Samarium cobalt permanent magnet and preparation method thereof

Abstract

The invention relates to a samarium cobalt permanent magnet and a preparation method thereof. The preparation method comprises the following steps: providing a samarium-cobalt alloy; the samarium-cobalt alloy is subjected to oxidation heat treatment, the oxidation heat treatment process meets the following relational expression: t = kP / T, t is the heat preservation time, and the unit is h; t is the heating temperature, and the unit is DEG C; p is the vacuum degree, and the unit is Pa; k is a coefficient, and k is equal to 100 to 5000; crushing and pulverizing the samarium-cobalt alloy subjected to oxidation heat treatment to obtain alloy powder; and carrying out orientation molding on the alloy powder to obtain a samarium-cobalt green body, and carrying out sintering treatment to obtain the samarium-cobalt permanent magnet. According to the preparation method, the bending strength can be greatly improved while the high-hardness magnetic performance of the samarium-cobalt permanent magnet is guaranteed, the preparation process is simple and efficient, and the preparation method is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet preparation, in particular to a samarium cobalt permanent magnet and a preparation method thereof. Background Art

[0002] As the second-generation rare earth permanent magnet material, samarium cobalt permanent magnet material has significant advantages such as high Curie temperature, high magnetic energy product, excellent temperature stability and strong corrosion resistance. It is widely used in cutting-edge equipment in the fields of magnetic power, sensing and communication, and plays an irreplaceable role in aerospace, radar communications and national defense industry.

[0003] However, due to the inherent crystal structure, strong magnetic anisotropy, orientation molding process, and internal stresses and defects generated during the sintering process, rare earth permanent magnets have poor toughness. Samarium cobalt permanent magnets, in particular, exhibit cleavage brittle fracture and a bending strength of typically only 80MPa-120MPa. This makes them prone to cracking and chipping during processing, significantly reducing the yield and processing accuracy of the magnets, increasing processing costs, and limiting their application in high-precision, seismic, and impact-resistant applications.

[0004] Existing technology improves mechanical strength by pre-oxidizing ultrafine powder (0.01μm-2μm) to increase its oxygen content to 4000ppm-10000ppm, then mixing it with conventional powder in a proportional manner. However, these methods, which rely on adding additives or mixing multiple materials, not only increase costs but also make it difficult to ensure uniform mixing. For example, the addition of samarium oxide easily leads to agglomeration, while the addition of ultrafine powder oxides results in a concentrated distribution of fine grains. This leads to localized stress concentration in the magnet, resulting in reduced consistency and stability of the magnet's magnetic and mechanical properties.

[0005] Therefore, how to improve the toughness of SmCo permanent magnets while ensuring their high hard magnetic properties has become an urgent and important problem. Summary of the Invention

[0006] Based on this, it is necessary to provide a samarium cobalt permanent magnet and a preparation method thereof to address the above problems; the preparation method can achieve a significant improvement in bending strength while ensuring the high hard magnetic properties of the samarium cobalt permanent magnet, and the preparation process is simple and efficient, and is suitable for industrial production.

[0007] A method for preparing a samarium cobalt permanent magnet comprises the following steps:

[0008] Provide samarium cobalt alloy;

[0009] The samarium-cobalt alloy is subjected to an oxidation heat treatment, wherein the oxidation heat treatment process satisfies the following relationship: t=kP / T, wherein t is the holding time in hours; T is the heating temperature in degrees Celsius; P is the vacuum degree in Pa; and k is a coefficient, k=100-5000.

[0010] Crushing and pulverizing the samarium-cobalt alloy after the oxidation heat treatment to obtain alloy powder;

[0011] The alloy powder is oriented and formed into a samarium-cobalt green compact, and then the samarium-cobalt permanent magnet is prepared by sintering.

[0012] In one embodiment, the heating temperature T is 300° C.-1200° C.;

[0013] And / or, the vacuum degree P is 0.1Pa-20Pa.

[0014] In one embodiment, when P ≥ 10 Pa, 100 ≤ k ≤ 300, 300° C. ≤ T < 600° C.;

[0015] Or, when 5Pa≤P<10Pa, 200 <k≤500,500℃<T<800℃;

[0016] Or, when 1Pa≤P<5Pa, 400 <k≤800,700℃<T<1000℃;

[0017] Or, when 0.1Pa≤P<1Pa, 800 <k≤3000,900℃<T≤1200℃。

[0018] In one embodiment, the composition of the samarium-cobalt alloy includes: 23%-28% Sm, 13%-25% Fe, 4%-10% Cu, 1.5%-3.5% Zr, and the balance Co.

[0019] In one embodiment, the thickness of the oxide layer on the surface of the samarium-cobalt alloy after the oxidation heat treatment is 1 μm-5 μm;

[0020] And / or, the oxygen content of the samarium-cobalt alloy after the oxidation heat treatment is 1500 ppm-4000 ppm.

[0021] In one embodiment, the particle size of the coarse particles obtained by crushing is less than 5 mm;

[0022] And / or, the alloy powder has an average specific surface area particle size of 3 μm-8 μm, and a maximum particle size of less than or equal to 35 μm.

[0023] In one embodiment, in the orientation forming step, the magnetic field strength is greater than or equal to 2T;

[0024] And / or, the density of the samarium cobalt green body is 4.5 g / cm 3 -5.5g / cm 3 .

[0025] In one embodiment, the sintering treatment includes sintering and solid solution treatment, and the sintering and solid solution treatment process includes: under the condition of vacuum degree less than or equal to 0.05 Pa, heating to 1130℃-1180℃ at a heating rate of 0.5℃ / min-10℃ / min and keeping warm for 0.5h-5h for pre-sintering, then heating to 1170℃-1240℃ in an inert gas environment and keeping warm for 1h-8h for sintering, then cooling to 1110℃-1180℃ at a cooling rate of 0.2℃ / min-5℃ / min and keeping warm for 2h-72h for solid solution treatment, and after the solid solution treatment, rapid quenching to below 400℃ at a cooling rate of 40℃ / min-200℃ / min;

[0026] And / or, the sintering treatment also includes tempering and aging, and the tempering and aging process includes: in an inert gas environment or under vacuum conditions of ≤0.1 Pa, heating to 750°C-900°C at a heating rate of 0.5°C / min-10°C / min and keeping warm for 1h-50h, and then cooling to 300°C-500°C at a cooling rate of 0.1°C / min-1°C / min and keeping warm for 1h-30h.

[0027] A samarium cobalt permanent magnet is prepared by the above-mentioned preparation method, and the oxygen content of the samarium cobalt permanent magnet is 3500ppm-6000ppm.

[0028] In one embodiment, the average grain size of the samarium cobalt permanent magnet is 30 μm-80 μm;

[0029] And / or, the maximum grain size of the samarium cobalt permanent magnet is less than 170 μm.

[0030] The preparation method described in the present invention achieves regulation of the oxide content and distribution by strictly controlling the process conditions during the oxidation heat treatment of the samarium-cobalt alloy, thereby ensuring that the hard magnetic properties of the magnet are not damaged while achieving high bending strength, effectively improving the component segregation of the samarium-cobalt alloy, further optimizing the consistency and stability of the magnet, and then relying on high-melting-point oxides to refine the grains of the samarium-cobalt magnet and hinder crack propagation, thereby achieving a significant increase in bending strength. In addition, the samarium-cobalt alloy after the oxidation heat treatment is subjected to processes such as pulverization to uniformly disperse the oxides in the magnet, thereby achieving a relatively uniform distribution of oxides or fine grains in the magnet, which is conducive to further enhancing the consistency and stability of the magnetic and mechanical properties of the magnet.

[0031] Therefore, the preparation method of the present invention not only successfully achieves a balance between high hard magnetic properties and high bending strength of the samarium cobalt permanent magnet, but also does not require the addition of external additives or materials to the samarium cobalt alloy. The preparation method is simple, efficient, and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is a scanning electron microscope (SEM) image of the cross section of the oxidized samarium-cobalt alloy prepared in Example 1;

[0034] Figure 2 This is a metallographic photograph of the samarium cobalt permanent magnet obtained in Example 1;

[0035] Figure 3 This is a metallographic photograph of the samarium cobalt permanent magnet prepared in Comparative Example 1;

[0036] Figure 4 This is a scanning electron microscope (SEM) image of the cross section of the oxidized samarium-cobalt alloy prepared in Comparative Example 3;

[0037] Figure 5 This is a metallographic photograph of the samarium cobalt permanent magnet prepared in Comparative Example 4. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments or embodiments and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, including any two related listed items, any more related listed items, or the combination of all related listed items.

[0040] The present invention provides a method for preparing a samarium cobalt permanent magnet, comprising the following steps:

[0041] S1, provides samarium cobalt alloy;

[0042] S2, performing an oxidation heat treatment on the samarium-cobalt alloy, wherein the oxidation heat treatment process satisfies the following relationship: t=kP / T, wherein t is the holding time in hours; T is the heating temperature in degrees Celsius; P is the vacuum degree in Pa; and k is a coefficient, k=100-5000;

[0043] S3, crushing and pulverizing the samarium-cobalt alloy after the oxidation heat treatment to obtain alloy powder;

[0044] S4, after orienting and shaping the alloy powder to obtain a samarium-cobalt green body, sintering the green body to obtain a samarium-cobalt permanent magnet.

[0045] The present invention does not limit the samarium-cobalt alloy used in step S1. Existing samarium-cobalt alloys can be used, or the raw metal can be poured into a crucible for induction melting, and then poured into a water-cooled mold to prepare a master alloy ingot after being melted into molten steel.

[0046] In one embodiment, the composition of the samarium-cobalt alloy includes: 23%-28% Sm, 13%-25% Fe, 4%-10% Cu, 1.5%-3.5% Zr, and the balance Co.

[0047] In step S2, by strictly controlling the process conditions during the oxidation heat treatment of the samarium cobalt alloy, the oxide content and distribution can be regulated, thereby ensuring that the hard magnetic properties of the magnet are not damaged while achieving high bending strength, and effectively improving the composition segregation of the samarium cobalt alloy, further optimizing the consistency and stability of the magnet. Furthermore, by relying on high-melting-point oxides, the grains of the samarium cobalt magnet are refined and crack propagation is hindered, thereby achieving a significant increase in bending strength.

[0048] It should be noted that the relationship formula of the oxidation heat treatment process is only a quantitative relationship conversion and does not involve unit conversion.

[0049] Preferably, the heating temperature T is 300°C-1200°C, including but not limited to any one point value of 300°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, and 1200°C, or a range value consisting of any two point values.

[0050] Preferably, the vacuum degree P is 0.1Pa-20Pa, including but not limited to any one point value of 0.1Pa, 0.5Pa, 1Pa, 5Pa, 10Pa, 15Pa, 20Pa or a range value consisting of any two point values.

[0051] In one embodiment, when P ≥ 10 Pa, 100 ≤ k ≤ 300, 300°C ≤ T < 600°C. Preferably, when 10 Pa ≤ P < 20 Pa, 100 ≤ k ≤ 200, 500°C ≤ T < 600°C.

[0052] In one embodiment, when 5 Pa ≤ P < 10 Pa, 200 < k ≤ 500, 500°C < T < 800°C. Preferably, 600°C ≤ T < 800°C.

[0053] In one embodiment, when 1 Pa ≤ P < 5 Pa, 400 < k ≤ 800, 700°C < T < 1000°C. Preferably, when 1 Pa ≤ P < 5 Pa, 500 < k ≤ 800, 800°C ≤ T ≤ 900°C.

[0054] In one embodiment, when 0.1 Pa ≤ P < 1 Pa, 800 < k ≤ 3000, 900°C < T ≤ 1200°C.

[0055] In one embodiment, the thickness of the surface oxide layer of the samarium cobalt alloy after oxidation heat treatment is 1 μm - 5 μm, including but not limited to any one point value or the range value formed by any two point values among 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm.

[0056] In one embodiment, the oxygen content of the samarium cobalt alloy after oxidation heat treatment is 1500 ppm - 4000 ppm, including but not limited to any one point value or the range value formed by any two point values among 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm.

[0057] In step S3, processes such as powder making are performed on the samarium cobalt alloy after oxidation heat treatment, so that the oxides are uniformly dispersed in the magnet, and a relatively uniform distribution of oxides or fine grains in the magnet can be achieved, which is beneficial to further enhancing the magnetic properties of the magnet and the consistency and stability of mechanical properties.

[0058] In one embodiment, the crushing process includes but is not limited to mechanical crushing. The present invention preferably uses mechanical crushing.

[0059] In one embodiment, the particle size of the coarse particles obtained by crushing is less than 5 mm.

[0060] In one embodiment, the powder making process includes but is not limited to jet milling or ball milling.

[0061] In one embodiment, the specific surface average particle size (SMD) of the alloy powder is 3 μm - 8 μm, and the maximum particle size in the alloy powder is less than or equal to 35 μm.

[0062] The present invention does not limit the orientation forming and sintering process used in step S4, and existing processes can be used.

[0063] In one embodiment, the orientation forming process comprises: orienting and forming the alloy powder under the action of a magnetic field, and further performing isostatic pressing to obtain a samarium-cobalt green body.

[0064] Preferably, the magnetic field intensity of the orientation molding is greater than or equal to 2T; the density of the green compact after magnetic field orientation molding is preferably 3.5g / cm 3 -4.5g / cm 3 The density of the samarium-cobalt green body obtained after isostatic pressing is preferably 4.5 g / cm 3 -5.5g / cm 3 .

[0065] In one embodiment, the sintering process includes sintering solid solution and tempering aging, wherein the sintering solid solution includes: oxygen-free sintering the samarium cobalt green body, performing solid solution treatment after sintering to denseness, and rapid quenching and cooling after the solid solution is completed.

[0066] Preferably, the sintering and solution treatment process specifically includes the following steps: under the condition of a vacuum degree less than or equal to 0.05 Pa, heating to 1130℃-1180℃ at a heating rate of 0.5℃ / min-10℃ / min and keeping warm for 0.5h-5h for pre-sintering, then heating to 1170℃-1240℃ in an inert gas environment and keeping warm for 1h-8h for sintering, then cooling to 1110℃-1180℃ at a cooling rate of 0.2℃ / min-5℃ / min and keeping warm for 2h-72h for solution treatment, and after the solution treatment, rapidly quenching to below 400℃ at a cooling rate of 40℃ / min-200℃ / min.

[0067] It should be noted that the present invention is not limited to one-step or multi-step treatment for each stage in the above-mentioned sintering and solution treatment process. For example, in the pre-sintering process, it can be first heated to 300°C and kept warm for 1 hour, then heated to 800°C and kept warm for 1.5 hours, and then heated to the pre-sintering temperature, or directly heated to the pre-sintering temperature; in the solution treatment process, it can be first cooled to 1170°C and kept warm for 2 hours, then cooled to 1150°C and kept warm for 4 hours, then cooled to 1130°C and kept warm for 10 hours, or directly cooled to the solution treatment temperature.

[0068] In one embodiment, the tempering aging process preferably includes the following steps: in an inert gas environment or under a vacuum degree of ≤0.1 Pa, heating to 750°C-900°C at a heating rate of 0.5°C / min-10°C / min and holding for 1h-50h, then cooling to 300°C-500°C at a cooling rate of 0.1°C / min-1°C / min and holding for 1h-30h.

[0069] It should be noted that the present invention is not limited to one-step or multi-step treatment for each stage in the above-mentioned tempering and aging process. For example, in the heating process, it can be first heated to 300°C and kept for 1 hour, then heated to 600°C and kept for 2 hours, and then heated to the primary aging temperature, or it can be heated to the tempering temperature in one step; in the cooling process, it can be first cooled to 700°C and kept for 2 hours, then cooled to 600°C and kept for 4 hours, and then cooled to the final aging temperature, or it can be cooled to the secondary aging temperature in one step.

[0070] Therefore, the preparation method of the present invention not only successfully achieves a balance between high hard magnetic properties and high bending strength of the samarium cobalt permanent magnet, but also does not require the addition of external additives or materials to the samarium cobalt alloy. The preparation method is simple, efficient, and suitable for industrial production.

[0071] The present invention also provides a samarium cobalt permanent magnet, which is prepared by the preparation method as described above. The oxygen content of the samarium cobalt permanent magnet is 3500ppm-6000ppm, including but not limited to any one point value of 3500ppm, 4000ppm, 4500ppm, 5000ppm, 5500ppm, and 6000ppm, or a range value consisting of any two point values.

[0072] In one embodiment, the average grain size of the samarium cobalt permanent magnet is 30 μm-80 μm, including but not limited to any one value among 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, and 80 μm, or a range consisting of any two values.

[0073] In one embodiment, the maximum grain size of the samarium cobalt permanent magnet is less than 170 μm, including but not limited to any one of 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, and 150 μm, or a range consisting of any two of the values.

[0074] The samarium cobalt permanent magnet and its preparation method will be further described below by the following specific examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention. Where specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, for which the manufacturer is not specified, are all commercially available conventional products.

[0075] Example 1

[0076] A total of 100 kg of raw metal was prepared with a mass percentage of 25% Sm, 17% Fe, 5% Cu, 3% Zr, and the balance Co. This was then induction-melted to produce a SmCo alloy ingot. The ingot was then subjected to an oxidation heat treatment: the ingot was heated to 1000°C under a vacuum of 0.5 Pa for 1 hour and then cooled to room temperature. The cross-section of the oxidized SmCo alloy ingot was characterized using a scanning electron microscope (SEM). Figure 1 As shown, it can be found that the thickness of the ingot oxide layer is about 3.5μm, and the overall oxygen content of the ingot is further measured to be 2684ppm.

[0077] The ingot was then mechanically crushed into coarse particles less than 1 mm, and then jet milled to produce a powder with a surface average particle size (SMD) of 4.35 μm and a maximum particle size of no more than 23.41 μm. The powder was then mixed evenly using a three-dimensional mixer. The mixed fine powder was oriented and formed in a 2T magnetic field, and the green compact density was 4.2 g / cm 3 , then isostatically pressed at 230 MPa for 30 min to obtain a density of 5.0 g / cm 3 of the green body.

[0078] The green body was placed in a sintering furnace, evacuated to below 0.01 Pa, and pre-sintered at a heating rate of 2°C / min to 450°C, held for 2 hours, then at a heating rate of 3°C / min to 950°C, held for 2 hours, and finally at a heating rate of 3.33°C / min to 1150°C, held for 1 hour. Argon was then introduced, and the body was sintered at a heating rate of 0.83°C / min to 1200°C, held for 3 hours. After sintering, the body was cooled at a cooling rate of 1°C / min to 1180°C, held for 4 hours, for solution treatment. After solution treatment, the body was rapidly cooled to room temperature at a cooling rate of 65°C / min to obtain a sintered blank.

[0079] Afterwards, the sintered blank was placed in a vacuum environment of less than 0.1 Pa, heated to 650°C at a heating rate of 10°C / min and kept warm for 1 hour, then heated to 810°C at a heating rate of 2°C / min and kept warm for 10 hours for primary aging, then slowly cooled to 400°C at a cooling rate of 0.7°C / min and kept warm for 4 hours for secondary aging, and finally cooled to room temperature with the furnace to obtain samarium cobalt permanent magnets.

[0080] The metallographic characterization of the prepared samarium cobalt permanent magnet was carried out, and the results were as follows: Figure 2 As shown, the average grain size of the magnet is 62.8μm, the maximum size is 136μm, the oxygen content of the magnet is 4316ppm, and the oxide (white substance in the metallographic image) is dispersed relatively evenly in the magnet.

[0081] Example 2

[0082] A total of 40 kg of raw metal, consisting of 24.8% Sm, 19.3% Fe, 5% Cu, 2.7% Zr, and the balance Co, was induction melted to produce a samarium-cobalt alloy ingot. The ingot underwent an oxidative heat treatment: heating to 550°C at 12 Pa for 3.5 hours and then cooling to room temperature. The ingot's oxide layer thickness was measured to be approximately 2.8 μm, and the overall oxygen content was 2210 ppm.

[0083] The ingots were then mechanically crushed into coarse particles less than 1 mm, and then jet milled and ball milled to produce powders with surface average particle sizes (SMD) of 4.58 μm and 3.95 μm, respectively, and a maximum particle size of no more than 23.41 μm. The powders were then mixed evenly using a three-dimensional mixer. The mixed fine powders were oriented and formed in a 2T magnetic field, with a green compact density of 4.0 g / cm 3 , then isostatically pressed at 250 MPa for 30 min to obtain a density of 5.1 g / cm 3 of the green body.

[0084] The green body was placed in a sintering furnace, evacuated to below 0.01 Pa, and heated to 300°C at a heating rate of 2°C / min and held for 2 hours, then heated to 850°C at a heating rate of 3.5°C / min and held for 2 hours, then heated to 1000°C at a heating rate of 2.5°C / min and held for 1 hour, and then heated to 1180°C at a heating rate of 3°C / min and held for 1 hour for pre-sintering. Subsequently, argon was filled in, and the temperature was increased to 1195°C at a heating rate of 0.83°C / min and held for 2.5 hours for sintering. After sintering, the temperature was cooled to 1175°C at a cooling rate of 1°C / min and held for 2 hours, then cooled to 1165°C at a cooling rate of 0.7°C / min and held for 4 hours, and then cooled to 1160°C at a cooling rate of 0.7°C / min and held for 12 hours for solution treatment. After the solutionization was completed, the mixture was rapidly cooled to room temperature at a cooling rate of 80°C / min to obtain a sintered blank.

[0085] Afterwards, the sintered blank was placed in a vacuum environment of less than 0.1 Pa, heated to 600°C at a heating rate of 10°C / min and kept warm for 1 hour, then heated to 820°C at a heating rate of 2°C / min and kept warm for 15 hours for primary aging, then slowly cooled to 400°C at a cooling rate of 0.5°C / min and kept warm for 6 hours for secondary aging, and finally cooled to room temperature with the furnace to obtain samarium cobalt permanent magnets.

[0086] Example 3

[0087] A total of 100 kg of raw metal, consisting of 24.8% Sm, 23% Fe, 5% Cu, 2.5% Zr, and the balance Co, was induction melted to produce a samarium-cobalt alloy ingot. The ingot underwent an oxidation heat treatment: heating to 750°C for 3.2 hours under a vacuum of 8 Pa, then cooling to room temperature. The oxide layer thickness of the ingot was measured to be approximately 4.6 μm, and the overall oxygen content of the ingot was 3413 ppm.

[0088] The slabs were then mechanically crushed into coarse particles less than 2 mm, and then jet milled to produce a powder with a surface average diameter (SMD) of 4.14 μm and a maximum particle size of no more than 21.67 μm. The powders were then mixed evenly using a three-dimensional mixer. The mixed fine powders were oriented and formed in a 2T magnetic field, resulting in a compact density of 3.8 g / cm 3 , then isostatically pressed at 250 MPa for 45 min to obtain a density of 5.1 g / cm 3 of the green body.

[0089] The green body was placed in a sintering furnace, evacuated to below 0.01 Pa, and heated to 300°C at a heating rate of 2°C / min and held for 2 hours, then heated to 850°C at a heating rate of 3.5°C / min and held for 2 hours, then heated to 1000°C at a heating rate of 2.5°C / min and held for 1 hour, and then heated to 1180°C at a heating rate of 3°C / min and held for 1 hour for pre-sintering. Subsequently, argon was filled in, and the temperature was increased to 1193°C at a heating rate of 0.83°C / min and held for 2.5 hours for sintering. After sintering, the temperature was cooled to 1160°C at a cooling rate of 1°C / min and held for 2 hours, then cooled to 1150°C at a cooling rate of 1°C / min and held for 8 hours, and then cooled to 1140°C at a cooling rate of 0.7°C / min and held for 15 hours for solution treatment. After the solutionization was completed, the mixture was rapidly cooled to room temperature at a cooling rate of 80°C / min to obtain a sintered blank.

[0090] Afterwards, the sintered blank was placed in a vacuum environment of less than 0.1 Pa, heated to 600°C at a heating rate of 10°C / min and kept warm for 1 hour, then heated to 810°C at a heating rate of 2°C / min and kept warm for 20 hours for primary aging, then slowly cooled to 400°C at a cooling rate of 0.3°C / min and kept warm for 10 hours for secondary aging, and finally cooled to room temperature with the furnace to obtain the final samarium cobalt magnet.

[0091] Example 4

[0092] A total of 40 kg of raw metal, consisting of 25% Sm, 21.5% Fe, 5% Cu, 3% Zr, and the balance Co, was induction melted to produce a SmCo alloy ingot. The ingot underwent an oxidative heat treatment: heating to 800°C at 2 Pa for 1.5 hours and then cooling to room temperature. The oxide layer thickness of the ingot was measured to be approximately 2.5 μm, and the overall oxygen content of the ingot was 1897 ppm.

[0093] The ingots were then mechanically crushed into coarse particles less than 1 mm, and then jet milled and ball milled to produce powders with surface average particle sizes (SMD) of 4.5 μm and 4.0 μm, respectively, and a maximum particle size of no more than 23.66 μm. The powders were then mixed evenly using a three-dimensional mixer. The mixed fine powders were oriented and formed in a 2.3 T magnetic field, resulting in a compact density of 4.15 g / cm 3 , then isostatically pressed at 250 MPa for 30 min to obtain a density of 5.1 g / cm 3 of the green body.

[0094] The green body was placed in a sintering furnace, evacuated to below 0.01 Pa, and heated to 300°C at a heating rate of 2°C / min and held for 2 hours, then heated to 850°C at a heating rate of 3.5°C / min and held for 2 hours, then heated to 1000°C at a heating rate of 2.5°C / min and held for 1 hour, and then heated to 1180°C at a heating rate of 3°C / min and held for 1 hour for pre-sintering. Subsequently, argon was filled in, and the temperature was increased to 1195°C at a heating rate of 0.83°C / min and held for 2.5 hours for sintering. After sintering, the temperature was cooled to 1175°C at a cooling rate of 1°C / min and held for 2 hours, then cooled to 1165°C at a cooling rate of 0.7°C / min and held for 4 hours, and then cooled to 1160°C at a cooling rate of 0.7°C / min and held for 12 hours for solution treatment. After the solutionization was completed, the mixture was rapidly cooled to room temperature at a cooling rate of 80°C / min to obtain a sintered blank.

[0095] Afterwards, the sintered blank was placed in a vacuum environment of less than 0.1 Pa, heated to 600°C at a heating rate of 10°C / min and kept warm for 1 hour, then heated to 820°C at a heating rate of 2°C / min and kept warm for 15 hours for primary aging, then slowly cooled to 400°C at a cooling rate of 0.5°C / min and kept warm for 6 hours for secondary aging, and finally cooled to room temperature with the furnace to obtain samarium cobalt permanent magnets.

[0096] Comparative Example 1

[0097] The difference between Comparative Example 1 and Example 1 is that the ingot is not subjected to oxidation heat treatment, and the oxygen content of the ingot as a whole is 427ppm, the oxygen content of the magnet is 2568ppm, and the metallurgical structure of the magnet is as follows: Figure 3As shown, the average grain size is 85.3 μm, the maximum grain size is 194 μm, and the oxide distribution is significantly lower than that of the magnet in Example 1. The magnetic properties are remanence Br = 11.21 kGs, intrinsic coercivity Hcj = 28.78 kOe, and maximum magnetic energy product (BH)max = 31.05 MGOe, indicating that the magnetic properties are similar to those of the magnet in Example 1, but the bending strength is only 117 MPa.

[0098] Comparative Example 2

[0099] The difference between Comparative Example 2 and Example 2 is that the ingot is subjected to oxidation heat treatment: the ingot is heated to 100°C at 12 Pa and kept warm for 1.5 hours, and then cooled to room temperature. The overall oxygen content of the ingot is measured to be 1098 ppm, and the oxygen content of the magnet is 2688 ppm.

[0100] Comparative Example 3

[0101] The difference between Comparative Example 3 and Example 1 is that the ingot is subjected to an oxidation heat treatment: the ingot is heated to 1000°C under a vacuum of 30 Pa for 2 hours and then cooled to room temperature. The cross section of the ingot is characterized by scanning electron microscopy (SEM). The results are as follows: Figure 4 As shown, it can be found that the thickness of the ingot oxide layer is about 5.8μm. The oxygen content of the entire ingot is further measured to be 5238ppm, and the oxygen content of the magnet is 9897ppm.

[0102] Comparative Example 4

[0103] The difference between Comparative Example 4 and Comparative Example 1 is that an appropriate amount of the powder of Comparative Example 1 is taken, 3 wt% of samarium oxide is added, uniformly mixed, pressed, sintered, solid-solutionized and tempered to obtain a magnet. The oxygen content of the magnet is 2787 ppm, which is close to that of Comparative Example 1. The magnet is characterized by metallography. The results are as follows: Figure 5 As shown, samarium oxide (white substance in the figure) is agglomerated and has local fine grains concentrated.

[0104] The preparation parameters of Examples 1-4 and Comparative Examples 1-4 are shown in Table 1.

[0105] Table 1

[0106]

[0107] The magnetic properties of the magnets prepared in Examples 1-4 and Comparative Examples 1-4 were measured, and the flexural strength was measured in accordance with the standard "Test Methods for Physical Properties of Rare Earth Permanent Magnet Materials Part 2: Determination of Flexural Strength and Fracture Toughness" (GB / T 31967.2-2015). The results are shown in Table 2.

[0108] Table 2

[0109]

[0110] According to Examples 1-4 in Table 2, under different raw material ratios, the samarium cobalt permanent magnets obtained by the preparation method of the present invention can simultaneously have high hard magnetic properties and high flexural strength. The samarium cobalt permanent magnet obtained in Comparative Example 1 has a remanence of 11.21 kGs, an intrinsic coercive force of 28.78 kOe, and a maximum magnetic energy product of 31.05 MGOe. Under the same raw material ratio, although the magnetic properties are similar to those of Example 1, the flexural strength is only 117 MPa. The samarium cobalt permanent magnet obtained in Comparative Example 2 has a remanence of 11.61 kGs, an intrinsic coercive force of 26.13 kOe, and a maximum magnetic energy product of 32.01 MGOe. Under the same raw material ratio, although the magnetic properties are similar to those of Example 2, the flexural strength is only 122 MPa. Due to the excessively high oxygen content in Comparative Example 3, the hard magnetic properties of the magnet are significantly reduced. In Comparative Example 4, since samarium oxide is a non-magnetic material, its aggregation not only reduces the consistency and stability of the magnetic properties of the magnet, but also causes local stress concentration to affect the mechanical properties. As a result, under the same raw material ratio, the bending strength is reduced by 11 MPa compared with Example 1.

[0111] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0112] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a samarium cobalt permanent magnet, characterized in that: The preparation method comprises the following steps: Provide samarium cobalt alloy; The samarium-cobalt alloy is subjected to an oxidation heat treatment, wherein the oxidation heat treatment process satisfies the following relationship: t=kP / T, wherein t is the holding time in hours; T is the heating temperature in degrees Celsius; P is the vacuum degree in Pa; and k is a coefficient, k=100-5000. Crushing and pulverizing the samarium-cobalt alloy after the oxidation heat treatment to obtain alloy powder; The alloy powder is oriented and formed into a samarium-cobalt green compact, and then the samarium-cobalt permanent magnet is prepared by sintering.

2. The method for preparing a samarium cobalt permanent magnet according to claim 1, wherein: The heating temperature T is 300°C-1200°C; And / or, the vacuum degree P is 0.1Pa-20Pa.

3. The method for preparing a samarium cobalt permanent magnet according to claim 1, wherein: When P≥10Pa, 100≤k≤300, 300℃≤T<600℃; Or, when 5Pa≤P<10Pa, 200 <k≤500,500℃<T<800℃; Or, when 1Pa≤P<5Pa, 400 <k≤800,700℃<T<1000℃; Or, when 0.1Pa≤P<1Pa, 800 <k≤3000,900℃<T≤1200℃。 4. The method for preparing a samarium cobalt permanent magnet according to claim 1, wherein: The components of the samarium-cobalt alloy include: 23%-28% Sm, 13%-25% Fe, 4%-10% Cu, 1.5%-3.5% Zr and the balance Co.

5. The method for preparing a samarium cobalt permanent magnet according to claim 1, wherein: The thickness of the oxide layer on the surface of the samarium-cobalt alloy after oxidation heat treatment is 1 μm-5 μm; And / or, the oxygen content of the samarium-cobalt alloy after the oxidation heat treatment is 1500 ppm-4000 ppm.

6. The method for preparing a samarium cobalt permanent magnet according to claim 1, wherein: The particle size of the coarse particles obtained by crushing is less than 5 mm; And / or, the alloy powder has an average specific surface area particle size of 3 μm-8 μm, and a maximum particle size of less than or equal to 35 μm.

7. The method for preparing a samarium cobalt permanent magnet according to claim 1, wherein: In the orientation forming step, the magnetic field strength is greater than or equal to 2T; And / or, the density of the samarium cobalt green body is 4.5 g / cm 3 -5.5g / cm 3 .

8. The method for preparing a samarium cobalt permanent magnet according to claim 1, wherein: The sintering treatment includes sintering and solid solution treatment, and the sintering and solid solution treatment process includes: under the condition of vacuum degree less than or equal to 0.05 Pa, heating to 1130°C-1180°C at a heating rate of 0.5°C / min-10°C / min and keeping warm for 0.5h-5h for pre-sintering, then heating to 1170°C-1240°C in an inert gas environment and keeping warm for 1h-8h for sintering, then cooling to 1110°C-1180°C at a cooling rate of 0.2°C / min-5°C / min and keeping warm for 2h-72h for solid solution treatment, and after the solid solution treatment, rapid quenching to below 400°C at a cooling rate of 40°C / min-200°C / min; And / or, the sintering treatment also includes tempering and aging, and the tempering and aging process includes: in an inert gas environment or under vacuum conditions of ≤0.1 Pa, heating to 750°C-900°C at a heating rate of 0.5°C / min-10°C / min and keeping warm for 1h-50h, and then cooling to 300°C-500°C at a cooling rate of 0.1°C / min-1°C / min and keeping warm for 1h-30h.

9. A samarium cobalt permanent magnet, characterized in that: The samarium cobalt permanent magnet is prepared by the preparation method according to any one of claims 1 to 8, and the oxygen content of the samarium cobalt permanent magnet is 3500ppm-6000ppm.

10. The samarium cobalt permanent magnet according to claim 9, characterized in that The average grain size of the samarium cobalt permanent magnet is 30 μm-80 μm; And / or, the maximum grain size of the samarium cobalt permanent magnet is less than 170 μm.

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