Sintered R-Fe-B permanent magnets and their manufacturing methods and applications

Abstract

To provide a sintered R-Fe-B permanent magnet that has high coercivity magnetic performance and squareness, and significantly improves the magnet's resistance to high temperature demagnetization and a manufacturing method and application thereof.SOLUTION: A sintered R-Fe-B permanent magnet includes at least a grain boundary containing an RH-rich phase and a composite main phase crystal grain, the RH-rich phase has a nodular shape and is distributed within the grain boundaries between the composite main phase crystal grains, and is preferably located at the boundary of any three or more adjacent composite main phase crystal grains, has a thin band shape, and is continuously distributed along the grain boundary. The RH content at the grain boundaries is greater than a RH content at the main phase crystal grains. The composite main phase crystal grain has a core-shell structure including a core structure having an R-T-B type phase structure and a shell structure in an outer layer of the core structure, and the core structure includes Ce-rich main phase crystal grains and Ce-deficient main phase crystal grains.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from a prior application bearing patent application number 202210962847.2 and entitled "Sintered R-Fe-B permanent magnet, its manufacturing method and application," filed with the State Intellectual Property Office of the People's Republic of China on August 11, 2022. The prior application is incorporated herein by reference in its entirety.

[0002] [Technical Field] The present invention relates to the technical field of manufacturing rare earth permanent magnet materials, and more particularly to a sintered R-Fe-B permanent magnet with grain boundary diffusion, its manufacturing method and applications. [Background technology]

[0003] Sintered neodymium iron boron magnets, a third-generation rare earth permanent magnet material primarily composed of rare earth elements PrNd, iron, and boron, are widely used in various rare earth permanent magnet motors, smart consumer electronics, medical devices, and other applications due to their excellent magnetic properties and high cost-effectiveness. With the rapid development of a low-carbon, environmentally friendly economy and high technology, demand for sintered neodymium iron boron magnets is growing, significantly increasing the consumption of rare earth PrNd resources and gradually raising the price of PrNd. La and Ce share similar chemical properties to PrNd and are the most abundant rare earth elements, but their relatively poor intrinsic magnetic properties limit their application in rare earth permanent magnet materials. Currently, one of the research topics for rare earth conservation is how to increase the amount of La and Ce to reduce costs without affecting magnetic performance.

[0004] In the prior art, there are several main methods for adding La and Ce to magnets. The first is to add them in the form of an alloy, i.e., adding metallic La and Ce raw materials during the smelting process. The second is to add them in the form of a dual alloy, i.e., first smelting (R, LaCe)-Fe-B and R-Fe-B alloy flakes (where R is one or more selected from Nd, Pr, Dy, Tb, Ho, and Gd) separately, then mixing the alloy flakes in a certain ratio and pressure sintering them. The third method is to attach La and Ce compounds or alloys to the magnet surface, followed by an appropriate heat treatment process to diffuse the La and Ce into the magnet.

[0005] In the above method, the addition of La and Ce in the form of alloying causes them to penetrate into the main phase crystal grains, reducing the saturation polarization strength, Curie temperature, and magnetocrystalline anisotropy field of the main phase crystal grains, and further reducing the initial performance of the magnet, limiting its application and development. However, the diffusion method of incorporating La and Ce into the magnet has technical drawbacks, such as a complex and cumbersome process, insufficient La and Ce addition, and difficulty in improving the magnet's coercivity, resulting in low cost performance and disadvantages in its application and development. The dual alloying method can prevent La and Ce from penetrating into the main phase crystal grains to a certain extent, and is therefore the main manufacturing process for NdFeB magnets containing La and Ce.

[0006] However, to achieve high-performance NdFeB magnets containing La and Ce and compensate for the decreased magnetic performance caused by the addition of La and Ce, heavy rare earth elements such as Dy and Tb are typically added to La- and Ce-rich magnets to improve their magnetic performance. Heavy rare earth grain boundary diffusion technology is currently the most effective and feasible method. Therefore, research has been conducted to combine NdCeFeB dual alloys with grain boundary diffusion technology to produce high-coercivity magnets, but the resulting magnets have not performed as expected. The main reason for this is that the grain boundary phase composition and structure of the diffusion substrate magnet play a crucial role in the penetration of heavy rare earth elements and their flow and dispersion within the magnet.

[0007] In neodymium-cerium-iron-boron magnets manufactured using the dual alloying method, the differences in the composition of the main and auxiliary phases result in significant differences in the concentrations of the constituent elements, which significantly impacts the penetration of heavy rare earth elements into the magnet and ultimately results in a less significant improvement in the magnet's coercivity. Because the distribution of rare earth elements in the two main phases is uneven, the grain boundary diffusion of heavy rare earth elements involves multiple scenarios. On the one hand, diffusion replaces Nd in the Nd2Fe14B main phase, and on the other hand, diffusion replaces Ce in the Ce2Fe14B main phase. These two processes compete with each other, and the replaced Nd or Ce undergoes further diffusion and replacement processes, resulting in the heavy rare earth elements being substituted into the main phase, resulting in a low utilization rate of the heavy rare earth elements and a decrease in the coercivity of the magnet after diffusion. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides an R-Fe-B permanent magnet with high coercivity, its manufacturing method and application.

[0009] The present invention provides an R—Fe—B permanent magnet including at least grain boundaries and composite main phase grains, the grain boundaries contain RH-rich phases, the RH-rich phases are nodular and distributed within the grain boundaries between the composite main phase crystal grains, and are preferably located at the boundaries of any three or more adjacent composite main phase crystal grains, and the RH-rich phases may be thin band-like and continuously distributed along the grain boundaries; the content of RH in the grain boundaries is greater than the content of RH in the main phase crystal grains, and RH is at least one selected from heavy rare earth metals such as Dy, Tb, and Ho; The composite main phase crystal grains have a core-shell structure including a core structure having an RTB type phase structure and a shell structure located on the outer layer of the core structure, The core structure includes Ce-rich main phase crystal grains and Ce-deficient main phase crystal grains, and the Ce-rich main phase crystal grains have a Ce content of 1 to 15 wt%, while the Ce-deficient main phase crystal grains have a Ce content of 0 to 1 wt%.

[0010] According to an embodiment of the present invention, the content of RH in the grain boundary is preferably greater than the content of RH in the shell structure.

[0011] According to an embodiment of the present invention, the content of RL in the shell structure is equal to or greater than the content of RL in the core structure.

[0012] According to an embodiment of the present invention, RL is at least one selected from light rare earth metals such as Pr and Nd.

[0013] According to an embodiment of the present invention, the permanent magnet has a structure shown in FIG. 1 , and the permanent magnet includes at least grain boundaries and composite main phase crystal grains having a core-shell structure, the core structure includes Ce-rich main phase crystal grains and Ce-deficient main phase crystal grains, and has a shell structure on the outer layer of the core structure, the content of RL in the shell structure is equal to or greater than the content of RL in the core structure, and the content of RH in the grain boundaries is greater than the content of RH in the main phase crystal grains.

[0014] According to an embodiment of the present invention, the RTB type phase structure comprises at least the following components: R, in weight percentages of 28%≦R≦35%, is at least one selected from neodymium (Nd), cerium (Ce), and optionally included or not included scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); B, whose weight percentage is 0.8%≦B≦1.2%; M is at least one selected from aluminum (Al), titanium (Ti), copper (Cu), gallium (Ga), zirconium (Zr), and niobium (Nb), and the weight percentage of M is 0≦M≦5%; and the balance being T selected from iron (Fe), and optionally included or not included cobalt (Co).

[0015] According to an embodiment of the present invention, the permanent magnet is obtained by mixing a powder of a low-Ce main alloy and a powder of a high-Ce auxiliary alloy, press-molding, sintering, and then subjecting the mixture to composite diffusion.

[0016] Preferably, in the low Ce main alloy, the Ce content is 1 wt% or less, and more preferably 0 to 1 wt%.

[0017] Preferably, in the high Ce auxiliary alloy, the Ce content is greater than 1 wt% and less than or equal to 15 wt%.

[0018] According to an embodiment of the present invention, the permanent magnet has a phase structure of the grain boundaries and composite main phase crystal grains from the surface to the core. In the present invention, the core of the permanent magnet means a position at least 500 μm away from the magnet surface.

[0019] According to an embodiment of the present invention, the Ce content in the grain boundary phase is not specifically limited.

[0020] The present invention further provides a method for producing the above-mentioned permanent magnet, which includes mixing a low-Ce main alloy powder and a high-Ce auxiliary alloy powder, press-molding the mixture, sintering the mixture to obtain a billet, and then subjecting the billet to composite diffusion to obtain the above-mentioned permanent magnet.

[0021] Preferably, in the above-mentioned low Ce main alloy, the Ce content is 1 wt% or less, preferably 0 to 1 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%.

[0022] Preferably, in the high Ce auxiliary alloy, the Ce content is greater than 1 wt% and less than or equal to 15 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%.

[0023] According to an embodiment of the present invention, the low-Ce main alloy powder and the high-Ce auxiliary alloy powder can be produced by a method known in the art, for example, by hydrogen pulverization, dehydrogenation, and pulverization of alloy flakes. The hydrogen pulverization, dehydrogenation, and pulverization can be performed by a method known in the art.

[0024] For example, main alloy flakes are produced from a low-Ce main alloy, and the main alloy flakes are then subjected to hydrogen pulverization, dehydrogenation, and powdering to produce a powder of the low-Ce main alloy.

[0025] For example, auxiliary alloy flakes are produced from a high Ce auxiliary alloy, and then the auxiliary alloy flakes are subjected to hydrogen pulverization, dehydrogenation, and powdering to produce a powder of the high Ce auxiliary alloy.

[0026] According to an embodiment of the present invention, the mass ratio of the low-Ce main alloy powder to the high-Ce auxiliary alloy powder is (1 to 50):1, for example, 1:1, 5:1, 10:1, or 20:1.

[0027] According to an embodiment of the present invention, the press-molding step includes mixing a powder of a low-Ce main alloy and a powder of a high-Ce auxiliary alloy, and then press-molding the mixture under the action of a magnetic field to obtain a green compact.

[0028] Preferably, the magnetic field can be selected from those known in the art, for example, a magnetic field having a field strength of 2T.

[0029] According to embodiments of the present invention, the pressing may be performed in equipment known in the art, for example, in a press die cavity.

[0030] According to an embodiment of the present invention, after press forming, a cold isostatic pressing process may be performed to further increase the billet density.

[0031] According to an embodiment of the present invention, the sintering process includes heat treating the powder compact by increasing the temperature to 1000 to 1100° C. in a vacuum atmosphere, and then obtaining a billet.

[0032] According to an embodiment of the present invention, the composite diffusion treatment includes providing a diffusion material on the surface of the billet and heat treating it.

[0033] According to an embodiment of the present invention, the diffusion material can be provided on the surface of the billet by a method known in the art, and is not specifically limited in the present invention.

[0034] According to an embodiment of the present invention, a slurry containing the diffusion material is uniformly applied to the surface of the billet.

[0035] According to an embodiment of the present invention, the diffusion material comprises RH, RL, and optionally added or unadded M powder.

[0036] Preferably, the RH is at least one selected from heavy rare earth metals such as Dy, Tb, and Ho.

[0037] Preferably, the RL is at least one selected from light rare earth metals such as Pr and Nd.

[0038] Preferably, the M powder is selected from Ga and / or Cu.

[0039] According to an embodiment of the present invention, the diffusion material includes the following components: RH content of 20-70 wt%, RL content of 20-70 wt%, and M powder content of 0-10 wt%.

[0040] Preferably, in the diffusion material, the mass ratio of the RH, RL and M powders is (1-10):(1-5):(0-2), for example, 8:3:0, 4:4:0, 4:3.5:0.5.

[0041] According to an embodiment of the present invention, the RH and RL are provided by RH powder and RL powder, respectively.

[0042] Preferably, the RH powder is at least one selected from a single metal RH, an alloy of RH, an oxide, fluoride, hydride, and oxyfluoride of RH. Exemplarily, the RH powder is at least one selected from a single metal, alloy, oxide, fluoride, hydride, and oxyfluoride of Dy. Exemplarily, the RH powder is at least one selected from a single metal, alloy, oxide, fluoride, hydride, and oxyfluoride of Tb. Exemplarily, the RH powder is at least one selected from a single metal, alloy, oxide, fluoride, hydride, and oxyfluoride of Ho.

[0043] Preferably, the RL powder is at least one selected from the group consisting of a single metal RL, an alloy RL, an oxide RL, a fluoride RL, a hydride RL, and an oxyfluoride RL. Exemplarily, the RL powder is at least one selected from the group consisting of a single metal Pr, an alloy Pr, an oxide Pr, a fluoride Pr, a hydride Pr, and an oxyfluoride Pr. Exemplarily, the RL powder is at least one selected from the group consisting of a single metal Pr, an alloy Pr, an oxide Pr, a fluoride Pr, a hydride Pr, and an oxyfluoride Pr.

[0044] According to an embodiment of the present invention, the diffusion material may further contain a diffusion aid and / or a solvent. The diffusion aid and solvent may be selected from materials known in the art. For example, the diffusion aid is 4-hexylresorcinol, and the solvent is ethanol.

[0045] Preferably, in the present invention, the amount of the diffusion aid and / or solvent used is not specifically limited as long as the diffusion of the diffusion material can be realized.

[0046] Illustratively, in the diffusion material, the mass ratio of RH, diffusion aid, and solvent is (1-5):(0-3):(0-3), for example, 4:2:1.

[0047] In the present invention, there are clear differences in the components between the composite main phase crystal grains and within the single composite main phase crystal grains. These non-uniform chemical components and distributions cause short-range strong exchange interactions and long-range magnetostatic coupling interactions within the magnet, effectively improving the nucleation field of the reverse magnetization domains of the magnet, suppressing the nucleation of the reverse magnetization domains, and preventing the expansion of the reverse magnetization domains, thereby significantly improving the coercive force of the magnet.

[0048] However, when permanent magnets are manufactured using a Ce or Nd single alloy process and a composite diffusion process, or when permanent magnets are manufactured using a Nd and Ce dual alloy process and an RH diffusion process, the same performance level cannot be obtained. The reason for this is that the components of the main phase crystal grains are basically the same, exhibiting homogeneity and not being able to achieve long-range magnetostatic coupling, so that Hcj performance equivalent to that of the present invention cannot be obtained under the same components and process conditions.

[0049] The present invention further provides applications of the permanent magnet, such as motor applications. [Effects of the Invention]

[0050] 1. The permanent magnet produced by the present invention contains two different types of composite main-phase crystal grains. Due to the long-range magnetostatic coupling between the crystal grains and the short-range strong exchange interaction within the single composite main-phase crystal grain, the magnet has high coercivity.

[0051] 2. The composite diffusion process of the present invention ensures deeper diffusion of the heavy rare earth elements on the magnet surface, resulting in better diffusion effects. The structural characteristics of the composite phase are also present in the core of the magnet, which is far from the surface (i.e., 500 μm from the surface), ensuring a uniform distribution throughout the magnet's structure, effectively improving the magnet's coercive force and squareness, and significantly improving the magnet's resistance to high-temperature demagnetization.

[0052] 3. Furthermore, the present invention uses a composite diffusion source to effectively lower the melting point of the grain boundary phase, increase the diffusion channels for the heavy rare earth elements, and improve the diffusion distance of the heavy rare earth elements within the magnet, ensuring that every micro-region within the magnet can form composite main phase grains, improving the uniformity of the microstructure distribution and further improving the Hcj and squareness of the magnet. [Brief explanation of the drawings]

[0053] [Figure 1] FIG. 2 is a schematic diagram illustrating the characteristics of the main phase and grain boundary phase in the surface layer of the magnet of Example 1-1. [Figure 2] FIG. 1 is a scanning electron microscope backscattering diagram of the magnet core part (50 μm from the magnet surface) of Example 1-1. [Figure 3] 1 shows EPMA images of Dy and Pr elements in a cross section of the magnet core (50 μm from the magnet surface) of Example 1-1 (a is a Dy element distribution map, and b is a Pr element distribution map). [Figure 4] 1 is an EPMA image of a linear scan of the Ce element content passing through the main phase crystal grains in a cross section of the magnet core portion (50 μm from the magnet surface) of Example 1-1. [Figure 5] 1A is a scanning electron microscope backscattering pattern of the magnet core (50 μm from the magnet surface) of Comparative Example 1-1, and FIG. 1B is an EMPA image of Dy element in a cross section of the core. [Example]

[0054] The technical solutions of the present invention will be described in more detail below with reference to specific examples. It should be understood that the following examples are merely for illustrative purposes and should not be construed as limiting the scope of the claims of the present invention. Any technology realized based on the above content of the present invention is included within the scope of the claims of the present invention.

[0055] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0056] Example 1-1 The manufacturing method of the R-Fe-B permanent magnet is as follows.

[0057] (1) Production of alloy flakes: The raw materials were weighed according to the compositions of the main phase alloy and auxiliary phase alloy shown in Table 1, and the main phase alloy flakes and auxiliary phase alloy flakes were produced using the following method: A vacuum induction smelting furnace was used to smelt under the protection of an Ar gas atmosphere, and the molten liquid was poured onto a quench roll rotating at a speed of 32 rpm, at a liquid pouring temperature of 1400°C, producing main phase alloy flakes with an average thickness of 0.25 mm and auxiliary phase alloy flakes with an average thickness of 0.30 mm.

[0058] (2) Preparation of alloy powder: The main phase alloy flakes and the auxiliary phase alloy flakes were subjected to hydrogen pulverization, dehydrogenation, and jet milling, respectively, to produce main phase alloy powders and auxiliary phase alloy powders with average particle sizes of 3.0 μm and 2.8 μm. The main phase alloy powder and the auxiliary phase alloy powder were mixed in a mass ratio of 3:1 under the protection of a N2 gas atmosphere, and an antioxidant lubricant of 0.05 wt% was added and stirred to mix uniformly.

[0059] (3) Press molding: Under the protection of N2 gas atmosphere, the mixed powder was filled into the cavity of the press molding equipment mold, and then subjected to orientation molding pressing with an orientation magnetic field strength of 3 T, followed by isostatic treatment at a pressure of 180 MPa in an isostatic press to obtain a pressed billet.

[0060] (4) Sintering treatment: The pressed billet from step (3) was placed in a vacuum sintering furnace, heated to 300-400°C at a heating rate of 3°C / min, then heated to 670°C at a heating rate of 5°C / min, held at 670°C for 70 minutes, then heated to 1040°C at a heating rate of 8°C / min, and sintered for 5 hours, followed by primary aging at 900°C for 4 hours and secondary aging at 530°C for 3 hours to obtain a sintered billet. The billet was processed into a sheet with a size of 40 x 25 mm and a thickness of 5 mm in the orientation direction.

[0061] (5) Diffusion Treatment: The materials were mixed in a mass ratio of 4:4:2:1 (Dy, Pr, 4-hexylresorcinol, and ethanol). The mixture was then mechanically stirred for 2 hours to obtain a diffusion slurry containing Dy and Pr. The diffusion slurry was evenly applied to the surface of the sheet obtained in step (4) so ​​that the coating amount was 1% of the base magnet mass. The sheet was then dried at 60°C for 5 minutes to obtain a Dy and Pr metal diffusion source-coated sheet. The sheet was then vacuum infiltrated at 740°C for 4 hours, then at 930°C for 6 hours, and finally vacuum aged at 500°C for 4.5 hours to obtain an R-Fe-B permanent magnet M1 after the Dy and Pr mixed diffusion treatment.

[0062] [Table 1]

[0063] Example 1-2 The method for producing a permanent magnet of this example is basically the same as that of Example 1-1, except that Pr in the diffusion slurry in step (5) is replaced with Nd.

[0064] Examples 1-3 The manufacturing method of the permanent magnet of this example is basically the same as that of Example 1-1, except that the diffusion slurry in step (5) further contains Cu, and the diffusion slurry is a mixture of Dy single metal, Pr single metal, Cu metal, 4-hexylresorcinol, and ethanol in a mass ratio of 4:3.5:0.5:2:1.

[0065] Comparative Example 1-1 The method for producing a permanent magnet of this comparative example was basically the same as that of Example 1-1, except that Pr was not included in the diffusion slurry in step (5).

[0066] Table 2 shows the test results of the magnetic properties of the sintered billet in Example 1-1 and the permanent magnets produced in Examples 1-1 to 1-4. [Table 2]

[0067] FIG. 1 is a characteristic schematic diagram of the main phase and grain boundary phase of the surface layer of the permanent magnet of Example 1-1.

[0068] FIG. 2 is a characteristic schematic diagram of the main phase and grain boundary phase of the permanent magnet core portion (500 μm from the magnet surface) of Example 1-1.

[0069] FIG. 3 shows EPMA images of Dy and Pr elements in a cross section of the magnet core (50 μm from the magnet surface) of Example 1-1 (the left image is a Dy element distribution map, and the right image is a Pr element distribution map).

[0070] FIG. 4 is an EPMA image of a linear scan of the Ce element content passing through the main phase crystal grains in a cross section of the magnet core (50 μm from the magnet surface) of Example 1-1.

[0071] As can be seen from Figures 1 to 4, the permanent magnet includes at least grain boundaries and composite main phase crystal grains, the grain boundaries include RH-rich phases, the RH-rich phases are nodular and distributed within the grain boundaries between the composite main phase crystal grains, and are preferably located at the boundaries between any three or more adjacent composite main phase crystal grains, and the RH-rich phases are thin band-like and continuously distributed along the grain boundaries.

[0072] As can be seen from Figures 2 and 3, the RH-rich phase in the permanent magnet appears as a bright white area in the backscattered imaging mode of a scanning electron microscope. It is distributed between adjacent main phase grains or at the boundaries of three or more main phase grains, and its RH content is greater than that of the main phase crystal grains.

[0073] 2 and 4, the composite main phase grains include Ce-rich and Ce-deficient main phase grains, which are shown in dark gray areas in the backscattered imaging mode of a scanning electron microscope. The Ce content in the Ce-rich main phase grains is 14.5 wt%, and the Ce content in the Ce-deficient main phase grains is 0.5 wt%.

[0074] As can be seen from Figures 2 and 3, the composite main phase grains have a core-shell structure, of which the shell structure is the light gray area in the backscattered scanning electron microscope imaging mode and is rich in RL elements, with the RL content in the shell structure being equal to or greater than that in the core structure.

[0075] Furthermore, Figure 3 shows the distribution of Dy in a cross section of the magnet core (50 μm from the magnet surface) of Example 1-1, and Figure 5 shows the distribution of Dy in a cross section of the magnet core (50 μm from the magnet surface) of Comparative Example 1-1. As can be seen from Figures 3 and 5, Example 1-1 and Comparative Example 1-1 were subjected to complex diffusion using sintered billets of the same composition. As can be seen from the measurement results in Figures 3 and 4, changing the diffusion treatment method did not cause a change in the Dy content inside the magnet along the diffusion direction, but the coercivity inside the magnet was significantly improved. The inventors believe that the difference in coercivity between the permanent magnets obtained using the two diffusion methods is due not to a concentration gradient but to differences in microstructure. Observation of a cross section 50 μm from the magnet surface revealed that the sample of Example 1 had more continuous Dy enrichment stripes along the grain boundaries, while the sample of Comparative Example 1 did not enrich at the grain boundaries and was instead replaced within the main phase through a diffusion and replacement process. The reason is that when the diffusion material contains RL, it diffuses more easily into the main phase than RH, so the main phase forms a core-shell structure, and the content of RL in the surface shell structure is relatively high, which prevents RH from replacing the main phase structure in the diffusion material, allowing the Dy element to diffuse into the core part of the permanent magnet along the grain boundaries.

[0076] As can be seen from the above analysis, in the grain boundary phase of the permanent magnet manufactured according to the present invention, the RH element can diffuse to a position deeper in the core region than in the surface layer of the magnet, demonstrating the excellent composite diffusion effect of the present invention.

[0077] Example 2-1 The method for manufacturing the permanent magnet of this example is basically the same as that of Example 1-1, except that the raw materials are weighed according to the compositions of the main phase alloy and auxiliary phase alloy shown in Table 3. [Table 3]

[0078] Example 2-2 The method for producing a permanent magnet of this example is basically the same as that of Example 2-1, except that Pr in the diffusion slurry in step (5) is replaced with Nd.

[0079] Example 2-3 The manufacturing method of the permanent magnet of this example is basically the same as that of Example 2-1, except that the diffusion slurry in step (5) further contains Cu, and the diffusion slurry is a mixture of Dy single metal, Pr single metal, Cu metal, 4-hexylresorcinol, and ethanol in a mass ratio of 4:3.5:0.5:2:1.

[0080] Comparative Example 2-1 The method for producing a permanent magnet of this comparative example was basically the same as that of Example 2-1, except that Pr was not included in the diffusion slurry in step (5).

[0081] Table 4 shows the test results of the magnetic properties of the sintered billet of Example 2-1 and the permanent magnets produced in Examples 2-1 to 2-4. [Table 4]

[0082] As can be seen from Tables 3 and 4, when the composite diffusion material contained RH and RL, the Hcj amplification of the permanent magnet was obvious.

[0083] Comparative Example 3 The manufacturing method of the permanent magnet of this comparative example is basically the same as that of Example 1-1, except that the raw materials are weighed according to the compositions of the main phase alloy and auxiliary phase alloy shown in Table 5. [Table 5]

[0084] Table 6 shows the test results of the magnetic properties of the sintered billet and permanent magnet produced in Comparative Example 3. [Table 6]

[0085] As can be seen from a comparison of Tables 2, 4, and 6, when complex diffusion is performed when the Ce content in the main phase alloy is 0 to 1%, the improvement in performance is relatively clear, but when the main phase alloy is not within this range, the improvement in coercivity of the billet obtained by sintering is limited.

[0086] Comparative Example 4 The manufacturing method of the permanent magnet of this comparative example was basically the same as that of Example 1-1, except that the alloy was manufactured by weighing the raw materials shown in Table 7, i.e., the main phase alloy and auxiliary phase alloy were not used to manufacture the billet. [Table 7]

[0087] The test results of the magnetic properties of the sintered billet and permanent magnet produced in Comparative Example 4 are shown in Table 8. [Table 8]

[0088] In Comparative Example 4, a permanent magnet containing Ce was produced using a conventional method, i.e., the Ce raw material was added directly during smelting without producing a billet using a main phase alloy and an auxiliary phase alloy. As can be seen from Table 8, in the case of a sintered billet produced using a conventional method, the improvement in coercivity of the permanent magnet was limited even after the composite diffusion treatment of the present invention was performed.

[0089] The inventors discovered that there are clear differences in the components between the composite main phase crystal grains and within the single composite main phase crystal grains, and that these non-uniformities in chemical composition and distribution cause short-range strong exchange interactions and long-range magnetostatic coupling interactions within the magnet, effectively improving the nucleation field of the reverse magnetization domains of the magnet, suppressing the nucleation of the reverse magnetization domains, and preventing the expansion of the reverse magnetization domains, thereby significantly improving the coercive force of the magnet.

[0090] However, when a permanent magnet is manufactured using a Ce or Nd single alloy process and a composite diffusion process, or when a permanent magnet is manufactured using a Ce and Nd dual alloy and an RH diffusion process, the same performance level cannot be obtained. The reason for this is that the components of the main phase crystal grains are basically the same, exhibiting homogeneity and not being able to achieve long-range magnetostatic coupling, so that with the same components and process conditions, it is not possible to obtain Hcj performance equivalent to that of the present invention.

[0091] Although exemplary embodiments of the present invention have been described above, the scope of the claims of the present application is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art without departing from the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for producing an R-Fe-B permanent magnet, comprising the steps of: The manufacturing method includes mixing a low-Ce main alloy powder and a high-Ce auxiliary alloy powder, press-molding the mixture, and sintering the mixture to obtain a billet, and then subjecting the billet to composite diffusion to obtain the permanent magnet, The composite diffusion treatment includes applying a diffusion material to the surface of the billet and heat treating the material; The diffusion material comprises the following components: RH content is 20-70 wt%, RL content is 20-70 wt%, and M powder content is 0-10 wt%, The RH is at least one selected from the heavy rare earth metals Dy, Tb, and Ho, RL is at least one selected from Pr and Nd light rare earth metals, The M powder is selected from Ga and / or Cu; the permanent magnet includes at least grain boundaries and composite main phase grains; the grain boundaries contain RH-rich phases, the RH-rich phases are nodular and distributed within the grain boundaries between the composite main phase crystal grains, and the RH-rich phases are thin band-like and continuously distributed along the grain boundaries; the content of RH in the grain boundaries is greater than the content of RH in the main phase crystal grains, and RH is at least one selected from the heavy rare earth metals Dy, Tb, and Ho; The composite main phase crystal grains have a core-shell structure including a core structure having an RTB type phase structure and a shell structure located on the outer layer of the core structure, the core structure includes Ce-rich main phase crystal grains and Ce-deficient main phase crystal grains, the Ce content of the Ce-rich main phase crystal grains is 1 to 15 wt%, and the Ce content of the Ce-deficient main phase crystal grains is 0 to 1 wt%; A manufacturing method characterized by:

2. 2. The manufacturing method according to claim 1, wherein the low-Cerium main alloy has a Ce content of 1 wt% or less.

3. The press forming step includes mixing a powder of a low-Cerium main alloy and a powder of a high-Cerium auxiliary alloy, and then press forming the mixture under the action of a magnetic field to obtain a green compact.

3. The method according to claim 1 or 2.

4. The content of RH in the grain boundary is greater than the content of RH in the shell structure, 3. The method according to claim 1 or 2.

5. The RTB type phase structure comprises at least the following components: R, in a weight percentage of 28%≦R≦35%, being at least one selected from neodymium (Nd), cerium (Ce), and optionally included or not included scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); B, whose weight percentage is 0.8%≦B≦1.2%; M is at least one selected from aluminum (Al), titanium (Ti), copper (Cu), gallium (Ga), zirconium (Zr), and niobium (Nb), with a weight percentage of 0≦M≦5%; and the balance being T selected from iron (Fe), and optionally cobalt (Co), which may or may not be included; 3. The method according to claim 1 or 2.

6. The manufacturing method according to claim 1, wherein the permanent magnet has a phase structure of the grain boundaries and composite main phase crystal grains throughout the entire surface to the core.

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