Hot-pressing thermal deformation composite permanent magnet and preparation method thereof

Abstract

The invention provides a hot-pressing thermal deformation composite permanent magnet and a preparation method thereof, the hot-pressing thermal deformation composite permanent magnet comprises a coarse grain area and a fine grain area, and the coarse grain area comprises a neodymium iron boron main phase and a rare earth high-entropy alloy phase; in the coarse grain area, grains of the neodymium iron boron main phase are equiaxed crystals, the D50 grain size of the equiaxed crystals is 600-1300 nm, and the rare earth high-entropy alloy phase is distributed among the equiaxed crystals in a strip shape; the rare earth high-entropy alloy phase comprises transition metal elements and at least four rare earth elements. Based on the hot-pressing thermal deformation composite permanent magnet, the problems that in the prior art, magnetic performance attenuation of a neodymium iron boron permanent magnet is fast, and the machining performance and the mechanical performance are poor are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and in particular, to a hot-pressed and hot-deformed composite permanent magnet and a preparation method thereof. Background Art

[0002] Permanent magnet materials are key materials indispensable to modern high-tech industries. Especially in the fields of aerospace, electronics, medical devices, new energy vehicles, communications, industrial automation, and household appliances, their applications are becoming increasingly widespread. The rare-earth permanent magnet material neodymium iron boron (NdFeB) is widely used in various high-tech fields due to its high magnetic energy product and coercivity. Hot-pressed / hot-deformed magnets have become one of the basic production process routes for preparing fully dense anisotropic high-performance rare-earth permanent magnet materials due to their unique densification and orientation processes. And by utilizing the characteristic that the orientation of the magnet is along the pressure direction, the hot-pressed / hot-deformed process has great advantages in the preparation of anisotropic permanent magnets. However, the magnetic properties of these materials decay rapidly in high-temperature environments, and their mechanical properties are poor, which limits their applications under certain extreme conditions. CN105321645A discloses a method for preparing a high-coercivity nanocrystalline hot-deformed NdFeB permanent magnet. By adding refractory carbides, nitrides, and oxides to the NdFeB magnet, the invention inhibits grain growth and achieves the effect of improving the coercivity of the magnet. However, the added refractory substances have poor plastic deformation ability and are non-magnetic phases, which affect the processing performance and mechanical properties of the magnet. Summary of the Invention

[0003] The main object of the present invention is to provide a hot-pressed and hot-deformed composite permanent magnet and a preparation method thereof to solve the problems of rapid magnetic property decay, poor processing performance, and poor mechanical properties of NdFeB permanent magnets in the prior art.

[0004] To achieve the above object, according to one aspect of the present invention, there is provided a hot-pressed and hot-deformed composite permanent magnet, which includes a coarse-grained region and a fine-grained region. The coarse-grained region includes a NdFeB main phase and a rare-earth high-entropy alloy phase; the grains of the NdFeB main phase in the coarse-grained region are equiaxed grains, the D50 particle size of the equiaxed grains is 600 nm to 1300 nm, and the rare-earth high-entropy alloy phase is distributed in a strip shape between the equiaxed grains; the rare-earth high-entropy alloy phase includes transition metal elements and at least four rare-earth elements.

[0005] Further, the D50 particle size of the equiaxed grains is 800 nm to 1200 nm.

[0006] Further, the rare-earth high-entropy alloy phase includes the following components in atomic percentage: TM 10% to 30%, and the balance is Re; wherein, Re is selected from more than four elements among La, Ce, Pr, Nd, Sm, Eu, and Gd, and TM is selected from at least one of Fe, Co, and Ni.

[0007] Furthermore, in the hot-pressed and hot-deformed composite permanent magnet, the content of the rare-earth high-entropy alloy phase is greater than 0 and less than or equal to 10% by weight percentage.

[0008] Furthermore, the maximum magnetic energy product of the hot-pressed and hot-deformed composite permanent magnet is 30 MGOe to 50 MGOe.

[0009] According to another aspect of the present invention, there is provided a method for preparing the above-mentioned hot-pressed and hot-deformed composite permanent magnet, including the following steps:

[0010] Step S1, under the protection of an inert gas, mix rare-earth high-entropy alloy powder and neodymium-iron-boron alloy powder to obtain a mixed powder body, and then hot-press and form the mixed powder body to obtain a hot-pressed magnet; the temperature of the hot-press forming is 550°C to 750°C, the pressure of the hot-press forming is 50 MPa to 300 MPa, and the time of the hot-press forming is 1 min to 10 min; the D50 particle size of the rare-earth high-entropy alloy powder is 1 μm to 5 μm, and the D50 particle size of the neodymium-iron-boron powder is 30 μm to 150 μm;

[0011] Step S2, under an inert atmosphere, perform hot-deformation treatment on the hot-pressed magnet to make its deformation degree reach 50% to 80% to obtain a hot-deformed magnet; the temperature of the hot-deformation treatment is 600°C to 750°C, and the pressure of the hot-deformation treatment is 20 MPa to 100 MPa;

[0012] Step S3, perform aging treatment on the hot-deformed magnet to obtain a hot-pressed and hot-deformed composite permanent magnet; wherein, the aging temperature is 400°C to 600°C, and the aging time is 1 h to 3 h.

[0013] Furthermore, the rare-earth high-entropy alloy powder is obtained by crushing a rare-earth high-entropy alloy ingot.

[0014] Preferably, under an inert gas environment, melt the rare-earth high-entropy alloy raw material in at least one of a vacuum arc furnace, an induction furnace, and a high-frequency furnace, and the number of melting times is 5 to 6 times. After casting and cooling, a rare-earth high-entropy alloy ingot is obtained;

[0015] Preferably, the impurity content in the rare-earth high-entropy alloy ingot is <0.05% by weight percentage.

[0016] Furthermore, under an inert atmosphere, initially crush the rare-earth high-entropy alloy ingot by mechanical crushing or gas atomization, and then perform ball milling treatment to obtain rare-earth high-entropy alloy powder.

[0017] Preferably, the D50 particle size of the powder particles obtained by the initial crushing is 10 μm to 50 μm.

[0018] Preferably, in the ball milling treatment, the ball-to-material ratio is 10:1 to 20:1, and the ball milling time is 10 h to 20 h.

[0019] Further, in step S1, the hot pressing and forming of the mixed powder includes the following steps: placing the mixed powder in a first mold, then heating to the hot pressing and forming temperature, holding for 10S to 20S, and then applying pressure to the hot pressing and forming pressure.

[0020] Further, in step S2, the hot deformation treatment of the hot-pressed magnet includes the following steps: placing the hot-pressed magnet in a second mold, then heating to the hot deformation treatment temperature, holding for 30S to 120S, and then applying pressure to the hot deformation treatment pressure.

[0021] Applying the technical solution of the present invention, in the coarse grain region of the hot-pressed and hot-deformed composite permanent magnet, the grains of the NdFeB main phase are equiaxed grains, and the D50 particle size of the equiaxed grains is 600nm to 1300nm. The grains of this size can improve the magnetic properties and mechanical strength of the composite permanent magnet. The size of the grains is relatively small, close to the single-domain critical size of NdFeB, which is beneficial to the formation of a stable magnetic domain structure, improving the coercivity of the composite permanent magnet. Moreover, through the strip-like distribution of equiaxed grains with a specific size in the NdFeB main phase and the rare earth high-entropy alloy phase, the efficient exchange coupling between the hard magnetic phase (NdFeB main phase) and the soft magnetic phase (rare earth high-entropy alloy) is realized, which can further improve the coercivity. In addition, the rare earth high-entropy alloy has strong plastic deformation ability. The plastic deformation ability of the rare earth high-entropy alloy and the fine particle size of the NdFeB main phase not only enhance the mechanical toughness and tissue stability of the composite permanent magnet, but also optimize the magnetic properties, thermal stability and mechanical strength. Furthermore, the rare earth elements in the rare earth high-entropy alloy can promote the establishment of a denser oxide or hydroxide corrosion film, thereby enhancing the corrosion resistance of the material surface.

[0022] Based on the hot-pressed and hot-deformed composite permanent magnet of the present invention, by controlling the grain size and shape of the NdFeB main phase and introducing a rare earth high-entropy alloy with plastic deformation ability between the equiaxed grains of the NdFeB main phase, the improvement of magnetic properties (remanent magnetism, magnetic energy product, coercivity), mechanical properties and corrosion resistance is realized, and a high-performance hot-pressed and hot-deformed composite permanent magnet is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0024] Figure 1 Shows the metallographic structure diagram of the hot-pressed and hot-deformed composite permanent magnet in Embodiment 1 of the present invention;

[0025] Figure 2 is Figure 1 An enlarged view of the coarse grain region in the metallographic structure diagram of the hot-pressed and hot-deformed composite permanent magnet in. Detailed implementation manners

[0026] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0027] As described in the background art, there are problems in the prior art such as relatively fast magnetic property attenuation of NdFeB permanent magnets, poor processing performance and mechanical performance. In order to solve the above problems, according to one aspect of the present invention, a hot-pressed and hot-deformed composite permanent magnet is provided. The hot-pressed and hot-deformed composite permanent magnet includes a coarse-grained region and a fine-grained region. The coarse-grained region includes a NdFeB main phase and a rare-earth high-entropy alloy phase; the grains of the NdFeB main phase in the coarse-grained region are equiaxed grains, and the D50 particle size of the equiaxed grains is 600 nm to 1300 nm. The rare-earth high-entropy alloy phase is distributed in a strip shape between the equiaxed grains; the rare-earth high-entropy alloy phase includes transition metal elements and at least four rare-earth elements.

[0028] Based on the hot-pressed and hot-deformed composite permanent magnet of the present invention, in the coarse-grained region, the grains of the NdFeB main phase are equiaxed grains, and the D50 particle size of the equiaxed grains is 600 nm to 1300. The grains of this size can improve the magnetic properties and mechanical strength of the composite permanent magnet. The size of the grains is relatively small, close to the single-domain critical size of NdFeB, which is beneficial to the formation of a stable magnetic domain structure, improves the coercivity of the composite permanent magnet, and through the strip-shaped distribution of the equiaxed grains with a specific size in the NdFeB main phase and the rare-earth high-entropy alloy phase, efficient exchange coupling between the hard magnetic phase (NdFeB main phase) and the soft magnetic phase (rare-earth high-entropy alloy) is realized, and the coercivity can be further improved. In addition, the rare-earth high-entropy alloy has strong plastic deformation ability. The plastic deformation ability of the rare-earth high-entropy alloy and the small particle size of the NdFeB main phase not only enhance the mechanical toughness and tissue stability of the composite permanent magnet, but also optimize the magnetic properties, thermal stability and mechanical strength. Moreover, the rare-earth elements in the rare-earth high-entropy alloy can promote the establishment of a denser oxide or hydroxide corrosion film, thereby enhancing the corrosion resistance of the material surface.

[0029] In some embodiments, the D50 particle size of the equiaxed grains is 800 nm to 1200 nm.

[0030] Based on the technical solution of the embodiments of the present invention, adding a rare-earth high-entropy alloy helps to inhibit grain growth, makes the grain size closer to the single-domain critical size of NdFeB, and is beneficial to improving the coercivity; the composite magnet with equiaxed grains of the above size has a high coercivity and is more likely to be arranged along the direction of the applied pressure during the preparation process, so as to form a highly oriented magnet structure, which is beneficial to improving the remanence and magnetic energy product and obtaining a high-performance hot-pressed and hot-deformed composite permanent magnet.

[0031] In one embodiment, in order to obtain higher coercivity, remanence and maximum energy product, the equiaxed crystal has a D50 particle size of 800 nm to 1200 nm, specifically, it can be 800 nm, 820 nm, 840 nm, 860 nm, 880 nm, 900 nm, 920 nm, 940 nm, 960 nm, 980 nm, 1000 nm, 1020 nm, 1050 nm, 1060, 1080, 1100 nm, 1120 nm, 1150 nm, 1160, 1180, 1200 nm.

[0032] In some embodiments, the rare earth high-entropy alloy phase includes the following components by atomic percentage: TM 10% to 30%, and the balance is Re; wherein, Re is selected from four or more elements among La, Ce, Pr, Nd, Sm, Eu, Gd, and TM is selected from at least one of Fe, Co, and Ni.

[0033] Based on the technical solution of the embodiments of the present invention, by controlling the ratio of the rare earth element Re and the transition metal TM (Fe, Co, Ni) (10% ≤ x ≤ 30%), a good balance between the magnetic properties and the plastic deformation ability can be achieved in the alloy. The control of the above rare earth elements and their contents is beneficial to obtaining higher soft magnetic properties of the rare earth high-entropy alloy, while the control of the above transition metals and their contents is beneficial to providing higher plastic deformation ability of the rare earth high-entropy alloy, enabling the rare earth high-entropy alloy phase to be evenly distributed and effectively fill the grain gaps of the NdFeB main phase during the hot pressing and hot deformation process, improving the maximum energy product, coercivity and mechanical toughness of the composite permanent magnet; and the transition metal elements with the above contents in the rare earth high-entropy alloy can enhance the interfacial interaction between the rare earth high-entropy alloy and the NdFeB main phase matrix, which is beneficial to increasing the resistance to the movement of local magnetic domain walls and improving the coercivity of the composite permanent magnet.

[0034] In one embodiment, the rare earth high-entropy alloy phase includes the following components by atomic percentage: TM 10% to 30%, Re 1 10% to 30%, Re 2 10% to 30%, Re 3 10% to 30%, Re 4 10% to 30%; wherein, Re 1 、Re 2 、Re 3 、Re 3 are independently selected from one of La, Ce, Pr, Nd, Sm, Eu, Gd respectively, and Re 1 、Re 2 、Re 3 、Re 4 are all different, and TM is selected from at least one of Fe, Co, and Ni.

[0035] In some embodiments, in the hot-pressed and hot-deformed composite permanent magnet, the content of the rare-earth high-entropy alloy phase is greater than 0 and less than or equal to 10% by weight.

[0036] Based on the technical solution of the embodiments of the present invention, by adopting the above addition amount of the rare-earth high-entropy alloy phase, its dispersed distribution in the NdFeB matrix can be realized, which can not only effectively refine the grain structure of the NdFeB matrix, enhance the coercivity and magnetic energy product, but also enhance the bonding force and plastic deformation ability between the main-phase grains of NdFeB, and effectively improve the mechanical properties of the composite permanent magnet, such as increasing the crack resistance and toughness.

[0037] In one embodiment, in the hot-pressed and hot-deformed composite permanent magnet, the content of the rare-earth high-entropy alloy is greater than or equal to 0.2% and less than or equal to 3% by weight, and specifically can be 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 2.8%, 3.0%. Of course, it can also be other values within the above range, which are not limited herein.

[0038] Based on the technical solution of the embodiments of the present invention, by adopting the above addition amount of the rare-earth high-entropy alloy phase, it is beneficial to optimize the microstructure of the magnet, improve the mechanical properties of the composite permanent magnet, and at the same time realize the uniform distribution of the rare-earth high-entropy alloy in the magnet. Combining with the hot-pressed and hot-deformed process, the magnetic properties of the magnet can be improved.

[0039] In some embodiments, the maximum magnetic energy product of the hot-pressed and hot-deformed composite permanent magnet is 30 MGOe to 50 MGOe.

[0040] Based on the hot-pressed and hot-deformed composite permanent magnet of the embodiments of the present invention, not only does it have excellent coercivity and remanence characteristics, but by precisely controlling the hot-pressed and hot-deformed process parameters, including temperature, pressure, aging time, and the content and distribution of the rare-earth high-entropy alloy phase, its maximum magnetic energy product can reach a high-performance level of 30 MGOe to 50 MGOe. Under the same volume, the magnet can generate a stronger magnetic field and store more magnetic energy, so in practical applications, such as in the fields of motors, generators, magnetic resonance imaging (MRI) equipment, etc., it shows higher efficiency and smaller volume, meeting the requirements of high performance and miniaturization development.

[0041] According to another aspect of the present invention, there is provided a method for preparing a hot-pressed and hot-deformed composite permanent magnet as above, including the following steps:

[0042] Step S1, under the protection of inert gas, rare earth high-entropy alloy powder and NdFeB alloy powder are mixed to obtain a mixed powder, and then the mixed powder is hot-pressed into a hot-pressed magnet; the hot-pressing temperature is 550°C to 750°C, the hot-pressing pressure is 50 MPa to 300 MPa, and the hot-pressing time is 1 min to 10 min; the D50 particle size of the rare earth high-entropy alloy powder is 1 μm to 5 μm, and the D50 particle size of the NdFeB powder is 30 μm to 150 μm;

[0043] Step S2, under an inert atmosphere, the hot-pressed magnet is subjected to hot deformation treatment to make its deformation degree reach 50% to 80%, obtaining a hot-deformed magnet; the hot-deformation treatment temperature is 600°C to 750°C, and the hot-deformation treatment pressure is 20 MPa to 100 MPa;

[0044] Step S3, the hot-deformed magnet is subjected to aging treatment to obtain a hot-pressed and hot-deformed composite permanent magnet; among them, the aging temperature is 400°C to 600°C, and the aging time is 1 h to 3 h.

[0045] Based on the preparation method of the hot-pressed and hot-deformed composite permanent magnet of the present invention, using NdFeB alloy powder as the main phase raw material and adding rare earth high-entropy alloy powder for compounding, the rare earth high-entropy alloy has a relatively high melting point and is not easily melted during the hot-pressing and hot-deformation treatment processes. The high-melting-point rare earth high-entropy alloy phase is uniformly distributed among the grains of the NdFeB alloy phase, which can inhibit the growth of the coarse grain area and grains, refine the grain structure, making the formed grain size relatively small, thereby improving the magnetic properties and mechanical strength of the composite permanent magnet. In addition, after hot-pressing and hot-deformation treatment, the added rare earth high-entropy alloy phase with good soft magnetic properties is distributed in a strip shape among the equiaxed grains of the NdFeB main phase in the composite permanent magnet, which is conducive to the exchange coupling effect between the generated soft magnetic phase (rare earth high-entropy alloy) and the hard magnetic phase (NdFeB main phase), so as to achieve the effect of improving the coercivity of the composite permanent magnet. Moreover, the rare earth high-entropy alloy phase has strong plastic deformation ability. Through hot-pressing, hot-deformation treatment and aging treatment, the rare earth high-entropy alloy phase is dispersed in the NdFeB main phase, playing a role in strengthening and toughening the structure of the composite permanent magnet, which is beneficial to improving the mechanical properties of the hot-pressed and hot-deformed composite permanent magnet.

[0046] In some embodiments, the rare earth high-entropy alloy powder is obtained by crushing a rare earth high-entropy alloy ingot.

[0047] Based on the preparation method of the embodiments of the present invention, the powder prepared by ingot crushing has a relatively uniform chemical composition and microstructure. Using it as a raw material is conducive to obtaining rare earth high-entropy alloy powder of higher quality, which helps to achieve the uniform distribution of rare earth high-entropy alloy in the composite permanent magnet.

[0048] In one implementation, in an inert gas environment, the rare earth high-entropy alloy raw materials are melted in at least one of a vacuum arc furnace, an induction furnace, and a high-frequency furnace. The melting is carried out 5 to 6 times. After casting and cooling, a rare earth high-entropy alloy ingot is obtained. By repeating melting and cooling, the purity of the alloy ingot is significantly improved, and the microstructure is more uniform and dense, providing high-quality raw materials for subsequent powder preparation. Moreover, multiple melting can effectively reduce defects such as pores and inclusions, improving the performance of the rare earth high-entropy alloy ingot.

[0049] In one implementation, by weight percentage, the impurity content in the rare earth high-entropy alloy ingot is <0.05%. The strict control of the impurity content ensures the high purity of the rare earth high-entropy alloy ingot, which is crucial for maintaining the high-entropy effect and thermal stability of the rare earth high-entropy alloy. The powder prepared from the high-purity ingot can play a more effective role in the subsequent hot-pressed and hot-deformed composite permanent magnets, which is beneficial to improving the magnetic properties of the magnets.

[0050] In some embodiments, in an inert atmosphere, the rare earth high-entropy alloy ingot is preliminarily crushed by mechanical crushing, gas atomization, or other methods, and then subjected to ball milling to obtain rare earth high-entropy alloy powder. Melting and crushing carried out in an inert atmosphere are beneficial to better maintaining the high purity and surface activity of the rare earth high-entropy alloy powder. Through ball milling, the D50 particle size of the powder is refined to 1 μm to 5 μm, which is beneficial to achieving the uniform distribution and strengthening effect of the rare earth high-entropy alloy in the composite permanent magnet.

[0051] In one implementation, the D50 particle size of the powder particles obtained by preliminary crushing is 10 μm to 50 μm to improve the efficiency and effect of the subsequent ball milling process.

[0052] In one implementation, in the ball milling process, the ball-to-material ratio is 10:1 to 20:1, and the ball milling time is 10 h to 20 h. This is beneficial to obtaining a uniform powder particle size and high surface activity, which helps to achieve uniform mixing and densification with neodymium iron boron alloy powder (i.e., NdFeB magnetic powder) during hot pressing and hot deformation processes, improving the magnetic properties and mechanical properties of the composite permanent magnet.

[0053] In some embodiments, in step S1, the hot pressing of the mixed powder includes the following steps: placing the mixed powder in a first mold, then heating to the hot pressing temperature, holding for 10 s to 20 s, and then applying pressure to the hot pressing pressure. The above hot pressing process is beneficial to the good combination and orientation of NdFeB magnetic powder and rare earth high-entropy alloy powder, improving the remanence and coercivity of the composite permanent magnet, and at the same time achieving high densification of the magnet and improving its mechanical properties.

[0054] In some embodiments, in step S2, the hot-pressed magnet is subjected to hot deformation treatment, which includes the following steps: placing the hot-pressed magnet into the second mold, then heating it to the temperature of the hot deformation treatment, holding for 30S to 120S, and then applying pressure to the pressure of the hot deformation treatment. The hot deformation treatment enables the magnet material to reorient and densify through plastic flow when pressure is applied, improving the density and degree of orientation of the hot-deformed magnet, refining the grains, so that the hot-deformed magnet can form a more optimized magnetic property structure during subsequent aging treatment, thereby enhancing the coercivity and magnetic energy product of the composite permanent magnet. The inert atmosphere is to prevent the magnet from oxidizing at high temperatures and maintain the stability of the material properties. The holding stage enables the material to reach a uniform distribution of the temperature required for hot deformation, ensuring that the entire material is uniformly heated and providing consistent conditions for subsequent deformation. The pressurization stage is to apply sufficient stress to cause plastic flow of the material, realizing grain refinement and improvement of the degree of orientation.

[0055] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0056] Example 1

[0057] A hot-pressed and hot-deformed composite permanent magnet (with a composition of 0.2% La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Fe 0.2 / 99.8% Nd 2 Fe 14 B), including a coarse grain region and a fine grain region. The coarse grain region includes a neodymium iron boron main phase and a rare earth high-entropy alloy phase; in the coarse grain region, the grains of the neodymium iron boron main phase are equiaxed crystals, and the rare earth high-entropy alloy phase is distributed in a strip shape between the equiaxed crystals. The rare earth high-entropy alloy phase, by atomic percentage, includes the following components: La 20%, Ce 20%, Pr 20%, Nd 20%, Fe 20% (with a composition of La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Fe 0.2 ); the neodymium iron boron main phase has a composition of Nd 2 Fe 14 B; by weight percentage, the content of the rare earth high-entropy alloy in the hot-pressed and hot-deformed composite permanent magnet is 0.2%.

[0058] The preparation steps of the hot-pressed and hot-deformed composite permanent magnet are as follows:

[0059] Step 1: Under an inert gas environment, the rare-earth high-entropy alloy raw materials are melted according to the composition ratio of the rare-earth high-entropy alloy phase. Melting is carried out in a vacuum arc furnace, and the number of melting times is 5 times. After casting and cooling, a rare-earth high-entropy alloy ingot is obtained. Under an inert atmosphere, the rare-earth high-entropy alloy ingot is preliminarily crushed by mechanical crushing to obtain powder particles with a D50 particle size of 30 μm, and then ball milling treatment is carried out. The ball-to-material ratio is 15:1, and the ball milling time is 15 h to obtain rare-earth high-entropy alloy powder. The D50 particle size of the rare-earth high-entropy alloy powder is 3 μm.

[0060] Step 2: Under an inert atmosphere, the rare-earth high-entropy alloy powder and the neodymium-iron-boron alloy powder with the composition of Nd 2 Fe 14 B are mixed to obtain a mixed powder body. The mixed powder body is placed in a first mold, then heated to 650 °C, held for 15 s, and then pressurized to 200 MPa with a pressurization time of 5 min to obtain a hot-pressed magnet. Among them, by weight percentage, the content of the rare-earth high-entropy alloy powder in the mixed powder body is 0.2%.

[0061] Step 3: Under an inert atmosphere, the hot-pressed magnet is placed in a second mold, then heated to 600 °C, held for 80 s, and then pressurized to 60 MPa to make the deformation degree reach 45% to obtain a hot-deformed magnet.

[0062] Step 4: The hot-deformed magnet is subjected to aging treatment to obtain a hot-pressed and hot-deformed composite permanent magnet. Among them, the aging temperature is 500 °C and the aging time is 2 h.

[0063] Figure 1 It is the metallographic structure diagram of the hot-pressed and hot-deformed composite permanent magnet in Example 1. It can be seen from Figure 1 that the rare-earth high-entropy alloy phase is doped and distributed in a strip shape in the hot-pressed and hot-deformed composite permanent magnet. Figure 2 It is the enlarged view of the coarse grain area in the metallographic structure diagram of the hot-pressed and hot-deformed composite permanent magnet. It can be seen from Figure 2 that in the coarse grain area of the hot-pressed and hot-deformed composite permanent magnet, the D50 particle size of the equiaxed grains is 1200 nm.

[0064] Example 2

[0065] A hot-pressed and hot-deformed composite permanent magnet (with the composition of 0.2% La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Fe 0.2 / 99.8% Nd 2 Fe 14B), including a coarse-grained region and a fine-grained region. The coarse-grained region includes a NdFeB main phase and a rare-earth high-entropy alloy phase. In the coarse-grained region, the grains of the NdFeB main phase are equiaxed crystals, and the rare-earth high-entropy alloy phase is distributed in a strip shape between the equiaxed crystals. The rare-earth high-entropy alloy phase, by atomic percentage, includes the following components: La 20%, Ce 20%, Pr 20%, Nd 20%, Fe 20% (the composition is La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Fe 0.2 ); The composition of the NdFeB main phase is Nd 2 Fe 14 B; By weight percentage, in the hot-pressed and hot-deformed composite permanent magnet, the content of the rare-earth high-entropy alloy is 0.2%.

[0066] The preparation steps of the hot-pressed and hot-deformed composite permanent magnet are as follows:

[0067] Step 1, in an inert gas environment, the rare-earth high-entropy alloy raw materials are proportioned according to the composition of the rare-earth high-entropy alloy phase and melted. Melting is carried out in a vacuum arc furnace, and the number of melting times is 5 times. After casting and cooling, a rare-earth high-entropy alloy ingot is obtained; in an inert atmosphere, the rare-earth high-entropy alloy ingot is preliminarily crushed by mechanical crushing to obtain powder particles with a D50 particle size of 10 μm, and then ball-milled. The ball-to-material ratio is 10:1, and the ball-milling time is 10 h to obtain rare-earth high-entropy alloy powder. The D50 particle size of the rare-earth high-entropy alloy powder is 5 μm.

[0068] Step 2, in an inert atmosphere, the rare-earth high-entropy alloy powder and the Nd 2 Fe 14 B NdFeB alloy powder are mixed to obtain a mixed powder body. The mixed powder body is placed in a first mold, then heated to 550 °C, held for 10 s, and then pressurized to 50 MPa. The pressurization time is 10 min to obtain a hot-pressed magnet; among them, by weight percentage, the content of the rare-earth high-entropy alloy powder in the mixed powder body is 0.2%.

[0069] Step 3, in an inert atmosphere, the hot-pressed magnet is placed in a second mold, then heated to 600 °C, held for 30 s, and then pressurized to 20 MPa to make the deformation degree reach 50% to obtain a hot-deformed magnet.

[0070] Step 4, the hot-deformed magnet is subjected to aging treatment to obtain a hot-pressed and hot-deformed composite permanent magnet; among them, the aging temperature is 400 °C and the aging time is 1 h.

[0071] Example 3

[0072] A hot-pressed and hot-deformed composite permanent magnet (the composition is 0.2% La 0.2 Ce 0.2Pr 0.2 Nd 0.2 Fe 0.2 / 99.8% Nd 2 Fe 14 B), including a coarse-grained region and a fine-grained region. The coarse-grained region includes a neodymium-iron-boron main phase and a rare-earth high-entropy alloy phase; within the coarse-grained region, the grains of the neodymium-iron-boron main phase are equiaxed crystals, and the rare-earth high-entropy alloy phase is distributed in a strip shape between the equiaxed crystals. The rare-earth high-entropy alloy phase, calculated by atomic percentage, includes the following components: La 20%, Ce 20%, Pr 20%, Nd 20%, Fe 20% (the composition is La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Fe 0.2 ); The composition of the neodymium-iron-boron main phase is Nd 2 Fe 14 B; By weight percentage, in the hot-pressed and hot-deformed composite permanent magnet, the content of the rare-earth high-entropy alloy is 0.2%.

[0073] The preparation steps of the hot-pressed and hot-deformed composite permanent magnet are as follows:

[0074] Step 1, in an inert gas environment, melt the rare-earth high-entropy alloy raw materials according to the composition ratio of the rare-earth high-entropy alloy phase. The melting is carried out in a vacuum arc furnace, and the number of melting times is 5 times. After casting and cooling, a rare-earth high-entropy alloy ingot is obtained; in an inert atmosphere, the rare-earth high-entropy alloy ingot is preliminarily crushed by mechanical crushing to obtain powder particles with a D50 particle size of 50 μm, and then ball-milled. The ball-to-material ratio is 20:1, and the ball-milling time is 20 h to obtain rare-earth high-entropy alloy powder with a D50 particle size of 1 μm.

[0075] Step 2, in an inert atmosphere, mix the rare-earth high-entropy alloy powder and the neodymium-iron-boron alloy powder with the composition of Nd 2 Fe 14 B to obtain a mixed powder. Place the mixed powder in a first mold, then heat it to 750 °C, hold for 20 s, and then pressurize it to 300 MPa for 1 min to obtain a hot-pressed magnet; among them, by weight percentage, the content of the rare-earth high-entropy alloy powder in the mixed powder is 0.2%.

[0076] Step 3, in an inert atmosphere, put the hot-pressed magnet into a second mold, then heat it to 750 °C, hold for 120 s, and then pressurize it to 100 MPa to make the deformation degree reach 80% to obtain a hot-deformed magnet.

[0077] Step 4, perform aging treatment on the hot-deformed magnet to obtain a hot-pressed and hot-deformed composite permanent magnet; among them, the aging temperature is 600 °C and the aging time is 3 h.

[0078] Example 4

[0079] The difference from Example 1 is only that:

[0080] In step one, the rare earth high-entropy alloy raw materials are melted according to the composition of the rare earth high-entropy alloy phase as Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 Co 0.2 proportion and melted.

[0081] In step two, by weight percentage, the content of the rare earth high-entropy alloy powder in the mixed powder is 1%.

[0082] Example 5

[0083] The difference from Example 1 is only that:

[0084] In step two, by weight percentage, the content of the rare earth high-entropy alloy powder in the mixed powder is 1.5%.

[0085] Example 6

[0086] The difference from Example 1 is only that:

[0087] In step two, by weight percentage, the content of the rare earth high-entropy alloy powder in the mixed powder is 3%.

[0088] Example 7

[0089] The difference from Example 1 is only that:

[0090] In step one, the rare earth high-entropy alloy raw materials are melted according to the composition of the rare earth high-entropy alloy phase as Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 Co 0.2 proportion and melted;

[0091] In step two, by weight percentage, the content of the rare earth high-entropy alloy powder in the mixed powder is 7%.

[0092] Example 8

[0093] The difference from Example 1 is only that:

[0094] In step one, the rare earth high-entropy alloy raw materials are melted according to the composition of the rare earth high-entropy alloy phase as La 0.2 Gd 0.2 Eu 0.2 Sm 0.2 Ni 0.2 proportion and melted.

[0095] In Step 2, the content of the rare-earth high-entropy alloy powder in the mixed powder is 10% by weight.

[0096] Example 9

[0097] The difference from Example 1 is only that:

[0098] In Step 1, the D50 particle size of the rare-earth high-entropy alloy powder is 5 μm.

[0099] Example 10

[0100] The difference from Example 1 is only that:

[0101] In Step 1, the D50 particle size of the NdFeB powder is 150 μm.

[0102] Example 11

[0103] The difference from Example 1 is only that:

[0104] In Step 2, the content of the rare-earth high-entropy alloy powder in the mixed powder is 10% by weight.

[0105] Example 12

[0106] The difference from Example 1 is only that:

[0107] In Step 2, the content of the rare-earth high-entropy alloy powder in the mixed powder is 15% by weight.

[0108] Example 13

[0109] The difference from Example 1 is only that:

[0110] In Step 4, the aging time is 3 h.

[0111] Example 14

[0112] The difference from Example 1 is only that:

[0113] In Step 2, the pressurization time is 10 min.

[0114] Example 15

[0115] The difference from Example 1 is only that:

[0116] In Step 3, the degree of deformation in the hot deformation treatment is 80%.

[0117] Comparative Example 1

[0118] A hot-pressed and hot-deformed NdFeB permanent magnet, with the composition of Nd 2 Fe 14B. The preparation steps of the neodymium iron boron permanent magnet are as follows:

[0119] Step 1, in an inert atmosphere, place the Nd 2 Fe 14 B neodymium iron boron alloy powder in the first mold, then heat it to 650 °C, keep it warm for 15 s, and then apply a pressure of 200 MPa to obtain a hot-pressed magnet.

[0120] Step 2, in an inert atmosphere, put the hot-pressed magnet into the second mold, then heat it to 600 °C, keep it warm for 80 s, and then apply a pressure of 60 MPa to make the deformation degree reach 45% to obtain a hot-deformed magnet.

[0121] Step 3, perform aging treatment on the hot-deformed magnet to obtain a hot-pressed and hot-deformed composite permanent magnet; among them, the aging temperature is 500 °C and the aging time is 2 h.

[0122] Comparative Example 2

[0123] A hot-pressed and hot-deformed neodymium iron boron permanent magnet, the composition of which is 0.2% Fe 2 CoNiAlTi 0.4 Cu 0.4 / 99.8% Nd 2 Fe 14 B.

[0124] The difference between its preparation steps and the preparation steps in Example 1 is only that:

[0125] Replace the rare earth high-entropy alloy raw material in Step 1 with an alloy raw material prepared according to the alloy composition of Fe 2 CoNiAlTi 0.4 Cu 0.4 for proportioning.

[0126] Comparative Example 3

[0127] A hot-pressed and hot-deformed neodymium iron boron permanent magnet, the composition of which is 0.2% Er 0.2 Ho 0.2 Gd 0.2 Ni 0.2 Co 0.2 / 99.8% Nd 2 Fe 14 B.

[0128] The difference between its preparation steps and the preparation steps in Example 1 is only that:

[0129] In Step 1, the rare earth high-entropy alloy raw material is in accordance with the composition of the rare earth high-entropy alloy phase of Er 0.2 Ho 0.2 Gd 0.2 Ni 0.2 Co0.2 Mix the proportions and carry out smelting.

[0130] Comparative Example 4

[0131] The only difference from Example 1 is that:

[0132] In Step 1, the D50 particle size of the rare earth high-entropy alloy powder is 10 μm.

[0133] Comparative Example 5

[0134] The only difference from Example 1 is that:

[0135] In Step 1, the D50 particle size of the NdFeB powder is 200 μm.

[0136] Comparative Example 6

[0137] The only difference from Example 1 is that:

[0138] In Step 4, the aging time is 5 h.

[0139] Comparative Example 7

[0140] The only difference from Example 1 is that:

[0141] In Step 2, the pressurization time is 15 min.

[0142] Comparative Example 8

[0143] The only difference from Example 1 is that:

[0144] In Step 3, the degree of deformation of the hot deformation treatment is 90%.

[0145] Performance Test

[0146] 1. Use a scanning electron microscope to detect the microstructure of the permanent magnets in the examples and comparative examples, determine the particle size of each grain, and statistically obtain the D50 particle size.

[0147] 2. Mechanical property test: Use a universal mechanical testing machine to test the mechanical properties of the hot-pressed and hot-deformed magnets. The size of the hot-pressed and hot-deformed magnets is 3 mm (length) × 3 mm (width) × 6 mm (thickness). The test results of the compressive strength are shown in Table 1.

[0148] 3. Test the magnetic properties of the permanent magnets in the examples and comparative examples. The test results of the remanence (Br), coercivity (Hcj), and maximum magnetic energy product ((BH)max) are shown in Table 1.

[0149] Table 1

[0150]

[0151]

[0152] As can be seen from Table 1, compared with Comparative Examples 1-8, the hot-pressed and hot-deformed composite permanent magnet based on the embodiments of the present invention has higher remanence, coercivity, magnetic energy product and mechanical properties, realizing the optimization of the magnetic properties and mechanical properties of the NdFeB magnet.

[0153] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A hot pressed and hot deformed composite permanent magnet, characterized in that: The hot-pressed and hot-deformed composite permanent magnet includes a coarse-grained region and a fine-grained region, wherein the coarse-grained region includes a NdFeB main phase and a rare earth high-entropy alloy phase; within the coarse-grained region, the grains of the NdFeB main phase are equiaxed crystals, and the D50 particle size of the equiaxed crystals is 600nm to 1300nm, and the rare earth high-entropy alloy phase is distributed in strips between the equiaxed crystals, and the rare earth high-entropy alloy phase includes transition metal elements and at least four rare earth elements.

2. The hot pressed and hot deformed composite permanent magnet according to claim 1, characterized in that: The D50 particle size of the equiaxed crystal is 800nm ​​to 1200nm.

3. The hot pressed and hot deformed composite permanent magnet according to claim 1, characterized in that: The rare earth high entropy alloy phase includes the following components in atomic percentage: TM 10% to 30%, and the balance is Re; wherein Re is selected from at least four elements of La, Ce, Pr, Nd, Sm, Eu, and Gd, and the TM is selected from at least one of Fe, Co, and Ni.

4. The hot pressed and hot deformed composite permanent magnet according to any one of claims 1 to 3, characterized in that: In terms of weight percentage, in the hot-pressed and hot-deformed composite permanent magnet, the content of the rare earth high-entropy alloy phase is greater than 0 and less than or equal to 10%.

5. The hot pressed and hot deformed composite permanent magnet according to any one of claims 1 to 3, characterized in that: The maximum magnetic energy product of the hot-pressed and hot-deformed composite permanent magnet is 30MGOe to 50MGOe.

6. A method for preparing a hot pressed and hot deformed composite permanent magnet according to any one of claims 1 to 5, characterized in that: The steps include: Step S1, under the protection of inert gas, rare earth high entropy alloy powder and neodymium iron boron alloy powder are mixed to obtain a mixed powder, and then the mixed powder is hot pressed to obtain a hot pressed magnet; the hot pressing temperature is 550°C to 750°C, the hot pressing pressure is 50MPa to 300MPa, and the hot pressing time is 1min to 10min; the D50 particle size of the rare earth high entropy alloy powder is 1μm to 5μm, and the D50 particle size of the neodymium iron boron powder is 30μm to 150μm; Step S2, in an inert atmosphere, performing a heat deformation treatment on the hot pressed magnet so that its deformation degree reaches 50% to 80%, thereby obtaining a heat deformed magnet; the temperature of the heat deformation treatment is 600° C. to 750° C., and the pressure of the heat deformation treatment is 20 MPa to 100 MPa; Step S3, performing aging treatment on the heat-deformed magnet to obtain a hot-pressed and hot-deformed composite permanent magnet; wherein the aging temperature is 400° C. to 600° C., and the aging time is 1 hour to 3 hours.

7. The method for preparing a hot pressed and hot deformed composite permanent magnet according to claim 6, characterized in that: The rare earth high entropy alloy powder is obtained by crushing a rare earth high entropy alloy ingot; Preferably, in an inert gas environment, the rare earth high entropy alloy raw material is smelted in at least one of a vacuum arc furnace, an induction furnace, and a high-frequency furnace, the smelting times are 5 to 6 times, and the rare earth high entropy alloy ingot is obtained after casting and cooling; Preferably, in terms of weight percentage, the impurity content in the rare earth high entropy alloy ingot is less than 0.05%.

8. The method for preparing a hot pressed and hot deformed composite permanent magnet according to claim 7, characterized in that: Under an inert atmosphere, the rare earth high entropy alloy ingot is preliminarily crushed by mechanical crushing or gas atomization, and then ball milled to obtain the rare earth high entropy alloy powder; Preferably, the D50 particle size of the powder particles obtained by the preliminary crushing is 10 μm to 50 μm; Preferably, in the ball milling process, the ball-to-material ratio is 10:1 to 20:1, and the ball milling time is 10 h to 20 h.

9. The method for preparing a hot pressed and hot deformed composite permanent magnet according to claim 6, characterized in that: In the step S1, the hot pressing molding of the mixed powder includes the following steps: placing the mixed powder in a first mold, then heating to the hot pressing molding temperature, keeping the temperature for 10S to 20S, and then pressurizing to the hot pressing molding pressure.

10. The method for preparing a hot pressed and hot deformed composite permanent magnet according to any one of claims 6 to 9, characterized in that: In step S2, the hot-pressed magnet is subjected to heat deformation treatment, including the following steps: placing the hot-pressed magnet in a second mold, then heating it to the heat deformation treatment temperature, keeping the temperature for 30S to 120S, and then pressurizing it to the heat deformation treatment pressure.

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