Method for preparing iron-rich samarium-cobalt-based permanent magnet through praseodymium copper powder doping modification

Abstract

The invention relates to a method for preparing an iron-rich samarium-cobalt-based permanent magnet by doping modification of praseodymium copper powder, and belongs to the technical field of magnetic materials, the method comprises the following steps: firstly, preparing an iron-rich samarium-cobalt-based cast sheet by adopting a secondary smelting process of vacuum smelting and ingot casting, and then carrying out rapid hardening and sheet throwing, so as to obtain the iron-rich samarium-cobalt-based permanent magnet. The preparation method comprises the following steps: preparing micron-sized praseodymium copper alloy powder by adopting methods of vacuum melting and ingot casting, hydrogen absorption crushing and high-energy ball milling, then uniformly mixing the praseodymium copper alloy powder with iron-rich samarium-cobalt-based powder according to a ratio, and sequentially carrying out orientation compression, cold isostatic pressing, sintering and heat treatment to obtain the samarium-cobalt-based sintered permanent magnet. The praseodymium-copper low-melting-point alloy powder is uniformly doped, so that the crystal boundary copper-poor phenomenon in the iron-rich sintered magnet is obviously improved, the room-temperature coercive force is greatly improved, meanwhile, the density and residual magnetism of the magnet are improved, the comprehensive magnetic performance is remarkably improved, an effective method is provided for improving the magnetic performance of the samarium-cobalt magnet, and the method is suitable for industrial production. Therefore, the application range is widened.

Description

Technical Field

[0001] The invention provides a method for preparing an iron-rich samarium-cobalt-based permanent magnet by doping and modifying praseodymium-copper powder, in particular to a samarium-cobalt-based rare earth permanent magnet and a preparation method thereof, belonging to the technical field of magnetic materials. Background Art

[0002] Rare earth permanent magnet materials are one of the most strategic emerging materials with unique resource characteristics in my country. They are key strategic resources for promoting scientific and technological innovation, promoting industrial upgrading, ensuring national defense security and achieving sustainable development. Among them, 2:17 type Sm (CoFeCuZr) z Permanent magnet materials have rapidly developed into the first choice for high-temperature service permanent magnet materials due to their comprehensive advantages, including good intrinsic magnetic properties, excellent temperature stability, and excellent corrosion resistance. They have an irreplaceable position. However, the magnetic energy product of sintered samarium cobalt permanent magnets prepared by traditional methods is relatively low. The maximum magnetic energy product reported so far is only 35.4 MGOe, less than 60% of the theoretical value, leaving significant room for improvement. In addition, the rapid development of high-tech fields such as aerospace and modern weaponry, advanced rail transportation, energy-saving and new energy permanent magnet motors has placed higher requirements on the magnetic properties and high-temperature characteristics of samarium cobalt permanent magnet materials, and the high-end market demand has huge potential.

[0003] Previous studies have shown that in Sm(CoFeCuZr) z Increasing the Fe content in the composition can obtain high saturation magnetization and remanence, thereby increasing the magnetic energy product. Despite this, this method has two shortcomings: First, the Fe element will increase the process sensitivity, resulting in incompatibility with key preparation processes such as traditional mechanical crushing and ball milling, sintering and heat treatment, and is difficult to control. Secondly, the introduction of iron-rich content is often accompanied by problems such as microstructural inhomogeneity, complex evolution of nanocellular organizational structure, and the demagnetization of grain boundaries before the interior of the grains during the demagnetization process, resulting in deterioration of squareness and a sharp decrease in coercivity.

[0004] In order to improve the high coercivity of iron-rich samarium cobalt permanent magnets, Chinese patent applications No. 201210012944.1 and 201811313384.7 use a small amount of nano-scale Cu powder, micron-scale or nano-scale CuO powder and Sm (CoFeCuZr) z The magnetic powder is fully mixed and sintered to repair the copper deficiency in the grain boundary area and improve the coercivity and squareness of the magnet. However, this method will reduce the remanence of the magnet, limiting the improvement of the overall magnetic performance. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems by adopting a method different from the prior art, and to propose a method for preparing iron-rich samarium-cobalt based permanent magnets by doping and modifying praseodymium copper powder.

[0006] The technical solution of the present invention is achieved as follows: a method for preparing an iron-rich samarium-cobalt-based permanent magnet by doping and modifying praseodymium-copper powder, wherein the praseodymium-copper powder is doped in the iron-rich samarium-cobalt-based permanent magnet, and the iron-rich samarium-cobalt powder used has the following components by mass percentage: Sm: 24.5-26.5wt.%; Fe: 20.7wt.%; Cu: 4.1wt.%; Zr: 2.9wt.%; Co: balance; to compensate for the burnout of rare earth Sm during the smelting process, after the basic ratio is completed and before the smelting begins, an additional Sm raw material is added, which accounts for 8wt.% of the Sm mass in the above ratio;

[0007] Praseodymium copper powder by mass percentage: Cu: 15.5-17.5wt.%, Pr: balance;

[0008] Calculated by mass percentage: the praseodymium copper powder accounts for 1 to 4 wt.%, and the rest is iron-rich samarium-cobalt magnetic powder.

[0009] Preferably, the method for preparing an iron-rich samarium-cobalt-based permanent magnet by doping and modifying praseodymium-copper powder comprises the following steps:

[0010] (1) Preparation of iron-rich samarium-cobalt-based cast alloy: First, metal raw materials are selected according to the mass percentage of Sm: 24.5-26.5 wt.%; Fe: 20.7 wt.%; Cu: 4.1 wt.%; Zr: 2.9 wt.%; Co: the balance, and then Sm raw material is added in an amount of 8 wt.% of the Sm mass in the above ratio;

[0011] The metal raw materials are subjected to medium-frequency induction melting in a vacuum to convert them into alloy liquid. After a 3-minute refining process, the alloy liquid is poured into a copper mold with circulating cooling water and cooled to obtain a plate-shaped iron-rich samarium-cobalt-based cast alloy.

[0012] In order to improve the composition uniformity of the alloy ingot, the prepared plate-shaped ingot was then subjected to the rapid solidification belt method to obtain samarium-cobalt rapid solidification casting sheets.

[0013] (2) Preparation of iron-rich samarium-cobalt-based alloy powder: The rapidly solidified casting sheet obtained in step (1) is mechanically crushed into flakes, which are then sealed and placed in a high-temperature autoclave. After evacuation, 3-5 MPa of hydrogen is introduced, and the mixture is heated to 80-100°C and kept warm for 20-40 hours. The mixture is cooled to room temperature with the furnace to obtain a coarse powder with a particle size of less than 110 μm after hydrogen absorption and crushing. The coarse powder is then sealed and placed in a stainless steel tank with No. 120 aviation gasoline as the medium for rolling ball milling for 4-6 hours. The powder is then dried in a vacuum drying oven and dried to obtain a fine powder with an average particle size distribution of 3 μm to 5 μm.

[0014] (3) Preparation of praseodymium-copper cast alloy: metallic praseodymium and copper are selected as raw materials and smelted into alloy ingots in a vacuum induction heating furnace. The ingot composition is: Cu: 15.5-17.5 wt.%, Pr: balance;

[0015] (4) Preparation of praseodymium-copper alloy powder: The ingot obtained in step (3) is crushed into blocks, placed in a sealed high-temperature and high-pressure reactor, and 0.1-0.5 MPa of hydrogen is introduced after vacuuming, and maintained at room temperature for 0.5-1 hour to obtain a coarse powder with a particle size of less than 150 μm after hydrogen absorption and crushing. Then, the coarse powder is subjected to high-energy ball milling for 2-3 hours, dried in a vacuum drying oven, and dried to obtain a Pr-Cu alloy fine powder with an average particle size distribution of 3 μm to 5 μm;

[0016] (5) Powder mixing and green compacting: The iron-rich samarium-cobalt powder and the praseodymium-copper powder with a particle size distribution of 3 μm to 5 μm obtained in steps (2) and (4) above are placed in a mixer according to the above proportions and mixed for 8 to 10 hours to obtain a mixed powder. The mixed powder is then placed in a dedicated non-magnetic steel mold and subjected to vertical pressing and orientation molding in a magnetic field of 15 kOe. The green compact is then subjected to cold isostatic pressing at a pressure of 250 to 280 MPa and a holding time of 120 to 180 seconds to obtain a dense green compact.

[0017] (6) Sintering treatment: The green compact obtained by cold isostatic pressing in step (5) is placed in a vacuum sintering furnace for sintering. First, the temperature is raised from room temperature to 400°C under vacuum, kept at this temperature for 1 hour, and then raised to 1170-1185°C for pre-sintering for 0.5-2 hours; then the temperature is gradually raised to 1215-1220°C and sintered under argon protection for 0.5-2 hours, with 0.45 MPa of inert Ar gas introduced during the sintering process;

[0018] (7) Solution treatment: After the sintering time in step (6) is completed, the temperature is slowly lowered to 1170-1180°C for solution treatment, and the temperature is kept at this temperature for 5-10 hours, followed by air cooling to room temperature to obtain a supersaturated solid solution;

[0019] (8) Aging treatment: The obtained solid solution is kept at 810°C for 40 hours, then cooled to 410°C at a cooling rate of 0.6°C / min and kept at this temperature for 10 hours. Finally, it is air-cooled in the furnace or naturally cooled to room temperature to obtain an iron-rich samarium-cobalt-based magnet doped with praseodymium copper.

[0020] Preferably, in the method for preparing iron-rich samarium-cobalt-based permanent magnets by doping and modifying praseodymium copper powder, the purity of each component in the iron-rich samarium-cobalt-based cast alloy is: Sm ≥ 99.9%, Fe ≥ 99.8%, Cu ≥ 99.5%, Zr ≥ 99.9%, Co ≥ 99.8%; the purity of each component in the praseodymium copper cast alloy is: Pr ≥ 99.9%, Cu ≥ 99.5%.

[0021] Preferably, in the method for preparing iron-rich samarium-cobalt-based permanent magnets by doping and modifying praseodymium-copper powder, in the step (2), the iron-rich samarium-cobalt-based alloy fragments are 3 to 5 g / piece.

[0022] Beneficial effects of the present invention:

[0023] The present invention adopts a method for preparing iron-rich samarium-cobalt-based permanent magnets by doping and modifying praseodymium-copper powder. By utilizing the technology of liquid-phase assisted sintering of a low-melting-point eutectic praseodymium-copper alloy and the regulation of the preparation process, the density of the magnet is improved, the copper-poor phenomenon at the grain boundaries is repaired, and the cell wall phase and the cellular structure near the grain boundaries of the magnet are more uniform and complete. Compared with magnets not doped with praseodymium-copper powder, the samarium-cobalt-based sintered magnets prepared using the method of the present invention improve the coercive force of the magnet while maintaining and improving the high remanence. As the doping amount of praseodymium-copper powder increases, the coercive force of the magnet is significantly increased to 1.4 to 2.7 times. Moreover, when the doping amount of praseodymium-copper powder is 1 to 4 wt.%, the coercive force and magnetic energy product of the magnet are significantly higher than those of undoped magnets. Therefore, the praseodymium-copper powder-doped magnets prepared by the method of the present invention have the advantage of being used in high-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0025] Figure 1 This is a process flow chart for preparing iron-rich samarium-cobalt-based permanent magnets by doping and modifying praseodymium-copper powder according to the present invention. DETAILED DESCRIPTION

[0026] Based on the above research background, the present invention provides a praseodymium-copper powder doping and modification method for preparing iron-rich samarium-cobalt-based permanent magnets. This method uses doped low-melting-point praseodymium-copper alloy powder for liquid-phase assisted sintering to promote the diffusion of copper elements to the grain boundaries, thereby increasing the copper content at the grain boundaries of the iron-rich samarium-cobalt-based alloy magnets, repairing the copper-poor phenomenon at the grain boundaries, and significantly improving the copper-poor phenomenon at the grain boundaries of the iron-rich sintered magnets. The room temperature coercivity is greatly improved, and at the same time, the density and remanence of the magnet are improved. This method includes the following specific implementation process:

[0027] (1) Preparation of iron-rich samarium-cobalt-based cast alloy: First, metal raw materials are selected according to the mass percentage of Sm: 24.5-26.5 wt.%; Fe: 20.7 wt.%; Cu: 4.1 wt.%; Zr: 2.9 wt.%; Co: balance. After the metal raw materials are prepared, Sm raw materials are added in an amount of 8 wt.% of the Sm mass in the above ratio.

[0028] Then, the metal raw materials with the good proportions are melted by medium frequency induction in a vacuum to convert them into alloy liquid. After 3 minutes of refining, they are poured into a copper mold with circulating cooling water and cooled to obtain a plate-shaped alloy casting.

[0029] Furthermore, in order to improve the composition uniformity of the alloy ingot, the prepared plate-shaped ingot is then subjected to a rapid solidification strip throwing method to obtain samarium-cobalt rapid solidification casting sheets.

[0030] (2) Preparation of iron-rich samarium-cobalt-based alloy powder: The rapidly solidified casting sheet obtained in step (1) was mechanically crushed into flakes, each weighing less than 5 g. The casting sheet was then sealed and placed in a high-temperature autoclave, and vacuumed to a pressure of less than 1×10 -3 pa, then 4MPa hydrogen is introduced, auxiliary heating is performed to 80°C, and the temperature is kept for 20 hours. After cooling to room temperature with the furnace, a coarse powder with a particle size of less than 110 microns after hydrogen absorption and crushing is obtained. Then, the coarse powder is sealed and placed in a stainless steel tank with No. 120 aviation gasoline as the medium for rolling ball milling for 6 hours, and then dried in a vacuum drying oven. After drying, fine powder with an average particle size distribution of 3 microns to 5 microns is obtained.

[0031] (3) Preparation of praseodymium-copper cast alloy: metallic praseodymium and copper are selected as raw materials and smelted into alloy ingots in a vacuum induction heating furnace. The ingot composition is: Cu: 15.5-17.5wt.%, Pr: balance.

[0032] (4) Preparation of praseodymium copper alloy powder: The ingot obtained in step (3) was crushed into blocks, sealed and placed in a high-temperature autoclave, and vacuumed to a pressure of less than 1×10 -3 After pa, 0.5MPa hydrogen was introduced and the mixture was kept at room temperature for 0.5 hour to obtain a coarse powder with a particle size of less than 20 microns after hydrogen absorption and crushing. Furthermore, the coarse powder was sealed and placed in a stainless steel tank with n-heptane as the medium for high-energy ball milling for 2 hours, and then dried in a vacuum drying oven. After drying, praseodymium copper powder with an average particle size distribution of 3 microns to 5 microns was obtained.

[0033] (5) Powder mixing and green compacting: The iron-rich samarium-cobalt magnetic powder with a particle size distribution of 3 μm to 5 μm obtained in the above steps (2) and (4) and the praseodymium-copper powder are placed in a mixer according to the above proportions and mixed for 10 hours to obtain a mixed powder. Then, the mixed powder is placed in a special non-magnetic steel mold and vertically pressed and oriented in a magnetic field of 15 kOe. Subsequently, the green compact is cold isostatically pressed at a pressure of 250 MPa and a holding time of 180 seconds to obtain a dense green compact.

[0034] (6) Sintering treatment: The green compact obtained by cold isostatic pressing in step (5) is placed in a vacuum sintering furnace for sintering. First, the temperature is raised from room temperature to 400°C under vacuum, kept at this temperature for 1 hour, and then raised to 1180°C for pre-sintering for 1 hour; then the temperature is gradually raised to 1215-1220°C and sintered under argon protection for 1 hour, and 0.45 MPa of inert Ar gas is introduced during the sintering process.

[0035] (7) Solution treatment: After the sintering time in step (6) is completed, the temperature is slowly lowered to 1170-1180°C for solution treatment, kept at this temperature for 5 hours, and then air-cooled to room temperature to obtain a supersaturated solid solution.

[0036] (8) Aging treatment: The supersaturated solid solution obtained in step (7) is kept at 810°C for 40 hours, then cooled to 410°C at a cooling rate of 0.6°C / min, kept at this temperature for 10 hours, and finally cooled with furnace air or naturally cooled to room temperature to obtain an iron-rich samarium-cobalt-based magnet doped with praseodymium copper.

[0037] The following will be combined with the embodiments of the present invention to describe the concept of the present invention in more detail. Obviously, the described embodiments are only part of the embodiments of the present invention, and other process or component improvements that do not exceed the concept of the present invention are within the scope of protection of the patent of this invention.

[0038] Example 1

[0039] (1) Preparation of iron-rich samarium-cobalt-based cast alloy: First, metal raw materials are selected according to the mass percentage: Sm: 24.5 wt.%; Fe: 20.7 wt.%; Cu: 4.1 wt.%; Zr: 2.9 wt.%; Co: the balance, and then Sm raw material is added in an amount of 8 wt.% of the Sm mass in the above ratio;

[0040] The metal raw materials are subjected to medium-frequency induction melting in a vacuum to convert them into alloy liquid. After a 3-minute refining process, the alloy liquid is poured into a copper mold with circulating cooling water and cooled to obtain a plate-shaped iron-rich samarium-cobalt-based cast alloy.

[0041] In order to improve the composition uniformity of the alloy ingot, the prepared plate-shaped ingot is then subjected to the rapid solidification strip method to obtain samarium-cobalt rapid solidification casting sheets.

[0042] (2) Preparation of iron-rich samarium-cobalt-based alloy powder: The rapidly solidified casting sheet obtained in step (1) was mechanically crushed into flakes, each weighing less than 5 g. The casting sheet was then sealed and placed in a high-temperature autoclave, and vacuumed to a pressure of less than 1×10 -3 pa, then 4MPa hydrogen is introduced, auxiliary heating is performed to 80°C, and the temperature is kept for 20 hours. After cooling to room temperature with the furnace, a coarse powder with a particle size of less than 110 microns after hydrogen absorption and crushing is obtained. Then, the coarse powder is sealed and placed in a stainless steel tank with No. 120 aviation gasoline as the medium for rolling ball milling for 6 hours, and then dried in a vacuum drying oven. After drying, fine powder with an average particle size distribution of 3 microns to 5 microns is obtained.

[0043] (3) Preparation of praseodymium-copper cast alloy: Metal praseodymium and copper were used as raw materials and smelted in a vacuum induction heating furnace to form an alloy ingot. The ingot composition was: Cu: 15.5 wt.%, Pr: balance.

[0044] (4) Preparation of praseodymium copper alloy powder: The ingot obtained in step (3) was crushed into blocks, sealed and placed in a high-temperature and high-pressure reactor, and vacuumed to a pressure of less than 1×10 -3 After pa, 0.5MPa hydrogen was introduced and the mixture was kept at room temperature for 0.5 hour to obtain a coarse powder with a particle size of less than 20 microns after hydrogen absorption and crushing. Furthermore, the coarse powder was sealed and placed in a stainless steel tank with n-heptane as the medium for high-energy ball milling for 2 hours, and then dried in a vacuum drying oven. After drying, praseodymium copper powder with an average particle size distribution of 3 microns to 5 microns was obtained.

[0045] (5) Powder mixing and compacting: The iron-rich samarium-cobalt magnetic powder with a particle size distribution of 3 μm to 5 μm obtained in the above steps (2) and (4) and the praseodymium-copper powder are placed in a mixer and mixed for 10 hours to obtain a mixed powder. Then, the mixed powder is loaded into a special non-magnetic steel mold and vertically pressed and oriented in a magnetic field of 15 kOe. Subsequently, the green body is cold isostatically pressed at a pressure of 250 MPa and a holding time of 180 seconds to obtain a dense compact.

[0046] (6) Sintering treatment: The green compact obtained by cold isostatic pressing in step (5) is placed in a vacuum sintering furnace for sintering. First, the temperature is raised from room temperature to 400°C under vacuum, kept at this temperature for 1 hour, and then raised to 1180°C for pre-sintering for 1 hour; then the temperature is gradually raised to 1215-1220°C and sintered under argon protection for 1 hour, and 0.45 MPa of inert Ar gas is introduced during the sintering process.

[0047] (7) Solution treatment: After the sintering time in step (6) is completed, the temperature is slowly lowered to 1180°C for solution treatment, kept at this temperature for 5 hours, and then air-cooled to room temperature to obtain a supersaturated solid solution.

[0048] (8) Aging treatment: The supersaturated solid solution obtained in step (7) was kept at 810°C for 40 hours, then cooled to 410°C at a cooling rate of 0.6°C / min and kept at this temperature for 10 hours. Finally, it was air-cooled in the furnace or naturally cooled to room temperature to obtain an iron-rich samarium-cobalt-based magnet doped with praseodymium copper. The magnetic properties of the magnet are listed in Table 3.

[0049] Examples 2, 3, and 4 in Tables 1 and 2 all employ the method of Example 1 to prepare iron-rich samarium-cobalt-based magnets doped with praseodymium copper. The differences lie in the raw metal content, praseodymium copper powder content, sintering temperature, and solution temperature. The raw metal content parameters for each example are shown in Table 1, and the praseodymium copper powder content, sintering temperature, and solution temperature parameters for each example are shown in Table 2.

[0050] Table 1:

[0051] Serial number Sm (wt.%) Fe (wt.%) Cu (wt.%) Zr (wt.%) Co (wt.%) Example 1 24.5 20.7 4.1 2.9 margin Example 2 25.5 20.7 4.1 2.9 margin Example 3 25.5 20.7 4.1 2.9 margin Example 4 26.5 20.7 4.1 2.9 margin

[0052] Table 2:

[0053]

[0054] Comparative Example 1

[0055] Unlike the embodiment, the comparative example does not adopt the method of doping praseodymium copper powder, but adopts the traditional powder metallurgy method to prepare the iron-rich samarium-cobalt-based magnet without praseodymium copper doping. The specific preparation method is as follows:

[0056] (1) Preparation of iron-rich samarium-cobalt-based cast alloy: First, metal raw materials are selected according to the mass percentage of Sm: 24.5 wt.%; Fe: 20.7 wt.%; Cu: 4.1 wt.%; Zr: 2.9 wt.%; Co: the balance, and then Sm raw material is added in an amount of 8 wt.% of the Sm mass in the above ratio;

[0057] The metal raw materials are subjected to medium-frequency induction melting in a vacuum to convert them into alloy liquid. After a 3-minute refining process, the alloy liquid is poured into a copper mold with circulating cooling water and cooled to obtain a plate-shaped iron-rich samarium-cobalt-based cast alloy.

[0058] In order to improve the composition uniformity of the alloy ingot, the prepared plate-shaped ingot is then subjected to the rapid solidification strip method to obtain samarium-cobalt rapid solidification casting sheets.

[0059] (2) Preparation of iron-rich samarium-cobalt-based alloy powder: The rapidly solidified casting sheet obtained in step (1) is mechanically crushed into flakes, and then sealed and placed in a high-temperature autoclave. After evacuation, 4 MPa hydrogen is introduced, and the powder is heated to 80°C and kept warm for 20 hours. The powder is cooled to room temperature with the furnace to obtain a coarse powder with a particle size of less than 110 μm. Then, the coarse powder is sealed and placed in a stainless steel tank with No. 120 aviation gasoline as the medium for rolling ball milling for 6 hours. The powder is then dried in a vacuum drying oven and dried to obtain a fine powder with an average particle size distribution of 3 μm to 5 μm.

[0060] (3) Compacting: The iron-rich samarium-cobalt powder with a particle size distribution of 3 μm to 5 μm obtained in the above step (2) is loaded into a special non-magnetic steel mold and vertically pressed and oriented in a magnetic field of 15 kOe. The green body is then cold isostatically pressed at a pressure of 250 MPa and a holding time of 180 seconds to obtain a dense compact.

[0061] (4) Sintering treatment: The green compact obtained by cold isostatic pressing in step (3) is placed in a vacuum sintering furnace for sintering. First, the temperature is raised from room temperature to 400°C under vacuum, kept at this temperature for 1 hour, and then raised to 1180°C for pre-sintering for 1 hour; then the temperature is gradually raised to 1216°C and sintered under argon protection for 1 hour, with 0.45 MPa of inert Ar gas introduced during the sintering process.

[0062] (5) After the sintering time in step (4) is completed, the temperature is slowly lowered to 1175°C for solution treatment, and the temperature is kept at this temperature for 5 hours, followed by air cooling to room temperature to obtain a supersaturated solid solution.

[0063] (6) Aging treatment: The supersaturated solid solution obtained in step (5) was kept at 810°C for 40 hours, then cooled to 410°C at a cooling rate of 0.6°C / min and kept at this temperature for 10 hours. Finally, it was air-cooled in the furnace or naturally cooled to room temperature to obtain an iron-rich samarium-cobalt-based magnet not doped with praseodymium copper. The magnetic properties of the magnet are listed in Table 3.

[0064] Table 3:

[0065]

[0066] The above results demonstrate that, compared to undoped magnets, the praseodymium-copper powder-doped iron-rich samarium-cobalt permanent magnets prepared using the technical solution provided by the present invention exhibit improved grain boundary copper depletion and significantly improved room-temperature coercivity with increasing praseodymium-copper powder doping, while also enhancing the density and remanence of the magnets. In particular, at a doping level of 3wt%, the room-temperature coercivity of the iron-rich samarium-cobalt permanent magnets increased by nearly 127%, and the remanence density by approximately 3%. This present invention provides an effective method for improving the magnetic properties of samarium-cobalt magnets, thereby broadening their scope of application.

Claims

1. A method for preparing iron-rich samarium-cobalt-based permanent magnets by doping and modifying praseodymium-copper powder, characterized in that: Praseodymium copper powder is doped in an iron-rich samarium-cobalt-based permanent magnet. The iron-rich samarium-cobalt powder composition is as follows: Sm: 24.5-26.5 wt.%, Fe: 20.7 wt.%, Cu: 4.1 wt.%, Zr: 2.9 wt.%, and Co: the balance. To compensate for the burnout of rare earth Sm during the smelting process, an additional Sm raw material (8 wt.% of the Sm mass in the above ratio) is added after the basic ratio is completed and before smelting begins. Praseodymium copper powder by mass percentage: Cu: 15.5-17.5wt.%, Pr: balance; Calculated by mass percentage: the praseodymium copper powder accounts for 1 to 4 wt.%, and the rest is iron-rich samarium-cobalt magnetic powder.

2. The method for preparing an iron-rich samarium-cobalt-based permanent magnet by doping and modifying praseodymium copper powder according to claim 1, characterized in that: The following steps are involved: (1) Preparation of iron-rich samarium-cobalt-based cast alloy: First, metal raw materials are selected according to the mass percentage of Sm: 24.5-26.5 wt.%; Fe: 20.7 wt.%; Cu: 4.1 wt.%; Zr: 2.9 wt.%; Co: the balance, and then Sm raw material is added in an amount of 8 wt.% of the Sm mass in the above ratio; The metal raw materials are subjected to medium-frequency induction melting in a vacuum to convert them into alloy liquid. After a 3-minute refining process, the alloy liquid is poured into a copper mold with circulating cooling water and cooled to obtain a plate-shaped iron-rich samarium-cobalt-based cast alloy. In order to improve the composition uniformity of the alloy ingot, the prepared plate-shaped ingot was then subjected to the rapid solidification belt method to obtain samarium-cobalt rapid solidification casting sheets. (2) Preparation of iron-rich samarium-cobalt-based alloy powder: The rapidly solidified casting sheet obtained in step (1) is mechanically crushed into flakes, and then sealed and placed in a high-temperature autoclave. After evacuation, 3-5 MPa hydrogen is introduced, and the mixture is heated to 80-100°C and kept warm for 20-40 hours. After cooling to room temperature with the furnace, a coarse powder with a particle size of less than 110 μm is obtained. Then, the coarse powder is sealed and placed in a stainless steel tank with No. 120 aviation gasoline as the medium for rolling ball milling for 4-8 hours, and then dried in a vacuum drying oven to obtain a fine powder with an average particle size distribution of 3 μm to 5 μm. (3) Preparation of praseodymium-copper cast alloy: metallic praseodymium and copper are selected as raw materials and smelted into alloy ingots in a vacuum induction heating furnace. The ingot composition is: Cu: 15.5-17.5 wt.%, Pr: balance; (4) Preparation of praseodymium copper alloy powder: The ingot obtained in step (3) is crushed into blocks, sealed and placed in a high-temperature and high-pressure reactor, evacuated, and then introduced with 0.1-0.5 MPa hydrogen gas, and maintained at room temperature for 0.5-1 hour to obtain a coarse powder with a particle size of less than 150 μm. Then, the coarse powder is subjected to high-energy ball milling for 2-3 hours, dried in a vacuum drying oven, and dried to obtain a praseodymium copper powder with an average particle size distribution of 3 μm to 5 μm; (5) Powder mixing and green compacting: The iron-rich samarium-cobalt powder and the praseodymium-copper powder with a particle size distribution of 3 μm to 5 μm obtained in steps (2) and (4) above are placed in a mixer according to the above proportions and mixed for 8 to 10 hours to obtain a mixed powder. The mixed powder is then placed in a dedicated non-magnetic steel mold and subjected to vertical pressing and orientation molding in a magnetic field of 15 kOe. The green compact is then subjected to cold isostatic pressing at a pressure of 250 to 280 MPa and a holding time of 120 to 180 seconds to obtain a dense green compact. (6) Sintering treatment: The green compact obtained by cold isostatic pressing in step (5) is placed in a vacuum sintering furnace for sintering. First, the temperature is raised from room temperature to 400°C under vacuum, kept at this temperature for 1 hour, and then raised to 1170-1185°C for pre-sintering for 0.5-2 hours; then the temperature is gradually raised to 1215-1220°C and sintered under argon protection for 0.5-2 hours, with 0.45 MPa of inert Ar gas introduced during the sintering process; (7) Solution treatment: After the sintering time in step (6) is completed, the temperature is slowly lowered to 1170-1180°C for solution treatment, and the temperature is kept at this temperature for 5-10 hours, followed by air cooling to room temperature to obtain a supersaturated solid solution; (8) Aging treatment: The supersaturated solid solution obtained in step (7) is kept at 810°C for 40 hours, then cooled to 410°C at a cooling rate of 0.6°C / min, kept at this temperature for 10 hours, and finally cooled with furnace air or naturally cooled to room temperature to obtain an iron-rich samarium-cobalt-based magnet doped with praseodymium copper.

3. The method for preparing an iron-rich samarium-cobalt-based permanent magnet by doping and modifying praseodymium copper powder according to claim 2, characterized in that: The purity of each component in the iron-rich samarium-cobalt-based cast alloy is: Sm≥99.9%, Fe≥99.8%, Cu≥99.5%, Zr≥99.9%, Co≥99.8%; the purity of each component in the praseodymium-copper cast alloy is: Pr≥99.9%, Cu≥99.5%.

4. The method for preparing an iron-rich samarium-cobalt-based permanent magnet by doping and modifying praseodymium-copper powder according to claim 2 or 3, characterized in that: In step (2), the iron-rich samarium-cobalt-based alloy fragments are 3 to 5 g / piece.

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