Preparation method of high-performance rare-earth-free neodymium-iron-boron magnet

Abstract

The application discloses a preparation method of high-performance heavy-rare-earth-free neodymium-iron-boron magnets, which comprises the following steps: preparing a main alloy and an auxiliary alloy sheet, wherein the auxiliary alloy sheet has a dispersedly distributed spherical structure of a high-Fe component; then mixing the neodymium-iron-boron main alloy R1FeBM sheet with the R2NT auxiliary alloy sheet containing the spherical structure of the high-Fe component; and finally obtaining the high-performance heavy-rare-earth-free neodymium-iron-boron magnet through hydrogen crushing, airflow grinding, forming and sintering aging treatment processes. In the application, the auxiliary alloy with a special structure is uniformly distributed around the main alloy, and after sintering and aging, a smooth, continuous and clear rare-earth-rich layer wrapping the main phase particles is formed, so that the grain boundary structure is optimized, and finally the coercivity of the magnet is significantly improved. Moreover, the main alloy and the auxiliary alloy do not contain expensive heavy rare earth elements, the production cost is greatly reduced, and the application can be applied to large-scale preparation and production.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials technology, and in particular to a method for preparing high-performance heavy earth-free neodymium iron boron magnets. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets, third-generation rare-earth permanent magnets, possess excellent magnetic properties and are widely used in industries such as new energy vehicles, wind power generation, and consumer electronics. Typically, to further enhance the magnet's coercivity, heavy rare-earth elements such as Dy and Tb are added to NdFeB magnets. However, these heavy rare-earth elements are scarce, expensive, and highly volatile due to supply and demand fluctuations. Furthermore, the 3d electron spin magnetic moment in heavy rare-earth compounds... magnetic moments of rare earth metal atoms The magnets are arranged in antiparallel pairs, therefore the presence of heavy rare earth elements in the main phase will lead to a saturation magnetization M. s Therefore, the development of heavy rare-earth-free NdFeB magnets is of practical significance for reducing the manufacturing cost of magnetic materials, promoting the sustainable development of the industry, and further obtaining magnets with higher magnetic properties. Common indicators for evaluating magnetic properties include: remanence (B). r Innate coercivity H cJ Magnetic energy product (BH) max Industry professionals aim to manufacture products with high performance in all three key areas: the remanence of the magnet is close to the theoretical limit (approaching 90% of the theoretical value), but the intrinsic coercivity is still far from the theoretical value (usually 30% lower).

[0003] Generally, methods to improve the coercivity of materials include: 1. Adding heavy rare earth elements. This method is a conventional approach for preparing high-coercivity NdFeB magnets. By adding elements such as Dy and Tb to the NdFeB magnet, a magnetocrystalline anisotropy constant H is formed. A Much higher than Nd2Fe 14 1. The tetragonal structure of B significantly enhances the coercivity of the magnet; 2. Grain refinement, which improves the coercivity of the magnet. cJ An important approach is to reduce the grain size to a critical size before the magnet H... cJ The magnetic properties of sintered NdFeB magnets are gradually improved with grain refinement; 3. Grain boundary optimization: Numerous studies have confirmed that the magnetic properties of sintered NdFeB magnets are closely related to their microstructure, especially the microstructure and chemical composition at grain boundaries. If the morphology and distribution of the intergranular structure can be adjusted, a significant increase in coercivity can be achieved with minimal changes to the magnet composition. Option 1 contradicts the research and development objective of developing heavy rare-earth-free magnets and will lead to a decrease in remanence. Option 2 produces powder particles that are too fine, making them prone to oxidation and fire hazards, which is detrimental to large-scale factory production management. Therefore, this patent uses a dual-alloy method to optimize the grain boundary structure, achieving a significant increase in magnet coercivity at the cost of less remanence.

[0004] The dual-alloy method refers to the process of preparing magnets by separately melting a main alloy and a secondary alloy, then mixing them in a specific ratio. The main alloy composition is close to Nd₂Fe. 14 The primary phase (B) is a rare-earth-rich grain boundary phase. Elements such as Al, Co, Cu, Ga, Ti, Zr, Nb, Hf, and V can be doped into the primary alloy. By controlling the mixing ratio of the primary and secondary alloys, the proportion of the primary phase in the magnet can be indirectly controlled, thus affecting the remanence of the magnet. The metallic elements added to the secondary alloy can influence the composition and distribution of the grain boundary phase, resulting in a more ideal grain boundary structure, which plays a crucial role in improving coercivity. Ultimately, a magnet with high remanence and coercivity is prepared through the combined action of the primary and secondary alloys.

[0005] This invention employs a dual-alloy method, designing a primary alloy and an auxiliary alloy separately. The auxiliary alloy's fluidity is improved by adding low-melting-point elements Al, Cu, and Ga. Furthermore, high-melting-point elements Ti, Zr, and V are added to the auxiliary alloy to increase the sintering temperature and prevent abnormal grain growth. Then, elements such as Hf and Co are added to improve the magnet's temperature coefficient and extend its operating temperature range. In this invention, an auxiliary alloy with a high-Fe content and spherical structure is obtained by optimizing the auxiliary alloy composition and preparation process. Subsequently, the primary and auxiliary alloys are mixed in a specific ratio and subjected to hydrogen crushing, air jet milling, and uniform stirring. The auxiliary alloy with a specific structure is evenly distributed around the primary alloy. After sintering and aging, a continuous, smooth, and clear rare-earth-rich layer is formed near the primary phase particles. This layer effectively isolates the exchange coupling between the primary phases, thereby significantly improving coercivity. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing high-performance NdFeB magnets without heavy rare earth elements. This method has the advantages of ensuring magnet coercivity and obtaining NdFeB magnets with high overall performance without consuming heavy rare earth resources.

[0007] The technical solution of this invention: A method for preparing a high-performance heavy rare-earth NdFeB magnet, comprising the following steps: preparing a main alloy and an auxiliary alloy sheet, wherein the auxiliary alloy sheet has a diffusely distributed spherical structure with high Fe content; then mixing the NdFeB main alloy R1FeBM sheet with the R2NT auxiliary alloy sheet containing a spherical structure with high Fe content; and then obtaining a high-performance heavy rare-earth NdFeB magnet through hydrogen crushing, air jet milling, forming and sintering aging processes.

[0008] In the aforementioned method for preparing a high-performance, heavy-earth-free NdFeB magnet, the mass ratio of the NdFeB main alloy is R1. x Fe 100-x-y-z B y M zR1 is one or more of Nd, La, Ce, and Pr, and M is one or more of Al, Ti, Co, Cu, Ga, Zr, Nb, Hf, and V, with weight percentages of 26wt.%≤x≤31wt.%, 0.86wt.%≤y≤1.00wt.%, and 0.1wt.%≤z≤5wt.%.

[0009] In the aforementioned method for preparing a high-performance neodymium iron boron magnet without heavy rare earth elements, the neodymium iron boron main alloy sheet is prepared by a rapid solidification process, with a thickness of 0.1 mm to 0.5 mm, a grain boundary phase ratio of 2% to 5%, and a grain boundary phase width less than 2% of the width of the main phase columnar crystals. The thickness of the neodymium iron boron main alloy sheet is preferably 0.15 mm to 0.35 mm.

[0010] In the aforementioned method for preparing a high-performance, weightless rare-earth neodymium iron boron magnet, the mass ratio of the R2NT auxiliary alloy sheet is R2. a N 100-b-a T b The N contains Fe and one or more of Al, Co, Cu, and Ga; the T contains B and one or more of Ti, Zr, Nb, Hf, and V; and the R2 contains at least one of Nd and Pr, with the weight percentages being 26wt.% ≤ a ≤ 50wt.% and 0.1wt.% ≤ b ≤ 8wt.%.

[0011] In the aforementioned method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, the R2NT auxiliary alloy sheet is prepared using, but is not limited to, a rapid solidification process or a rapid quenching process, and the thickness of the auxiliary alloy sheet is 0.01 mm to 1 mm.

[0012] In the aforementioned method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, when the process is a rapid quenching process, the R2NT auxiliary alloy melt is prepared into a thin strip at a speed of 1m / s-25m / s.

[0013] In the aforementioned method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, the R2NT auxiliary alloy rapid quenching process for preparing thin sheets is preferably carried out by vacuum annealing at 500℃-900℃ for 2h-24h.

[0014] In the aforementioned method for preparing a high-performance heavy-earth-free neodymium iron boron magnet, the R2NT auxiliary alloy sheet accounts for 2%-10% of the total mass after mixing.

[0015] In the aforementioned method for preparing a high-performance, heavy-earth-free NdFeB magnet, the high-Fe spherical structure contains 55 wt.% ≤ Fe content ≤ 95 wt.%.

[0016] In the aforementioned method for preparing a high-performance heavy-earth-free NdFeB magnet, the high-Fe spherical structure accounts for 10%-50% of the volume of the auxiliary alloy sheet and is diffusely distributed.

[0017] In the aforementioned method for preparing a high-performance heavy-earth-free NdFeB magnet, the diameter of the high-Fe spherical structure is from 0.1 μm to 200 μm.

[0018] In the aforementioned method for preparing a high-performance, heavy-earth-free neodymium iron boron magnet, the high-Fe spherical structure preferably has a diameter of 1 μm to 50 μm.

[0019] In the aforementioned method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, the volume of the high-Fe spherical structure with a diameter greater than 3.5 μm accounts for more than 90% of the total volume of the spherical structure.

[0020] In the aforementioned method for preparing a high-performance heavy-earth-free neodymium iron boron magnet, powder with a surface area average particle size (SMD) of 2μm-4μm is obtained by using the air jet mill abrasive.

[0021] In the aforementioned method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, the powder is placed under an external magnetic field of 1.2T-2.6T during the pressing process.

[0022] In the aforementioned method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, the sintering and aging process involves a sintering temperature of 1000-1120℃ and a sintering time of 3-10h, a first-stage aging temperature range of 850℃-950℃ and an aging time of 2-20h, and a second-stage aging temperature range of 400℃-580℃ and an aging time of 2-10h.

[0023] In the aforementioned method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, the first-stage aging heating section has a heat preservation platform with a temperature of 600℃-850℃ and a heat preservation time of 0.5h-10h.

[0024] Compared with existing technologies, the beneficial effects of this invention are as follows: The main and auxiliary phase alloy composition is designed based on the dual-alloy principle. High-melting-point elements are added to the auxiliary alloy to prevent abnormal grain growth, while low-melting-point elements with high fluidity ensure that the high-Fe spherical structure formed by the high-melting-point elements can be uniformly dispersed around the main phase. During sintering and aging, the high-Fe spherical structure exchanges matter with the surrounding rare-earth-rich phase to form a non-magnetic structure, achieving the effect of pinning grain boundaries and improving coercivity. Furthermore, during aging, the original rare-earth-rich phase at the grain boundaries of the auxiliary and main alloys forms a core-shell structure that encapsulates the main phase particles, effectively isolating the exchange coupling between the main phases, thereby further improving the magnet's coercivity. Using this invention, a significant improvement in coercivity can be achieved with a low amount of auxiliary alloy added. In addition, since this magnet does not contain heavy rare-earth elements, the resulting magnet has higher remanence. Attached Figure Description

[0025] Figure 1 This is a thickness distribution diagram of the main alloy M1 of this invention;

[0026] Figure 2 This is a thickness distribution diagram of the auxiliary alloy P1 of the present invention;

[0027] Figure 3 This is a scanning electron microscope image of the cross-section of the main alloy M1 casting of this invention;

[0028] Figure 4 This is a scanning electron microscope image of the cross-section of the auxiliary alloy P1 casting of this invention;

[0029] Figure 5 It is the auxiliary alloy P7 casting sheet of Embodiment 8 of the present invention;

[0030] Figure 6 This is the comparative example 3 auxiliary alloy P8 casting of the present invention;

[0031] Figure 7 It is the auxiliary alloy P9 casting sheet of Embodiment 9 of the present invention;

[0032] Figure 8 This is the microstructure of the auxiliary alloy P7 casting of the present invention;

[0033] Figure 9 This is the microstructure of the auxiliary alloy P8 casting sheet of the present invention;

[0034] Figure 10 This is the microstructure of the auxiliary alloy P9 casting sheet of the present invention;

[0035] Figure 11 This is a scanned image of the composition of the auxiliary alloy P7 casting of this invention;

[0036] Figure 12 This is a scanned image of the composition of the auxiliary alloy P8 casting sheet of the present invention;

[0037] Figure 13 This is a scanned image of the composition of the auxiliary alloy P9 casting sheet of this invention. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0039] The composition and average thickness of the main alloy and auxiliary alloy sheets used in Examples 1-10 and Comparative Examples 1-3 are shown in Table 1.

[0040] Table 1. Composition and average thickness of the main alloy and auxiliary alloy sheets used in Examples 1-10 and Comparative Examples 1-3

[0041]

[0042] Example 1: A method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, comprising the following steps:

[0043] (1) The raw materials for the main phase alloy and the auxiliary phase alloy were prepared separately using a dual alloying scheme;

[0044] (2) The main alloy adopts a vacuum melting scheme, and its composition is based on the main alloy M1;

[0045] (3) The auxiliary alloy also adopts the vacuum melting scheme, and the composition is the same as that of auxiliary alloy P1;

[0046] (4) In the vacuum melting process, the main alloy raw material is placed into a vacuum induction furnace and the temperature is raised to 1550°C under argon protection (29.7 kPa). After the material is completely melted, it is left to stand for 7 minutes before casting. After casting is completed, it is cooled for 180 minutes before being taken out of the furnace to obtain the main alloy M1 casting.

[0047] (5) The auxiliary alloy raw materials are placed into a vacuum induction furnace and the temperature is raised to 1490°C under argon protection (30kPa). After the material is completely melted, it is left to stand for 7 minutes before casting. After casting is completed, it is cooled for 120 minutes before being taken out of the furnace to obtain the auxiliary alloy P1 casting.

[0048] (6) The obtained main alloy casting and auxiliary alloy casting are mixed at a mass ratio of 96:4 and saturated with hydrogen at room temperature, and then dehydrogenated to obtain hydrogen fragments.

[0049] (7) Add antioxidant (1.0 g / kg) to the above hydrogen-rich powder and then place it on a three-dimensional mixer and stir for 120 min;

[0050] (8) The well-stirred hydrogen powder was crushed by an air jet mill, and the oxygen content was controlled. No oxygen was added during the crushing process to prepare fine powder with SMD of 2.85 μm.

[0051] (9) Place the obtained fine powder on a three-dimensional powder mixer and stir for 180 min to obtain uniform fine powder;

[0052] (10) The uniform fine powder obtained above is molded under a 2T orientation field. The oxygen content must be controlled below 50ppm throughout the molding process.

[0053] (11) The shaped compact is placed in a vacuum sintering furnace for sintering. The sintering process is 1080℃×4h+1090℃×4h. Then it is aged at 900℃ for 5h, and finally aged at 400℃-500℃ (see Table 3 for specific process) to obtain the magnet.

[0054] Depend on Figure 1 and Figure 2 It can be seen that the thickness of the main alloy M1 is mainly distributed in the range of 0.26μm-0.36μm; the thickness of the auxiliary alloy P1 is mainly distributed in the range of 0.22μm-0.38μm.

[0055] Depend on Figure 3 It can be seen that the average thickness of the NdFeB main alloy M1 sheet prepared by the rapid solidification process is 0.316 mm. Statistical analysis using software... Figure 3 In the images with different contrast areas, the proportion of grain boundary phase (higher contrast) was found to be 4.32% (<5%). Furthermore, measurements of the thickness of the grain boundary phase and the main phase columnar crystals showed that the width of the grain boundary phase was less than 2% of the width of the main phase columnar crystals.

[0056] Depend on Figure 4 It can be seen that the thickness of the auxiliary alloy P1 sheet prepared by the rapid solidification process is 0.381 mm. In addition, a diffusely distributed spherical structure can be observed from the figure, and the diameter of most of these spherical structures is less than 50 μm.

[0057] Comparative Example 1: The NdFeB magnet prepared according to the scheme of Example 1. Its main difference from Example 1 is that Comparative Example 1 contains only the main alloy M1. The sintering and aging process is shown in Table 2.

[0058] Comparative Example 2: This is an NdFeB magnet prepared according to the scheme of Example 1. The main difference between Comparative Example 2 and Example 1 is that auxiliary alloy P2 is used. The sintering and aging process is shown in Table 2.

[0059] Example 2: This is an NdFeB magnet prepared according to the scheme of Example 1. The main difference between Example 2 and Example 1 is that the auxiliary alloy P3 is prepared by vacuum rapid quenching process. The sintering and aging process is shown in Table 2.

[0060] Examples 3 / 4: NdFeB magnets prepared according to the scheme of Example 1. The main difference between Examples 3 / 4 and Example 1 is that the main alloy M2 and the auxiliary alloy P4 are used. The main difference between Examples 3 / 4 is the mixing ratio of the main and auxiliary alloys. In addition, the sintering and aging process is shown in Table 2.

[0061] Examples 5 / 6: The main difference between Examples 5 / 6 and Examples 1 is that Examples 5 / 6 use main alloy M2 and auxiliary alloy P5. The main difference between Examples 5 / 6 is the mixing ratio of main and auxiliary alloys and SMD. In addition, the sintering and aging process is shown in Table 2.

[0062] Example 7: The main difference between Example 7 and Example 1 is that Example 7 uses main alloy M3 and auxiliary alloy P6. In addition, the sintering and aging process is shown in Table 2.

[0063] Table 2 shows the main and auxiliary phase alloy ratios, SMD, sintering processes, and first-stage aging processes for Comparative Examples 1-2 and Examples 1-7.

[0064]

[0065] The magnetic properties of the above examples and comparative examples under different two-stage aging processes were tested. All test samples used were... The results for the cylinder are shown in Table 3.

[0066] Table 3 lists the secondary aging process and magnetic properties of Comparative Examples 1-2 and Examples 1-7.

[0067]

[0068]

[0069] As can be seen from Comparative Example 1, without the addition of auxiliary alloys, the coercivity of the pure main alloy magnet after aging increased from at least 11.2 kOe (unaged) to over 13.5 kOe (second-order aging), while the remanence did not decrease significantly. After adding 4 wt.% auxiliary alloy P1 sheets and sintering and aging, the coercivity of Example 1 (aged at 440℃) increased by 3.2 kOe compared to the coercivity of Comparative Example 1 (aged at 450℃), while the remanence decreased by approximately 0.28 kGs. The main difference between Example 1 and Comparative Example 2 is that heavy rare earth elements were added in Comparative Example 2. With good squareness (H... k / H cJUnder the premise of ≥95%, the optimal coercivity of the magnet after aging in Comparative Example 2 (aging at 440℃) is basically the same as that in Example 1 (aging at 440℃), but the remanence decreased by 0.06 kGs, indicating that the performance of the magnet prepared by this experimental scheme can approach that of magnets with added heavy rare earth elements. Example 2 used a rapid quenching method to prepare the auxiliary alloy. The optimal coercivity of the magnet after aging (19.28 kOe) was higher than that in Example 1 (17.06 kOe), indicating that different preparation methods of the auxiliary alloy have a significant impact on the magnet performance. The rapid quenching method is superior to the rapid solidification method in improving coercivity. Examples 3 and 4 investigated the effect of changing the auxiliary alloy ratio on the magnet performance. With further increases in the auxiliary alloy ratio, the coercivity increased from 17.7 kOe to 19.17 kOe at the same aging temperature, but the remanence of the magnet deteriorated significantly, decreasing from 13.98 kGs to 13.5 kGs. Therefore, it is not recommended to add an excessive proportion of auxiliary alloys to the magnet. This rule was also verified in Examples 5, 6, and 7, where the main and auxiliary alloys were changed.

[0070] Example 8: A method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, comprising the following steps:

[0071] (1) The raw materials for the main phase alloy and the auxiliary phase alloy were prepared separately using a dual alloying scheme;

[0072] (2) The main alloy adopts a vacuum melting scheme, and the composition is based on the main alloy sheet M4;

[0073] (3) The auxiliary alloy also adopts the vacuum melting scheme, and the composition is referenced from auxiliary alloy sheet P7;

[0074] (4) In the vacuum melting process, the main alloy raw material is placed into a vacuum induction furnace, and the temperature is raised to 1550°C under argon protection (29.7 kPa). After the material is completely melted, it is left to stand for 8 minutes before casting. After casting is completed, it is cooled for 180 minutes before being taken out of the furnace to obtain the main alloy M4 casting.

[0075] (5) The auxiliary alloy raw materials are placed into a vacuum induction furnace and the temperature is raised to 1480°C under argon protection (30kPa). After the material is completely melted, it is left to stand for 5-10 minutes before casting. After casting, it is cooled for 120 minutes before being taken out of the furnace to obtain the auxiliary alloy P7 casting.

[0076] (6) The obtained main alloy casting and auxiliary alloy casting are mixed at a mass ratio of 95.5:4.5 and saturated with hydrogen at room temperature, and then dehydrogenated to obtain hydrogen fragments;

[0077] (7) Add antioxidant (0.7 g / kg) to the above hydrogen-rich powder and then place it on a three-dimensional mixer and stir for 120 min;

[0078] (8) The well-stirred hydrogen powder was crushed by an air jet mill, and the oxygen content was controlled. No oxygen was added during the crushing process, and fine powder with a particle size SMD of 2.86 μm was prepared.

[0079] (9) Place the obtained fine powder on a three-dimensional powder mixer and stir for 180 min to obtain uniform fine powder;

[0080] (10) The uniform fine powder obtained above is molded under a 2T orientation field. The oxygen content must be controlled below 50ppm throughout the molding process.

[0081] (11) The shaped compact is placed in a vacuum sintering furnace for sintering at a temperature of 1100℃ for 4.5h. Then it is aged at 900℃ for 2.5h and finally aged at 450℃ for 5h to obtain the sintered magnet.

[0082] Comparative Example 3: A magnet prepared according to the scheme of Example 8, but differing from Example 8 in the auxiliary alloy composition (see P8). In addition, during the preparation process, the copper roller speed was reduced to obtain an auxiliary phase P8 casting with an average sheet thickness of 0.96 mm. The remaining steps were performed according to Example 8.

[0083] Example 9: A magnet prepared according to the scheme of Example 8, but differing from Example 8 in the auxiliary alloy composition (see P9). In addition, during the preparation process, the copper roller speed was reduced to obtain an auxiliary phase P9 casting with an average sheet thickness of 0.36 mm. The remaining steps were performed according to Example 8.

[0084] Depend on Figure 8 , 9 10. It can be seen that the auxiliary alloy casting in Example 8 contains a diffusely distributed spherical structure. Statistical analysis revealed... Figure 8 The CCP has 531 spherical tissues, approximately 80 μm in size. 2 A spherical structure was found. One hundred of these structures were selected and their diameters measured. It was found that the vast majority of the spherical structures (87 in total) were distributed between 3.5 μm and 5.5 μm in size, with an average size of approximately 4.26 μm. Based on the above data, the following conclusions can be drawn: 1. The volume of spherical structures with a diameter greater than 3.5 μm accounts for more than 90% of the total volume of all spherical structures; 2. The spherical structure accounts for approximately 50.44% of the auxiliary alloy volume. Due to the undulations in the auxiliary alloy sheet in Comparative Example 3, Figure 9 for Figure 6 In the convex portion of Example 3, only a small amount of spherical structure exists, and its diameter distribution is extremely dispersed. The auxiliary alloy casting of Example 9 contains diffusely distributed spherical structure, but its distribution is less uniform and its size varies significantly compared to the spherical structure of Example 8. [The last sentence appears to be incomplete and possibly refers to a different context.] Figure 8 Statistical methods revealed that spherical structures accounted for approximately 23% of the volume of the auxiliary alloy casting.

[0085] Table 4. Test results of spherical tissue components in Example 8, Comparative Example 3, and Example 9.

[0086]

[0087] As shown in Table 4, the Re and Fe composition of the spherical tissue in Example 8 is similar to that of the gray area in Comparative Example 3. The main difference between the two lies in their tissue morphology.

[0088] The magnetic properties of Example 8, Comparative Example 3 and Example 9 were measured using a magnetic measuring instrument. The test results are shown in the table below.

[0089] Table 5 Magnetic properties of Example 8, Comparative Example 3 and Example 9

[0090]

[0091] As shown in Table 5, the coercivity of Example 8 is approximately 18 kOe, which is significantly higher than the 14.5 kOe of Comparative Example 3. This indicates that the diffusely distributed spherical structure in the auxiliary phase is superior to the non-diffusely distributed spherical structure in terms of improving coercivity. It is also higher than the 17.61 kOe of Example 9, indicating that the uniformly distributed high-Fe spherical structure improves coercivity to a greater extent.

[0092] Example 10: A method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, specifically including the following steps:

[0093] (1) The raw materials for the main phase alloy and the auxiliary phase alloy were prepared separately using a dual alloying scheme;

[0094] (2) Among them, the main alloy adopts a vacuum melting scheme, and the main alloy proportion is based on M2;

[0095] (3) The auxiliary alloy also adopts the vacuum rapid quenching scheme, and the auxiliary alloy ratio is referenced in P3;

[0096] (4) In the vacuum melting process, the main alloy raw material is placed into a vacuum induction furnace, and the temperature is raised to 1510°C under argon protection (30kPa). After the material is completely melted, it is left to stand for 10 minutes before casting. After casting is completed, it is cooled for 180 minutes before being taken out of the furnace to obtain the main alloy casting.

[0097] (5) In the vacuum rapid quenching process, the auxiliary alloy raw material is first vacuum melted, and the alloy is repeatedly melted more than 3 times to obtain a master alloy ingot with uniform composition. Then the sub-alloy ingot is transferred to the rapid quenching furnace and melted. The melt flows into a high-speed rotating metal wheel and solidifies under the action of the metal wheel to form an alloy strip. The rotation speed of the metal wheel is 20m / s. The obtained auxiliary alloy strip is vacuum annealed at 800℃ for 12h.

[0098] (6) The obtained main alloy casting and auxiliary alloy casting are mixed at a mass ratio of 95:5 and saturated with hydrogen at room temperature, and then dehydrogenated to obtain hydrogen fragments.

[0099] (7) Add antioxidant (0.5 g / kg) to the above hydrogen-rich powder and place it on a three-dimensional mixer and stir for 90 min;

[0100] (8) The uniformly stirred hydrogen powder is crushed by air jet mill, and the oxygen content is controlled. No oxygen is added during the crushing process to prepare fine powder with a particle SMD of 2.68μm.

[0101] (9) Place the obtained fine powder on a three-dimensional powder mixer and stir for 240 minutes to obtain uniform fine powder;

[0102] (10) The uniform fine powder obtained above is molded under a 2T orientation field. The oxygen content must be controlled below 50ppm throughout the molding process.

[0103] (11) The shaped compact is placed in a vacuum sintering furnace for sintering at a temperature of 1100℃ for 4.5h. Then it is aged at 900℃ for 2.5h and finally aged at 450℃ for 5h to obtain the sintered magnet.

[0104] Example 11: An NdFeB magnet prepared according to the scheme of Example 10. The only difference between it and Example 10 is that no annealing crystallization treatment was performed after the preparation of the auxiliary alloy strip.

[0105] Example 12: An NdFeB magnet prepared according to the scheme of Example 10, the only difference from Example 10 is that the vacuum annealing time for preparing the auxiliary alloy strip is reduced to 4h.

[0106] The following are magnetic performance tables for Examples 10, 11, and 12.

[0107] Table 6 lists the magnetic properties of Examples 10, 11, and 12.

[0108]

[0109] As shown in Table 6, by comparing Examples 10 and 11, it was found that the crystallized magnet has higher coercivity; by comparing Examples 10 and 12, it was found that when the crystallization time is reduced, the effect of the auxiliary alloy in improving coercivity decreases.

[0110] Example 13, a method for preparing a high-performance heavy rare-earth neodymium iron boron magnet, specifically includes the following steps:

[0111] (1) The raw materials for the main phase alloy and the auxiliary phase alloy were prepared separately using a dual alloy scheme.

[0112] (2) The main alloy adopts a vacuum melting scheme, and the composition is based on M1;

[0113] (3) The auxiliary alloy also adopts the vacuum melting method, and the composition is referenced in P4;

[0114] (4) In the vacuum melting process, the main alloy raw material is placed into a vacuum induction furnace, and the temperature is raised to 1510°C under argon protection (30kPa). After the material is completely melted, it is left to stand for 17 minutes before casting. After casting is completed, it is cooled for 240 minutes before being taken out of the furnace to obtain the main alloy casting.

[0115] (5) The auxiliary alloy raw materials are placed into a vacuum induction furnace and the temperature is raised to 1520°C under argon protection (30kPa). After the material is completely melted, it is left to stand for 3 minutes before casting. After casting is completed, it is cooled for 180 minutes before being taken out of the furnace to obtain the auxiliary alloy casting sheet.

[0116] (6) The obtained main alloy casting and auxiliary alloy casting are mixed at a mass ratio of 96:4 and saturated with hydrogen at room temperature, and then dehydrogenated to obtain hydrogen fragments.

[0117] (7) Add antioxidant (0.6 g / kg) to the above hydrogen-rich powder and then place it on a three-dimensional mixer and stir for 180 min;

[0118] (8) The well-stirred hydrogen powder was crushed by an air jet mill, and the oxygen content was controlled. No oxygen was added during the crushing process, and fine powder with a particle size SMD of 2.93 μm was prepared.

[0119] (9) Place the obtained fine powder on a three-dimensional powder mixer and stir for 280 min to obtain uniform fine powder;

[0120] (10) The uniform fine powder obtained above is molded under a 2T orientation field. The oxygen content must be controlled below 50ppm throughout the molding process.

[0121] (11) The shaped compact is placed in a vacuum sintering furnace for sintering at a temperature of 1110℃ for 4.5h. Then it is aged at 900℃ for 2.5h and finally aged at 450℃ for 5h to obtain the sintered magnet.

[0122] Example 14 is a magnet prepared according to the scheme of Example 13, but it differs from Example 13 in that:

[0123] (1) Extend the heat preservation platform of 760℃ in the first-stage aging heating section to 6 hours;

[0124] (2) The first-level aging process was changed to 900℃×16h. The remaining steps were carried out in accordance with Example 13.

[0125] The following are the magnetic properties tables for Examples 13 and 14.

[0126] Table 7 List of magnetic properties of Examples 13 and 14

[0127]

[0128] As shown in Table 7, comparing Examples 13 and 14 reveals that extending the insulation platform and the first-stage aging time can effectively improve the H of the magnet. k / H cJ At the same time, it improves coercivity because the addition of a heat preservation platform and a longer first-stage aging time helps the auxiliary alloy to be more evenly distributed around the main alloy, promotes magnet homogenization, optimizes grain boundary structure, and further improves coercivity.

[0129] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing high-performance rare-earth-free neodymium-iron-boron magnets, characterized in that The process includes the following steps: preparing main alloy and auxiliary alloy sheets, wherein the auxiliary alloy sheet has a dispersed spherical structure with high Fe content; then mixing the NdFeB main alloy sheet R1FeBM with the R2NT auxiliary alloy sheet containing a spherical structure with high Fe content; and then obtaining a high-performance heavy rare earth-free NdFeB magnet through hydrogen crushing, air jet milling, forming and sintering aging treatment processes. The R2 NT alloy flake mass ratio is R2 a N 100-b-a T b wherein N comprises Fe and comprises one or more of Al, Co, Cu, Ga, T comprises B and comprises one or more of Ti, Zr, Nb, Hf, V, in a weight ratio of 26 wt.% < a < 50 wt.%, 0.1 wt.% < b < 8 wt.%. Wherein, R1 is one or more of Nd, La, Ce, and Pr, and R2 contains at least one of Nd and Pr; The NdFeB main alloy sheet is produced using a rapid solidification process, with a thickness of 0.1mm-0.5mm, a grain boundary phase ratio of 2%-5%, and a grain boundary phase width less than 2% of the width of the main phase columnar crystals. In the high-Fe spherical structure, the Fe content is 55wt.%≤95wt.%, the high-Fe spherical structure accounts for 10%-74% of the volume of the auxiliary alloy sheet, and is diffusely distributed. The diameter of the high-Fe spherical structure is 0.1μm to 200μm, and the volume of the high-Fe spherical structure with a diameter greater than 3.5μm accounts for more than 90% of the total volume of the spherical structure.

2. The method for preparing a high-performance heavy-earth-free NdFeB magnet according to claim 1, characterized in that, The mass ratio of the neodymium-iron-boron master alloy is R1 x Fe 100-x-y-z B y M z wherein M is one or more of Al, Ti, Co, Cu, Ga, Zr, Nb, Hf, V, in a weight ratio of 26 wt.%≤x≤31 wt.%, 0.86 wt.%≤y≤1.00 wt.%, 0.1 wt.%≤z≤5 wt.%.

3. The method for preparing a high-performance heavy-earth-free NdFeB magnet according to claim 1, characterized in that, The R2NT auxiliary alloy sheet is prepared by rapid solidification or rapid quenching process, and the thickness of the auxiliary alloy sheet is 0.01mm-1mm.

4. The method for preparing a high-performance heavy-earth-free NdFeB magnet according to claim 3, characterized in that, When the process is a rapid quenching process, the R2NT auxiliary alloy melt is prepared into a thin strip at a speed of 1m / s-25m / s.

5. The method for preparing a high-performance heavy-earth-free neodymium iron boron magnet according to claim 3, characterized in that, R2NT auxiliary alloy rapid quenching process for thin sheet preparation involves vacuum annealing at 500℃-900℃ for 2h-24h.

6. The method according to claim 3, wherein the high-performance rare-earth-free Nd-Fe-B magnet is prepared by the following steps: (1) preparing a raw material mixture; (2) preparing a sintered magnet; (3) performing a surface treatment on the sintered magnet; and (4) performing a heat treatment on the sintered magnet. The R2NT auxiliary alloy sheet accounts for 2%-10% of the total mass after mixing.

7. The method for preparing a high-performance heavy-earth-free NdFeB magnet according to claim 1, characterized in that, The diameter of the high-Fe spherical tissue ranges from 1 μm to 50 μm.

8. The method for preparing a high-performance heavy-earth-free NdFeB magnet according to claim 1, characterized in that, Powder with a surface area average particle size (SMD) of 2μm-4μm was obtained by the air jet mill abrasive.

9. The method according to claim 8, wherein the high-performance rare-earth-free Nd-Fe-B magnet is prepared by the following steps: The molding process involves placing the powder under an external magnetic field of 1.2T-2.6T. ​ 10. The method for preparing a high-performance heavy-earth-free NdFeB magnet according to claim 1, characterized in that, The sintering and aging process involves a sintering temperature of 1000-1120℃ and a sintering time of 3-10 hours; a first-stage aging temperature range of 850℃-950℃ and an aging time of 2-20 hours; and a second-stage aging temperature range of 400℃-580℃ and an aging time of 2-10 hours.

11. The method for preparing a high-performance heavy-earth-free neodymium iron boron magnet according to claim 10, characterized in that, The first-stage aging heating section has a heat preservation platform with a temperature of 600℃-850℃ and a heat preservation time of 0.5h-10h.

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