Method for preparing high-performance cerium neodymium iron boron magnet based on powder modification process

Abstract

The invention discloses a method for preparing a high-performance cerium neodymium iron boron magnet based on a powder modification process, and belongs to the technical field of rare earth permanent magnet materials. The component-process collaborative optimization strategy is characterized in that a proper low-melting-point rare earth alloy diffusion source is selected and a magnetic powder rotating coating process is combined according to the change characteristics of magnetocrystalline anisotropy fields HA in main phase grain cores with different Ce substitution amounts based on magnet component design; and a high-HA magnetic hardening shell layer is constructed on the surface layer of the main phase crystal grains in situ. Therefore, by regulating and controlling the components of the shell layer, the HA in the core and the HA in the shell layer reach a dynamic synergistically enhanced balance state, and the synchronous reversal of the core-shell structure in the demagnetization process is ensured, so that the demagnetization process is inhibited to the greatest extent, and the coercive force of the magnet is improved.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials technology, specifically to a method for preparing high-performance cerium-neodymium iron boron magnets through synergistic optimization of magnet composition design and magnetic powder rotational coating modification. Background Technology

[0002] Since their introduction in the 1980s, sintered neodymium iron boron (Nd-Fe-B) rare-earth permanent magnets have become the preferred functional material in aerospace, energy and transportation, medical equipment, and electronic communications due to their excellent comprehensive magnetic properties. They are widely used in core components such as servo motors, miniature speakers, and disk drives. However, with the continuous expansion of market demand, the problem of unbalanced utilization of rare-earth resources has become increasingly prominent. Therefore, partially replacing neodymium (Nd) in sintered Nd-Fe-B magnets with cerium (Ce), which has high natural abundance and low price, while ensuring that the magnets still maintain the high magnetic properties required for practical applications, has become an important technical problem that researchers urgently need to solve.

[0003] However, Ce2Fe 14 The magnetocrystalline anisotropy field of B (H) A = 26 kOe) significantly lower than Nd2Fe 14 B(H) A = 73 kOe), the introduction of Ce element will significantly reduce the H of the grain itself. A This exacerbates the difficulty of controlling the magnetic properties of the magnet. Furthermore, various defects present in actual sintered magnets will further weaken the magnetocrystalline anisotropy field H of the epitaxial layer. A This makes it a demagnetizing nucleation point, preferentially causing magnetization reversal, resulting in the coercivity of the entire magnet being far lower than the theoretical value. From the perspective of coercivity nucleation field theory, the key to improving the magnetic properties of the magnet lies in constructing a highly magnetocrystalline anisotropic field H around the main phase grains. A The magnetically hardened shell. In existing technologies, it is common to enhance the H of the host phase grain epitaxial layer by introducing additional rare earth elements. A This effectively improves the coercivity of the magnet. However, when rare earth alloys are mixed with the main phase alloy powder via grain boundary doping and then sintered at high temperatures, the introduced rare earth elements undergo excessive diffusion, penetrating extensively into the main phase grains, which negatively impacts the remanence and maximum energy product of the magnet. If the heavy rare earth surface grain boundary diffusion process is directly used to treat cerium-neodymium iron boron magnets, a significant concentration gradient will form from the magnet surface to the interior, resulting in uneven coercivity distribution and a serious waste of heavy rare earth resources. Further research indicates that during demagnetization, the reverse domains of grains forming a core-shell structure in the magnet preferentially form in the internal core region, and then appear in the shell region near the grain boundaries. Furthermore, as the H of the shell layer continues to increase... AHowever, this also fails to significantly improve coercivity. Therefore, it is necessary to study the magnetic properties of the main phase grains under different Ce substitution amounts, especially H. A Based on the changing characteristics, a suitable low-melting-point alloy diffusion source is selected and combined with magnetic powder surface modification processes (such as spin coating) to construct a RE-rich magnetic hardening shell in the epitaxial layer of the main phase grains, promoting H within the core. A H with the shell A To achieve a dynamic and synergistic balance, thereby avoiding the waste of rare earth resources while maximizing the coercivity of cerium-neodymium iron boron magnets.

[0004] Based on the above background, this invention innovatively proposes an optimization strategy for synergistic control of composition and process, aiming to achieve synchronous magnetization reversal of the core-shell structure during demagnetization, effectively suppressing the demagnetization process, and ultimately achieving controllable optimization and stable preparation of Nd-Ce-Fe-B magnets with different Ce substitution amounts. Furthermore, the introduced low-melting-point rare-earth alloy not only lowers the sintering temperature and avoids excessive diffusion of the introduced rare-earth elements, but also allows them to enter the grain boundaries in a liquid state, increasing the content and fluidity of the grain boundary phase, promoting the homogenization of the magnet's microstructure, repairing defects around the main phase grains, and enhancing the demagnetizing coupling effect, thereby improving the demagnetizing domain nucleation field and providing a key guarantee for improving the coercivity of cerium-neodymium iron boron magnets. Summary of the Invention

[0005] This invention provides a composition-process synergistic optimization strategy to solve the aforementioned technical problems. The core lies in targeting the main phase grains (Ce) with different Ce substitution amounts. x , Nd 1-x )2Fe 14 The magnetocrystalline anisotropy field H within the nucleus of B A The nucleus variation characteristics were determined by selecting a low-melting-point rare-earth alloy diffusion source and combining it with a magnetic powder spin coating process, and designing the coating amount. Due to the low-melting-point alloy coating on the magnetic powder surface, densification sintering was achieved at a lower temperature based on the selected coating amount, resulting in the in-situ formation of a RE-rich magnetically hardened shell, namely (Ce, Nd, RE)₂Fe, within the main phase grains. 14 By using a B-shell layer, synchronous magnetization reversal can be achieved in the core-shell structure during demagnetization. This enables the preparation of high-performance cerium-neodymium iron boron magnets with different Ce substitution amounts at lower sintering temperatures, maximizing the magnetic properties of the magnets while avoiding the waste of rare earth resources.

[0006] The first objective of this invention is to provide a method for preparing a high-performance cerium-neodymium iron boron magnet, comprising the following steps:

[0007] (1) Prepare cerium-neodymium iron boron magnetic powder A with different Ce substitution amounts as the main phase alloy, the nominal composition of which is (Ce x , Nd 1-x )α Fe 100-α-β-γ M β B γ (wt.%), M is one or more of Al, Cu, Nb, Co, Ga, Ti, Zr, Mn, Ni, Si, and Cr, where x, α, β, and γ are the weight percentage contents of each element, satisfying the following relationships: 0 ≤ x ≤ 0.6, 29 ≤ α ≤ 33, 0.5 ≤ β ≤ 3.0, 0.7 ≤ γ ≤ 1.2;

[0008] The main phase grains in the main phase alloy are (Ce) x , Nd 1-x )2Fe 14 B, (Ce) x , Nd 1-x )2Fe 14 The anisotropic field of B magnetocrystalline crystal is denoted as the anisotropic field within the nucleus, H. A核 satisfy:

[0009] ;

[0010] (2) Based on the cerium-neodymium iron boron magnetic powder A prepared in step (1), the main phase grains (Ce) x , Nd 1-x )2Fe 14 The magnetocrystalline anisotropy field H within the nucleus of B A核 Based on the changing characteristics, select a suitable low-melting-point rare earth alloy RE a N 100-a (wt.%) as diffusion source B;

[0011] The rare earth alloy RE a N 100-a The alloy contains at least one rare earth element RE, selected from Nd, Pr, Ho, Dy, or Gd, and at least one non-rare earth metal element M, selected from Al, Cu, or Ga, with 'a' representing the weight percentage content and satisfying the following relationship: 60 ≤ a ≤ 97, and the alloy's melting point T... m Satisfying 400 ℃ ≤ T m < 800 ℃;

[0012] (3) The main phase alloy cerium-neodymium iron boron magnetic powder A with different Ce substitution amounts in step (1) is mixed with the rare earth alloy RE selected in step (2) after crushing. a N 100-a After being thoroughly mixed at a mass ratio of 1:2 – 3:1, the rapidly solidifying flakes (or rapidly quenched strip fragments) are placed in a rotatable tube furnace and heated at a rotation speed of 5 r / min and a coating temperature of T. 包覆 The RE was subjected to heat treatment for 5 hours to allow it to precipitate. a N100-a The alloy diffuses to the surface of the main phase grains to form an RE-rich coating layer;

[0013] (4) The cerium-neodymium iron boron magnetic powder coated in step (3) is mixed with rare earth alloy RE a N 100-a The rapid-setting flakes (or rapid-quenching belt fragments) are screened to recover unreacted rare earth alloy RE. a N 100-a The rapidly solidifying flakes (or rapidly quenched strip fragments) can be reused in the next batch of reaction. The resulting rare-earth alloy-coated air-jet milled magnetic powder is then subjected to orientation molding and isostatic pressing to produce a green compact. Based on the amount of rare-earth alloy coating, a suitable low temperature T is selected. 烧结 The green billets are sintered in a vacuum sintering furnace and then subjected to two-stage tempering heat treatment.

[0014] (5) A high-performance cerium-neodymium iron boron magnet with a RE-rich magnetic hardening shell on the surface of the main phase grains is finally obtained, characterized in that the prepared magnet has a core-shell structure, and the core is (Ce x , Nd 1-x )2Fe 14 B, the shell is a RE-rich magnetically hardened shell, i.e., (Ce, Nd, RE)2Fe. 14 B, and the relationship is: 0.90 ≤ H A核 H A壳 ≤ 1.00, achieving synchronous reversal of the core-shell structure during demagnetization, maximizing the coercivity of cerium-neodymium iron boron magnets while avoiding the waste of rare earth resources.

[0015] Furthermore, the low-melting-point rare earth alloy RE selected in step (2) a N 100-a The relationship between RE in the figure and the substitution amount x of Ce in the main phase alloy cerium-neodymium iron boron magnetic powder A described in step (1) is as follows:

[0016] When 0.0 ≤ x ≤ 0.2, the selected RE a N 100-a RE represents the Dy element;

[0017] When 0.2 < x ≤ 0.4, the selected RE a N 100-a RE in the text represents one or both of the elements Pr and Ho.

[0018] When 0.4 < x ≤ 0.6, the selected RE a N 100-a RE can be one or both of Nd and Gd elements.

[0019] When the Ce substitution amount in the main phase grains is low, i.e., 0.0 ≤ x ≤ 0.2, RE2Fe will be selected. 14 The magnetocrystalline anisotropy field H of B A Higher RE alloy content; when the Ce substitution content in the main phase grains is high, i.e., 0.4 < x ≤ 0.6, RE2Fe will be selected. 14 The magnetocrystalline anisotropy field H of B A Lower RE alloy.

[0020] Furthermore, the low-melting-point rare earth alloy RE selected in step (2) a N 100-a melting point T m The rotational coating temperature T mentioned in step (3) 包覆 The temperature difference between them is ΔT, where ΔT = T m – T 包覆 The coating amount w on the main phase alloy cerium-neodymium iron boron magnetic powder satisfies the following correspondence:

[0021] When 40 ℃ < ΔT ≤ 60 ℃, 0.0 wt.% < w ≤ 1.0 wt.%;

[0022] When 25 ℃ < ΔT ≤ 40 ℃, 1.0 wt.% < w ≤ 2.0 wt.%;

[0023] When 10 ℃ < ΔT ≤ 25 ℃, 2.0 wt.% < w ≤ 3.0 wt.%;

[0024] When 0 ℃ < ΔT ≤ 10 ℃, 3.0 wt.% < w ≤ 4.5 wt.%.

[0025] The coating amount w increases as the temperature difference ΔT decreases;

[0026] Furthermore, the coating amount w obtained by the surface rotation diffusion process of the main phase alloy magnetic powder A is the same as the low-temperature sintering temperature T of the green body mentioned in step (4). 烧结 The following correspondence is satisfied:

[0027] When 0.0 wt.% < w ≤ 1.0 wt.%, 990 ℃ ≤ T 烧结 ≤ 1020 ℃;

[0028] When 1.0 wt.% < w ≤ 2.0 wt.%, 970 ℃ ≤ T 烧结 < 990 ℃;

[0029] When 2.0 wt.% < w ≤ 3.0 wt.%, 950 ℃ ≤ T 烧结 < 970 ℃;

[0030] When 3.0 wt.% < w ≤ 4.5 wt.%, 900 ℃ ≤ T 烧结 < 950 ℃.

[0031] The holding time for the sintering process is 3 h – 6 h.

[0032] Furthermore, the tempering heat treatment described in step (4) has a first-stage temperature of 780 ℃ – 900 ℃ and a holding time of 3 h – 5 h, and a second-stage temperature of 380 ℃ – 660 ℃ and a holding time of 3 h – 5 h.

[0033] Furthermore, the RE-rich magnetic hardening shell formed in step (4) has a RE-rich content of y%, and its anisotropic field H A壳 satisfy,

[0034] .

[0035] The second objective of this invention is to achieve synchronous magnetization reversal in the core-shell structure of the prepared cerium-neodymium iron boron magnet by designing the composition of the interior of the main phase grains and the in-situ shell.

[0036] The advantages of this invention compared to the prior art are as follows:

[0037] (1) The composition-process synergistic optimization strategy adopted in this invention is based on magnet composition design, targeting the magnetocrystalline anisotropy field H within the core of the main phase grains with different Ce substitution amounts. A The variation characteristics were analyzed by selecting a suitable low-melting-point rare earth alloy as a diffusion source and combining it with magnetic powder spin coating technology to construct a high-H₂O₅ composition in situ on the surface of the main phase grains. A The magnetically hardened shell. By controlling the shell composition, H1 in the core and shell can be achieved. A Achieving a dynamic and synergistic balance not only efficiently enhances the coercivity of the magnet but also avoids the waste of rare earth resources.

[0038] (2) The low-melting-point rare earth alloy introduced by the spin coating process of this invention can not only reduce the sintering temperature and avoid excessive diffusion of the introduced rare earth elements, but also allow them to enter the grain boundary in a liquid state, increase the content and fluidity of the grain boundary phase, promote the homogenization of the magnet structure composition, repair the defects around the main phase grains of the magnet, enhance the demagnetizing coupling effect, thereby improving the antimagnetizing domain nucleation field, and providing a key guarantee for improving the coercivity of cerium-neodymium iron boron magnets.

[0039] (3) By optimizing the composition design and using unique rotary coating and low-temperature sintering processes, this invention reduces the dependence on high-priced heavy rare earths (Tb, Dy, etc.), reduces costs through the interaction of light rare earths and transition metals, and uses low-melting-point rare earth alloy quick-setting sheets (or quick-quenching strips) that can be reused, thus achieving a double reduction in production costs and energy consumption, which is in line with the concept of green manufacturing and sustainable development. Attached Figure Description

[0040] Figure 1 Flowchart for the rotary coating of low-melting-point alloys with cerium-neodymium-iron-boron air-jet milled magnetic powder

[0041] Figure 2 SEM images of the surfaces of uncoated and coated air-jet milled magnetic powder;

[0042] Figure 3 This is a schematic diagram of the structure of a cerium-neodymium iron boron magnet prepared by low-temperature sintering and heat treatment. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0044] Unless otherwise specified, all methods used in the examples were conventional or performed according to techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents and instruments used without specified manufacturers were all conventional products that could be purchased from legitimate channels.

[0045] Comparative Example 1

[0046] Based on the original alloy nominal composition Nd 31 Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce0, is used to prepare rapidly solidified thin strips of Al composition. After hydrogen crushing and dehydrogenation, NdFeB coarse powder Al is obtained. Then, it is ground into powder by air jet milling under argon protection. The average particle size of the obtained NdFeB air jet milled powder Al is 3.0 μm.

[0047] In a glove box, Al component air-milled fine powder was oriented and shaped under an inert gas protective atmosphere to obtain a green blank. The green blank was vacuum sealed and subjected to cold isostatic pressing before being placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 1050℃ and held for 3 h. Then, argon gas was passed through for air cooling. After that, a first-stage heat treatment was performed at 900 ℃ for 3 h, and finally a second-stage heat treatment was performed at 480 ℃ for 4 h to obtain Ce0 NdFeB magnet C1 with a Ce content of 0 wt.% of the total rare earth content.

[0048] The Ce0 NdFeB magnet C1 was subjected to BH magnetic property testing. The test results for the magnetic properties at room temperature were: B r =14.27 kG, H cj = 13.18 kOe, (BH) max = 48.32 MGOe, H k / H cj = 97.2%.

[0049] Comparative Example 2

[0050] Based on the original alloy nominal composition Nd 31 Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce0, is used to prepare rapidly solidified thin strips of Al composition. After hydrogen crushing and dehydrogenation, NdFeB coarse powder Al is obtained. Then, it is ground into powder by air jet milling under argon protection. The average particle size of the obtained NdFeB air jet milled powder Al is 3.0 μm.

[0051] According to the nominal composition of rare earth alloys, Dy 86 Cu 14 (wt.%), prepared rapidly solidified thin strips or rapidly quenched strips of component B1, with a melting point of 794.08 ℃. After hydrogen crushing and dehydrogenation, cerium-neodymium iron boron coarse powder B1 was obtained, and then subjected to air jet milling under argon protection. The average particle size of the obtained cerium-neodymium iron boron air jet milled powder B1 was 3.0 μm.

[0052] In a glove box, fine powders of components A1 and B1 were mixed at a mass ratio of 98:2. After thorough mixing, the mixture was oriented and shaped under an inert gas atmosphere to obtain a green compact. The green compact was vacuum-sealed and subjected to cold isostatic pressing before being placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 1040 °C and held for 3 h, followed by argon air cooling. Then, a primary heat treatment was performed at 900 °C for 3 h, and finally a secondary heat treatment was performed at 480 °C for 4 h to obtain a 2.0 wt.% Dy doped product. 86 Cu 14Neodymium iron boron magnet C2 produced by air jet milling of rare earth alloys.

[0053] rare earth alloy Dy 86 Cu 14 The BH magnetic properties of the grain boundary-doped NdFeB magnet C2 were tested. The test results for the magnetic properties at room temperature were: B r = 13.98 kG, H cj = 15.03 kOe, (BH) max = 47.25 MGOe, H k / H cj = 96.5%.

[0054] Comparative Example 3

[0055] Based on the original alloy nominal composition Nd 31 Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce0, is used to prepare rapidly solidified thin strips of Al composition. After hydrogen crushing and dehydrogenation, NdFeB coarse powder Al is obtained. Then, it is ground into powder by air jet milling under argon protection. The average particle size of the obtained NdFeB air jet milled powder Al is 3.0 μm.

[0056] According to the nominal composition of rare earth alloys, Dy 86 Cu 14 (wt.%), prepared rapidly solidified thin strips or rapidly quenched strips of component B1, with a melting point of 794.08 ℃. After hydrogen crushing and dehydrogenation, cerium-neodymium iron boron coarse powder B1 was obtained, and then subjected to air jet milling under argon protection. The average particle size of the obtained cerium-neodymium iron boron air jet milled powder B1 was 3.0 μm.

[0057] In a glove box, Al component air-milled fine powder was oriented and shaped under an inert gas protective atmosphere to obtain a green blank. The green blank was vacuum sealed and subjected to cold isostatic pressing before being placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 1050℃ and held for 3 h. Then, argon gas was passed through for air cooling. After that, a first-stage heat treatment was performed at 900 ℃ for 3 h, and finally a second-stage heat treatment was performed at 480 ℃ for 4 h to obtain Ce0 NdFeB magnet C1 with a Ce content of 0 wt.% of the total rare earth content.

[0058] Ce0 NdFeB magnets were subjected to grain boundary diffusion (C1) at a weight gain of 0.5 wt.% and then air-milled with a B1 composition. The magnets were then placed in a tube furnace and held at 900 °C for 10 h for grain boundary diffusion treatment. Finally, a secondary diffusion heat treatment was performed at 480 °C for 4 h to obtain diffused Dy. 86 Cu 14Neodymium iron boron magnets of rare earth alloy C3.

[0059] rare earth alloy Dy 86 Cu 14 The grain boundary diffused NdFeB magnet C3 underwent BH magnetic property testing. The test results for the magnetic properties at room temperature were: B r = 13.93 kG, H cj = 18.97 kOe, (BH) max = 47.27 MGOe, H k / H cj = 91.8%.

[0060] Comparative Example 4

[0061] According to the original alloy nominal composition (Ce) 0.4 Nd 0.6 ) 31 Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce40, was used to prepare rapidly solidified thin strips of component A2. After hydrogen crushing and dehydrogenation, cerium-neodymium iron boron coarse powder A2 was obtained. Then, it was subjected to air jet milling under argon protection. The average particle size of the obtained cerium-neodymium iron boron air jet milled powder A2 was 3.0 μm.

[0062] In a glove box, A2 component was air-milled into fine powder under an inert gas protective atmosphere and oriented to obtain a green blank. The green blank was vacuum-sealed and subjected to cold isostatic pressing before being placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 1050℃ and held for 3 h. Then, argon gas was passed through for air cooling. After that, a first-stage heat treatment was performed at 820℃ for 3 h, and finally a second-stage heat treatment was performed at 390℃ for 4 h to obtain Ce40 cerium neodymium iron boron magnet C4 with a Ce content of 40 wt.% of the total rare earth content.

[0063] The C4 cerium-neodymium iron boron magnet (C4) was subjected to BH magnetic property testing. The test results for the magnetic properties at room temperature were: B r =12.58 kG, H cj =9.76 kOe, (BH) max = 38.13 MGOe, H k / H cj = 96.7%.

[0064] Comparative Example 5

[0065] According to the original alloy nominal composition (Ce) 0.6 Nd 0.4 ) 31Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce60, was used to prepare rapidly solidified thin strips of component A3. After hydrogen crushing and dehydrogenation, cerium-neodymium iron boron coarse powder A3 was obtained. Then, it was subjected to air jet milling under argon protection. The average particle size of the obtained cerium-neodymium iron boron air jet milled powder A3 was 3.0 μm.

[0066] In a glove box, the A3 component was air-milled into fine powder under an inert gas protective atmosphere and oriented to obtain a green blank. The green blank was vacuum-sealed and subjected to cold isostatic pressing before being placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 1020℃ and held for 3 h. Then, it was cooled by argon gas. After that, it was subjected to a first-stage heat treatment at 820℃ for 3 h, and finally a second-stage heat treatment at 390℃ for 4 h to obtain Ce60 cerium neodymium iron boron magnet C5 with a Ce content of 60 wt.% of the total rare earth content.

[0067] The C5 cerium-neodymium iron boron magnet (C5) underwent BH magnetic property testing. The test results for the magnetic properties at room temperature were: B r =11.46 kG, H cj = 4.37 kOe, (BH) max = 28.20 MGOe, H k / H cj = 94.8%.

[0068] Example 1

[0069] According to the original alloy nominal Nd 31 Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce0, is used to prepare rapidly solidified thin strips of Al composition. After hydrogen crushing and dehydrogenation, NdFeB coarse powder Al is obtained. Then, it is ground into powder by air jet milling under argon protection. The average particle size of the obtained NdFeB air jet milled powder Al is 3.0 μm.

[0070] For NdFeB sintered magnets with 0 wt.% Ce substitution, due to the magnetocrystalline anisotropy field H of the main phase grains... A The magnetocrystalline anisotropy field H of cerium-neodymium-iron-boron main phase grains with a high Ce content A The value is relatively high, therefore Dy is chosen. 86 Cu 14 Rare earth alloys are used as a diffusion source. Based on the nominal composition Dy of the rare earth alloy... 86 Cu14 (wt.%), prepare rapidly solidified thin strips or quick-quenched strips of component B1, the melting point is determined to be 794.08 ℃, after coarse crushing, store in a glove box for later use.

[0071] In a glove box, the air-jet milled powder of component A1 and the fragments of component B1 are mixed evenly at a mass ratio of 1:1 and then placed into a rotatable tube furnace. The vacuum degree inside the furnace is then evacuated to 6.0 × 10⁻⁶. -3 After the pressure drops below 0.05 MPa, the vacuum valve is closed, and argon gas at 0.05 MPa is introduced. Rotary heating is then initiated at a furnace speed of 5 r / min, a heating temperature of 735 ℃, and a heating rate of 10 ℃ / min for 5 h of rotary diffusion heat treatment. Unreacted B1 component fragments are sieved and recovered for use in the next reaction. Then, the air-jet milled powder and B1 component fragments are sieved to obtain NdFeB air-jet milled powder A1 coated with a low-melting-point alloy. ′ The coating amount w1 = 0.93 wt.%.

[0072] Place A1 in the glove box ′ The constituent airflow milled powder was oriented and shaped under an inert gas protective atmosphere to obtain a green blank. The green blank was vacuum sealed and subjected to cold isostatic pressing before being placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 1020℃ and held for 3 h. Then, it was cooled by argon gas and subjected to a first-stage heat treatment at 900℃ for 3 h. Finally, it was subjected to a second-stage heat treatment at 480℃ for 4 h to obtain cerium neodymium iron boron magnet C6.

[0073] The NdFeB magnet C6 prepared by powder modification was subjected to BH magnetic property testing. The test results of the magnetic properties at room temperature were: B r = 14.19 kG, H cj = 21.52 kOe, (BH) max = 47.69 MGOe, H k / H cj = 96.1%.

[0074] Example 2

[0075] According to the original alloy nominal composition (Ce) 0.4 Nd 0.6 ) 31 Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce40, was used to prepare rapidly solidified thin strips of component A2. After hydrogen crushing and dehydrogenation, cerium-neodymium iron boron coarse powder A2 was obtained. Then, it was subjected to air jet milling under argon protection. The average particle size of the obtained cerium-neodymium iron boron air jet milled powder A2 was 3.0 μm.

[0076] For cerium-neodymium-iron-boron sintered magnets with a Ce substitution of 40 wt.%, due to the magnetocrystalline anisotropy of the main phase grains H... A The magnetocrystalline anisotropy field H of the cerium-neodymium-iron-boron main phase grains with Ce substitution of 60 wt.% A The relative level is higher, and Pr2Fe 14 B's H A Higher than Nd2Fe 14 B's H A Therefore, Pr is selected. 82 Cu 18 Rare earth alloys serve as a diffusion source. Based on the nominal designation of rare earth alloys as Pr... 82 Cu 18 (wt.%), prepare rapidly solidified thin strips or quick-quenched strips of component B2, determine the melting point to be 477.5 ℃, and store them in a glove box for later use after coarse crushing.

[0077] In a glove box, the air-jet milled powder of component A2 and the fragments of component B2 are mixed evenly at a mass ratio of 1:1 and then placed into a rotatable tube furnace. The vacuum degree inside the furnace is then evacuated to 6.0 × 10⁻⁶. -3 After the pressure drops below Pa, the vacuum valve is closed, and argon gas at a pressure of 0.05 MPa is introduced. Rotary heating is then initiated at a furnace speed of 5 r / min, a heating temperature of 465 ℃, and a heating rate of 10 ℃ / min for 5 h of rotary diffusion heat treatment. The air-jet milled powder and B2 component fragments are then sieved, and the unreacted B2 component fragments are recovered for use in the next reaction, yielding cerium-neodymium iron boron air-jet milled powder A2 coated with a low-melting-point alloy. ′ The coating amount is w2 = 3.0 wt.%.

[0078] Place A2 in the glove box ′ The constituent airflow milled fine powder was oriented and shaped under an inert gas protective atmosphere to obtain a green blank. The green blank was vacuum sealed and subjected to cold isostatic pressing before being placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 965 ℃ and held for 3 h. Then, argon gas was passed through for air cooling. After that, a first-stage heat treatment was performed at 820 ℃ for 3 h, and finally a second-stage heat treatment was performed at 390 ℃ for 4 h to obtain cerium neodymium iron boron magnet C7.

[0079] The cerium-neodymium iron boron magnet C7, prepared by powder modification, was subjected to BH magnetic property testing. The test results of the magnetic properties at room temperature were: B r = 12.43 kG, H cj = 15.81 kOe, (BH) max = 37.84 MGOe, H k / H cj = 95.7%.

[0080] Example 3

[0081] According to the original alloy nominal composition (Ce) 0.6 Nd 0.4 ) 31 Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce60, was used to prepare rapidly solidified thin strips of component A3. After hydrogen crushing and dehydrogenation, cerium-neodymium iron boron coarse powder A3 was obtained. Then, it was subjected to air jet milling under argon protection. The average particle size of the obtained cerium-neodymium iron boron air jet milled powder A3 was 3.0 μm.

[0082] For cerium-neodymium-iron-boron sintered magnets with a Ce substitution of 60 wt.%, due to the magnetocrystalline anisotropy of the main phase grains H... A The magnetocrystalline anisotropy field H of the cerium-neodymium-iron-boron main phase grains with a Ce substitution amount of 40 wt.% A The relative lower level, and Nd2Fe 14 B's H A Lower than Pr2Fe 14 B's H A Therefore, Nd is chosen. 84 Cu 16 Rare earth alloys are used as diffusion sources, based on the nominal composition of rare earth alloys, Nd 84 Cu 16 (wt.%), prepare rapidly solidified thin strips or quick-quenched strips of component B3, and determine the melting point to be 519.3 ℃. After coarse crushing, store them in a glove box for later use.

[0083] In a glove box, the air-jet milled powder of component A3 and the fragments of component B3 are mixed evenly at a mass ratio of 1:1 and then placed into a rotatable tube furnace. The vacuum degree inside the furnace is then evacuated to 6.0 × 10⁻⁶. -3 After the pressure drops below Pa, the vacuum valve is closed, and argon gas at a pressure of 0.05 MPa is introduced. Rotary heating is then initiated at a furnace speed of 5 r / min, a heating temperature of 497 ℃, and a heating rate of 10 ℃ / min, for 5 h of rotary thermal diffusion treatment. The air-jet milled powder and B3 component fragments are then sieved, and unreacted B2 component fragments are recovered for use in the next reaction, yielding cerium-neodymium iron boron air-jet milled powder A3 coated with a low-melting-point alloy. ′ The coating amount is w3 = 2.8wt.%.

[0084] Place A3 in the glove box ′The components were finely ground by airflow milling and oriented under an inert gas protective atmosphere to obtain a green blank. The green blank was vacuum-sealed and cold isostatically pressed, and then placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 960 ℃ and held for 3 h. Then, argon gas was passed through for air cooling. After that, a first-stage heat treatment was carried out at 820 ℃ for 3 h, and finally a second-stage heat treatment was carried out at 390 ℃ for 4 h to obtain a cerium neodymium iron boron magnet C8.

[0085] The cerium-neodymium iron boron magnet C8, prepared by powder modification, was subjected to BH magnetic property testing. The test results of the magnetic properties at room temperature were: B r = 11.37 kG, H cj = 10.49 kOe, (BH) max = 28.97 MGOe, H k / H cj = 95.6%.

[0086] Example 4

[0087] According to the original alloy nominal composition (Ce) 0.6 Nd 0.4 ) 31 Fe bal Al 0.2 Cu 0.2 Co1Ga 0.35 Zr 0.2 B 0.96 (wt.%), abbreviated as Ce60, was used to prepare rapidly solidified thin strips of component A3. After hydrogen crushing and dehydrogenation, cerium-neodymium iron boron coarse powder A3 was obtained. Then, it was subjected to air jet milling under argon protection. The average particle size of the obtained cerium-neodymium iron boron air jet milled powder A3 was 3.0 μm.

[0088] For cerium-neodymium-iron-boron sintered magnets with a Ce substitution of 60 wt.%, due to the magnetocrystalline anisotropy of the main phase grains H... A The magnetocrystalline anisotropy field H of the cerium-neodymium-iron-boron main phase grains with a Ce substitution amount of 40 wt.% A The relative lower level, and Nd2Fe 14 B's H A Lower than Pr2Fe 14 B's H A Therefore, Nd is chosen. 84 Cu 16 Rare earth alloys are used as a diffusion source. Based on the nominal composition of the rare earth alloy, Nd... 84 Cu 16 (wt.%), prepare B3 component rapid solidification thin strips or rapid quenching strips, the melting point is determined to be 519.3 ℃, after coarse crushing, store in glove box for later use.

[0089] In a glove box, the air-jet milled powder of component A3 and the fragments of component B3 are mixed evenly at a mass ratio of 1:1 and then placed into a rotatable tube furnace. The vacuum degree inside the furnace is then evacuated to 6.0 × 10⁻⁶. -3 After the pressure drops below Pa, the vacuum valve is closed, and argon gas at a pressure of 0.05 MPa is introduced. Rotary heating is then initiated at a furnace speed of 5 r / min, a heating temperature of 510 ℃, and a heating rate of 10 ℃ / min for 5 h of rotary diffusion treatment. The air-jet milled powder and B component fragments are then sieved, and the unreacted B2 component fragments are recovered for use in the next reaction, yielding cerium-neodymium iron boron air-jet milled powder A3 coated with a low-melting-point alloy. ′′ The coating amount is w4 = 4.3wt.%.

[0090] Place A3 in the glove box ′′ The constituent airflow milled powder was oriented and shaped under an inert gas protective atmosphere to obtain a green blank. The green blank was vacuum sealed and subjected to cold isostatic pressing before being placed in a vacuum sintering furnace for sintering and heat treatment. The sintering temperature was 935℃ and held for 3 h. Then, argon gas was passed through for air cooling. After that, a first-stage heat treatment was performed at 820℃ for 3 h, and finally a second-stage heat treatment was performed at 390℃ for 4 h to obtain cerium neodymium iron boron magnet C9.

[0091] The cerium-neodymium iron boron magnet C9, prepared by powder modification, was subjected to BH magnetic property testing. The test results of the magnetic properties at room temperature were: B r = 11.21 kG, H cj = 10.53 kOe, (BH) max = 27.37 MGOe, H k / H cj = 93.2%.

[0092] The comparison results of remanence, coercivity, maximum energy product and squareness of each cerium-neodymium iron boron magnet in the above comparative examples and embodiments are shown in Table 1.

[0093] Table 1 Performance of each magnet in the comparative examples and embodiments

[0094] In summary, based on an innovative composition-process synergistic optimization strategy, for NdFeB sintered magnets with 0 wt.% Ce substitution, due to the magnetocrystalline anisotropy field H of the main phase grains... A The magnetocrystalline anisotropy field H of cerium-neodymium-iron-boron main phase grains with a high Ce content A The value is relatively high, therefore Dy is chosen. 86 Cu 14Using rare-earth alloys as a diffusion source, comparative examples 2 and 3 revealed that grain boundary doping and diffusion resulted in limited improvement in coercivity and a significant decrease in remanence in the magnets. While grain boundary diffusion effectively improved the coercivity, it also reduced remanence and squareness to 91.8%. 86 Cu 14 Neodymium iron boron (NdFeB) magnets prepared by sintering modified rare-earth alloy powders have the advantage of forming a uniform and controllable film on the surface of NdFeB magnetic powders, thus reducing the required Dy 86 Cu 14 The rare-earth alloy powder, smaller than the grain boundary-doped magnet in Comparative Example 2, showed a significant improvement in coercivity while only a slight decrease in remanence, resulting in a significant improvement in overall magnetic properties. Regarding Comparative Example 3, the (Dy, Nd)₂Fe formed in Example 1... 14 The B-shell is more uniform, avoiding the (Dy, Nd)2Fe in Comparative Example 3. 14 Due to the gradient problem of multiple centers and few centers on the surface of the B-shell, Example 1 exhibits better squareness; for the cerium-neodymium-iron-boron sintered magnet with a Ce substitution amount of 40 wt.%, the magnetocrystalline anisotropy field H of its main phase grains... A The magnetocrystalline anisotropy field H of the cerium-neodymium-iron-boron main phase grains with Ce substitution of 60 wt.% A The relative level is higher, and Pr2Fe 14 B's H A Higher than Nd2Fe 14 B's H A Therefore, Pr is selected. 82 Cu 18 Using rare earth alloys as a diffusion source, a comparison of the original sintered magnets and powder-modified sintered magnets in Example 4 and Example 2 revealed that the magnetic properties of the cerium-neodymium iron boron sintered magnets modified with rare earth alloy powder were significantly improved. Furthermore, a (Ce, Pr, Nd)₂Fe₂ containing Pr element was formed outside the main phase grain nuclei. 14 B-shell; for cerium-neodymium-iron-boron sintered magnets with 60 wt.% Ce substitution, due to the magnetocrystalline anisotropy of the main phase grains H A The magnetocrystalline anisotropy field H of the cerium-neodymium-iron-boron main phase grains with a Ce substitution amount of 40 wt.% A The relative lower level, and Nd2Fe 14 B's H A Lower than Pr2Fe 14 B's H A Therefore, Nd is chosen. 84 Cu 16Using rare earth alloys as a diffusion source, a comparison of the original sintered magnets and powder-modified sintered magnets in Examples 5, 3, and 4 revealed that the magnetic properties of the cerium-neodymium iron boron sintered magnets modified with rare earth alloy powder were significantly improved. Furthermore, (Ce, Nd)₂Fe₂ containing more Nd elements was formed outside the main phase grain nuclei. 14 In the B-shell layer, when the coating thickness is further increased (Example 4), the coercivity only increases slightly, while the remanence decreases significantly. This indicates that when the core of the main phase grain and the H-shell layer are in contact, the coercivity increases only slightly, while the remanence decreases significantly. A When dynamic synergistic enhancement is achieved, introducing diffusion sources will not further increase the coercivity of the magnet. By controlling the composition of the shell layer and targeting the main phase grain composition, the coercivity of the magnet can be efficiently improved while avoiding the waste of rare earth resources.

[0095] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method of producing high performance cerium-neodymium-iron-boron magnets based on a powder modification process, characterized in that, comprising the steps of: (1) preparing main phase alloy cerium neodymium iron boron magnetic powder A with different Ce substitution amount, whose nominal composition is (Ce x , Nd 1-x ) α Fe 100-α-β-γ M β B γ (wt.%), M is one or several of Al, Cu, Nb, Co, Ga, Ti, Zr, Mn, Ni, Si, Cr, wherein x, α, β, γ are weight percentage contents of each element, satisfying the following relationship: 0 ≤ x ≤ 0.6, 29 ≤ α ≤ 33, 0.5≤ β ≤ 3.0, 0.7 ≤ γ ≤ 1.2; The main phase grains of the main phase alloy are (Ce x , Nd 1-x )2Fe 14 B, and a magnetic crystal anisotropy field H A核 satisfies: H A核 = x + (1 – x) ; (2) The low-melting-point rare earth alloy RE a N 100-a (wt.%) is selected as the diffusion source B according to the variation characteristics of the magnetic crystal anisotropy field H A核 of the core of the main phase crystal grains (Ce x , Nd 1-x )2Fe 14 B of the cerium-neodymium-iron-boron magnetic powder A prepared in step (1); The rare earth alloy RE a N 100-a comprising at least one rare earth element RE selected from the group consisting of Nd, Pr, Ho, Dy or Gd, and at least one non-rare earth metal element M selected from the group consisting of Al, Cu or Ga, a being the weight percentage content and satisfying the following relationship: 60 ≤ a ≤ 97, and the alloy melting point T m satisfying 400 ℃ ≤ T m < 800 ℃; (3) The main phase alloy cerium neodymium iron boron magnetic powder A with different Ce substitution amount in step (1) is mixed with the selected broken rare earth alloy RE in step (2) to obtain a mixture a N 100-a The mixture of the rapid solidification strip fragments (or the rapid quenching strip fragments) is mixed uniformly at a mass ratio of 1:2-3:1, and then is placed in a rotatable tube furnace at a rotating speed of 5 r / min and a coating temperature T 包覆 The mixture is heat treated for 5 h to make the RE a N 100-a alloy diffuse to the surface layer of the main phase crystal grains to form a RE-rich coating layer. (4) The cerium-neodymium iron boron magnetic powder coated in step (3) is mixed with rare earth alloy RE a N 100-a The rapid-setting flakes (or rapid-quenching belt fragments) are screened to recover unreacted rare earth alloy RE. a N 100-a The rapidly solidifying flakes (or rapidly quenched strip fragments) can be reused in the next batch of reaction. The resulting rare-earth alloy-coated air-jet milled magnetic powder is then subjected to orientation molding and isostatic pressing to produce a green compact. Based on the amount of rare-earth alloy coating, a suitable low temperature T is selected. 烧结 The green billets are sintered in a vacuum sintering furnace and then subjected to two-stage tempering heat treatment. (5) The high-performance cerium-neodymium-iron-boron magnet with a RE-rich magnetic hardening shell layer on the surface of the main phase crystal grain is finally obtained, and the magnet has a core-shell structure, the core is (Ce x , Nd 1-x )2Fe 14 B, and the shell is a RE-rich magnetic hardening shell layer, that is, (Ce, Nd, RE)2Fe 14 , and the relationship satisfies 0.90 ≤ H A核 : H A壳 ≤ 1.00, the synchronous reverse of the core-shell structure in the demagnetization process is realized, the waste of rare earth resources is avoided, and the coercivity of the cerium-neodymium-iron-boron magnet is maximized.

2. The method of manufacturing high performance Ce- Nd-Fe-B magnets based on powder modification process according to claim 1, characterized in that, The low melting point rare earth alloy RE selected in step (2) a N 100-a The relationship between RE in the above formula and the substitution amount x of Ce in the main phase alloy cerium-neodymium-iron-boron magnetic powder A in step (1) is: When 0.0 ≤ x ≤ 0.2, RE is selected a N 100-a RE is Dy element; When 0.2 < x ≤ 0.4, RE is selected a N 100-a RE is one or both of Pr and Ho elements; when 0.4 < x ≤ 0.6, RE is selected a N 100-a RE is one or both of Nd and Gd elements; where the Ce substitution in the main phase grains is low, i.e. 0.0 < x < 0.2, the RE2Fe 14 the magnetic crystalline anisotropy field H A a higher RE alloy. Where the Ce substitution in the main phase grains is high, i.e. 0.4 < x < 0.6, the RE2Fe 14 the magnetic crystalline anisotropy field H A a lower RE alloy.

3. The method of manufacturing high performance Ce- Nd-Fe-B magnets based on powder modification process according to claim 1, characterized in that, The low-melting rare earth alloy RE a N 100-a The temperature difference between the melting point T m The temperature difference between the melting point T 包覆 The temperature difference between the melting point T m – T 包覆 The coating amount w on the main phase alloy cerium-neodymium-iron-boron magnetic powder satisfies the following corresponding relationship: 0.0 wt.% < w < 1.0 wt.% when 40 °C < ΔΤ≤ 60 °C; 1.0 wt.% < w < 2.0 wt.% when 25 °C < ΔΤ≤ 40 °C; 2.0 wt.% < w < 3.0 wt.% when 10 °C < ΔΤ≤ 25 °C; 3.0 wt.% < w < 4.5 wt.% when 0 °C < ΔΤ≤ 10 °C.

4. wherein said coating amount w increases with decreasing said temperature difference ΔΤ.

5. The method of manufacturing high performance Ce- Nd-Fe-B magnets based on powder modification process as claimed in claim 1, wherein, The coating amount w of the main phase alloy magnetic powder A obtained by the surface spin diffusion process and the green body low-temperature sintering temperature T described in step (4) satisfy the following correspondence relationship: 烧结 satisfy the following correspondence relationship: when 0.0 wt.% < w ≤ 1.0 wt.%, 烧结 ≤ 1020 ℃; 970 °C < T < 990 °C when 1.0 wt.% < w < 2.0 wt.% 烧结 < 990 ℃; 950 °C < T < 970 °C when 2.0 wt.% < w < 3.0 wt.% 烧结 < 970 °C; 900 °C ≤ T < 950 °C when 3.0 wt.% < w ≤ 4.5 wt.%. 烧结 < 950 ℃.

6. wherein said sintering treatment phase has a holding time of 3 h - 6 h.

7. The method of manufacturing high performance Ce- Nd-Fe-B magnets based on powder modification process as claimed in claim 1, wherein, said tempering heat treatment in step (4) has a first temperature of 780 °C - 900 °C with a holding time of 3 h - 5 h and a second temperature of 380 °C - 660 °C with a holding time of 3 h - 5 h.

8. The method of manufacturing high performance Ce- Nd-Fe-B magnets based on powder modification process as claimed in claim 1 wherein, The RE-rich content in the RE-rich hardening shell layer formed in Step (4) is y %, and the anisotropic field H A壳 satisfies, H A壳 = y % + (1 – y %) .

9. A high-performance cerium-neodymium iron boron magnet prepared based on a powder modification process, characterized in that, which is prepared by the method of any one of claims 1-6, said magnet having a core-shell structure, the core being (Ce x , Nd 1-x )2Fe 14 B, and the shell being a RE-rich magnetic hardening layer, the ratio of the magnetocrystalline anisotropy fields of the core and the shell H A核 : H A壳 being between 0.90 and 1.00, the synchronous reversal of the core-shell during the demagnetization process being achieved, and the coercivity of the magnet being significantly improved.

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