Aluminum-containing metal foil for grain boundary diffusion, neodymium-iron-boron diffusion magnet, and method of making

Abstract

This invention discloses an aluminum-containing metal foil for grain boundary diffusion, a neodymium iron boron (NdFeB) diffusion magnet, and a preparation method thereof. The aluminum-containing metal foil for grain boundary diffusion of this invention is made by depositing a rare-earth alloy thin film on the surface of an aluminum foil or an aluminum-silicon alloy foil; the rare-earth element in the rare-earth alloy thin film is selected from at least one of Tb and Pr; the alloying element in the rare-earth alloy thin film is selected from at least one of Cu, Mg, Fe, and Sn; the atomic percentage content of the rare-earth element in the rare-earth alloy thin film is 20–55 at%; the mass ratio of aluminum to silicon in the aluminum-silicon alloy foil is (75–98 wt%):(2–25 wt%). The aluminum-containing metal foil of this invention can improve the utilization efficiency of heavy rare earth elements, reduce the diffusion temperature, and shorten the diffusion time. The NdFeB diffusion magnet obtained by the preparation method of this invention significantly improves the coercivity of the magnet while reducing the decrease in remanence.

Description

Technical Field

[0001] This invention relates to an aluminum-containing metal foil for grain boundary diffusion, a neodymium iron boron diffusion magnet, and a method for its preparation. Background Technology

[0002] Neodymium iron boron (Nd-Fe-B) magnets possess excellent magnetic properties and have become a key functional material for the development of high-precision industries. However, the magnetic properties of currently mass-produced Nd-Fe-B magnets are unsatisfactory and cannot meet the requirements of numerous high-temperature service scenarios. Therefore, improving the magnetic properties of Nd-Fe-B magnets to suppress high-temperature thermal demagnetization has become a critical issue that urgently needs to be addressed. To solve this problem, those skilled in the art have been continuously improving existing grain boundary diffusion technologies.

[0003] CN118507186A discloses a rare-earth amorphous alloy and its diffusion process for grain boundary diffusion in iron-based rare-earth permanent magnets. The rare-earth amorphous alloy film has a continuous and uniform amorphous structure, a resistivity between 150 and 285 mΩcm, a glass transition temperature less than 650℃, and contains no organic matter. Furthermore, the rare-earth amorphous alloy contains rare-earth elements, which may be a single light rare-earth element, a single heavy rare-earth element, or a combination of both. This film is directly deposited onto the magnet surface, resulting in a small deposition amount per pass. It requires a fixture for fixation, and the magnet specifications affect the deposition efficiency and target utilization rate, hindering rapid fabrication and making it unsuitable for mass production.

[0004] CN113299476A discloses a method for preparing a large-size NdFeB diffused magnet. This method first forms a heavy rare earth metal layer on the surface of a metal foil to obtain a modified metal foil; then, N pieces of NdFeB magnets to be diffused and sintered are combined with N-1 pieces of the modified metal foil to obtain an assembly; finally, the assembly is heat-treated to obtain a large-size NdFeB diffused magnet. The main purpose of this method is to simultaneously achieve diffusion and bonding in a single heat treatment process, thereby obtaining a large-size diffused magnet. In contrast, other methods rely on depositing only heavy rare earth metals such as dysprosium or terbium on the surface of aluminum or copper foil, which is costly and produces unsatisfactory diffusion results.

[0005] CN116313468A discloses a diffusion method for large-size NdFeB magnets. A composite diffusion source is obtained by sputtering a heavy rare earth layer onto the surface of an ultrathin aluminum foil. This composite diffusion source is then coated onto the surface of a corresponding NdFeB magnet. The NdFeB magnet coated with the composite diffusion source undergoes diffusion heat treatment to obtain a large-size, high-performance NdFeB magnet. As can be seen from the embodiments in this patent document, the diffusion source in this method is also simply the deposition of heavy rare earth metals dysprosium or terbium on the aluminum foil surface, which is also costly and results in unsatisfactory diffusion effects. Summary of the Invention

[0006] In view of this, one object of the present invention is to provide an aluminum-containing metal foil for grain boundary diffusion, which can solve the problems of low efficiency, high cost, and single composition in the preparation of magnet grain boundary diffusion sources, realize gravity-assisted diffusion and magnet selective diffusion, and improve the utilization rate of heavy rare earth elements in grain boundary diffusion. Another object of the present invention is to provide a method for preparing the aluminum-containing metal foil for grain boundary diffusion. A further object of the present invention is to provide a method for preparing a neodymium iron boron (NdFeB) diffusion magnet. Yet another object of the present invention is to provide a NdFeB diffusion magnet.

[0007] The present invention achieves the above objectives using the following technical solutions.

[0008] On one hand, the present invention provides an aluminum-containing metal foil for grain boundary diffusion, wherein the aluminum-containing metal foil is made by depositing a rare earth alloy film on the surface of an aluminum foil or an aluminum-silicon alloy foil;

[0009] The rare earth element in the rare earth alloy film is selected from at least one of Tb and Pr; the alloying element in the rare earth alloy film is selected from at least one of Cu, Mg, Fe, and Sn; the atomic percentage content of the rare earth element in the rare earth alloy film is 20-55 at%.

[0010] The mass ratio of aluminum to silicon in the aluminum-silicon alloy foil is (75-98 wt%):(2-25 wt%).

[0011] According to the aluminum-containing metal foil for grain boundary diffusion of the present invention, preferably, the rare earth element in the rare earth alloy film is Tb or a combination of Tb and Pr.

[0012] According to the aluminum-containing metal foil for grain boundary diffusion of the present invention, preferably, the aluminum foil or aluminum-silicon alloy foil has a thickness of 3 to 12 μm and a surface roughness of 0.5 to 3 μm.

[0013] On the other hand, the present invention also provides a method for preparing the above-mentioned aluminum-containing metal foil for grain boundary diffusion, comprising the following steps:

[0014] 1) Select an aluminum foil or aluminum-silicon alloy foil with a thickness D0 of 3 to 12 μm as the coating substrate, and deposit rare earth alloy elements onto at least one surface of the aluminum foil or aluminum-silicon alloy foil, wherein the thickness D1 of the rare earth alloy film formed by single-sided deposition of rare earth alloy elements is 2 to 7 times that of D0, and obtain the coated aluminum foil or aluminum-silicon alloy foil.

[0015] 2) Heat-treat the coated aluminum foil or aluminum-silicon alloy foil obtained in step 1) to obtain an aluminum-containing metal foil for grain boundary diffusion.

[0016] According to the preparation method of the present invention, preferably, in step 2), the temperature of the heat treatment is 200-500°C.

[0017] Furthermore, the present invention also provides a method for preparing a neodymium iron boron diffused magnet, comprising the following steps:

[0018] A) At least one layer of the aluminum-containing metal foil used for grain boundary diffusion described above is bonded to the neodymium iron boron magnet to be diffused to obtain the sample to be diffused at the grain boundary;

[0019] B) Perform vacuum heat treatment on the sample to be diffused at the grain boundary as described in step A) to obtain a neodymium iron boron diffusion magnet.

[0020] According to the method for preparing the neodymium iron boron diffused magnet of the present invention, preferably, the vacuum heat treatment step includes:

[0021] S1. Place the sample to be diffused at the grain boundary in a vacuum heat treatment furnace and evacuate it. Then heat it to the first temperature and perform heat treatment for 30 to 150 minutes.

[0022] S2. After step S1 is completed, continue to heat to the second temperature and perform heat treatment for 240-540 minutes, then cool to room temperature.

[0023] After steps S3 and S2 are completed, continue to evacuate the vacuum, then raise the temperature to the third temperature and perform heat treatment for 60-150 minutes. After cooling, neodymium iron boron diffused magnets are obtained.

[0024] According to the preparation method of the present invention, preferably, the first temperature is 550-800°C, the second temperature is 850-950°C, and the third temperature is 400-550°C.

[0025] According to the preparation method of the present invention, preferably, the combination of the aluminum-containing metal foil for grain boundary diffusion and the NdFeB magnet to be diffused is as follows:

[0026] A single layer of aluminum-containing metal foil for grain boundary diffusion is bonded to at least one surface of the NdFeB magnet to be diffused; or,

[0027] At least two layers of aluminum-containing metal foil for grain boundary diffusion are stacked together, and one side of the foil is attached to at least one surface of the neodymium iron boron magnet to be diffused.

[0028] In another aspect, the present invention also provides a neodymium iron boron diffused magnet prepared by the above-described preparation method, wherein, compared with the neodymium iron boron magnet to be diffused, the remanence of the neodymium iron boron diffused magnet decreases by 0.1% to 0.8% and the coercivity increases by 95% to 115%.

[0029] This invention uses aluminum foil or aluminum-silicon alloy foil as a substrate for coating, enabling the low-cost acquisition of high-quality aluminum-containing metal foil for grain boundary diffusion. This aluminum-containing metal foil can improve the utilization efficiency of heavy rare earth elements, reduce the diffusion temperature, and shorten the diffusion time. This invention uses a magnet to cover the aluminum-containing metal foil as a diffusion source, facilitating selective diffusion. The neodymium iron boron diffusion magnet obtained by the preparation method of this invention significantly improves the coercivity of the magnet while reducing the decrease in remanence. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] The "remanence" mentioned in this invention refers to the ability of a magnet to maintain a certain magnetization intensity in the original direction of the external magnetic field after the magnet has been magnetized to saturation and the external magnetic field has been removed. It is usually denoted as B. r The unit is Tesla (T) or Gauss (G).

[0032] The "intrinsic coercivity" mentioned in this invention refers to the strength of the reverse magnetic field applied when the vector sum of the microscopic magnetic dipole moments inside the magnet drops to zero, usually denoted as H. cj The unit is ozt (Oe) or ampere per meter (A / m).

[0033] The "maximum magnetic energy product" mentioned in this invention refers to the maximum value of the product of magnetic flux density (B) and corresponding magnetic field strength (H) on the demagnetization curve, usually denoted as (BH). max The unit is megagauss-oersted (GOe).

[0034] The "vacuum degree" mentioned in this invention refers to the absolute vacuum degree; the smaller the value, the higher the vacuum degree.

[0035] <Aluminum-containing metal foil for grain boundary diffusion>

[0036] The aluminum-containing metal foil of the present invention is made by depositing a rare earth alloy film on the surface of an aluminum foil or an aluminum-silicon alloy foil.

[0037] According to one embodiment of the present invention, the rare earth element in the rare earth alloy film is selected from at least one of Tb (terbium) and Pr (praseodymium); the alloying element in the rare earth alloy film is selected from at least one of Cu (copper), Mg (magnesium), Fe (iron), and Sn (tin); the atomic percentage content of the rare earth element in the rare earth alloy film can be 20-55 at%, preferably 22-53 at%, and more preferably 25-50 at%.

[0038] According to one embodiment of the present invention, the rare earth element in the rare earth alloy film is preferably Tb or a combination of Tb and Pr. When the rare earth element is a combination of Tb and Pr, the atomic ratio of Tb to Pr can be any value, and is not particularly limited here. Preferably, it is 1:5 to 5:1.

[0039] In this invention, when there are two or more alloying elements, the atomic ratio between the alloying elements can be any value, and no particular limitation is made here.

[0040] By controlling the elemental ratio of the rare earth alloy film within the above range, it is possible to ensure that the rare earth alloy elements and the substrate metal foil undergo better in-situ alloying reaction during high-temperature vacuum heating, which is conducive to forming a high-activity, high-purity, low-melting-point high-quality rare earth alloy diffusion source; and can improve the magnetic properties of neodymium iron boron magnets during grain boundary diffusion.

[0041] According to one embodiment of the present invention, the mass ratio of aluminum to silicon in the aluminum-silicon alloy foil can be (75-98 wt%):(2-25 wt%); preferably (85-98 wt%):(2-15 wt%); more preferably (90-95 wt%):(5-10 wt%). A reasonable mass ratio of aluminum to silicon is more conducive to obtaining a high-quality silicon-containing rare earth alloy diffusion source, ensuring the improvement of the magnetic properties of the neodymium iron boron magnet.

[0042] Rare earth alloy thin films can be single-layer or multi-layer films. They can be simultaneously fabricated alloy films or films in which rare earth metals (elemental rare earth elements or combinations of two or more rare earth elements) and alloying elements are deposited and stacked separately. Aluminum foil or aluminum-silicon alloy foil serves as a flexible support material, enabling secondary processing such as cutting, stacking, winding, and welding. This facilitates the combined design of diffusion components for different substrate magnets; simultaneously, it improves coating efficiency and target utilization, enabling the mass production of diffusion alloys.

[0043] According to one embodiment of the present invention, the thickness of the aluminum foil or aluminum-silicon alloy foil can be 3–12 μm; preferably 5–12 μm; more preferably 5–8 μm. The surface roughness can be 0.5–3 μm; preferably 1–3 μm; more preferably 1–2 μm.

[0044] Reasonable metal foil thickness and roughness can ensure good adhesion between the metal foil and the rare earth alloy film, which is conducive to the stable deposition of the rare earth alloy film and prevents the rare earth alloy film from falling off.

[0045] <Preparation method of aluminum-containing metal foil for grain boundary diffusion>

[0046] The above-mentioned method for preparing aluminum-containing metal foil includes a coating step and a heat treatment step. These are described in detail below.

[0047] Coating steps

[0048] Aluminum foil or aluminum-silicon alloy foil is selected as the coating substrate, and rare earth alloy elements are deposited onto at least one surface of the aluminum foil or aluminum-silicon alloy foil to obtain the coated aluminum foil or aluminum-silicon alloy foil.

[0049] According to one embodiment of the present invention, the thickness of the aluminum foil or aluminum-silicon alloy foil is D0. D0 can be 3 to 12 μm; preferably 5 to 12 μm; more preferably 5 to 8 μm.

[0050] According to one embodiment of the present invention, the thickness of the single-sided deposited rare earth alloy film is D1. D1 can be 2 to 7 times D0; preferably 2 to 5 times; more preferably 3 to 5 times.

[0051] The coating is preferably deposited using magnetron sputtering technology. The sputtering power of the rare earth target can be 5-10 kW, preferably 6-9 kW, and more preferably 6-7 kW. The sputtering power of the alloy target can be 0.5-3 kW, preferably 0.8-2.5 kW, and more preferably 1-2 kW.

[0052] In this invention, the purity of the element or alloy used is at least industrially pure (99.9 wt%).

[0053] Heat treatment steps

[0054] The coated aluminum foil or aluminum-silicon alloy foil is heat-treated to obtain an aluminum-containing metal foil for grain boundary diffusion.

[0055] According to one embodiment of the present invention, the heat treatment may be vacuum heat treatment. The vacuum level may be 1 to 9 Pa; preferably 2 to 8 Pa; more preferably 3 to 6 Pa.

[0056] According to one embodiment of the present invention, the heat treatment temperature can be 200-500°C; preferably 250-450°C; more preferably 300-450°C.

[0057] According to one embodiment of the present invention, the heat treatment time can be 10 to 150 min; preferably 30 to 150 min; more preferably 30 to 130 min.

[0058] Reasonable heat treatment conditions help eliminate foil warping caused by stress after coating, preventing the foil from failing to adhere tightly to the magnet surface. Furthermore, reasonable heat treatment conditions also ensure better in-situ alloying reactions between rare earth alloying elements and the base metal foil, facilitating the formation of a high-activity, high-purity, low-melting-point high-quality rare earth alloy diffusion source.

[0059] <Preparation Method of Neodymium Iron Boron Diffused Magnets>

[0060] The preparation method of neodymium iron boron diffusion magnets includes the steps of preparing the sample to be diffused at grain boundaries and vacuum heat treatment. These are described in detail below.

[0061] Steps for preparing samples for grain boundary diffusion

[0062] At least one layer of the aluminum-containing metal foil used for grain boundary diffusion described above is bonded to the neodymium iron boron magnet to be diffused to obtain the sample to be diffused at the grain boundary.

[0063] In this invention, there are various combinations of aluminum-containing metal foil for grain boundary diffusion and neodymium iron boron magnet to be diffused. For example, only one layer of aluminum-containing metal foil for grain boundary diffusion as described above is bonded to at least one surface of the neodymium iron boron magnet to be diffused. Alternatively, at least two or more layers of aluminum-containing metal foil for grain boundary diffusion can be stacked and one side of the foil can be bonded to at least one surface of the neodymium iron boron magnet to be diffused.

[0064] According to one embodiment of the present invention, the combination of the aluminum-containing metal foil used for grain boundary diffusion and the NdFeB magnet to be diffused can be as follows:

[0065] A single layer of aluminum-containing metal foil for grain boundary diffusion is bonded to at least one surface of the NdFeB magnet to be diffused. Preferably, the aluminum-containing metal foil for grain boundary diffusion is bonded to the larger surface area of ​​the NdFeB magnet to be diffused.

[0066] According to another embodiment of the present invention, the combination of the aluminum-containing metal foil used for grain boundary diffusion and the neodymium iron boron magnet to be diffused can be as follows:

[0067] At least two layers of aluminum-containing metal foil for grain boundary diffusion are stacked together, and one side of the foil is then bonded to at least one surface of the NdFeB magnet to be diffused. Preferably, at least two layers of aluminum-containing metal foil for grain boundary diffusion are stacked together, and one side of the foil is then bonded to the larger surface area of ​​the NdFeB magnet to be diffused.

[0068] Vacuum heat treatment steps

[0069] The sample to be diffused at the grain boundary was subjected to vacuum heat treatment to obtain a neodymium iron boron diffusion magnet.

[0070] According to one embodiment of the present invention, the vacuum heat treatment step may include:

[0071] S1. Place the sample to be diffused at the grain boundary in a vacuum heat treatment furnace and evacuate it. Then heat it to the first temperature and perform the first heat treatment.

[0072] S2. After step S1 is completed, continue to heat to the second temperature and perform the second heat treatment, then cool to room temperature;

[0073] After step S3 and step S1 are completed, vacuuming continues, then the temperature is raised to the third temperature and a third heat treatment is performed. After cooling, a neodymium iron boron diffused magnet is obtained.

[0074] In this invention, the vacuum degree in step S1 can be 1 to 9 Pa; preferably 2 to 8 Pa; more preferably 3 to 6 Pa.

[0075] The vacuum level in step S3 can be 1 to 30 Pa; preferably 5 to 25 Pa; more preferably 5 to 20 Pa.

[0076] Heating begins when the vacuum level is 1–9 Pa. The temperature is increased from room temperature (25°C) to a first temperature at a heating rate of 2–8°C / min, preferably 3–7°C / min, more preferably 5–6°C / min. The first temperature can be 550–800°C, preferably 580–780°C, more preferably 600–750°C. The duration of the first heat treatment is 30–150 min, preferably 50–130 min, more preferably 60–120 min. Heating continues at a heating rate of 2–8°C / min, preferably 3–7°C / min, more preferably 5–6°C / min, to a second temperature. The second temperature can be 850–950°C, preferably 860–920°C, more preferably 880–920°C. The duration of the second heat treatment is 240–540 min, preferably 270–510 min, more preferably 300–480 min. Cool to room temperature at a cooling rate of 2–8 °C / min, preferably 3–7 °C / min, more preferably 5–6 °C / min. When the vacuum level is 1–30 Pa, reheating begins, with a heating rate of 2–8 °C / min, preferably 3–7 °C / min, more preferably 5–6 °C / min, to a third temperature. The third temperature can be 400–550 °C, preferably 450–540 °C, more preferably 480–540 °C. The duration of the third heat treatment can be 60–150 min, preferably 80–130 min, more preferably 90–120 min.

[0077] In this invention, the NdFeB magnet after the third heat treatment can also be cooled to room temperature to obtain a NdFeB diffused magnet. The cooling rate can be 2–8 °C / min, preferably 3–7 °C / min, and more preferably 5–6 °C / min.

[0078] The vacuum heat treatment furnace of the present invention can be any furnace body device known in the art that can realize vacuum heating, and is not particularly limited herein. For example, but not limited to, it can be a vacuum sintering furnace.

[0079] Using such heat treatment conditions is more conducive to the diffusion of aluminum-containing metal foil, which acts as a diffusion source, into the NdFeB magnet at the grain boundaries, thereby improving the magnetic properties of the NdFeB magnet and ensuring that the magnet increases its coercivity while reducing the decrease in remanence.

[0080] The heat treatment process of this invention, combined with aluminum-containing metal foil for grain boundary diffusion, can ensure a significant improvement in the magnetic properties of neodymium iron boron magnets.

[0081] The NdFeB diffusion magnet to be diffused in this invention is preferably a sintered NdFeB magnet.

[0082] According to one embodiment of the present invention, the composition of the sintered NdFeB magnet, based on the total weight of the sintered NdFeB magnet, is as follows:

[0083] Al 0.2wt%–0.6wt%, B 0.85wt%–0.95wt%, Ce 0.03wt%–12.5wt%, Co 0.2wt%–0.6wt%, Cu 0.1wt%–0.8wt%, Dy 0.001wt%–4.2wt%, Ga 0.1wt%–0.5wt%, Nd 20wt%–25wt%, Pr 6wt%–8wt%, Zr 0.1wt%–0.3wt%, balance Fe.

[0084] According to another embodiment of the present invention, the composition of the sintered NdFeB magnet, based on the total weight of the sintered NdFeB magnet, is as follows:

[0085] Al 0.35wt%–0.45wt%, B 0.9wt%–0.95wt%, Ce 0.04wt%–12.0wt%, Co 0.5wt%–0.6wt%, Cu 0.15wt%–0.75wt%, Dy 0.0012wt%–4.0wt%, Ga 0.15wt%–0.35wt%, Nd 21wt%–23wt%, Pr 6.5wt%–7.5wt%, Zr 0.15wt%–0.28wt%, balance Fe.

[0086] Neodymium iron boron diffused magnets

[0087] The neodymium iron boron diffused magnet of the present invention can be prepared by using the above-described method for preparing neodymium iron boron magnets.

[0088] Compared with the NdFeB magnet to be diffused, the NdFeB diffused magnet of the present invention has a remanence reduction of 0.1% to 0.8%, preferably 0.1% to 0.7%, more preferably 0.12% to 0.7%, and a coercivity increase of 95% to 115%, preferably 96% to 115%, more preferably 96% to 110%.

[0089] <Testing Method>

[0090] The magnetic properties of neodymium iron boron magnets were determined using a NIM-10000HC permanent magnet non-destructive testing instrument at room temperature (25℃); the test standard was GB / T 3217-2013.

[0091] The calculation of the remanence decrease is as follows: Remanence decrease / Remanence of the NdFeB magnet to be treated × 100%. Wherein, remanence decrease = Remanence of the NdFeB magnet to be treated - Remanence of the obtained NdFeB diffused magnet.

[0092] The coercivity improvement is calculated as follows: Coercivity improvement value / Coercivity of the NdFeB magnet to be treated × 100%. Wherein, coercivity improvement value = Coercivity of the obtained NdFeB diffused magnet - Coercivity of the NdFeB magnet to be treated.

[0093] <Ingredient Description>

[0094] Unless otherwise specified, all raw materials used in the following examples are commercially available products.

[0095] The NdFeB magnets used in the following examples are sintered NdFeB magnets, and their chemical composition by mass percentage (wt%) is as follows:

[0096] Al 0.4472, B 0.9500, Ce 0.0485, Co 0.56, Cu 0.1500, Dy 0.0012, Ga 0.1927, Nd22.8000, Pr 7.2000, Zr 0.17580, the balance is Fe.

[0097] Preparation Example 1

[0098] The coating substrate is a 5μm thick aluminum foil with both surfaces roughened to a surface roughness of 1.8μm. The substrate is based on the chemical composition Tb. 50 Cu 50 (That is, the atomic ratio of Tb to Cu is 50:50) Raw materials for the rare earth alloy thin film were prepared. Terbium was used as the rare earth element sputtering target, and copper was used as the alloying element sputtering target. The sputtering power of the terbium target was 6 kW, and the sputtering power of the copper target was 1 kW. Sputtering was performed on both surfaces of an aluminum foil. During sputtering, the aluminum foil moving speed was 1.5 cm / min. Sputtering was stopped when the thickness of the double-sided terbium-copper alloy thin film was 20 μm. After the film was deposited, the aluminum foil was heat-treated under a vacuum of 5 Pa at a temperature of 350 °C for 60 min. After heat treatment, a double-sided aluminum foil loaded with terbium-copper alloy was obtained.

[0099] Preparation Example 2

[0100] The coating substrate is a 5μm thick aluminum foil with both surfaces roughened to a surface roughness of 1.8μm. The substrate is based on the chemical composition Tb.50 (CuMg) 50 (That is, the ratio of Tb atoms to the sum of Cu and Mg atoms is 50:50) Raw materials for rare earth alloy thin films were prepared. Terbium was used as the rare earth element sputtering target, and copper-magnesium alloy (copper to magnesium atomic ratio of 1:1) was used as the alloying element sputtering target. The sputtering power of the terbium target was 6 kW, and the sputtering power of the copper-magnesium alloy target was 1 kW. Sputtering was performed on both surfaces of an aluminum foil. During sputtering, the aluminum foil moving speed was 1.0 cm / min. Sputtering was stopped when the thickness of the terbium-copper-magnesium alloy thin film deposited on one side reached 20 μm. After the film was deposited, the aluminum foil was heat-treated under a vacuum of 5 Pa at a temperature of 300 °C for 120 min. After heat treatment, a double-sided aluminum foil loaded with terbium-copper-magnesium alloy was obtained.

[0101] Preparation Example 3

[0102] The coating substrate is a 5μm thick aluminum foil with both surfaces roughened to a roughness of 1.8μm. The chemical composition is (Tb... 0.25 Pr 0.75 ) 50 Cu 50 (That is, the ratio of the sum of Tb and Pr atoms to the number of Cu atoms is 50:50) Raw materials for preparing rare earth alloy thin films were prepared. Terbium-praseodymium alloy (terbium to praseodymium atomic ratio of 0.25:0.75) was used as the rare earth element sputtering target, and copper was used as the alloying element sputtering target. The sputtering power of the terbium-praseodymium alloy target was 6.8 kW, and the sputtering power of the copper target was 1.2 kW. Sputtering was performed on both surfaces of an aluminum foil. During sputtering, the aluminum foil moving speed was 1.2 cm / min. Sputtering was stopped when the thickness of the terbium-praseodymium copper alloy thin film deposited on one side reached 20 μm. After the coating was completed, the aluminum foil was heat-treated under a vacuum of 5 Pa at a temperature of 450 °C for 30 min. After heat treatment, an aluminum foil with double-sided terbium-praseodymium copper alloy was obtained.

[0103] Preparation Example 4

[0104] The coating substrate is an aluminum-silicon alloy foil with a thickness of 5 μm (aluminum to silicon mass ratio of 90 wt%:10 wt%). Both surfaces of the aluminum-silicon alloy foil are roughened with a roughness of 1.2 μm. The chemical composition is (Tb) 50 (Cu 0.8 Fe 0.2 ) 50(That is, the ratio of Tb atoms to the sum of Cu and Fe atoms is 50:50) Rare earth alloy thin film raw materials were prepared. Terbium was used as the rare earth element sputtering target, and copper-iron alloy (copper to iron atomic ratio of 0.8:0.2) was used as the alloying element sputtering target. The sputtering power of the terbium target was 7 kW, and the sputtering power of the copper-iron alloy target was 1.6 kW. Sputtering was performed on one surface of an aluminum-silicon alloy foil. During sputtering, the aluminum-silicon alloy foil moved at a speed of 1.5 cm / min. Sputtering was stopped when the thickness of the terbium-copper-iron alloy thin film deposited on one side reached 20 μm. After the film was deposited, the aluminum-silicon alloy foil was heat-treated under a vacuum of 5 Pa at a temperature of 300 °C for 130 min. After heat treatment, an aluminum-silicon alloy foil with terbium-copper-iron alloy loaded on one side was obtained.

[0105] Comparative Preparation Example 1

[0106] The substrate selected for coating was a 5μm thick aluminum foil with both surfaces roughened to a surface roughness of 1.8μm. Tb was used as the raw material for the rare earth metal thin film. Terbium was used as the sputtering target. The sputtering power of the terbium target was 6kW, and sputtering was performed on both surfaces of the aluminum foil. During sputtering, the aluminum foil moving speed was 1.5cm / min, and sputtering was stopped when the double-sided terbium metal thin film thickness reached 20μm. After coating, the aluminum foil was heat-treated under a vacuum of 5Pa at a temperature of 350℃, resulting in a double-sided terbium-loaded aluminum foil.

[0107] Comparative Preparation Example 2

[0108] The substrate selected for coating was a 5 μm thick aluminum-magnesium alloy foil (aluminum to magnesium mass ratio of 90 wt%:10 wt%), with both sides of the foil having a rough surface of 1.8 μm. Tb was used as the raw material for the rare earth metal thin film. Terbium was used as the sputtering target. The terbium target sputtering power was 6 kW, and sputtering was performed on one surface of the aluminum-magnesium alloy foil. During sputtering, the aluminum-magnesium alloy foil moved at a speed of 1.5 cm / min, and sputtering was stopped when the thickness of the terbium metal thin film deposited on one side reached 20 μm. After coating, the aluminum-magnesium alloy foil was heat-treated under a vacuum of 5 Pa at a temperature of 350 °C, resulting in an aluminum-magnesium alloy foil with terbium metal loaded on one side.

[0109] Example 1

[0110] Prepare a neodymium iron boron magnet to be diffused, with a length, width, and height of 30 mm, 20 mm, and 4 mm, respectively, where the height direction is the easy magnetization axis. First, place the neodymium iron boron magnet to be diffused on an alumina crucible, with one 30×20 mm surface facing upwards. Then, completely cover the upward-facing 30×20 mm surface of the neodymium iron boron magnet with a 30×20 mm double-sided loaded terbium praseodymium copper alloy aluminum foil obtained in Preparation Example 1, completing the tray mounting.

[0111] The alumina crucible, after being loaded into a tray, was placed in a vacuum sintering furnace and evacuated. Heating began when the vacuum reached 5 Pa, with the temperature increasing from room temperature to 600 °C at a rate of 5 °C / min. This temperature was then heat-treated at 600 °C for 60 min. After heat treatment, the temperature was increased to 910 °C at a rate of 5 °C / min and heat-treated at 910 °C for 300 min. Finally, the temperature was cooled to room temperature at a rate of 5 °C / min to obtain the intermediate NdFeB magnet. Alternatively, the vacuum in the sintering furnace was adjusted to 10 Pa, and heating began when the temperature increased to 505 °C at a rate of 5 °C / min. This temperature was then heat-treated at 505 °C for 120 min. After heat treatment, the temperature was cooled to room temperature at a rate of 5 °C / min to obtain the NdFeB diffused magnet.

[0112] Example 2

[0113] Prepare a neodymium iron boron magnet to be diffused, with a length, width, and height of 10 mm, 10 mm, and 5 mm, respectively, where the height direction is the easy magnetization axis. First, place the neodymium iron boron magnet to be diffused on an alumina crucible, with one 10×10 mm surface facing upwards. Then, completely cover the 10×10 mm surface of the neodymium iron boron magnet with a 10×10 mm double-sided loaded terbium copper-magnesium alloy aluminum foil obtained in Preparation Example 2, thus completing the tray loading.

[0114] The alumina crucible, after being loaded into a tray, was placed in a vacuum sintering furnace and evacuated. Heating began when the vacuum reached 5 Pa, with the temperature increasing from room temperature to 715 °C at a rate of 5 °C / min. This temperature was then heat-treated at 715 °C for 60 min. After heat treatment, the temperature was increased to 910 °C at a rate of 5 °C / min and heat-treated at 910 °C for 325 min. Finally, the temperature was cooled to room temperature at a rate of 5 °C / min. The vacuum in the sintering furnace was then adjusted to 5 Pa, and heating began when the temperature increased to 500 °C at a rate of 5 °C / min. This temperature was then heat-treated at 500 °C for 120 min. After heat treatment, the temperature was cooled to room temperature at a rate of 5 °C / min, thus obtaining a neodymium iron boron diffused magnet.

[0115] Example 3

[0116] Prepare the NdFeB magnet to be diffused. Its length, width, and height are 30mm, 20mm, and 4mm, respectively, with the height direction aligned with the easy magnetization axis. First, place a 30×20mm aluminum foil with double-sided terbium-praseodymium copper alloy loading on an alumina crucible. Then, attach one 30×20mm surface of the NdFeB magnet to be diffused to the aluminum foil with double-sided terbium-praseodymium copper alloy loading. Next, completely cover the other 30×20mm surface of the NdFeB magnet with another 30×20mm aluminum foil with double-sided terbium-praseodymium copper alloy loading, completing the mounting process.

[0117] The alumina crucible, after being loaded into a tray, was placed in a vacuum sintering furnace and evacuated. Heating began when the vacuum reached 5 Pa. The NdFeB magnet to be diffused was heated from room temperature to 750°C at a rate of 5°C / min, and heat-treated at 750°C for 90 min. After heat treatment, the temperature was increased to 900°C at a rate of 5°C / min, and heat-treated at 900°C for 300 min. After heat treatment, the temperature was cooled to room temperature at a rate of 5°C / min. The vacuum in the sintering furnace was then adjusted to 5 Pa, and heating began. The temperature was increased to 480°C at a rate of 5°C / min, and heat-treated at 480°C for 120 min. After heat treatment, the temperature was cooled to room temperature at a rate of 5°C / min, thus obtaining the NdFeB diffused magnet.

[0118] Example 4

[0119] Prepare a neodymium iron boron magnet to be diffused, with a length, width, and height of 10 mm, 10 mm, and 5 mm, respectively, where the height direction is the easy magnetization axis. First, place the neodymium iron boron magnet to be diffused on an alumina crucible, with one 10×10 mm surface facing upwards. Then, completely cover the upward-facing 10×10 mm surface of the neodymium iron boron magnet with a 10×10 mm aluminum-silicon alloy foil with a single-sided terbium copper-iron alloy loading obtained in Preparation Example 4, thus completing the tray loading.

[0120] The alumina crucible, after being loaded into a tray, was placed in a vacuum sintering furnace and evacuated. Heating began when the vacuum reached 50 Pa, with the temperature increasing from room temperature to 650 °C at a rate of 5 °C / min. This temperature was then heat-treated at 650 °C for 120 min. After heat treatment, the temperature was increased to 880 °C at a rate of 5 °C / min and heat-treated at 880 °C for 480 min. Finally, the temperature was cooled to room temperature at a rate of 5 °C / min. The vacuum in the sintering furnace was then adjusted to 5 Pa, and heating began when the temperature increased to 510 °C at a rate of 5 °C / min. This temperature was then heat-treated at 510 °C for 90 min. After heat treatment, the temperature was cooled to room temperature at a rate of 5 °C / min, thus obtaining a neodymium iron boron diffused magnet.

[0121] Example 5

[0122] Prepare a neodymium iron boron magnet to be diffused, with a length, width, and height of 30 mm, 20 mm, and 4 mm, respectively, where the height direction is the easy magnetization axis. First, place the neodymium iron boron magnet to be diffused on an alumina crucible, with one 30×20 mm surface facing upwards. Then, stack the aluminum foil with double-sided terbium-praseodymium copper alloy obtained in Preparation Example 3 and the aluminum-silicon alloy foil with single-sided terbium-copper-iron alloy obtained in Preparation Example 4 to form an aluminum-containing metal foil group. Completely cover the 30×20 mm surface of the neodymium iron boron magnet with the aluminum-containing metal foil group of 30×20 mm in size, and complete the tray loading.

[0123] The alumina crucible, after being loaded into a tray, was placed in a vacuum sintering furnace and evacuated. Heating began when the vacuum reached 5 Pa, with the temperature increasing from room temperature to 780 °C at a rate of 5 °C / min. This temperature was then heat-treated at 780 °C for 90 min. After heat treatment, the temperature was increased to 880 °C at a rate of 5 °C / min and heat-treated at 880 °C for 420 min. Finally, the temperature was cooled to room temperature at a rate of 5 °C / min. The vacuum in the sintering furnace was then adjusted to 5 Pa, and heating began when the temperature increased to 515 °C at a rate of 5 °C / min. This temperature was then heat-treated at 515 °C for 180 min. After heat treatment, the temperature was cooled to room temperature at a rate of 5 °C / min, thus obtaining a neodymium iron boron diffused magnet.

[0124] Comparative Example 1

[0125] The neodymium iron boron magnet to be diffused has a length, width, and height of 30 mm, 20 mm, and 4 mm, respectively, with the height direction being the easy magnetization axis. First, the neodymium iron boron magnet to be diffused is placed on an alumina crucible, with one 30×20 mm surface facing upwards. Then, a 30×20 mm aluminum foil with double-sided terbium metal loading, obtained from Comparative Preparation Example 1, is used to completely cover the upward-facing 30×20 mm surface of the neodymium iron boron magnet, completing the tray mounting.

[0126] The alumina crucible, after being loaded into a tray, was placed in a vacuum sintering furnace and evacuated. Heating began when the vacuum reached 5 Pa, with the temperature increasing from room temperature to 600 °C at a rate of 5 °C / min. This temperature was then heat-treated at 600 °C for 60 min. After heat treatment, the temperature was increased to 910 °C at a rate of 5 °C / min and heat-treated at 910 °C for 300 min. Finally, the temperature was cooled to room temperature at a rate of 5 °C / min to obtain the intermediate NdFeB magnet. Alternatively, the vacuum in the sintering furnace was adjusted to 10 Pa, and heating began when the temperature increased to 505 °C at a rate of 5 °C / min. This temperature was then heat-treated at 505 °C for 120 min. After heat treatment, the temperature was cooled to room temperature at a rate of 5 °C / min to obtain the NdFeB diffused magnet.

[0127] Comparative Example 2

[0128] The neodymium iron boron magnet to be diffused has a length, width, and height of 10 mm, 10 mm, and 5 mm, respectively, with the height direction being the easy magnetization axis. First, the neodymium iron boron magnet to be diffused is placed on an alumina crucible with one 10×10 mm surface facing upwards. Then, an aluminum-magnesium alloy foil with a single-sided terbium metal loading of 10×10 mm, obtained from Comparative Preparation Example 2, is completely covered to complete the 10×10 mm surface of the neodymium iron boron magnet facing upwards, thus completing the tray mounting.

[0129] The alumina crucible, after being loaded into a tray, was placed in a vacuum sintering furnace and evacuated. Heating began when the vacuum reached 5 Pa, with the temperature increasing from room temperature to 715 °C at a rate of 5 °C / min. This temperature was then heat-treated at 715 °C for 60 min. After heat treatment, the temperature was increased to 910 °C at a rate of 5 °C / min and heat-treated at 910 °C for 325 min. Finally, the temperature was cooled to room temperature at a rate of 5 °C / min. The vacuum in the sintering furnace was then adjusted to 5 Pa, and heating began when the temperature increased to 500 °C at a rate of 5 °C / min. This temperature was then heat-treated at 500 °C for 120 min. After heat treatment, the temperature was cooled to room temperature at a rate of 5 °C / min, thus obtaining a neodymium iron boron diffused magnet.

[0130] Experimental Example 1

[0131] The magnetic properties of neodymium iron boron magnets of the same size before and after grain boundary diffusion in Examples 1-5 and Comparative Examples 1-2 were tested respectively, and the results are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] As shown in Table 1, the NdFeB diffused magnet prepared by this invention is significantly better than the comparative example in both the magnitude of remanence reduction and the magnitude of coercivity improvement.

[0136] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. An aluminum-containing metal foil for grain boundary diffusion, characterized in that, The aluminum-containing metal foil is made by depositing a rare earth alloy film on the surface of an aluminum foil or an aluminum-silicon alloy foil; The rare earth element in the rare earth alloy film is selected from at least one of Tb and Pr; the alloying element in the rare earth alloy film is selected from at least one of Cu, Mg, Fe, and Sn; the atomic percentage content of the rare earth element in the rare earth alloy film is 20-55 at%. The mass ratio of aluminum to silicon in the aluminum-silicon alloy foil is (75-98 wt%):(2-25 wt%).

2. The aluminum-containing metal foil for grain boundary diffusion according to claim 1, characterized in that, The rare earth element in the rare earth alloy film is Tb or a combination of Tb and Pr.

3. The aluminum-containing metal foil for grain boundary diffusion according to claim 1, characterized in that, The aluminum foil or aluminum-silicon alloy foil has a thickness of 3–12 μm and a surface roughness of 0.5–3 μm.

4. A method for preparing an aluminum-containing metal foil for grain boundary diffusion as described in any one of claims 1 to 3, comprising the following steps: 1) Select an aluminum foil or aluminum-silicon alloy foil with a thickness D0 of 3 to 12 μm as the coating substrate, and deposit rare earth alloy elements onto at least one surface of the aluminum foil or aluminum-silicon alloy foil, wherein the thickness D1 of the rare earth alloy film formed by single-sided deposition of rare earth alloy elements is 2 to 7 times that of D0, and obtain the coated aluminum foil or aluminum-silicon alloy foil. 2) Heat-treat the coated aluminum foil or aluminum-silicon alloy foil obtained in step 1) to obtain an aluminum-containing metal foil for grain boundary diffusion.

5. The preparation method according to claim 4, characterized in that, In step 2), the temperature of the heat treatment is 200–500°C.

6. A method for preparing a neodymium iron boron diffused magnet, comprising the following steps: A) At least one layer of aluminum-containing metal foil for grain boundary diffusion as described in any one of claims 1 to 3 is bonded to a neodymium iron boron magnet to be diffused to obtain a sample for grain boundary diffusion; B) Perform vacuum heat treatment on the sample to be diffused at the grain boundary as described in step A) to obtain a neodymium iron boron diffusion magnet.

7. The preparation method according to claim 6, characterized in that, The steps of vacuum heat treatment include: S1. Place the sample to be diffused at the grain boundary in a vacuum heat treatment furnace and evacuate it. Then heat it to the first temperature and perform heat treatment for 30 to 150 minutes. S2. After step S1 is completed, continue to heat to the second temperature and perform heat treatment for 240-540 minutes, then cool to room temperature. After steps S3 and S2 are completed, continue to evacuate the vacuum, then raise the temperature to the third temperature and perform heat treatment for 60-150 minutes. After cooling, neodymium iron boron diffused magnets are obtained.

8. The preparation method according to claim 7, characterized in that, The first temperature is 550–800℃, the second temperature is 850–950℃, and the third temperature is 400–550℃.

9. The preparation method according to any one of claims 6 to 8, characterized in that, The combination of the aluminum-containing metal foil used for grain boundary diffusion and the neodymium iron boron magnet to be diffused is as follows: A single layer of aluminum-containing metal foil for grain boundary diffusion is bonded to at least one surface of the NdFeB magnet to be diffused; or, At least two layers of aluminum-containing metal foil for grain boundary diffusion are stacked together, and one side of the foil is attached to at least one surface of the neodymium iron boron magnet to be diffused.

10. A neodymium iron boron diffused magnet prepared by the preparation method according to any one of claims 6 to 9, characterized in that, Compared with the NdFeB magnet to be diffused, the remanence of the NdFeB diffused magnet decreases by 0.1% to 0.8%; the coercivity increases by 95% to 115%.

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