A method for improving the coercivity of samarium cobalt magnets by high-stress electric pulse heating pre-aging

Abstract

This application relates to the technical field of magnetic materials, and particularly to a method for improving the coercivity of samarium-cobalt magnets by high-stress electric pulse heating pre-aging, which includes the following steps: placing metal raw materials in a vacuum induction furnace according to the ratio for melting to obtain an ingot, and crushing the ingot to obtain alloy powder; molding the alloy powder in a magnetic field by die pressing and obtaining a green compact by cold isostatic pressing; sintering and solution treating the green compact to obtain a solution-treated samarium-cobalt magnet; performing high-stress pre-aging treatment on the solution-treated samarium-cobalt magnet by using plasma discharge sintering technology; sequentially performing the first aging treatment and the second aging treatment on the sample after high-stress pre-aging treatment to obtain a samarium-cobalt magnet. This application conducts high-stress pulsed current heating pre-aging treatment on the samarium-cobalt solution-treated sample. By using this process, the stress and defects in the sample before the aging process can be regulated, and then the microstructure and magnetism of the final sample can be regulated, especially manifested as a significant increase in coercivity.

Description

Technical Field

[0001] This application relates to the technical field of magnetic materials, and particularly relates to a method for improving the coercivity of samarium-cobalt magnets by high-stress electric pulse heating pre-aging. Background Art

[0002] Bulk permanent magnet materials play a huge role in modern science and technology and industrial applications. Permanent magnet materials usually have strong magnetism, and are characterized by still retaining permanent magnetism after being magnetized to saturation by an external magnetic field and then removing the external magnetic field. As a renewable resource, permanent magnet materials have the characteristics of energy saving, high efficiency, and small size. Nowadays, electronic devices are developing towards miniaturization and microminiaturization, so the requirements for the magnetic properties of rare earth permanent magnet materials are getting higher and higher. The development of high-performance rare earth permanent magnet materials has gone through three generations: SmCo5, Sm2Co 17 and Nd2Fe 14 B. These three generations of rare earth permanent magnet materials have developed into an important material basis for the national economy and national defense construction, and play an irreplaceable role in fields such as electronic devices and magnetic sensors, electric vehicles, nuclear magnetic resonance, and aerospace. The second-generation 2:17 type samarium-cobalt permanent magnet materials have advantages such as a high Curie temperature, a relatively high magnetic energy product, good corrosion resistance, and thermal stability, and can still work normally in a high-temperature environment where the temperature exceeds 400 °C, and are the most important high-temperature permanent magnets.

[0003] The magnetic energy product is an important parameter for measuring the energy stored in a magnet. As is well known, the maximum theoretical magnetic energy product of a magnet is proportional to the square of the saturation magnetization M s , so a higher magnetic energy product can be obtained by increasing the saturation magnetization. At present, in order to obtain 2:17 type samarium-cobalt magnets with a higher magnetic energy product, the main method used is to replace Co atoms with Fe atoms with a high atomic magnetic moment. This can not only increase the theoretical magnetic energy product, but also reduce the raw material cost, which is an important development direction in this field. When the mass fraction of Fe is in the range of 15% - 20%, Sm2Co 17 has excellent comprehensive performance; however, the increase in Fe content is often accompanied by a decrease in coercivity. When the mass fraction of Fe approaches or exceeds 20%, the cellular structure of such magnets is difficult to effectively form, resulting in a sharp decrease in coercivity, which severely limits the development of high-Fe samarium-cobalt magnets.

[0004] Coercivity is one of the most important magnetic parameters and an important physical quantity to measure the demagnetization resistance of magnets. High coercivity is the key to maintaining high stability of magnets in service environments. During the use of magnets, the higher the coercivity of the magnet, the better the temperature stability. The second-generation 2:17 type samarium cobalt permanent magnet material belongs to a precipitation-strengthened compound, and its excellent performance comes from its unique cell wall structure: the intracellular phase, the cell wall phase, and the flake phase. The intracellular phase is the rhombohedral structure 2:17R main phase rich in Fe, which is the source of the high saturation magnetization of the magnet; the cell wall phase is the hexagonal structure 1:5H phase rich in Cu, and the cell wall phase provides the high coercivity of the magnet through domain wall pinning.

[0005] Currently, in addition to adjusting the original composition ratio, generally, the isothermal aging process is improved to promote the formation of precipitation phases, thereby achieving an increase in coercivity. For example, the coercivity of magnets is increased by extending the aging time or by stepwise aging. Some studies have shown that pressure can have an important impact on the structure and magnetism of 2:17 type samarium cobalt permanent magnet materials. However, currently, there is still a lack of effective methods for regulating the coercivity of samarium cobalt magnets with high Fe content. Summary of the Invention

[0006] The embodiments of the present application provide a method for improving the coercivity of samarium cobalt magnets by high-stress electric pulse heating pre-aging. By performing high-stress pulsed current heating pre-aging treatment on samarium cobalt solid solution samples, this process can regulate the stress and defects in the samples before the aging process, and further regulate the microstructure and magnetism of the final samples, especially manifested as a significant increase in coercivity.

[0007] To solve the above technical problems, the embodiments of the present application provide a method for improving the coercivity of samarium cobalt magnets by high-stress electric pulse heating pre-aging. The method includes the following steps: First, place metal raw materials in a vacuum induction furnace according to the ratio for melting to obtain an ingot, and crush the ingot to obtain alloy powder; then, mold the alloy powder under a magnetic field and obtain a green compact by cold isostatic pressing; after sintering and solution treatment of the green compact, obtain a solid solution state samarium cobalt magnet; next, perform high-stress pre-aging treatment on the solid solution state samarium cobalt magnet using plasma discharge sintering technology; finally, perform the first aging treatment and the second aging treatment on the samples after high-stress pre-aging treatment in sequence to obtain samarium cobalt magnets.

[0008] In some exemplary embodiments, the pressure of the high-stress pre-aging treatment is 50 MPa to 80 MPa, the temperature is 750 °C, and the holding time under pressure is 30 min to 100 min.

[0009] In some exemplary embodiments, place the samples after high-stress pre-aging treatment in a muffle furnace and perform the first aging treatment and the second aging treatment in sequence; among them, the temperature of the first aging treatment is 840 °C, and the aging time is 10 h; the temperature of the second aging treatment is 400 °C, and the aging time is 1 h to 10 h.

[0010] In some exemplary embodiments, during the first-step aging treatment, the heating process is as follows: heating from 0 °C to 790 °C at a heating rate of 5 °C / min for 158 min; heating from 790 °C to 830 °C at a heating rate of 2 °C / min for 20 min; heating from 830 °C to 840 °C at a heating rate of 1 °C / min for 10 min.

[0011] In some exemplary embodiments, after the first-step aging treatment, it is cooled to 400 °C at a cooling rate of 0.7 °C / min for the second-step aging treatment; after the second-step aging treatment, it is cooled to room temperature in the furnace to obtain a samarium-cobalt magnet.

[0012] In some exemplary embodiments, during the high-stress pre-aging treatment, after the heat preservation and pressure holding are completed, the heating is stopped, the pressure is reduced to 0, and then the sample is taken out to complete the high-stress pre-aging treatment.

[0013] In some exemplary embodiments, the metal raw materials are industrial Sm, Co, Cu, Fe, Zr with a purity > 99.5 wt%, and the metal raw materials are placed in an intermediate-frequency vacuum induction furnace according to the ratio and melted under argon protection to form a high-Fe alloy ingot; the alloy composition of the high-Fe alloy ingot is Sm 25 Co bla Fe x Cu 5.6 Zr 3.0 (x = 19.5 wt.% to 21.5 wt.%).

[0014] In some exemplary embodiments, the preparation process of the solution-treated samarium-cobalt magnet includes: pressing and forming the coarsely crushed and ball-milled alloy powder in a magnetic field > 10 kOe, and cold isostatically pressing at 200 MPa to form a green body; sintering the green body at 1180 °C to 1200 °C for 60 min to 90 min under argon protection, and then solution-treating at 1150 °C to 1170 °C for 60 min to obtain a solution-treated samarium-cobalt magnet.

[0015] In some exemplary embodiments, after obtaining the solution-treated samarium-cobalt magnet, before performing the high-stress pre-aging treatment on the solution-treated samarium-cobalt magnet using the plasma discharge sintering technology, it further includes: cutting the solution-treated samarium-cobalt magnet into cylindrical samples by wire cutting; grinding the surface of the cylindrical samples with sandpaper until smooth, and then stacking the samples and steel columns in a steel sleeve and performing the high-stress pre-aging treatment using the plasma discharge sintering technology.

[0016] In some exemplary embodiments, the specifications of the cylindrical samples are: diameter 6 mm, height 3 mm.

[0017] The technical solution provided by the embodiment of the present application has at least the following advantages:

[0018] The embodiment of the present application provides a method for improving the coercivity of samarium-cobalt magnets by high-stress electric pulse heating pre-aging. The method includes the following steps: First, place metal raw materials in a vacuum induction furnace according to the ratio for melting to obtain an ingot, and crush the ingot to obtain alloy powder; then, mold the alloy powder in a magnetic field and obtain a green compact by cold isostatic pressing; after sintering and solution treatment of the green compact, obtain a solution-state samarium-cobalt magnet; next, perform high-stress pre-aging treatment on the solution-state samarium-cobalt magnet by using plasma discharge sintering technology; finally, perform the first aging treatment and the second aging treatment on the sample after high-stress pre-aging treatment in sequence to obtain a samarium-cobalt magnet.

[0019] The present application aims to provide a simple method for improving the coercivity of 2:17 type samarium-cobalt magnets. By combining high stress and pulse current heating methods, the solution-state samarium-cobalt alloy is subjected to high-stress pulse current heating pre-aging treatment by using plasma discharge sintering technology (SPS), and then conventional aging treatment is performed. Experimental results show that compared with the sample without high-stress pulse current heating pre-aging treatment, the coercivity of the samarium-cobalt magnet subjected to high-stress (50 MPa - 80 MPa) pulse current heating pre-aging treatment for 30 min - 100 min is increased by 31.2% - 89.3%. Description of the Drawings

[0020] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a proportional limitation.

[0021] Figure 1 It is a schematic flow chart of the method for improving the coercivity of samarium-cobalt magnets by high-stress electric pulse heating pre-aging provided by an embodiment of the present application.

[0022] Figure 2 It is the demagnetization curve of the hysteresis loop of the sample in Embodiment 1 of the present application.

[0023] Figure 3 It is the demagnetization curve of the hysteresis loop of the sample in Embodiment 2 of the present application.

[0024] Figure 4 It is the demagnetization curve of the hysteresis loop of the sample in Embodiment 3 of the present application.

[0025] Figure 5 It is the demagnetization curve of the hysteresis loop of Comparative Example 1 of the present application.

[0026] Figure 6 It is the demagnetization curve of the hysteresis loop of the sample in Embodiment 4 of the present application.

[0027] Figure 7 It is the demagnetization curve of the hysteresis loop of Comparative Example 2 of the present application. Specific Embodiments

[0028] As can be seen from the background art, the prior art still lacks an effective method for regulating the coercivity of high-Fe-content samarium cobalt magnets.

[0029] In the technology of improving the coercivity by promoting the formation of precipitation phases through improving the isothermal aging process, and in the related technologies of improving the coercivity of magnets by extending the aging time or step aging, Chinese Patent Document CN116504477A proposes a method for improving the coercivity of samarium cobalt magnets through rapid heating and cooling pretreatment. After heating the solution-state alloy to 400°C - 800°C at a heating rate of 50°C / s - 150°C / s and holding for 30s - 300s in a special rapid heat treatment furnace, and then performing a conventional aging treatment at 800°C - 850°C, the coercivity of the magnet is effectively improved.

[0030] Pressure is an important parameter for regulating phase transformation. In recent years, people have begun to pay attention to how to use high pressure to control the structure and magnetism of 2:17 type samarium cobalt permanent magnet materials. Chinese Patent Document CN201811060403.X generates a super high pressure of 900MPa - 1100MPa through Ar gas during the magnet sintering (1000°C - 1010°C), solution treatment (980°C - 990°C) and tempering (780°C - 790°C), that is, during the aging process, and then obtains a magnet with high coercivity, but the Fe content in the sample is not mentioned in the patent. Chinese Patent Document CN201910671594.1 generates a super high pressure of 900MPa - 1100MPa through Ar gas during the pre-tempering and tempering (i.e., pre-aging and aging) of magnets with an Fe content of 15wt% - 15.8wt%. The temperature of pre-tempering is 720°C - 740°C, and the tempering temperature is not given, and then a magnet with high coercivity is obtained. Chinese Patent Document 202110244313.1 applies a long-term compressive stress (30MPa - 100MPa) during the aging process (810°C - 850°C) of this type of magnet, and then obtains a magnet with high coercivity. It can be seen from the above reports that pressure can have an important impact on the structure and magnetism of 2:17 type samarium cobalt permanent magnet materials. However, at present, people still lack an effective method for regulating the coercivity of high-Fe-content samarium cobalt magnets.

[0031] To solve the above technical problems, an embodiment of the present application provides a method for improving the coercivity of a samarium-cobalt magnet by high-stress electric pulse heating pre-aging. The method includes the following steps: First, place metal raw materials in a vacuum induction furnace according to a ratio for melting to obtain an ingot, and crush the ingot to obtain alloy powder; then, mold the alloy powder in a magnetic field and obtain a green compact by cold isostatic pressing; after sintering and solution treatment of the green compact, obtain a solution-state samarium-cobalt magnet; next, use plasma discharge sintering technology to perform high-stress pre-aging treatment on the solution-state samarium-cobalt magnet; finally, perform the first aging treatment and the second aging treatment on the sample after high-stress pre-aging treatment in sequence to obtain a samarium-cobalt magnet. An embodiment of the present application provides a method for improving the coercivity of a samarium-cobalt magnet by high-stress electric pulse heating pre-aging. By performing high-stress pulsed current heating pre-aging treatment on the samarium-cobalt solution-state sample, this process can regulate the stress and defects in the sample before the aging process, and further regulate the microstructure and magnetism of the final-state sample, especially manifested as a significant increase in coercivity.

[0032] The following will elaborate on each embodiment of the present application in conjunction with the accompanying drawings. However, those of ordinary skill in the art can understand that in each embodiment of the present application, many technical details are proposed for the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be achieved.

[0033] See Figure 1 , an embodiment of the present application provides a method for improving the coercivity of a samarium-cobalt magnet by high-stress electric pulse heating pre-aging, including the following steps:

[0034] Step S1: Place metal raw materials in a vacuum induction furnace according to a ratio for melting to obtain an ingot, and crush the ingot to obtain alloy powder.

[0035] Step S2: Mold the alloy powder in a magnetic field and obtain a green compact by cold isostatic pressing; after sintering and solution treatment of the green compact, obtain a solution-state samarium-cobalt magnet.

[0036] Step S3: Use plasma discharge sintering technology to perform high-stress pre-aging treatment on the solution-state samarium-cobalt magnet.

[0037] Step S4: Perform the first aging treatment and the second aging treatment on the sample after high-stress pre-aging treatment in sequence to obtain a samarium-cobalt magnet.

[0038] In some embodiments, in step S3, the pressure of the high-stress pre-aging treatment is 50 MPa to 80 MPa, the temperature is 750 °C, and the holding pressure time is 30 min to 100 min.

[0039] In this application, the plasma discharge sintering (SPS) technology is used to perform electro-pulse heating pre-aging treatment on the solid-solution state samarium-cobalt magnet under high stress. By controlling the SPS pulse current heating program and the pressure control program, the sample pressure is first increased to the target pressure (50 MPa to 80 MPa), then the sample temperature is raised from room temperature to 750 °C within 5 minutes, followed by holding the temperature and pressure for 30 minutes to 100 minutes, and then rapidly cooling and depressurizing to complete the high-stress pre-aging treatment.

[0040] Usually, when people carry out the aging treatment process of samarium-cobalt magnets, the electric furnace heating method is usually adopted. In comparison, electro-pulse heating can not only increase the temperature rapidly, but also there is an interaction between the pulse current and the microstructure (including crystal defects, etc.) in the material during the heating process, which in turn affects the recrystallization, phase transformation and other behaviors of the material. The present invention innovatively combines high stress and the electro-pulse heating method, and uses the plasma discharge sintering technology to perform high-stress pulse current heating pre-aging treatment on the solid-solution state samarium-cobalt alloy, and then performs the conventional aging treatment. The experimental results show that compared with the samples without high-stress pulse current heating pre-aging treatment, the coercivity of the samarium-cobalt magnets after 30 minutes to 100 minutes of high-stress (50 MPa to 80 MPa) pulse current heating pre-aging treatment has increased by 31.2% to 89.3%.

[0041] In some embodiments, in step S4, the sample after the high-stress pre-aging treatment is placed in a muffle furnace and subjected to the first-step aging treatment and the second-step aging treatment in sequence; wherein, the temperature of the first-step aging treatment is 840 °C and the aging time is 10 h; the temperature of the second-step aging treatment is 400 °C and the aging time is 1 h to 10 h.

[0042] In some embodiments, during the first-step aging treatment in step S4, the heating process is as follows: the temperature is raised from 0 °C to 790 °C at a heating rate of 5 °C / min for 158 minutes; the temperature is raised from 790 °C to 830 °C at a heating rate of 2 °C / min for 20 minutes; the temperature is raised from 830 °C to 840 °C at a heating rate of 1 °C / min for 10 minutes.

[0043] In some embodiments, after the first-step aging treatment, it is cooled to 400 °C at a cooling rate of 0.7 °C / min for the second-step aging treatment; after the second-step aging treatment, it is cooled to room temperature with the furnace to obtain the samarium-cobalt magnet.

[0044] In some embodiments, during the high-stress pre-aging treatment in step S3, after the heat preservation and pressure holding are completed, the heating is stopped and the pressure is reduced to 0, and then the sample is taken out to complete the high-stress pre-aging treatment.

[0045] In some embodiments, in step S1, industrial Sm, Co, Cu, Fe, and Zr with a purity > 99.5 wt% are used as metal raw materials. The metal raw materials are placed in an intermediate frequency vacuum induction furnace according to the ratio and melted under argon protection to form a high-Fe alloy ingot; the alloy composition of the high-Fe alloy ingot is Sm 25 Co bla Fe x Cu 5.6 Zr 3.0 (x = 19.5 wt.% - 21.5 wt.%).

[0046] In this application, a solution-state 2:17 type samarium cobalt magnet with an Fe content of 19.5 wt% - 21.5 wt% is selected. Using the plasma discharge sintering technology, by controlling the SPS pulse current heating program and the pressure control program, first raise the sample pressure to the target pressure (50 MPa - 80 MPa), and then raise the sample temperature from room temperature to 750 °C within 5 min, and perform high-stress pre-aging on the solution-state sample for 30 min - 100 min; afterwards, perform conventional aging treatment on the sample with high-stress pulse current heating pre-aging to obtain a 2:17 type samarium cobalt magnet with high coercivity.

[0047] In some embodiments, the preparation process of the solution-state samarium cobalt magnet in step S2 includes: pressing and forming the alloy powder after coarse crushing and ball milling in a magnetic field > 10 kOe, and forming a green body by cold isostatic pressing at 200 MPa; sintering the green body at 1180 °C - 1200 °C for 60 min - 90 min under argon protection, and then performing solution treatment at 1150 °C - 1170 °C for 60 min to obtain the solution-state samarium cobalt magnet.

[0048] In some embodiments, after obtaining the solution-state samarium cobalt magnet in step S2 and before performing high-stress pre-aging treatment on the solution-state samarium cobalt magnet using the plasma discharge sintering technology in step S3, it further includes: cutting the solution-state samarium cobalt magnet into a cylindrical sample by wire cutting; grinding the surface of the cylindrical sample with sandpaper until it is smooth, and then stacking the sample and the steel column in a steel sleeve and performing high-stress pre-aging treatment using the plasma discharge sintering technology.

[0049] Specifically, after obtaining the solid-solution state samarium cobalt magnet and before the high-stress pre-aging treatment, the solid-solution state 2:17 type samarium cobalt permanent magnet with an Fe content of 19.5wt% - 21.5wt% is cut into a cylindrical shape by wire cutting. The sample specifications are: a diameter of 6 mm and a height of 3 mm; after wire cutting, the surface of the sample is polished with sandpaper until it is smooth. Prepare a steel sleeve with an inner diameter of 6 mm, an outer diameter of 20 mm, and a height of 9 mm, and a steel column with a diameter of 6 mm and a height of 3 mm. Stack the sample and the steel column in the steel sleeve in the order of "steel column / sample / steel column", and ensure that the cumulative height of the sample and the steel is equal to the height of the steel sleeve. Then, weld a thermocouple for temperature measurement in the middle of the steel sleeve for temperature monitoring. The high-stress pre-aging is carried out by using the spark plasma sintering (SPS) technology. The specific method is: by controlling the SPS pulse current heating program and the pressure control program, first raise the sample pressure to the target pressure (50 MPa - 80 MPa), then raise the sample temperature from room temperature to 750 °C within 5 minutes, then hold the temperature and pressure for 30 min - 100 min, and then quickly cool down and reduce the pressure to complete the high-stress pre-aging.

[0050] In some embodiments, the cylindrical sample specifications are: a diameter of 6 mm and a height of 3 mm.

[0051] Finally, the samples after the aging treatment are processed and tested. Specifically, the samples after the aging treatment are cut into small cylinders by wire cutting, polished with sandpaper until the diameter and height are both about 1 mm, and the hysteresis loop of the magnet is measured by using a physical property measurement system (PPMS).

[0052] The method for improving the coercivity of samarium cobalt magnets by high-stress electric pulse heating pre-aging provided by the present application is introduced in detail through specific embodiments below.

[0053] Example 1

[0054] (1) The solid-solution state 2:17 type samarium cobalt permanent magnet with an Fe content of 21.5wt% is cut into a cylindrical shape by wire cutting. The sample specifications are: a diameter of 6 mm and a height of 3 mm; after wire cutting, the surface of the sample is polished with sandpaper until it is smooth. Prepare a steel sleeve with an inner diameter of 6 mm, an outer diameter of 20 mm, and a height of 9 mm, and a steel column with a diameter of 6 mm and a height of 3 mm. Stack the sample and the steel column in the steel sleeve in the order of "steel column / sample / steel column", and ensure that the cumulative height of the sample and the steel is equal to the height of the steel sleeve. Then, weld a thermocouple for temperature measurement in the middle of the steel sleeve for temperature monitoring. The high-stress pre-aging is carried out by using the spark plasma sintering (SPS) technology. The specific method is: by controlling the SPS temperature and pressure control program, first raise the sample pressure to 50 MPa, then raise the sample temperature from room temperature to 750 °C within 5 minutes, then hold the temperature and pressure for 30 min, and then cool down and reduce the pressure to take out the sample to complete the pre-aging.

[0055] (2) Use wire cutting to take out the pre-aged sample and polish it smoothly. Then, conduct conventional aging treatment on the pre-aged sample. Specifically: heat from 0 °C to 790 °C at a heating rate of 5 °C / min for 158 min; then heat from 790 °C to 830 °C at a heating rate of 2 °C / min for 20 min; then heat from 830 °C to 840 °C at a heating rate of 1 °C / min for 10 min; subsequently, conduct heat treatment at 840 °C for 10 h; finally, cool to 400 °C at a cooling rate of 0.7 °C / min and then to room temperature.

[0056] (3) Conduct magnetic property testing on the aged sample to obtain a magnet with relatively high magnetic properties (H ci = 16.14 kOe, B r = 12.0 kGs, (BH) max = 30.63 MGOe). Figure 2 is the demagnetization curve of the hysteresis loop of the sample in Example 1 of this application. Compared with the sample without pre-aging (Comparative Example 1), the coercivity is increased by 31.2%.

[0057] Example 2

[0058] (1) Cut a solution-treated 2:17 type samarium-cobalt permanent magnet with a Fe content of 21.5 wt% into a cylindrical shape using wire cutting. The sample specifications are: diameter 6 mm, height 3 mm; after wire cutting, polish the sample surface to be smooth. Prepare a steel sleeve with an inner diameter of 6 mm, an outer diameter of 20 mm, and a height of 9 mm, and a steel column with a diameter of 6 mm and a height of 3 mm. Stack the sample and the steel column in the steel sleeve in the order of "steel column / sample / steel column", and ensure that the cumulative height of the sample and the steel is equal to the height of the steel sleeve. Then, weld a thermocouple for temperature monitoring at the exact middle part of the steel sleeve. Use spark plasma sintering (SPS) technology for high-stress pre-aging. The specific method is: by controlling the SPS temperature and pressure control program, first raise the sample pressure to 50 MPa, then raise the sample temperature from room temperature to 750 °C within 5 min, then hold the temperature and pressure for 70 min, and then cool down and reduce the pressure to take out the sample to complete the pre-aging.

[0059] (2) Use wire cutting to take out the pre-aged sample and polish it smoothly. Then, conduct conventional aging treatment on the pre-aged sample (the same as step 2 of Example 1).

[0060] (3) Conduct magnetic property testing on the aged sample to obtain a magnet with relatively high magnetic properties (H ci = 22.19 kOe, B r = 11.9 kGs, (BH) max = 27.84 MGOe). Figure 3It is the demagnetization curve of the hysteresis loop of the sample in Example 2 of this application. Compared with the sample without pre-aging (Comparative Example 1), the coercivity has increased by 80.4%.

[0061] Example 3

[0062] (1) The solution-state 2:17 type samarium-cobalt permanent magnet with a Fe content of 21.5 wt% was cut into a cylindrical shape by wire cutting. The sample specifications are: diameter 6 mm, height 3 mm; after wire cutting, the surface of the sample was polished with sandpaper until smooth. A steel sleeve with an inner diameter of 6 mm, an outer diameter of 20 mm, and a height of 9 mm and a steel column with a diameter of 6 mm and a height of 3 mm were prepared. The sample and the steel column were stacked in the steel sleeve in the order of "steel column / sample / steel column", and it was ensured that the cumulative height of the sample and the steel was equal to the height of the steel sleeve. Then, a thermocouple for temperature monitoring was welded at the exact middle part of the steel sleeve. The high-stress pre-aging was carried out by using the spark plasma sintering (SPS) technique. The specific method is: by controlling the SPS temperature and pressure control program, first raise the sample pressure to 50 MPa, then raise the sample temperature from room temperature to 750 °C within 5 minutes, then hold the temperature and pressure for 100 minutes, and then cool down and reduce the pressure to take out the sample to complete the pre-aging.

[0063] (2) The pre-aged sample was taken out by wire cutting and polished smoothly, and then the pre-aged sample was subjected to conventional aging treatment (the same as step 2 of Example 1).

[0064] (4) The magnetic properties of the aged sample were tested, and a magnet with relatively high magnetic properties was obtained (H ci = 23.28 kOe, B r = 11.8 kGs, (BH) max = 27.31 MGOe). Figure 4 It is the demagnetization curve of the hysteresis loop of the sample in Example 3 of this application. Compared with the sample without pre-aging (Comparative Example 1), the coercivity has increased by 89.3%.

[0065] Comparative Example 1

[0066] (1) A solution-state 2:17 type samarium-cobalt magnet with a Fe content of 21.5% was taken, and it was cut into a cylinder with a diameter of 5 mm and a height of 2 mm by wire cutting. The sample was subjected to conventional aging treatment, and the specific process was the same as step 2 of Example 1.

[0067] (2) The magnetic properties of the aged sample were tested, and the magnetic properties of the magnet were obtained as: H ci = 12.30 kOe, B r = 11.90 kGs, (BH) max = 30.08 MGOe. Figure 5 It is the demagnetization curve of the hysteresis loop of Comparative Example 1 of this application.

[0068] Example 4

[0069] (1) The solution-state 2:17 type samarium-cobalt permanent magnet with 19.5 wt% Fe content was cut into a cylindrical shape by wire cutting. The sample specifications were: diameter 6 mm, height 3 mm; after wire cutting, the sample surface was polished with sandpaper until smooth. A steel sleeve with an inner diameter of 6 mm, an outer diameter of 20 mm, and a height of 9 mm and a steel column with a diameter of 6 mm and a height of 3 mm were prepared. The sample and the steel column were stacked in the steel sleeve in the order of "steel column / sample / steel column", and it was ensured that the cumulative height of the sample and the steel was equal to the height of the steel sleeve. Then, a thermocouple for temperature measurement was welded at the exact middle position of the steel sleeve for temperature monitoring. The high-stress pre-aging was carried out by using the spark plasma sintering (SPS) technology. The specific method was: by controlling the SPS temperature and pressure control program, the sample pressure was first raised to 80 MPa, then the sample temperature was raised from room temperature to 750 °C within 5 min, then held at constant temperature and pressure for 30 min, and then the sample was taken out after cooling and depressurizing to complete the pre-aging.

[0070] (2) The pre-aged sample was taken out by wire cutting and polished smooth, and then the pre-aged sample was subjected to conventional aging treatment (the same as step 2 of Example 1).

[0071] (3) The magnetic properties of the aged sample were tested, and a magnet with relatively high magnetic properties was obtained (H ci = 24.8 kOe, B r = 11.4 kGs, (BH) max = 29.74 MGOe). Figure 6 is the demagnetization curve of the hysteresis loop of the sample in Example 4 of this application. Compared with the sample without pre-aging (Comparative Example 2), the coercivity was increased by 37.0%.

[0072] Comparative Example 2

[0073] (1) A solution-state 2:17 type samarium-cobalt magnet with 19.5% Fe content was taken, and it was cut into a cylinder with a diameter of 5 mm and a height of 2 mm by wire cutting. The sample was subjected to conventional aging treatment, and the specific process was the same as step 2 of Example 1.

[0074] (2) The magnetic properties of the aged sample were tested, and the magnetic properties of the magnet were: H ci = 18.1 kOe, B r = 11.70 kGs, (BH) max = 30.62 MGOe. Figure 7 is the demagnetization curve of the hysteresis loop of Comparative Example 2 of this application.

[0075] The comparison of the magnetic properties of the samples in the above embodiments and the comparative example samples of this application is shown in Table 1 below.

[0076] Table 1 Comparison of Magnetic Properties between Samples of Embodiments and Comparative Examples

[0077]

[0078] Compared with the prior art, the advantages of the present application are as follows: The present application innovatively adopts a pre-aging method coupling high stress and pulsed current heating. At a temperature of 750 °C and a pressure of 50 MPa to 80 MPa, a high-stress pulsed current heating pre-aging treatment is performed on the samarium-cobalt solid solution state sample. By using this process, the stress and defects in the sample before the aging process can be regulated, and then the microstructure and magnetism of the final state sample can be regulated, especially manifested as a significant increase in coercivity. The present application is significantly different from the regulation of the coercivity of low-Fe content magnets in the existing samarium-cobalt high-pressure related patents and reports, and is also significantly different from the atmospheric pressure pre-aging process or low-pressure long-time aging process of samarium-cobalt magnets.

[0079] According to the above technical solution, an embodiment of the present application provides a method for improving the coercivity of a samarium-cobalt magnet by high-stress electric pulse heating pre-aging. The method includes the following steps: First, metal raw materials are placed in a vacuum induction furnace according to a ratio for melting to obtain an ingot, and the ingot is crushed to obtain alloy powder; then, the alloy powder is molded under a magnetic field and cold isostatic pressing is used to obtain a green body; after the green body is sintered and solution-treated, a solid solution state samarium-cobalt magnet is obtained; next, a high-stress pre-aging treatment is performed on the solid solution state samarium-cobalt magnet by using a plasma discharge sintering technology; finally, the sample after the high-stress pre-aging treatment is sequentially subjected to a first aging treatment and a second aging treatment to obtain a samarium-cobalt magnet.

[0080] The present application aims to provide a simple method for improving the coercivity of 2:17 type samarium-cobalt magnets. By combining high stress and pulsed current heating methods, a high-stress pulsed current heating pre-aging treatment is performed on the solid solution state samarium-cobalt alloy by using a plasma discharge sintering technology (SPS) technology, and then a conventional aging treatment is performed. The experimental results show that compared with the samples without high-stress pulsed current heating pre-aging treatment, the coercivity of the samarium-cobalt magnets subjected to high-stress (50 MPa to 80 MPa) pulsed current heating pre-aging treatment for 30 min to 100 min is increased by 31.2% to 89.3%.

[0081] Those of ordinary skill in the art can understand that the above embodiments are specific embodiments for implementing the present application. In actual applications, various changes can be made in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make their own changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be subject to the scope defined by the claims.

Claims

1. A method for improving the coercivity of samarium cobalt magnets by high stress electric pulse heating pre-aging, characterized in that: The following steps are involved: Placing metal raw materials in a vacuum induction furnace according to a proportion to obtain an ingot for smelting, and crushing the ingot to obtain an alloy powder; The alloy powder is molded in a magnetic field, and a green body is obtained by cold isostatic pressing; the green body is sintered and solution treated to obtain a solid solution samarium cobalt magnet; the Fe content of the solid solution samarium cobalt magnet is 19.5wt% to 21.5wt%; After obtaining the solid solution samarium cobalt magnet and before the high stress pre-aging treatment, the solid solution 2:17 type samarium cobalt permanent magnet is cut into cylindrical samples by wire cutting; the sample and the steel column are stacked in a steel sleeve in the order of "steel column / sample / steel column" to ensure that the cumulative height of the sample and the steel column is equal to the height of the steel sleeve; then a thermocouple for temperature measurement is welded in the middle of the steel sleeve for temperature monitoring; the solid solution samarium cobalt magnet is subjected to high stress pre-aging treatment by plasma discharge sintering technology, and the high stress pre-aging treatment method includes: by controlling the pulse current heating program and the pressure control program of the plasma discharge sintering technology, firstly the sample pressure is increased to 50MPa to 80MPa, then the sample temperature is increased from room temperature to 750°C within 5min, then the sample is kept warm and pressure maintained for 30min to 100min, and after the heat preservation and pressure maintenance are completed, the heating is stopped and the pressure is reduced to 0 before the sample is taken out to complete the high stress pre-aging treatment; The sample after high stress pre-aging treatment is subjected to first-step aging treatment and second-step aging treatment in sequence to obtain samarium cobalt magnet; wherein, the temperature of the first-step aging treatment is 840°C, and the aging time is 10h; the temperature of the second-step aging treatment is 400°C, and the aging time is 1h to 10h.

2. The method for improving the coercive force of samarium cobalt magnets by high stress electric pulse heating pre-aging according to claim 1, characterized in that: The sample after high stress pre-aging treatment is placed in a muffle furnace and subjected to the first step aging treatment and the second step aging treatment in sequence.

3. The method for improving the coercive force of samarium cobalt magnets by high stress electric pulse heating pre-aging according to claim 1, characterized in that: In the first step of aging treatment, the heating process is: The temperature was raised from 0°C to 790°C at a rate of 5°C / min for 158 min; The temperature was raised from 790°C to 830°C at a heating rate of 2°C / min for 20 min; The temperature was raised from 830°C to 840°C at a heating rate of 1°C / min for 10 min.

4. The method for improving the coercivity of samarium cobalt magnets by high stress electric pulse heating pre-aging according to claim 1, characterized in that: After the first aging treatment, the temperature is lowered to 400°C at a cooling rate of 0.7°C / min for the second aging treatment; after the second aging treatment, the furnace is cooled to room temperature to obtain a samarium cobalt magnet.

5. The method for improving the coercive force of samarium cobalt magnets by high stress electric pulse heating pre-aging according to claim 1, characterized in that: The metal raw materials are industrial Sm, Co, Cu, Fe and Zr with a purity of more than 99.5wt%. The metal raw materials are placed in a medium-frequency vacuum induction furnace according to a proportion and smelted under argon protection to form a high-Fe alloy ingot; the alloy composition of the high-Fe alloy ingot is Sm 25 Co bla Fe x Cu 5.6 Zr 3.0 , x =19.5wt.%~21.5wt.%.

6. The method for improving the coercive force of samarium cobalt magnets by high stress electric pulse heating pre-aging according to claim 1, characterized in that: The preparation process of the solid solution samarium cobalt magnet comprises: The coarsely crushed and ball-milled alloy powder is pressed in a magnetic field of >10kOe, and is formed into a green embryo by cold isostatic pressing at 200MPa; the green embryo is sintered at 1180℃~1200℃ for 60min~90min under argon protection, and then solution treated at 1150℃~1170℃ for 60min to obtain a solid solution samarium cobalt magnet.

7. The method for improving the coercive force of samarium cobalt magnets by high stress electric pulse heating pre-aging according to claim 1, characterized in that: After obtaining a solid solution samarium cobalt magnet, before using plasma discharge sintering technology to perform high stress pre-aging treatment on the solid solution samarium cobalt magnet, the method also includes: grinding the surface of the cylindrical sample with sandpaper until it is smooth, then stacking the sample and the steel column in a steel sleeve, and performing high stress pre-aging treatment by plasma discharge sintering technology.

8. The method for improving the coercivity of samarium cobalt magnets by high stress electric pulse heating pre-aging according to claim 7, characterized in that: The specifications of the cylindrical sample are: 6 mm in diameter and 3 mm in height.

Images