A magnetic material, its preparation method and application

Abstract

The present invention provides a magnetic material, a preparation method thereof and an application. The R-T-B based magnet contains an Al element, and the concentration of the Al element in the grain boundary is greater than its concentration in the grain. The R-T-B based magnet is obtained by subjecting an R-T-B based sintered substrate to a diffusion treatment using a diffusion source. The rare earth sintered R-T-B based magnet provided by the present invention has a gradient distribution of Al element and heavy rare earth element from the surface to the center. By controlling the content of key elements in the R-T-B based sintered substrate, using an auxiliary diffusion material, and controlling the diffusion treatment method, the heavy rare earth element further diffuses into the magnet interior, and the Hcj of the obtained magnet is significantly improved compared with the magnet substrate before diffusion.

Description

Technical Field

[0001] The present invention belongs to the field of rare earth permanent magnet materials, and relates to a high-performance R-Fe-B type sintered magnetic material, a preparation method thereof, and an application thereof. Background Art

[0002] Nd-Fe-B based magnets are widely used due to their excellent properties. Due to the demand for energy-saving motors in the automotive and electronic application fields, the market application of sintered Nd-Fe-B will be further expanded. The improvement of the remanence and coercivity of Nd-Fe-B materials is beneficial to its rapid growth in the motor market. However, the improvement of the coercivity in the traditional process always comes at the cost of sacrificing the remanence, and a large proportion of heavy rare earth elements Dy / Tb must be used to improve the coercivity, resulting in a sharp increase in the cost of the magnet. Therefore, reducing the usage amount of heavy rare earth elements has become a research hotspot in the field of rare earth permanent magnets. Through the analysis of the microstructure of the magnet, it is confirmed that the way of intergranular diffusion of heavy rare earth elements can effectively reduce the grain boundary scattering field, weaken the magnetic exchange coupling effect, and harden the grain boundary magnetically. On the premise that the remanence of the magnet is basically not reduced, the coercivity is greatly improved. By improving the magnet performance in this way, the cost of the magnet can be effectively controlled.

[0003] In order to improve the coercivity of Nd-Fe-B based sintered magnets, the intergranular diffusion method mainly diffuses Dy or Tb elements from the magnet surface along the grain boundaries into the magnet interior.

[0004] Patent Document 1 (CN101521068B) discloses a surface coating diffusion method. In the sintering stage, a metal, alloy or compound containing a heavy rare earth element RH is coated on the surface of the magnet and heat-treated to make it diffuse. However, due to uneven coating, the penetration amount is not balanced, resulting in differences in magnetic properties in the end, and this method is not applicable to the production of special-shaped tile products.

[0005] Patent Document 2 (CN101331566B) discloses an evaporation diffusion method. By heating, heavy rare earth elements form steam and then slowly diffuse into the magnet interior. The evaporation method isolates the magnet and the heavy rare earth diffusion source through components such as brackets. In the actual operation process, the arrangement of the support frame is relatively complex, greatly increasing the difficulty of placing materials. The steam concentration in the evaporation method is difficult to control, and there is a problem of poor batch productivity.

[0006] Patent Document 3 (CN102473515B) and Patent Document 4 (CN10404654B) disclose a dynamic contact diffusion method of mixing a magnet and a diffusion source. According to the method of Patent Document 3, at a temperature of 500°C - 850°C, the RH diffusion source is dynamically close to or in contact with the R-T-B system sintered magnet, so that the RH diffusion source supplies the heavy rare earth element RH, which diffuses into its interior through the grain boundary. The diffusion source used in the method is Dy metal, or Tb metal, or a Dy alloy with Dy > 70%, or a Tb alloy with Tb > 70%. However, at a treatment temperature above 850°C, this kind of RH diffusion source will weld with the magnet. Therefore, the diffusion process cannot be accelerated by increasing the treatment temperature, and the diffusion temperature must be lower than 850°C, resulting in low diffusion efficiency and long production cycle. Patent Document 4 improves the composition of the diffusion source, using an alloy of the heavy rare earth element RH and Fe as the diffusion source, where the content of Fe is in the range of 30 - 80%, and the content of R in the substrate is limited to increase the ratio of the R-rich phase and widen the grain boundary, and dynamic contact diffusion is carried out at a diffusion temperature of 860 - 970°C. This method can increase the diffusion temperature, shorten the diffusion time, and there is no welding between the magnet and the diffusion source. In order to avoid welding between the magnet and the diffusion source, the content of the heavy rare earth in the diffusion source is reduced, and more diffusion substitution is carried out through contact diffusion, so that the heavy rare earth element RH and Nd, Pr in the magnet are diffused and replaced. However, due to the reduction of the rare earth content, the diffusion efficiency is reduced. At the same time, the diffusion devices described in Patent Document 3 and Patent Document 4 also have the following problems: after the diffusion treatment, it is necessary to take out all the diffusion source and the magnet and then screen them to obtain the diffused product. This process can only be carried out after the magnet and the diffusion source are completely cooled, resulting in a reduction in the processing capacity and output. Summary of the Invention

[0007] In order to improve the above technical problems, the present invention provides an R-T-B system magnet, and the R-T-B system magnet contains an Al element, and the concentration of the Al element in the grain boundary is greater than its concentration in the grain.

[0008] Preferably, the concentration of the Al element in the grain boundary is denoted as A, and the concentration of the Al element in the grain is denoted as a, and the value range of A / a is 1.5 - 4, such as 1.7 - 3, and exemplarily 1.5, 1.53, 1.78, 2, 2.06, 2.38, 2.5, 2.63, 2.68, 3 or a number between any two points. Among them, the concentration is the concentration value at a distance of 500 ± 10 μm from the surface of the R-T-B system magnet.

[0009] According to the embodiment of the present invention, the Al element is enriched at the grain boundary and the triple point of the R-T-B system magnet. For example, the EPMA diagram of the Al element in the R-T-B system magnet is basically as Figure 2 shown.

[0010] According to an embodiment of the present invention, the Al element is distributed in a gradient from the surface to the center of the R-T-B based magnet. For example, the concentration distribution of the Al element in the R-T-B based magnet is substantially as Figure 3 shown.

[0011] According to an embodiment of the present invention, the mass content of Al in the R-T-B based magnet is 0.5-2.5%.

[0012] According to an embodiment of the present invention, the R-T-B based magnet contains a heavy rare earth element RH. For example, the heavy rare earth element RH is selected from at least one of Dy or Tb, and is exemplarily Tb.

[0013] According to an embodiment of the present invention, the concentration of the RH element in the grain boundary is greater than its concentration in the grain;

[0014] Preferably, the concentration of the RH element in the grain boundary is denoted as C, the concentration of the RH element in the grain is denoted as c, and the value range of C / c > 2, for example, is 3-8, and is exemplarily 3.26, 4, 5, 5.60. Wherein, the concentration is the concentration value at a distance of 500±10 μm from the surface of the R-T-B based magnet.

[0015] According to an embodiment of the present invention, the EPMA diagram of the RH element in the R-T-B based magnet is substantially as Figure 4 shown.

[0016] According to an embodiment of the present invention, the RH element is distributed in a gradient from the surface to the center of the R-T-B based magnet. For example, the concentration distribution of the RH element in the R-T-B based magnet is substantially as Figure 5 shown.

[0017] According to an embodiment of the present invention, the Hcj of the R-T-B based magnet is not less than 1800.

[0018] According to an embodiment of the present invention, the R-T-B based magnet is obtained by subjecting an R-T-B based sintered substrate to a diffusion treatment with a diffusion source.

[0019] According to an embodiment of the present invention, the raw material of the R-T-B based sintered substrate contains one, two or three of Al, B and Co;

[0020] For example, the mass content of Al in the raw material is 0-1.0%, preferably 0-0.3%, and is exemplarily 0, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%;

[0021] Preferably, the mass content of B in the raw material is 0.8-1.15%, preferably 0.8-0.92%;

[0022] Preferably, the mass content of Co in the raw material is 0.1-3.0%, preferably 0.1-0.5%, for example 0.1%, 0.2%, 0.3%, 0.4%, 0.5%.

[0023] According to an embodiment of the present invention, the diffusion source includes a heavy rare earth element RH diffusion source and an auxiliary diffusion source;

[0024] For example, the mass content of the heavy rare earth element RH in the heavy rare earth element RH diffusion source is not less than 60%, for example, 60-100%, exemplified by 70%, 75%, 80%, 90%, or 100%.

[0025] Preferably, the heavy rare earth element RH diffusion source may also contain one, two or more elements selected from Fe, B, Ti, Zr, etc., such as Fe and B, Fe and Ti, and Fe and Zr.

[0026] For example, the heavy rare earth element RH diffusion source can be Tb 80 Fe 20 、Tb 80 Fe 10 B 10 、Tb 80 Fe 10 Ti 10 or Tb 80 Fe 10 Zr 10 . Using heavy rare earth element RH diffusion source Tb 80 Fe 20 For example, it contains 80% by mass of Tb and 20% by mass of Fe.

[0027] According to an embodiment of the present invention, the RH diffusion source may be in a block shape, for example, a regular block with a size of 20 cm*5 cm*3 cm.

[0028] According to an embodiment of the present invention, the auxiliary diffusion source contains Al element with a mass fraction of not less than 60%, for example, 60-100%, exemplified by 60%, 70%, 80%, 90%, and 100%.

[0029] According to an embodiment of the present invention, the auxiliary diffusion source may contain other elements, such as one, two or more of Pr, Nd, La, Ce, Y and Sm, for example, Pr, Nd or Ce.

[0030] For example, the auxiliary diffusion source may be Al 100 、Al90 Pr 10 、 Al 80 Pr 20 、 Al 70 Pr 30 、 Al 60 Pr 40 、 Al 90 Nd 10 or Al 90 Ce 10 。 Taking the auxiliary diffusion source Al 90 Pr 10 as an example, it contains 90% by mass of Al element and 10% by mass of Pr element.

[0031] According to an embodiment of the present invention, the auxiliary diffusion source is spherical, for example, spherical with a diameter of 0.5 - 2 cm.

[0032] According to an embodiment of the present invention, the heavy rare earth element RH diffusion source may further contain impurity elements; for example, the impurity elements are one, two or more of Cu, Zn, Ni, Mn, V, Mo, Pb, and Si, etc.

[0033] According to an embodiment of the present invention, the auxiliary diffusion source may further contain impurity elements; for example, the impurity elements are one, two or more of Ti, Cu, Zn, Ni, Mn, V, Mo, Pb, and Si, etc.

[0034] According to an embodiment of the present invention, the diffusion treatment includes: making the R - T - B - based sintered substrate come into dynamic contact with the auxiliary diffusion source and the heavy rare earth element RH diffusion source, and performing sufficient diffusion.

[0035] According to an embodiment of the present invention, the diffusion treatment is carried out in a diffusion chamber.

[0036] According to an embodiment of the present invention, the dynamic contact can be achieved in the following way: dispersing and fixing the heavy rare earth element RH diffusion source on the inner wall of the cavity of the diffusion chamber, placing the auxiliary diffusion source and the R - T - B - based sintered substrate in the cavity of the diffusion chamber, and with the overall rotation, vibration, and flipping of the diffusion chamber, making the R - T - B - based sintered substrate, the auxiliary diffusion source, and the heavy rare earth element RH diffusion source come into dynamic contact. According to an embodiment of the present invention, the diffusion treatment includes: the first heating diffusion, the first cooling, the second heating diffusion, and the second cooling.

[0037] According to an embodiment of the present invention, the temperature of the first heating diffusion is 400 - 600 °C, preferably 450 - 550 °C, for example, 450 °C, 500 °C, 550 °C;

[0038] According to an embodiment of the present invention, the time of the first heat diffusion is 1 - 5 h, for example, 1, 2, 3, 4, 5 h.

[0039] According to an embodiment of the present invention, the heating rate of the first heat diffusion is 10 - 30 °C / min.

[0040] According to an embodiment of the present invention, the temperature of the first cooling is 100 - 300 °C, and the treatment time is 30 min - 120 min, for example, 30 min, 45 min, 80 min;

[0041] According to an embodiment of the present invention, the temperature of the second heat diffusion is 700 - 950 °C, preferably 750 - 850 °C, such as 750 °C, 800 °C, 850 °C;

[0042] According to an embodiment of the present invention, the time of the second heat diffusion is 1 - 5 h, for example, 1, 2, 3, 4, 5 h.

[0043] According to an embodiment of the present invention, the temperature of the second cooling is cooled to below 50 °C. Preferably, the cooling is selected from any one of vacuum cooling, slow cooling with inert gas filling, and cooling with a blower.

[0044] The present invention also provides a method for element diffusion, including performing diffusion treatment on the R - T - B - based sintered matrix using a diffusion source; the diffusion treatment includes: making the R - T - B - based sintered matrix come into dynamic contact with the auxiliary diffusion source and the heavy rare earth element RH diffusion source, and performing sufficient diffusion.

[0045] According to an embodiment of the present invention, the diffusion source includes the auxiliary diffusion source and the heavy rare earth element RH diffusion source.

[0046] Furthermore, the R - T - B - based sintered matrix, the auxiliary diffusion source, the heavy rare earth element RH diffusion source, dynamic diffusion, and diffusion treatment all have the definitions as shown above.

[0047] The present invention also provides a method for preparing the above - mentioned R - T - B - based magnet, including the following steps: performing diffusion treatment on the above - mentioned R - T - B - based sintered matrix using the above - mentioned diffusion source to obtain the above - mentioned R - T - B - based magnet.

[0048] According to an embodiment of the present invention, the raw material composition of the R - T - B - based sintered matrix includes:

[0049] RL elements: one, two or more elements selected from Nd, Pr, La, and Ce, for example, with a mass content of 26 - 33%;

[0050] RH elements: Dy and / or Tb, for example, with a mass content of 0 - 1%;

[0051] Element B, such as with a mass content of 0.8 - 1.15%;

[0052] One, two or three of the elements Zr, Ti and Nb, for example, with a mass content of 0 - 1.0%;

[0053] Element Co, such as with a mass content of 0.1 - 3.0%;

[0054] Element Cu, such as with a mass content of 0 - 1.0%;

[0055] Element Al, such as with a mass content of 0 - 1.0%.

[0056] According to an embodiment of the present invention, the raw material composition of the R - T - B - based sintered matrix further includes Fe and inevitable impurity elements. For example, the impurity elements include oxygen (O), nitrogen (N), carbon (C), sulfur (S) and / or calcium (Ca).

[0057] According to an embodiment of the present invention, the R - T - B - based sintered matrix can be prepared by the following method, and the method includes: (a) Melting process: The raw materials of the above - mentioned R - T - B - based sintered matrix are melted at high temperature, cast and cooled to form alloy sheets; (b) Powder - making process: The alloy sheets are crushed into alloy powders; (c) Pressing process: The alloy powders are pressed into shape under the action of a magnetic field to obtain a green body; (d) Sintering process: The green body is sintered at high temperature to obtain the R - T - B - based sintered matrix.

[0058] According to an embodiment of the present invention, the diffusion source has the definition as shown above.

[0059] According to an embodiment of the present invention, the diffusion treatment has the definition as shown above.

[0060] The present invention also provides an R - T - B - based magnet prepared by the above - mentioned method.

[0061] The present invention also provides the application of the above - mentioned R - T - B - based magnet in the field of motors.

[0062] Advantages of the present invention

[0063] The rare - earth sintered R - T - B - based magnet provided by the present invention has Al elements and heavy rare - earth elements distributed in a gradient from the surface to the center. By controlling the content of key elements in the R - T - B - based sintered matrix, using auxiliary diffusion materials, and controlling the diffusion treatment method, the heavy rare - earth elements further diffuse into the magnet interior, and the Hcj of the obtained magnet is significantly improved compared with the magnet matrix before diffusion. Description of the drawings

[0064] Figure 1Schematic structural diagram of the diffusion chamber for diffusion treatment;

[0065] Reference numerals: ① Diffusion chamber, ② Diffusion source of heavy rare earth element RH, ③ Auxiliary diffusion source, ④ R-T-B series sintered substrate.

[0066] Figure 2 EPMA diagram of Al element in the magnet, where Al is distributed along the grain boundaries;

[0067] Figure 3 Concentration distribution diagram of Al element in the magnet (from left to right: from the center to the surface);

[0068] Figure 4 EPMA diagram of Tb element in the magnet, where Tb is distributed along the grain boundaries;

[0069] Figure 5 Concentration distribution diagram of Tb element in the magnet (from left to right: from the center to the surface). Specific implementation method

[0070] In the aforementioned R-T-B series magnet and its preparation method, the preparation method of the R-T-B series sintered substrate includes: (a) Melting process: The raw materials of the R-T-B series sintered substrate are melted, poured, and cooled to form alloy sheets; (b) Powder making process: The alloy sheets are crushed into alloy powders; (c) Compression molding process: The alloy powders are pressed into shape under the action of a magnetic field to obtain a green body; (d) Sintering process: The green body is subjected to high-temperature sintering treatment to obtain the R-T-B series sintered substrate.

[0071] [Raw materials of the R-T-B series sintered substrate]

[0072] The raw material composition of the R-T-B series sintered substrate includes:

[0073] RL elements: One, two or more elements selected from Nd, Pr, La, and Ce, for example, with a mass content of 26-33%;

[0074] RH elements: Dy and / or Tb, for example, with a mass content of 0-1%;

[0075] B element, for example, with a mass content of 0.8-1.15%;

[0076] One, two or three elements selected from Zr, Ti, and Nb, for example, with a mass content of 0-1.0%;

[0077] Co element, for example, with a mass content of 0.1-3.0%;

[0078] Cu element, for example, with a mass content of 0-1.0%, for example, 0.05%, 0.3%;

[0079] The Al element, for example, has a mass content of 0 - 1.0%.

[0080] Preferably, the mass content of Al in the raw material is 0 - 0.3%, for example, 0, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%;

[0081] Preferably, the mass content of B in the raw material is 0.8 - 0.92%;

[0082] Preferably, the mass content of Co in the raw material is 0.1 - 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%.

[0083] According to an embodiment of the present invention, the raw material composition of the R - T - B - based sintered matrix further includes Fe and inevitable impurity elements. For example, the impurity elements include oxygen (O), nitrogen (N), carbon (C), sulfur (S) and / or calcium (Ca).

[0084] Exemplarily, the raw material composition of the R - T - B - based sintered matrix includes: Nd 29 - 30%, Dy 0.5%, B 0.8 - 0.99%, Co 0.1 - 0.5%, Al 0 - 0.3%, Ti 0.2%, Cu 0.05 - 0.3%, Ga 0.25%, Zr 0.2%, and the balance is Fe and impurity elements.

[0085] The addition of the Al element can inhibit the phase separation between Co and Cu, so that the magnetic interaction between grains can be fully blocked. However, a high content of Al will replace Fe in the main phase of the magnet, resulting in a decrease in the remanence. Since Al is a non - magnetic element, when present in the grains, it will cause a slight decrease in magnetization. Therefore, in the R - T - B - based magnet according to the present invention, it is desirable that the Al content is higher at the grain boundaries than in the grains. This enables Al to be enriched at the grain boundaries, thickening the diffusion channels and promoting the deeper diffusion of heavy rare - earth elements. The present invention uses a special diffusion method to enrich the Al element along the grain - boundary phase. Therefore, it is necessary to control the Al content in the sintered matrix. However, an excessive amount of Al in the matrix will also cause a loss of magnetic properties.

[0086] [Preparation process of the R - T - B - based sintered matrix]

[0087] According to an embodiment of the present invention, the (a) smelting process further includes: melting the raw materials of the R-T-B series sintered matrix in a vacuum or inert gas atmosphere to obtain an alloy liquid with uniform and stable composition, and then pouring the alloy liquid onto a chill roll to form an alloy sheet. For example, the pouring temperature is 1300 °C to 1600 °C, preferably 1400 °C to 1500 °C. For example, the rotation speed of the chill roll is 20 to 60 r / min, preferably 30 to 50 r / min. Preferably, a cooling fluid, such as cooling water, is passed through the chill roll.

[0088] According to an embodiment of the present invention, the (b) powder making process includes coarse crushing and fine crushing.

[0089] Preferably, the coarse crushing is selected from hydrogen embrittlement and / or medium grinding.

[0090] Preferably, the fine crushing is selected from jet mills. Preferably, the jet mill is carried out in an inert gas atmosphere. Preferably, the inert atmosphere is provided by nitrogen, helium, neon, argon, etc.

[0091] In the present invention, the hydrogen embrittlement, medium grinding or jet mill can adopt operations known in the art.

[0092] Preferably, after the fine crushing, screening is also required, for example, through a classification wheel.

[0093] Preferably, the particle size SMD of the alloy powder is 1 to 10 μm, preferably 1 to 9 μm, 2 to 5 μm, 6 to 8 μm, and exemplarily 2.8 μm. Preferably, the average particle size of the alloy powder is measured by laser diffraction method using dry dispersion.

[0094] According to an embodiment of the present invention, the (c) compacting process includes: adding a lubricant to the alloy powder and then compacting it under the action of a magnetic field to obtain a green body.

[0095] Preferably, the lubricant is selected from reagents known in the art and the amounts known in the art to achieve sufficient mixing of the powder and easy forming. Exemplarily, the lubricant is selected from volatile organic solvents such as esters or alcohols, for example, zinc stearate.

[0096] Exemplarily, the addition amount of the lubricant is 0.1 - 1 wt% of the total mass of the preparation raw materials.

[0097] Preferably, after adding the lubricant, mixing is also required. Preferably, the mixing time is 3 - 6 h.

[0098] The mixing in the present invention can be carried out by methods known in the technical field, for example, placing it in a mixer for mixing.

[0099] Preferably, the compacting is carried out in the cavity of a press die.

[0100] Preferably, before pressing and forming, orientation magnetization and forming should be carried out under a magnetic field intensity of 2 - 3T.

[0101] Preferably, after pressing and forming, a reverse magnetic field is applied for demagnetization.

[0102] Preferably, the formed green body can also be processed in a cold isostatic press to further increase the density of the green body.

[0103] According to the embodiment of the present invention, the sintering process (d) includes: the green body is subjected to high - temperature sintering, cooling, aging process, and then cooling to obtain the R - T - B - based sintered matrix.

[0104] Preferably, the temperature of the high - temperature sintering is 1000°C - 1100°C, and the time of the high - temperature sintering is 4 - 10h. Preferably, the temperature of the high - temperature sintering is 1020 - 1080°C, for example, 1020°C. Preferably, the time of the high - temperature sintering is 5 - 10h, for example, 4, 5, 6, 7, 8, 9, 10h.

[0105] Preferably, the aging process includes: the treatment temperature is 500 - 750°C, preferably 530 - 600°C, 600 - 650°C; the treatment time is 4h - 10h, for example, 4, 5, 6, 7, 8, 9, 10h.

[0106] Preferably, the cooling in the sintering process means cooling to below 50°C.

[0107] Preferably, the sintering process is carried out in an inert atmosphere.

[0108] In the aforementioned R - T - B - based magnet and its preparation method, the diffusion treatment involved further includes the following content:

[0109] [Prepare the RH diffusion source and the auxiliary diffusion source]

[0110] The diffusion source in the present invention can be prepared by methods known in the art. Exemplarily, after mixing and melting the diffusion source metals in proportion, they are poured into a mold for forming. Its forms are, for example: spherical, plate - shaped, block - shaped, powder, etc.

[0111] [Diffusion process]

[0112] The diffusion treatment includes: making the R - T - B - based sintered matrix come into dynamic contact with the auxiliary diffusion source and the heavy rare - earth element RH diffusion source for sufficient diffusion.

[0113] According to the embodiment of the present invention, the diffusion treatment is carried out in a diffusion chamber.

[0114] According to an embodiment of the present invention, the dynamic contact can be achieved in the following manner: the heavy rare earth element RH diffusion source is dispersed and fixed on the inner wall of the cavity of the diffusion chamber, the auxiliary diffusion source and the R-T-B system sintered substrate are placed in the cavity of the diffusion chamber, and with the overall rotation, vibration, and flipping of the diffusion chamber, the R-T-B system sintered substrate, the auxiliary diffusion source, and the heavy rare earth element RH diffusion source are in dynamic contact.

[0115] Preferably, the diffusion chamber includes a diffusion chamber body and a diffusion chamber cavity, and a fixing position for the heavy rare earth element RH diffusion source is provided on the inner wall of the diffusion chamber cavity, so that the heavy rare earth element RH diffusion source is distributed and fixed on the inner wall. After the diffusion treatment is completed, it is convenient to pour out the magnet, thus eliminating the process of separating the heavy rare earth element RH diffusion source and the magnet.

[0116] According to an embodiment of the present invention, stirring blades are further provided in the diffusion chamber to enable the R-T-B system sintered substrate and the auxiliary diffusion source, or the R-T-B system sintered substrate, the auxiliary diffusion source, and the co-diffusion component to be in sufficient contact.

[0117] Preferably, the number of groups of the stirring blades is at least two groups.

[0118] According to an embodiment of the present invention, the diffusion treatment further includes being carried out in the presence of a co-diffusion component. For example, the co-diffusion component is a stainless steel ball, a silicon carbide ball, a boron carbide ball, a zirconia ball, a yttria ball, etc.

[0119] According to an embodiment of the present invention, the auxiliary diffusion source and the R-T-B system sintered substrate are added to the diffusion chamber cavity, and the heavy rare earth element RH diffusion source is fixed in each dispersed fixing position, and then the diffusion treatment is carried out.

[0120] According to an embodiment of the present invention, in the diffusion treatment, the diffusion chamber is driven to rotate by a mechanical shaft. For example, the circumferential speed of the diffusion chamber rotation is controlled to be more than 0.01 m / s and less than 0.5 m / s, preferably 0.1 m / s.

[0121] According to an embodiment of the present invention, the diffusion chamber is further provided with a ventilation and exhaust device, so that a vacuum or an atmosphere containing an inert gas is maintained in the diffusion chamber.

[0122] According to an embodiment of the present invention, a heating device is provided on the outer peripheral part of the diffusion chamber, and through heat conduction, the R-T-B system sintered substrate, the auxiliary diffusion source, and the heavy rare earth element RH diffusion source inside the diffusion chamber are heated. For example: the heating method can adopt electromagnetic induction heating.

[0123] The RTB sintered matrix in the diffusion chamber is in dynamic contact with the auxiliary diffusion source, which has a higher diffusion efficiency. This prevents welding during the diffusion of the auxiliary diffusion source with a high Al content, and allows the Al element to be more evenly distributed in the grain boundary phase of the magnet.

[0124] As mentioned above, the diffusion process includes: a first heating diffusion, a first cooling, a second heating diffusion, and a second cooling.

[0125] By controlling the temperature and time of the two-stage diffusion heating, the diffusion order of the auxiliary diffusion source and the heavy rare earth element RH diffusion source is controlled. The auxiliary diffusion source is extremely sensitive to temperature changes. First, a heating temperature of 400-600°C is used to control the heating rate and cooling rate so that the auxiliary diffusion metal Al is distributed along the grain boundaries. The Al element in the auxiliary diffusion source is first enriched in large quantities at the grain boundaries, thickening the inherent grain boundary size. Then, a heating temperature of 700-950°C is used to control the heating rate and cooling rate so that the RH diffusion source diffuses into the interior of the magnet along the thickened grain boundaries. The use of a dynamic contact diffusion method of RTB-based sintered matrix and heavy rare earth element RH diffusion source not only solves the problems of welding and adhesion between the magnet matrix and the diffusion source during the diffusion process, but also solves the problem of low efficiency of rotational diffusion, so that the diffusion source can be maximized, thereby achieving cost reduction and source saving.

[0126] The rare earth sintered magnet produced by the present invention has Al elements and heavy rare earth elements distributed in a gradient from the surface to the center. Due to the use of auxiliary diffusion material, the heavy rare earth elements are further diffused into the interior of the magnet, so that the Hcj of the magnet is significantly improved compared with the magnet matrix before diffusion.

[0127] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0128] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0129] The diffusion treatment in the following experimental examples is Figure 1 The diffusion device shown is carried out, and the diffusion device includes: a diffusion chamber ①; a fixing position of a heavy metal element RH diffusion source ② arranged on the inner wall of the diffusion chamber 1, using a slot to fix the heavy metal element RH diffusion block or a molybdenum mesh to fix the heavy metal element RD diffusion plate; a heating device arranged on the periphery of the diffusion chamber ①, which heats the RTB system sintered matrix ④, auxiliary diffusion source ③, and heavy rare earth element RH diffusion source inside the diffusion chamber through heat conduction, and the heating method adopts electromagnetic induction heating.

[0130] The content units of each element in Table 1, Table 3, Table 5 and Table 7 are mass%; the unit of temperature in Table 2, Table 4, Table 6 and Table 8 is °C, the unit of time is h, the unit of Hcj is kA / m, and the unit of Br is kGs.

[0131] Influence of Al in the base material formula of Experimental Example 1

[0132] Prepare the neodymium iron boron alloy sheet according to the raw material composition of the magnet in Table 1, and use the strip casting process. The casting temperature is 1400 °C, the rotation speed of the chill roll is controlled at 35 r / min. After the alloy sheet is cooled and detached from the chill roll, it is sprayed with low-temperature argon for secondary cooling. The alloy sheet is cooled at a cooling rate of 10 °C / s for secondary cooling to obtain the alloy sheet, and the alloy sheet falls on the water-cooled disc for recovery, thus obtaining an alloy sheet with an average thickness of 0.25 mm.

[0133] Use the hydrogen embrittlement process to coarsely crush the above alloy thin sheet to obtain powder. Add 0.1 wt% of zinc stearate based on the mass of the raw material as a lubricant to the powder, and mix for 60 min. The mixed material is finely crushed in a fluidized bed jet mill, using nitrogen as the grinding gas, to obtain the jet mill powder with a target particle size SMD = 3.0 μm.

[0134] Add 0.2 wt% of lubricant to the obtained jet mill powder. After mixing in a mixer for 2 h, pour it into the mold cavity of the press, and under the action of an external magnetic field of 2.5 T (such as a magnetic field of 15 Koe), it is oriented and pressed into shape in an inert gas atmosphere.

[0135] Place the green body in a sintering furnace. In a vacuum atmosphere, carry out the first sintering at a temperature of 1020 °C, hold for 6 h, then fill with argon and slowly cool to 100 °C. Carry out the second sintering aging, heat up to 550 °C for holding, after holding for 5 h, fill with argon and slowly cool to room temperature.

[0136] Through mechanical processing, it is processed into a sintered magnet of 40 mm * 15 mm * 15 mm, and use Figure 1The device shown performs diffusion treatment. Weigh 20% by mass of Fe metal powder and 80% by mass of Tb metal powder, melt them and pour them into a block with dimensions of 200 mm * 50 mm * 20 mm to make an RH diffusion source. Insert this diffusion source inside the diffusion chamber and fix it with a molybdenum mesh. Put 500 g of sintered magnet and 5 g of auxiliary diffusion source into it. The auxiliary diffusion source is a pure Al metal ball with a diameter of 10 mm, and 10 g of zirconia balls are put in. Use electromagnetic induction heating to heat the diffusion chamber, heating while rotating. The circumferential speed of the diffusion furnace rotation is 0.15 m / s. The heating rate for the first-stage diffusion treatment is 30 °C / min. After cooling to 100 °C in the first stage, perform the second-stage diffusion treatment, and the heating time is 100 min. The temperature and time during the diffusion treatment are shown in Table 2.

[0137] Table 1

[0138]

[0139]

[0140] Table 2

[0141]

[0142] In Examples 1 - 6, the only variable in the matrix formula is the Al content. From the test results of the sintered magnet before and after diffusion, it can be seen that when the Al content in the matrix exceeds 0.3%, the Hcj and Br of the magnet decrease, and the increment of Hcj after diffusion also decreases. Therefore, it is preferred that the Al content in the diffusion matrix does not exceed 0.3%.

[0143] In Examples 6 and 7, the only variable in the matrix formula is the B content. The B content in Example 7 is less than that in Example 6. The Hcj before diffusion is basically the same, but after diffusion, the increment in Example 7 is greater than that in Example 6. Therefore, it is preferred that the B content in the diffusion matrix is 0.8 - 0.92%.

[0144] In Examples 2 and 8, the only variable in the matrix formula is Co. The Co content in Example 8 is less than that in Example 2. The Hcj before diffusion is the same, but after diffusion, the increment in Example 8 is greater than that in Example 2. Therefore, it is preferred that the Co content in the diffusion matrix is 0.1 - 0.5%.

[0145] The increment of Hcj after diffusion in Examples 9 and 10 (low B, low Co, low Al) is relatively large.

[0146] Influence of different diffusion sources in Experimental Example 2

[0147] Configure the composition of the sintered matrix according to Table 3, adopt the same manufacturing method as in Example 1 to prepare the sintered matrix, and through machining it, process it into a sintered magnet with dimensions of 40 mm * 15 mm * 15 mm, and use Figure 1The device shown performs diffusion treatment. Weigh metal powders of specific components according to Table 4, melt them and pour them into blocks with dimensions of 200mm * 50mm * 20mm to fabricate RH diffusion sources. Insert the diffusion source inside the diffusion chamber and fix it with molybdenum mesh. Put 500g of sintered magnets, 5g of auxiliary diffusion source (the auxiliary diffusion source is a pure Al metal ball with a diameter of 10mm), and 10g of zirconia balls. Heat the diffusion chamber by electromagnetic induction heating, heating while rotating. The circumferential speed of the diffusion furnace rotation is 0.15m / s. The heating rate for the first-stage diffusion treatment is 30°C / min. Cool to 100°C for the second-stage diffusion treatment, and the heating time is 100min. The temperature during the diffusion treatment is as shown in Table 4.

[0148] Table 3

[0149] No. Nd Pr Dy Tb B Co Al Ti Cu Ga Zr Fe and impurity elements 2 29 0 0.5 0 0.99 1.00 0.05 0.2 0.05 0.25 0.20 Balance

[0150] Table 4

[0151]

[0152] Experimental data shows that different RH diffusion sources have no effect on the Al increment, but Fe, B, Ti, and Zr in the RH diffusion source play a role in increasing the melting point and reducing the excessive volatilization of heavy rare earth RH. By using the method of dynamic contact diffusion of RH diffusion source, auxiliary diffusion source and magnet, even in the state of high heavy rare earth content, there is no welding phenomenon, and the diffusion efficiency is improved. When the heavy rare earth RH content < 60%, due to the low heavy rare earth content, the diffusion efficiency decreases, which hinders the entry of heavy rare earth RH into the magnet interior, and the increase amplitude of the coercivity after diffusion decreases. Therefore, it is preferred that the heavy rare earth content in the RH diffusion source is not less than 60%.

[0153] Influence of Different Auxiliary Metal Sources in Experimental Example 3

[0154] Configure the composition of the sintered matrix according to Table 5, adopt the manufacturing method of Example 1 to prepare the sintered matrix, and through machining, process it into a sintered magnet with dimensions of 40mm * 15mm * 15mm, and use Figure 1The device shown performs diffusion treatment. Weigh 20% by mass of Fe metal powder and 80% by mass of Tb metal powder, melt them and pour them into a block with dimensions of 200 mm * 50 mm * 20 mm to make an RH diffusion source. Insert this diffusion source inside the diffusion chamber and fix it with a molybdenum mesh. Put 500 g of sintered magnet and 5 g of auxiliary diffusion source into it. The auxiliary diffusion source is prepared by the casting method according to the composition in Table 6 to make a metal ingot containing Al, and put 10 g of zirconia balls into it. Heat the diffusion chamber by electromagnetic induction heating, heating while rotating. The circumferential speed of the diffusion furnace rotation is 0.15 m / s. The heating rate of the first-stage diffusion treatment is 30 °C / min. Cool to 100 °C in the first stage and then perform the second-stage diffusion treatment for 100 min. The temperature during the diffusion treatment is as shown in Table 6.

[0155] Table 5

[0156] No. Nd Pr Dy Tb B Co Al Ti Cu Ga Zr Fe and impurity elements 10 30 0 0.5 0 0.82 0.10 0.10 0.2 0.30 0.25 0.20 Balance

[0157] Table 6

[0158]

[0159] Experimental data show that adding an auxiliary diffusion source has a great effect on improving the coercivity Hcj. The auxiliary diffusion source enters the grain boundary phase through the way of flipping dynamic diffusion, opening a diffusion channel for the subsequent diffusion of heavy rare earths. Figure 2 This is the EPMA map of Al element in the magnet for sample 10-1. It can be seen that the Al element is enriched at the grain boundaries and triple points. Figure 3 This is the concentration distribution map of Al element in the magnet. It can be seen that the concentration of Al element is high at the grain boundaries and low inside the grains. At a distance of 500 um from the magnet surface, use EPMA to perform fixed-point analysis of Al element in the grain boundaries and inside the grains. The results are as shown in Table 6, where A represents the concentration of Al element in the grain boundaries, a represents the concentration of Al element in the grains, and A / a represents the ratio of Al element between the grain boundaries and inside the grains. The proportion of Al content in the auxiliary diffusion source affects the distribution of Al element in the magnet. When the Al content in the auxiliary diffusion source does not exceed 60%, the Al content in the grain boundaries decreases and the ratio of A / a decreases. Under the condition of using the same diffusion amount and diffusion conditions of heavy rare earths, for magnets with the ratio of A / a between 1.5 - 4, the increment of Hcj is the largest and the utilization rate of heavy rare earths is the highest.

[0160] Influence of different diffusion methods in Experimental Example 4

[0161] Configure the composition of the sintered matrix according to Table 7, adopt the manufacturing method of Example 1 to prepare the sintered matrix, and through machining it, process it into a sintered magnet with dimensions of 40 mm * 15 mm * 15 mm, and use Figure 1The device shown performs diffusion treatment. Weigh metal powders of specific components according to Table 8, melt them and pour them into blocks with dimensions of 200mm * 50mm * 20mm to make RH diffusion sources. Insert this diffusion source inside the diffusion chamber and fix it with a molybdenum mesh. Put 500g of sintered magnets, 5g of auxiliary diffusion source (the auxiliary diffusion source is a pure Al metal ball with a diameter of 10mm), and 10g of zirconia balls. Heat the diffusion chamber by electromagnetic induction heating, heating while rotating. The circumferential speed of the diffusion furnace rotation is 0.15m / s. The heating rate of the first-stage diffusion treatment is 30°C / min. Cool to 100°C for the second-stage diffusion treatment, and the treatment time is 100min. The temperature during the diffusion treatment is as shown in Table 8.

[0162] Table 7

[0163] No. Nd Pr Dy Tb B Co Al Ti Cu Ga Zr Fe and impurity elements 10 30 0 0.5 0 0.82 0.10 0.10 0.2 0.30 0.25 0.20 Balance

[0164] Table 8

[0165]

[0166]

[0167] Figure 4 It is the EPMA diagram of the Tb element in the magnet for Sample 10-9. It can be seen that the Tb element is enriched at the grain boundaries and triple points. Figure 5 It is the concentration distribution diagram of the Tb element in the magnet. It can be seen that the concentration of the Tb element is high at the grain boundaries and low inside the grains. At a distance of 500um from the magnet surface, use EPMA to perform fixed-point analysis of the Tb element in the grain boundaries and inside the grains. The results are as shown in Table 8, where C represents the concentration of the Tb element in the grain boundaries, c represents the concentration of the Tb element in the grains, and C / c represents the ratio of the Tb element between the grain boundaries and inside the grains. The diffusion temperature affects the distribution of the Tb element in the magnet. High Br and high Hcj are obtained when the temperature of the first heating diffusion of the present invention is 400 - 600°C and the temperature of the second heating diffusion is 700 - 950°C. Additionally, as shown in Table 8, higher Hcj is obtained when the first heating diffusion temperature is 450 - 550°C and the second heating diffusion temperature is 750 - 850°C. In contrast, when either the first heating diffusion temperature or the second heating diffusion temperature is outside the scope of the present invention, higher Hcj cannot be obtained.

[0168] Above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An element diffusion method, characterized in that, The method comprises bringing an RTB-based sintered matrix into dynamic contact with an auxiliary diffusion source and a heavy rare earth element RH diffusion source to fully diffuse the matrix and obtain an RTB-based magnet; The raw material of the RTB-based sintered matrix contains Al, B and Co, wherein the mass content of Al in the raw material is greater than 0 and does not exceed 0.3%, the mass content of B in the raw material is 0.8-0.92%, and the mass content of Co in the raw material is 0.1-0.5%; The mass content of the heavy rare earth element RH in the heavy rare earth element RH diffusion source is not less than 60%, and the heavy rare earth element RH is selected from at least one of Dy and Tb; The auxiliary diffusion source contains an Al element with a mass fraction of not less than 60%; The diffusion process includes: a first heating diffusion, a first cooling, a second heating diffusion, and a second cooling; The temperature of the first heating diffusion is 400-600° C., and the time of the first heating diffusion is 1-5 hours; The first cooling temperature is 100-300°C and the treatment time is 30min-120min; The temperature of the second heating diffusion is 700-950°C, and the time of the second heating diffusion is 1-5h; The second cooling temperature is cooled to below 50°C; The concentration of the Al element in the grain boundary is recorded as A, the concentration of the Al element in the grain is recorded as a, and the value range of A / a is 1.5~4; wherein the concentration is the concentration value at 500±10μm away from the surface of the RTB magnet; The concentration of the RH element in the grain boundary is recorded as C, the concentration of the RH element in the grain is recorded as c, and the value range of C / c is 3~8; wherein, the concentration is the concentration value at 500±10μm away from the surface of the RTB magnet.

2. The element diffusion method according to claim 1, characterized in that, The diffusion process is carried out in a diffusion chamber; The dynamic contact is achieved by dispersing and fixing the heavy rare earth element RH diffusion source on the inner wall of the diffusion chamber, placing the auxiliary diffusion source and the RTB-based sintered substrate in the cavity of the diffusion chamber, and as the diffusion chamber rotates, vibrates, and flips as a whole, the RTB-based sintered substrate, the auxiliary diffusion source, and the heavy rare earth element RH diffusion source are in dynamic contact.

3. The element diffusion method according to claim 2, characterized in that, The diffusion chamber includes a diffusion chamber body and a diffusion chamber cavity. A fixing position of a heavy rare earth element RH diffusion source is arranged on the inner wall of the diffusion chamber cavity, so that the heavy rare earth element RH diffusion source is distributed and fixed on the inner wall.

4. The element diffusion method according to claim 2, characterized in that, A stirring blade is also provided in the diffusion chamber; And / or, the diffusion chamber further comprises a mechanical shaft, and the mechanical shaft drives the diffusion chamber to rotate; And / or, the diffusion chamber is further provided with a ventilation and exhaust device so as to maintain a vacuum or an atmosphere containing an inert gas in the diffusion chamber; And / or, a heating device is provided on the periphery of the diffusion chamber.

5. The element diffusion method according to claim 1, characterized in that The heavy rare earth element RH diffusion source further contains one, two or more of Fe, B, Ti and Zr elements; And / or, the auxiliary diffusion source further contains one, two or more elements selected from the group consisting of Pr, Nd, La, Ce, Y and Sm.

6. The element diffusion method according to claim 1, characterized in that The heavy rare earth element RH diffusion source is Tb 80 Fe 20 、Tb 80 Fe 10 B 10 、Tb 80 Fe 10 Ti 10 or Tb 80 Fe 10 Zr 10 ; And / or, the auxiliary diffusion source is Al 100 、Al 90 Pr 10 、Al 80 Pr 20 、Al 70 Pr 30 、Al 60 Pr 40 、Al 90 Nd 10 or Al 90 Ce 10 .

7. The element diffusion method according to claim 1, wherein The heavy rare earth element RH diffusion source is block-shaped, and / or the auxiliary diffusion source is spherical.

8. The element diffusion method according to claim 1, characterized in that, The raw material composition of the R-T-B series sintered matrix includes: RL elements: one, two or more elements among Nd, Pr, La and Ce, with a mass content of 26-33%; RH elements: Dy and / or Tb, with a mass content of 0-1%; B element, with a mass content of 0.8-0.92%; One, two or three of Zr, Ti and Nb elements, with a mass content of 0-1.0%; Co element, with a mass content of 0.1-0.5%; Cu element, with a mass content of 0-1.0%; Al element, with a mass content of 0-0.3%.

9. The element diffusion method according to claim 1, characterized in that, The raw material composition of the R-T-B series sintered matrix further includes Fe and inevitable impurity elements.

10. The element diffusion method according to claim 1, characterized in that, The raw material composition of the R-T-B series sintered matrix includes: Nd 29-30%, Dy 0.5%, B 0.8-0.99%, Co 0.1-0.5%, Al 0-0.3%, Ti 0.2%, Cu 0.05-0.3%, Ga 0.25%, Zr 0.2%, and the rest are Fe and impurity elements.

11. A method for preparing an R-T-B-based magnet, characterized in that, The preparation method includes the following steps: using an auxiliary diffusion source and a heavy rare earth element RH diffusion source to perform diffusion treatment on the R-T-B series sintered matrix to obtain the R-T-B series magnet; The diffusion treatment is carried out by using the element diffusion method described in any one of claims 1 to 10.

12. The preparation method according to claim 11, characterized in that, The preparation method of the R-T-B series sintered matrix: (a) Melting process: The raw materials of the above R-T-B series sintered matrix are melted, cast and cooled to form alloy sheets; (b) Powder making process: The alloy sheets are crushed into alloy powders; (c) Compression molding process: The alloy powders are pressed into shape under the action of a magnetic field to obtain a green body; (d) Sintering process: The green body is subjected to high-temperature sintering treatment to obtain the R-T-B series sintered matrix.

13. The preparation method according to claim 11 or 12, characterized in that, The R-T-B series magnet contains Al element, and the concentration of the Al element in the grain boundary is greater than its concentration in the grain; The Al element is enriched at the grain boundaries and triple points of the R-T-B series magnet, and the Al element shows a gradient distribution from the surface to the center of the R-T-B series magnet.

14. The preparation method according to claim 13, characterized in that, The mass content of Al in the R-T-B series magnet is 0.5-2.5%.

15. The preparation method according to claim 11, wherein In the R-T-B series magnet, the concentration of the heavy rare earth element RH in the grain boundary is greater than its concentration in the grain; the RH element shows a gradient distribution from the surface to the center of the R-T-B series magnet.

16. The preparation method according to claim 11, wherein The Hcj of the R-T-B series magnet is not less than 1800.

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