleeve is directly hot-rolled using a three-pass rolling process with a reduction rate of 90%. Boron nitride release agent is uniformly applied to the inner wall of the steel sleeve beforehand, and samarium cobalt hot-deformation magnets are obtained by mechanical cutting.

[0056] Test case

[0057] The magnetic properties of the hot-deformed magnets prepared in the above embodiments and comparative examples were tested. Specifically, a 1.5×1.5×1.5mm sample was cut from the front, middle, and rear ends of the strip magnet removed after hot rolling. After the samples were magnetized, their hysteresis loop was measured using a vibrating sample magnetometer to obtain the coercivity of the magnet.

[0058] The results are shown in Table 1.

[0059] Table 1. Coercivity of magnets (unit: kOe)

[0060] front-end sample Middle sample Backend Samples Example 1 17.2 17.4 17.3 Comparative Example 1 1.2 1.1 1.1 Example 2 33.5 33.6 33.5 Comparative Example 2 12.1 13.2 10.8

[0061] As can be seen from Table 1, the magnet prepared by the method of the present invention has high magnet coercivity. At the same time, according to the test results of the magnet at different positions, the magnet prepared by the present invention has very good uniformity, is easy to mass-produce in the industrial sector, and will not cause a large amount of material waste.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a heat-deformable magnet, characterized in that, include: After amorphous or nanocrystalline magnetic powder is hot-pressed into a precursor, the precursor is encapsulated in a steel sleeve and vacuum-treated. Then, it is held at 600~1000℃ and hot-rolled. The hot-pressing temperature is 300~500℃ and the hot-pressing pressure is 500~1000 MPa. The hot-rolling temperature is the same as the holding temperature. The holding time is 10~30 min. The precursor has internal grains with a size of less than 50 nanometers; the amorphous or nanocrystalline magnetic powder is RE2Fe. 14 B or RECo5 single-phase alloy, where RE represents Nd, Sm or other rare earth elements or combinations thereof.

2. The preparation method according to claim 1, characterized in that, The reduction rate during the hot rolling process is over 60%.

3. The preparation method according to claim 1, characterized in that, The hot pressing time is 1 to 5 minutes.

4. The preparation method according to claim 1 or 2, characterized in that, The density of the precursor is more than 95% of the theoretical density of the magnetic powder material.

5. The preparation method according to claim 1 or 2, characterized in that, The vacuum level during the vacuuming process is below 0.06 Pa.

6. The preparation method according to claim 1 or 2, characterized in that, Also includes: The steel sleeve is cut after hot rolling to obtain a hot-deformed magnet.

7. The preparation method according to claim 6, characterized in that, Before vacuuming, molybdenum disulfide and / or boron nitride are coated on the inner wall of the steel sleeve as a release agent.

8. A heat-deformable magnet, characterized in that, It is prepared by any one of claims 1 to 7.

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