Neodymium iron boron substrate, sintered neodymium iron boron magnet, its preparation method and permanent magnet equipment

Abstract

This application provides a neodymium iron boron substrate, a sintered neodymium iron boron magnet, a method for preparing the same, and a permanent magnet device, with the chemical formula RE. a Ho b Ce c Fe （1‑a‑b‑c‑d‑e‑f‑g） B d Ga e Ti f M g a, b, c, d, e, f, and g represent the mass percentages of the corresponding elements in the NdFeB substrate, with 16% ≤ a ≤ 22%, 2% ≤ b ≤ 5%, 7% ≤ c ≤ 13%, 0.8% ≤ d ≤ 1%, 0.1% ≤ e ≤ 0.3%, 0.15% ≤ f ≤ 0.22%, 1% ≤ g ≤ 2%, and 24% ≤ 42%. RE is selected from one or more of Pr and Nd, and M is selected from one or more of Al, Cu, Co, Zr, and Nb. By replacing some Nd and Pr with Ce, and adding Ho, Ti, and Ga with optimized dosages, the coercivity of the Ce-rich NdFeB substrate is improved.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet technology, and in particular to neodymium iron boron substrates, sintered neodymium iron boron magnets, their preparation methods, and permanent magnet equipment. Background Technology

[0002] Permanent magnets are materials with high magnetic energy density, high coercivity, and high remanence, which enable them to maintain a strong magnetic field for a long time without relying on an external power source. They are key components for realizing the interconversion between mechanical energy and electromagnetic energy and are widely used in fields such as electric motors and sensors.

[0003] Grain boundary diffusion is a method to improve the magnetic properties of permanent magnets. Specifically, a diffusion source is uniformly coated onto the surface of a NdFeB substrate. Under vacuum or an inert atmosphere, the diffusion source melts and diffuses along the grain boundaries into the magnet's interior. This causes the metal from the diffusion source to deposit around the substrate grains, forming a core-shell structure, thereby improving magnetic properties such as coercivity. Traditional research on grain boundary diffusion has focused on maximizing the diffusion effect while maintaining the magnet's remanence and minimizing the use of heavy rare earth resources, with little attention paid to improving the coercivity of NdFeB substrates.

[0004] Rare earth raw materials account for more than half of the cost of permanent magnets. With the continuous depletion of rare earth elements such as Pr, Nd, Dy, and Tb, which are low in abundance and expensive, high-abundance Ce is gradually being developed as a raw material for permanent magnet substrates. (Nd₂Fe) 14 The saturation magnetization of B is 16 kGs, and the maximum energy product is 73 kGs; compared to Nd₂Fe 14 B, Ce2Fe 14 B has low intrinsic magnetic properties, Ce2Fe 14 The saturation magnetization of Ce-rich NdFeB is 11.7 kGs, and the maximum energy product is 26 kOe. Therefore, it is difficult to prepare Ce-rich NdFeB substrates with high coercivity using traditional methods. Summary of the Invention

[0005] Therefore, it is necessary to provide NdFeB substrates, their preparation methods, and applications, with the aim of improving the coercivity of Ce-rich NdFeB substrates.

[0006] In one aspect, the present invention provides a neodymium iron boron substrate, wherein the chemical formula of the neodymium iron boron substrate is RE. a Ho b Ce c Fe （1-a-b-c-d-e-f-g） B d Ga e Ti f M g ;

[0007] Where a, b, c, d, e, f, and g are the mass percentages of the corresponding elements, 16%≤a≤22%, 2%≤b≤5%, 7%≤c≤13%, 0.8%≤d≤1%, 0.1%≤e≤0.3%, 0.15%≤f≤0.22%, 1%≤g≤2%, 24%≤ ≤42%;

[0008] RE is selected from one or more of Pr and Nd, and M is selected from one or more of Al, Cu, Co, Zr and Nb.

[0009] The aforementioned NdFeB substrate uses Ce to replace some Nd and Pr in its elemental composition, while optimizing the design of other elements; Ho, Ti and Ga are added and the amount of these three elements is specifically optimized. Combined with the combination of other metal elements, a Ce-rich NdFeB substrate with high coercivity is obtained.

[0010] In some embodiments, one or more of the following conditions are met:

[0011] (1) 6%≤ ≤15%

[0012] (2) 1.5% ≤ e + f + g ≤ 2%;

[0013] (3) 20%≤a+b+c≤34%.

[0014] In some embodiments, the NdFeB substrate comprises: 16%~22% PrNd, 2%~5% Ho, 0.8%~1% B, 7%~13% Ce, 0.1%~0.3% Ga, 0.15%~0.22% Ti, 1%~2% M, and the balance Fe.

[0015] In some embodiments, the remanence Br of the NdFeB substrate is ≥12 kGs, and the intrinsic coercivity Hcj of the NdFeB substrate is ≥12 kOe.

[0016] In another aspect, the present invention provides a method for preparing a neodymium iron boron substrate, comprising the following steps S10 to S40:

[0017] S10. Mix the various raw materials of the NdFeB substrate according to the ratio, and then successively pass them through melting treatment and rapid solidification treatment to obtain NdFeB substrate rapid solidification sheet.

[0018] S20. The neodymium iron boron substrate rapid solidification sheet is subjected to hydrogen crushing and air jet milling in sequence to obtain neodymium iron boron substrate powder;

[0019] S30. The neodymium iron boron substrate powder is subjected to orientation molding and cold isostatic pressing in sequence to obtain a neodymium iron boron substrate blank;

[0020] S40. The NdFeB substrate blank is subjected to sintering and aging treatment in sequence to obtain NdFeB substrate.

[0021] The above-mentioned method for preparing NdFeB substrates can produce NdFeB substrates with high coercivity, and substrates of different thicknesses have better consistency in magnetic properties.

[0022] In some embodiments, one or more of the following conditions are met:

[0023] (1) The thickness of the neodymium iron boron substrate quick-setting sheet is 0.15mm~0.5mm;

[0024] (2) Additives are added to the particles obtained after hydrogen crushing of the NdFeB substrate rapid solidification sheet to obtain a mixed powder, and the mixed powder is subjected to air jet milling;

[0025] (3) The average particle size of the neodymium iron boron substrate powder is 2μm~4μm;

[0026] (4) The density of the NdFeB substrate preform is 7.4 g / cm³. 3 ~7.7g / cm 3 .

[0027] Another aspect of the present invention provides a method for preparing a sintered NdFeB magnet, comprising the following steps:

[0028] A heavy rare earth hydride solution is coated onto the surface of a NdFeB substrate as described above or a NdFeB substrate prepared by the above method, and then subjected to grain boundary diffusion treatment.

[0029] In the above-mentioned method for preparing sintered NdFeB magnets, the heavy rare earth hydride solution can penetrate along the grain boundaries of the substrate relatively quickly and is not prone to excessive diffusion, thereby improving coercivity while retaining remanence.

[0030] In some embodiments, one or more of the following conditions are met:

[0031] (1) The heavy rare earth hydrides include one or more of DyH3, HoH3 and ErH3;

[0032] (2) The NdFeB substrate is coated with the heavy rare earth hydride solution and dried to obtain a sintered NdFeB magnet blank. The weight gain of the sintered NdFeB magnet blank compared to the NdFeB substrate is 0.4wt%~1.2wt%.

[0033] In another aspect, the present invention provides a sintered NdFeB magnet prepared by the above-described preparation method.

[0034] The sintered NdFeB magnets described above have high coercivity and remanence.

[0035] In another aspect, the present invention provides a permanent magnet device comprising one or more of the above-described NdFeB substrate, the NdFeB substrate prepared by the above-described method, and the above-described sintered NdFeB magnet.

[0036] In some embodiments, the permanent magnet device includes one or more of an electric motor and a sensor.

[0037] In some of these embodiments, the permanent magnet device can be applied to wind power generation equipment, new energy vehicles, rail transit equipment, humanoid robots, or low-altitude aircraft. Detailed Implementation

[0038] To facilitate understanding of the present invention, a more complete description will be given below with reference to relevant embodiments. Preferred embodiments of the invention are shown below. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough and complete understanding of the disclosure of the invention will be achieved.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] Sintered NdFeB magnets are widely used in modern industry due to their excellent magnetic properties. With the rapid development of high-end equipment and new energy fields, higher technical requirements have been placed on the coercivity of magnets. Traditional direct doping with heavy rare earth elements can significantly improve coercivity, but it will cause a significant decrease in remanence and the raw material cost remains high. Grain boundary diffusion technology can efficiently enhance coercivity with low impact on remanence and has become a research hotspot in the field of high-performance NdFeB magnet modification.

[0041] Meanwhile, the development of Ce-rich NdFeB magnets is an important trend for achieving efficient utilization and low cost of rare earth resources. However, the combination of Ce-rich substrates and grain boundary diffusion technology still faces key scientific and technological challenges: the introduction of Ce can easily induce the formation of harmful impurity phases, significantly reduce the magnetocrystalline anisotropy field of the main phase, and result in low intrinsic coercivity of the substrate; at the same time, Ce can disrupt the continuity of the grain boundary phase, reduce the fluidity and wettability of the grain boundary phase, and block the diffusion channels of heavy rare earths along the grain boundaries, making conventional diffusion processes weak in Ce-rich magnets and easily leading to problems such as uneven diffusion and limited improvement in coercivity.

[0042] Furthermore, existing grain boundary diffusion processes and cooling regimes are designed based on traditional low-Ce systems, which have poor compatibility with Ce-rich substrates and make it difficult to achieve coercivity enhancement, remanence retention, and structural stability in a coordinated manner.

[0043] Therefore, the development of substrate formulations, dedicated grain boundary diffusion strategies, and matched heat treatment regimes for optimizing the characteristics of Ce-rich systems has significant academic and engineering value and represents a crucial technological bottleneck that urgently needs to be overcome in the current process of achieving high performance in Ce-rich NdFeB magnets.

[0044] This application provides a neodymium iron boron substrate, the chemical formula of which is RE. a Ho b Ce c Fe （1-a-b-c-d-e-f-g） B d Ga e Ti f M g ;

[0045] Where a, b, c, d, e, f, and g are the mass percentages of the corresponding elements, 16%≤a≤22%, 2%≤b≤5%, 7%≤c≤13%, 0.8%≤d≤1%, 0.1%≤e≤0.3%, 0.15%≤f≤0.22%, 1%≤g≤2%, 24%≤ ≤42%;

[0046] RE is selected from one or more of Pr and Nd, and M is selected from one or more of Al, Cu, Co, Zr and Nb.

[0047] The aforementioned NdFeB substrate uses Ce to replace some Nd and Pr in its elemental composition, while optimizing the design of other elements; Ho, Ti and Ga are added and the amount of these three elements is specifically optimized. Combined with the combination of other metal elements, a Ce-rich NdFeB substrate with high coercivity is obtained.

[0048] As an example, the mass percentage a in Pr and / or Nd may be 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, or within any of the above values.

[0049] Furthermore, the mass ratio of Pr to Nd is (20~30):(70~80).

[0050] As an example, the mass percentage b of Ho can be 2%, 2.2%, 2.5%, 3%, 3.5%, 4%, 4.2%, 4.5%, 5%, or any of the above values.

[0051] As an example, the mass percentage c of Ce can be 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.2%, 12.5%, 13%, or within any of the above values.

[0052] As an example, the mass percentage d of B can be 0.8%, 0.86%, 0.92%, 0.98%, 1%, or any of the above values.

[0053] As an example, the mass percentage e of Ga can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or within any of the above values.

[0054] In the aforementioned NdFeB substrate, Ga can control the grain growth process, reduce grain size, increase grain specific surface area, and improve coercivity. Simultaneously, it leads to a more uniform grain distribution, resulting in more grain boundaries, which facilitates the formation and movement of magnetic domains. Ga is mainly distributed at the grain boundaries, thus forming Nd6Fe. 13 Ga phase inhibits the formation of ferromagnetic materials at grain boundaries and enhances the magnetic properties of the substrate. Ga lowers the melting point of Ce-rich grain boundary phases and improves their wettability, allowing Ce-rich grain boundary phases to spread more uniformly and form a continuous and interconnected grain boundary network for subsequent grain boundary diffusion treatment.

[0055] As an example, the mass percentage f of Ti can be 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, or within any of the above values.

[0056] In the aforementioned NdFeB substrate, Ti can form a Ti-rich phase during sintering of cerium and combine with B to form a TiB2 phase at the grain boundaries, which pins the grain boundaries while inhibiting grain growth and improving the coercivity of the NdFeB substrate.

[0057] Furthermore, M is selected from one or more of Al, Cu, and Co.

[0058] Furthermore, M is selected from Al, Cu, and Co. As an example, the sum of the mass percentages (g) of Al, Cu, and Co can be 1%, 1.5%, 2%, and 2.5%, respectively.

[0059] Furthermore, the mass content of Al is 0.01%~0.06%, the mass content of Cu is 0.01%~0.06%, and the mass content of Co is 0.1%~2.5%.

[0060] Understandably, This represents the mass percentage of Ce relative to all rare earth elements. For example, the mass percentage of Ce relative to all rare earth elements could be 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, or any of the above values.

[0061] The aforementioned NdFeB substrate uses a high-abundance Ce, which has abundant reserves, to partially replace Pr and Nd, balancing the development of light and heavy rare earth elements and achieving the goal of balanced resource utilization. At the same time, Ce tends to agglomerate at grain boundaries in the NdFeB matrix, forming a Ce-rich grain boundary phase. Ce works synergistically with other elements to form a continuous and interconnected grain boundary network. This grain boundary network reduces the resistance to the diffusion of heavy rare earth elements along the grain boundaries in the NdFeB matrix, allowing the heavy rare earth elements to penetrate deeper and be more evenly distributed.

[0062] In some of these embodiments, 6% ≤ ≤15%. Understandably, The percentage of Ho relative to all rare earth elements by mass is given. For example, the percentage of Ho relative to all rare earth elements by mass may be 6%, 8%, 9%, 10%, 11%, 12%, 14%, 15%, or any of the above values.

[0063] The aforementioned NdFeB substrate incorporates a certain proportion of Ho, which can suppress the formation of α-Fe, reduce the agglomeration of Nd-rich phases, and promote the growth of Fe-Nd-B phases. At the same time, Ho plays a role in refining grains at grain boundaries, reducing grain surface defects, and thereby improving the intrinsic coercivity of the NdFeB matrix.

[0064] In some embodiments, 20% ≤ a + b + c ≤ 34%. Understandably, a + b + c is the sum of the mass percentages of Pr, Nd, Ho, and Ce in the NdFeB substrate, i.e., the mass percentages of all rare earth elements. As an example, the mass percentages of all rare earth elements may be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, or within any range of these values.

[0065] In some embodiments, 1.5% ≤ e+f+g ≤ 2%. Understandably, e+f+g is the sum of the mass percentages of Ga, Ti, Al, Cu, Co, Zr, and Nb in the NdFeB substrate, i.e., the mass percentages of all transition metal elements except Fe. As an example, the mass percentages of all transition metal elements except Fe may be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or within any range of these values.

[0066] In some embodiments, the mass percentages of each element in the NdFeB substrate are as follows: 16%~22% PrNd, 2%~5% Ho, 0.8%~1% B, 7%~13% Ce, 0.1%~0.3% Ga, 0.15%~0.22% Ti, 1%~2% M, and the balance Fe. Further, M is one or more of Al, Co, and Cu.

[0067] In some embodiments, the mass percentages of each element in the NdFeB substrate are as follows: 16%~22% PrNd, 2%~5% Ho, 0.8%~1% B, 7%~13% Ce, 0.1%~0.3% Ga, 0.15%~0.22% Ti, 0.08%~0.12% Al, 0.8%~1.2% Co, and 0.3%~0.4% Cu.

[0068] In some embodiments, the mass percentages of each element in the NdFeB substrate are as follows: PrNd - 19.3%, Ho - 2.5%, B - 0.92%, Ce - 9.2%, Al - 0.1%, Co - 1.0%, Ga - 0.2%, Ti - 0.18%, Cu - 0.35%, with the balance being Fe.

[0069] In some embodiments, the remanence Br of the neodymium iron boron substrate is ≥12 kGs, and can be selected as 12.6 kGs~12.9 kGs.

[0070] In some embodiments, the intrinsic coercivity Hcj of the NdFeB substrate is ≥12 kOe, and can be selected as 12 kOe~16 kOe.

[0071] The aforementioned NdFeB substrate has a stable, continuous, and interconnected grain boundary network, providing a complete and continuous channel for subsequent grain boundary diffusion treatment. This avoids the blockage of diffusion sources during grain boundary diffusion and overcomes problems such as uneven grain boundary diffusion and limited coercivity improvement. At the same time, specific amounts of Ce and Ca can form thin-layer grain boundaries, overcoming the problem of excessive diffusion of heavy rare earth elements during grain boundary diffusion treatment, improving coercivity while retaining remanence.

[0072] This application also provides a method for preparing a neodymium iron boron substrate, comprising the following steps S10 to S40:

[0073] S10. Mix the various raw materials of NdFeB substrate according to the ratio, and then process them in sequence through melting and quick-setting treatment to obtain NdFeB substrate quick-setting sheet.

[0074] S20. The neodymium iron boron substrate rapid solidification sheet is subjected to hydrogen crushing and air jet milling in sequence to obtain neodymium iron boron substrate powder;

[0075] S30. The neodymium iron boron substrate powder is subjected to orientation molding and cold isostatic pressing in sequence to obtain a neodymium iron boron substrate blank;

[0076] S40. The neodymium iron boron substrate blank is subjected to sintering and aging treatment in sequence to obtain neodymium iron boron substrate.

[0077] The above-mentioned method for preparing NdFeB substrates can produce NdFeB substrates with high coercivity, and substrates of different thicknesses have better consistency in magnetic properties.

[0078] In some embodiments, the melting process includes vacuum induction melting, specifically comprising the following steps: adding the mixed raw materials into a vacuum induction melting furnace, wherein the vacuum degree of the vacuum induction melting furnace is 1Pa~20Pa, the melting temperature is 1400℃~1500℃, the power of the vacuum induction melting furnace is 530kW~590kW, and the melting time is 5min~20min; after all raw materials are melted, they are held at 1350℃~1490℃ for 3min~5min.

[0079] In some embodiments, after smelting, a melt is obtained, and the melt at 1350℃~1490℃ is cast onto a copper roller at a rotation speed of 40±5 rpm and a temperature of 20±5℃ to obtain a neodymium iron boron substrate quick-setting sheet.

[0080] In some embodiments, the thickness of the NdFeB substrate quick-setting sheet is 0.15 mm to 0.5 mm. As an example, the thickness of the NdFeB substrate quick-setting sheet can be 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.32 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, or within any range of these values, such as 0.2 mm to 0.32 mm.

[0081] The above-mentioned method for preparing NdFeB substrates involves specific melting and rapid solidification processes to obtain rapidly solidified NdFeB substrate sheets of a specific thickness, thereby suppressing the precipitation of α-Fe soft magnetic phase.

[0082] In some embodiments, NdFeB substrate rapid-forming sheets are added to a rotary hydrogen crushing furnace, which is filled with hydrogen gas. After the NdFeB substrate rapid-forming sheets are saturated with hydrogen, they are heated to 500°C~600°C for hydrogen crushing, followed by 2h~10h dehydrogenation to obtain hydrogen-crushed coarse material. The hydrogen mass content in the hydrogen-crushed coarse material is 700ppm~2200ppm. As an example, the mass content in the hydrogen-crushed coarse material can be 700ppm, 800ppm, 1000ppm, 1500ppm, 2000ppm, 2200ppm, or within any range of the above values, such as 800ppm~1500ppm.

[0083] The above-mentioned method for preparing NdFeB substrates uses hydrogen-crushed coarse material with a specific hydrogen content, ensuring sufficient hydrogen crushing without damaging the grain boundaries.

[0084] In some embodiments, additives are incorporated into the hydrogen-crushed coarse material to obtain a mixed powder, which is then subjected to an air jet mill.

[0085] In some embodiments, the additive is present in a mass percentage of 0.05 wt% to 6 wt% relative to the hydrogen-crushed feedstock, and the additive includes a lubricant and / or an antioxidant. Understandably, the lubricant is a commercially available lubricant commonly used in the art, and the antioxidant is a commercially available antioxidant commonly used in the art.

[0086] In some embodiments, the air jet mill uses a nitrogen gas flow, and the mixed powder rotates at a speed of 3000 rpm to 6000 rpm in the nitrogen gas flow; the nitrogen gas flow also includes 0 ppm to 60 ppm of oxygen.

[0087] In some embodiments, the average particle size of the NdFeB substrate powder is 2 μm to 4 μm. As an example, the average particle size of the NdFeB substrate powder may be 2 μm, 2.5 μm, 2.7 μm, 3 μm, 3.2 μm, 3.5 μm, 3.7 μm, 4 μm, or within any range of the above values, such as 2.7 μm to 3 μm.

[0088] The above-mentioned method for preparing NdFeB substrates, with NdFeB substrate powder of a specific average particle size, can ensure powder flowability, molding effect, and fine-grained microstructure of the subsequent substrate.

[0089] In some embodiments, the orientation magnetic field strength for oriented molding of the NdFeB substrate powder is 1.5T~3T, the time is 1s~50s, and the density of the preform after orientation molding is 4±0.2g / cm³. 3 .

[0090] In some embodiments, the orientation-molded preform is subjected to cold isostatic pressing to obtain a NdFeB substrate preform. The cold isostatic pressing pressure is 100MPa~300MPa, the holding time is 1s~60s, and the medium is water and / or oil.

[0091] The above-mentioned method for preparing NdFeB substrates, with its specific orientation molding and cold isostatic pressing processes, can ensure the density and uniformity of the green body, providing a high-quality green body for subsequent sintering.

[0092] In some embodiments, the density of the NdFeB substrate preform is 7.4 g / cm³. 3 ~7.7g / cm 3 .

[0093] In some embodiments, the sintering process includes two stages, comprising the following steps: the first stage includes heating at 5°C / min to 7°C / min to 350°C to 450°C and holding for 1.5h to 2.5h, then heating at 4°C / min to 6°C / min to 550°C to 650°C and holding for 1.5h to 2.5h, then heating at 3°C / min to 5°C / min to 750°C to 850°C and holding for 1.5h to 2.5h, then heating at 2°C / min to 4°C / min to 1000°C to 1050°C and holding for 7h to 8h. After holding, inert gas is introduced and the temperature is cooled to below 100°C. The second stage includes heating at 4°C / min to 8°C / min to 1000°C to 1050°C and holding for 3h to 6h. After holding, the temperature is cooled to below 100°C.

[0094] The above-mentioned method for preparing NdFeB substrate involves a first-stage sintering process at a specific temperature to achieve densification, followed by controlling the continuity and distribution of the grain boundary phase through specific temperatures and holding times to form a grain boundary network.

[0095] In some embodiments, the aging process includes three stages of aging. The first stage of aging is performed at a temperature of 830°C to 950°C for 2 hours to 7 hours, followed by air cooling to below 100°C. The second stage of aging is performed at a temperature of 440°C to 550°C for 3 hours to 8 hours, followed by air cooling to below 100°C. The third stage of aging is performed at a temperature of 600°C to 700°C for 3 hours to 8 hours, followed by natural cooling to 200°C, and then the introduction of inert gas and air cooling to below 70°C.

[0096] The above-mentioned method for preparing NdFeB substrates involves controlling and stabilizing the grain boundary phase through specific aging treatments. The first-stage aging treatment reduces the boron-rich phase, which is detrimental to magnetic properties, while simultaneously promoting the growth of Nd2Fe. 14 The formation of the B phase improves magnetic properties; the second-stage aging treatment promotes the transformation of the Nd-rich phase from solid to liquid and back to solid to control the microstructure and improve the coercivity of the substrate; the third-stage aging treatment stabilizes the Ce-rich grain boundary phase, which can maintain continuity and stability in subsequent diffusion heat treatment of grain boundary diffusion.

[0097] This application also provides a method for preparing a sintered NdFeB magnet, comprising the following steps:

[0098] S50. A heavy rare earth hydride solution is coated onto the surface of a neodymium iron boron substrate as described above or onto the surface of a neodymium iron boron substrate prepared by the above method, and then subjected to grain boundary diffusion treatment.

[0099] In the above-mentioned method for preparing sintered NdFeB magnets, the heavy rare earth hydride solution can penetrate along the grain boundaries of the substrate relatively quickly and is not prone to excessive diffusion, thereby improving coercivity while retaining remanence.

[0100] Understandably, the NdFeB substrate surface comprises two symmetrical surfaces of the NdFeB substrate, to which a heavy rare earth hydride solution is coated. Further, in some examples, the rare earth hydride solution is coated on the entire surface of the NdFeB substrate.

[0101] In some embodiments, the grain boundary diffusion treatment includes a three-stage diffusion heat treatment under an inert gas atmosphere: the first stage diffusion heat treatment is held at 880°C to 900°C for 20 to 30 hours; the second stage diffusion heat treatment is held at 480°C to 520°C for 6 to 10 hours; and the third stage diffusion heat treatment is held at 600°C to 650°C for 4 to 8 hours.

[0102] In some embodiments, after three-stage diffusion heat treatment, an inert gas is introduced for air cooling to 25±5°C.

[0103] In some of these embodiments, the heavy rare earth hydrides include one or more of DyH3, HoH3, and ErH3.

[0104] In some embodiments, the heavy rare earth hydride solution is prepared by stirring heavy rare earth hydride particles dissolved in a solvent. The average particle size of the heavy rare earth hydride particles is 2.5 μm to 3 μm. The solvent includes one or more of anhydrous ethanol and acetone. The stirring speed is 200 rpm to 600 rpm.

[0105] In some embodiments, a NdFeB substrate is coated with a heavy rare earth hydride solution and dried to obtain a sintered NdFeB magnet blank. The weight gain of the sintered NdFeB magnet blank relative to the NdFeB substrate is 0.4 wt% to 1.2 wt%. Understandably, the weight gain of the sintered NdFeB magnet blank relative to the NdFeB substrate refers to the difference between the sintered NdFeB magnet blank and the NdFeB substrate, relative to the mass content of the NdFeB substrate. As an example, the weight gain of the sintered NdFeB magnet blank relative to the NdFeB substrate may be 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, or within any range of these values, for example, 0.6 wt% to 1 wt%.

[0106] In some embodiments, the inert gas includes one or more of nitrogen and argon, with a purity >99.99%.

[0107] This application also provides a sintered NdFeB magnet, which is prepared using the above-described method.

[0108] The sintered NdFeB magnets described above have high coercivity and remanence.

[0109] In some embodiments, the thickness of the sintered NdFeB magnet is 2 mm to 10 mm. As an example, the thickness of the sintered NdFeB magnet can be 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, or within any range of the above values, such as 2 mm to 8 mm.

[0110] The sintered NdFeB magnets mentioned above still have high coercivity and remanence even when the thickness is large (≥2mm, or even 8mm).

[0111] In some embodiments, the remanence Br of the sintered NdFeB magnet is ≥12.3 kGs, and the intrinsic coercivity Hcj of the NdFeB substrate is ≥20.5 kOe.

[0112] In another aspect, this application provides a permanent magnet device, comprising one or more of the above-mentioned neodymium iron boron substrate, neodymium iron boron substrate prepared by the above-mentioned method, and the above-mentioned sintered neodymium iron boron magnet.

[0113] In some embodiments, the permanent magnet device includes one or more of an electric motor and a sensor.

[0114] In some of these embodiments, the permanent magnet device can be applied in wind power generation, new energy vehicles, rail transit, humanoid robots, or low-altitude aircraft.

[0115] The following are specific examples.

[0116] Example 1

[0117] S11. Ingredients. Ingredients are prepared according to the components of Example 1 shown in Table 1.

[0118] S12. Vacuum induction melting. The raw material powders are placed in the vacuum induction melting furnace in descending order of their melting points and melted under an argon atmosphere. The induction melting power is 560kW. After each raw material melts, it is held at the temperature for 5 minutes to obtain the melt.

[0119] S13, rapid solidification during casting. The molten metal at 1460°C is cast onto a copper roller at 1420°C and 41 rpm to obtain an alloy sheet with an average thickness of 0.22 μm.

[0120] S21. Hydrogen crushing. The alloy sheet is hydrogen crushed using a rotary hydrogen crushing furnace. The alloy sheet is placed in a reactor, saturated with hydrogen, and then dehydrogenated at 580℃ for 2 hours. The mass content of hydrogen in the hydrogen-crushed raw material is 800ppm~1500ppm.

[0121] S22. Powder Mixing. 600 kg of hydrogen-crushed coarse material, commercially available lubricant, antioxidant, and trace amounts of dysprosium powder are mixed once in a mixer to obtain a mixed powder. The amount of lubricant and antioxidant added accounts for 0.06 wt% to 0.25 wt% of the mass of the hydrogen-crushed coarse powder.

[0122] S23. Airflow mill. The mixed powder is placed in an airflow mill filled with nitrogen and supplemented with 18ppm~25ppm of oxygen. The rotation speed of the mixed powder during airflow milling is 3450rpm until the average particle size of the powder is 2.8μm.

[0123] S31. Orientation Molding. Under the protection of an inert gas, the powder is filled into a mold and subjected to magnetic orientation molding treatment for 40 seconds under a magnetic field of 1.8T. At this time, the density of the substrate preform is 4±0.02g / cm³. 3 .

[0124] S32. Cold isostatic pressing. In an oil medium, a 12-second cold isostatic pressing process is performed at a pressure of 180 MPa, yielding a density of 4.0 g / cm³. 3 ~5.5g / cm 3 The substrate preform.

[0125] S41. First stage sintering. The substrate blank is placed in a vacuum sintering furnace, heated to 400℃ at 6℃ / min and held for 2 hours, heated to 600℃ at 5℃ / min and held for 2 hours, heated to 800℃ at 4℃ / min and held for 2 hours, heated to 1045℃ at 3℃ / min and held for 7.5 hours, and after the holding period, it is naturally cooled to 650±10℃ and then air-cooled to ≤100℃ under an inert atmosphere.

[0126] S42, Second stage sintering. Heat to 1020℃ at 6℃ / min and hold for 5 hours. After holding, air cool to ≤100℃ under an inert atmosphere.

[0127] S43, Level 1 aging. Hold at 900℃ for 3.5 hours, then air-cool to below 100℃ after the holding period.

[0128] Second-level aging. Incubate at 500℃ for 5 hours, then air-cool to below 100℃ after the insulation period.

[0129] The third stage of aging involves holding the material at 630℃ for 6 hours, followed by natural cooling to 200℃ and then air cooling to below 70℃ to obtain a NdFeB substrate with a density of 7.6 g / cm³. 3 .

[0130] S44. Machining of NdFeB substrate. The substrate is machined into a block shape of 40mm×25mm×2.1mm, with a tolerance of 0.05mm for length, width and thickness.

[0131] S51. Prepare and spray the diffusion solution. Prepare the diffusion solution according to 49.75wt% DyH3, 49.75wt% alcohol and 0.5wt% polyvinyl butyral, spray it on two symmetrical surfaces of the substrate and dry it. The weight gain percentage after drying is 0.8%.

[0132] S52. Diffusion heat treatment under an inert atmosphere. High-temperature diffusion: 900℃ for 25 hours. Low-temperature tempering: 500℃ for 8 hours. Medium-temperature stabilization: 630℃ for 6 hours, then naturally cooled to 200℃ and air-cooled to below 70℃.

[0133] S53. After diffusion heat treatment, perform aging process; same as step S43.

[0134] S54. Machining permanent magnets. The permanent magnets are machined into block-shaped permanent magnets of 40mm×25mm×2mm.

[0135] Example 2

[0136] The preparation method of Example 2 is basically the same as that of Example 1, except that the thickness of the bulk substrate in step S46 and the thickness of the bulk permanent magnet in step S53 are different.

[0137] Specifically as follows:

[0138] S46. Machining of NdFeB substrate. The substrate is machined into a block shape of 40mm×25mm×4.1mm, with a tolerance of 0.05mm for length, width and thickness.

[0139] S53. Machining permanent magnets. The permanent magnets are machined into block-shaped permanent magnets of 40mm×25mm×4mm.

[0140] The remaining steps are the same as in Example 1.

[0141] Example 3

[0142] The preparation method of Example 3 is basically the same as that of Example 1, except that the thickness of the bulk substrate in step S46 and the thickness of the bulk permanent magnet in step S53 are different.

[0143] Specifically as follows:

[0144] S46. Machining of NdFeB substrate. The substrate is machined into a block shape of 40mm×25mm×6.1mm, with a tolerance of 0.05mm for length, width and thickness.

[0145] S53. Machining permanent magnets. The permanent magnets are machined into block-shaped permanent magnets of 40mm×25mm×6mm.

[0146] The remaining steps are the same as in Example 1.

[0147] Example 4

[0148] The preparation method of Example 4 is basically the same as that of Example 1, except that the thickness of the block substrate in step S46 and the thickness of the block permanent magnet in step S53 are different.

[0149] Specifically as follows:

[0150] S46. Machining of NdFeB substrate. The substrate is machined into a block shape of 40mm×25mm×8.1mm, with a tolerance of 0.05mm for length, width and thickness.

[0151] S53. Machining permanent magnets. The permanent magnets are machined into block-shaped permanent magnets of 40mm×25mm×8mm.

[0152] The remaining steps are the same as in Example 1.

[0153] Example 5

[0154] The preparation method of Example 5 is basically the same as that of Example 4, except that the mass content of each element in the permanent magnet is not exactly the same, as shown in Table 1 and Table 2.

[0155] Example 6

[0156] The preparation method of Example 6 is basically the same as that of Example 4, except that the mass content of each element in the permanent magnet is not exactly the same, as shown in Table 1 and Table 2.

[0157] Example 7

[0158] The preparation method of Example 7 is basically the same as that of Example 4, except that the mass content of each element in the permanent magnet is not exactly the same, as shown in Tables 1 and 2.

[0159] Example 8

[0160] The preparation method of Example 8 is basically the same as that of Example 4, except that the mass content of each element in the permanent magnet is not exactly the same, as shown in Tables 1 and 2.

[0161] Comparative Example 1

[0162] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that PrNd replaces Ce with an equal mass percentage.

[0163] Comparative Example 2

[0164] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that Fe replaces Ga by an equal mass percentage.

[0165] Comparative Example 3

[0166] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that Fe replaces Ti by an equal mass percentage.

[0167] Table 1

[0168]

[0169] Table 2

[0170]

[0171] The substrates and permanent magnets prepared in the examples and comparative examples were subjected to performance tests. The magnetic properties of the permanent magnets were tested by sampling using the five-point method. The test results are shown in Table 3 below.

[0172] Table 3

[0173]

[0174] As can be seen from Examples 1-8, Comparative Examples 1-3, and Tables 1-3, Comparative Example 1 omitted the high-abundance Ce, and its substrate remanence of 13.9 kGs was higher than that of Examples 1-8. However, after grain boundary diffusion, the remanence was 97.12%, lower than that of Examples 1-8. This indicates that the introduction of Ce in the substrate plays a key role in forming a continuous grain boundary suitable for diffusion. The substrate and permanent magnet prepared in this application can balance the relationship with cost. Comparative Example 2 omitted Ga, and the coercivity of the substrate was 14.26 kOe, the coercivity of the permanent magnet was 20.33 kGs, and the squareness was 93.6%, both significantly lower than that of Example 1. This indicates that Ga can refine grains and optimize the grain boundary phase. Comparative Example 3 omitted Ti, and its coercivity increment was 4.9 kOe, and its squareness was 90%. This indicates that Ti can suppress abnormal grain growth in the substrate and help to generate a grain boundary phase suitable for diffusion.

[0175] In Examples 1-4, the substrate thicknesses varied (from 2.1 mm to 8.1 mm), and both exhibited excellent remanence and coercivity with good performance consistency. The coercivity of the obtained permanent magnets was all >20.5 kOe, and the retention rate of remanence after grain boundary diffusion treatment was all >98%. In particular, the permanent magnets in the examples had a thickness of up to 8 mm, and their coercivity was 20.52 kOe. This shows that the preparation method of this application can overcome the problems of uneven diffusion and limited improvement of coercivity during grain boundary diffusion of thick, Ce-rich substrates.

[0176] Examples 1-8 show that the composition of each element and its specific content have a synergistic effect on improving the remanence and coercivity of the permanent magnet after diffusion into the substrate and grain boundaries.

[0177] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0178] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A neodymium iron boron substrate, characterized in that, The chemical formula of the neodymium iron boron substrate is RE a Ho b Ce c Fe （1-a-b-c-d-e-f-g） B d Ga e Ti f M g ; Where a, b, c, d, e, f, and g are the mass percentages of the corresponding elements in the NdFeB substrate, 16%≤a≤22%, 2%≤b≤5%, 7%≤c≤13%, 0.8%≤d≤1%, 0.1%≤e≤0.3%, 0.15%≤f≤0.22%, 1%≤g≤2%, 24%≤ ≤42%; RE is selected from one or more of Pr and Nd, and M is selected from one or more of Al, Cu, Co, Zr and Nb.

2. The NdFeB substrate as described in claim 1, characterized in that, One or more of the following conditions must be met: （1）6%≤ ≤15%； (2) 1.5% ≤ e + f + g ≤ 2%; (3) 30%≤a+b+c≤34%.

3. The NdFeB substrate as described in any one of claims 1 to 2, characterized in that, The neodymium iron boron substrate includes: 16%~22% PrNd, 2%~5% Ho, 0.8%~1% B, 7%~13% Ce, 0.1%~0.3% Ga, 0.15%~0.22% Ti, 1%~2% M and the balance Fe.

4. The NdFeB substrate as described in any one of claims 1 to 2, characterized in that, The remanence of the NdFeB substrate is Br≥12kGs, and the intrinsic coercivity of the NdFeB substrate is Hcj≥12 kOe.

5. A method for preparing a NdFeB substrate as described in any one of claims 1 to 4, characterized in that, Includes the following steps S10~S40: S10. Mix the raw materials of the NdFeB substrate according to the ratio, and then successively pass through melting treatment and rapid solidification treatment to obtain NdFeB substrate rapid solidification sheet. S20. The neodymium iron boron substrate rapid solidification sheet is subjected to hydrogen crushing and air jet milling in sequence to obtain neodymium iron boron substrate powder; S30. The neodymium iron boron substrate powder is subjected to orientation molding and cold isostatic pressing in sequence to obtain a neodymium iron boron substrate blank; S40. The NdFeB substrate blank is subjected to sintering and aging treatment in sequence to obtain NdFeB substrate.

6. The method for preparing the NdFeB substrate as described in claim 5, characterized in that, One or more of the following conditions must be met: (1) The thickness of the neodymium iron boron substrate quick-setting sheet is 0.15mm~0.5mm; (2) Additives are added to the particles obtained after hydrogen crushing of the NdFeB substrate rapid solidification sheet to obtain a mixed powder, and the mixed powder is subjected to air jet milling; (3) The average particle size of the neodymium iron boron substrate powder is 2μm~4μm; (4) The density of the NdFeB substrate preform is 7.4 g / cm³. 3 ~7.7g / cm 3 .

7. A method for preparing a sintered NdFeB magnet, characterized in that, Includes the following steps: A heavy rare earth hydride solution is coated onto the surface of a NdFeB substrate as described in any one of claims 1 to 4 or a NdFeB substrate prepared by the preparation method as described in any one of claims 5 to 6, and then subjected to grain boundary diffusion treatment to obtain a sintered NdFeB magnet.

8. The method for preparing the sintered NdFeB magnet as described in claim 7, characterized in that, One or more of the following conditions must be met: (1) The heavy rare earth hydrides include one or more of DyH3, HoH3 and ErH3; (2) The NdFeB substrate is coated with the heavy rare earth hydride solution and dried to obtain a sintered NdFeB magnet blank. The weight gain of the sintered NdFeB magnet blank compared to the NdFeB substrate is 0.4wt%~1.2wt%.

9. A sintered NdFeB magnet, characterized in that, It is prepared by the preparation method described in any one of claims 7 to 8.

10. A permanent magnet device, characterized in that, It includes one or more of the following: the NdFeB substrate surface as described in any one of claims 1 to 4, the NdFeB substrate prepared by the preparation method as described in any one of claims 5 to 6, and the sintered NdFeB magnet as described in claim 9.

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