High-performance low-mechanical-anisotropy rare earth permanent magnet and preparation method thereof

Abstract

The invention discloses a rare earth permanent magnet with high performance and low mechanical anisotropy and a preparation method of the rare earth permanent magnet, and belongs to the technical field of rare earth permanent magnet materials, used raw materials are composed of a main alloy and a second phase alloy, the chemical composition of the main alloy is Sm (CobalFex Cuy Zrk) z, z = 6.90-8.0, x = 0.10-0.34, y = 0.05-0.1 and k = 0.01-0.03, and the second phase alloy is oxide particles ZrO2; by adding a certain amount of specific second-phase particles, the prepared permanent magnet alloy has excellent magnetic performance ((BH) max is greater than or equal to 24MGOe), the mechanical strength of an alloy sample in three different orientation directions can be obviously improved, the maximum bending strength reaches about 200MPa, and the anisotropy difference value is less than 25MPa.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth permanent magnet materials, and particularly relates to a high-performance low-mechanical anisotropy rare earth permanent magnet and a preparation method thereof. Background Art

[0002] Rare earth cobalt permanent magnet materials with characteristics such as high magnetic energy product, high coercivity, good corrosion resistance, and excellent thermal stability are the core materials for control systems of missiles, rockets, satellites, aircraft, etc., and are also the key materials for modern radars, microwave communications, electronic warfare systems, etc. They are widely used in military electronic equipment such as avionics and electromagnetic space warfare. Rare earth permanent magnets play a crucial role and are irreplaceable in modern weaponry. However, due to its cleavage transgranular fracture mode, rare earth cobalt permanent magnet materials have intrinsic brittleness, which greatly limits the wider application of rare earth permanent magnets.

[0003] Li Wei et al. studied the fracture mode of Sm2Co 17 anisotropic magnets. According to the analysis of the fracture surface morphology, the fracture mode of the magnet is cleavage transgranular fracture, and river patterns and cleavage steps can be clearly observed in the fracture surface. Sm2Co 17 magnets are anisotropic materials, and their fracture behavior also shows anisotropy. Mechanical property tests are usually carried out with reference to the national standard GB / T31967.2-2015 Test methods for physical properties of rare earth permanent magnet materials - Part 2: Determination of flexural strength and fracture toughness. The specimen sizes for flexural strength and fracture toughness are respectively ( h × b × L ) 5×6×20 and ( B × W × L ) 5×10×45. Therefore, when the orientation direction is different from the direction of the mechanical test specimen, its mechanical properties have directional differences. The results show that when the specimen orientation c is parallel to the span direction L , the mechanical properties are generally poor. The statistical results of mechanical tests show that c / / L direction is often more than 40 MPa lower than c / / h and c / / b directions, resulting in a great risk to the use of the magnet when the orientation direction is stressed.

[0004] Chinese Patent CN102568738A discloses that through microalloying (adding Ti and Co elements), second phases (TiB2, NdFeCoTi) dispersed within grains are formed in the alloy, enhancing the mechanical properties of the alloy, and finally obtaining a neodymium-iron-boron magnet with a flexural strength of not less than 500 MPa; Chinese Patent CN113936880A discloses that by adding Zr element to the neodymium-iron-boron magnet, through a certain process, Zr precipitates in the R-rich phase at the grain boundary in the form of fibrous compounds, improving the strength of the R-rich phase and thus enhancing the flexural strength of the magnet; however, the above two methods for improving the mechanical strength of neodymium-iron-boron magnets are not applicable to rare-earth cobalt permanent magnet materials.

[0005] Chinese Patent CN113517104A discloses that by adding a secondary phase alloy RE 1-u-v- w Fe u Cu v TM w , where RE is selected from one or more of Sm, Nd, Pr, Dy, Tb, Gd, and Ho. The Sm and Cu elements in the magnet diffuse from the grain boundary phase into the interior of the alloy matrix grains, improving the cellular microstructure of the alloy, optimizing the magnetic properties of the alloy. The low-melting-point secondary phase also forms a bonding layer between the grains, enhancing the mechanical properties of the magnet. The prepared samarium-cobalt permanent magnet material has excellent remanence, coercivity, squareness, and good mechanical properties. However, for the rare-earth permanent magnet prepared by this method, the anisotropic characteristics of its mechanical properties (large directional differences in mechanical properties) have not been significantly improved. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a high-performance rare-earth permanent magnet with low mechanical anisotropy to solve the above problems.

[0007] To achieve the above objective, the technical solution adopted by the present invention is as follows: A high-performance rare-earth permanent magnet with low mechanical anisotropy, the raw materials used are composed of a main alloy and a second-phase alloy. Among them, the chemical composition of the main alloy is Sm(Co bal Fe x Cu y Zr k ) z , where z = 6.90 - 8.0, x = 0.10 - 0.34, y = 0.05 - 0.1, k = 0.01 - 0.03, bal + x + y + k = 1, and the second-phase alloy is Sm2O3 or ZrO2.

[0008] As a preferred technical solution, second-phase particles with good chemical compatibility with the main phase are selected. The second-phase particles do not chemically react with the main phase, so they have a relatively small impact on magnetic properties. At the same time, the second-phase particles can inhibit grain growth during the sintering process and improve the mechanical properties of the magnet. Preferably, the second-phase particles are Sm2O3 or ZrO2. The addition amount of Sm2O3 is 1.0% - 2.0 wt% of the master alloy, and the addition amount of ZrO2 is 1.0 - 3.0 wt% of the master alloy.

[0009] In the present invention, by adding specific second-phase particles in an appropriate proportion, the second-phase particles are mainly distributed at the alloy grain boundaries. During the sintering and heat treatment processes, the alloy grain coarsening is inhibited through the Zener effect. According to , F p is the pinning force, f is the volume fraction of the second-phase particles, γGB is the grain boundary energy per unit area, r is the radius of the second-phase particles. The smaller the particle size of the second-phase particles, the larger the volume fraction, the more dispersed the distribution, the stronger the pinning effect, and the better the inhibitory effect on alloy grain coarsening. As shown in the metallographic microstructures of the alloy magnets in Figure 1 and Figure 2 , in the figure, the precipitation phase 1 is mainly the Zr-rich 2:7 phase, which is a common precipitation phase in samarium cobalt alloys and is not easily corroded, and its metallography is white. The second-phase particles 2 are samarium oxide or zirconium oxide particles, which are easily corroded, and their metallography is black. Figure 1 is the microstructure diagram of the magnet alloy without adding the second-phase particles 2, and the average grain size is about 40 μm; Figure 2 is the microstructure of the magnet alloy with the second-phase particles 2 added. The black particles in the figure are the second-phase particles 2 added to the alloy, which are mainly distributed at the alloy grain boundaries, and the average grain size is about 10 μm. From the comparison between Figure 1 and Figure 2 , it can be seen that adding second-phase particles with good chemical compatibility to the alloy significantly refines the alloy microstructure. The fine alloy grains can inhibit crack propagation during the alloy fracture process and have a more obvious energy absorption effect, so the alloy exhibits higher flexural strength.

[0010] In the present invention, the flexural strength of the magnet is improved by reducing the magnet grain size. Since the mechanical properties of the magnet have obvious anisotropic characteristics, when the orientation direction c is parallel to the span direction L , the flexural strength of the material is generally the lowest. c / / b and c / / hThe direction is higher because the magnet is most prone to cleavage after being subjected to tensile stress along the orientation direction. By reducing the grain size, while improving the magnet, the present invention reduces the influence of the tensile stress-induced cleavage of the basal plane in the orientation direction, achieving the purpose of reducing the anisotropy difference in the three directions.

[0011] The second object of the present invention is to provide a method for preparing the above-mentioned high-performance low-mechanical anisotropy rare-earth permanent magnet. The technical solution adopted is that its steps sequentially include master alloy batching, master alloy melting into an alloy ingot, master alloy crushing, master alloy grinding, adding a second-phase alloy, mixing, forming, and sintering heat treatment.

[0012] As a preferred technical solution, the raw materials used are metallic samarium with a purity of 99.9 wt%, cobalt metal, pure iron rods, electrolytic copper, and zirconium metal.

[0013] As a preferred technical solution, the master alloy grinding uses a jet mill. The parameters of the jet mill are: the working sorting wheel speed is 2000 - 6000 r / min, the working medium pressure is 0.4 - 0.8 MPa, the grinding chamber pressure is 0.02 - 0.06 MPa, and the gas used is high-purity nitrogen. Finally, alloy powder with a size of 2 - 5 mm is obtained.

[0014] As a preferred technical solution, the particle size of the added second-phase alloy is 0.1 - 0.9 μm.

[0015] As a preferred technical solution, the mixing is carried out under the protection of an inert gas for uniform mixing. Steel balls with a ball radius of 8 - 15 mm are added to the mixing material tank. The addition amount of the steel balls is steel ball mass / powder mass = 1 / 2 - 1 / 3, and the mixing time is not less than 8 h.

[0016] As a preferred technical solution, the forming is magnetic field forming. Using a semi-automatic magnetic field forming press, the uniformly mixed alloy powder is formed into a square or cylinder in a magnetic field and cold isostatically pressed to obtain a green body; the magnetization current used is 60 - 80 A, the demagnetization current is 20 - 30 A, the forming pressure is 5 - 12 MPa, and the isostatic pressure is 200 - 250 MPa.

[0017] As a preferred technical solution, the vacuum degree during the sintering process is better than 5×10 -3 Pa, and it is kept at a sintering temperature of 1090 - 1220 °C for 0.5 - 2 h, cooled to 1000 - 1198 °C for solution treatment, kept for 0.5 - 2 h, and quickly cooled to room temperature to finally obtain a solution-treated magnet.

[0018] As a preferred technical solution, the vacuum degree during the heat treatment process is better than 5×10 -3Pa, heat at 790 - 810 °C for 20 - 30 h, cool down to 380 - 420 °C, hold for 10 - 20 h, and then cool to room temperature to obtain the final magnet sample.

[0019] Compared with the prior art, the advantages of the present invention are as follows: by adding a certain content of specific second-phase particles, the prepared permanent magnet alloy has excellent magnetic properties ( BH ) max ≥24 MGOe), the mechanical strength of the alloy is significantly improved, the difference in flexural strength anisotropy of the magnet alloy is <25 MPa, and the maximum flexural strength reaches nearly 200 MPa, which is significantly better than the current industry level. Description of the Drawings

[0020] Figure 1 is the metallographic structure diagram of the magnet without the second phase in Comparative Example 1; Figure 2 is the metallographic structure diagram of the magnet with 2 wt% Sm2O3 second phase added in Example 3; Detailed Embodiments

[0021] The present invention will be further described below in conjunction with the embodiments.

[0022] Example 1

[0023] A high-performance rare-earth permanent magnet with low mechanical anisotropy, the components of the raw materials used for preparation are: Sm(Co 0.675 Fe 0.22 Cu 0.08 Zr 0.025 ) 7.6 +1.0 wt% Sm2O3, The preparation method is as follows: first, use metallic samarium, metallic cobalt, pure iron rods, electrolytic copper, and metallic zirconium with a purity of 99.9 wt% to proportion the materials according to the above ratio; then melt them into alloy ingots, and the melting process parameters of this example are shown in Table 1; Table 1. Melting process parameters of Example 1

[0024] Crush them respectively and make fine powders by air jet milling. The parameters of the air jet mill are: the sorting wheel speed is 3000 r / min, the working medium pressure is 0.5 MPa, the grinding chamber pressure is 0.05 MPa, and the gas is high-purity nitrogen. Finally, alloy powders with a size of 3 - 4 mm are obtained; then add second-phase Sm2O3, ZrO2, Sm 0.5 Fe 0.15 Cu 0.2 Al 0.15, and under the protection of inert gas, the powders were uniformly mixed; a square green compact with dimensions of 60 mm × 56 mm × 52 mm was obtained by magnetic field forming and cold isostatic pressing, with a forming pressure of 6 MPa and an isostatic pressure of 250 MPa; the green compact was placed in a tube-type sintering furnace for sintering, with the vacuum degree reaching 5´10 -3 Pa, the sintering temperature was 1090 °C to 1220 °C, holding for 60 min, then cooling by 20 °C and holding for 60 min, and then quickly cooling to room temperature to take out the sample. After testing the density of the sample and meeting the requirements, the sample was placed in a tube-type sintering furnace for heat treatment, with the vacuum degree reaching 5×10 -3 Pa, the heat treatment temperature was 810 °C, holding for 24 h, cooling to 400 °C, holding for 10 h, and cooling to room temperature to take out the sample.

[0025] Example 2

[0026] In this example, the composition of the alloy was Sm(Co 0.675 Fe 0.22 Cu 0.08 Zr 0.025 ) 7.6 +1.5 wt% (Sm2O3), and the powders were uniformly mixed; the rest was the same as in Example 1.

[0027] Example 3

[0028] In this example, the composition of the alloy was Sm(Co 0.675 Fe 0.22 Cu 0.08 Zr 0.025 ) 7.6 +2.0 wt% (Sm2O3), and the powders were uniformly mixed; the rest was the same as in Example 1.

[0029] Example 4

[0030] In this example, the composition of the alloy was Sm(Co 0.65 Fe 0.27 Cu 0.06 Zr 0.02 ) 7.2 +1.0 wt% (ZrO2), and the powders were uniformly mixed; the rest was the same as in Example 1.

[0031] Example 5

[0032] In this example, the composition of the alloy was Sm(Co 0.65 Fe 0.27 Cu 0.06 Zr 0.02 ) 7.2 +1.5 wt% (ZrO2), and the powders were uniformly mixed; the rest was the same as in Example 1.

[0033] Example 6

[0034] In this example, the composition of the alloy is Sm(Co 0.65 Fe 0.27 Cu 0.06 Zr 0.02 ) 7.2 + 3.0 wt% (ZrO2). The powders are uniformly mixed; the rest is the same as in Example 1.

[0035] Comparative Example 1 In this comparative example, the composition of the alloy is Sm(Co 0.675 Fe 0.22 Cu 0.08 Zr 0.025 ) 7.6 , and no second-phase powder is added in this example. The rest is the same as in Example 1.

[0036] Comparative Example 2 In this example, the composition of the alloy is Sm(Co 0.675 Fe 0.22 Cu 0.08 Zr 0.025 ) 7.6 + 3.0 wt% (Sm2O3). The powders are uniformly mixed. The rest is the same as in Example 1.

[0037] Comparative Example 3 In this comparative example, the composition of the alloy is Sm(Co 0.65 Fe 0.27 Cu 0.06 Zr 0.02 ) 7.2 + 0.5 wt% (ZrO2). The powders are uniformly mixed. The rest is the same as in Example 1.

[0038] Comparative Example 4 In this comparative example, the composition of the alloy is Sm(Co 0.65 Fe 0.27 Cu 0.06 Zr 0.02 ) 7.2 + 3.5 wt% (ZrO2). The powders are uniformly mixed. The rest is the same as in Example 1.

[0039] Comparative Example 5 In this comparative example, the composition of the alloy is Sm(Co 0.65 Fe 0.27 Cu 0.06 Zr 0.02 ) 7.2 + 1.0 wt% (Sm 0.5 Fe 0.15 Cu0.2 Al 0.15 ), the powders were uniformly mixed, and the rest was the same as in Example 1.

[0040] The magnetic properties and mechanical strength of the permanent magnets obtained in the above examples and comparative examples were tested, where B r 、 i H c 、( BH ) max The magnetic property test was carried out according to GB / T3217-2013 "Magnetic Test Methods for Permanent (Hard Magnetic) Materials". It was measured by a PFM12 type pulsed magnetic field magnetometer, and a φ10×10mm cylindrical sample was used for measurement at 23°C. The flexural strength was based on GB / T31967.2-2015 "Test Methods for Physical Properties of Rare Earth Permanent Magnet Materials - Part 2: Determination of Flexural Strength and Fracture Toughness". A Sansi Zongheng UTM6104X universal testing machine (tensile and compression loading module) was used, and the specimen size was h × b × L =5×6×20mm, the loading rate was 0.1mm / min, and the results are shown in Tables 2 and 3.

[0041] Table 2. Magnetic Property Test Results

[0042] Table 3. Comparison of Flexural Strength of Each Example and Each Comparative Example

[0043] It can be seen from Comparative Examples 1 and 2 in Tables 2 and 3 that on the premise of using the same preparation process, compared with the case of not adding Sm2O3 second-phase particles, when adding 1.0wt% Sm2O3 second-phase particles, the magnetic properties of the magnet have no obvious change, and the flexural strength values of the magnet are significantly improved; from Comparative Example 1 and Examples 1, 2, and 3, it can be obtained that on the premise of using the same preparation process, after the content of the added Sm2O3 second-phase particles exceeds the optimal value (2 wt%), the pinning effect of the Sm2O3 second-phase particles in the magnet alloy structure no longer increases, and the refinement effect on the alloy structure no longer increases, manifested as the flexural strength of the magnet no longer increases. On the contrary, excessive addition will cause the proportion of the main magnetic phase to decrease, and the magnetic properties of the magnet will show a significant decrease. Similarly, adding ZrO2 second-phase particles to the alloy has a similar law. Different types of second-phase particles, when adding the same content to the alloy, show different gain effects. Compared with Sm2O3 second-phase particles, the weakening effect of ZrO2 on the magnetic properties of the alloy is more obvious.

[0044] It can be seen from the examples in Table 2 and Table 3 that by adding a certain content of second-phase particles, the alloy has excellent magnetic properties ( BH ) max ³24MGOe). The strength of the alloy in three different test directions has been significantly improved. The maximum flexural strength of the magnet alloy reaches nearly 200 MPa, and the maximum difference in the three directions of the magnet is less than 25 MPa. The flexural strength of the magnet is significantly improved in all three directions, and the strength difference of the magnet caused by anisotropy is reduced. Compared with the examples, by adding the auxiliary phase alloy Sm 0.5 Fe 0.15 Cu 0.2 Al 0.15 The flexural strength of the magnet in three directions has been improved, but the maximum difference in the three directions is large.

[0045] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-performance, low-mechanical anisotropy rare earth permanent magnet, characterized in that: The raw materials used are composed of a main alloy and a second phase alloy, wherein the chemical composition of the main alloy is Sm(Co bal Fe x Cu y Zr k ) z , where z=6.90~8.0, x=0.10~0.34, y=0.05~0.1, k=0.01~0.03, bal+x+y+k=1, and the second phase alloy is ZrO2.

2. The high performance, low mechanical anisotropy rare earth permanent magnet according to claim 1, characterized in that: The added amount of ZrO2 is 1.0 to 3.0 wt % of the main alloy.

3. The high performance, low mechanical anisotropy rare earth permanent magnet according to claim 1, characterized in that: The particle size of the ZrO2 is 100-300 nm.

4. The method for preparing a high-performance, low-mechanical anisotropy rare earth permanent magnet according to claim 1 or 2, characterized in that: The steps include main alloy batching, main alloy smelting into alloy ingot, main alloy crushing, main alloy grinding, adding second phase alloy, mixing, molding, sintering and heat treatment.

5. The method according to claim 4, characterized in that The raw materials used are metallic cobalt with a purity of 99.9wt%, pure iron rod, electrolytic copper and metallic zirconium.

6. The method according to claim 4, characterized in that The main alloy abrasive adopts air flow mill, and the parameters of the air flow mill are: the speed of the work separation wheel is 2000-6000r / min, the working fluid pressure is 0.4-0.8MPa, the grinding chamber pressure is 0.02-0.06MPa, and the gas adopts high-purity nitrogen, and finally 2-5mm alloy powder is obtained.

7. The method according to claim 4, characterized in that The mixed materials are uniformly mixed under the protection of inert gas, and steel balls with a ball radius of 8 to 15 mm are added to the mixing tank. The amount of steel balls added is steel ball mass / powder mass = 1 / 2 to 1 / 3, and the mixing time is not less than 8 hours.

8. The method according to claim 4, characterized in that The forming is magnetic field forming, using a semi-automatic magnetic field forming press to magnetic field-form the uniformly mixed alloy powder into blocks or cylinders, and then cold isostatic pressing is performed to obtain a green body; the magnetizing current used is 60-80A, the demagnetizing current is 20-30A, the forming pressure is 5-12MPa, and the isostatic pressure is 200-250MPa.

9. The method according to claim 4, characterized in that The vacuum degree during the sintering process is better than 5×10 -3 Pa, keep the sintering temperature at 1090-1220°C for 0.5-2h, cool to 1000-1198°C for solution treatment, keep it for 0.5-2h, quickly cool to room temperature, and finally obtain a solid solution magnet.

10. The method according to claim 4, characterized in that The vacuum degree during the heat treatment is better than 5×10 - 3 Pa, keep the heat treatment temperature at 790-810°C for 20-30h, cool to 380-420°C, keep it for 10-20h, cool to room temperature, and obtain the final magnet sample.

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