A method for preparing high-performance low-temperature coefficient Sm-Co permanent magnet material

Abstract

This invention relates to a method for preparing high-performance, low-temperature-coefficient Sm-Co permanent magnet materials, belonging to the technical field of samarium-cobalt permanent magnet materials. It solves the problem in the prior art where the magnetic properties and temperature coefficient are difficult to balance due to the addition of heavy rare earth elements in 2:17 type samarium-cobalt magnets. The method includes: S1, preparing the alloy composition Sm according to a mass percentage... a Ho b Co c Fe d Cu e Zr f Where a, b, c, d, e, and f are the mass percentages of Sm, Ho, Co, Fe, Cu, and Zr, respectively, and satisfy the following conditions: 18≤a≤25, 1≤b≤5, 40≤c≤50, 19≤d≤24, 5≤e≤6, 2.5≤f≤3.5, and a+b+c+d+e+f=100; S2, induction melting and casting; S3, medium crushing; S4, sequentially pulverizing and sieving by fluidized bed jet milling, followed by ball milling under nitrogen protection; S5, magnetic field orientation and delayed pressure molding; S6, sintering, solution treatment, and aging treatment under micro-negative pressure. The magnet prepared by this invention has a room temperature remanence Br≥11kGs, and the absolute value of the remanence temperature coefficient |α|≤0.03% / ℃ in the range of 25~150℃, achieving a good balance between high remanence and low temperature coefficient, which can meet the long-term service requirements of precision instruments in a wide temperature range environment.

Description

Technical Field

[0001] This invention relates to the field of samarium-cobalt permanent magnet materials technology, and in particular to a method for preparing high-performance, low-temperature-coefficient Sm-Co permanent magnet materials. Background Technology

[0002] 2:17 type Sm-Co rare earth permanent magnet material has the advantages of high coercivity, high Curie temperature (>820℃) and excellent corrosion resistance. It is an irreplaceable key functional material in high-end fields such as aerospace and defense industry. It is especially suitable for precision devices such as vacuum traveling wave tubes that have strict requirements for temperature stability.

[0003] Existing technologies typically improve the remanence of magnets by increasing the Fe content, but this leads to an increase in the remanence temperature coefficient and a decrease in thermal stability. To address this issue, a conventional method is to add heavy rare earth elements such as Gd and Ho to the alloy to reduce the remanence temperature coefficient. However, the addition of heavy rare earth elements worsens the uniformity of the magnet's microstructure, resulting in a significant decrease in magnetic properties; for example, remanence decreases by more than 5% and coercivity by more than 25% when used at 150°C. To address this, some existing technologies have proposed process improvements such as isothermal annealing of ingots, but these still fail to effectively resolve the contradiction between remanence loss and temperature coefficient optimization after the addition of heavy rare earth elements. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a method for preparing high-performance, low-temperature-coefficient Sm-Co permanent magnet materials, in order to at least solve one of the problems in the prior art where the magnetic properties and temperature coefficient are difficult to balance due to the addition of heavy rare earth elements in 2:17 type samarium-cobalt magnets.

[0005] On one hand, embodiments of the present invention provide a method for preparing high-performance, low-temperature-coefficient Sm-Co permanent magnet materials, comprising the following steps: S1. The alloy composition is prepared according to the mass percentage, and its expression is Sm. a Ho b Co c Fe d Cu e Zr f Where a, b, c, d, e, and f are the mass percentages of Sm, Ho, Co, Fe, Cu, and Zr, respectively, and satisfy the following conditions: 18≤a≤25, 1≤b≤5, 40≤c≤50, 19≤d≤24, 5≤e≤6, 2.5≤f≤3.5, and a+b+c+d+e+f=100; S2. The raw materials prepared in S1 are induction melted under Ar gas protection and cast to obtain alloy ingots. S3. The alloy ingot is subjected to medium crushing to obtain coarse powder; S4. The coarse powder is successively subjected to fluidized bed jet milling and sieving to obtain fine powder. Then, the fine powder is further ball-milled under nitrogen protection to modify the powder particle morphology. S5. The powder obtained in S4 is oriented by a magnetic field and then subjected to delayed pressure molding to obtain a high initial density compact. S6. The pressed blank is sintered, solution-treated and aged under a slight negative pressure to obtain a samarium cobalt sintered magnet.

[0006] Furthermore, in S1, the Ho replaces part of the Sm position in the alloy, forming a cellular structure mainly of type 2:17.

[0007] Furthermore, in S4, the ball-to-material ratio of the ball mill is 3~6:1, the ball milling speed is 250~350 rpm, and the ball milling time is 1~3 h.

[0008] Furthermore, in S5, the delayed pressure molding specifically involves: after magnetic field orientation, holding the pressure at 200~300 MPa for 60~90 s.

[0009] Furthermore, in S6, the pressure of the micro-negative pressure sintering is 60~90 kPa, the sintering temperature is 1200~1230℃, and the sintering time is 2~4 h.

[0010] Furthermore, in S6, the solution treatment is a segmented solution treatment, with the first segment having a solution temperature of 1170~1200℃ and a solution time of 0.5~2 h; and the second segment having a solution temperature of 1150~1170℃ and a solution time of 15~35 h.

[0011] Furthermore, in S6, the aging treatment temperature is 810~840℃, and the aging time is 20~35 h.

[0012] Furthermore, in S4, the average particle size of the ball-milled powder is 5~8 μm, and the powder particles are spherical.

[0013] Furthermore, in S4, the sieving is carried out in a vacuum glove box with a 40-mesh sieve.

[0014] On the other hand, embodiments of the present invention provide a high-performance, low-temperature-coefficient Sm-Co permanent magnet material, which is prepared by the method described above. Its remanence at room temperature is Br≥11 kGs, and the absolute value of the remanence temperature coefficient in the range of 25~150℃ is |α|≤0.03 % / ℃.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1) By controlling the composition and ratio of the permanent magnet material, and by using the alloy expression Sm aHo b Co c Fe d Cu e Zr f The mass percentage (b) of Ho in the medium was controlled within a specific range of 1 to 5. This, combined with a combined process of "nitrogen-protected ball milling—delayed pressure molding—micro-negative pressure sintering," effectively improved the microstructural disturbances and interference with cell wall phase element distribution caused by single heavy rare earth doping. Simultaneously, it balanced the control of magnetic powder particle size distribution and oxygen content, achieving a balance between high remanence and low temperature coefficient. The prepared magnets exhibited a room-temperature remanence (Br) exceeding 11 kGs, and the absolute value of the remanence temperature coefficient |α| within the 25–150 °C range was controlled below 0.03 % / ℃.

[0016] 2) The powder preparation method adopts fluidized bed air jet mill combined with nitrogen-protected ball milling. Nitrogen protection avoids powder oxidation, while ball milling modifies the particle edges and improves the powder morphology, making the powder particles spherical with an average particle size of 5~8 μm. The powder flowability is significantly improved, providing favorable conditions for subsequent orientation molding.

[0017] 3) By combining delayed pressure molding and micro-negative pressure sintering, after holding the pressure at 200~300 MPa cold isostatic pressure for 60~90s, it is then sintered in a micro-negative pressure atmosphere of 60~90 kPa. This reduces the volatilization loss of rare earth element Sm and improves the density of the magnet, ultimately obtaining a samarium cobalt permanent magnet with uniform microstructure and excellent comprehensive magnetic properties.

[0018] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0019] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0020] Figure 1 shows scanning electron microscope images of the magnetic powder prepared by nitrogen-protected ball milling in Example 1 at different magnifications; Figure 2 The particle size distribution curve and overall flowability index of the final powder prepared in Example 1 are shown. Figure 3 The images are scanning electron microscope (SEM) images of the magnetic powder prepared by the conventional air jet mill in Comparative Example 1 at different magnifications. Figure 4The particle size distribution curve and overall flowability index of the powder prepared by the conventional air jet mill in Comparative Example 1 are shown. Figure 5 These are scanning electron microscope (SEM) images of the magnetic powder prepared by nitrogen-protected ball milling in Example 2 at different magnifications. Figure 6 The particle size distribution curve and overall flowability index of the final powder prepared in Example 2 are shown. Figure 7 These are scanning electron microscope images of the magnetic powder prepared by wet ball milling in Comparative Example 2 at different magnifications. Figure 8 The particle size distribution curve and overall flowability index of the powder prepared by wet ball milling in Comparative Example 2 are shown. Figure 9 These are scanning electron microscope (SEM) images of the magnetic powder prepared by nitrogen-protected ball milling in Example 3 at different magnifications. Figure 10 The particle size distribution curve and overall flowability index of the final powder prepared in Example 3 are shown. Figure 11 Comparison of SEM characterization of magnets prepared in Comparative Example 3 and Example 3.

[0021] Figure 12 Comparative microstructures of magnets prepared in Comparative Example 4 and Example 4. Detailed Implementation

[0022] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0023] In the development of 2:17 type samarium cobalt permanent magnet materials, maintaining high remanence while reducing the temperature coefficient of remanence has always been a technical challenge in this field. Although adding heavy rare earth elements can effectively reduce the temperature coefficient, conventional addition methods often lead to disturbances in the magnet's microstructure and interference with the distribution of cell wall phase elements, resulting in a loss of magnetic properties. Therefore, this invention aims to solve the above-mentioned technical problems by optimizing the doping amount of heavy rare earth Ho and combining it with specific powder preparation, molding, and sintering processes.

[0024] A specific embodiment of the present invention discloses a method for preparing high-performance, low-temperature-coefficient Sm-Co permanent magnet materials, comprising the following steps: S1. The alloy composition is prepared according to the mass percentage, and its expression is Sm. a Ho b Co c Fe d Cu e Zr fWhere a, b, c, d, e, and f are the mass percentages of Sm, Ho, Co, Fe, Cu, and Zr, respectively, and satisfy the following conditions: 18≤a≤25, 1≤b≤5, 40≤c≤50, 19≤d≤24, 5≤e≤6, 2.5≤f≤3.5, and a+b+c+d+e+f=100; S2. The raw materials prepared in S1 are induction melted under Ar gas protection and cast to obtain alloy ingots. S3. The alloy ingot is subjected to medium crushing to obtain coarse powder; S4. The coarse powder is successively subjected to fluidized bed jet milling and sieving to obtain fine powder. Then, the fine powder is further ball-milled under nitrogen protection to modify the powder particle morphology. S5. The powder obtained in S4 is oriented by a magnetic field and then subjected to delayed pressure molding to obtain a high initial density compact. S6. The pressed blank is sintered, solution-treated and aged under a slight negative pressure to obtain a samarium cobalt sintered magnet.

[0025] To clearly understand the above scheme, the specific implementation methods and process principles of each step are explained in detail below.

[0026] The alloy expression Sm of the present invention a Ho b Co c Fe d Cu e Zr f It encompasses the essential elements required to form 2:17 type samarium-cobalt permanent magnets. Among them, Sm and Co are responsible for forming the 2:17 type main phase (Sm₂Co). 17 The six elements (Fe, Sm, and Fe) provide the basic magnetic properties. Fe doping aims to replace some of Co to increase the saturation magnetization of the magnet, thereby enhancing remanence. Cu and Zr are key elements in forming a uniform cellular microstructure. Cu is enriched in the 1:5H phase of the cell wall, while Zr is enriched in the 1:3R lamellar phase at the interface between the 2:17R phase and the cell wall phase, serving as channels for Cu diffusion into the cell wall. Their synergistic effect refines and stabilizes the cellular structure, a prerequisite for high coercivity. The doping of heavy rare earth element Ho aims to replace some of Sm in the lattice. Utilizing the different magnetic moment coupling characteristics of Ho with the Co and Fe sublattices, it compensates for changes in magnetic moment with temperature, thus reducing the temperature coefficient of remanence. Therefore, these six elements work together and are indispensable.

[0027] In this invention, the limitation of the content range of each element is based on achieving the best balance between high remanence and low temperature coefficient, and is the result of close coordination with subsequent processes.

[0028] Specifically, the mass percentage (a) of Sm is limited to 18–25% (e.g., 18, 19, 20, 21, 22, 23, 24, 25). Sm is an essential element for the formation of the 2:17 phase. If a is below 18 wt.%, a soft magnetic Co-Fe-rich phase is likely to appear in the alloy, leading to a sharp decrease in coercivity; if a is above 25 wt.%, the rare earth-rich phase increases, the proportion of the main phase decreases, and the remanence and energy product of the magnet will be significantly reduced.

[0029] The mass percentage of Ho, b, is limited to 1–5 (e.g., 1, 2, 3, 4, 5). Ho is a key doping element for achieving a low temperature coefficient. As a heavy rare earth element, Ho, after entering the crystal lattice, can replace some of the Sm positions in the alloy, forming a cellular structure dominated by the 2:17 type. This can adjust the magnetocrystalline anisotropy field and Curie temperature of the magnet, thereby reducing the remanence temperature coefficient. Simultaneously, appropriate Ho doping helps to form a uniform and fine cellular structure, which is crucial for the high coercivity and good squareness of 2:17 type samarium-cobalt magnets. If b is below 1 wt.%, its temperature compensation effect is negligible, and the absolute value of the remanence temperature coefficient |α| of the magnet is difficult to stably control below 0.03 % / ℃; if b is above 5 wt.%, excessive non-magnetic Ho atoms will excessively dilute the magnetization of the main phase, leading to a severe decrease in remanence, and will also destroy the uniformity of the cellular structure, which contradicts the original intention of this invention to "balance remanence and temperature coefficient". Therefore, this invention limits b to the range of 1–5.

[0030] The mass percentage of Co, c, is limited to 40-50% (e.g., 40, 42, 43, 45, 46, 48, 50). As a matrix element, too low a content of Co is not conducive to the formation of a stable 2:17 phase, while too high a content will squeeze out the proportion of other functional elements and affect the regulatory role of Fe, Cu, and Zr.

[0031] The mass percentage (d) of Fe is limited to 19–24 (e.g., 19, 20, 21, 22, 23, 24). Fe is the main element for improving remanence, but excessively high Fe content leads to a rapid decrease in Curie temperature and poor high-temperature thermal stability. If d is below 19 wt.%, the improvement in remanence is not significant; if it is above 24 wt.%, the loss of magnetic properties at high temperatures intensifies, which offsets the temperature coefficient improvement effect brought by Ho doping. This invention limits d to this range to utilize its high magnetic moment while suppressing its negative effects through coordination with Ho doping and subsequent processes.

[0032] The mass percentage (e) of Cu is limited to 5–6 (e.g., 5.0, 5.2, 5.3, 5.5, 5.6, 5.8, 6.0), and the mass percentage (f) of Zr is limited to 2.5–3.5 (e.g., 2.5, 2.7, 2.9, 3.0, 3.2, 3.5). Cu and Zr are essential for the formation of an ideal cellular structure. When their content is below the lower limit, the cellular structure is coarse or incomplete, resulting in insufficient coercivity; when their content is above the upper limit, excessive non-magnetic phases will form, impairing remanence and potentially leading to poor sintering performance.

[0033] The total quantity relationship is a+b+c+d+e+f=100, where a, b, c, d, e, and f represent the mass percentage (wt%) of each corresponding element. This total quantity relationship is the basic conservation relationship of alloy composition, ensuring the completeness and uniqueness of the composition definition.

[0034] Specifically, in S2, metal raw materials with a purity greater than 99.5% are weighed according to the above target composition and induction melting is carried out under argon protection. When the vacuum degree of the melting furnace is ≤5 Pa, heating is started and Ar gas is introduced into the furnace. The melting temperature reaches 1220~1500℃. The temperature is held to fully melt and mix the raw materials evenly. Then, it is poured into the ingot mold and rapidly cooled to obtain an alloy ingot.

[0035] In S3, the alloy ingot is crushed into coarse powder with an average particle size of 20~30 μm by a medium crusher.

[0036] In step S4, the coarse powder is pulverized and sieved using a fluidized bed jet mill to obtain fine powder with an average particle size in the range of 5-8 μm. The sieving is performed in a vacuum glove box using a 40-mesh sieve. Considering that powder is easily oxidized by contact with air during sieving, performing sieving in a vacuum glove box effectively avoids contact between the fine powder and air, reducing oxygen content and preventing powder oxidation. The 40-mesh sieve is chosen to remove any small amount of coarse particles or agglomerates that may exist during the jet milling process, ensuring a concentrated powder particle size distribution.

[0037] Furthermore, in S4, after the fine powder is obtained by air jet milling and sieving, the fine powder is further ball-milled under nitrogen protection. This has the following three effects: First, the grinding action of the ball milling media modifies the edges and corners of the powder particles obtained by air jet milling, making the particle morphology more spherical, thereby improving the flowability of the powder; Second, nitrogen, as a protective atmosphere, can effectively prevent the fine powder from oxidizing due to contact with air during ball milling, thus controlling the oxygen content of the powder; Third, the ball milling process helps to disperse agglomerates that may be generated during air jet milling, resulting in better powder dispersibility.

[0038] Furthermore, in S4, the ball-to-particle ratio in the ball mill is 3~6:1 (e.g., 3:1, 4:1, 5:1, 6:1), the ball milling speed is 250~350 rpm (e.g., 250 rpm, 280 rpm, 300 rpm, 320 rpm, 350 rpm), and the ball milling time is 1~3 h (e.g., 1 h, 1.5 h, 2 h, 2.5 h, 3 h). Controlling the ball-to-particle ratio, speed, and time within these ranges effectively modifies the powder particle edges and improves morphology while avoiding over-milling that leads to excessive powder refinement or introduces too many defects. A ball-to-particle ratio that is too low will result in insignificant milling effects and limited improvement in particle morphology; a ball-to-particle ratio that is too high may lead to powder cold welding or agglomeration. Excessively high speed or excessively long time will result in excessively fine powder particles, increasing the risk of oxidation and orientation difficulty; excessively low speed or excessively short time will result in insufficient morphology modification.

[0039] By optimizing ball milling parameters, powders with an average particle size of 5–8 μm (e.g., 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm) and a near-spherical shape can be obtained. This particle size ensures sintering activity while avoiding the oxidation risk associated with excessively fine powder. The near-spherical shape indicates good powder flowability, allowing it to rotate freely during magnetic field orientation and fully fill the gaps between the powder and the mold cavity. This is beneficial for improving orientation degree, increasing initial density, and thus enhancing remanence. Furthermore, the near-spherical particles fill uniformly during pressing, resulting in high compact density and uniform pore distribution, which is conducive to obtaining sintered magnets with a homogeneous microstructure.

[0040] Furthermore, in S5, the delayed pressure molding specifically involves: after magnetic field orientation, holding the pressure at 200~300 MPa (e.g., 200 MPa, 220 MPa, 250 MPa, 280 MPa, 300 MPa) for 60~90 s (e.g., 60 s, 65 s, 70 s, 75 s, 80 s, 85 s, 90 s) is maintained.

[0041] It should be noted that the "delayed pressure forming" described in this invention refers to further cold isostatic pressing of the compact after the magnetic field orientation is completed, that is, holding it under a certain pressure for a period of time. Its function is to allow the oriented powder particles to fully rearrange under continuous pressure, eliminate the bridging phenomenon between particles, further improve the density and uniformity of the compact, and lay the foundation for obtaining a high-density magnet through subsequent sintering.

[0042] Controlling the pressure to 200-300 MPa and the holding time to 60-90 s ensures a sufficiently high initial density while avoiding excessive pressure that could lead to particle breakage or orientation disorder. If the holding time is too short, insufficient particle rearrangement results in a low compact density; conversely, if the holding time is too long, production efficiency decreases, and the density improvement effect is not significant. Increasing the compact density facilitates subsequent sintering densification, reduces sintering shrinkage, and ultimately yields magnets with precise dimensions and uniform microstructure.

[0043] Furthermore, in S6, the pressure of the micro-negative pressure sintering is 60~90 kPa (e.g., 60 kPa, 65 kPa, 70 kPa, 75 kPa, 80 kPa, 85 kPa, 90 kPa), the sintering temperature is 1200~1230℃ (e.g., 1200℃, 1205℃, 1210℃, 1215℃, 1220℃, 1225℃, 1230℃), and the sintering time is 2~4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h, 4 h).

[0044] This invention employs micro-negative pressure inert gas protected sintering, rather than conventional vacuum sintering. Micro-negative pressure sintering refers to sintering under inert gas pressure slightly below atmospheric pressure, controlled at 60-90 kPa. This micro-negative pressure environment effectively removes gases generated during sintering, promoting densification, and also prevents severe volatilization of rare earth element Sm under high vacuum conditions, thereby preventing deviations in magnet composition and reducing the formation of Sm₂O₃. Compared to conventional vacuum sintering, micro-negative pressure sintering helps obtain magnets with accurate composition, high density, and uniform microstructure.

[0045] Sintering temperature of 1200~1230℃ and holding time of 2~4 h are key parameters for obtaining high density and moderate grain size. If the temperature is too low or the time is too short, sintering will be insufficient, resulting in low magnet density and poor performance; if the temperature is too high or the time is too long, the grains will grow abnormally and the coercivity will decrease.

[0046] Furthermore, in S6, the solution treatment is a segmented solution treatment. The first segment solution temperature is 1170~1200℃ (e.g., 1170℃, 1175℃, 1180℃, 1185℃, 1190℃, 1195℃, 1200℃), and the solution time is 0.5~2 h (e.g., 0.5h, 0.8h, 1.0h, 1.2h, 1.5h, 1.8h, 2.0h). The second segment solution temperature is 1150~1170℃ (e.g., 1150℃, 1155℃, 1160℃, 1165℃, 1170℃), and the solution time is 15~35 h (e.g., 15h, 18h, 20h, 25h, 28h, 30h, 32h, 35h).

[0047] The first stage of high-temperature, short-time solution treatment aims to fully dissolve the copper-rich phase, forming a homogeneous supersaturated solid solution. The second stage of medium-temperature, long-time solution treatment aims to further promote element diffusion, homogenize the composition, and provide favorable conditions for the formation of a uniform, fine cellular structure during subsequent aging. Using a single-stage solution treatment makes it difficult to simultaneously achieve both the full dissolution of the copper-rich phase and the homogenization of the overall composition. Through staged solution treatment, magnets with a uniform microstructure and fine cellular structure can be obtained, thereby improving overall magnetic properties.

[0048] Furthermore, in S6, the aging treatment temperature is 810~840℃ (e.g., 810℃, 815℃, 820℃, 825℃, 830℃, 835℃, 840℃), and the aging time is 20~35 h (e.g., 20h, 22h, 25h, 28h, 30h, 32h, 35h). Sufficient holding time within this temperature range allows the supersaturated solid solution to decompose and form a cellular structure composed of a 2:17 intracellular phase and a 1:5 cell wall phase. If the aging temperature is too low or the time is too short, the cellular structure will not form sufficiently, resulting in insufficient coercivity; if the aging temperature is too high or the time is too long, the cellular structure will coarsen, and the magnetic properties will decrease. Controlling the aging temperature at 810~840℃ and the time at 20~35 h yields a cellular structure with uniform size and a continuous cell wall phase, thereby achieving high coercivity and good temperature stability.

[0049] This invention also provides a high-performance, low-temperature-coefficient Sm-Co permanent magnet material, prepared by the methods described above. Its remanence at room temperature is Br≥11 kGs, and the absolute value of its remanence temperature coefficient |α| ≤0.03% / ℃ in the range of 25~150℃. This magnet maintains high remanence while exhibiting excellent temperature stability, meeting the requirements for long-term stable operation of precision devices such as vacuum traveling wave tubes in a wide temperature range.

[0050] Compared with existing technologies, the preparation method provided by this invention effectively solves the problems of magnetic microstructure disturbance and interference with cell wall phase element distribution caused by single heavy rare earth doping by controlling the doping amount of heavy rare earth Ho within a specific range of 1~5 wt.%, and combining it with nitrogen-protected ball milling to modify powder morphology, delayed pressure molding to improve compact density, and micro-negative pressure sintering to suppress element volatilization. This achieves a balance and optimization of remanence and temperature coefficient. The prepared magnet can achieve a room temperature remanence of over 11 kGs, and the absolute value of the remanence temperature coefficient |α| in the range of 25~150℃ can be controlled below 0.03 % / ℃.

[0051] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0052] In this invention, the powder morphology was observed using a Hitachi S-3400 scanning electron microscope (SEM); the powder particle size distribution was measured using a HELOS / BR-MUTI laser particle size analyzer; the powder flowability index was measured using a PT-X integrated powder analyzer; and the magnetic properties of the magnet at room temperature and 150°C were tested using a Hirst ultra-high coercivity permanent magnet pulse measuring instrument.

[0053] Example 1 S1. Ingredients: Select metal raw materials with a purity greater than 99.5%, according to the nominal composition Sm 20.3 Ho 4.5 Co 45.1 Fe 22 Cu 5.1 Zr3 is used in the ingredients, and the sum of the mass percentages is 100%.

[0054] S2. Melting and casting: The weighed raw materials are placed in the crucible of the vacuum induction melting furnace. When the vacuum degree of the melting furnace is ≤5 Pa, heating is started and Ar gas is introduced into the furnace. After Ar is introduced, the melting temperature reaches 1240℃ and is held for 10 minutes to fully melt and mix the various raw materials in the furnace. Then, the mixture is poured into the ingot mold and rapidly cooled to form a single alloy ingot.

[0055] S3. Medium crushing: The alloy ingot is crushed by a medium crusher to obtain coarse powder with an average particle size of 20~30 μm.

[0056] S4. Powder Preparation: The coarse powder is progressively crushed and refined using a fluidized bed jet mill at 4300 rpm, resulting in a fine powder with an average particle size of 6.34 μm. This fine powder is then sieved through a 40-mesh sieve within a vacuum glove box. Finally, the sieved fine powder is poured into a custom-made ball mill jar equipped with an air valve, and stainless steel grinding balls of different sizes are added, with a 3 mm to 5 mm ball ratio of 6:4. High-purity nitrogen is then introduced through the air valve at the top of the ball mill jar lid as a protective medium. The ball-to-powder ratio is 3:1, the ball milling speed is kept constant at 300 rpm, and the milling time is 1 hour. The morphology of the prepared magnetic powder is as follows: Figure 1 (a) and Figure 1 As shown in (b), the magnetic powder has relatively smooth edges and rounded corners, exhibiting a large number of near-spherical particles with good dispersibility. The particle size distribution curve is shown in Figure 1. Figure 2 As shown, the average particle size is 5.94 μm and the overall flowability index is 53.

[0057] S5. Delayed pressure forming: The above-mentioned samarium cobalt alloy powder is poured into the mold cavity and vertically oriented under a magnetic field of 2T. Then, the blank is subjected to delayed pressure and held under cold isostatic pressure of 300 MPa for 90 s to produce a Φ17 mm cylindrical blank with high initial density.

[0058] S6. Heat Treatment: The pressed compact was sintered, solution-treated, and aged in a vacuum sintering furnace to obtain samarium-cobalt permanent magnets. Specifically, the pressed compact was sintered under a slightly negative pressure at a furnace pressure of 90 kPa under inert gas protection, at a sintering temperature of 1215℃ for 2 hours. Solution treatment was performed in stages: the first stage was at 1190℃ for 1 hour, and the second stage was at 1165℃ for 30 hours. Aging was performed at 825℃ for 32 hours, followed by furnace cooling to room temperature. This resulted in a 2:17 type samarium-cobalt permanent magnet with high remanence and a low temperature coefficient.

[0059] S7. Machining and Performance Testing: The sintered magnet obtained from the final heat treatment was wire-cut into a Φ10*10 mm sample cylinder. Then, various magnetic properties were tested and the remanence temperature coefficient was calculated at room temperature and 150℃, respectively. The calculation formula is shown in Equation (1). The magnet's strength at room temperature was Br=11.02 KGs, and at 150℃ it was Br=10.64 KGs. The absolute value of the remanence temperature coefficient |α|(25~150 ℃)=0.028 % / ℃.

[0060] (1) Comparative Example 1 The only difference between this comparative example and Example 1 is the powder preparation method.

[0061] This comparative example uses only the traditional air jet milling process for powder preparation, without additional nitrogen-protected ball milling. The medium-sized powder is further refined by air jet milling at 4300 rpm, resulting in a fine powder with an average particle size of 6.34 μm. The powder particle morphology is as follows: Figure 3 (a) and Figure 3 As shown in (b), the particle size distribution curve and the overall flowability index are as follows: Figure 4 As shown. The results show that the conventional air jet mill produces irregular fragments, and the flowability is reduced by 9.4% compared to the powder in Example 1. The magnet produced has a room temperature Br=10.65 KGs, a 150℃ Br=10.24 KGs, and an absolute value of the remanence temperature coefficient |α|(25~150 ℃)=0.031 % / ℃, all of which are inferior to those of Example 1.

[0062] Example 2 The only difference from Example 1 is that the ball-to-material ratio of the ball milling parameters is different under nitrogen protection.

[0063] S1~S3 are the same as in Example 1.

[0064] S4. Powder Preparation: The coarse powder is progressively crushed and refined using a fluidized bed air jet mill to obtain a fine powder with an average particle size of 6.34 μm. This fine powder is then sieved through a 40-mesh sieve in a vacuum glove box. Finally, the sieved fine powder is poured into a custom-made ball mill jar equipped with an air valve. Stainless steel grinding balls of different sizes are added, with a 3 mm to 5 mm ball ratio of 6:4. High-purity nitrogen is then introduced through the air valve at the top of the ball mill jar lid as a protective medium. The ball-to-powder ratio is 4:1, the ball milling speed is kept constant at 300 rpm, and the milling time is 1 hour. The morphology of the prepared magnetic powder is as follows: Figure 5 (a) and Figure 5 As shown in (b), the magnetic powder has relatively smooth edges and rounded corners, exhibiting a large number of near-spherical particles with good dispersibility. The particle size distribution curve is shown in Figure 1. Figure 6 As shown, the average particle size is 5.75 μm and the overall flowability index is 54.

[0065] S5~S7 are the same as in Example 1. The magnet's temperature coefficient at room temperature was measured to be Br=11.04 KGs, at 150℃ it was Br=10.67 KGs, and the absolute value of the remanence temperature coefficient |α|(25~150 ℃)=0.027 % / ℃.

[0066] Comparative Example 2 The only difference between this comparative example and Example 2 is the powder preparation method.

[0067] This comparative example uses a combination of traditional air jet milling and wet ball milling for powder preparation. The medium-sized powder is further refined by air jet milling at 4300 rpm, resulting in a fine powder with an average particle size of 6.34 μm. This fine powder is then sieved through a 40-mesh sieve in a vacuum glove box. Finally, the sieved fine powder is poured into a ball mill jar, and stainless steel grinding balls of different sizes are added, with a 3 mm to 5 mm ball ratio of 6:4. Anhydrous ethanol is then added as a protective medium, resulting in a ball-to-powder ratio of 4:1. The ball milling speed is kept constant at 300 rpm, and the milling time is 1 hour. The powder particle morphology is as follows. Figure 7 As shown, the particle size distribution curve and the overall flowability index are as follows: Figure 8 As shown. The results indicate that the powder prepared by wet ball milling has low sphericity, and due to the unavoidable oxygen exposure and liquid residue during the solid-liquid separation stage, the powder's flowability is significantly weakened compared to Example 2, decreasing by 7.4%. The magnet prepared has a room temperature Br=10.59 KGs, a Br=10.21 KGs at 150℃, and an absolute value of the remanence temperature coefficient |α|(25~150 ℃)=0.029 % / ℃, all of which are inferior to Example 2.

[0068] Example 3 The only difference from Example 1 is that the ball milling parameters and ball milling time are different under nitrogen protection.

[0069] S1~S3 are the same as in Example 1.

[0070] S4. Powder Preparation: The medium-sized and coarse powder is progressively crushed and refined using a fluidized bed air jet mill to obtain a fine powder with an average particle size of 6.34 μm. This fine powder is then sieved through a 40-mesh sieve in a vacuum glove box. Finally, the sieved fine powder is poured into a custom-made ball mill jar equipped with an air valve, and stainless steel grinding balls of different sizes are added, with a 3 mm to 5 mm ball ratio of 6:4. High-purity nitrogen is then introduced through the air valve at the top of the ball mill jar lid as a protective medium. The ball-to-powder ratio is 3:1, the ball milling speed is kept constant at 300 rpm, and the milling time is 1.5 h. The morphology of the prepared magnetic powder is as follows: Figure 9 (a) and Figure 9 As shown in (b), the magnetic powder has relatively smooth edges and rounded corners, exhibiting a large number of near-spherical particles with good dispersibility. The particle size distribution curve is shown in Figure 1. Figure 10 As shown, the average particle size is 5.43 μm and the overall flowability index is 53.

[0071] S5~S7 are the same as in Example 1. The magnet's temperature coefficient at room temperature was measured to be Br=11.03 KGs, at 150℃ it was Br=10.67 KGs, and the absolute value of the remanence temperature coefficient |α|(25~150 ℃)=0.026 % / ℃.

[0072] Comparative Example 3 The only difference between this comparative example and Example 3 is the cold isostatic pressing parameters.

[0073] S1~S4 are the same as in Example 3.

[0074] S5. Delayed-pressure molding: The samarium-cobalt alloy powder was poured into the mold cavity and vertically oriented under a 2T magnetic field. Then, the blank was subjected to conventional cold isostatic pressing, i.e., held under 180 MPa cold isostatic pressing for 50 s to form a compact. The density of the final magnet was 1.3% lower than that of Example 3.

[0075] S6~S7 are the same as in Example 3.

[0076] SEM characterization of the magnets prepared in this comparative example and Example 3 is shown in [the figure]. Figure 11 (a) and Figure 11 (b) As shown in the figure, compared with the magnet of Example 3, more pores and defects can be observed on the surface of the comparative magnet. The magnet produced has a room temperature Br=10.87KGs, a Br=10.41 KGs at 150℃, and an absolute value of the remanence temperature coefficient |α|(25~150 ℃)=0.034 % / ℃, all of which are lower than those of Example 3.

[0077] Example 4 The only difference between this embodiment and Embodiment 1 is that the pressure inside the micro-negative pressure sintering furnace is different.

[0078] S1~S5 are the same as in Example 1.

[0079] S6. Heat Treatment: The pressed billet is sintered, solution-treated, and aged in a vacuum sintering furnace to obtain samarium cobalt permanent magnets. Specifically, the pressed billet is sintered under a slightly negative pressure at a furnace pressure of 80 kPa inert atmosphere for 2 hours at a temperature of 1215℃. Solution treatment is performed in stages: the first stage is at 1190℃ for 1 hour, and the second stage is at 1165℃ for 30 hours. Aging is performed at 825℃ for 32 hours, and the billet is finally cooled to room temperature in the furnace.

[0080] S7 is the same as in Example 1.

[0081] The magnet's remanence temperature coefficient was measured to be Br = 11.01 kGs at room temperature and Br = 10.66 kGs at 150℃. The absolute value of the remanence temperature coefficient |α|(25~150℃) = 0.025 % / ℃.

[0082] Comparative Example 4 The only difference between this comparative example and Example 4 is the sintering method.

[0083] S1~S5 are the same as in Example 4.

[0084] S6. Heat Treatment: The pressed billet was subjected to conventional vacuum sintering, solution treatment, and aging in a vacuum sintering furnace to obtain samarium-cobalt permanent magnets. The pressed billet was sintered under a vacuum condition of ≤0.1 kPa in the furnace, with the sintering, solution treatment, and aging processes identical to those in Example 4. Finally, it was cooled to room temperature in the furnace. In the sintering stage, this comparative example used conventional vacuum sintering instead of micro-negative pressure sintering. This resulted in less basic oxidation of the magnet, but increased volatilization of the key rare earth element Sm during the heating stage, ultimately leading to a deviation in the magnet composition and an increase in non-magnetic phases. Furthermore, to maintain a high vacuum in the furnace, the diffusion pump needed to be continuously running, resulting in higher operating costs.

[0085] S7 is the same as in Example 4.

[0086] The microstructure of the magnets prepared in this comparative example and Example 4 is shown in the following figures. Figure 12 (a) and Figure 12 (b) As shown in the figure, compared to the magnet of Example 4, the comparative magnet exhibits more pinhole-like pores and white streaky impurities on its surface. The density of the prepared magnet is 1.2% lower than that of Example 4. The magnet's remanence temperature coefficient was measured to be Br = 10.78 kGs at room temperature and Br = 10.34 kGs at 150°C, with an absolute value of |α|(25~150°C) = 0.033 % / °C, all of which are lower than those of Example 4.

[0087] Characterization results and analysis The magnetic properties of the magnets prepared in the above embodiments and comparative examples are summarized in Table 1.

[0088] Table 1 Magnetic property parameters of magnets prepared in each embodiment and comparative example

[0089] Note: Comparative Example 3 and Example 3 used the same powder preparation and sintering process, and Comparative Example 4 and Example 4 used the same powder preparation and molding process. Therefore, the powder flowability index is similar, and the difference in their magnetic properties mainly comes from the different molding and sintering processes.

[0090] As shown in Table 1, the magnets of Examples 1-4 prepared using the method of this invention all achieved a remanence of over 11 kGs at room temperature, and the absolute value of the remanence temperature coefficient within the range of 25-150℃ was controlled below 0.03 % / ℃. However, Comparative Example 1, due to the lack of nitrogen-protected ball milling, had poor powder flowability, resulting in magnet remanence and a lower temperature coefficient than Example 1. Comparative Example 2, due to wet ball milling, suffered from powder oxidation and liquid residue, leading to decreased flowability and magnetic properties inferior to Example 2. Comparative Example 3, due to conventional cold isostatic pressing, had insufficient initial density and a short holding time, resulting in more internal pores and a decrease in remanence and a temperature coefficient exceeding 0.03 % / ℃, thus its magnetic properties were inferior to Example 3. Comparative Example 4, due to conventional vacuum sintering instead of micro-negative pressure sintering, experienced increased Sm volatilization, resulting in a deviation in magnet composition and the appearance of more impurity phases, leading to a decrease in remanence and a temperature coefficient exceeding 0.03 % / ℃, thus its magnetic properties were inferior to Example 4.

[0091] In summary, this invention effectively improves the problems of magnetic microstructure disturbance and interference with cell wall phase element distribution caused by single heavy rare earth doping by controlling the doping amount of heavy rare earth Ho within a specific range of 1~5 wt.% and adopting a combined process of "nitrogen-protected ball milling - delayed pressure molding - micro negative pressure sintering". It achieves a balance optimization between remanence and temperature coefficient, and successfully prepares high-performance low temperature coefficient Sm-Co permanent magnet materials with room temperature remanence ≥11 kGs and absolute value of remanence temperature coefficient |α|≤0.03 % / ℃ at 25~150℃.

[0092] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high performance low temperature coefficient Sm-Co permanent magnetic material, characterized in that, The method comprises the following steps: S1, alloy components are prepared according to mass percentage, which is expressed as Sm a Ho b Co c Fe d Cu e Zr f wherein a, b, c, d, e, f are mass percentage values of Sm, Ho, Co, Fe, Cu, Zr respectively, and satisfy: 18≤a≤25, 1≤b≤5, 40≤c≤50, 19≤d≤24, 5≤e≤6, 2.5≤f≤3.5, and a+b+c+d+e+f=100. S2, the raw materials prepared in S1 are subjected to induction smelting under Ar protection, and an alloy ingot is obtained by casting; S3, the alloy ingot is subjected to medium crushing treatment, and a coarse powder is obtained; S4, the coarse powder is subjected to fluidized bed type airflow milling and sieving treatment in sequence, a fine powder is obtained, and the fine powder is further subjected to ball milling under nitrogen protection to modify the powder particle morphology; S5, the powder obtained in S4 is subjected to magnetic field orientation, and then subjected to time-delayed pressure forming to obtain a high-initial-density compact; S6, the compact is subjected to sintering, solid solution and aging treatment under micro-negative pressure conditions, and a samarium-cobalt sintered magnet is obtained.

2. The production method according to claim 1, characterized by, In S1, the Ho-substituted alloy replaces part of the Sm to form a cell structure mainly in the form of 2:

17.

3. The preparation method according to claim 1, characterized in that, In S4, the ball-to-material ratio of the ball milling is 3-6:1, the ball milling speed is 250-350 rpm, and the ball milling time is 1-3 h.

4. The method of claim 1, wherein, In S5, the time-delayed pressure forming after the magnetic field orientation is specifically: first, cold isostatic pressing at 200-300 MPa for 60-90 s.

5. The preparation method according to claim 1, characterized in that, In S6, the micro-negative pressure sintering is performed at a pressure of 60-90 kPa, a sintering temperature of 1200-1230℃, and a sintering time of 2-4 h.

6. The method of claim 1, wherein, In S6, the solid solution treatment is a segmented solid solution, the first segment has a solid solution temperature of 1170-1200℃ and a solid solution time of 0.5-2 h, and the second segment has a solid solution temperature of 1150-1170℃ and a solid solution time of 15-35 h.

7. The preparation method according to claim 1, characterized in that, In S6, the aging treatment has a temperature of 810-840℃ and an aging time of 20-35 h.

8. The production method according to any one of claims 1 to 4, characterized by, In S4, the average particle size of the powder after the ball milling is 5-8 μm, and the powder particles are approximately spherical.

9. The production method according to any one of claims 1 to 4, characterized by, In S4, the sieving is performed in a vacuum glove box, and the sieve mesh is 40 mesh.

10. A high performance low temperature coefficient Sm-Co permanent magnetic material, characterized in that, The method is prepared according to any one of claims 1-9, has a residual magnetism Br≥11 kGs at room temperature, and has an absolute value |α|≤0.03 % / ℃ of the residual magnetism temperature coefficient in the range of 25-150℃.

Images