Production method of high-performance sintered neodymium-iron-boron magnet

Abstract

The invention discloses a production method of a high-performance sintered neodymium-iron-boron magnet. The production method comprises the steps of rapid quenching flaking, hydrogen decrepitation mixing, magnetic field forming, multi-stage treatment and composite coating. A nanocrystalline sheet is prepared through a rapid quenching technology, and uniform distribution of a grain boundary phase and rare earth elements is achieved through hydrogen decrepitation and material mixing; forming in a strong magnetic field and applying high pressure to improve the orientation degree; through high-temperature sintering, medium-temperature annealing and low-temperature aging treatment, magnet densification, grain boundary phase reconstruction and a magnetic domain structure are optimized; and finally, the corrosion resistance is improved by adopting a composite coating. The high-performance sintered neodymium-iron-boron magnet produced by the method comprises a main phase alloy, a grain boundary phase additive and a rare earth supplementary phase. Through low-oxygen nanocrystal preparation, grain boundary coordinated regulation and green process integration, compatibility of high performance, low cost and environmental protection is realized, and sustainable development of the rare earth permanent magnet material is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth permanent magnet materials, and specifically relates to a production method of high-performance sintered NdFeB magnets, which is applicable to high-tech fields such as motors, wind power generation, and new energy vehicle drive systems. Background Art

[0002] As the third-generation rare earth permanent magnet material, sintered NdFeB magnets are widely used in new energy, motors, and electronic devices due to their excellent magnetic properties. However, there are still multiple bottlenecks in improving their performance: on the one hand, to increase the coercivity, traditional technologies rely on adding heavy rare earth elements (such as dysprosium and terbium), but the reserves of such elements are scarce and the prices are expensive, significantly increasing the manufacturing cost; on the other hand, conventional sintering processes are prone to cause coarsening of the main phase grains and insufficient continuity of the grain boundary phase, resulting in deterioration of magnetic properties. In addition, although the grain boundary diffusion process in the existing technology can locally improve the coercivity, the problem of uneven distribution of heavy rare earth elements still exists, and the volatilization of rare earth elements during the high-temperature sintering process will exacerbate the composition segregation, further affecting the magnet stability. At the same time, the characteristics of easy oxidation and corrosion on the magnet surface force most products to rely on electroplating or coating protection, increasing the complexity of the process flow. In recent years, researchers have tried to reduce the heavy rare earth usage through microalloying or process optimization, but it is often difficult to balance high remanence and high coercivity, and the effect of grain boundary phase regulation is limited. Summary of the Invention

[0003] The purpose of the present invention is to provide a production method of a new type of sintered NdFeB magnet, which can significantly improve the magnetic properties, corrosion resistance, and high-temperature stability while reducing the heavy rare earth usage by optimizing the composition ratio, introducing a composite grain boundary phase regulation technology, and a multi-stage sintering process.

[0004] The present invention provides a production method of high-performance sintered NdFeB magnets with low cost and low heavy rare earth dependence, which synergistically regulates the grain boundary phase through composition optimization and multi-stage sintering process, significantly improving the magnetic properties and corrosion resistance, and is applicable to high-end permanent magnet application fields.

[0005] The high-performance sintered NdFeB magnet produced by the present invention basically consists of a main phase alloy, a grain boundary phase additive, and a rare earth supplement phase, wherein the main phase alloy is Nd a Pr b Fe c B d Co e Ga f , where a, b, c, d, e, f are mass percentages, 26 ≤ a ≤ 32, 0.1 ≤ b ≤ 1.0, 65 ≤ c ≤ 71, 0.5 ≤ d ≤ 2.0, 1 ≤ e ≤ 5, 0.1 ≤ f ≤ 1.0, and a + b + c + d + e + f = 100.

[0006] In the present invention, the main-phase alloy is the core carrier of the magnet performance. Through the innovative design of the component ratio, the contradiction of traditional NdFeB magnets in terms of high coercivity, high-temperature stability, and low heavy rare-earth dependence is solved by means of multi-element cooperative substitution and lattice regulation. Among them, Nd (neodymium) is used as the main rare-earth element to form Nd2Fe 14 B hard magnetic phase, which directly determines the remanence and magnetic energy product; the lower limit of Nd of 26% ensures that the volume fraction of the main phase > 85%, avoiding the formation of non-magnetic phases (such as α-Fe) due to insufficient Nd; the upper limit of 32% prevents the formation of coarse Nd-rich grain boundary phases due to excessive Nd, which hinders the movement of magnetic domain walls and reduces the coercivity. Pr (praseodymium) partially replaces Nd, enhances the coercivity by increasing the anisotropy field of the main phase, and reduces the usage of heavy rare earths at the same time; the atomic radii of Pr and Nd are similar (Pr: 1.82 Å, Nd: 1.82 Å), and when the substitution amount < 1.0%, lattice distortion can be avoided and the stability of the main phase can be maintained; the addition of Pr can increase the coercivity. Fe (iron) forms the framework structure of the Nd2Fe 14 B phase, maintaining high saturation magnetization; the lower limit of Fe of 65% ensures that the Fe content is sufficient to form a complete main phase, avoiding the formation of B-rich non-magnetic phases (such as FeB); the upper limit of 71% prevents the precipitation of α-Fe soft magnetic phase due to excessive Fe, which damages the coercivity. B (boron) promotes the formation of the Nd2Fe 14 B phase and regulates the grain size of the main phase; the lower limit of B is 0.5%, below which insufficient main phase cannot be formed and the magnetic properties will decrease sharply; the upper limit is 2.0%, and excessive B will lead to the formation of B-rich phases (such as FeB), reducing Br and HcJ. Co (cobalt) replaces Fe atoms, increases the Curie temperature, and enhances the high-temperature stability; inhibits oxidation, reduces the activity of Fe, and decreases the oxidation tendency of the magnet; when Co > 5%, the lattice constant of the main phase changes significantly (the c-axis shrinks), resulting in a decrease in the magnetocrystalline anisotropy field (Ha). Ga (gallium) refines grains, inhibits abnormal grain growth during sintering; forms a eutectic structure with the Nd-rich phase, hinders the nucleation of anti-magnetic domains, and enhances grain boundary pinning; when Ga > 1.0%, it is easy to segregate at the grain boundary to form Ga-Fe non-magnetic phases, reducing Br. The ternary cooperation of Pr-Co-Ga, Pr enhances the anisotropy field, Co increases the Curie temperature, and Ga refines grains; when the addition amount of Dy2O3 is only 0.5 - 1.2%, high performance of sintered NdFeB magnets is achieved.

[0007] By limiting the cooperative ratio range of Pr, Co, and Ga and combining the grain boundary phase regulation technology, the main-phase alloy is clearly different from traditional high-Dy formulations or single-element modification schemes, forming the core points of low heavy rare earths and high comprehensive performance.

[0008] In the present invention, the grain boundary phase additive significantly improves the coercivity (HcJ), corrosion resistance, and thermal stability of the magnet by regulating the composition, distribution, and microstructure of the grain boundary phase. The grain boundary phase is optimized to match the matrix phase. Among them, the Cu / Al additive reduces the melting point of the grain boundary phase, promotes liquid-phase sintering, and forms a continuous grain boundary network; Zr inhibits grain coarsening and synergistically with Ga achieves uniform grain size.

[0009] In the sintered Nd-Fe-B magnet of the present invention, the grain boundary phase additive comprises 0.2-0.8% Cu, 0.1-0.5% Al, and 0.05-0.3% Zr. Among them, Cu (copper) reduces the melting point of the grain boundary phase. Cu forms a eutectic liquid phase with the Nd-rich phase, promotes the fluidity of the grain boundary phase during sintering, fills the gaps between the matrix phase grains, and forms a continuous and dense grain boundary network; inhibits the coarsening of the matrix phase grains. Through the liquid-phase wetting effect, it blocks the direct contact between grains and inhibits abnormal grain growth; when Cu < 0.2%, insufficient liquid phase is generated and the grain boundary is discontinuous; when Cu > 0.8%, excessive liquid phase causes the matrix phase grains to be overly wrapped and the magnetic properties to decline. Al (aluminum) enhances the oxidation resistance of the grain boundary. Al has a strong affinity for oxygen and preferentially oxidizes to form an Al2O3 protective film, reducing the oxidation loss of Nd at the grain boundary and improving the corrosion resistance of the magnet; Al forms a composite liquid phase (Cu-Al eutectic) with Cu, synergistically regulates the grain boundary phase with Cu, further refines the grain boundary thickness, and enhances the grain boundary pinning effect; when Al < 0.1%, the oxidation resistance effect is insufficient; when Al > 0.5%, excessive Al2O3 is generated, resulting in grain boundary embrittlement and the magnet being prone to cracking. Zr (zirconium) inhibits abnormal grain growth. Zr segregates at the grain boundary during sintering to form high-melting-point compounds such as ZrB2, hinders grain boundary migration, and refines grains; improves high-temperature stability. The addition of Zr makes the thermal expansion coefficient of the grain boundary phase match that of the matrix phase, reducing the magnetic property attenuation caused by grain boundary thermal stress at high temperatures; when Zr < 0.05%, the effect of inhibiting grain coarsening is weak; when Zr > 0.3%, excessive precipitation of ZrB2 hinders the continuity of the grain boundary phase and the coercivity decreases.

[0010] In this grain boundary phase additive, Cu-Al-Zr synergistically cooperate. Cu and Al form a low-melting-point liquid phase to optimize the grain boundary distribution; Zr refines grains and stabilizes the grain boundary structure; the grain boundary coverage rate is increased, and the coercivity HcJ is improved. Compared with the traditional technology, through the synergistic regulation of Cu-Al-Zr in the present invention, the coercivity is significantly improved and the cost is reduced. By limiting the synergistic addition range of Cu, Al, and Zr, the dual functions of grain boundary phase regulation and grain refinement are clarified, forming a technical solution different from single additives or high-heavy rare earth formulations.

[0011] In the present invention, the rare earth supplementary phase directionally enhances the coercivity of the magnet through grain boundary diffusion technology, breaking through the technical bottleneck of traditional high-heavy rare earth addition. In the sintered Nd-Fe-B magnet of the present invention, the rare earth supplementary phase comprises 0.5-1.2% Dy2O3 nanoparticles.

[0012] Dy2O3 nanoparticles (particle size 50 - 100 nm) preferentially enter the surface layer of the main phase grains through the grain boundary diffusion path during the sintering process, forming a (Nd,Dy)2Fe 14 B shell structure, significantly enhancing the anisotropy field of the main phase, thereby greatly improving the coercivity. Compared with the traditional process, the traditional method needs to add 3 - 5% Dy in the melting stage, while the present invention only needs to add 0.5 - 1.2% Dy2O3, and the consumption of heavy rare earths is significantly reduced. Dy segregates near the grain boundaries, forming a high anisotropy shell, effectively blocking the nucleation and expansion of antiferromagnetic domains at the grain boundaries, and making the magnetic properties of the magnet more stable under high temperature or reverse magnetic field. The high specific surface area of the nanoparticles improves the diffusion efficiency and shortens the process time; the nanoparticles are uniformly mixed with the magnetic powder through the hydrogen decrepitation process, avoiding the surface enrichment problem of the traditional grain boundary diffusion method. When the Dy2O3 content is <0.5%, the Dy atoms diffusing into the main phase grains are insufficient to form a continuous high anisotropy shell, and the effect of coercivity improvement is weak. When Dy2O3 > 1.2%, excessive Dy forms a non-magnetic Dy-O phase at the grain boundaries, hindering the magnetic coupling of the main phase and resulting in a significant decrease in the remanence and magnetic energy product.

[0013] By limiting the addition ratio and particle size range of Dy2O3 nanoparticles and combining with the grain boundary diffusion process, the rare earth supplementary phase forms a unique technical solution with low heavy rare earth and high coercivity, which is different from the traditional melting addition or bulk Dy diffusion technology, meets the stringent requirements of new energy vehicle drive motors for high coercivity and high temperature stability, reduces the environmental pressure caused by heavy rare earth mining; the manufacturing cost per ton of magnet is reduced, and the competitiveness of domestic magnets is improved.

[0014] The production method of the high-performance sintered Nd-Fe-B magnet provided by the present invention includes the steps of rapid quenching and flaking, hydrogen decrepitation and mixing, magnetic field forming, multi-stage treatment and composite plating. Through five core steps of rapid quenching nanocrystal regulation, multi-element synergistic hydrogen decrepitation, high-pressure magnetic field orientation, multi-stage sintering aging and composite coating protection, the present production method realizes the preparation of sintered Nd-Fe-B magnets with low heavy rare earth, high coercivity and high corrosion resistance, and specifically includes the following operations: Step 1. Rapid quenching and flaking: Weigh high-purity metal raw materials Nd, Pr, Fe, B, Co, Ga, and prepare Nd-Fe-B rapid solidification thin sheets through vacuum rapid quenching technology to obtain a nanocrystal structure; Step 2. Hydrogen decrepitation and mixing: Mix and crush the rapid solidification thin sheets, Dy2O3 nanoparticles and Cu, Al, Zr powders in hydrogen to 3 - 5 μm to optimize the grain boundary phase distribution; Step 3. Magnetic field forming: Use the combined action of a 1.5T vertical magnetic field and 200 - 400 MPa isostatic pressure to achieve high orientation degree of magnetic powder and densification of the green body; Step 4. Multi-stage treatment: Three-stage heat treatment including sintering at 1050 - 1080 °C, annealing at 900 - 950 °C, and aging at 500 - 600 °C is adopted to synergistically improve the magnet density, coercivity, and high-temperature stability; Step 5. Composite coating: Using the multi-element composite plating technology, an Al ion plating layer and an epoxy resin SiO2 composite coating are sequentially deposited on the magnet surface to obtain a high-performance sintered NdFeB magnet.

[0015] A production method of a high-performance sintered NdFeB magnet provided by the present invention specifically includes: Step 1. Rapid quenching and sheet making: Weigh high-purity metal raw materials Nd a Pr b Fe c B d Co e Ga f Weigh high-purity metal raw materials Nd, Pr, Fe, B, Co, Ga, and place them in a vacuum induction melting furnace. Among them, a, b, c, d, e, f are mass percentages, 26 ≤ a ≤ 32, 0.1 ≤ b ≤ 1.0, 65 ≤ c ≤ 71, 0.5 ≤ d ≤ 2.0, 1 ≤ e ≤ 5, 0.1 ≤ f ≤ 1.0, and a + b + c + d + e + f = 100; Use the vacuum rapid quenching technology to prepare a Nd-Fe-B rapid solidification thin sheet with a thickness ≤ 0.3 mm, control the cooling rate ≥ 10 5 K / s to obtain a nanocrystalline structure; Use the vacuum rapid quenching technology to rapidly cool the molten alloy into a thin sheet with a thickness ≤ 0.3 mm at a cooling rate ≥ 10 5 K / s to inhibit grain growth and form a uniform nanocrystalline. Nanocrystals have higher magnetocrystalline anisotropy than the micron-sized grains of traditional ingots, providing fine and uniform raw materials for subsequent hydrogen embrittlement; The cooling rate ≥ 10 5 K / s ensures an amorphous / nanocrystalline mixed structure and avoids the precipitation of the α-Fe phase.

[0016] Step 2. Hydrogen embrittlement and mixing: Mix the rapid solidification thin sheet, 0.5 - 1.2% Dy2O3 nanoparticles, and 0.2 - 0.8% Cu, 0.1 - 0.5% Al, 0.05 - 0.3% Zr powders in proportion, and crush them to a particle size of 3 - 5 μm in a hydrogen atmosphere; Hydrogen embrittlement means that in an H2 atmosphere, the rapid solidification thin sheet absorbs hydrogen and embrittles, and is crushed into fine powders of 3 - 5 μm; Simultaneously add Dy2O3 nanoparticles and Cu, Al, Zr powders for multi-element mixing to achieve uniform distribution of grain boundary phase elements. Grain boundary diffusion premixing, Dy2O3 nanoparticles are mixed with magnetic powder during the hydrogen embrittlement stage to avoid the uneven distribution of Dy in the traditional post-diffusion method; H2 reacts with Nd to form NdH2, reducing the powder hardness and reducing the crushing energy consumption.

[0017] Step 3. Magnetic field forming: Molding under a 1.5T vertical magnetic field, while applying an isostatic pressure of 200 - 400 MPa to increase the orientation degree to over 96%; the vertical magnetic field aligns the c-axis of Nd2Fe 14 B grains along the magnetic field direction, with an orientation degree ≥ 96%; synchronously applying a high pressure of 200 - 400 MPa of isostatic pressure to eliminate pores and lock the orientation, and the green density reaches 4.2 - 4.5 g / cm 3 . The synergy of magnetic field - pressure, the high pressure inhibits the rotation and offset of grains, and the orientation degree is improved; the BN coating reduces the orientation disorder caused by friction, optimizes the die lubrication, and the standard deviation of grain arrangement < 2°.

[0018] Step 4. Multi - stage treatment: Through a three - stage stepped treatment of high - temperature sintering at 1050 - 1080 °C, medium - temperature annealing at 900 - 950 °C, and two - stage aging at 500 - 600 °C, the densification of the magnet, the reconstruction of the grain boundary phase, and the refinement of magnetic domains are realized in sequence, simultaneously improving the coercivity and high - temperature stability; the first - stage sintering at 1050 - 1080 °C: densification of the main - phase grains, density > 7.5 g / cm 3 ; the second - stage annealing at 900 - 950 °C: the liquid phase of Cu and Al reconstructs the continuous grain boundary, and Dy2O3 diffuses to form a (Nd,Dy)2Fe 14 B shell; the third - stage aging at 500 - 600 °C: rapid cooling in cooperation with slow cooling eliminates internal stress, and the magnetic domain width is refined. The stepped temperature field design breaks through the grain coarsening limit of traditional single - stage sintering; the Dy diffusion is completed in the second - stage annealing stage, and the integration of Dy grain - boundary diffusion omits the traditional independent diffusion process, shortening the process time.

[0019] Step 5. Composite coating: Adopting a multi - element composite plating technology, an Al ion plating layer and an epoxy resin - nano - SiO2 composite coating are sequentially deposited on the magnet surface to improve the corrosion resistance, and a high - performance sintered Nd - Fe - B magnet is prepared; the Al ion plating layer is 2 - 5 μm, and a dense Al layer is formed by physical vapor deposition (PVD) to block the penetration of corrosive media; the epoxy resin - silica coating is 10 - 15 μm, and nano - SiO2 fills the micropores of the epoxy resin to form a "labyrinth effect" barrier. The dual - coating provides collaborative protection, improving the salt - spray resistance performance; there is no cyanide - containing wastewater, and the VOC emissions are reduced.

[0020] Through the collaborative innovation of composition - process - structure, the present invention achieves a breakthrough in magnetic properties and corrosion resistance under the condition of low heavy rare earths. Rapid quenching, hydrogen - decrepitation mixing, multi - stage sintering and aging, and composite coating provide full - link protection, with the triple advantages of low cost, high performance, and green manufacturing, providing a domestic solution for high - end permanent magnet applications.

[0021] In the production method of the present invention, in step 1, Nd-Fe-B rapid solidification flakes are prepared by the rapid solidification technology with an ultra-high cooling rate to obtain a nanocrystalline / amorphous hybrid structure, which lays a foundation for subsequent hydrogen decrepitation and grain boundary regulation, avoids the coarse columnar crystals (>50 μm) of the traditional ingot casting process, inhibits grain coarsening, and forms uniform nanocrystals with a size of 50-100 nm; eliminates the precipitation of α-Fe phase, the rapid solidification inhibits the segregation of Fe element, and reduces the damage of the soft magnetic phase (α-Fe) to the magnetic properties; the composition is uniform, and the compositional fluctuation at the nanoscale is <1%, improving the sintering consistency.

[0022] In the production method of the sintered Nd-Fe-B magnet of the present invention, the specific operation of step 1 is as follows: Weigh high-purity metal raw materials Nd, Pr, Fe, B, Co, Ga according to the main phase composition, with a purity ≥99.9%, and place them in a vacuum induction melting furnace to reduce the influence of impurities (O, C, N) on the magnetic properties; evacuate to ≤5×10 -3 Pa, and introduce high-purity argon gas with a purity of 99.999% as a protective atmosphere to prevent metal oxidation (especially active elements such as Nd and Pr); heat up to 1550-1600 °C, which is higher than the liquidus of the Nd-Fe-B alloy, to ensure complete melting and uniform composition, and melt into a uniform alloy liquid. Spray the molten alloy liquid onto the surface of a high-speed rotating water-cooled copper roller through a quartz nozzle, with a rotation speed of 20-30 m / s, and the temperature of the copper roller is controlled at 15-25 °C; by adjusting the rotation speed of the copper roller and the melt injection pressure, the alloy liquid solidifies at a cooling rate of ≥10 5 K / s to form continuous flakes with a thickness ≤0.3 mm; rapidly solidify into flakes, with the rotation speed of the water-cooled copper roller being 20-30 m / s, and the linear velocity of the roller surface matching the melt flow rate to ensure that the thickness of the flakes ≤0.3 mm; maintain a low temperature at 15-25 °C through internal circulating cooling water to achieve an ultra-high cooling rate of ≥10 5 K / s; when the melt contacts the copper roller, the heat is rapidly dissipated to form an amorphous / nanocrystalline hybrid structure. After the flakes are peeled off, they are crushed and screened to obtain sheet-like particles with a particle size ≤2 mm, which are stored in an argon protection box for standby; the continuous flakes are coarsely crushed to ≤2 mm sheet-like particles by a jaw crusher to avoid excessive energy consumption in subsequent hydrogen decrepitation; store under argon protection, with an oxygen content <10 ppm, to prevent the oxidation of Nd and Pr to form Nd2O3 / Pr2O3.

[0023] This step limits the ultra-high cooling rate (≥10 5The process parameters with a speed of K / s and a sheet thickness ≤ 0.3 mm, combined with the microscopic characteristics of the nanocrystalline / amorphous hybrid structure, form an innovative preparation method different from traditional ingot casting or ordinary rapid quenching technology, providing the core precursor material for low-oxygen-content and high-uniformity sintered Nd-Fe-B magnets. In the present invention, the grain size is refined to 50 - 100 nm, and the anisotropy field is enhanced; the sheet thickness ≤ 0.3 mm, and too thick a thickness (> 0.5 mm) will lead to insufficient central cooling rate and grain coarsening; the rapidly quenched sheet is directly hydrogenated and crushed, eliminating multiple processes such as traditional ingot casting - hydrogen crushing - powder making, and reducing energy consumption. The strong correlation design of solidification rate - microstructure - magnetic properties in this step suppresses grain boundary segregation and the formation of soft magnetic phases through extreme rapid cooling, laying the foundation for subsequent low-heavy-rare-earth and high-coercivity magnets.

[0024] In the production method of the present invention, step 2 realizes the uniform mixing and ultra-fine powder preparation of the main phase alloy, grain boundary phase additive, and rare-earth supplementary phase through a five-step process of mechanical crushing - three-dimensional mixing - hydrogen crushing - dehydrogenation - jet milling, ensuring the uniform distribution of Dy2O3 nanoparticles and Cu, Al, Zr in the magnetic powder; activating the grain boundary through hydrogen crushing, laying the foundation for the directional diffusion of Dy in subsequent sintering; obtaining ultra-fine powder with a particle size of 3 - 5 μm, improving the sintering density and magnet orientation degree.

[0025] In the production method of the sintered Nd-Fe-B magnet of the present invention, the specific operation of step 2 is as follows: The rapidly solidified sheet of the Nd-Fe-B main phase alloy is preliminarily coarsely pulverized by mechanical crushing to a particle size ≤ 500 μm; through mechanical crushing and coarsening, the rapidly solidified sheet of Nd-Fe-B (thickness ≤ 0.3 mm) is preliminarily crushed to a coarse powder of ≤ 500 μm by a jaw crusher or a ball mill, reducing the energy consumption of subsequent hydrogen crushing; too coarse a particle size (> 1 mm) will lead to uneven hydrogen penetration, and too fine a particle size (< 100 μm) is prone to oxidation and agglomeration. Weigh the Dy2O3 nanoparticles with a particle size of 50 - 100 nm and the metal powders of Cu, Al, Zr with a purity ≥ 99.9% according to the ratio and set aside; Dy2O3 nanoparticles (50 - 100 nm), with a high specific surface area (> 20 m 2 / g) Improve the diffusion efficiency and reduce the Dy dosage. The traditional process requires adding 3 - 5% Dy, which accounts for a large proportion of the cost; controlling the particle size < 100nm ensures that the nanoparticles can be embedded in the main phase grain boundaries to avoid agglomeration and blockage of the diffusion path; Cu and Al form a low-melting-point liquid phase, and Zr inhibits grain coarsening; the impurities (such as O, C) < 0.1% to prevent the formation of non-magnetic phases (such as Al2O3). Use a three-dimensional mixer to mix the rapidly solidified flake coarse powder, Dy2O3, and Cu, Al, Zr powders under argon protection, with a rotation speed of 30 - 50 rpm and a time of 2 - 4 hours to ensure uniform dispersion; the three-dimensional motion mixing realizes the segregation-free mixing of multiple components through the rolling, rotation, and translation of the container; under argon protection, the oxygen content < 10 ppm to prevent the oxidation of active elements such as Nd and Dy; too low a rotation speed (< 20 rpm) results in uneven mixing, and too high a speed (> 60 rpm) causes cold welding of the powders. Load the mixed powder into a hydrogenation reaction furnace for hydrogen crushing. After evacuating, introduce high-purity hydrogen with a pressure of 0.1 - 0.3 MPa; during the hydrogen absorption stage, hydrogen embrittlement occurs. After Nd absorbs hydrogen, its volume expands, and the lattice stress causes the powder to self-crush; H2 penetrates to the grain boundaries to activate the grain boundaries and pre-set channels for the diffusion of Dy2O3; the hydrogen absorption rate is too low when the temperature is below 300°C, and the precipitation of the Fe phase occurs when the temperature is above 400°C; too high a pressure (> 0.5 MPa) will cause an explosion risk. Raise the temperature to 300 - 400°C for hydrogen absorption for 2 - 4 hours to hydrogen embrittle the alloy powder; then raise the temperature to 600 - 700°C again and dehydrogenate in vacuum for 1 - 2 hours to obtain a porous and loose powder; during the dehydrogenation stage, the residual hydrogen is removed to prevent the release of H2 during sintering from causing pores; the temperature of 600 - 700°C ensures the complete decomposition of NdH2 and at the same time avoids the growth of the main phase grains (< 700°C); the vacuum degree ≤ 1×10 -2 Pa promotes the rapid discharge of H2 and reduces the oxidation risk. After secondary crushing by a jet mill to the target particle size of 3 - 5μm; use the high-speed airflow to carry the powder to collide to achieve ultra-fine crushing. In the present invention, the pre-mixing of Dy2O3 and hydrogen crushing synergistically realizes the dispersion of Dy2O3 and the activation of the grain boundaries during the hydrogen crushing stage, and the Dy dosage is only 0.5 - 1.2%; different from the traditional process where Dy is added by melting in the form of metal or by post-sintering grain boundary diffusion.

[0026] This step forms an innovative production method different from the traditional step-by-step diffusion and mechanical mixing by defining the integrated process of pre-mixing Dy2O3 nanoparticles and hydrogen crushing to activate the grain boundaries, combined with the precise control of three-dimensional mixing and classification jet milling, to achieve the preparation of powders with low oxygen content and high uniformity; the Dy dosage is reduced, and the cost per ton of magnets; hydrogen crushing replaces part of the mechanical energy, reducing energy consumption; the powder uniformity and particle size control lay the foundation for high-orientation degree (≥96%) sintering.

[0027] In the production method of the present invention, step 3 realizes a high orientation degree (≥96%) and low porosity (< 2%) of the magnetic powder through a three-step process of magnetic field orientation arrangement - die pressing preforming - cold isostatic pressing densification. Through a strong magnetic field, Nd2Fe14 The c-axis of B grains is arranged along the magnetic field direction, laying the foundation for high remanence (Br); pores are eliminated through staged pressure (die pressing + isostatic pressing) to increase the density of the sintered magnet; pressure is applied while maintaining the magnetic field to inhibit grain rotation and offset and ensure orientation stability.

[0028] In the method for producing a sintered Nd-Fe-B magnet of the present invention, the specific operation of step 3 is as follows: the hydrogenated and crushed magnetic powder is uniformly filled into a molding die, and the loading density is controlled to be 2.5 - 3.0 g / cm 3 , and the hydrogenated and crushed magnetic powder (3 - 5 μm) is uniformly filled into the die cavity through a vibrating feeding device. If the loading density is too low (< 2.5 g / cm 3 ), it will cause uneven powder flow during subsequent pressing, and if the density is too high (> 3.0 g / cm 3 ), it is likely to cause the "arch effect" to form internal cavities. A density of 2.5 - 3.0 g / cm 3 can balance the powder fluidity and the requirements of pre-pressing densification, and avoid green body cracking or density gradient. Subsequently, a 1.5 T vertical static magnetic field is applied in a closed chamber for 10 - 15 seconds to orient the magnetic powder along the magnetic field direction; the magnetic field strength of 1.5 T is much higher than that of traditional processes (usually ≤ 1.2 T), and the strong magnetic field provides sufficient magnetization force to overcome the frictional resistance between the powders, so that Nd2Fe 14The c-axis of B grains is highly aligned along the magnetic field direction; 10 - 15 seconds are ensured to allow the grains to fully rotate to the magnetic field direction (the rotation relaxation time is about 5 - 8 seconds), while avoiding excessive time which may lead to increased energy consumption of the equipment. The mold is made of high-permeability material (such as pure iron), the magnetic field non-uniformity is < ±3%, and the standard deviation of the grain orientation angle decreases; the chamber is filled with argon (O2 < 10 ppm), sealed to prevent oxidation, and prevent the magnetic powder from being oxidized at high temperatures. While maintaining the magnetic field, an initial pressure of 50 - 100 MPa is applied by die pressing to form a green compact. Under the continuous action of the magnetic field, a unidirectional pressure is applied by the upper punch to preliminarily densify the loose magnetic powder and form a green compact with a certain strength; the pressure is 50 - 100 MPa. If it is too low (< 50 MPa), the orientation cannot be fixed, and if it is too high (> 100 MPa), it will cause elastic deformation of the mold and a decrease in the orientation degree. The pressure generates mechanical interlocking between the magnetic powders, reducing the grain offset during subsequent isostatic pressing; the porosity can be reduced after pre-pressing. Then it is transferred to a cold isostatic pressing equipment and kept under pressure at 200 - 400 MPa for 3 - 5 minutes. Cold isostatic pressing strengthens the pre-pressed green compact by placing it in a high-pressure container and applying isotropic pressure through a liquid medium (oil or water) to uniformly compress the powder and eliminate local density differences; the pressure is 200 - 400 MPa. When the pressure < 200 MPa, the densification is insufficient, and when > 400 MPa, it is easy to cause the green compact to crack; keeping the pressure for 3 - 5 minutes ensures that the pressure is fully transmitted to the inside of the billet, achieving a porosity < 2%. Gradient pressure is applied, and the pressure rises step by step at a rate of 50 MPa / s to avoid structural defects caused by stress mutation; a boron nitride (BN) lubricating layer is sprayed on the inner wall of the mold to optimize the lubrication of the mold, with a friction coefficient < 0.1, reducing the orientation offset, ensuring the densification of the billet and meeting the crystal orientation degree standard.

[0029] This step forms a method for preparing a green compact with high orientation and low porosity by defining a process combination of strong magnetic field (1.5 T) orientation - die pressing preforming - cold isostatic pressing strengthening, combined with the control of the loading density and pressure gradient, laying the core structural foundation for high-performance sintered NdFeB magnets. The isostatic pressing process replaces part of the hot pressing process, reducing costs while ensuring a high yield.

[0030] In the production method of the present invention, step 4 realizes the densification of the magnet, the optimization of the grain boundary phase, and the refinement of magnetic domains through three-stage heat treatment of vacuum sintering - grain boundary annealing - step aging. The first-stage high-temperature sintering eliminates pores and allows the main phase grains to fully diffuse and combine; the second-stage annealing reconstructs the grain boundaries, promotes the flow of the Cu / Al liquid phase, and forms a continuous grain boundary network; the third-stage aging regulates the magnetic domains, and through the combination of rapid cooling - slow cooling, the internal stress is eliminated and the magnetic domains are refined to ≤300 nm, improving the coercivity.

[0031] In the production method of the sintered NdFeB magnet of the present invention, the specific operation of the said step 4 is as follows: Primary sintering: Vacuum sintering at 1050 - 1080 °C for 2 - 3 hours, introducing high-purity argon with a flow rate controlled at 50 - 100 mL / min to inhibit Nd volatilization; High-temperature sintering means that the grains of the Nd2Fe 14 B main phase diffuse and connect at a temperature close to the melting point (the melting point of Nd is 1024 °C), the pores close, and the density increases from 4.2 g / cm 3 of the green compact to > 7.5 g / cm 3 ; Argon protection inhibits Nd volatilization through a dynamic slightly positive pressure (0.1 - 0.3 kPa); When the temperature is lower than 1050 °C, densification is insufficient, and when it is higher than 1080 °C, abnormal grain growth (> 8 μm) occurs.

[0032] Secondary sintering: After the primary sintering is completed, cool down to 900 - 950 °C at a rate of 5 °C / min, switch to an inert gas, and perform low-temperature annealing for 3 - 5 hours to promote grain boundary phase reconstruction; Low-temperature annealing means that Cu (melting point 1083 °C) and Al (660 °C) form a eutectic liquid phase (the Cu - Al eutectic point is 548 °C) at 900 - 950 °C, filling the grain boundary gaps and forming a continuous grain boundary phase with a thickness of 1 - 3 nm; H2 in the inert gas reduces the grain boundary oxides (such as Nd2O3), enhancing the grain boundary wettability and increasing the coverage rate. Grain boundary diffusion is completed synchronously. Dy2O3 nanoparticles are reduced to Dy atoms by H2 during the annealing stage and diffuse along the grain boundaries to the surface layer of the main phase, forming a (Nd,Dy)2Fe 14 B shell layer, and the coercivity is increased; The cooling rate is 5 °C / min to avoid grain boundary cracking due to thermal stress.

[0033] Tertiary aging: Two-stage aging at 500 - 600 °C, with fast cooling first and then slow cooling; Among them, in the first-stage aging, the magnet is quickly cooled to 600 °C at a rate of 20 °C / min and held for 1 - 2 hours to eliminate internal stress and stabilize the magnetic domain structure; The first-stage aging quickly freezes the high-temperature magnetic domain structure, eliminates the sintering stress, and prevents grain coarsening; The fast cooling mechanism is that the cooling rate of 20 °C / min skips the α-Fe phase precipitation window (800 - 600 °C) to avoid the formation of soft magnetic phases. In the second-stage aging, continue to cool slowly to 500 °C at a rate of 2 °C / min and hold for 2 - 4 hours to further refine the magnetic domain size and increase the coercivity; Argon is introduced for protection throughout the process, and finally cooled to room temperature with the furnace; Slow cooling promotes the migration of magnetic domain walls, refines the magnetic domain size to 200 - 300 nm, and increases the coercivity; Argon protection prevents grain boundary oxidation at high temperatures.

[0034] This step forms a production method for sintered NdFeB magnets with low heavy rare earth, high coercivity, and high stability by defining the process parameter combination of three-stage step heat treatment (high-temperature densification - medium-temperature grain boundary reconstruction - low-temperature magnetic domain refinement), combining dynamic gas protection (argon and H2 reduction) with fast cooling - slow cooling synergistic aging, breaking through the technical limitations of traditional single-stage sintering. The high coercivity and low loss magnetic rate extend the magnet life, and the argon circulation system reduces gas consumption and reduces the process carbon footprint.

[0035] The composite coating of the present invention realizes the long-term corrosion resistance of the magnet under the premise of low thickness and high protection through the synergistic effect of physical shielding (Al layer) and chemical protection (epoxy / SiO2), while avoiding the environmental pollution problems of traditional electroplating processes (such as Ni-Cu-Ni plating). Among them, the Al ion coating with a thickness of 2-5 μm forms a dense metal barrier to block the physical penetration of corrosion media such as Cl - , H2O, etc.; the epoxy resin nano-SiO2 coating with a thickness of 10-15 μm delays the electrochemical corrosion reaction through the "labyrinth effect" of nano-particles and the chemical inertness of the resin; a thickness balance is achieved among the protection performance, cost, and magnet size accuracy.

[0036] In the production method of the sintered Nd-Fe-B magnet of the present invention, in step 5, the Al ion coating is 2-5 μm, and the epoxy resin nano-SiO2 composite coating is 10-15 μm. The Al ion coating can effectively isolate the penetration of oxygen and moisture; the standard electrode potential of Al (-1.66V) is lower than that of Fe (-0.44V), which acts as a sacrificial anode to delay the corrosion of the substrate; Al has a high thermal conductivity, which is beneficial to the heat dissipation of the magnet and reduces the risk of high-temperature demagnetization. When the thickness is <2 μm, there are local pinholes in the coating, and substrate rust appears after the salt spray test <500 h; when the thickness >5 μm, the internal stress in the Al layer increases, which easily leads to cracking or peeling of the coating; an overly thick metal layer causes interface peeling due to the difference in thermal expansion coefficients at high temperatures. In the epoxy resin nano-SiO2 composite coating, the epoxy resin cross-linked network resists the erosion of acids, alkalis, and salts; 30-50 nm nano-SiO2 particles fill the micropores formed by the curing shrinkage of the resin; the hardness of the coating is increased to buffer external force impacts and prevent scratching of the Al layer. When the thickness is <10 μm, the coating is difficult to completely cover the micro-defects on the magnet surface, and pitting corrosion appears after the salt spray test for 600 h; when the thickness >15 μm, the internal stress of the coating causes warping, and the curing time is prolonged, resulting in a decrease in production efficiency; an overly thick coating affects the assembly accuracy of the magnet steel in the motor.

[0037] This step forms a surface protection solution with high corrosion resistance, strong adhesion, and environmental protection advantages by defining the double-layer structure and thickness range of the Al ion coating and the epoxy resin nano-SiO2 composite coating, combining PVD deposition and nano-dispersion processes, replacing traditional electroplating technology, and adapting to high-end permanent magnet application scenarios. The design of the composite coating with this thickness minimizes the impact on the magnet size and magnetic properties while ensuring the protection performance, and the process cost is lower than that of electroplating, becoming an important technical support for the industrialization of the magnet of the present invention.

[0038] In summary, the present invention has the following beneficial effects: 1. The present invention introduces Dy2O3 nanoparticles through the grain boundary diffusion technology. Only 0.5 - 1.2% of Dy2O3 needs to be added, which significantly reduces the consumption of heavy rare earths compared with the traditional process that adds 3 - 5% of heavy rare earth elements in the smelting stage. By combining the ternary synergy of Pr - Co - Ga to optimize the anisotropy field of the main phase and grain refinement, high - performance indicators are achieved under low Dy conditions. This not only reduces the raw material cost but also decreases the dependence on scarce and expensive heavy rare earth resources. At the same time, it avoids the volatilization and segregation problems of heavy rare earth elements during high - temperature sintering, effectively solving the problem of magnetic property deterioration caused by uneven distribution of heavy rare earths in the prior art. 2. The main - phase alloy adopts Nd a Pr b Fe c B d Co e Ga f composition system. By limiting the content range of each element and combining the synergy of Pr, Co, and Ga, the grain structure of the main phase is optimized. Under the synergistic regulation of the grain - boundary - phase additives Cu, Al, and Zr, the coercivity and corrosion resistance of the magnet are improved. At the same time, the multi - stage sintering process realizes magnet densification, grain - boundary - phase reconstruction, and magnetic - domain refinement in sequence, significantly improving the key magnetic property indicators such as remanence, coercivity, and maximum energy product of the magnet, meeting the requirements of high - performance magnets in high - end permanent - magnet application fields. 3. The multi - element composite plating technology is adopted to deposit a 2 - 5μm Al - ion plating layer and a 10 - 15μm epoxy resin - nano - SiO2 composite coating on the magnet surface in sequence. The Al - ion plating layer forms a dense metal barrier, effectively blocking the penetration of corrosive media, while the epoxy resin - nano - SiO2 composite coating fills the micropores with nano - SiO2 particles, enhancing the density and protective performance of the coating. Compared with the traditional electroplating process, the salt - spray resistance performance is greatly improved, and the environmental pollution problems generated during electroplating are avoided, realizing green manufacturing. 4. The present invention uses a three - stage step - by - step treatment of high - temperature sintering at 1050 - 1080°C, medium - temperature annealing at 900 - 950°C, and two - stage aging at 500 - 600°C to solve the problems of magnet densification, grain - boundary - phase reconstruction, and magnetic - domain refinement in sequence. High - temperature sintering eliminates pores, medium - temperature annealing promotes the flow of the Cu - Al liquid phase to form a continuous grain - boundary network, and at the same time completes the grain - boundary diffusion of Dy2O3. Low - temperature aging eliminates internal stress and refines magnetic domains and improves coercivity through a combination of rapid cooling and slow cooling. The comprehensive performance is superior to the traditional single - stage sintering process. 5. The production method of the present invention integrates five core steps: rapid quenching and sheet making, hydrogen crushing and mixing, magnetic field forming, multi-stage treatment, and composite coating. By directly hydrogenating and crushing the rapidly quenched sheets, multiple traditional processes such as ingot casting and powder making are omitted, reducing energy consumption. The prepared nanocrystalline sheets provide uniform and fine raw materials for subsequent processes. The hydrogen crushing and mixing achieve uniform distribution of grain boundary phases and rare earth elements. The strong magnetic field forming combined with high pressure improves the orientation degree, and the multi-stage sintering treatment precisely regulates the microstructure of the magnet. The entire process flow is highly coordinated, reducing multiple processes in traditional processes, lowering production energy consumption and costs, while improving production efficiency and product consistency, which is conducive to large-scale industrial production. Specific embodiments

[0039] This specific embodiment is only an explanation of the present invention and does not limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0040] Example 1

[0041] Step 1. Rapid quenching and sheet making: Weigh high-purity metal raw materials (mol%) according to the main phase alloy composition ratio: Nd 30, Pr 0.5, Fe 66, B 1.2, Co 2, Ga 0.3, and place them in a vacuum induction melting furnace. Use vacuum rapid quenching technology to prepare Nd-Fe-B rapid solidification sheets. The melt cooling rate is 1.2×10 5 K / s, and the sheet thickness is 0.25 mm to obtain a nanocrystalline structure; Step 2. Hydrogen crushing and mixing: Mix the rapid solidification sheets, 0.8% Dy2O3 nanoparticles, and 0.5% Cu, 0.3% Al, 0.15% Zr powders in proportion, and crush them to a particle size of 4 μm in a hydrogen atmosphere; Step 3. Magnetic field forming: Press and form in a 1.5 T vertical magnetic field, and apply 300 MPa isostatic pressure at the same time to increase the orientation degree to 97%; Step 4. Multi-stage treatment: The first-stage sintering is vacuum sintering at 1060 °C for 2 hours, the second-stage sintering is annealing at 930 °C for 4 hours, and the third-stage aging is heat preservation at 600 °C for 1.5 hours and slow cooling to 500 °C for heat preservation for 3 hours; Step 5. Composite coating: Adopt a multi-element composite plating technology to sequentially deposit a 4-μm Al ion coating and a 12-μm epoxy resin nano-SiO2 composite coating on the surface of the magnet to improve corrosion resistance and obtain a high-performance sintered Nd-Fe-B magnet.

[0042] Example 2

[0043] Step 1. Rapid quenching and sheet making: Weigh high-purity metal raw materials according to the main-phase alloy composition ratio (mol%): Nd 28, Pr 0.1, Fe 70.7, B 0.5, Co 1, Ga 0.1. Place them in a vacuum induction melting furnace and use the vacuum rapid quenching technology to prepare Nd-Fe-B rapidly solidified sheets. The melt cooling rate is 1.0×10 5 K / s, the sheet thickness is 0.2 mm, and a nanocrystalline structure is obtained; Step 2. Hydrogen crushing and mixing: Mix the rapidly solidified sheets, 0.5% Dy2O3 nanoparticles, and 0.2% Cu, 0.1% Al, 0.05% Zr powders in proportion and crush them to a particle size of 3 μm in a hydrogen atmosphere; Step 3. Magnetic field forming: Mould and form in a 1.5 T vertical magnetic field, and apply an isostatic pressure of 200 MPa at the same time to increase the orientation degree to 96.5%; Step 4. Multi-stage treatment: The first-stage sintering is vacuum sintering at 1050 °C for 2 hours, the second-stage sintering is annealing at 900 °C for 3 hours, and the third-stage aging is heat preservation at 600 °C for 1 hour and slow cooling to 500 °C for heat preservation for 2 hours; Step 5. Composite coating: Adopt the multi-element composite plating technology to sequentially deposit a 2-μm Al ion coating and a 10-μm epoxy resin nano-SiO2 composite coating on the surface of the magnet to improve the corrosion resistance and obtain a high-performance sintered Nd-Fe-B magnet.

[0044] Example 3

[0045] Step 1. Rapid quenching and sheet making: Weigh high-purity metal raw materials according to the main-phase alloy composition ratio (mol%): Nd 26, Pr 1.0, Fe 65, B 2.0, Co 5, Ga 1.0. Place them in a vacuum induction melting furnace and use the vacuum rapid quenching technology to prepare Nd-Fe-B rapidly solidified sheets. The melt cooling rate is 1.5×10 5 K / s, the sheet thickness is 0.3 mm, and a nanocrystalline structure is obtained; Step 2. Hydrogen crushing and mixing: Mix the rapidly solidified sheets, 1.2% Dy2O3 nanoparticles, and 0.8% Cu, 0.5% Al, 0.3% Zr powders in proportion and crush them to a particle size of 5 μm in a hydrogen atmosphere; Step 3. Magnetic field forming: Mould and form in a 1.5 T vertical magnetic field, and apply an isostatic pressure of 400 MPa at the same time to increase the orientation degree to 97%; Step 4. Multi-stage treatment: The first-stage sintering is vacuum sintering at 1080 °C for 3 hours, the second-stage sintering is annealing at 950 °C for 5 hours, and the third-stage aging is heat preservation at 600 °C for 2 hours and slow cooling to 500 °C for heat preservation for 4 hours; Step 5. Composite coating: Using the multi-component composite plating technology, a 5-μm Al ion plating layer and a 15-μm epoxy resin nano-SiO2 composite coating are sequentially deposited on the surface of the magnet to improve the corrosion resistance, and a high-performance sintered NdFeB magnet is prepared.

[0046] Example 4

[0047] Steps 1 and 2 are the same as those in Example 2, and steps 3, 4, and 5 are the same as those in Example 3, to obtain a high-performance sintered NdFeB magnet.

[0048] Example 5

[0049] Steps 1 and 2 are the same as those in Example 3, and steps 3, 4, and 5 are the same as those in Example 2, to obtain a high-performance sintered NdFeB magnet.

[0050] Comparative Example 1 Step 1. Traditional ingot casting: The metal raw materials (mol%) after melting according to the main phase composition: Nd 30.8, Pr 0, Fe 68, B 1.2, Co 0, Ga 0 are cast into an ingot under a protective atmosphere, and the cooling rate is 10 3 K / s, to obtain grains larger than 50 μm; Step 2. Mechanical crushing: The ingot is mechanically crushed to obtain a powder with a particle size of 10 μm; Step 3. Magnetic field forming: Forming is carried out in a magnetic field of 1.0 T, and isostatic pressure of 100 MPa is applied to obtain an orientation degree of 92%; Step 4. Single-stage sintering: Single-stage sintering is carried out at 1100 °C for 4 hours; Step 5. Surface electroplating: Using the traditional Ni-Cu-Ni electroplating process with a total thickness of 20 μm, to obtain the finished sintered NdFeB magnet.

[0051] Comparative Example 2 Compared with Example 1, in the hydrogenation and mixing step, Cu, Al, and Zr powders are not added, and the remaining steps are the same as those in Example 1, to obtain the finished sintered NdFeB magnet.

[0052] Comparative Example 3 Compared with Example 1, in the multi-stage treatment step, the low-temperature two-stage aging treatment is omitted, and only high-temperature sintering and medium-temperature annealing are carried out, and the remaining steps are the same as those in Example 1, to obtain the finished sintered NdFeB magnet.

[0053] Performance test Perform performance tests on the high-performance sintered NdFeB magnets prepared in Examples 1-5 and the finished sintered NdFeB magnets prepared in Comparative Examples 1-3, including magnetic properties, thermal stability, corrosion resistance, and mechanical property tests.

[0054] 1. Magnetic property test 1.1 Residual Magnetism (Br) Detection method: According to the standard of GB / T 3834.1-2022, use a gaussmeter to measure the residual magnetic induction intensity of the magnet after saturation magnetization. Place the magnet near the probe of the gaussmeter, ensure that the measurement surface of the magnet is in close contact with the surface of the probe, and read and record the residual magnetism value displayed by the gaussmeter. The higher the residual magnetism, the stronger the ability of the magnet to maintain magnetism without an external magnetic field.

[0055] 1.2 Coercivity (Hcj) Detection method: According to the standard of GB / T 3834.2-2022, use a vibrating sample magnetometer (VSM) to measure the reverse magnetic field intensity required to reduce the magnetization intensity of the magnet to zero. Fix the magnet on the sample holder of the VSM, ensure that the measurement direction of the magnet is consistent with the magnetic field direction, run the VSM equipment and record the coercivity value. The higher the coercivity, the stronger the demagnetization resistance ability of the magnet.

[0056] 1.3 Maximum Energy Product (BH)max Detection: Refer to the standard of GB / T 3834.3-2022, by measuring the residual magnetism (Br) and coercivity (Hcj) of the magnet, calculate the maximum energy product using the formula (BH)max = Br × Hcj / 2. This index combines the factors of residual magnetism and coercivity, reflecting the ability of the magnet to store magnetic energy.

[0057] 2. Thermal Stability Test 2.1 Operating Temperature Range Detection method: According to the standard of IEC 60068-2-14:2019, place the magnet in a temperature-adjustable constant temperature oven, gradually increase the temperature from low temperature (-40°C) to high temperature (200°C), keep it for 2 hours at each temperature point, and measure the change of the magnetic properties of the magnet. Record the temperature point at which the magnetic properties of the magnet start to decline significantly as the maximum operating temperature. The magnet should be able to work normally within this temperature range, and the magnetic properties should not change significantly.

[0058] 2.2 Retention Rate of Energy Product Detection method: According to the standard of GB / T 3834.4-2022, place the magnet at 150°C for 1000 hours, then measure the energy product of the magnet and compare it with the initial value to calculate the retention rate of the energy product and evaluate its high-temperature stability.

[0059] 3. Corrosion Resistance Test 3.1 Salt Spray Test Detection method: According to the standard of GB / T 10125-2022, place the magnet in a salt spray test chamber, use a 5% NaCl solution, and continuously spray at a temperature of 35°C ± 2°C for 1000 hours. During the test, observe whether there are corrosion, rust and other phenomena on the surface of the magnet. It is qualified if there is no obvious corrosion and no red rust on the surface of the magnet.

[0060] 3.2 Damp heat aging test Test method: Refer to IEC 60068-2-67 standard, place the magnet specimen in a thermostatic and humid test chamber, set the temperature to 85°C ± 2°C and the relative humidity to 85% ± 3%, and continuously expose it for 1000 hours; take samples every 240 hours during the test, use electrochemical impedance spectroscopy (EIS) to detect the coating impedance value under the same conditions, and observe whether there are bubbles, cracks or rust on the surface. At the same time, test the irreversible magnetic loss rate of the magnet (compare the demagnetization curves at 150°C), and the impedance value > 1×109 Ω·cm 2 And the magnetic loss ≤ 3% is qualified.

[0061] 4. Mechanical property test 4.1 Density measurement Test method: Refer to GB / T 3834.5-2022 standard, use a densitometer to measure the density of the magnet. Immerse the magnet in the measuring liquid of the densitometer and read the indication of the densitometer to understand the compactness of its internal structure.

[0062] 4.2 Hardness test Test method: According to GB / T 230.1-2018 standard, use a Rockwell hardness tester to measure the surface hardness of the magnet. Place the magnet on the workbench of the hardness tester, apply the specified test force, and read the hardness value after maintaining for a certain time. Magnets with high hardness have better wear resistance and scratch resistance.

[0063] 4.3 Flexural strength test Test method: According to GB / T 3834.6-2022 standard, make the magnet into a standard bending specimen, place it on the supports of a universal material testing machine, apply a bending stress to the specimen at a specified loading speed until the specimen breaks, record the maximum load, calculate the flexural strength, and evaluate the mechanical strength and toughness of the magnet.

[0064] 5. Results and analysis Table 1 Summary of the performance test results of the sintered NdFeB magnet products in each group

[0065] Results analysis: The remanence values of Examples 1-5 are between 1.35 - 1.39 T, which are relatively close as a whole and are all higher than the remanence values of Comparative Examples 1-3, which are 1.32 - 1.34 T. This indicates that the magnets prepared by the method of the present invention have a strong ability to maintain magnetism without an external magnetic field. Among them, the remanence of Example 4 is the highest, which is 1.39 T.

[0066] The coercivity values of Examples 1-5 are significantly higher than those of Comparative Examples 1-3. The coercivity of Examples 1-5 is between 1570-1620 kA / m, while that of Comparative Examples 1-3 is between 1200-1280 kA / m, indicating that the demagnetization resistance of the magnets prepared by the method of the present invention is significantly enhanced. Among them, the coercivity of Example 4 is the highest, reaching 1620 kA / m. This is mainly due to the synergistic regulation of Dy2O3 nanoparticles introduced by the grain boundary diffusion technology and grain boundary phase additives Cu, Al, and Zr, which effectively improves the anisotropy field of the magnet, thereby greatly increasing the coercivity.

[0067] The maximum energy product of Examples 1-5 is between 252-265 kJ / m³, which is significantly higher than that of Comparative Examples 1-3 (220-230 kJ / m³). The maximum energy product is a comprehensive reflection of the remanence and coercivity. The magnets prepared by the method of the present invention have a higher maximum energy product, indicating that they have a stronger ability to store magnetic energy. Among them, the maximum energy product of Example 4 is the highest, reaching 265 kJ / m³.

[0068] The maximum operating temperature of Examples 1-5 is between 170-185 °C, all of which are higher than that of Comparative Examples 1-3 (150-165 °C), indicating that the magnets prepared by the method of the present invention can still maintain good magnetic properties in a high-temperature environment and have a wider operating temperature range. Among them, the maximum operating temperature of Example 3 is the highest, reaching 185 °C.

[0069] The magnetic energy product retention rate of Examples 1-5 after being placed at 150 °C for 1000 hours is between 90%-93%, while that of Comparative Examples 1-3 is between 75%-85%. This shows that during the long-term use of the magnets prepared by the method of the present invention at high temperature, the attenuation of the magnetic energy product is small and the high-temperature stability is better. Among them, the magnetic energy product retention rate of Example 4 is the highest, reaching 93%.

[0070] The salt spray test time of Examples 1-5 is between 970-1020 hours, which is much higher than that of Comparative Examples 1-3 (450-500 hours), indicating that the magnets prepared by the method of the present invention have stronger corrosion resistance in a salt spray environment and better surface protection performance. Among them, the salt spray test time of Example 4 is the longest, reaching 1020 hours.

[0071] The impedance values of the damp heat aging tests of Examples 1-5 are all greater than 1×10 9 Ω·cm², and the magnetic loss rates of the damp heat aging are all less than 3%. While the impedance values of Comparative Examples 1-3 are between 4×10 8 -5×10 8 Ω·cm², and the magnetic loss rates are between 3.5%-5%. This shows that the coating protection performance of the magnets prepared by the method of the present invention is better in a damp heat environment, and the irreversible magnetic loss rate of the magnets is lower. Among them, the impedance value of the damp heat aging test of Example 1 is the largest, and the magnetic loss rate of the damp heat aging is the smallest, being 2%.

[0072] The density of Examples 1-5 is between 7.45-7.55 g / cm 3 and is overall higher than that of Comparative Examples 1-3 which is 7.3-7.4 g / cm 3 , indicating that the internal structure of the magnet prepared by the method of the present invention is denser.

[0073] The hardness of Examples 1-5 is between 60-63 HRC, higher than that of Comparative Examples 1-3 which is 55-57 HRC, indicating that the magnet prepared by the method of the present invention has better wear resistance and scratch resistance.

[0074] The flexural strength of Examples 1-5 is between 340-360 MPa, higher than that of Comparative Examples 1-3 which is 300-320 MPa, indicating that the magnet prepared by the method of the present invention has higher mechanical strength and toughness.

[0075] By introducing Dy2O3 nanoparticles through the grain boundary diffusion technology, optimizing the main phase alloy composition, adding grain boundary phase additives, and adopting a multi-stage sintering process and a composite coating technology, etc., the present invention significantly improves the magnetic properties, thermal stability, corrosion resistance and mechanical properties of the sintered Nd-Fe-B magnet. The comprehensive performance of Examples 1-5 is better than that of Comparative Examples 1-3. Among them, Example 4 is the most prominent in key indicators such as remanence, coercivity, maximum magnetic energy product, salt spray test time, magnetic energy product retention rate, etc., indicating that the high-performance sintered Nd-Fe-B magnet prepared by the method of the present invention has broad application prospects and significant advantages.

Claims

1. A production method of a high-performance sintered neodymium iron boron magnet, characterized in that, It includes the following steps: Step 1. Rapid quenching and flaking: Weigh high-purity metal raw materials Nd, Pr, Fe, B, Co, and Ga, and prepare Nd-Fe-B rapid solidification flakes through vacuum rapid quenching technology to obtain a nanocrystalline structure; Step 2. Hydrogenation pulverization and mixing: Mix and crush the rapid solidification flakes, Dy2O3 nanoparticles, and Cu, Al, Zr powders in hydrogen to 3 - 5 μm to optimize the grain boundary phase distribution; Step 3. Magnetic field forming: Utilize the combined action of a 1.5T vertical magnetic field and 200 - 400 MPa isostatic pressing to achieve high orientation degree of magnetic powder and densification of the green body; Step 4. Multi-stage treatment: Adopt three-stage heat treatment of sintering at 1050 - 1080 °C, annealing at 900 - 950 °C, and aging at 500 - 600 °C to synergistically improve the density, coercivity, and high-temperature stability of the magnet; Step 5. Composite coating: Adopt a multi-element composite plating technology to sequentially deposit an Al ion coating and an epoxy resin SiO2 composite coating on the surface of the magnet to obtain a high-performance sintered Nd-Fe-B magnet.

2. The production method of the sintered neodymium iron boron magnet according to claim 1, characterized in that, It includes the following steps: Step 1. Rapid quenching to form flakes: Weigh high-purity metal raw materials Nd, Pr, Fe, B, Co, and Ga according to the main-phase alloy composition ratio, place them in a vacuum induction melting furnace, and use the vacuum rapid quenching technology to prepare Nd-Fe-B rapid solidification flakes with a thickness ≤ 0.3 mm, controlling the cooling rate ≥ 10 5 K / s to obtain a nanocrystalline structure; where a, b, c, d, e, and f are mass percentages, 26 ≤ a ≤ 32, 0.1 ≤ b ≤ 1.0, 65 ≤ c ≤ 71, 0.5 ≤ d ≤ 2.0, 1 ≤ e ≤ 5, 0.1 ≤ f ≤ 1.0, and a + b + c + d + e + f = 100; Step 2. Hydrogenation pulverization and mixing: Mix the rapid solidification flakes, 0.5 - 1.2% Dy2O3 nanoparticles, and 0.2 - 0.8% Cu, 0.1 - 0.5% Al, 0.05 - 0.3% Zr powders in proportion, and crush them to a particle size of 3 - 5 μm in a hydrogen atmosphere; Step 3. Magnetic field forming: Mold and form in a 1.5T vertical magnetic field, and simultaneously apply 200 - 400 MPa isostatic pressing to increase the orientation degree to more than 96%; Step 4. Multi-stage treatment: Through three-stage stepped treatment of high-temperature sintering at 1050 - 1080 °C, medium-temperature annealing at 900 - 950 °C, and low-temperature aging at 500 - 600 °C, sequentially achieve densification of the magnet, reconstruction of the grain boundary phase, and refinement of magnetic domains, and simultaneously improve the coercivity and high-temperature stability; Step 5. Composite coating: Adopt a multi-element composite plating technology to sequentially deposit an Al ion coating and an epoxy resin nano-SiO2 composite coating on the surface of the magnet to improve the corrosion resistance and obtain a high-performance sintered Nd-Fe-B magnet.

3. The production method of the sintered neodymium iron boron magnet according to claim 1, characterized in that Step 1 specifically includes the following operations: Weigh high-purity metal raw materials Nd, Pr, Fe, B, Co, and Ga according to the main phase composition, with a purity of ≥99.9%, and place them in a vacuum induction melting furnace; evacuate to ≤5×10 -3 Pa, introduce high-purity argon with a purity of 99.999% as a protective atmosphere, and heat up to 1550 - 1600 °C to melt into a uniform alloy liquid; spray the molten alloy liquid onto the surface of a high-speed rotating water-cooled copper roll through a quartz nozzle, with a rotational speed of 20 - 30 m / s, and the temperature of the copper roll is controlled at 15 - 25 °C; by adjusting the rotational speed of the copper roll and the melt spraying pressure, the alloy liquid solidifies at a cooling rate of ≥10 5 K / s to form a continuous thin sheet with a thickness of ≤0.3 mm; after the thin sheet is peeled off, it is crushed and screened to obtain flaky particles with a particle size of ≤2 mm, which are stored in an argon protection box for standby.

4. The production method of the sintered neodymium iron boron magnet according to claim 1, characterized in that, The specific operations of the said Step 2 include the following: Mechanically crush the Nd-Fe-B main phase alloy rapid solidification flakes to initially coarsen the powder to a particle size ≤ 500 μm; Weigh Dy2O3 nanoparticles with a particle size of 50 - 100 nm and Cu, Al, Zr metal powders with a purity ≥ 99.9% in proportion for standby; Use a three-dimensional mixer to mix the rapid solidification flake coarse powder, Dy2O3, and Cu, Al, Zr powders under argon protection, with a rotation speed of 30 - 50 rpm and a time of 2 - 4 hours to ensure uniform dispersion; Load the mixed powder into a hydrogenation reaction furnace for hydrogen crushing, evacuate and then introduce high-purity hydrogen, with a pressure of 0.1 - 0.3 MPa; Heat up to 300 - 400 °C to absorb hydrogen for 2 - 4 hours to embrittle the alloy powder; Heat up again to 600 - 700 °C and dehydrogenate in vacuum for 1 - 2 hours to obtain a porous and loose powder; Crush it to the target particle size of 3 - 5 μm through a jet mill for the second time.

5. The production method of the sintered neodymium iron boron magnet according to claim 1, wherein, Step 3 specifically includes the following operations: uniformly filling the hydrogen-crushed magnetic powder into a molding die, and controlling the loading density to be 2.5-3.0 g / cm 3 , then applying a 1.5T vertical static magnetic field in a closed chamber for 10-15 seconds to orient the magnetic powder along the magnetic field direction; while maintaining the magnetic field, applying an initial pressure of 50-100 MPa through molding to form a green body, and then transferring it to a cold isostatic pressing device to hold the pressure at 200-400 MPa for 3-5 minutes to ensure the densification of the green body and the crystal orientation degree meets the standard.

6. The production method of the sintered neodymium-iron-boron magnet according to claim 1, wherein The specific operations of the said Step 4 include the following: Primary sintering: Vacuum sinter at 1050 - 1080 °C for 2 - 3 hours, introduce high-purity argon gas, control the flow rate at 50 - 100 mL / min to inhibit Nd volatilization; Secondary sintering: After the primary sintering is completed, cool down to 900 - 950 °C at a rate of 5 °C / min, switch to inert gas, and perform low-temperature annealing for 3 - 5 hours to promote grain boundary phase reconstruction; Tertiary aging: Two-stage aging at 500 - 600 °C, with rapid cooling first and then slow cooling; among them, in the first-stage aging, the magnet is rapidly cooled to 600 °C at 20 °C / min and held for 1 - 2 hours to eliminate internal stress and stabilize the magnetic domain structure; in the second-stage aging, continue to slow cool to 500 °C at 2 °C / min and hold for 2 - 4 hours to further refine the magnetic domain size and improve the coercivity; argon gas is introduced for protection throughout the process, and finally cooled to room temperature with the furnace.

7. The production method of the sintered neodymium iron boron magnet according to claim 1, characterized in that, In step 5, the Al ion coating is 2 - 5 μm, and the epoxy resin nano-SiO2 composite coating is 10 - 15 μm.

8. The production method of the sintered neodymium iron boron magnet according to claim 1, characterized in that, One of the basic components of the high-performance sintered NdFeB magnet produced by it includes a main-phase alloy, a grain-boundary-phase additive, and a rare-earth supplementary phase. The main-phase alloy is Nd a Pr b Fe c B d Co e Ga f , where a, b, c, d, e, and f are mass percentages, 26 ≤ a ≤ 32, 0.1 ≤ b ≤ 1.0, 65 ≤ c ≤ 71, 0.5 ≤ d ≤ 2.0, 1 ≤ e ≤ 5, 0.1 ≤ f ≤ 1.0, and a + b + c + d + e + f = 100; the grain-boundary-phase additive includes 0.2-0.8% Cu, 0.1-0.5% Al, and 0.05-0.3% Zr; the rare-earth supplementary phase includes 0.5-1.2% Dy2O3 nanoparticles.

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