High abundance rare earth sintered nd-ce-gd-pr-fe-b magnet and method for manufacturing the same

Abstract

The application discloses a high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet and a preparation method thereof, and belongs to the technical field of rare earth permanent magnet materials. The magnet comprises, in percentage by weight, 30.0-33.0wt% of rare earth elements RE, 0.90-1.00wt% of B elements, 0.80-1.30wt% of trace elements M, and the balance of Fe and inevitable impurities; the RE comprises 0.5-1.0wt% of Nd, 15.0-20.0wt% of Ce, 0.5-2.5wt% of Gd and 10.0-15.0wt% of Pr; and the M comprises Cu, Al, Zr and Ti. The application realizes the synergistic improvement of the magnetic performance and corrosion resistance of the magnet by precisely regulating the multi-rare earth synergistic proportion and trace elements, inhibiting the generation of CeFe2 heterogeneous phases from the source, optimizing the grain boundary structure and relieving the magnetic dilution effect, while greatly reducing the raw material cost. The preparation method adopts conventional industrial equipment, the process parameter window is wide, the production is stable and controllable, is suitable for large-scale continuous production, and the prepared magnet can be widely applied in the fields of new energy vehicles, energy-saving household appliances, industrial motors and the like.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, specifically relating to a high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet and its preparation method. Background Technology

[0002] Sintered NdFeB permanent magnets, due to their excellent magnetic properties, are widely used in new energy vehicles, energy-saving home appliances, industrial motors, and consumer electronics, making them an indispensable key functional material in modern industry. Currently, commercially available sintered NdFeB magnets primarily use light rare earth elements such as Pr and Nd as their core. With the rapid development of the new energy industry, the demand for Pr and Nd resources continues to rise, leading to a significant increase in their prices and a substantial rise in magnet manufacturing costs. Meanwhile, high-abundance rare earth elements such as Ce and La account for over 80% of rare earth minerals, but due to their poor magnetic properties, their utilization rate is extremely low, resulting in a serious imbalance and waste of rare earth resources.

[0003] To reduce magnet manufacturing costs and achieve high-value utilization of abundant rare earth resources, the industry commonly uses Ce to partially replace Nd to prepare high-abundance rare earth sintered NdFeB magnets. However, existing technologies for high Ce-substituted NdFeB magnets suffer from the following intractable technical drawbacks: Firstly, the atomic radius and electronic structure of Ce differ from those of Nd, and a high Ce substitution ratio can lead to RE2Fe... 14 The intrinsic magnetic properties of the B hard magnetic main phase decrease, resulting in a severe magnetic dilution effect and a significant decrease in the remanence and maximum energy product of the magnet. Secondly, Ce elements are prone to segregation during sintering and tempering, reacting with Fe elements to form the CeFe2 soft magnetic Laves phase. This impurity phase severely damages the magnetic properties of the magnet, increases the phase interface inside the magnet, exacerbates galvanic corrosion, and leads to a significant deterioration in the corrosion resistance of the magnet. Thirdly, high Ce substitution leads to a decrease in the wettability of the rare earth-rich grain boundary phase, and the grain boundary phase distribution is discontinuous, failing to form a complete network coating structure. The main phase grains are in direct contact, resulting in poor magnetic decoupling effect. The coercivity and squareness of the demagnetization curve of the magnet decrease significantly, failing to meet the requirements of practical applications.

[0004] To address the aforementioned issues, existing technologies primarily enhance magnet coercivity by adding heavy rare earth elements Dy and Tb. However, Dy and Tb resources are scarce and expensive, completely negating the cost advantages of Ce substitution. Other technologies optimize magnet performance through grain boundary diffusion processes, but these processes are complex, have long production cycles, are costly, and are difficult to scale up for industrial production. Furthermore, they fail to fundamentally solve the core problems of CeFe2 impurity phase formation and grain boundary structure deterioration. Therefore, developing a high-abundance rare earth sintered NdFeB magnet that combines low cost, excellent magnetic properties, and corrosion resistance, while employing a suitable industrial preparation method, is a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing high-Ce-substitute sintered NdFeB magnets, such as the excessive formation of CeFe2 soft magnetic impurities, severe magnetic dilution effect, deterioration of grain boundary structure, inability to simultaneously achieve both magnetic properties and corrosion resistance, and complex, costly, and unsuitable-for-large-scale industrial production processes, this invention aims to provide a high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet and its preparation method. By synergistically proportioning multiple rare earth elements and precisely controlling trace elements, the generation of CeFe2 impurities is suppressed at the source, the grain boundary structure is optimized, and the magnetic dilution effect is mitigated. This significantly reduces raw material costs while achieving a synergistic improvement in both magnetic properties and corrosion resistance. Furthermore, the preparation method of this invention utilizes conventional industrial equipment, has a wide process parameter window, and offers stable and controllable production, making it suitable for large-scale continuous production.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet, comprising the following components by total weight percentage: rare earth element RE 30.0-33.0wt%, element B 0.90-1.00wt%, trace element M 0.80-1.30wt%, with the balance being Fe and unavoidable impurities;

[0008] The rare earth elements (RE) comprise, by weight percentage of the total magnet,: Nd 0.5-1.0 wt%, Ce 15.0-20.0 wt%, Gd 0.5-2.5 wt%, and Pr 10.0-15.0 wt%.

[0009] The trace element M, by weight percentage of the magnet, includes: Cu 0.15-0.25wt%, Al 0.50-0.70wt%, Zr 0.08-0.15wt%, and Ti 0.08-0.12wt%.

[0010] Preferably, the total content of the unavoidable impurities is ≤0.1wt%.

[0011] Preferably, the high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet comprises the following components by weight percentage: a total content of rare earth element RE of 32.85 wt%, a content of element B of 0.95 wt%, a total content of trace element M of 1.02 wt%, and the balance being Fe and unavoidable impurities, with a total impurity content of 0.09 wt%.

[0012] Preferably, the rare earth elements RE, based on the total weight percentage of the magnet, include: 0.64 wt% Nd, 15.94 wt% Ce, 2.42 wt% Gd, and 13.85 wt% Pr.

[0013] Preferably, the trace element M, based on the total weight percentage of the magnet, includes: Cu 0.20 wt%, Al 0.60 wt%, Zr 0.12 wt%, and Ti 0.10 wt%.

[0014] This invention also provides a method for preparing a high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet, comprising the following steps:

[0015] Step 1: Ingredient preparation: Weigh each raw material according to the weight percentage of the component design and complete the preparation under inert gas protection;

[0016] Step 2 Vacuum melting and strip casting: Place the prepared raw materials in a vacuum induction melting furnace, evacuate the furnace and fill it with inert gas, heat it to 1430-1470℃ for melting, hold it at the temperature to homogenize it, and then cast the alloy liquid onto a copper roller with a rotation speed of 29-31m / s to prepare a rapid quenching thin strip.

[0017] Step 3: Hydrogen explosion powder preparation: The rapidly quenched thin strip is placed in a hydrogen explosion furnace for hydrogenation treatment, and then heated to remove hydrogen to obtain hydrogen explosion powder.

[0018] Step 4: Grinding with an air jet mill: The hydrogen explosion powder is ground by an air jet mill to prepare ultrafine magnetic powder with an average particle size of 3.0-3.5 μm;

[0019] Step 5: Magnetic field orientation and pressing: The ultrafine magnetic powder is pre-pressed in an orientation magnetic field of 1.8-2.2T, and then cold isostatically pressed to obtain a green body;

[0020] Step 6 Vacuum sintering: Place the green blank in a vacuum sintering furnace, evacuate the vacuum, raise the temperature to 1030-1040℃, and sinter at that temperature for 3.5-4.5 hours;

[0021] Step 7 Tempering treatment: After sintering, first tempering is performed, followed by second tempering at 630-650℃, and the temperature is lowered to 3.5-4.5h. After cooling, the magnet is obtained.

[0022] Preferably, in step 2, the prepared raw materials are placed into the alumina crucible of the vacuum induction melting furnace, and the furnace is evacuated until the vacuum level is ≤5×10⁻⁶. -3 Pa, then high-purity argon gas is introduced into the furnace to a pressure of 0.05 MPa, and the temperature is raised to 1430-1470℃ for melting. The temperature is held for 20 minutes to completely melt the raw materials and homogenize the alloy liquid.

[0023] Preferably, in step 3, the rapidly quenched thin strip is placed in a hydrogen explosion furnace, and a vacuum is first drawn until the vacuum level inside the furnace is ≤1×10⁻⁶. -2 The pressure was increased to 0.12 MPa, and then high-purity hydrogen was introduced into the furnace. Hydrogen was absorbed at room temperature for 2 hours to fully hydrogenate and fragment the thin strip. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min for dehydrogenation treatment, held at that temperature for 4 hours, and then evacuated to a vacuum level ≤1×10⁻⁶. -2 Pa, after cooling to room temperature, yields hydrogen explosion powder.

[0024] Preferably, in step 5, the ultrafine magnetic powder is placed into the non-magnetic mold of the parallel magnetic field press and oriented in a uniform magnetic field with an orientation magnetic field strength of 1.8-2.2T. At the same time, pre-pressing is performed with a pre-pressing pressure of 15MPa and a holding pressure of 10s. Then, the pre-pressed blank is placed into a cold isostatic press and cold isostatically pressed at a pressure of 200MPa for 30s to obtain the pressed green blank.

[0025] Preferably, the temperature of the first-stage tempering in step 7 is 880-920℃, and the holding time is 0.8-1.2h.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. This invention utilizes a quaternary rare earth element synergistic design (Nd-Ce-Gd-Pr) with high-abundance Ce as the main rare earth component, significantly reducing the amount of Pr and Nd used, thereby substantially lowering the raw material cost of magnets. Simultaneously, it achieves high-value utilization of high-abundance rare earth resources, alleviating the industry pain point of supply-demand imbalance in rare earth resources. Furthermore, the synergistic addition of Gd and Pr effectively stabilizes RE2Fe. 14 The lattice structure of the B main phase suppresses the segregation and valence fluctuation of Ce elements, significantly alleviates the magnetic dilution effect caused by high Ce substitution, ensures the intrinsic magnetic properties of the main phase, and promotes the uniform enrichment of rare earth elements at the grain boundaries, thus optimizing the grain boundary structure.

[0028] 2. This invention achieves the dual effects of impurity phase suppression and grain boundary optimization through the precise synergistic regulation of four trace elements: Cu, Al, Zr, and Ti. Ti can form high-melting-point compounds with Ce and Fe, suppressing the formation of CeFe2 soft magnetic impurities at the source and significantly increasing the proportion of the hard magnetic main phase. Zr can suppress abnormal growth of the main phase grains during sintering, refine the grains, and improve the magnet's coercivity. Cu and Al can significantly lower the melting point of rare-earth-rich grain boundary phases, improve the wettability of the grain boundary phases, promote the formation of a continuous and uniform network coating structure, achieve effective magnetic decoupling between the main phase grains, significantly improve the magnet's coercivity and demagnetization curve squareness, while reducing internal porosity defects, increasing density, blocking the intrusion channels of corrosive media, and significantly improving the magnet's corrosion resistance.

[0029] 3. This invention, through synergistic optimization of component design and preparation process, determines the optimal melting, sintering, and tempering process parameter window, which can further promote uniform element distribution, optimize phase composition and grain boundary structure. Under the premise of high Ce substitution, it achieves a synergistic improvement in the magnetic properties and corrosion resistance of the magnet. The prepared magnet has a remanence Br ≥ 9.19 kGs and an intrinsic coercivity H. cj ≥5.686kOe, maximum energy product (BH) max ≥20.676 MGOe, demagnetization curve squareness H k / H cj With a purity of ≥90.501%, it also possesses excellent corrosion resistance and can be widely used in various application scenarios ranging from low-end to mid-to-high-end.

[0030] 4. During the research process of this invention, electron probe microanalysis (EPMA) line scan results revealed a steep elemental concentration gradient across phase boundaries. This characteristic indicates that the continuous distribution of non-magnetic grain boundary phases can effectively promote magnetic decoupling between hard magnetic grains. Simultaneously, high-cerium magnets exhibit superior corrosion resistance due to their ability to form more rare-earth-rich grain boundary phases. These findings demonstrate that precisely controlling the Ce / Gd elemental ratio and suppressing the generation of microscopic defects such as porosity are key technical strategies for developing high-performance, low-cost, high-abundance rare-earth permanent magnet materials.

[0031] 5. The preparation method of the present invention uses conventional equipment and standard procedures for the industrial production of sintered NdFeB magnets, without the need for additional complex equipment and extra procedures. It has a wide process parameter window, stable and controllable production process, good product performance consistency, and is suitable for large-scale industrial continuous production. It has extremely high economic value and industrial application prospects. Attached Figure Description

[0032] Figure 1 The XRD pattern of the magnet prepared in Example 1 of this invention;

[0033] Figure 2 The XRD pattern of the magnet prepared in Example 2 of this invention;

[0034] Figure 3 The XRD pattern of the magnet prepared in Example 3 of this invention;

[0035] Figure 4 The XRD pattern of the magnet prepared in Example 4 of this invention;

[0036] Figure 5 The XRD pattern of the magnet prepared in Example 5 of this invention;

[0037] Figure 6 This is a microstructure image of the magnet prepared in Example 1 of the present invention;

[0038] Figure 7 This is a microstructure image of the magnet prepared in Example 2 of the present invention;

[0039] Figure 8 This is a microstructure image of the magnet prepared in Example 3 of the present invention;

[0040] Figure 9 This is a microstructure image of the magnet prepared in Example 4 of the present invention;

[0041] Figure 10 This is an EPMA surface scan analysis image of the magnet prepared in Example 5 of the present invention, wherein... Figure 10 (1) is a microscopic image of the magnet, with the red circle representing the scanned area; Figure 10 (2) is a map showing the intensity distribution of iron. Figure 10 (3) is a map showing the intensity distribution of cerium; Figure 10 (4) is a distribution map of neodymium intensity; Figure 10 (5) is a distribution map of praseodymium element intensity; Figure 10 (6) is a map showing the intensity distribution of gadolinium.

[0042] Figure 11 This is a graph showing the room temperature demagnetization curve of the magnet, where... Figure 11 (a) is a demagnetization curve at room temperature for Examples 1-2 of the present invention. Figure 11 (b) is a demagnetization curve at room temperature for Examples 3-5 of the present invention;

[0043] Figure 12 The image shows the metallographic morphology of the magnet after corrosion, prepared in Example 1 of this invention.

[0044] Figure 13 The image shows the metallographic morphology of the magnet prepared in Comparative Example 1 after corrosion. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0046] Experimental materials and instruments:

[0047] All raw materials used in the embodiments and comparative examples of this invention are commercially available industrial-grade conventional raw materials, wherein the purity of metals Nd, Ce, Gd, Pr, Cu, Al, Zr and Ti is ≥99.5%, and the purity of Fe is ≥99.8%; all raw material preparation and transfer processes are carried out in argon-protected glove boxes to avoid oxidation of raw materials.

[0048] The equipment used in this invention are all conventional equipment for the industrial production of sintered NdFeB magnets, including vacuum induction melting furnace, hydrogen explosion furnace, air jet mill, parallel magnetic field press, cold isostatic press, and vacuum sintering furnace; the instruments used for performance testing are all industry-standard instruments.

[0049] Magnet performance testing methods:

[0050] 1. Magnetic performance testing: Using an NIM-2000 permanent magnet material measuring instrument, and in accordance with GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials" (currently valid), the remanence Br and intrinsic coercivity H of the magnet were tested at room temperature (25℃). cj Maximum energy product (BH) max Demagnetization curve squareness H k / H cj (where H) k (This refers to the knee magnetic field).

[0051] 2. Phase composition test: A D8 Advance X-ray diffractometer (XRD) was used with Cu target Kα radiation. The test range was 20°-80°, the scan rate was 5° / min, the step size was 0.02°, and the mass percentage of each phase was calculated using Rietveld refinement.

[0052] 3. Microscopic morphology and elemental distribution test: The microscopic morphology of the magnet was observed using the backscattered electron (BSE) mode of a SU8010 scanning electron microscope (SEM), and the elemental surface distribution of the magnet was tested using the X-ray energy dispersive spectrometer (EDS) equipped with the equipment.

[0053] 4. Density Test: The density of the magnet was tested using the Archimedes' displacement method according to GB / T 3850-2015 "Method for Determination of Density of Dense Sintered Metallic Materials and Hard Alloys"; the theoretical density for sintered NdFeB magnets was referenced to 7.5-7.6 g / cm³. 3 The density was calculated as measured density / theoretical density × 100%. Each sample was tested three times and the average value was taken.

[0054] 5. Corrosion Resistance Test: A CHI660E electrochemical workstation was used with a three-electrode system (the working electrode was the magnet to be tested; the sample needed to be sealed before testing, exposing only the working surface, and degreasing and descaling were performed; the reference electrode was a saturated calomel electrode, and the auxiliary electrode was a platinum electrode). The test medium was a 3.5wt% NaCl aqueous solution, and the potentiodynamic polarization curve was tested at room temperature. Before testing, the sample was placed in the test medium, and the test was started after the open circuit potential stabilized for 30 minutes. The scan rate was 1mV / s, and the test range was -1.2V to -0.2V. The corrosion potential Ecorr and corrosion current density icorr were obtained by Tafel extrapolation.

[0055] In an embodiment of the present invention, a high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet comprises, by weight percentage of the total magnet, the following components: rare earth element RE 30.0-33.0 wt%, element B 0.90-1.00 wt%, trace element M 0.80-1.30 wt%, with the balance being Fe and unavoidable impurities, wherein the total content of the unavoidable impurities is ≤0.1 wt%.

[0056] The rare earth elements (RE) comprise, by weight percentage of the total magnet,: Nd 10.0-15.0 wt%, Ce 15.0-20.0 wt%, Gd 0.5-2.5 wt%, and Pr 0.5-1.0 wt%.

[0057] The trace element M, by weight percentage of the magnet, includes: Cu 0.15-0.25wt%, Al 0.50-0.70wt%, Zr 0.08-0.15wt%, and Ti 0.08-0.12wt%.

[0058] The method for preparing the high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet includes the following steps:

[0059] Step 1: Ingredient preparation: Weigh each raw material according to the weight percentage of the component design and complete the preparation under inert gas protection;

[0060] Step 2 Vacuum melting and strip casting: Place the prepared raw materials in a vacuum induction melting furnace, evacuate the furnace and fill it with inert gas, heat it to 1430-1470℃ for melting, hold it at the temperature to homogenize it, and then cast the alloy liquid onto a copper roller with a rotation speed of 29-31m / s to prepare a rapid quenching thin strip.

[0061] Step 3: Hydrogen explosion powder preparation: The rapidly quenched thin strip is placed in a hydrogen explosion furnace for hydrogenation treatment, and then heated to remove hydrogen to obtain hydrogen explosion powder.

[0062] Step 4: Grinding with an air jet mill: The hydrogen explosion powder is ground by an air jet mill to prepare ultrafine magnetic powder with an average particle size of 3.0-3.5 μm;

[0063] Step 5: Magnetic field orientation and pressing: The ultrafine magnetic powder is pre-pressed in an orientation magnetic field of 1.8-2.2T, and then cold isostatically pressed to obtain a green body;

[0064] Step 6 Vacuum sintering: Place the green blank in a vacuum sintering furnace, evacuate the vacuum, raise the temperature to 1030-1040℃, and sinter at that temperature for 3.5-4.5 hours;

[0065] Step 7 Tempering treatment: After sintering, a first-stage tempering is performed at a temperature of 880-920℃ for 0.8-1.2h; then the temperature is lowered to 630-650℃ for a second-stage tempering, which is held for 3.5-4.5h. After cooling, the magnet is obtained.

[0066] Technical principle of the invention:

[0067] This invention takes the synergistic ratio of Nd-Ce-Gd-Pr quaternary rare earth elements as the core framework, combined with precise control of trace elements such as Cu, Al, Zr, and Ti, and customized melting-sintering-tempering process parameters. It addresses the performance defects of high Ce replacement of NdFeB magnets from four dimensions: suppressing CeFe2 soft magnetic impurity phase, stabilizing hard magnetic main phase, optimizing grain boundary structure, and mitigating magnetic dilution effect. This results in a synergistic breakthrough of low cost, high magnetic performance, and high corrosion resistance.

[0068] I. The core role of each raw material component

[0069] (a) Rare earth element RE (total content 30.0-33.0 wt%)

[0070] 1. Ce (15.0-20.0wt%): A core component of high-abundance rare earth elements, which can significantly replace high-priced Pr and Nd, thereby significantly reducing raw material costs and realizing the high-value utilization of high-abundance rare earth resources; however, adding it alone in a high proportion can lead to magnetic dilution, CeFe2 impurity phase formation, and deterioration of grain boundary structure.

[0071] 2. Nd (0.5-1.0 wt%): RE2Fe 14 B is the core constituent element of the hard magnetic main phase, ensuring the basic hard magnetic properties of the magnet and serving as the foundation for a stable main phase lattice structure.

[0072] 3. Gd (0.5-2.5wt%): stabilizes RE2Fe 14 The B-phase lattice suppresses Ce element segregation and valence state fluctuations, fundamentally alleviating the magnetic dilution effect caused by high Ce substitution and assisting in the uniform enrichment of rare earth elements at grain boundaries.

[0073] 4. Pr (10.0-15.0wt%): Synergistically enhances the intrinsic magnetic properties of the main phase with Gd, compensates for the magnetic property decay caused by Ce substitution, and optimizes the continuity of grain boundary phase distribution.

[0074] (II) Key Nonmetallic Elements

[0075] B (0.90-1.00wt%): Combines with rare earth elements and Fe to form RE2Fe. 14 B, the hard magnetic main phase, is the core guarantee of the permanent magnet properties of the magnet. Precise content can avoid the generation of non-hard magnetic impurities.

[0076] (iii) Trace elements M (total content 0.80-1.30wt%)

[0077] 1. Ti (0.08-0.12wt%): forms high-melting-point compounds with Ce and Fe, blocking the formation of CeFe2 soft magnetic Laves phase from the source and increasing the proportion of hard magnetic main phase.

[0078] 2. Zr (0.08-0.15wt%): Suppresses abnormal growth of main phase grains during sintering, refines grain size, and directly improves magnet coercivity.

[0079] 3. Cu (0.15-0.25wt%): Reduces the melting point of rare earth-rich grain boundary phases, significantly improves the wettability of grain boundary phases, and provides a basis for the formation of continuous grain boundary structures.

[0080] 4. Al (0.50-0.70wt%): Synergistically with Cu, it lowers the melting point of grain boundaries, optimizes wettability, reduces internal pore defects in magnets, increases density, and blocks the intrusion channels of corrosive media.

[0081] (iv) Matrix elements

[0082] Fe: The matrix phase of the magnet, together with RE and B, constitutes the hard magnetic main phase, providing the structural carrier for magnetic properties. The balance ratio ensures the balance between the magnet structure and performance.

[0083] II. Synergistic Mechanism among Raw Materials

[0084] 1. Quaternary rare earth synergy: a balance between cost and performance

[0085] Cost reduction is achieved by focusing on high-abundance Ce and stabilizing RE2Fe through the synergistic effect of Gd+Pr. 14 The B-phase lattice suppresses Ce segregation and valence state fluctuations, mitigating the magnetic dilution effect; Nd retains the basic hard magnetic properties. The combination of these four elements achieves a triple effect of high Ce substitution, stable main phase performance, and uniform distribution of rare earth elements at grain boundaries.

[0086] 2. Synergistic effect of quaternary trace elements: impurity phase suppression and grain boundary reconstruction

[0087] Ti-specific suppression of CeFe2 soft magnetic phase eliminates the damage to magnetic properties caused by soft magnetic phase;

[0088] Zr refines grain size and improves coercivity;

[0089] The Cu+Al dual-element synergy lowers the melting point of grain boundaries and improves wettability, forming a continuous and uniform network grain boundary coating structure, thereby achieving magnetic decoupling of the main phase grains.

[0090] The trace element system simultaneously improves the density and corrosion resistance of magnets, achieving the triple goals of impurity phase suppression, grain refinement, and grain boundary optimization.

[0091] 3. Synergistic effects of rare earth elements and trace elements across systems

[0092] Rare earth elements optimize the distribution of rare earth elements in the main phase lattice and grain boundaries, while trace elements specifically address the problems of impurities, grain boundaries, and grains caused by high Ce. The two complement each other, eliminating the need to add high-priced heavy rare earth elements such as Dy and Tb, thus offsetting the performance defects of high Ce and retaining the cost advantage.

[0093] III. Necessity and Importance of Process Parameter Selection

[0094] This invention employs a standardized process: vacuum melting and belt spinning → hydrogen explosion → air jet milling → magnetic field orientation pressing → vacuum sintering → secondary tempering. All parameters are custom-designed to match the composition. The core necessity and importance are as follows:

[0095] 1. Vacuum melting and belt spinning (melting at 1430-1470℃, copper roller speed 29-31m / s)

[0096] Necessity: The vacuum environment prevents the oxidation of raw materials, the melting temperature ensures complete melting of the alloy and homogenization of elements; the rapid quenching rate prepares uniform thin strips and refines the alloy structure.

[0097] Importance: Insufficient temperature can lead to component segregation, and improper spinning rate can cause structural defects, directly determining the basic quality of subsequent magnetic powder and magnets.

[0098] 2. Airflow milled powder (particle size 3.0-3.5μm)

[0099] Necessity: Precise control of particle size to ensure the uniformity of magnetic powder is a prerequisite for sufficient magnetic field orientation and sintering density.

[0100] Importance: Excessively large particle size leads to insufficient orientation, while excessively small particle size makes it prone to oxidation and causes abnormal grain growth, both of which will significantly reduce magnetic properties.

[0101] 3. Magnetic field orientation suppression (1.8-2.2T orientation magnetic field)

[0102] Necessity: This magnetic field strength ensures that the magnetic powder is fully oriented along the easy magnetization direction, guaranteeing that the remanence and maximum magnetic energy product meet the standards.

[0103] Importance: Insufficient magnetic field strength will result in low orientation degree, and the core magnetic properties will not meet the application requirements.

[0104] 4. Vacuum sintering (1030-1040℃, holding time 3.5-4.5h)

[0105] Necessity: The temperature range is adapted to the composition characteristics to ensure the densification of the green body while avoiding grain coarsening, Ce segregation and CeFe2 impurity phase formation; the holding time ensures sintering uniformity.

[0106] Importance: Too low a temperature results in insufficient density, while too high a temperature causes the precipitation of impurity phases, leading to a sharp drop in magnetic properties and corrosion resistance.

[0107] 5. Secondary tempering (first-stage tempering at 880-920℃; second-stage tempering at 630-650℃)

[0108] Necessity: First-stage tempering eliminates internal stress and optimizes grain boundary distribution; second-stage tempering stabilizes grain boundary morphology and forms a complete network of grain boundaries.

[0109] Importance: Improper tempering parameters can lead to grain boundary deterioration, residual internal stress, and failure to meet coercivity and squareness standards.

[0110] IV. Unexpected Technical Effects of Process Parameter Selection

[0111] 1. Wide process window, breaking through the bottleneck of large-scale production.

[0112] The process parameters of this invention have strong adaptability and a wide window, requiring no strict and precise control. Stable production can be achieved using conventional industrial equipment, and the product performance consistency far exceeds that of traditional high-Ce magnet processes. This invention solves the industry problem of the complexity and inability to mass-produce traditional high-Ce magnet processes.

[0113] 2. Magnetic properties exceed expectations with high Ce substitution.

[0114] With a high Ce substitution rate of 15-20 wt% and a customized process, the magnet achieves Br ≥ 9.19 kGs and intrinsic coercivity H. cj ≥5.686kOe, maximum energy product (BH) max ≥20.676 MGOe, demagnetization curve squareness H k / H cj With a purity of ≥90.501%, it achieves mid-to-high-end magnet performance without the need for heavy rare earth elements, achieving an unexpected balance between low cost and high performance.

[0115] 3. Breakthrough improvement in corrosion resistance

[0116] The synergistic effect of process and composition results in continuous and dense grain boundaries, absence of CeFe2 impurity phase, and extremely high density. This significantly reduces the corrosion current density of the magnet, shifts the corrosion potential positively, and greatly improves its corrosion resistance compared to traditional high-Ce magnets, thus solving the technical pain point of easy corrosion of high-Ce magnets.

[0117] 4. The magnetic decoupling effect far exceeded expectations.

[0118] The tempering process, in synergy with Cu / Al and combined with the suppression of impurity phases by Ti, forms a complete network coating at the grain boundaries, resulting in significant magnetic decoupling of the main phase grains. The squareness of the demagnetization curve exceeds 90%, solving the core defect of poor squareness in high Ce magnets.

[0119] To make the present invention more fully disclosed, more specific embodiments are described below.

[0120] Example 1

[0121] A high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet has the following composition design based on the total weight percentage of the magnet: the total content of rare earth element RE is 33.0 wt%, of which Nd is 0.5 wt%, Ce is 20.0 wt%, Gd is 2.0 wt%, and Pr is 10.5 wt%; the content of element B is 0.95 wt%; the total content of trace element M is 1.02 wt%, of which Cu is 0.20 wt%, Al is 0.60 wt%, Zr is 0.12 wt%, and Ti is 0.10 wt%; the balance is Fe and unavoidable impurities, with a total impurity content of 0.1 wt%.

[0122] The method for preparing the high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet includes the following steps:

[0123] Step 1: Ingredient preparation: Weigh each raw material according to the weight percentage designed above. The total weight of the ingredients is 5kg. The preparation process is completed in an argon-protected glove box.

[0124] Step 2: Vacuum Melting and Belt Spinning: Place the prepared raw materials into the alumina crucible of the vacuum induction melting furnace, and evacuate the furnace until the vacuum degree is ≤5×10⁻⁶. -3 Pa, then high-purity argon gas is introduced into the furnace to a pressure of 0.05 MPa, and the temperature is raised to 1430℃ for melting. The temperature is held for 22 minutes to completely melt the raw materials and homogenize the alloy liquid. The molten alloy liquid is then smoothly poured onto a high-speed rotating copper roller, with the rotation speed of the copper roller controlled at 29 m / s, to prepare a rapid quenching thin strip with a thickness of 0.26-0.34 mm.

[0125] Step 3: Hydrogen Explosion Powder Preparation: Place the rapidly quenched thin strip into the hydrogen explosion furnace, and first evacuate the furnace until the vacuum level is ≤1×10⁻⁶. -2 The pressure was increased to 0.12 MPa, and then high-purity hydrogen was introduced into the furnace. Hydrogen was absorbed at room temperature for 2 hours to fully hydrogenate and fragment the thin strip. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min for dehydrogenation treatment, held at that temperature for 4 hours, and then evacuated to a vacuum level ≤1×10⁻⁶. -2 Pa, after cooling to room temperature, yields hydrogen explosion powder;

[0126] Step 4: Airflow milling: Add the hydrogen explosion powder to a closed-loop airflow mill, using high-purity nitrogen as the protective and grinding medium, control the grinding pressure at 0.6 MPa and the classifier wheel speed at 4500 r / min, and prepare ultrafine magnetic powder with an average particle size of 3.0 μm.

[0127] Step 5: Magnetic field orientation and pressing: The ultrafine magnetic powder is placed into the non-magnetic mold of the parallel magnetic field press and oriented in a uniform magnetic field with an orientation magnetic field strength of 1.8T. At the same time, pre-pressing is performed with a pre-pressing pressure of 15MPa and a holding pressure of 10s. Then, the pre-pressed blank is placed in a cold isostatic press and cold isostatically pressed at a pressure of 200MPa for 30s to obtain the pressed green blank.

[0128] Step 6 Vacuum Sintering: Place the green billet into a high-vacuum sintering furnace and evacuate the furnace until the vacuum level is ≤5×10⁻⁶. -3 Pa, heated to 1030℃ at a heating rate of 5℃ / min, and sintered at that temperature for 4.5h to fully densify the green body;

[0129] Step 7 Tempering: After sintering, the furnace temperature is lowered to 880℃ and held for 1.2 hours for primary tempering. Then, the furnace temperature is lowered to 630℃ and held for 4.5 hours for secondary tempering. After tempering, the furnace temperature is cooled to room temperature. The magnet is then removed and machined to obtain a high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet for subsequent performance testing.

[0130] Example 2

[0131] A high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet has the following composition design based on the total weight percentage of the magnet: the total content of rare earth element RE is 33.0 wt%, of which Nd is 0.5 wt%, Ce is 20.0 wt%, Gd is 2.3 wt%, and Pr is 10.2 wt%; the content of element B is 0.95 wt%; the total content of trace element M is 1.02 wt%, of which Cu is 0.16 wt%, Al is 0.54 wt%, Zr is 0.09 wt%, and Ti is 0.10 wt%; the balance is Fe and unavoidable impurities, with a total impurity content of 0.09 wt%.

[0132] The method for preparing the high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet includes the following steps:

[0133] Step 1: Ingredient preparation: Weigh each raw material according to the weight percentage designed above. The total weight of the ingredients is 5kg. The preparation process is completed in an argon-protected glove box.

[0134] Step 2: Vacuum Melting and Belt Spinning: Place the prepared raw materials into the alumina crucible of the vacuum induction melting furnace, and evacuate the furnace until the vacuum degree is ≤5×10⁻⁶. -3Pa, then high-purity argon gas is introduced into the furnace to a pressure of 0.05 MPa, and the temperature is raised to 1450℃ for melting. The temperature is held for 20 minutes to completely melt the raw materials and homogenize the alloy liquid. The molten alloy liquid is then smoothly poured onto a high-speed rotating copper roller, with the rotation speed of the copper roller controlled at 29 m / s, to prepare a rapid quenching thin strip with a thickness of 0.27-0.35 mm.

[0135] Step 3: Hydrogen Explosion Powder Preparation: Place the rapidly quenched thin strip into the hydrogen explosion furnace, and first evacuate the furnace until the vacuum level is ≤1×10⁻⁶. -2 The pressure was increased to 0.12 MPa, and then high-purity hydrogen was introduced into the furnace. Hydrogen was absorbed at room temperature for 2 hours to fully hydrogenate and fragment the thin strip. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min for dehydrogenation treatment, held at that temperature for 4 hours, and then evacuated to a vacuum level ≤1×10⁻⁶. -2 Pa, after cooling to room temperature, yields hydrogen explosion powder;

[0136] Step 4: Airflow milling: The hydrogen explosion powder is added to a closed-loop airflow mill, with high-purity nitrogen as the protective and grinding medium. The grinding pressure is controlled at 0.6 MPa and the classifier speed is 4500 r / min to prepare ultrafine magnetic powder with an average particle size of 3.3 μm.

[0137] Step 5: Magnetic field orientation and pressing: The ultrafine magnetic powder is placed into the non-magnetic mold of the parallel magnetic field press and oriented in a uniform magnetic field with an orientation magnetic field strength of 1.9T. At the same time, pre-pressing is performed with a pre-pressing pressure of 15MPa and a holding pressure of 10s. Then, the pre-pressed blank is placed in a cold isostatic press and cold isostatically pressed at a pressure of 200MPa for 30s to obtain the pressed green blank.

[0138] Step 6 Vacuum Sintering: Place the green billet into a high-vacuum sintering furnace and evacuate the furnace until the vacuum level is ≤5×10⁻⁶. -3 Pa, heated to 1040℃ at a heating rate of 5℃ / min, and sintered at that temperature for 3.5h to fully densify the green body;

[0139] Step 7 Tempering: After sintering, the furnace temperature is lowered to 920℃ and held for 0.8h for primary tempering. Then, the furnace temperature is lowered to 650℃ and held for 3.5h for secondary tempering. After tempering, the furnace temperature is cooled to room temperature. The magnet is then removed and machined to obtain a high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet for subsequent performance testing.

[0140] Example 3

[0141] A high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet has the following composition design based on the total weight percentage of the magnet: the total content of rare earth element RE is 32.81wt%, of which Nd is 0.6wt%, Ce is 17.54wt%, Gd is 2.02wt%, and Pr is 12.65wt%; the content of element B is 0.95wt%; the total content of trace element M is 1.02wt%, of which Cu is 0.23wt%, Al is 0.65wt%, Zr is 0.12wt%, and Ti is 0.11wt%; the balance is Fe and unavoidable impurities, with a total impurity content of 0.08wt%.

[0142] The method for preparing the high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet includes the following steps:

[0143] Step 1: Ingredient preparation: Weigh each raw material according to the weight percentage designed above. The total weight of the ingredients is 5kg. The preparation process is completed in an argon-protected glove box.

[0144] Step 2: Vacuum Melting and Belt Spinning: Place the prepared raw materials into the alumina crucible of the vacuum induction melting furnace, and evacuate the furnace until the vacuum degree is ≤5×10⁻⁶. -3 Pa, then high-purity argon gas is introduced into the furnace to a pressure of 0.05 MPa, and the temperature is raised to 1470℃ for melting. The temperature is held for 18 minutes to completely melt the raw materials and homogenize the alloy liquid. The molten alloy liquid is then smoothly poured onto a high-speed rotating copper roller, with the rotation speed of the copper roller controlled at 31 m / s, to prepare a rapid quenching thin strip with a thickness of 0.25-0.33 mm.

[0145] Step 3: Hydrogen Explosion Powder Preparation: Place the rapidly quenched thin strip into the hydrogen explosion furnace, and first evacuate the furnace until the vacuum level is ≤1×10⁻⁶. -2 The pressure was increased to 0.12 MPa, and then high-purity hydrogen was introduced into the furnace. Hydrogen was absorbed at room temperature for 2 hours to fully hydrogenate and fragment the thin strip. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min for dehydrogenation treatment, held at that temperature for 4 hours, and then evacuated to a vacuum level ≤1×10⁻⁶. -2 Pa, after cooling to room temperature, yields hydrogen explosion powder;

[0146] Step 4: Airflow milling: Add the hydrogen explosion powder to a closed-loop airflow mill, using high-purity nitrogen as the protective and grinding medium, control the grinding pressure at 0.6 MPa and the classifier wheel speed at 4500 r / min, and prepare ultrafine magnetic powder with an average particle size of 3.5 μm.

[0147] Step 5: Magnetic field orientation and pressing: The ultrafine magnetic powder is placed into the non-magnetic mold of the parallel magnetic field press and oriented in a uniform magnetic field with an orientation magnetic field strength of 2.2T. At the same time, pre-pressing is performed with a pre-pressing pressure of 15MPa and a holding pressure of 10s. Then, the pre-pressed green body is placed in a cold isostatic press and cold isostatically pressed at a pressure of 200MPa for 30s to obtain the pressed green body.

[0148] Step 6 Vacuum Sintering: Place the green billet into a high-vacuum sintering furnace and evacuate the furnace until the vacuum level is ≤5×10⁻⁶. -3 Pa, heated to 1035℃ at a heating rate of 5℃ / min, and sintered at that temperature for 4 hours to fully densify the green body;

[0149] Step 7 Tempering: After sintering, the furnace is cooled to 900℃ and held for 1 hour for primary tempering. Then, the furnace is cooled to 640℃ and held for 4 hours for secondary tempering. After tempering, the furnace is cooled to room temperature and then removed for machining to obtain high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnets for subsequent performance testing.

[0150] Example 4

[0151] A high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet has the following composition design based on the total weight percentage of the magnet: the total content of rare earth element RE is 32.85wt%, of which Nd is 0.64wt%, Ce is 15.94wt%, Gd is 2.42wt%, and Pr is 13.85wt%; the content of element B is 0.95wt%; the total content of trace element M is 1.02wt%, of which Cu is 0.20wt%, Al is 0.60wt%, Zr is 0.12wt%, and Ti is 0.10wt%; the balance is Fe and unavoidable impurities, with a total impurity content of 0.09wt%.

[0152] The method for preparing the high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet includes the following steps:

[0153] Step 1: Ingredient preparation: Weigh each raw material according to the weight percentage designed above. The total weight of the ingredients is 5kg. The preparation process is completed in an argon-protected glove box.

[0154] Step 2: Vacuum Melting and Belt Spinning: Place the prepared raw materials into the alumina crucible of the vacuum induction melting furnace, and evacuate the furnace until the vacuum degree is ≤5×10⁻⁶. -3Pa, then high-purity argon gas is introduced into the furnace to a pressure of 0.05 MPa, and the temperature is raised to 1450℃ for melting. The temperature is held for 20 minutes to completely melt the raw materials and homogenize the alloy liquid. The molten alloy liquid is then smoothly poured onto a high-speed rotating copper roller, with the rotation speed of the copper roller controlled at 30 m / s, to prepare a fast-quenching thin strip with a thickness of 0.25-0.35 mm.

[0155] Step 3: Hydrogen Explosion Powder Preparation: Place the rapidly quenched thin strip into the hydrogen explosion furnace, and first evacuate the furnace until the vacuum level is ≤1×10⁻⁶. -2 The pressure was increased to 0.12 MPa, and then high-purity hydrogen was introduced into the furnace. Hydrogen was absorbed at room temperature for 2 hours to fully hydrogenate and fragment the thin strip. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min for dehydrogenation treatment, held at that temperature for 4 hours, and then evacuated to a vacuum level ≤1×10⁻⁶. -2 Pa, after cooling to room temperature, yields hydrogen explosion powder;

[0156] Step 4: Airflow milling: Add the hydrogen explosion powder to a closed-loop airflow mill, using high-purity nitrogen as the protective and grinding medium, control the grinding pressure at 0.6 MPa and the classifier wheel speed at 4500 r / min, and prepare ultrafine magnetic powder with an average particle size of 3.2 μm.

[0157] Step 5: Magnetic field orientation and pressing: The ultrafine magnetic powder is placed into the non-magnetic mold of the parallel magnetic field press and oriented in a uniform magnetic field with an orientation magnetic field strength of 2.0T. At the same time, pre-pressing is performed with a pre-pressing pressure of 15MPa and a holding pressure of 10s. Then, the pre-pressed green body is placed in a cold isostatic press and cold isostatically pressed at a pressure of 200MPa for 30s to obtain the pressed green body.

[0158] Step 6 Vacuum Sintering: Place the green billet into a high-vacuum sintering furnace and evacuate the furnace until the vacuum level is ≤5×10⁻⁶. -3 Pa, heated to 1035℃ at a heating rate of 5℃ / min, and sintered at that temperature for 4 hours to fully densify the green body;

[0159] Step 7 Tempering: After sintering, the furnace is cooled to 900℃ and held for 1 hour for primary tempering. Then, the furnace is cooled to 640℃ and held for 4 hours for secondary tempering. After tempering, the furnace is cooled to room temperature and then removed for machining to obtain high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnets for subsequent performance testing.

[0160] Example 5

[0161] A high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet has the following composition design based on the total weight percentage of the magnet: the total content of rare earth element RE is 32.89wt%, of which Nd is 0.68wt%, Ce is 19.94wt%, Gd is 1.42wt%, and Pr is 10.85wt%; the content of element B is 1.0wt%; the total content of trace element M is 1.30wt%, of which Cu is 0.25wt%, Al is 0.70wt%, Zr is 0.15wt%, and Ti is 0.12wt%; the balance is Fe and unavoidable impurities, with a total impurity content of 0.09wt%.

[0162] The method for preparing the high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet includes the following steps:

[0163] Step 1: Ingredient preparation: Weigh each raw material according to the weight percentage designed above. The total weight of the ingredients is 5kg. The preparation process is completed in an argon-protected glove box.

[0164] Step 2: Vacuum Melting and Belt Spinning: Place the prepared raw materials into the alumina crucible of the vacuum induction melting furnace, and evacuate the furnace until the vacuum degree is ≤5×10⁻⁶. -3 Pa, then high-purity argon gas is introduced into the furnace to a pressure of 0.05 MPa, and the temperature is raised to 1470℃ for melting. The temperature is held for 18 minutes to completely melt the raw materials and homogenize the alloy liquid. The molten alloy liquid is then smoothly poured onto a high-speed rotating copper roller, with the rotation speed of the copper roller controlled at 31 m / s, to prepare a rapid quenching thin strip with a thickness of 0.28-0.35 mm.

[0165] Step 3: Hydrogen Explosion Powder Preparation: Place the rapidly quenched thin strip into the hydrogen explosion furnace, and first evacuate the furnace until the vacuum level is ≤1×10⁻⁶. -2 The pressure was increased to 0.12 MPa, and then high-purity hydrogen was introduced into the furnace. Hydrogen was absorbed at room temperature for 2 hours to fully hydrogenate and fragment the thin strip. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min for dehydrogenation treatment, held at that temperature for 4 hours, and then evacuated to a vacuum level ≤1×10⁻⁶. -2 Pa, after cooling to room temperature, yields hydrogen explosion powder;

[0166] Step 4: Airflow milling: Add the hydrogen explosion powder to a closed-loop airflow mill, using high-purity nitrogen as the protective and grinding medium, control the grinding pressure at 0.6 MPa and the classifier wheel speed at 4500 r / min, and prepare ultrafine magnetic powder with an average particle size of 3.4 μm.

[0167] Step 5: Magnetic field orientation and pressing: The ultrafine magnetic powder is placed into the non-magnetic mold of the parallel magnetic field press and oriented in a uniform magnetic field with an orientation magnetic field strength of 2.1T. At the same time, pre-pressing is performed with a pre-pressing pressure of 15MPa and a holding pressure of 10s. Then, the pre-pressed green body is placed in a cold isostatic press and cold isostatically pressed at a pressure of 200MPa for 30s to obtain the pressed green body.

[0168] Step 6 Vacuum Sintering: Place the green billet into a high-vacuum sintering furnace and evacuate the furnace until the vacuum level is ≤5×10⁻⁶. -3 Pa, heated to 1040℃ at a heating rate of 5℃ / min, and sintered at that temperature for 3.5h to fully densify the green body;

[0169] Step 7 Tempering: After sintering, the furnace temperature is lowered to 900℃ and held for 1 hour for primary tempering. Then, the furnace temperature is lowered to 650℃ and held for 3.5 hours for secondary tempering. After tempering, the furnace temperature is cooled to room temperature. The magnet is then removed and machined to obtain a high-abundance rare earth sintered Nd-Ce-Gd-Pr-Fe-B magnet for subsequent performance testing.

[0170] Comparative Example 1

[0171] A rare earth sintered NdFeB magnet has the following composition design based on the total weight percentage of the magnet: the total content of rare earth element RE is 33.0 wt%, of which Nd is 12.0 wt% and Ce is 21.0 wt%, with no added Gd or Pr elements; the content of element B is 0.95 wt%; the total content of trace element M is 1.02 wt%, of which Cu is 0.20 wt%, Al is 0.60 wt%, Zr is 0.12 wt%, and Ti is 0.10 wt%; the balance is Fe and unavoidable impurities, with a total impurity content of 0.1 wt%.

[0172] The preparation method of this comparative example is exactly the same as that of Example 1, except that Gd and Pr elements are removed in the component design and the contents of Nd and Ce are adjusted accordingly. All other process parameters remain the same.

[0173] Comparative Example 2

[0174] A rare earth sintered NdFeB magnet has the following composition by weight percentage: the total content of rare earth element RE is 33.0 wt%, of which Nd is 0.5 wt%, Ce is 20.0 wt%, Gd is 2.0 wt%, and Pr is 10.5 wt%; the content of element B is 0.95 wt%; the total content of trace element M is 0.92 wt%, of which Cu is 0.20 wt%, Al is 0.60 wt%, and Zr is 0.12 wt%, with no element Ti added; the balance is Fe and unavoidable impurities, with a total impurity content of 0.1 wt%.

[0175] The preparation method of this comparative example is exactly the same as that of Example 1, except that Ti element is removed in the component design and the total content of trace elements is adjusted accordingly, while the other process parameters remain the same.

[0176] Comparative Example 3

[0177] A rare earth sintered NdFeB magnet has the following composition by weight percentage: the total content of rare earth element RE is 33.0 wt%, of which Nd is 0.2 wt%, Ce is 20.3 wt%, Gd is 2.0 wt%, and Pr is 10.5 wt%; the content of element B is 0.95 wt%; the total content of trace element M is 1.02 wt%, of which Cu is 0.20 wt%, Al is 0.60 wt%, Zr is 0.12 wt%, and Ti is 0.10 wt%; the balance is Fe and unavoidable impurities, with a total impurity content of 0.1 wt%.

[0178] The preparation method of this comparative example is exactly the same as that of Example 1, except that the Ce content in the component design exceeds the limit of the present invention and the Nd content is lower than the lower limit of the present invention, while the other process parameters remain the same.

[0179] Comparative Example 4

[0180] A rare earth sintered NdFeB magnet has the following composition design based on the total weight percentage of the magnet: the total content of rare earth element RE is 33.0 wt%, of which Nd is 0.5 wt%, Ce is 20.0 wt%, Gd is 2.0 wt%, and Pr is 10.5 wt%; the content of element B is 0.95 wt%; the total content of trace element M is 0.22 wt%, of which Zr is 0.12 wt% and Ti is 0.10 wt%, and Cu and Al elements are not added; the balance is Fe and unavoidable impurities, with a total impurity content of 0.1 wt%.

[0181] The preparation method of this comparative example is exactly the same as that of Example 1, except that Cu and Al elements are removed in the component design and the total content of trace elements is adjusted accordingly. All other process parameters remain the same.

[0182] Comparative Example 5

[0183] A rare earth sintered NdFeB magnet has the same composition design as in Example 1. The only difference in the preparation method is that the parameters of the vacuum sintering process in step 6 are adjusted to: sintering temperature 1060℃, holding sintering for 4h. All other process steps and parameters are consistent with those in Example 1.

[0184] Comparative Example 6

[0185] A rare earth sintered NdFeB magnet has the same composition design as in Example 1. The only difference in the preparation method is that the parameters of the secondary tempering process in step 7 are adjusted to: tempering temperature 600℃, holding tempering for 4h. All other process steps and parameters are consistent with those in Example 1.

[0186] Performance test results and analysis:

[0187] The magnets prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to various performance tests according to the unified test method described above. The test results are summarized in Tables 1 and 2.

[0188]

[0189]

[0190] Phase composition and microstructure analysis:

[0191] As can be seen from the test results in Table 1, the RE2Fe in Examples 1-5 of this invention... 14 The proportion of the hard magnetic main phase in all examples reached over 86.63 wt%, with the optimal example 4 reaching 92.40 wt%. The proportion of the harmful Laves phase CeFe2 did not exceed 10.67 wt%, with the optimal example 4 only at 6.43 wt%, which is far lower than the impurity phase proportion of over 19.18 wt% in comparative examples 1-3. This fully demonstrates that the present invention, through the synergistic effect of Nd-Ce-Gd-Pr multi-rare earth elements and precise control of Ti elements, can suppress the generation of CeFe2 soft magnetic impurity phase from the source, significantly increase the proportion of hard magnetic main phase, and solve the core pain point of uncontrolled impurity phase in high Ce substitute magnets.

[0192] In Comparative Example 1, without the addition of Gd and Pr elements, the CeFe2 phase accounted for as high as 16.25 wt%, while the main phase accounted for only 80.94 wt%, proving that the synergistic addition of Gd and Pr can stabilize the main phase lattice and suppress Ce element segregation and impurity phase formation. In Comparative Example 2, without the addition of Ti elements, the CeFe2 phase accounted for 14.67 wt%, verifying that Ti elements are the core trace elements for suppressing impurity phase formation. In Comparative Example 3, the Ce content exceeded the limit range, and the CeFe2 phase accounted for soaring to 19.15 wt%, while the main phase accounted for less than 80 wt%, proving that the rare earth ratio range limited by this invention is the optimal range that balances cost reduction and impurity phase control.

[0193] Comparative Example 4, without the introduction of Cu and Al elements, exhibited poor wettability at grain boundaries, resulting in a magnet density of only 7.32 g / cm³. 3 Significantly lower than the 7.53 g / cm³ in Example 1 3 The above density levels confirm that Cu and Al composite doping can synergistically improve grain boundary wetting properties and are key alloying elements for improving the density of sintered magnets.

[0194] X-ray diffraction (XRD) was used to characterize the phase structure of sintered NdFeB samples. The obtained XRD patterns were compared with standard PDF cards to accurately determine the phase types and compositions of each sample. The room temperature XRD test data were quantitatively fitted using the Rietveld refinement method, and the results are as follows: Figure 1-5 As shown, the main phase content of each sample ranged from 86.63% to 92.4%, the secondary phase from 6.43% to 10.66%, and the remaining phase was rare earth grain boundary phase. The reliability factor and difference curve of the refined fit showed no significant systematic bias, indicating good fitting performance and accurate and reliable quantitative phase analysis results.

[0195] XRD patterns can clearly distinguish three characteristic phases: Ce2Fe with the P42 / mnm space group. 14 B main phase, The space group contains CeFe2 subphase and trace amounts of rare-earth grain boundary phases. Test results show that the REFe2 impurity phase in the system is dominated by CeFe2, which is a room-temperature paramagnetic soft magnetic impurity phase that degrades the overall magnetic properties of the sintered magnet. On the one hand, the CeFe2 phase hinders the uniform distribution of rare-earth-rich grain boundary phases, worsening the grain boundary wetting state; on the other hand, its formation consumes a large amount of Ce rare-earth elements, resulting in the ineffective depletion of rare-earth resources. Combined with... Figure 3-5 Data analysis shows that the relative content of CeFe2 impurity phase decreased from 9.77% to 6.73% after modification. The effective suppression of harmful defect impurity phase is an important reason for the improvement of key magnetic properties such as magnet coercivity.

[0196] Combination Figure 6-9 As can be seen from the microstructure morphology images of the magnets, the rare earth-rich grain boundary phases of Examples 1-4 of the present invention continuously and uniformly coat the main phase grains, forming a complete network structure, without the phenomenon of grain boundary phase agglomeration into blocks, and the main phase grains are uniform in size without abnormal growth.

[0197] Figure 10 This is an EPMA surface scan analysis image of the magnet prepared in Example 5 of the present invention, wherein... Figure 10 (1) is a microscopic image of the magnet, with the red circle representing the scanned area; Figure 10 (2) is a map showing the intensity distribution of iron (Fe); Figure 10 (3) is the intensity distribution diagram of cerium (Ce); Figure 10 (4) is the intensity distribution diagram of neodymium (Nd); Figure 10 (5) is the intensity distribution map of praseodymium (Pr); Figure 10 (6) is the intensity distribution diagram of gadolinium (Gd).

[0198] from Figure 10The elemental distribution results show that Nd, Ce, Pr, and Gd in Example 5 are uniformly distributed in the main phase grains without obvious component segregation. Rare earth elements are significantly enriched at the grain boundaries to form a continuous rare earth-rich grain boundary phase. Fe elements are mainly concentrated inside the main phase, and the Fe content at the grain boundaries is extremely low. This further proves that the composition and process design of the present invention can achieve uniform elemental distribution, avoid Ce element grain boundary segregation, suppress the formation of CeFe2 impurity phase, and at the same time promote the uniform enrichment of rare earth elements at the grain boundaries to form a continuous network grain boundary structure.

[0199] Magnetic property analysis:

[0200] As can be seen from the test results in Table 2, the room temperature magnetic properties of Examples 1-5 of the present invention all satisfy the following: remanence Br ≥ 9.19 kGs, intrinsic coercivity H cj ≥5.686kOe, maximum energy product (BH) max ≥20.676 MGOe, demagnetization curve squareness H k / H cj ≥90.501%, fully meeting the expected performance indicators, achieving excellent overall magnetic properties under the premise of high Ce substitution. Among them, Example 4 has the best magnetic properties, with Br reaching 10.699 kGs and H... cj It can reach 8.645 kOe (BH). max With a performance of up to 25.889 MGOe and a squareness of up to 96.311%, it can meet the performance requirements of mid-to-high-end application scenarios.

[0201] In stark contrast, the overall magnetic properties of Comparative Examples 1-6 all deteriorated significantly. Comparative Example 1, lacking Gd and Pr elements, exhibited a severe magnetic dilution effect, with a coercivity of only 4.172 kOe, a maximum energy product of only 17.018 MGOe, and a squareness of less than 78%. This demonstrates that the synergistic ratio of the four rare earth elements is the core foundation for mitigating the magnetic dilution effect and ensuring the intrinsic magnetic properties of the main phase. Comparative Example 2, lacking Ti elements, resulted in the formation of a large amount of CeFe2 impurity phase, leading to a significant decrease in magnetic properties. In Comparative Example 3, the excessively high Ce content resulted in a precipitous drop in magnetic properties, verifying the rationality of the Ce content limitation range in this invention.

[0202] Comparative Example 4, lacking Cu and Al elements, exhibited deteriorated grain boundary structure, resulting in a significant decrease in coercivity and squareness. Comparative Example 5, with an excessively high sintering temperature, experienced abnormal grain growth in the main phase, leading to a substantial reduction in coercivity. Comparative Example 6, with an excessively low tempering temperature, suffered from insufficient optimization of the grain boundary phase, resulting in both squareness and coercivity failing to meet standards. These results fully demonstrate that this invention, through synergistic regulation of trace elements and optimization of the entire preparation process, achieves precise control of grain boundary structure and maximizes magnetic decoupling effects, significantly improving the coercivity, squareness, and overall magnetic properties of the magnet, thus overcoming the technical bottleneck of performance degradation in high-Ce substitute magnets.

[0203] Figure 11This is a graph showing the room temperature demagnetization curve of the magnet, where... Figure 11 (a) is a demagnetization curve at room temperature for Examples 1-2 of the present invention. Figure 11 (b) is a demagnetization curve at room temperature for Examples 3-5 of the present invention. Figure 11 (a) It can be seen that, under the condition that the content of the main added rare earth element cerium (Ce) is fixed, increasing the amount of gadolinium (Gd) will lead to a decrease in the key magnetic properties of the magnet, such as coercivity and remanence. Figure 11 (b) It can be seen that with the increase of the main rare earth element cerium (Ce), the coercivity of the magnet shows a significant decreasing trend, while the remanence, maximum energy product, squareness, and other magnetic properties show an improving trend: the coercivity decreases from 8.645 kOe to 6.68 kOe, the remanence increases from 9.572 kGs to 10.699 kGs, the maximum energy product increases from 20.676 MGOe to 25.889 MGOe, and the squareness is also improved to varying degrees. The essence of this phenomenon is the effect of magnetic dilution, that is, cerium (Ce) replaces neodymium (Nd) in the 2:14:1 phase lattice, which leads to a decrease in the intrinsic magnetic properties of the magnet.

[0204] Corrosion resistance analysis:

[0205] As can be seen from the potentiodynamic polarization test results in Table 2, the corrosion potential Ecorr of Examples 1-5 of this invention is ≥-0.65V, and the corrosion current density icorr is ≤8.6μA / cm. 2 It exhibits excellent corrosion resistance. Example 4 showed the highest corrosion potential (-0.615V) and the lowest corrosion current density (5.74μA / cm²). 2 (It has the best corrosion resistance.)

[0206] The corrosion potentials of comparative examples 1-6 were all below -0.65V, and the corrosion current densities were all above 10μA / cm². 2 The corrosion resistance deteriorated significantly. Comparative Examples 1 and 3 showed corrosion current densities as high as 15.63 μA / cm². 2 18.92μA / cm 2 The core reason is the formation of a large amount of CeFe2 impurity phase, which leads to an increase in the multiphase interface inside the magnet, exacerbating galvanic corrosion. At the same time, the uneven distribution of grain boundary phases increases the number of corrosion channels. In contrast, without the addition of Cu and Al elements, the magnet in Comparative Example 4 has low density, many internal pores and defects, and is easily penetrated by corrosive media, resulting in a significant decrease in corrosion resistance.

[0207] Figure 12 The image shows the metallographic morphology of the magnet after corrosion prepared in Example 5 of this invention. As can be seen from the image, the grain boundaries (GBs) are clearly distinguishable. The white contrast area corresponds to the rare earth (RE) grain boundary phase (GBP), and the black contrast area is Nd2Fe. 14The B matrix phase (i.e., the 2:14:1 phase) shows a clear boundary between it and the rare-earth-rich grain boundary phase, indicating that the magnet maintains good structural integrity even after electrochemical corrosion treatment. This contrasts sharply with... Figure 13 The grain boundaries of the medium magnet have been completely corroded and are indistinguishable. Obvious corrosion pits and grain detachment are also visible within the corroded areas. The rare-earth-rich grain boundary phase, which has relatively higher electrochemical activity, has completely dissolved or corroded. These morphological characteristics confirm that... Figure 13 The magnet prepared in Comparative Example 1 exhibited poor corrosion resistance and was more prone to electrochemical corrosion in a 3.5 wt% NaCl aqueous solution. These conclusions further verify that the present invention, through synergistic optimization of components, can fundamentally inhibit intergranular corrosion, significantly improve the corrosion resistance of magnets, and achieve a synergistic improvement in both magnetic properties and corrosion resistance.

[0208] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet, characterized in that, The magnet comprises the following components by weight percentage: rare earth element RE 30.0-33.0 wt%, boron element 0.90-1.00 wt%, trace element M 0.80-1.30 wt%, with the balance being Fe and unavoidable impurities; The rare earth elements (RE) comprise, by weight percentage of the total magnet,: Nd 0.5-1.0 wt%, Ce 15.0-20.0 wt%, Gd 0.5-2.5 wt%, and Pr 10.0-15.0 wt%. The trace element M, by weight percentage of the magnet, includes: Cu 0.15-0.25wt%, Al 0.50-0.70wt%, Zr 0.08-0.15wt%, and Ti 0.08-0.12wt%.

2. The high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to claim 1, characterized in that, The total content of the unavoidable impurities is ≤0.1wt%.

3. The high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to claim 1, characterized in that, Based on the total weight percentage of the magnet, it includes the following components: the total content of rare earth element RE is 32.85wt%, the content of element B is 0.95wt%, the total content of trace element M is 1.02wt%, and the balance is Fe and unavoidable impurities, with the total content of impurities being 0.09wt%.

4. The high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to claim 3, characterized in that, The rare earth elements RE, by weight percentage of the total magnet, include: 0.64 wt% Nd, 15.94 wt% Ce, 2.42 wt% Gd, and 13.85 wt% Pr.

5. The high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to claim 3, characterized in that, The trace element M, calculated as a percentage of the total weight of the magnet, includes: 0.20 wt% Cu, 0.60 wt% Al, 0.12 wt% Zr, and 0.10 wt% Ti.

6. A method for preparing a high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Ingredient preparation: Weigh each raw material according to the weight percentage of the component design and complete the preparation under inert gas protection; Step 2 Vacuum melting and strip casting: Place the prepared raw materials in a vacuum induction melting furnace, evacuate the furnace and fill it with inert gas, heat it to 1430-1470℃ for melting, hold it at the temperature to homogenize it, and then cast the alloy liquid onto a copper roller with a rotation speed of 29-31m / s to prepare a rapid quenching thin strip. Step 3: Hydrogen explosion powder preparation: The rapidly quenched thin strip is placed in a hydrogen explosion furnace for hydrogenation treatment, and then heated to remove hydrogen to obtain hydrogen explosion powder. Step 4: Grinding with an air jet mill: The hydrogen explosion powder is ground by an air jet mill to prepare ultrafine magnetic powder with an average particle size of 3.0-3.5 μm; Step 5: Magnetic field orientation and pressing: The ultrafine magnetic powder is pre-pressed in an orientation magnetic field of 1.8-2.2T, and then cold isostatically pressed to obtain a green body; Step 6 Vacuum sintering: Place the green blank in a vacuum sintering furnace, evacuate the vacuum, raise the temperature to 1030-1040℃, and sinter at that temperature for 3.5-4.5 hours; Step 7 Tempering treatment: After sintering, first tempering is performed, followed by second tempering at 630-650℃, and the temperature is lowered to 3.5-4.5h. After cooling, the magnet is obtained.

7. The method for preparing a high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to claim 6, characterized in that, In step 2, the prepared raw materials are placed into the alumina crucible of the vacuum induction melting furnace, and the furnace is evacuated until the vacuum level is ≤5×10⁻⁶. -3 Pa, then high-purity argon gas is introduced into the furnace to a pressure of 0.05 MPa, and the temperature is raised to 1430-1470℃ for melting. The temperature is held for 20 minutes to completely melt the raw materials and homogenize the alloy liquid.

8. The method for preparing a high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to claim 6, characterized in that, In step 3, the rapidly quenched thin strip is placed in the hydrogen explosion furnace, and a vacuum is first drawn until the vacuum degree inside the furnace is ≤1×10⁻⁶. -2 The pressure was increased to 0.12 MPa, and then high-purity hydrogen was introduced into the furnace. Hydrogen was absorbed at room temperature for 2 hours to fully hydrogenate and fragment the thin strip. Subsequently, the temperature was increased to 500℃ at a rate of 10℃ / min for dehydrogenation treatment, held at that temperature for 4 hours, and then evacuated to a vacuum level ≤1×10⁻⁶. -2 Pa, after cooling to room temperature, yields hydrogen explosion powder.

9. The method for preparing a high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to claim 6, characterized in that, In step 5, the ultrafine magnetic powder is placed into the non-magnetic mold of the parallel magnetic field press and oriented in a uniform magnetic field with an orientation magnetic field strength of 1.8-2.2T. At the same time, pre-pressing is performed with a pre-pressing pressure of 15MPa and a holding pressure of 10s. Then, the pre-pressed blank is placed into a cold isostatic press and cold isostatically pressed at a pressure of 200MPa for 30s to obtain the pressed green blank.

10. The method for preparing a high-abundance rare-earth sintered Nd-Ce-Gd-Pr-Fe-B magnet according to claim 6, characterized in that, The temperature of the first-stage tempering in step 7 is 880-920℃, and the holding time is 0.8-1.2h.

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