Preparation method and device of sintered neodymium-iron-boron permanent magnet

Abstract

The invention discloses a preparation method and device of a sintered neodymium-iron-boron permanent magnet, and relates to the technical field of permanent magnet material preparation.The method comprises the steps that rare earth tailings are pretreated, La / Ce mixed rare earth oxide is extracted, and a low-heavy rare earth mixed raw material is prepared; then carrying out double-stage sintering to prepare an ingot; coating closed-loop anti-oxidation powder preparation is carried out, and high-purity fine powder is obtained by adjusting and controlling parameters through an algorithm; then forming the matrix and carrying out laser cladding on a heavy rare earth alloy layer; finally, gradient heat treatment is carried out, the magnet is ground and polished after tempering and cooling, large-scale green production is achieved, multiple technologies are integrated to construct an efficient preparation system, rare earth tailings are utilized in a resource mode, and the proportion design of low heavy rare earth is achieved; dynamically regulating and controlling parameters to prevent oxidation in the powder preparation process; and forming and cladding are synergistically optimized, the stress uniformity is improved through gradient heat treatment, efficiency and quality are both considered, and a feasible path is provided for large-scale green production of the high-performance sintered neodymium-iron-boron permanent magnet.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and device of a sintered neodymium-iron-boron permanent magnet. BACKGROUND

[0002] The sintered neodymium-iron-boron permanent magnet occupies an important position in many fields such as new energy vehicles, electronic devices and aerospace due to excellent magnetic properties, and becomes an indispensable key material in modern industry. With the development of related industries towards high efficiency and miniaturization, higher requirements are put forward for the magnetic properties, stability and cost control of the permanent magnet. As the core raw material for preparing the sintered neodymium-iron-boron permanent magnet, the rational utilization and efficient recovery of rare earth resources directly affect the sustainable development of the industry. At present, the industry generally improves product performance by optimizing raw material ratio and improving preparation process, and at the same time, strives to reduce the amount of scarce heavy rare earth, realizes the dual goals of resource saving and cost optimization, and the innovation and upgrading of related preparation technology become the core driving force for the development of the industry.

[0003] The traditional preparation technology has many limitations in actual application. In terms of raw materials, it depends on primary rare earth ore, and the utilization rate of secondary resources such as rare earth tailings is low, which not only causes resource waste but also increases raw material cost. In the powder preparation process, the powder is easy to oxidize when it contacts with air, which reduces the purity of the powder and affects the final performance of the magnet. The traditional oxidation prevention and control means is passive protection, which is difficult to dynamically adjust according to real-time working conditions. In the forming and sintering link, it is often difficult to balance the density of the matrix and the uniformity of the microstructure. Some technologies use the method of adding heavy rare earth in the whole to improve the magnetic properties, which not only aggravates the consumption of scarce resources, but also may lead to uneven stress distribution in the magnet. The control effect of the post-processing process on the surface quality and dimensional accuracy is limited, which is difficult to meet the strict requirements of high-end application scenarios. These problems jointly restrict the performance improvement and large-scale green production of the sintered neodymium-iron-boron permanent magnet. SUMMARY

[0004] The purpose of the present application is to make up for the shortcomings of the prior art, and provide a preparation method and device of a sintered neodymium-iron-boron permanent magnet. Light rare earth oxide is extracted from rare earth tailings pretreatment, and a low-heavy rare earth mixed raw material is formed by matching multiple alloy elements. Through the coherent process of two-stage sintering ingot, coating closed-loop anti-oxidation powder, two-way pressing forming, laser cladding heavy rare earth layer and gradient heat treatment, the precise regulation and control of the whole process of magnet preparation is realized. The oxidation risk assessment algorithm is used to dynamically prevent and control oxidation in the powder preparation process. The forming and cladding process cooperatively improves the density and local performance of the magnet. The post-processing guarantees the surface quality and dimensional accuracy of the product. The whole method reduces the dependence on scarce heavy rare earth, balances resource recycling, cost control and high performance of the product, and adapts to the application requirements of multiple fields. The related device provides stable support for the process landing.

[0005] The application provides the following technical scheme to solve the above technical problems: on the one hand, a preparation method of sintered neodymium-iron-boron permanent magnet, the specific steps of the preparation method are as follows: S1, tailing pretreatment and raw material preparation: rare earth tailings are selected, crushed, ground, acid leached, extracted, back-extracted, calcined to extract La / Ce mixed rare earth oxides; Nd, La / Ce mixed rare earth oxides, Fe, B and Co, Cu and Al alloy elements are weighed according to the proportion and uniformly mixed to obtain low heavy rare earth mixed raw materials; S2, two-stage sintering ingot preparation: the low heavy rare earth mixed raw materials are placed in a segmented temperature control vacuum sintering furnace, vacuumized and sequentially subjected to low-temperature pre-sintering and high-temperature densification sintering, and the rare earth alloy ingot is obtained after cooling; S3, coating closed-loop anti-oxidation powder preparation: a rare earth composite coating is coated on the surface of the rare earth alloy ingot and solidified; the coated alloy ingot is placed in a hydrogen crushing-airflow milling closed loop system, argon is filled, hydrogen crushing and airflow milling are carried out, the parameters are regulated and controlled through an oxidation risk evaluation algorithm during the powder preparation process, and high-purity fine powder is obtained; S4, substrate forming and laser cladding: the high-purity fine powder is placed in a bidirectional pressing mold, argon is filled, and the magnet substrate is formed by pressing; after the surface of the substrate is cleaned, a heavy rare earth alloy layer is cladded on a specific area by using a fiber laser; S5, gradient heat treatment and post-treatment: the cladded magnet is placed in a segmented temperature control vacuum sintering furnace, vacuumized and sequentially subjected to primary tempering and secondary tempering, and the magnet is ground and polished after cooling.

[0006] Further, the rare earth tailings are rare earth tailings with a total content of La and Ce light rare earth elements of greater than or equal to 8%, the crushing is crushing to a particle size of less than or equal to 5 mm by using a jaw crusher, and the grinding is wet ball milling to a particle size of less than or equal to 100 microns to obtain tailing slurry.

[0007] Further, the acid leaching adopts a hydrochloric acid solution with a concentration of 3 mol / L, the solid-liquid ratio is controlled to be 1:4, the leaching temperature is 80 DEG C, and the leaching time is 4 hours; the extraction adopts P507 extractant, the volume ratio of the extractant to the rare earth leaching solution is 1:3; the back-extraction adopts a 2 mol / L hydrochloric acid solution; the calcination temperature is 800 DEG C, the calcination time is 2 hours, and the total purity of the obtained La / Ce mixed rare earth oxide product is greater than or equal to 99%.

[0008] Furthermore, the low-heavy rare earth mixed raw material comprises, by mass percentage: Nd: 12.5% ​​to 13.5%, La / Ce mixed rare earth oxides: 3.5% to 4.5%, B: 0.9% to 1.1%, Co: 0.05% to 0.15%, Cu: 0.05% to 0.15%, Al: 0.3% to 0.5%, with the balance being Fe and unavoidable impurities; the mixing is carried out in a vacuum mixer with a vacuum degree ≤10Pa, a rotation speed of 300r / min, and a mixing time of 60min; the mass ratio of Co to Cu is 1:1. The hydrogen crushing-airflow mill closed-loop system is filled with argon gas with a purity ≥99.999%, and the oxygen partial pressure within the system is ≤1 Pa. The hydrogen partial pressure for hydrogen crushing and embrittlement is 0.2 to 0.3 MPa, the temperature is 300℃ to 350℃, and the holding time is 2 to 3 hours. The coarse powder obtained after hydrogen crushing has a particle size ≤1 mm. The airflow mill uses nitrogen as the gas flow medium, with a gas flow pressure of 0.6 to 0.8 MPa and a classifying wheel speed of 20000 to 25000 r / min. The fine powder produced has a particle size of 3 to 5 μm. The oxidation risk assessment algorithm uses the following formula: ,in Represents the powder oxidation risk factor. Represents the temperature correction factor. This represents the specific surface area of ​​the powder. Represents the total surface area. Indicates the total volume. This represents the flour-making time. This represents the ambient oxygen partial pressure, and is a temperature correction factor at 25°C. ,when When the threshold value exceeds 0.05, the argon gas introduction rate increases by 20%~30%, and the classifier wheel speed decreases by 10%; the oxygen content of the prepared fine powder... ppm.

[0009] Furthermore, the vacuum degree of the segmented temperature-controlled vacuum sintering furnace is evacuated to 5×100. -3 The temperature is below Pa; the heating rate of the low-temperature pre-sintering is 5℃ / min, the temperature is 700℃ to 800℃, and the holding time is 2 to 4h; the heating rate of the high-temperature densification sintering is 3℃ / min, the temperature is 1050℃ to 1080℃, and the holding time is 4 to 6h; the cooling is carried out in the furnace to room temperature, and the density of the obtained rare earth alloy ingot is ≥90%.

[0010] Furthermore, the rare earth composite coating is formed by curing a coating slurry containing Nd2O3 and Al2O3; in the coating slurry, the mass percentage of Nd2O3 to Al2O3 is 60% to 70%: 30% to 40%, the solid-liquid ratio of the slurry is 1:5, the dispersant is anhydrous ethanol, and the slurry is ground in a ball mill for 2 hours to a particle size ≤5μm; the coating is applied by high-pressure electrostatic spraying, and the coating thickness is 10 to 15μm; the curing conditions are drying in an oven at 60℃ for 1 hour.

[0011] Furthermore, the inner wall of the bidirectional pressurized mold is coated with a 5 to 10 μm thick boron nitride release agent; the oxygen partial pressure in the mold cavity after argon filling is ≤0.5 Pa; the pressurization rate is 0.5 to 1 MPa / s, the molding pressure is 200 to 250 MPa, and the holding time is 2 to 3 min; the resulting magnet matrix has a density ≥65%.

[0012] Furthermore, the heavy rare earth alloy cladding powder used in the laser cladding has the following composition by mass percentage: Dy: 60% to 70%, Tb: 10% to 15%, Al: 5% to 8%, Fe: 10% to 15%, and the powder particle size is 50 to 100 μm; the fiber laser has a power of 500 to 800 W, a scanning speed of 5 to 10 mm / s, a spot diameter of 0.2 mm, and a powder feeding rate of 5 g / min; the cladding layer thickness is 50 to 100 μm, and the molten pool temperature is controlled at 1200℃ to 1300℃ during the cladding process.

[0013] Furthermore, the vacuum degree of the segmented temperature-controlled vacuum sintering furnace is evacuated to ≤5×10⁻⁶. -3 Pa; the heating rate of the first-stage tempering is 4℃ / min, the temperature is 500℃ to 550℃, and the holding time is 3 to 5h; the cooling rate of the second-stage tempering is 6℃ / min, the temperature is 450℃ to 480℃, and the holding time is 2 to 3h; the grinding uses a diamond grinding wheel, and the polishing uses a polishing slurry of diamond micro powder and anhydrous ethanol. After polishing, the surface roughness Ra of the magnet is ≤0.1μm, and the dimensional accuracy is controlled within ±0.05mm.

[0014] On the other hand, an apparatus for preparing sintered NdFeB permanent magnets is provided. This apparatus includes: a segmented temperature-controlled vacuum sintering furnace, a vacuum mixer, a hydrogen crushing-airflow mill closed-loop system, a bidirectional pressure mold, a fiber laser, and a diamond wheel polishing device. The segmented temperature-controlled vacuum sintering furnace can achieve a vacuum degree ≤5×10⁻⁶. -3 The vacuum environment and segmented temperature control function of Pa, the hydrogen crushing-flow mill closed-loop system can be filled with high-purity argon and maintain oxygen partial pressure ≤1Pa, the inner wall of the bidirectional pressure mold is coated with boron nitride release agent, and the power of the fiber laser is adjustable from 500 to 800W.

[0015] Compared with existing technologies, the preparation method and apparatus for sintered NdFeB permanent magnets have the following advantages: I. This invention utilizes rare earth tailings to extract light rare earth oxides as raw material components, and optimizes the raw material ratio with multiple alloying elements to achieve a balance between efficient resource recovery and low-cost preparation at the source. A two-stage sintering process is used to control the heating rate and holding process, combined with rare earth composite coating protection and a hydrogen crushing-airflow milling closed-loop powder preparation system to block oxidation risks throughout the entire preparation process, ensuring high purity and fine homogeneity of the magnet powder. Bidirectional pressure molding gives the matrix good density, and laser cladding technology forms a heavy rare earth reinforcement layer in specific areas. Gradient heat treatment refines the microstructure, synergistically improving the magnetic properties and structural stability of the magnet. At the same time, the post-processing process precisely controls the surface quality and dimensional accuracy, making the product have both excellent performance and application adaptability. II. This invention integrates multiple technologies such as segmented temperature-controlled vacuum sintering, closed-loop anti-oxidation powder preparation, and laser cladding to construct a coherent and efficient preparation system. The raw material stage achieves a low heavy rare earth ratio design, reducing dependence on scarce heavy rare earths and conforming to the concept of resource conservation. The powder preparation process uses an oxidation risk assessment algorithm to dynamically adjust parameters, breaking through the passive limitation of oxidation control in traditional powder preparation processes. The combined molding and cladding process achieves synergistic optimization of the matrix and functional layer, and gradient heat treatment further improves the internal stress uniformity of the magnet. The entire method takes into account both production efficiency and product quality. The components of the preparation device are precisely matched to process requirements, ensuring the stability and reliability of the technology implementation and providing a feasible path for the large-scale green production of high-performance sintered NdFeB permanent magnets. Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0017] Figure 1 This is an overall framework diagram of a method for preparing sintered NdFeB permanent magnets; Figure 2 This is a flow chart of an apparatus for preparing sintered NdFeB permanent magnets. Figure 3 This is a process input / output diagram of a method for preparing sintered NdFeB permanent magnets. Detailed Implementation

[0018] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below. Example 1

[0019] A method for preparing sintered NdFeB permanent magnets, the specific steps of which are as follows: Figure 1 As shown: S1, Tailings Pretreatment and Raw Material Preparation: Rare earth tailings with a total La and Ce light rare earth element content of 8% were selected and crushed to a particle size of 5 mm using a jaw crusher. The crushed tailings were then wet-milled to a particle size of 100 μm to obtain a tailings slurry. Acid leaching was performed using a 3 mol / L hydrochloric acid solution with a solid-liquid ratio of 1:4, a leaching temperature of 80℃, and a leaching time of 4 h. Subsequently, extraction was performed using P507 extractant with a volume ratio of extractant to rare earth leachate of 1:3. Back-extraction was then performed using a 2 mol / L hydrochloric acid solution. Finally, the slurry was calcined at 800℃ for 2 h to extract La / Ce mixed rare earth oxides. The total purity of the rare earth oxides in this product was 99%.

[0020] Weigh the following raw materials by mass percentage: Nd: 12.5%, La / Ce mixed rare earth oxide: 3.5%, B: 0.9%, Co: 0.05%, Cu: 0.05%, Al: 0.3%, with the balance being Fe and unavoidable impurities. The mass ratio of Co to Cu is 1:1. Place the above raw materials in a vacuum mixer and mix thoroughly. The vacuum degree of the vacuum mixer is 10 Pa, the rotation speed is 300 r / min, and the mixing time is 60 min to obtain a low-heavy rare earth mixed raw material.

[0021] S2, Two-stage sintering ingot preparation: The low-heavy rare earth mixed raw materials were placed in a segmented temperature-controlled vacuum sintering furnace and evacuated to a vacuum level of 5×10⁻⁶. -3 Below Pa. The temperature was increased to 700℃ at a heating rate of 5℃ / min and held for 2 hours for low-temperature pre-sintering; then the temperature was increased to 1050℃ at a heating rate of 3℃ / min and held for 4 hours for high-temperature densification sintering; after sintering, the furnace was cooled to room temperature to obtain a rare earth alloy ingot with a density of 90%.

[0022] S3, closed-loop coating for anti-oxidation powder production; A rare earth composite coating slurry was prepared, wherein the mass percentages of Nd₂O₃ and Al₂O₃ were 60% and 40% respectively, the solid-liquid ratio of the slurry was 1:5, and anhydrous ethanol was used as the dispersant. The slurry was ball-milled for 2 hours to a particle size of 5 μm. The slurry was then coated onto the surface of a rare earth alloy ingot using a high-voltage electrostatic spraying method, with a coating thickness of 10 μm, and subsequently cured by drying in an oven at 60 °C for 1 hour.

[0023] The coated alloy ingot was placed in a hydrogen crushing-air jet mill closed-loop system and filled with 99.999% pure argon gas to maintain the oxygen partial pressure at 1 Pa. Hydrogen crushing embrittlement was performed at a hydrogen partial pressure of 0.2 MPa and a temperature of 300℃ for 2 hours to obtain coarse powder with a particle size of 1 mm. Then, nitrogen was used as the gas flow medium, and air jet milling was performed at a gas flow pressure of 0.6 MPa and a classifier wheel speed of 20000 r / min for refining. An oxidation risk assessment algorithm was used to control parameters during the powder preparation process. The formula for the oxidation risk assessment algorithm is: ,in Represents the powder oxidation risk factor. Represents the temperature correction factor. This represents the specific surface area of ​​the powder. Represents the total surface area. Indicates the total volume. This represents the flour-making time. This represents the ambient oxygen partial pressure, and is a temperature correction factor at 25°C. ,when When the threshold of 0.05 is exceeded, the argon gas introduction rate is increased by 20%, the classifier speed is reduced by 10%, and finally a high-purity fine powder with an oxygen content of 150 ppm and a particle size of 3 μm is obtained.

[0024] S4, substrate forming and laser cladding; High-purity fine powder was placed in a bidirectional pressure mold. The inner wall of the mold was coated with a 5μm thick boron nitride release agent. After argon filling, the oxygen partial pressure inside the mold cavity was maintained at 0.5Pa. The pressure was increased to 200MPa at a rate of 0.5MPa / s and held for 2 minutes to obtain a magnet substrate with a density of 65%. After cleaning the substrate surface, a heavy rare earth alloy layer was clad in a specific area using a fiber laser. The heavy rare earth alloy cladding powder had the following composition by mass percentage: Dy: 60%, Tb: 10%, Al: 5%, Fe: 15%, with a powder particle size of 50μm. The fiber laser power was 500W, the scanning speed was 5mm / s, the spot diameter was 0.2mm, and the powder feed rate was 5g / min. The molten pool temperature was controlled at 1200℃ during the cladding process, and the cladding layer thickness was 50μm.

[0025] S5, gradient heat treatment and post-treatment; The clad magnet was placed in a segmented temperature-controlled vacuum sintering furnace and evacuated to 5×10⁻³ Pa. It was heated to 500℃ at a rate of 4℃ / min and held for 3 hours for primary tempering; then cooled to 450℃ at a rate of 6℃ / min and held for 2 hours for secondary tempering. After cooling, the magnet was ground with a diamond wheel and then polished with a polishing slurry composed of diamond micron powder and anhydrous ethanol. The surface roughness Ra of the polished magnet was 0.1μm, and the dimensional accuracy was controlled within ±0.05mm. Example 2

[0026] A method for preparing sintered NdFeB permanent magnets, the specific steps of which are as follows: S1, Tailings Pretreatment and Raw Material Preparation: Rare earth tailings with a total La and Ce light rare earth element content of 8.5% were selected and crushed to a particle size of 4.5 mm using a jaw crusher. The tailings were then wet-milled to a particle size of 90 μm to obtain a tailings slurry. Acid leaching was performed using a 3 mol / L hydrochloric acid solution with a solid-liquid ratio of 1:4, a leaching temperature of 80℃, and a leaching time of 4 h. Subsequently, extraction was performed using P507 extractant with a volume ratio of extractant to rare earth leachate of 1:3. Back-extraction was then performed using a 2 mol / L hydrochloric acid solution. Finally, the slurry was calcined at 800℃ for 2 h to extract La / Ce mixed rare earth oxides. The total purity of the rare earth oxides in this product was 99.2%.

[0027] Weigh the following raw materials by mass percentage: Nd: 13.0%, La / Ce mixed rare earth oxides: 4.0%, B: 1.0%, Co: 0.1%, Cu: 0.1%, Al: 0.4%, with the balance being Fe and unavoidable impurities. The mass ratio of Co to Cu is 1:1. Place the above raw materials in a vacuum mixer and mix thoroughly. The vacuum degree of the vacuum mixer is 8 Pa, the rotation speed is 300 r / min, and the mixing time is 60 min to obtain a low-heavy rare earth mixed raw material.

[0028] S2, Two-stage sintering ingot preparation: The low-heavy rare earth mixed raw materials were placed in a segmented temperature-controlled vacuum sintering furnace, and the vacuum was evacuated to below 4×10⁻³ Pa. The temperature was increased to 750℃ at a rate of 5℃ / min and held for 3 hours for low-temperature pre-sintering; then, the temperature was increased to 1065℃ at a rate of 3℃ / min and held for 5 hours for high-temperature densification sintering; after sintering, the furnace was cooled to room temperature to obtain a rare earth alloy ingot with a density of 92%. Figure 2 As shown.

[0029] S3, closed-loop coating for anti-oxidation powder production: A rare earth composite coating slurry was prepared, wherein the mass percentages of Nd₂O₃ and Al₂O₃ were 65% and 35%, respectively, the solid-liquid ratio of the slurry was 1:5, and anhydrous ethanol was used as the dispersant. The slurry was milled in a ball mill for 2 hours to a particle size of 4 μm. The slurry was then coated onto the surface of a rare earth alloy ingot using a high-voltage electrostatic spraying method, with a coating thickness of 12 μm, and subsequently cured by drying in an oven at 60 °C for 1 hour.

[0030] The coated alloy ingot was placed in a hydrogen crushing-air jet mill closed-loop system and filled with 99.999% pure argon gas to maintain the oxygen partial pressure at 0.8 Pa. Hydrogen crushing embrittlement was performed at 320°C and a hydrogen partial pressure of 0.25 MPa for 2.5 h, yielding coarse powder with a particle size of 0.8 mm. Then, nitrogen was used as the gas flow medium for air jet milling at a pressure of 0.7 MPa and a classifier speed of 22000 r / min. An oxidation risk assessment algorithm was used to control parameters during the powdering process. At 25°C, the temperature correction coefficient k = 0.012. When Rox exceeded the threshold of 0.05, the argon gas flow rate was increased by 25%, and the classifier speed was decreased by 10%, ultimately yielding high-purity fine powder with an oxygen content of 130 ppm and a particle size of 4 μm.

[0031] S4, Substrate forming and laser cladding: High-purity fine powder was placed in a bidirectional pressure mold. The inner wall of the mold was coated with an 8μm thick layer of boron nitride release agent. After argon filling, the oxygen partial pressure inside the mold cavity was maintained at 0.4Pa. The pressure was increased to 220MPa at a rate of 0.8MPa / s and held for 2.5min to obtain a magnet substrate with a density of 68%. After cleaning the substrate surface, a heavy rare earth alloy layer was clad in a specific area using a fiber laser. The heavy rare earth alloy cladding powder had the following composition by mass percentage: Dy: 65%, Tb: 12%, Al: 6%, Fe: 17%, with a powder particle size of 80μm. The fiber laser power was 650W, the scanning speed was 8mm / s, the spot diameter was 0.2mm, and the powder feed rate was 5g / min. The molten pool temperature was controlled at 1250℃ during the cladding process, and the cladding layer thickness was 80μm.

[0032] S5, Gradient heat treatment and post-treatment: The clad magnet was placed in a segmented temperature-controlled vacuum sintering furnace and evacuated to 4×10⁻³ Pa. It was heated to 520℃ at a rate of 4℃ / min and held for 4 hours for primary tempering; then cooled to 460℃ at a rate of 6℃ / min and held for 2.5 hours for secondary tempering. After cooling, the magnet was ground with a diamond wheel and then polished with a polishing slurry composed of diamond micron powder and anhydrous ethanol. The surface roughness Ra of the polished magnet was 0.08 μm, and the dimensional accuracy was controlled within ±0.05 mm.

[0033] To visually demonstrate the impact of process parameter adjustments on the performance of sintered NdFeB permanent magnets, this embodiment optimizes key parameters such as the light rare earth content of rare earth tailings, raw material ratio, sintering vacuum degree, coating parameters, powder preparation process, and heat treatment conditions based on the limited parameter range of Example 1. The purity of La / Ce mixed rare earth oxides, density of rare earth alloy ingots, and oxygen content of fine powder are tested using the same testing standards, resulting in the following performance comparison table with Example 1.

[0034] Performance index Example two Example one La / Ce mixed rare earth oxide purity 99.2% 99.0% Rare earth alloy ingot density 92% 90% High purity fine powder oxygen content 130 ppm 150 ppm High purity fine powder particle size 4 μm 3 μm Magnet matrix density 68% 65% Cladding layer thickness 80 μm 50 μm Magnet surface roughness Ra 0.08 μm 0.1 μm Compared with Example 1, Example 2 improved the purity of La / Ce mixed rare earth oxides by 0.2%, increased the density of rare earth alloy ingots by 2%, reduced the oxygen content of high-purity fine powder by 20ppm, increased the density of magnet substrate by 3%, increased the thickness of cladding layer by 30μm, and reduced the surface roughness Ra of magnet by 0.02μm by 30μm. This was achieved by optimizing the content of La and Ce light rare earth elements in rare earth tailings, adjusting the raw material ratio, increasing the vacuum degree of vacuum sintering furnace, optimizing coating composition and thickness, adjusting hydrogen crushing-airflow milling parameters, increasing forming pressure and rate, and optimizing laser cladding parameters and heat treatment process. All core performance indicators showed an optimization trend, verifying the positive impact of parameter adjustment on product performance. Example 3

[0035] A method for preparing sintered NdFeB permanent magnets, the specific steps of which are as follows: S1, Tailings Pretreatment and Raw Material Preparation: Rare earth tailings with a total La and Ce light rare earth element content of 9% were selected and crushed to a particle size of 4 mm using a jaw crusher. The crushed tailings were then wet-milled to a particle size of 80 μm to obtain a tailings slurry. Acid leaching was performed using a 3 mol / L hydrochloric acid solution with a solid-liquid ratio of 1:4, a leaching temperature of 80℃, and a leaching time of 4 h. Subsequently, extraction was performed using P507 extractant with a volume ratio of extractant to rare earth leachate of 1:3. Back-extraction was then performed using a 2 mol / L hydrochloric acid solution. Finally, the slurry was calcined at 800℃ for 2 h to extract La / Ce mixed rare earth oxides. The total purity of the rare earth oxides in this product was 99.4%.

[0036] Weigh the following raw materials by mass percentage: Nd: 13.2%, La / Ce mixed rare earth oxides: 4.2%, B: 1.05%, Co: 0.12%, Cu: 0.12%, Al: 0.45%, with the balance being Fe and unavoidable impurities. The mass ratio of Co to Cu is 1:1. Place the above raw materials in a vacuum mixer and mix thoroughly. The vacuum degree of the vacuum mixer is 5 Pa, the rotation speed is 300 r / min, and the mixing time is 60 min to obtain a low-heavy rare earth mixed raw material.

[0037] S2, Two-stage sintering ingot preparation: The mixed raw materials of low-heavy rare earth elements were placed in a segmented temperature-controlled vacuum sintering furnace and evacuated to below 3×10⁻³ Pa. The temperature was increased to 780℃ at a heating rate of 5℃ / min and held for 3.5h for low-temperature pre-sintering; then the temperature was increased to 1070℃ at a heating rate of 3℃ / min and held for 5.5h for high-temperature densification sintering; after sintering, the furnace was cooled to room temperature to obtain a rare earth alloy ingot with a density of 93%.

[0038] S3, closed-loop coating for anti-oxidation powder production: A rare earth composite coating slurry was prepared, wherein the mass percentages of Nd₂O₃ and Al₂O₃ were 68% and 32% respectively, the solid-liquid ratio of the slurry was 1:5, and anhydrous ethanol was used as the dispersant. The slurry was milled in a ball mill for 2 hours to a particle size of 3 μm. The above slurry was then coated onto the surface of a rare earth alloy ingot using a high-voltage electrostatic spraying method, with a coating thickness of 14 μm, and subsequently cured by drying in an oven at 60 °C for 1 hour.

[0039] The coated alloy ingot was placed in a hydrogen crushing-air jet mill closed-loop system and filled with 99.999% pure argon gas to maintain the oxygen partial pressure at 0.5 Pa. Hydrogen crushing embrittlement was performed at a hydrogen partial pressure of 0.28 MPa and a temperature of 340 °C for 2.8 h, yielding coarse powder with a particle size of 0.6 mm. Subsequently, nitrogen was used as the gas flow medium, and air jet milling was performed at a gas flow pressure of 0.75 MPa and a classifier wheel speed of 24000 r / min for refining. An oxidation risk assessment algorithm was used to control parameters during the powder production process, with a temperature correction coefficient at 25 °C. =0.012, when When the threshold of 0.05 is exceeded, the argon gas introduction rate increases by 28%, the classifier speed decreases by 10%, and finally a high-purity fine powder with an oxygen content of 110 ppm and a particle size of 4.5 μm is obtained.

[0040] S4, Substrate forming and laser cladding: High-purity fine powder was placed in a bidirectional pressure mold. The inner wall of the mold was coated with a 9μm thick layer of boron nitride release agent. After argon filling, the oxygen partial pressure inside the mold cavity was maintained at 0.3Pa. The pressure was increased to 240MPa at a rate of 0.9MPa / s and held for 2.8min to obtain a magnet substrate with a density of 70%. After cleaning the substrate surface, a heavy rare earth alloy layer was clad in a specific area using a fiber laser. The heavy rare earth alloy cladding powder had the following composition by mass percentage: Dy: 68%, Tb: 14%, Al: 7%, Fe: 11%, with a powder particle size of 90μm. The fiber laser power was 750W, the scanning speed was 9mm / s, the spot diameter was 0.2mm, and the powder feed rate was 5g / min. The molten pool temperature was controlled at 1280℃ during the cladding process, and the cladding layer thickness was 90μm.

[0041] S5, Gradient heat treatment and post-treatment: The clad magnet was placed in a segmented temperature-controlled vacuum sintering furnace and evacuated to 3 × 10⁻³ Pa. It was heated to 540℃ at a rate of 4℃ / min and held for 4.5 hours for primary tempering; then cooled to 470℃ at a rate of 6℃ / min and held for 2.8 hours for secondary tempering. After cooling, the magnet was ground with a diamond wheel and then polished with a polishing slurry of diamond micron powder and anhydrous ethanol. The surface roughness Ra of the polished magnet was 0.07 μm, and the dimensional accuracy was controlled within ±0.05 mm. Figure 3 As shown.

[0042] To verify the effect of gradient optimization of process parameters, this embodiment further adjusts parameters such as the particle size of rare earth tailings crushing and grinding, the vacuum degree of the vacuum mixer, the sintering temperature and holding time, the particle size of the coating slurry, the oxygen partial pressure of the hydrogen crushing-airflow mill system, and the forming pressure, based on Embodiments 1 and 2. All performance indicators are tested using unified testing methods and standards. Through multi-dimensional comparison with the previous two embodiments, the law of continuous parameter optimization improving product performance is clarified. The specific comparison results are shown in the table below.

[0043] Performance index Example three Example one Example two La / Ce mixed rare earth oxide purity 99.4% 99.0% 99.2% Rare earth alloy ingot density 93% 90% 92% High purity fine powder oxygen content 110 ppm 150 ppm 130 ppm High purity fine powder particle size 4.5 μm 3 μm 4 μm Magnet matrix density 70% 65% 68% Cladding layer thickness 90 μm 50 μm 80 μm Magnet surface roughness Ra 0.07 μm 0.1 μm 0.08 μm Compared to Examples 1 and 2, Example 3 further increased the content of light rare earth elements in rare earth tailings, reduced the particle size after crushing and grinding, and optimized key parameters such as vacuum degree of vacuum mixer, sintering temperature and holding time, particle size and thickness of coating slurry, oxygen partial pressure and process parameters of hydrogen crushing-air jet mill system, forming pressure and holding time, laser cladding power and molten pool temperature. The results showed that the purity of La / Ce mixed rare earth oxides increased by 0.4% compared to Example 1 and by 0.2% compared to Example 2; the density of rare earth alloy ingots increased by 3% and 1%, respectively; the oxygen content of high-purity fine powder decreased by 40 ppm and 20 ppm, respectively; the density of magnet matrix increased by 5% and 2%, respectively; and the surface roughness Ra of magnets further decreased. The overall performance showed a stepwise optimization, indicating that continuous optimization of process parameters has a significant effect on improving the core performance of the product. Example 4

[0044] A method for preparing sintered NdFeB permanent magnets, the specific steps of which are as follows: S1, Tailings Pretreatment and Raw Material Preparation: Rare earth tailings with a total La and Ce light rare earth element content of 10% were selected and crushed to a particle size of 3 mm using a jaw crusher. The crushed tailings were then wet-milled to a particle size of 70 μm to obtain a tailings slurry. Acid leaching was performed using a 3 mol / L hydrochloric acid solution with a solid-liquid ratio of 1:4, a leaching temperature of 80℃, and a leaching time of 4 h. Subsequently, extraction was performed using P507 extractant with a volume ratio of extractant to rare earth leachate of 1:3. Back-extraction was then performed using a 2 mol / L hydrochloric acid solution. Finally, the slurry was calcined at 800℃ for 2 h to extract La / Ce mixed rare earth oxides. The total purity of the rare earth oxides in this product was 99.5%.

[0045] Weigh the following raw materials by mass percentage: Nd: 13.5%, La / Ce mixed rare earth oxides: 4.5%, B: 1.1%, Co: 0.15%, Cu: 0.15%, Al: 0.5%, with the balance being Fe and unavoidable impurities. The mass ratio of Co to Cu is 1:1. Place the above raw materials in a vacuum mixer and mix thoroughly. The vacuum degree of the vacuum mixer is 3 Pa, the rotation speed is 300 r / min, and the mixing time is 60 min to obtain a low-heavy rare earth mixed raw material.

[0046] S2, Two-stage sintering ingot preparation: The mixed raw materials of low-heavy rare earth elements were placed in a segmented temperature-controlled vacuum sintering furnace and evacuated to below 2×10⁻³ Pa. The temperature was increased to 800℃ at a heating rate of 5℃ / min and held for 4 hours for low-temperature pre-sintering; then the temperature was increased to 1080℃ at a heating rate of 3℃ / min and held for 6 hours for high-temperature densification sintering; after sintering, the furnace was cooled to room temperature to obtain a rare earth alloy ingot with a density of 95%.

[0047] S3, closed-loop coating for anti-oxidation powder production: A rare earth composite coating slurry was prepared, wherein the mass percentages of Nd₂O₃ and Al₂O₃ were 70% and 30%, respectively, the solid-liquid ratio of the slurry was 1:5, and anhydrous ethanol was used as the dispersant. The slurry was milled in a ball mill for 2 hours to a particle size of 2 μm. The slurry was then coated onto the surface of a rare earth alloy ingot using a high-voltage electrostatic spraying method, with a coating thickness of 15 μm, and subsequently cured by drying in an oven at 60 °C for 1 hour.

[0048] The coated alloy ingot was placed in a hydrogen crushing-air jet mill closed-loop system and filled with 99.999% pure argon gas to maintain the oxygen partial pressure at 0.3 Pa. Hydrogen crushing embrittlement was performed at 350°C and a hydrogen partial pressure of 0.3 MPa for 3 hours, yielding coarse powder with a particle size of 0.5 mm. Subsequently, nitrogen was used as the gas flow medium, and air jet milling was performed at a pressure of 0.8 MPa and a classifier speed of 25000 r / min for refining. An oxidation risk assessment algorithm was used to control parameters during the powder production process, with a temperature correction coefficient at 25°C. =0.012, when When the threshold of 0.05 is exceeded, the argon gas introduction rate is increased by 30%, the classifier rotation speed is reduced by 10%, and finally a high-purity fine powder with an oxygen content of 100 ppm and a particle size of 5 μm is obtained.

[0049] S4, Substrate forming and laser cladding: High-purity fine powder was placed in a bidirectional pressure mold. The inner wall of the mold was coated with a 10 μm thick boron nitride release agent. After argon filling, the oxygen partial pressure inside the mold cavity was maintained at 0.2 Pa. The pressure was increased to 250 MPa at a rate of 1 MPa / s and held for 3 min to obtain a magnet substrate with a density of 72%. After cleaning the substrate surface, a heavy rare earth alloy layer was clad in a specific area using a fiber laser. The heavy rare earth alloy cladding powder had the following composition by mass percentage: Dy: 70%, Tb: 15%, Al: 8%, Fe: 7%, with a powder particle size of 100 μm. The fiber laser power was 800 W, the scanning speed was 10 mm / s, the spot diameter was 0.2 mm, and the powder feed rate was 5 g / min. The molten pool temperature was controlled at 1300℃ during the cladding process, and the cladding layer thickness was 100 μm.

[0050] S5, Gradient heat treatment and post-treatment: The clad magnet was placed in a segmented temperature-controlled vacuum sintering furnace and evacuated to 2×10⁻³ Pa. It was heated to 550℃ at a rate of 4℃ / min and held for 5 hours for primary tempering; then cooled to 480℃ at a rate of 6℃ / min and held for 3 hours for secondary tempering. After cooling, the magnet was ground with a diamond wheel and then polished with a polishing slurry composed of diamond micron powder and anhydrous ethanol. The surface roughness Ra of the polished magnet was 0.05 μm, and the dimensional accuracy was controlled within ±0.05 mm.

[0051] To fully demonstrate the optimal performance level of the preparation method of the present invention, this embodiment adopts the optimal parameter combination within a limited range. Based on the first three sets of embodiments, it maximizes the light rare earth content of rare earth tailings, optimizes the coating density, reduces the oxygen partial pressure of the powder preparation system, and increases the molding pressure and laser cladding power. All performance indicators are tested through standardized testing procedures. Through a comprehensive comparison with embodiments one to three, the scientificity and feasibility of the process parameter range of the present invention are verified. The specific comparison data is shown in the table below.

[0052] Performance index Example four Example one Example two Example three La / Ce mixed rare earth oxide purity 99.5% 99.0% 99.2% 99.4% Rare earth alloy ingot density 95% 90% 92% 93% High purity fine powder oxygen content 100 ppm 150 ppm 130 ppm 110 ppm High purity fine powder particle size 5 μm 3 μm 4 μm 4.5 μm Magnet matrix density 72% 65% 68% 70% Cladding layer thickness 100 μm 50 μm 80 μm 90 μm Magnet surface roughness Ra 0.05 μm 0.1 μm 0.08 μm 0.07 μm Example 4, as the most optimized scheme, adopted optimal values ​​within a limited range in terms of raw material selection and process parameter settings: the light rare earth content of rare earth tailings reached 10%, and the vacuum degree of the vacuum sintering furnace was reduced to 2×10⁻⁶. -3Pa represents the optimal coating thickness and density, the lowest oxygen partial pressure in the hydrogen crushing-air jet mill system, and optimal ranges for forming pressure and rate, laser cladding power, and molten pool temperature. Compared to the previous three examples, this one exhibits the highest purity of the La / Ce mixed rare earth oxide, a 5% increase in rare earth alloy ingot density (compared to Example 1), a 50ppm reduction in oxygen content of the high-purity fine powder, a 7% increase in magnet substrate density, a cladding layer thickness of 100μm, and a magnet surface roughness Ra of only 0.05μm. All core performance indicators have reached optimal levels.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a sintered NdFeB permanent magnet, characterized in that, The specific steps of this method are as follows: S1, Tailings Pretreatment and Raw Material Preparation: Select rare earth tailings, and extract La / Ce mixed rare earth oxides through crushing, grinding, acid leaching, extraction, back-extraction, and calcination; weigh Nd, La / Ce mixed rare earth oxides, Fe, B and Co, Cu, Al alloying elements according to the proportion, and mix them evenly to obtain low heavy rare earth mixed raw materials. S2, Two-stage sintering ingot preparation: The low-heavy rare earth mixed raw materials are placed in a segmented temperature-controlled vacuum sintering furnace, and after vacuuming, they are subjected to low-temperature pre-sintering and high-temperature densification sintering in sequence. After cooling, rare earth alloy ingots are obtained. S3, Coated Closed-Loop Anti-Oxidation Powder Making: A rare earth composite coating is coated on the surface of a rare earth alloy ingot and cured; the coated alloy ingot is placed in a hydrogen crushing-air jet mill closed-loop system, and after being filled with argon, it undergoes hydrogen crushing embrittlement and air jet milling. The powder making process is controlled by an oxidation risk assessment algorithm to obtain high-purity fine powder. S4, Substrate Forming and Laser Cladding: High-purity fine powder is placed in a bidirectional pressure mold, filled with argon gas, and then pressure-formed to obtain a magnet substrate; after cleaning the substrate surface, a fiber laser is used to clad a heavy rare earth alloy layer in a specific area. S5, Gradient heat treatment and post-treatment: The clad magnet is placed in a segmented temperature-controlled vacuum sintering furnace, and after vacuuming, it undergoes first-stage tempering and second-stage tempering in sequence. After cooling, the magnet is ground and polished.

2. The method for preparing a sintered NdFeB permanent magnet according to claim 1, characterized in that, In step S1, the rare earth tailings are rare earth tailings with a total content of La and Ce light rare earth elements ≥8%, the crushing is carried out by jaw crusher to crush to a particle size ≤5mm, and the grinding is carried out by wet ball milling to a particle size ≤100μm to obtain tailings slurry.

3. The method for preparing a sintered NdFeB permanent magnet according to claim 1, characterized in that, In step S1, the acid leaching uses a 3 mol / L hydrochloric acid solution with a solid-liquid ratio controlled at 1:4; the extraction uses P507 extractant with a volume ratio of 1:3 between the extractant and the rare earth leachate; the back-extraction uses a 2 mol / L hydrochloric acid solution; and the calcination temperature is 800℃ and the calcination time is 2 hours.

4. The method for preparing a sintered NdFeB permanent magnet according to claim 1, characterized in that, In step S1, the low heavy rare earth mixed raw material is composed of the following components by mass percentage: Nd: 12.5% ​​to 13.5%, La / Ce mixed rare earth oxide: 3.5% to 4.5%, B: 0.9% to 1.1%, Co: 0.05% to 0.15%, Cu: 0.05% to 0.15%, Al: 0.3% to 0.5%, with the balance being Fe and unavoidable impurities; the mixing is carried out in a vacuum mixer with a vacuum degree ≤10Pa; the mass ratio of Co to Cu is 1:

1.

5. The method for preparing a sintered NdFeB permanent magnet according to claim 1, characterized in that, In step S1, the vacuum level of the segmented temperature-controlled vacuum sintering furnace is evacuated to 5×100. -3 The temperature is below Pa; the heating rate of the low-temperature pre-sintering is 5℃ / min, and the temperature is 700℃ to 800℃; the heating rate of the high-temperature densification sintering is 3℃ / min, and the temperature is 1050℃ to 1080℃; the cooling is carried out in the furnace to room temperature, and the density of the obtained rare earth alloy ingot is ≥90%.

6. The method for preparing a sintered NdFeB permanent magnet according to claim 1, characterized in that, In step S3, the rare earth composite coating is formed by curing a coating slurry containing Nd2O3 and Al2O3; in the coating slurry, the mass percentage of Nd2O3 to Al2O3 is 60% to 70%: 30% to 40%, and the dispersant is anhydrous ethanol.

7. The method for preparing a sintered NdFeB permanent magnet according to claim 1, characterized in that, In step S4, the inner wall of the bidirectional pressurized mold is coated with a 5 to 10 μm thick boron nitride release agent; the oxygen partial pressure in the mold cavity after argon filling is ≤0.5 Pa; the pressurization rate is 0.5 to 1 MPa / s, and the molding pressure is 200 to 250 MPa.

8. The method for preparing a sintered NdFeB permanent magnet according to claim 1, characterized in that, In step S4, the heavy rare earth alloy cladding powder used for laser cladding has the following composition by mass percentage: Dy: 60% to 70%, Tb: 10% to 15%, Al: 5% to 8%, Fe: 10% to 15%, and the powder particle size is 50 to 100 μm.

9. The method for preparing a sintered NdFeB permanent magnet according to claim 1, characterized in that, In step S5, the vacuum degree of the segmented temperature-controlled vacuum sintering furnace is evacuated to ≤5×10⁻⁶. -3 Pa; the heating rate of the first-stage tempering is 4℃ / min, the temperature is 500℃ to 550℃, and the holding time is 3 to 5h; the cooling rate of the second-stage tempering is 6℃ / min, the temperature is 450℃ to 480℃, and the holding time is 2 to 3h.

10. An apparatus for preparing sintered NdFeB permanent magnets, the system being applicable to the method for preparing a sintered NdFeB permanent magnet according to any one of claims 1-9, characterized in that, The device includes: a segmented temperature-controlled vacuum sintering furnace, a vacuum mixer, a hydrogen crushing-airflow mill closed-loop system, a bidirectional pressure mold, a fiber laser, and a diamond wheel polishing device. The segmented temperature-controlled vacuum sintering furnace can achieve a vacuum degree ≤5×10⁻⁶. -3 The vacuum environment and segmented temperature control function of Pa, the hydrogen crushing-flow mill closed-loop system can be filled with high-purity argon and maintain oxygen partial pressure ≤1Pa, the inner wall of the bidirectional pressure mold is coated with boron nitride release agent, and the power of the fiber laser is adjustable from 500 to 800W.

Images