R-T-B series magnet and preparation method thereof

Abstract

The invention provides a high-performance R-T-B series magnet and a preparation method thereof. The R-T-B series magnet comprises an R element, an iron element and a boron element, the R element comprises a light rare earth element and a heavy rare earth element, the heavy rare earth element comprises terbium and / or dysprosium elements, and the heavy rare earth element diffuses from the surface of the R-T-B series magnet to the inside; the R-T-B series magnet comprises main phase crystal grains and crystal boundary phases located between the main phase crystal grains, and the main phase crystal grains comprise crystal grains of a core-shell structure; along the diffusion direction of the heavy rare earth elements, in a microscopic structure observation surface located in a region of 200 [mu] m inward from the surface of the R-T-B series magnet, the average heavy rare earth element content RH1 of the shell of the core-shell structure and the average heavy rare earth element content RH2 of the grain boundary phase satisfy the following conditions: RH1-RH2 > = 2.6 wt% and / or RH1 / RH2 > = 1.5, wherein the microscopic structure observation surface is perpendicular to the diffusion direction of the heavy rare earth element. In the R-T-B series magnet provided by the invention, the diffusion depth of the heavy rare earth element is relatively large, and the magnet performance is very good.

Description

Technical Field

[0001] This invention belongs to the field of RTB magnets, and in particular, relates to a high-performance RTB magnet and its preparation method. Background Technology

[0002] Neodymium iron boron (NdFeB) rare-earth permanent magnets are the strongest permanent magnet materials discovered to date, and their excellent magnetic properties have led to their widespread application in an increasing number of fields. With continuous advancements in manufacturing technology and increasing environmental awareness, they have attracted significant market attention in the fields of energy conservation, environmental protection, new energy, and new energy vehicles. Coercivity is a crucial indicator for evaluating the magnetic properties of magnets, and the heavy rare-earth elements dysprosium (Dy) and terbium (RH) are important elements for enhancing coercivity, effectively improving the magnetocrystalline anisotropy constant of the main phase; however, they are expensive. Current technologies generally improve coercivity and reduce magnet manufacturing costs through surface deposition and diffusion of heavy rare-earth elements Dy and RH. However, the concentration of heavy rare-earth elements decreases significantly from the surface inwards, resulting in shallow diffusion depth and limited performance improvement. In particular, preparing low-heavy-rare-earth content magnets with high remanence (Br), high coercivity (e.g., intrinsic coercivity, Hcj), and high squareness presents considerable challenges.

[0003] CN116564638A discloses a method for preparing high-performance magnets. The prepared magnets have magnetic properties of Br≥13.4kGs and Hcj≥25.86kOe, and possess high squareness. The main technical solution involves coating the substrate surface with an RH2M2 diffusion source alloy for grain boundary diffusion treatment. The grain boundary diffusion temperature can be 800~980℃, and the process is carried out in a high-purity Ar atmosphere at a pressure of (1×10⁻⁶). -4 )~(3×10 5 However, when this technology is applied to grain boundary diffusion treatment of substrates with a large thickness (diffusion depth), if the diffusion depth exceeds 5 mm, it will not achieve the aforementioned high magnetic performance standard. Furthermore, in mass production, oxidation of the diffusion source alloy on some substrate surfaces during the grain boundary diffusion treatment process causes inconsistencies in the magnetic properties between magnets after diffusion treatment.

[0004] The contents of the background technology section are merely the technologies known to the inventors and do not necessarily represent the existing technologies in this field. Summary of the Invention

[0005] The purpose of this invention is to provide an RTB-based magnet with high magnetic properties and low content of heavy rare earth elements.

[0006] To achieve the above objectives, the first aspect of this application provides an RTB-based magnet. The RTB-based magnet comprises R, iron, and boron, wherein the R element includes light rare earth elements and heavy rare earth elements, and the heavy rare earth elements include terbium and / or dysprosium.

[0007] The heavy rare earth elements diffuse from the surface of the RTB magnet to the interior; the RTB magnet includes main phase grains and grain boundary phases located between the main phase grains, and the main phase grains include grains with a core-shell structure.

[0008] Along the diffusion direction of the heavy rare earth elements, in the microstructure observation plane located in a region 200 μm inward from the surface of the RTB magnet, the average heavy rare earth element content RH1 of the shell of the core-shell structure and the average heavy rare earth element content RH2 of the grain boundary phase satisfy the following: RH1-RH2≥2.6wt% and / or RH1 / RH2≥1.5, wherein the microstructure observation plane is perpendicular to the diffusion direction of the heavy rare earth elements.

[0009] In some embodiments of this application, along the diffusion direction of the heavy rare earth elements, in the microstructure observation surface located in a region 500 μm inward from the surface of the RTB magnet, the number of grains with core-shell structures accounts for ≥90%.

[0010] In some embodiments of this application, along the diffusion direction of the heavy rare earth elements, in the microstructure observation surface located in a region 500 μm inward from the surface of the RTB magnet, the heavy rare earth element content of the shell of the core-shell structure is higher than that of the core of the core-shell structure, and the average heavy rare earth element content RH1 of the shell of the core-shell structure is ≥2.0 wt%.

[0011] In some embodiments of this application, the size of the microscopic tissue observation surface is ≤40000μm. 2 Optionally 2500μm 2 .

[0012] In some embodiments of this application, the microscopic tissue observation surface is a square or rectangular structure.

[0013] In some embodiments of this application, the composition of the RTB-based magnet is (PrNd). 27～29 Dy 0～0.65 Tb 0～ 1.2 Ga 0.1～0.65 Co 0.3～3.05 Cu 0.05～0.55 B 0.90～0.98 A 0.05～0.35 Al 0～0.25 Fe余量 A includes at least one element selected from Ti, Zr, and Nb.

[0014] In some embodiments of this application, the B of the RTB system magnet r ≥14.2kGs, H cJ ≥27kOe, H k / H cJ ≥94%

[0015] A second aspect of this application provides a method for preparing an RTB-based magnet, comprising:

[0016] The diffusion source alloy is attached to the surface of the substrate; and

[0017] The substrate with the diffusion source alloy attached is subjected to diffusion heat treatment and tempering treatment;

[0018] The diffusion source alloy includes a first rare earth element, which includes terbium and / or dysprosium.

[0019] The substrate includes light rare earth elements, second heavy rare earth elements, iron, and boron, wherein the second heavy rare earth elements include terbium and / or dysprosium.

[0020] The diffusion heat treatment includes a first heat treatment, a second heat treatment, and a cooling treatment between the first heat treatment and the second heat treatment. The first heat treatment includes: adjusting the temperature to 820℃~850℃ under vacuum and holding it at that temperature for 4~8 hours. The cooling treatment includes: cooling to below 100℃ under an inert atmosphere. The second heat treatment includes: adjusting the temperature to 900℃~950℃ under vacuum and holding it at that temperature for 20~24 hours.

[0021] The tempering process includes: adjusting the temperature to 460℃~500℃ under vacuum, then filling with inert gas to a pressure of 70~90kPa, and holding at that temperature for 8~12h.

[0022] In some embodiments of this application, the composition of the diffusion source alloy is RH' a Co b Al c Cu d Ga e RH' is the first heavy rare earth element, a = 70-90 wt%, b = 0-10 wt%, c = 0-10 wt%, d = 0-10 wt%, e = 0-10 wt%;

[0023] In some embodiments of this application, the substrate is composed of (PrNd). 27～29 Dy 0～0.5 Tb 0～0.6Ga 0.1～ 0.6 Co 0.3～3 Cu 0.05～0.5 B 0.90～0.98 A 0.05～0.35 Al 0～0.2 Fe 余量 A includes at least one element selected from Ti, Zr, and Nb.

[0024] In some embodiments of this application, at least one of coating, vacuum evaporation, and sputtering is used to attach the diffusion source alloy to the surface of the substrate.

[0025] In some embodiments of this application, when the diffusion source alloy is coated on the surface of the substrate, the weight gain of the substrate is 0.3 to 0.6 wt%.

[0026] In some embodiments of this application, when the diffusion source alloy is attached to the surface of the substrate by vacuum evaporation and / or sputtering, the thickness of the diffusion alloy layer formed on the surface of the substrate by the diffusion source alloy is 5 to 10 μm.

[0027] In some embodiments of this application, the diffusion source alloy is attached only to the diffusion surface of the substrate.

[0028] In some embodiments of this application, the coating includes at least one of dipping, spraying, and roller coating.

[0029] In some embodiments of this application, the slurry used for coating includes the diffusion source alloy, a binder, and a solvent; in the slurry, the mass ratio of the diffusion source alloy to the binder is (90-95):(5-10).

[0030] In some embodiments of this application, the preparation method further includes:

[0031] Preparation of alloy sheets;

[0032] The alloy sheet is crushed into alloy powder;

[0033] The alloy powder is pressed into a compact;

[0034] The pressed blank is sintered to obtain a sintered body; and

[0035] The sintered body is processed to obtain the substrate.

[0036] In some embodiments of this application, the preparation of the alloy sheet includes:

[0037] The raw materials are melted and then cast to obtain the alloy sheet;

[0038] The interlayer spacing of the neodymium-rich phase in the alloy sheet is less than 3 μm.

[0039] In some embodiments of this application, the D of the alloy powder 50 The diameter is 3.5–3.8 μm, D 90 / D 10 =4 to 4.6.

[0040] In some embodiments of this application, the density of the pressed blank is 4–4.3 g / cm³. 3 .

[0041] In some embodiments of this application, the sintering temperature is 1030℃~1050℃, and the holding time is 5~8h.

[0042] In some embodiments of this application, the density of the sintered body is 7.55–7.58 g / cm³. 3 The average grain size is 5.2–5.8 μm.

[0043] The RTB-based magnets provided in this application exhibit deep diffusion of heavy rare earth elements, resulting in excellent magnetic performance. This application employs diffusion heat treatment under vacuum followed by tempering under a certain inert atmosphere pressure, which allows heavy rare earth elements to diffuse deep into the substrate, thereby obtaining an RTB-based magnet with low heavy rare earth element content but excellent magnetic properties.

[0044] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0045] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0046] Figure 1 This is a process flow diagram of the fabrication process of a high-performance RTB magnet provided in one embodiment of this application.

[0047] Figure 2 This is a process flow diagram of the fabrication process of a high-performance RTB magnet provided in another embodiment of this application.

[0048] Figures 3(a) to 3(e) This is a scanning electron microscope image of the RTB-based magnet prepared in Embodiment 1 of this application.

[0049] Figures 4(a) to 4(e) This is a scanning electron microscope image of the RTB-based magnet prepared in Comparative Example 1 of this application. Detailed Implementation

[0050] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0051] Taking into account the measurements discussed and the errors associated with the measurement of a particular quantity (i.e., limitations of the measurement system), as used herein, “about” or “approximately” includes the stated value and means within an acceptable range of deviation from the particular value as determined by a person skilled in the art. For example, “about” may mean within one or more standard deviations, or within ±30%, ±20%, ±10%, or ±5% of the stated value.

[0052] This application provides a high-performance RTB-based magnet. In the RTB-based magnet, R represents the element Ra, T represents iron (Fe), and B represents boron (B). The RTB-based magnet in this application includes R, iron, and boron. The R element includes light rare earth elements (RL) and heavy rare earth elements (RH). Heavy rare earth elements include terbium (Tb) and / or dysprosium (Dy). Optionally, the RTB-based magnet also includes the M element, wherein the M element includes one or more of gallium (Ga), cobalt (Co), copper (Cu), titanium (Ti), aluminum (Al), zirconium (Zr), and niobium (Nb).

[0053] Optionally, the composition of the RTB-based magnet is (PrNd). 27～29 Dy 0～0.65 Tb 0～1.2 Ga 0.1～0.65 Co 0.3～ 3.05 Cu 0.05～0.55 B 0.90～0.98 A 0.05～0.35 Al 0～0.25 Fe 余量 A includes at least one element selected from Ti, Zr, and Nb. The ratio of each element is by weight.

[0054] In this application, heavy rare earth elements diffuse from the surface of the RTB-based magnet inwards. The RTB-based magnet comprises main phase grains and grain boundary phases located between the main phase grains. The main phase grains include grains with a core-shell structure. The grains with a core-shell structure are those formed after the heavy rare earth elements diffuse into the interior of the RTB-based magnet.

[0055] In this application, along the diffusion direction of heavy rare earth elements (HREEs), in the microstructure observation plane located within a region 200 μm inward from the surface of the RTB-based magnet, the average HREE content RH1 of the core-shell structure and the average HREE content RH2 of the grain boundary phase satisfy the following conditions: RH1-RH2≥2.6wt% and / or RH1 / RH2≥1.5. It is evident that in this application, even with a very low content of HREEs (total not exceeding 1.2wt%), the HREEs still maintain a high concentration after diffusion over 200 μm. Furthermore, the HREEs are primarily located in the main phase grains, with relatively small amounts in the grain boundary phase, which can improve the performance of the RTB-based magnet.

[0056] In this application, the average heavy rare earth element content is obtained by calculating the average heavy rare earth element content of one or more of the main phase grain nuclei, shells and adjacent grain boundary phases with core-shell structures that can be observed on the microstructure observation surface. Preferably, it is obtained by calculating the average heavy rare earth element content of the main phase grain nuclei, shells and adjacent grain boundary phases with all core-shell structures.

[0057] In some specific embodiments, the difference between RH1 and RH2 (RH1-RH2) can be 2.6 to 4.0 wt%, for example, 2.6 wt%, 2.8 wt%, 3.0 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, or 4.0 wt%.

[0058] In some specific embodiments, the ratio of RH1 to RH2 (RH1 / RH2) can be 1.5 to 2, for example, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95 or 2.

[0059] The diffusion direction of heavy rare earth elements (HREEs) within an RTB-based magnet is generally from the surface to the interior, but it is not necessarily parallel to the line connecting the surface of the RTB magnet to its center of gravity. The microstructure observation surface described in this application refers to a scanning image of the RTB magnet obtained using electron microscopy (e.g., scanning electron microscopy or transmission electron microscopy). In this application, the microstructure observation surface is perpendicular to the diffusion direction of HREEs, allowing for a more direct observation of the diffusion of HREEs.

[0060] There can be one or more microstructure observation surfaces located within a region 200 μm inward from the surface of the RTB magnet.

[0061] Optionally, along the diffusion direction of heavy rare earth elements, in the microstructure observation surface located within a region 500 μm inward from the surface of the RTB magnet, the proportion of grains with core-shell structures is ≥90%, for example, 91–96%. In some specific embodiments, the proportion of grains with core-shell structures can be 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, or 96%. This indicates that heavy rare earth elements still have a high concentration after diffusion of 500 μm.

[0062] Optionally, along the diffusion direction of heavy rare earth elements, in the microstructure observation surface located within a region 500 μm inward from the surface of the RTB magnet, the heavy rare earth element content in the shell of the core-shell structure is higher than that in the core. That is, in the grain structure formed by the diffusion of heavy rare earth elements, the heavy rare earth element content in the shell is always higher than that in the core.

[0063] Optionally, along the diffusion direction of heavy rare earth elements, in the microstructure observation surface located within a region 500 μm inward from the surface of the RTB magnet, the average heavy rare earth element content RH1 in the shell of the core-shell structure is ≥2.0 wt%. This shows that even with diffusion over 500 μm, heavy rare earth elements still maintain a relatively high concentration in the shell of the grain.

[0064] Similarly, the microstructure observation surface located in the region 500 μm inward from the surface of the RTB magnet can also be one or more.

[0065] Optionally, the size (area) of the microstructure observation surface is ≤40000μm. 2 Further optionally, it is 2500μm 2 Optionally, the microstructure observation surface is a square or rectangular structure. In some specific embodiments, the microstructure observation surface is square, specifically 50 μm × 50 μm or 100 μm × 100 μm. In some specific embodiments, the microstructure observation surface is rectangular, specifically 50 μm × 100 μm or 100 μm × 200 μm. A 50 μm × 50 μm shape is preferred, as this size is moderate and facilitates the observation of the diffusion of heavy rare earth elements.

[0066] Although the RTB-based magnet provided in this application has a low content of heavy rare earth elements, the diffusion depth of these elements is relatively deep, resulting in excellent magnetic performance. Optionally, the remanence (B) of the RTB-based magnet... r ≥14.2kGs, intrinsic coercivity (H cJ ≥27kOe, knee point coercivity (H k The ratio H to intrinsic coercivityk / H cJ ≥94%.

[0067] In some specific embodiments, the B of the RTB system magnet r It can be 14.3 to 14.6 kGs, for example, it can be 14.3 kGs, 14.32 kGs, 14.35 kGs, 14.38 kGs, 14.4 kGs, 14.43 kGs, 14.45 kGs, 14.47 kGs, 14.5 kGs, 14.52 kGs, 14.54 kGs, 14.56 kGs, 14.58 kGs or 14.6 kGs.

[0068] In some specific embodiments, the H of the RTB system magnet cJ It can be 27–29 kOe, for example, 27 kOe, 27.2 kOe, 27.4 kOe, 27.6 kOe, 27.8 kOe, 28 kOe, 28.2 kOe, 28.4 kOe, 28.6 kOe, 28.8 kOe or 29 kOe.

[0069] In some specific embodiments, the H of the RTB system magnet k / H cJ It can be 94% to 99%, for example, it can be 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, or 99%.

[0070] Figure 1 This application illustrates a method for fabricating a high-performance RTB magnet according to an embodiment, comprising the following steps S11 to S12:

[0071] S11: Attach the diffusion source alloy to the surface of the substrate.

[0072] The diffusion source alloy includes the first rare earth element. The first rare earth element includes terbium and / or dysprosium.

[0073] Optionally, the substrate includes light rare earth elements, secondary rare earth elements, iron, and boron. In addition to neodymium (Nd), the light rare earth elements may also include praseodymium (Pr). The secondary rare earth elements may include terbium and / or dysprosium. The substrate may also include element M, which may include one or more of gallium, cobalt, copper, titanium, aluminum, zirconium, and niobium. In this application, the primary and secondary rare earth elements may be the same or different.

[0074] Alternatively, the substrate may be composed of (PrNd). 27～29 Dy 0～0.5 Tb 0～0.6 Ga 0.1～0.6 Co0.3～3 Cu 0.05～ 0.5 B 0.90～0.98 A 0.05～0.35 Al 0～0.2 Fe 余量 A includes at least one element selected from Ti, Zr, and Nb. The ratio of each element is by weight.

[0075] Optionally, the composition of the diffusion source alloy is RH' a Co b Al c Cu d Ga e Wherein, RH' represents the first rare earth element, a = 70–90 wt%, b = 0–10 wt%, c = 0–10 wt%, d = 0–10 wt%, e = 0–10 wt%.

[0076] Optionally, at least one of coating, vacuum evaporation, and sputtering can be used to attach the diffusion source alloy to the substrate surface. In this application, at least one of coating, vacuum evaporation, and sputtering can be used to attach the diffusion source alloy to the substrate surface. Coating includes at least one of dipping, spraying, and roller coating. These methods are commonly used in the art, and their specific operation methods will not be described in detail here.

[0077] Optionally, when the diffusion source alloy is adhered to the substrate surface by coating, a slurry comprising the diffusion source alloy, binder, and solvent can be applied to the substrate surface. Optionally, after coating, the weight gain of the substrate can be 0.3–0.6 wt%. The weight gain mentioned here refers to the ratio of the weight of heavy rare earth elements in the diffusion source alloy coated on the substrate surface to the weight of the substrate after the slurry is applied to the substrate surface. For example, if the weight of heavy rare earth elements in the slurry coated on the substrate surface is 0.4 g, and the weight of the substrate is 100 g, then the weight gain is 0.4 wt%. In some specific embodiments, the weight gain can be 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, or 0.6 wt%.

[0078] Optionally, the mass ratio of the diffusion source alloy to the binder in the slurry is (90-95):(5-10). Optionally, the binder is polyvinyl butyral (PVB), and the solvent is alcohol.

[0079] When a diffusion source alloy is attached to a substrate surface using methods such as vacuum evaporation or sputtering, a diffusion alloy layer can be formed on the substrate surface. Optionally, the thickness of the diffusion alloy layer is 5–10 μm. In some specific embodiments, the thickness of the diffusion alloy layer can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or 10 μm. When the diffusion source alloy is attached to the substrate surface using methods such as vacuum evaporation or sputtering, the amount of diffusion source alloy attached can also be expressed using the aforementioned weight gain, which will not be elaborated further here.

[0080] Alternatively, the diffusion source alloy may be adhered only to the diffusion surface of the substrate. This ensures a minimum amount of diffusion source alloy is used.

[0081] It is evident that the amount of diffusion source alloy used in this application is very small, but the diffusion depth of heavy rare earth elements is very deep.

[0082] S12: The substrate with the diffusion source alloy attached is subjected to diffusion heat treatment and tempering treatment.

[0083] In this application, the diffusion heat treatment includes three stages: a first heat treatment, a second heat treatment, and a cooling treatment between the first and second heat treatments. The first heat treatment includes: adjusting the temperature to 820℃~850℃ under vacuum and holding it for 4~8 hours; the cooling treatment includes: cooling to below 100℃ under an inert atmosphere; and the second heat treatment includes: adjusting the temperature to 900℃~950℃ under vacuum and holding it for 20~24 hours. That is, the substrate with the diffusion source alloy attached is first adjusted to 820℃~850℃ under vacuum and held for 4~8 hours, then cooled to below 100℃ under an inert atmosphere, and then adjusted to 900℃~950℃ under vacuum and held for 20~24 hours. Optionally, the inert gas used for the cooling treatment is argon (Ar).

[0084] In some specific embodiments, the temperature of the first heat treatment stage can be 820°C, 825°C, 830°C, 835°C, 840°C, 845°C or 850°C, and the holding time can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h.

[0085] In some specific embodiments, the cooling process can cool the substrate after the first heat treatment to 98°C, 95°C, 92°C, 90°C, 85°C, or 80°C, etc.

[0086] In some specific embodiments, the temperature of the second heat treatment can be 900℃, 905℃, 910℃, 915℃, 920℃, 925℃, 930℃, 935℃, 940℃, 945℃ or 950℃, and the holding time can be 20h, 20.5h, 21h, 21.5h, 22h, 22.5h, 23h, 23.5h or 24h.

[0087] In this application, the tempering process includes: adjusting the temperature to 460℃~500℃ under vacuum, then filling with inert gas to a pressure of 70~90kPa, and holding at that temperature for 8~12 hours. That is, the substrate after diffusion heat treatment is first adjusted to 460℃~500℃ under vacuum, then filled with inert gas to a pressure of 70~90kPa, and held at that temperature for 8~12 hours. Optionally, the inert gas used in the tempering process is argon (Ar).

[0088] In some specific embodiments, the tempering temperature can be 460°C, 465°C, 470°C, 475°C, 480°C, 485°C, 490°C, 495°C, or 500°C, the pressure can be 70 kPa, 72 kPa, 75 kPa, 78 kPa, 80 kPa, 83 kPa, 85 kPa, 87 kPa, or 90 kPa, and the holding time can be 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, or 12 h.

[0089] Optionally, the sum of the holding times for diffusion heat treatment and tempering treatment is 35–40 h. In some specific embodiments, the sum of the holding times for diffusion heat treatment and tempering treatment can be 35 h, 35.5 h, 36 h, 36.5 h, 37 h, 37.5 h, 38 h, 38.5 h, 39 h, 39.5 h, or 40 h.

[0090] This application employs diffusion heat treatment under vacuum and tempering treatment under a certain inert atmosphere pressure, which allows heavy rare earth elements to diffuse into the interior of the substrate to a deeper level, thereby obtaining an RTB-based magnet with low heavy rare earth element content but excellent magnetic properties.

[0091] Figure 2 This application illustrates a method for preparing a high-performance RTB magnet according to another embodiment, including the following steps S21 to S25 and steps S11 and S12 as described above. Steps S11 and S12 will not be described again, and only steps S21 to S25 will be described in detail below.

[0092] S21: Prepare the alloy sheet. The composition of the alloy sheet is the same as that of the aforementioned substrate.

[0093] When the alloy sheet has the composition of (PrNd) 27～29 Dy 0～0.5 Tb0～0.6 Ga 0.1～0.6 Co 0.3～3 Cu 0.05～0.5 B 0.90～ 0.98 A 0.05～0.35 Al 0～0.2 Fe 余量 When A includes at least one element selected from Ti, Zr, and Nb, the alloy raw materials can be prepared first: Pr-Nd, DyFe, industrial Fe-B, industrial pure Fe, and metals such as Co, Cu, Ti, Ga, Tb, Al, Zr, and Nb with a purity of 99.9% are prepared according to the above alloy composition.

[0094] After preparing the raw materials, proceed with the melting process. Place the prepared raw materials into a high-frequency vacuum induction melting furnace and evacuate the furnace to approximately 10°C. -2 The alloy is heated to a certain temperature (Pa) for melting, and then cast onto a copper roller at a temperature of 1480℃~1520℃ to obtain a rapidly cooled alloy sheet. Optionally, the interlayer spacing of the neodymium-rich phase in the alloy sheet is less than 3μm.

[0095] Optionally, the thickness of the alloy sheet is 0.2–0.3 mm. In some specific embodiments, the thickness of the alloy sheet may be 0.2 mm, 0.22 mm, 0.24 mm, 0.26 mm, 0.28 mm, or 0.3 mm.

[0096] The interlayer spacing of the neodymium-rich phase in the alloy sheet is less than 3 μm, which is beneficial for the subsequent diffusion of terbium.

[0097] S22: Crush the alloy sheet into alloy powder.

[0098] Optionally, in this step, the alloy sheet is first subjected to hydrogen blasting, and then subjected to air jet milling.

[0099] Specifically, the alloy sheet can be placed in a hydrogen pulverizing furnace at room temperature and a vacuum is drawn. Then, hydrogen gas is introduced into the furnace to maintain a hydrogen pressure of approximately 0.2 MPa. After sufficient hydrogen absorption, the temperature is increased while maintaining a vacuum, and then a vacuum is drawn at approximately 540°C. After cooling for 10 hours, the hydrogen-pulverized powder is removed. Then, the hydrogen-pulverized powder is further pulverized by an air jet mill under a nitrogen atmosphere with an oxidizing gas content of less than approximately 100 ppm and a pulverizing chamber pressure of 0.6 MPa to 0.8 MPa to obtain alloy powder.

[0100] Optionally, the median particle size D of the alloy powder 50 The thickness is 3.5–3.8 μm. In some specific embodiments, D 50 It can be 3.5μm, 3.55μm, 3.6μm, 3.65μm, 3.7μm, 3.75μm or 3.8μm.

[0101] Optionally, the particle size D corresponding to the cumulative particle size distribution number of the alloy powder reaching 90% is... 90 The particle size D corresponding to when the cumulative particle size distribution number reaches 100% 10 The ratio D 90 / D 10 The value is 4.0 to 4.6. In some specific embodiments, D... 90 / D 10 It can be 4, 4.1, 4.2, 4.3, 4.4, 4.5 or 4.6.

[0102] The alloy powder obtained in this application has a small particle size and relatively uniform particle size.

[0103] S23: Pressing alloy powder into a compact.

[0104] Optionally, the alloy powder is pressed into a compact under a forming pressure of 15–20 MPa in an orientation magnetic field of not less than 1.8 T. In some specific embodiments, the forming pressure can be 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, or 20 MPa.

[0105] Optionally, the density of the pressed green body is 4–4.3 g / cm³. 3 In some specific embodiments, the density of the pressed preform can be 4 g / cm³. 3 4.05g / cm 3 4.1g / cm 3 4.15g / cm 3 4.2g / cm 3 4.25g / cm 3 Or 4.3g / cm 3 .

[0106] S24: Sinter the pressed blank to obtain a sintered body.

[0107] Optionally, the compact is sintered at a temperature of 1030–1050°C, held at that temperature for 5–8 hours, and then cooled to room temperature by introducing an inert gas (e.g., argon) to obtain a sintered body. In some specific embodiments, the sintering temperature can be 1030°C, 1035°C, 1040°C, 1045°C, or 1050°C. In some specific embodiments, the sintering holding time is 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, or 8 hours.

[0108] Optionally, the density of the sintered body is 7.55–7.58 g / cm³. 3 The average grain size is 5.2–5.8 μm. In some specific embodiments, the density of the sintered body can be 7.55 g / cm³. 3 7.56 g / cm 3 7.57 g / cm3 Or 7.58g / cm 3 In some specific embodiments, the average grain size of the sintered body is 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, or 5.8 μm.

[0109] This application uses a low-temperature long-sintering method to sinter the compact, resulting in better grain size.

[0110] S25: Process the sintered body to obtain a substrate.

[0111] The sintered body can be processed according to actual requirements. After processing, it should be cleaned, which is the aforementioned substrate.

[0112] The preparation method provided in this application can produce RTB-based magnets with high magnetic properties and low content of heavy rare earth elements.

[0113] The present invention will now be described with reference to specific embodiments. The process conditions used in the following embodiments and comparative examples are exemplary, and their possible ranges are as shown in the foregoing description of the invention. For process parameters not specifically noted, conventional techniques can be used. Unless otherwise specified, the reagents and instruments used in the technical solutions provided by the present invention can be purchased from conventional channels or the market. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Unless otherwise specified, the test methods used in the following embodiments and comparative examples are conventional experimental methods in the art.

[0114] Example 1

[0115] This embodiment prepares a high-performance RTB-based magnet, and the specific steps are as follows:

[0116] Prepare Pr-Nd, DyFe, industrial Fe-B, industrial pure Fe, and 99.9% pure Co, Cu, Ti, Ga, and Tb metals according to the alloy proportions in Table 1. Place the prepared raw materials into an alumina crucible and heat in a high-frequency vacuum induction furnace for approximately 10... -2 Vacuum melting is carried out in a vacuum at a temperature of approximately 1480°C.

[0117] After vacuum melting, Ar gas is introduced into the melting furnace, and casting is performed using a single-roll quenching method at approximately 4×10⁻⁶ rpm. 3 Neodymium iron boron alloy sheets were obtained by cooling at a rate of ℃ / s. The interlayer spacing of the neodymium-rich phase in the alloy sheet was less than 3 μm, and the average thickness of the alloy sheet was approximately 0.25 mm.

[0118] A hydrogen-crushing furnace containing the rapidly cooled alloy was evacuated at room temperature. Hydrogen gas was then introduced into the furnace, maintaining a pressure of approximately 0.2 MPa. After sufficient hydrogen absorption, the temperature was increased while maintaining a vacuum, reaching approximately 540°C before evacuation again. The furnace was then cooled for 10 hours, and the hydrogen-crushed powder was removed. This powder was then subjected to air jet milling for several hours under a nitrogen atmosphere with an oxidizing gas content below 100 ppm and a grinding chamber pressure of approximately 0.6 MPa to obtain alloy powder. The D of the alloy powder... 50 It is approximately 3.7 μm, D 90 / D 10 It is approximately 4.55.

[0119] Methyl octanoate was added to the powder after it had been pulverized by an air jet mill, at an amount of approximately 0.1 wt% of the total powder weight. The mixture was then thoroughly mixed using a V-type mixer. Using a right-angle orientation magnetic field forming machine, the powder containing methyl octanoate was formed in one pass under an orientation magnetic field of at least 1.8 T and a forming pressure of approximately 18 MPa. After the first pass, the powder was demagnetized in a magnetic field of approximately 0.2 T to obtain a compact. The compact density was approximately 4.1 g / cm³. 3 .

[0120] Each pressed billet is then transferred to a sintering furnace for sintering, which takes approximately 10 minutes. -1 Under a vacuum of 100 MPa, the sample was held at approximately 400°C and 800°C for approximately 2 hours each, then sintered at approximately 1050°C for approximately 3 hours. Afterwards, Ar gas was introduced to achieve a pressure of approximately 0.1 MPa, and the sample was cooled to room temperature. The density of the sintered body was approximately 7.55 g / cm³. 3 The average grain size is approximately 5.3 μm.

[0121] The sintered body was processed into a substrate with a length of 10 mm, a thickness of 7.5 mm, and a height of 7.62 mm, with the height direction aligned with the magnetic field orientation. The magnet was then degreased and cleaned (without acid pickling). The properties of the substrate are shown in Table 2.

[0122] Tb 90 Co5Al5 alloy powder was used as the diffusion source alloy, mixed with PVB binder and alcohol to prepare a slurry. The slurry was coated on the upper and lower surfaces (i.e., the height direction) of the substrate, but not on the sides (front, back, left, and right directions). After coating, the substrate gained approximately 0.6 wt% weight.

[0123] The substrate with the diffusion source alloy attached was placed in an atmosphere furnace. After evacuation, the furnace temperature was adjusted to approximately 820°C under vacuum and held for about 6 hours. Then, Ar gas was introduced into the furnace, and the substrate was cooled to approximately 95°C under the Ar atmosphere. The furnace was then evacuated again, and the furnace temperature was adjusted to approximately 900°C under vacuum and held for about 24 hours. Next, the furnace temperature was adjusted to approximately 480°C under vacuum, and then Ar gas was introduced to a pressure of approximately 70 kPa, and held for about 10 hours.

[0124] The elemental composition of the RTB-based magnets obtained by ICP analysis is shown in Table 2. The performance of the obtained RTB-based magnets is shown in Table 3. Table 4 shows the distribution of terbium in the grains and grain boundary phases with core-shell structures within the RTB-based magnets. Figure 3(a)~3(e) The images are scanning electron microscope (SEM) images taken along the diffusion direction of terbium in the regions of 0–50 μm, 50–100 μm, 100–150 μm, 250–300 μm, and 450–500 μm inward from the surface of the RTB magnet. In this embodiment, the microstructure observation surface is 50 μm × 50 μm in shape.

[0125] Example 2

[0126] The difference between this embodiment and Embodiment 1 is that the diffusion source alloy is attached to the substrate surface by sputtering. The thickness of the formed diffusion alloy layer is approximately 8 μm, with a weight gain of approximately 0.6 wt%.

[0127] The alloy ratio of the base material is shown in Table 1, the composition of the obtained RTB magnet is shown in Table 2, and the magnet properties are shown in Table 3.

[0128] Example 3

[0129] The difference between this embodiment and Embodiment 1 lies in the different elemental proportions of the alloy used, as detailed in Table 1. The composition of the obtained RTB-based magnet is shown in Table 2, and the magnet properties are shown in Table 3.

[0130] Example 4

[0131] The difference between this embodiment and Embodiment 3 is that the tempering treatment is performed at a pressure of approximately 89 kPa. The alloy composition of the base material is shown in Table 1, the composition of the obtained RTB magnet is shown in Table 2, and the magnet properties are shown in Table 3.

[0132] Example 5

[0133] The difference between this embodiment and Embodiment 1 is that the diffusion source alloy is Dy. 10 Tb 75 Co 10 Al2Cu2Ga1. The alloy composition of the substrate is shown in Table 1, the composition of the obtained RTB magnet is shown in Table 2, and the magnet properties are shown in Table 3.

[0134] Example 6

[0135] The difference between this embodiment and Embodiment 1 is that the diffusion source alloy is Dy. 10 Tb 75 Co 10 Al2Ga3. The alloy composition of the substrate is shown in Table 1, the composition of the obtained RTB magnet is shown in Table 2, and the magnet properties are shown in Table 3.

[0136] Comparative Example 1

[0137] The difference between this comparative example and Example 1 is that the specific steps of the diffusion heat treatment and tempering treatment are as follows:

[0138] The substrate with the diffusion source alloy attached was placed in a vacuum furnace. After evacuation, the furnace temperature was adjusted to approximately 820°C and held for about 6 hours under vacuum. Then, the furnace temperature was adjusted to approximately 900°C and held for about 24 hours. Finally, the furnace temperature was adjusted to approximately 480°C under vacuum and held for about 10 hours.

[0139] The alloy composition of the base material is shown in Table 1, the composition of the obtained RTB-based magnet is shown in Table 2, and the magnet properties are shown in Table 3. Table 5 shows the distribution of terbium in the grains and grain boundary phases with core-shell structure in the RTB-based magnet obtained in this comparative example. Figure 4(a)~4(e) The images are scanning electron microscope (SEM) images taken along the diffusion direction of terbium in the regions of 0–50 μm, 50–100 μm, 100–150 μm, 250–300 μm, and 450–500 μm inward from the surface of the RTB magnet. The microstructure observation surface is also 50 μm × 50 μm in shape.

[0140] Comparative Example 2

[0141] The difference between this comparative example and Example 1 is that the specific steps of the tempering treatment are as follows:

[0142] After the diffusion heat treatment is completed, the temperature inside the furnace is adjusted to about 480°C under vacuum, and then Ar gas is introduced to a pressure of about 60 kPa and held for about 10 hours.

[0143] The alloy ratio of the base material is shown in Table 1, the composition of the obtained RTB magnet is shown in Table 2, and the magnet properties are shown in Table 3.

[0144] Comparative Example 3

[0145] The difference between this comparative example and Example 1 is that the specific steps of the tempering treatment are as follows:

[0146] After the diffusion heat treatment is completed, the temperature inside the furnace is adjusted to about 480°C under vacuum, and then Ar gas is introduced to a pressure of about 100 kPa and held for about 10 hours.

[0147] The alloy ratio of the base material is shown in Table 1, the composition of the obtained RTB magnet is shown in Table 2, and the magnet properties are shown in Table 3.

[0148] Table 1

[0149]

[0150]

[0151] Table 2

[0152] Pr-Nd Dy Tb B Co Cu Ga Ti Al Fe Example 1 28.8 0.48 0.75 0.97 0.61 0.06 0.18 0.12 0.01 margin Example 2 28.8 0.48 0.75 0.96 0.61 0.06 0.18 0.12 0.01 margin Example 3 28.7 0 1.13 0.95 1.01 0.06 0.17 0.12 0.01 margin Example 4 28.8 0 1.16 0.95 1.01 0.06 0.18 0.12 0.01 margin Example 5 28.6 0.54 0.70 0.95 0.64 0.06 0.18 0.12 0.01 margin Example 6 28.7 0.55 0.69 0.96 0.63 0.06 0.19 0.12 0.01 margin Comparative Example 1 28.8 0.48 0.75 0.97 0.61 0.06 0.18 0.12 0.01 margin Comparative Example 2 28.8 0.48 0.75 0.97 0.61 0.06 0.18 0.12 0.01 margin Comparative Example 3 28.8 0.48 0.75 0.97 0.61 0.06 0.18 0.12 0.01 margin

[0153] Table 3

[0154]

[0155]

[0156] Table 4

[0157]

[0158] Table 5

[0159]

[0160] As can be seen from Table 3, the B of the RTB-based magnets prepared in this application r ≥14.2kGs, H cJ ≥27kOe, H k / H cJ ≥94%. The performance of RTB magnets obtained without using the preparation method of this application, especially without using the diffusion heat treatment and / or tempering method of this application, will be reduced.

[0161] As shown in Tables 4 and 5, in the RTB-based magnet prepared in Example 1, the diffusion depth of terbium is at least 500 μm, and within this depth range, the terbium content in the core-shell structured grains formed by the diffusion is also very high. In contrast, in the RTB-based magnet prepared in Comparative Example 1, although the diffusion depth of terbium is also relatively deep, the terbium content in the core-shell structured grains formed by diffusion is relatively low, and the diffusion uniformity is not good enough.

[0162] from Figure 3(a)~3(e)As can be seen, in the RTB-based magnet prepared in Example 1, even with a terbium diffusion depth of 500 μm, the core-shell structured grains formed by terbium diffusion still account for a very large proportion, ≥90%. Figure 4(a)~4(e) As can be seen, in the RTB-based magnet prepared in Comparative Example 1, the proportion of terbium-diffused grains with core-shell structures is relatively high when the terbium diffusion depth is 150 μm. However, the proportion of grains with core-shell structures becomes relatively low when the diffusion depth reaches approximately 300 μm and 500 μm, especially at 500 μm, where the proportion is only about 30%. Furthermore, in the magnet obtained in Example 1, the RH1 content is greater than 2.0 wt% within the diffusion depth range of 0–500 μm.

[0163] Obviously, the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An RTB-based magnet, characterized in that, The RTB-based magnet includes R, iron, and boron elements, wherein the R elements include light rare earth elements and heavy rare earth elements, and the heavy rare earth elements include terbium and / or dysprosium. The heavy rare earth elements diffuse from the surface of the RTB magnet to the interior; the RTB magnet includes main phase grains and grain boundary phases located between the main phase grains, and the main phase grains include grains with a core-shell structure. Along the diffusion direction of the heavy rare earth elements, in the microstructure observation plane located in a region 200 μm inward from the surface of the RTB magnet, the average heavy rare earth element content RH1 of the shell of the core-shell structure and the average heavy rare earth element content RH2 of the grain boundary phase satisfy the following: RH1-RH2≥2.6wt% and / or RH1 / RH2≥1.5, wherein the microstructure observation plane is perpendicular to the diffusion direction of the heavy rare earth elements.

2. The RTB-based magnet according to claim 1, characterized in that, Along the diffusion direction of the heavy rare earth elements, in the microstructure observation surface located in a region 500 μm inward from the surface of the RTB magnet, the proportion of the main phase grains with core-shell structure is ≥90%.

3. The RTB-based magnet according to claim 2, characterized in that, Along the diffusion direction of the heavy rare earth elements, in the microstructure observation surface located in the region 500 μm inward from the surface of the RTB magnet, the heavy rare earth element content of the shell of the core-shell structure is higher than that of the core of the core-shell structure, and the average heavy rare earth element content RH1 of the shell of the core-shell structure is ≥2.0 wt%.

4. The RTB-based magnet according to claim 1, characterized in that, The size of the microstructure observation surface is ≤40000 μm. 2 Optionally 2500μm 2 ; Optionally, the microscopic tissue observation surface is a square or rectangular structure.

5. The RTB-based magnet according to claim 1, characterized in that, The composition of the RTB-based magnet is (PrNd). 27～29 Dy 0～0.65 Tb 0～1.2 Ga 0.1～0.65 Co 0.3～3.05 Cu 0.05～0.55 B 0.90～0.98 A 0.05～0.35 Al 0～0.25 Fe 余量 A includes at least one element selected from Ti, Zr, and Nb.

6. The RTB-based magnet according to claim 1, characterized in that, The B of the RTB system magnet r ≥14.2kGs, H cJ ≥27kOe, H k / H cJ ≥94%.

7. A method for preparing an RTB-based magnet, characterized in that, include: The diffusion source alloy is attached to the surface of the substrate; as well as The substrate with the diffusion source alloy attached is subjected to diffusion heat treatment and tempering treatment; The diffusion source alloy includes a first rare earth element, which includes terbium and / or dysprosium. The substrate includes light rare earth elements, second heavy rare earth elements, iron, and boron, wherein the second heavy rare earth elements include terbium and / or dysprosium. The diffusion heat treatment includes a first heat treatment, a second heat treatment, and a cooling treatment between the first heat treatment and the second heat treatment. The first heat treatment includes: adjusting the temperature to 820℃~850℃ under vacuum and holding it at that temperature for 4~8 hours. The cooling treatment includes: cooling to below 100℃ under an inert atmosphere. The second heat treatment includes: adjusting the temperature to 900℃~950℃ under vacuum and holding it at that temperature for 20~24 hours. The tempering process includes: adjusting the temperature to 460℃~500℃ under vacuum, then filling with inert gas to a pressure of 70~90kPa, and holding at that temperature for 8~12h.

8. The preparation method according to claim 7, characterized in that, The composition of the diffusion source alloy is RH' a Co b Al c Cu d Ga e RH' is the first heavy rare earth element, a = 70-90 wt%, b = 0-10 wt%, c = 0-10 wt%, d = 0-10 wt%, e = 0-10 wt%; Optionally, the composition of the substrate is (PrNd). 27～29 Dy 0～0.5 Tb 0～0.6 Ga 0.1～0.6 Co 0.3～3 Cu 0.05～0.5 B 0.90～ 0.98 A 0.05～0.35 Al 0～0.2 Fe 余量 A includes at least one element selected from Ti, Zr, and Nb.

9. The preparation method according to claim 7, characterized in that, The diffusion source alloy is attached to the surface of the substrate by at least one of coating, vacuum evaporation, or sputtering. Optionally, when the diffusion source alloy is coated on the surface of the substrate, the weight gain of the substrate is 0.3 to 0.6 wt%. Optionally, when the diffusion source alloy is attached to the surface of the substrate by vacuum evaporation and / or sputtering, the thickness of the diffusion alloy layer formed on the surface of the substrate by the diffusion source alloy is 5 to 10 μm. Optionally, the diffusion source alloy is attached only to the diffusion surface of the substrate; Optionally, the coating includes at least one of dipping, spraying, screen printing coating, and roll coating; Optionally, the slurry used for coating includes the diffusion source alloy, binder and solvent; in the slurry, the mass ratio of the diffusion source alloy to the binder is (90-95):(5-10).

10. The preparation method according to claim 7, characterized in that, Also includes: Preparation of alloy sheets; The alloy sheet is crushed into alloy powder; The alloy powder is pressed into a compact; The pressed blank is sintered to obtain a sintered body; as well as The sintered body is processed to obtain the substrate.

11. The preparation method according to claim 10, characterized in that, The preparation of alloy sheets includes: The raw materials are melted and then cast to obtain the alloy sheet; The interlayer spacing of the neodymium-rich phase in the alloy sheet is less than 3 μm.

12. The preparation method according to claim 10, characterized in that, The alloy powder D 50 The diameter is 3.5–3.8 μm, D 90 / D 10 =4 to 4.6; Optionally, the density of the pressed blank is 4–4.3 g / cm³. 3 ; Optionally, the sintering temperature is 1030℃~1050℃, and the holding time is 5~8h; Optionally, the density of the sintered body is 7.55–7.58 g / cm³. 3 The average grain size is 5.2–5.8 μm.

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