Foamed metal foil for grain boundary diffusion, neodymium-iron-boron diffusion magnet, and method of manufacture

Abstract

The application discloses a kind of foamed metal foil for grain boundary diffusion, neodymium iron boron diffusion magnet and preparation method.The preparation method of the foamed metal foil for grain boundary diffusion of the application comprises the following steps:1) depositing a rare earth alloy film on the surface of a foamed metal foil sheet to obtain a coated foamed metal foil sheet;2) fold the coated foamed metal foil sheet obtained in step 1) in half, with the coated side facing in, and compress after folding to obtain a foamed metal foil for grain boundary diffusion.The foamed metal foil for grain boundary diffusion of the application enhances the adhesion of the rare earth alloy film, and when used for grain boundary diffusion, it increases the coercivity of the neodymium iron boron magnet while reducing the drop in remanence.

Description

Technical Field

[0001] This invention relates to a foamed metal foil for grain boundary diffusion, a neodymium iron boron diffusion magnet, and a method for preparing them. 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 is crucial. To address this, grain boundary diffusion technology has emerged.

[0003] Grain boundary diffusion (GBD) refers to the process of replacing Nd in the main phase with heavy rare earth (HRE) elements such as Dy and Tb to form (HRE,Nd)₂Fe with a higher magnetic anisotropy field. 14 The B phase enhances the coercivity of the magnet. Grain boundary diffusion processes create magnets with macroscopically uneven HRE distribution. High coercivity effectively resists the inherent demagnetizing field of the magnet at high temperatures. However, due to the high cost of heavy rare earth elements (HREEs), ensuring effective diffusion while reducing their usage remains a critical challenge in the field of grain boundary diffusion.

[0004] CN116190089A discloses a stepwise grain boundary diffusion method for high coercivity and high corrosion resistance sintered NdFeB magnets. This method involves sandwiching thin sheets of heavy rare earth elements or compounds containing heavy rare earth elements onto the surface of an acidified commercial N50 sintered NdFeB magnet. A first-stage vacuum heat treatment causes the heavy rare earth elements to diffuse along the grain boundaries into the magnet's interior, yielding a primary grain boundary diffusion sample. After a second pretreatment, a low-melting-point metal sheet is sandwiched onto the sample surface, followed by a second-stage vacuum heat treatment process to obtain a sintered NdFeB magnet with high coercivity and strong corrosion resistance. This method involves sandwiching heavy rare earth elements and a low-melting-point metal onto the surface of the sintered NdFeB magnet in two stages for heat treatment, primarily using heavy rare earth elements as the grain boundary diffusion source. This process is complex and not conducive to cost control. The thickness of the heavy rare earth element metal sheets, heavy rare earth element compound sheets, and low-melting-point metal sheets in this method is 1-2 mm, corresponding to 1000-2000 μm, which is far greater than the amount of material required for diffusion. This not only wastes expensive heavy rare earth resources but also severely degrades the magnet performance after diffusion, with only a small increase in coercivity. For example, the remanence of the magnet after diffusion in Example 1 decreased from 14.37 kGs to 11.99 kGs, a decrease of 16.56%; the decrease in remanence of the magnet after diffusion in Example 2 was 18.37%; the decrease in remanence of the magnet after diffusion in Example 3 was as high as 20.95%; and the decrease in remanence of the magnet after diffusion in Example 4 was 7.52%, all far exceeding the control target of 3%. The largest increase in coercivity was observed in the magnet after diffusion in Example 1, with an increase of only 39.90%. Obviously, the large consumption of heavy rare earth elements not only failed to improve the coercivity of the diffused magnet but also caused a serious decrease in remanence, resulting in poor overall magnet performance.

[0005] CN117004903A discloses a method for preparing a thin-film grain boundary diffusion source. This method prepares a heavy rare earth metal (HRE) diffusion source by electrophoretic deposition of heavy rare earth metal compounds on a flexible high-temperature resistant metal or alloy, and then performs a secondary electrophoretic deposition of a γ-Al₂O₃ microporous film on the surface of the HRE diffusion source. This method uses high-melting-point metal foil as a carrier for depositing heavy rare earth metal compounds, achieving low-cost preparation of the diffusion source. However, based on the performance of the diffusion magnet, problems such as high heavy rare earth element content and poor diffusion effect were found. Tantalum sheets do not play a role in accelerating diffusion; their high price and non-recyclable nature increase the process cost and are not conducive to the industrialization and promotion of the technology.

[0006] 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 ordinary aluminum or copper foil, which is costly and produces unsatisfactory diffusion results.

[0007] 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. However, this method also uses a diffusion source that involves depositing only heavy rare earth metals such as dysprosium or terbium on the aluminum foil surface, resulting in high cost and unsatisfactory diffusion effects. Summary of the Invention

[0008] In view of this, one object of the present invention is to provide a method for preparing a foamed metal foil for grain boundary diffusion. Using the prepared foamed metal foil for grain boundary diffusion can significantly improve the coercivity of NdFeB magnets while reducing the amount of heavy rare earth elements used, and the decrease in remanence is small. Another object of the present invention is to provide a foamed metal foil for grain boundary diffusion. A further object of the present invention is to provide a method for preparing a NdFeB diffusion magnet. Yet another object of the present invention is to provide a NdFeB diffusion magnet.

[0009] The present invention achieves the above objectives using the following technical solutions.

[0010] On one hand, the present invention provides a method for preparing a foamed metal foil for grain boundary diffusion, comprising the following steps:

[0011] 1) A rare earth alloy film is deposited on the surface of a foam metal foil to obtain a coated foam metal foil;

[0012] 2) Fold the coated foam metal foil obtained in step 1) in half so that the coated surfaces are in contact, compress it to 10-100 μm after folding, and obtain the foam metal foil for grain boundary diffusion.

[0013] The foamed metal foil has a porosity of over 90%, a pore size of 0.01–0.5 mm, and a thickness of 0.2–8 mm; the foamed metal foil is selected from at least one of Cu, Co, Ni, Fe, Ti, Zr, and Al, either as a metallic element or a metallic alloy.

[0014] The rare earth element in the rare earth alloy film is selected from at least one of light rare earth elements and heavy rare earth elements, and must contain heavy rare earth elements; the thickness of the rare earth alloy film is 2 to 50 μm.

[0015] According to the preparation method of the present invention, preferably, the light rare earth element is selected from at least one of Pr and Nd; and the heavy rare earth element is selected from at least one of Dy and Tb.

[0016] The rare earth alloy film also contains alloying elements, which are selected from at least one of Cu, Ga, Mg, Al, Mo, Fe, Zr, Nb, Sn, and Zn.

[0017] According to the preparation method of the present invention, preferably, in step 1), the method for depositing rare earth alloy thin films is selected from at least one of vacuum evaporation coating, magnetron sputtering coating, and vacuum ion plating.

[0018] According to the preparation method of the present invention, preferably, in step 2), the compression method is selected from at least one of rolling and pressing.

[0019] According to the preparation method of the present invention, preferably, the preparation method further includes the step of depositing a protective layer on the obtained foam metal foil for grain boundary diffusion; wherein the protective layer is an aluminum alloy thin film with a thickness of 0.1 to 3 μm.

[0020] On the other hand, the present invention also provides a foamed metal foil for grain boundary diffusion, wherein the foamed metal foil is prepared by the above-described preparation method.

[0021] Furthermore, the present invention also provides a method for preparing a neodymium iron boron diffused magnet, comprising the following steps:

[0022] S1) Cover at least one layer of the above-mentioned foam metal foil for grain boundary diffusion onto the surface of the NdFeB magnet to obtain the NdFeB magnet to be diffused;

[0023] S2) The NdFeB magnet to be diffused is subjected to vacuum heat treatment to obtain a NdFeB diffused magnet. According to the preparation method of the present invention, preferably, the vacuum heat treatment step includes:

[0024] a) The neodymium iron boron magnet to be diffused is heat-treated under vacuum conditions at 500–850°C, and then heat-treated again at 880–950°C. After cooling, the heat-treated neodymium iron boron magnet is obtained.

[0025] b) The heat-treated NdFeB magnets are further heat-treated under vacuum conditions at 400–660 °C to obtain NdFeB diffused magnets.

[0026] According to the preparation method of the present invention, preferably, in step S1), the neodymium iron boron magnet covered with foam metal foil is processed using a press or an ultrasonic welding machine to obtain the neodymium iron boron magnet to be diffused.

[0027] In another aspect, the present invention also provides a neodymium iron boron diffused magnet, which is prepared by the above-described preparation method.

[0028] This invention uses foamed metal foil as a substrate for coating, resulting in foamed metal foil for grain boundary diffusion that enhances the adhesion of rare earth alloy films. When used for grain boundary diffusion, it increases the coercivity of NdFeB magnets while reducing the decrease in remanence. Furthermore, this invention does not use organic solvents, which can reduce the content of harmful impurity elements in the diffusion source. Detailed Implementation

[0029] 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.

[0030] 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).

[0031] The "coercivity" mentioned in this invention refers to "intrinsic coercivity," which is 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).

[0032] The "vacuum degree" mentioned in this invention refers to the absolute vacuum degree; the smaller the value, the higher the vacuum degree.

[0033] <Preparation method of foamed metal foil for grain boundary diffusion>

[0034] The method for preparing foamed metal foil for grain boundary diffusion according to the present invention includes a coating step and a compression step. Optionally, it also includes a step of depositing a protective layer. A detailed description follows. In the prior art, ordinary metal foil is used as the carrier for the grain boundary diffusion source. When the thickness of the directly deposited rare earth alloy film is large, it easily leads to the rare earth alloy film detachment and warping, which is detrimental to the preparation of a high-quality rare earth alloy diffusion source. The present invention uses foamed metal foil as the carrier for the grain boundary diffusion source. By increasing the adhesion area, the thickness of the rare earth alloy film attached per unit surface is reduced, effectively overcoming the above-mentioned problems.

[0035] Coating steps

[0036] A rare earth alloy film is deposited on the surface of a foam metal foil to obtain a coated foam metal foil.

[0037] According to one embodiment of the present invention, the porosity of the foamed metal foil can be 90% or more; preferably 95% or more; more preferably 95-99%. The pore size of the foamed metal foil can be 0.01-0.5 mm; preferably 0.05-0.4 mm; more preferably 0.1-0.3 mm. The thickness of the foamed metal foil can be 0.2-8 mm; preferably 0.5-5 mm; more preferably 1-3 mm. The bulk density of the foamed metal foil can be 0.1-1 g / cm³. 3 Preferably, it is 0.1–0.8 g / cm³. 3 More preferably, it is 0.2–0.5 g / cm³. 3 .

[0038] According to one embodiment of the present invention, the foamed metal foil may be selected from at least one of the following metallic elements or metal alloys: Cu (copper), Co (cobalt), Ni (nickel), Fe (iron), Ti (titanium), Zr (zirconium), and Al (aluminum); preferably at least one of the following metallic elements or metal alloys: Cu, Co, Ni, Fe, and Ti; more preferably at least one of the following metallic elements or metal alloys: Cu, Ni, Fe, and Ti.

[0039] In this invention, the alloying element in the metal alloy can be selected from at least one of Cu (copper), Co (cobalt), Ga (gallium), Mg (magnesium), Al (aluminum), Mo (molybdenum), Fe (iron), Zr (zirconium), Nb (niobium), Sn (tin), Si (silicon), Zn (zinc), and V (vanadium); preferably at least one of Cu, Co, Mg, Al, Sn, Si, Zn, and V; more preferably at least one of Cu, Co, Mg, Al, Si, and V.

[0040] According to a preferred embodiment of the present invention, when the foamed metal foil is an alloy of two elements, the mass percentage content of the main metal element is at least 90 wt%, preferably at least 92 wt%.

[0041] When the foamed metal foil is an alloy of three or more elements, the mass percentage of the main metal element is at least 80 wt%, preferably at least 85 wt%.

[0042] According to one embodiment of the present invention, the foamed metal alloy can be formed from a homogeneous alloy.

[0043] According to another embodiment of the present invention, the foam metal alloy can also be formed by depositing an alloying element film on the surface of the foam metal containing the host metal element. The alloying elements adhere to the surface of the foam metal containing the host metal element, forming a non-uniformly distributed foam metal alloy.

[0044] By using properly designed foamed metal foils, the adhesion area of ​​rare earth alloys is increased, significantly reducing the amount of rare earth alloy deposited per unit area. This facilitates a reduction in the thickness of the rare earth alloy film, improves film-substrate adhesion, and prevents film detachment. The thickness of the rare earth alloy deposited on the surface of the foamed metal foil varies with the depth of the pores, achieving a gradient change in the content of grain boundary diffusion sources. This allows the rare earth alloy to gradually melt during subsequent heating, promoting stable grain boundary diffusion.

[0045] 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 light rare earth elements and heavy rare earth elements, and must contain heavy rare earth elements.

[0046] In this invention, the light rare earth element can be selected from at least one of Pr (praseodymium) and Nd (neodymium); preferably Pr or Nd. The heavy rare earth element can be selected from at least one of Dy (dysprosium) and Tb (terbium); preferably Dy or Tb.

[0047] In this invention, the rare earth alloy film also contains alloying elements, which can be selected from at least one of Cu (copper), Ga (gallium), Mg (magnesium), Al (aluminum), Mo (molybdenum), Fe (iron), Zr (zirconium), Nb (niobium), Sn (tin), and Zn (zinc); preferably at least one of Cu, Ga, Mg, Al, Mo, Fe, Sn, and Zn; more preferably at least one of Cu, Ga, Mg, Al, Mo, and Sn.

[0048] According to one embodiment of the present invention, preferably, when the foamed metal foil is elemental copper or an alloy of copper, the alloying element in the rare earth alloy film may be selected from at least one of Ga, Mg, Al, Mo, Fe, Zr, Nb, Sn, and Zn. When the foamed metal foil is elemental cobalt or nickel or an alloy of copper, the alloying element in the rare earth alloy film may be selected from at least one of Cu, Ga, Mg, Al, Mo, Zr, Nb, Sn, and Zn. When the foamed metal foil is elemental iron or an alloy of iron, the alloying element in the rare earth alloy film may be at least one of Cu, Ga, Mg, Al, Mo, Zr, Nb, Sn, and Zn. When the foamed metal foil is elemental titanium or zirconium or an alloy of titanium, the alloying element in the rare earth alloy film may be selected from at least one of Cu, Ga, Mg, Al, Mo, Sn, and Zn.

[0049] According to one embodiment of the present invention, the thickness of the rare earth alloy film can be 2 to 50 μm; preferably 10 to 50 μm; more preferably 10 to 45 μm.

[0050] In this invention, rare earth alloy films can be deposited on one or both sides of the foam metal foil; preferably, rare earth alloy films are deposited on one side of the foam metal foil.

[0051] According to one embodiment of the present invention, in step 1), the deposition can be performed using any method known in the art that enables stable adhesion of rare earth alloys to the foamed metal foil. Preferably, it is at least one of vacuum evaporation coating, magnetron sputtering coating, and vacuum ion plating; more preferably, it is magnetron sputtering coating.

[0052] According to a preferred embodiment of the present invention, the foam metal foil can be cleaned before coating to remove surface contaminants.

[0053] In this invention, C1-C5 alkyl alcohols can be used for ultrasonic cleaning of foamed metal foils. The C1-C5 alkyl alcohols can be C1-C3 alkyl alcohols; preferably C1-C3 n-alkyl alcohols; more preferably at least one of methanol and ethanol.

[0054] In this invention, the purity of the element or alloy used is at least industrial pure (99.9 wt%).

[0055] Compression steps

[0056] A coated foam metal foil is folded in half so that the coated surfaces are adhered, and then compressed to 10–100 μm to obtain a foam metal foil for grain boundary diffusion.

[0057] According to one embodiment of the present invention, in step 2), compression can be performed using any method known in the art that can reduce the thickness of the coated foam metal foil; preferably at least one of rolling and pressing; more preferably rolling.

[0058] According to one embodiment of the present invention, the material can be folded and compressed to 10–100 μm; preferably 20–80 μm; more preferably 25–70 μm.

[0059] In this invention, compression can be performed once or more than twice. The specific number of compressions is determined by compressing the coated foam metal foil to the target thickness, and is not specifically limited here.

[0060] Reasonable compression conditions are more conducive to the densification of foam metal foils used for grain boundary diffusion. In densified foam metal foils, the rare earth alloy film layers are in close contact, which increases the contact area with the substrate magnet during vacuum heat treatment, facilitating the migration of diffusing atoms. This further improves the coercivity of the magnet, with a significant increase in coercivity. Furthermore, as a grain boundary diffusion source, the densified foam metal foil creates conditions for low-temperature grain boundary diffusion and the optimal utilization of heavy rare earth elements while ensuring magnet performance. It also solves problems such as long diffusion time and high diffusion temperature while reducing the amount of heavy rare earth elements used.

[0061] According to one embodiment of the present invention, the preparation method of the present invention may further include the step of depositing a protective layer on the obtained foam metal foil for grain boundary diffusion.

[0062] In this invention, the protective layer can be an aluminum alloy film; preferably, it is one of an aluminum alloy film or a titanium-aluminum alloy film; more preferably, it is at least one of an aluminum-magnesium alloy film, an aluminum-copper alloy film, or a titanium-aluminum alloy film.

[0063] In this invention, the thickness of the protective layer can be 0.1–3 μm; preferably 0.2–2 μm; more preferably 0.5–2 μm.

[0064] A reasonable composition and thickness of the protective layer can improve the oxidation resistance of foam metal foil used for grain boundary diffusion.

[0065] <Foamed metal foil for grain boundary diffusion>

[0066] The foamed metal foil for grain boundary diffusion of the present invention is prepared by the above-described preparation method.

[0067] The foamed metal foil of the present invention for grain boundary diffusion has the capabilities of cutting, winding, and splicing. It can be cut, combined, and stacked according to the specifications and performance requirements of the diffusion magnet before being used for grain boundary diffusion of the magnet.

[0068] The foamed metal foil of this invention for grain boundary diffusion significantly increases the area of ​​metal loading by using foamed metal as a carrier for grain boundary diffusion sources, thereby increasing the total amount of rare earth alloy deposition and reducing the amount of heavy rare earth elements used. With a large deposition area, the amount of metal deposited per unit area is reduced, resulting in a thinner film and solving the problem of easy detachment caused by excessively thick films. Simultaneously, the increased deposition area increases the interface between the carrier and the rare earth alloy film, which is beneficial for mutual diffusion between the two during high-temperature heat treatment, accelerating the formation of high-quality grain boundary diffusion sources and lowering the diffusion heat treatment temperature.

[0069] <Preparation Method of Neodymium Iron Boron Diffused Magnets>

[0070] The method for preparing the neodymium iron boron diffusion magnet of the present invention includes a step of preparing the neodymium iron boron magnet to be diffused and a vacuum heat treatment step. This will be described in detail below.

[0071] Steps for preparing NdFeB magnets to be diffused

[0072] At least one layer of the aforementioned foam metal foil for grain boundary diffusion is applied to the surface of the NdFeB magnet to obtain the NdFeB magnet to be diffused.

[0073] According to one embodiment of the present invention, a NdFeB magnet covered with foam metal foil can be processed using a press or an ultrasonic welding machine to obtain a NdFeB magnet to be diffused.

[0074] According to a preferred embodiment of the invention, a press can be used to press neodymium iron boron magnets covered with foam metal foil.

[0075] In this invention, the pressing pressure can be 1–100 MPa, preferably 5–80 MPa, and more preferably 10–50 MPa. The pressing time can be 3–90 s, preferably 5–90 s, and more preferably 5–60 s. The pressing temperature can be 5–50 °C, preferably 10–45 °C, and more preferably 10–30 °C.

[0076] An ultrasonic welding machine can also be used to ultrasonically weld foam metal foil to neodymium iron boron magnets.

[0077] In this invention, the ultrasonic welding pressure can be 0.1–1.0 MPa, preferably 0.1–0.5 MPa, and more preferably 0.2–0.5 MPa. The ultrasonic welding frequency can be 5–30 kHz, preferably 10–25 kHz, and more preferably 10–20.5 kHz. The ultrasonic welding time can be 0.1–10 seconds, preferably 0.2–8 seconds, and more preferably 0.2–5 seconds. The ultrasonic energy density can be 0.1–10 J·mm². -3 Preferably, it is 0.2–8 J·mm -3 More preferably 0.5–5 J·mm -3 .

[0078] Reasonable pressing conditions or ultrasonic welding conditions can ensure that the foam metal foil used for grain boundary diffusion is more tightly bonded to the NdFeB magnet, which is more conducive to grain boundary diffusion.

[0079] The NdFeB diffusion magnet to be diffused in this invention is preferably a sintered NdFeB magnet.

[0080] The sintered NdFeB magnet of the present invention is made of Re2Fe 14 This invention relates to rare-earth sintered permanent magnets with type B compounds as the main phase. Re is selected from at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), and europium (Eu), and must contain Nd. The sintered NdFeB magnets of this invention may or may not contain heavy rare-earth elements. These heavy rare-earth elements may be selected from at least one of gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y).

[0081] According to one embodiment of the present invention, Re is selected from at least one of Pr and Nd, and must contain Nd. According to a preferred embodiment of the present invention, Re is Nd and Pr. In the present invention, B is boron.

[0082] In this invention, the sintered NdFeB magnet may also contain M, where M is selected from one or more of Cu, Co, Al, Ti, Ga, and Zr.

[0083] According to a specific embodiment of the present invention, the grade of the sintered NdFeB magnet can be either N or M.

[0084] Vacuum heat treatment steps

[0085] The neodymium iron boron magnet to be diffused is subjected to vacuum heat treatment to obtain a neodymium iron boron diffused magnet.

[0086] According to one embodiment of the present invention, the vacuum heat treatment step may include:

[0087] a) The neodymium iron boron magnet to be diffused is heat-treated under vacuum conditions at 500–850°C, and then heat-treated again at 880–950°C. After cooling, the heat-treated neodymium iron boron magnet is obtained.

[0088] b) The heat-treated NdFeB magnets are further heat-treated under vacuum conditions at 400–660 °C to obtain NdFeB diffused magnets.

[0089] In this invention, the vacuum degree in step a) can be 10. -5 ~10 -1 Pa; preferably 10 Pa; -4 ~10 -2 Pa; more preferably 10 Pa; -4 ~10 -3 Pa.

[0090] The vacuum level in step b) can be 10. -5 ~10 -1 Pa; preferably 10 Pa; -4 ~10 -2 Pa; more preferably 10 Pa; -4 ~10 -3 Pa.

[0091] In step a), when the vacuum degree is 10 -5 ~10 -1Heating begins at a temperature of Pa. The temperature is increased from room temperature (25°C) to a first temperature at a heating rate of 2–15°C / min, preferably 3–12°C / min, more preferably 5–12°C / min. The first temperature can be 500–850°C, preferably 580–850°C, more preferably 600–845°C. The duration of the first heat treatment is 100–300 min, preferably 150–270 min, more preferably 150–240 min. Heating continues at a heating rate of 2–15°C / min, preferably 3–12°C / min, more preferably 5–12°C / min, to a second temperature. The second temperature can be 880–950°C, preferably 890–930°C, more preferably 900–920°C. The duration of the second heat treatment is 240–480 min, preferably 270–450 min, more preferably 300–420 min. Cool to room temperature at a cooling rate of 2–15 °C / min, preferably 3–12 °C / min, and more preferably 5–12 °C / min.

[0092] In step b), when the vacuum degree is 10 -5 ~10 -1 Then, start heating again at 10. -5 ~10 -1 The temperature is increased to a third temperature at a rising rate. The third temperature can be 400–660°C, preferably 450–650°C, and more preferably 500–650°C. The duration of the third heat treatment can be 60–150 min, preferably 80–130 min, and more preferably 90–120 min.

[0093] In this invention, the neodymium iron boron magnet after the third heat treatment can also be rapidly cooled to room temperature.

[0094] The vacuum heat treatment of the present invention can be performed in any furnace device known in the art that can achieve vacuum heating, and is not particularly limited thereto. For example, but not limited to, it can be a vacuum sintering furnace.

[0095] Such heat treatment conditions are more conducive to the diffusion of neodymium iron boron magnets through grain boundaries by the foam metal foil, which acts as a diffusion source, thereby improving the magnetic properties of neodymium iron boron magnets.

[0096] The heat treatment process of this invention, combined with foamed metal foil for grain boundary diffusion, reduces the amount of heavy rare earth elements while ensuring a significant increase in the coercivity of neodymium iron boron magnets and a small decrease in remanence.

[0097] Neodymium iron boron diffused magnets

[0098] The neodymium iron boron diffused magnet of the present invention can be prepared by using the above-described method for preparing neodymium iron boron diffused magnets.

[0099] The NdFeB diffused magnet of the present invention increases the coercivity by at least 50% compared with that before diffusion, preferably by at least 55%, and more preferably by at least 59%.

[0100] The neodymium iron boron diffused magnet of the present invention exhibits a remanence reduction of up to 0.88% compared to before diffusion, preferably up to 0.85%; more preferably up to 0.8%.

[0101] <Testing Method>

[0102] 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.

[0103] The increase in coercivity is calculated as follows: (coercivity of the prepared rare earth iron-based permanent magnet material - coercivity of the rare earth iron-based magnet to be treated) / coercivity of the rare earth iron-based magnet to be treated × 100%.

[0104] The calculation of the decrease in remanence is as follows: (remanence of the rare earth iron-based magnet to be treated - remanence of the prepared rare earth iron-based permanent magnet material) / remanence of the rare earth iron-based magnet to be treated × 100%.

[0105] <Ingredient Description>

[0106] Unless otherwise specified, all raw materials used in the following examples are commercially available products.

[0107] The chemical composition of the sintered NdFeB magnet of grade N50 is as follows (wt%): PrNd 0.3wt%, B 0.94wt%, Al 0.52wt%, Cu 0.15wt%, Zr 0.18wt%, Ga 0.25wt%, Fe balance.

[0108] The chemical composition of the sintered NdFeB magnet of grade N38 is as follows (wt%): PrNd 18.2wt%, Ce 13wt%, B 0.91wt%, Al 0.3wt%, Cu 0.2wt%, Co 0.2wt%, Ti 0.25wt%, Fe balance.

[0109] Example 1

[0110] The selected copper foil foam has the following main technical parameters: pore size of 0.1 mm, porosity of 95%, and bulk density of 0.45 g / cm³. 3 The thickness is 2.5 mm. The foamed copper foil is ultrasonically cleaned with anhydrous ethanol and then vacuum dried to obtain a clean and uncontaminated foamed copper foil.

[0111] A TbGaAl alloy thin film was deposited on one surface of a dried copper foam foil using magnetron sputtering to obtain a coated copper foam foil. Specifically, a DC sputtering mode was used with a target sputtering power of 185W. The target material was a TbGaAl alloy with the following composition: Tb 65.8wt%, Ga 26.4wt%, and Al 7.8wt%. The thickness of the deposited TbGaAl alloy thin film was 32.4μm. After coating, the coated copper foam foil was folded in half so that the coated surfaces were in contact. The folded coated copper foam foil was then compressed using a roller press to a thickness of 61.8μm to obtain a copper foam foil for grain boundary diffusion.

[0112] A sintered NdFeB magnet of grade N50 was selected as the initial magnet, with dimensions of 20 mm in length and width, and a thickness of 6 mm. Two 20 mm × 20 mm pieces of copper foam foil, used for grain boundary diffusion, were applied to the top and bottom 20 mm × 20 mm surfaces of the sintered NdFeB magnet. The foil was then ultrasonically welded for 3 seconds to ensure a tight bond between the copper foam foil and the sintered NdFeB magnet, thus obtaining the NdFeB magnet to be diffused. The ultrasonic welding pressure was 0.3 MPa, the frequency was 15 kHz, and the ultrasonic energy density was 2 J·mm². -3 .

[0113] The neodymium iron boron magnet to be diffused is placed in a vacuum sintering furnace, and the vacuum degree of the vacuum sintering furnace is 10. -3 Heating began at a certain temperature (Pa), with the temperature increased from room temperature to 780℃ at a rate of 12℃ / min, and heat-treated at 780℃ for 180 min. Heating continued, increasing the temperature to 915℃ at a rate of 12℃ / min, and heat-treated at 915℃ for 350 min. After heat treatment, the temperature was cooled to room temperature at a rate of 12℃ / min. The vacuum degree of the vacuum sintering furnace was 10... -3 Heating was restarted at Pa, and the temperature was increased from room temperature to 515℃ at a rate of 12℃ / min. The temperature was then heat-treated at 515℃ for 120 min. After the heat treatment, the temperature was rapidly cooled to room temperature to obtain the neodymium iron boron diffused magnet.

[0114] The magnetic properties of the neodymium iron boron diffused magnets are shown in Table 1. Compared with the initial magnet, the coercivity H of the neodymium iron boron diffused magnets prepared in Example 1 is significantly higher. cj The coercivity increased by 12.92 kOe to 25.45 kOe, representing a 103% increase, while the remanence decreased by only 0.56%. The grade of the neodymium iron boron diffused magnet was upgraded from the initial N50 grade to the N50UH grade.

[0115] Table 1

[0116]

[0117] Comparative Example 1

[0118] The difference between Comparative Example 1 and Example 1 is as follows: the copper foil used was a 12μm electrolytic copper foil, the thickness of the TbGaAl alloy film deposited by single-sided sputtering was 32.4μm, and then the rare earth alloy was folded facet as a diffusion source for diffusion. Everything else was exactly the same.

[0119] The magnetic properties of the neodymium iron boron diffused magnets are shown in Table 2.

[0120] Table 2

[0121]

[0122] Comparative Example 1 presents significant challenges. Specifically, after fabricating a 32.4 μm thick rare-earth alloy film on a 12 μm thick copper foil, the film exhibits severe warping, making it difficult to adhere tightly to the magnet surface. Furthermore, the inability to rapidly form the rare-earth alloy during diffusion leads to substantial compositional deviations as the diffusion alloy changes over time, resulting in significant differential diffusion. Finally, the high stress on the copper foil surface makes it prone to tearing and breakage, causing some areas of the rare-earth alloy diffusion source to detach, failing to achieve uniform coverage of the diffusion source on the magnet surface. Therefore, these factors contribute to the poor performance of the diffusion magnet, particularly the difficulty in using planar dense foils for thick-film diffusion. Three-dimensional foamed metals, however, can achieve high-quality film loading.

[0123] Example 2

[0124] The selected nickel foam foil has the following main technical parameters: pore size of 0.2 mm, porosity of 98%, and bulk density of 0.4 g / cm³. 3 The thickness was 2 mm. The foamed elemental nickel foil was ultrasonically cleaned with anhydrous ethanol and then vacuum dried to obtain a clean and uncontaminated foamed elemental nickel foil. A 3.2 μm thick copper film was deposited on both surfaces of the dried foamed elemental nickel foil using chemical copper plating technology to obtain a foamed nickel-copper alloy foil.

[0125] A TbGaMgMo alloy thin film was deposited on one surface of a foamed nickel-copper alloy foil using magnetron sputtering to obtain a coated foamed nickel-copper alloy foil. Specifically, a DC sputtering mode was used with a target sputtering power of 100W. The target material was a TbGaMgMo alloy with the following composition: Tb 60.5wt%, Ga 29.4wt%, Mg 3.8wt%, and Mo 6.3wt%. The thickness of the deposited TbGaMgMo alloy thin film was 25.8μm. After coating, the coated foamed nickel-copper alloy foil was folded facet to make the coated surfaces contact each other. The folded coated foamed nickel-copper alloy foil was then compressed using a roll press to a thickness of 55μm to obtain a foamed nickel-copper alloy foil for grain boundary diffusion.

[0126] A sintered NdFeB magnet of grade N50 was selected as the initial magnet, with a length, width, and thickness of 10 mm and 5.5 mm respectively. A 10 mm × 10 mm foamed nickel-copper alloy foil for grain boundary diffusion was applied to the top and bottom 10 mm × 10 mm surfaces of the sintered NdFeB magnet. The magnet was then pressed at 50 MPa for 10 seconds at room temperature to ensure a tight bond between the foamed nickel-copper alloy foil and the sintered NdFeB magnet, thus obtaining the NdFeB magnet to be diffused.

[0127] The neodymium iron boron magnet to be diffused is placed in a vacuum sintering furnace, and the vacuum degree of the vacuum sintering furnace is 10. -3 Heating begins at a certain temperature (Pa), increasing the temperature from room temperature to 800℃ at a rate of 10℃ / min, and heat-treating at 800℃ for 240 min. Heating continues, increasing the temperature to 910℃ at a rate of 10℃ / min, and heat-treating at 910℃ for 300 min. After heat treatment, cooling to room temperature is performed at a rate of 10℃ / min. The vacuum degree of the vacuum sintering furnace is 10... -3 Heating was restarted at Pa, and the temperature was increased from room temperature to 510℃ at a rate of 10℃ / min. The temperature was then heat-treated at 510℃ for 120 min. After the heat treatment, the temperature was rapidly cooled to room temperature to obtain the neodymium iron boron diffused magnet.

[0128] The magnetic properties of the neodymium iron boron diffused magnets are shown in Table 3. Compared with the initial magnet, the coercivity H of the neodymium iron boron diffused magnets prepared in Example 2 is significantly higher. cj The coercivity increased by 12.91 kOe to 25.44 kOe, representing a 103% increase, while the remanence decreased by only 0.77%. The grade of the neodymium iron boron diffused magnet was upgraded from the initial N50 grade to the N50UH grade.

[0129] Table 3

[0130]

[0131] Example 3

[0132] A foamed copper-cobalt alloy foil was selected, in which copper accounted for 94 wt% and cobalt accounted for 6 wt%. The main technical parameters of this foamed copper-cobalt alloy foil are as follows: pore size of 0.1 mm, porosity of 95.5%, and bulk density of 0.4014 g / cm³. 3 The thickness is 1.5 mm. The foamed copper-cobalt alloy foil is ultrasonically cleaned with anhydrous ethanol and then vacuum dried to obtain a clean and uncontaminated foamed copper-cobalt alloy foil.

[0133] A PrTbMg alloy film was deposited on one surface of a dried copper-cobalt foam foil using magnetron sputtering to obtain a coated copper-cobalt foam foil. Specifically, a DC sputtering mode was used with a target sputtering power of 120W. The target material was a PrTbMg alloy with the following composition: Pr 49.7 wt%, Tb 43.0 wt%, and Mg 7.3 wt%. The thickness of the deposited PrTbMg alloy film was 28.5 μm. After the coating was completed, a 0.58 μm thick TiAl alloy film was further magnetron sputtered on the coated surface as an anti-oxidation protective layer. The TiAl alloy film contained 82.5 wt% Ti, with the remainder being Al. The coated copper-cobalt foam foil was folded in half so that the coated surfaces were in contact, and the folded coated copper-cobalt foam foil was compressed using a roller press to a thickness of 56.5 μm to obtain a copper-cobalt foam foil for grain boundary diffusion.

[0134] A sintered NdFeB magnet of grade N50 was selected as the initial magnet, with a length, width, and thickness of 10 mm and 5.5 mm respectively. A 10 mm × 10 mm foamed copper-cobalt alloy foil for grain boundary diffusion was applied to the top and bottom 10 mm × 10 mm surfaces of the sintered NdFeB magnet. At room temperature, the foil was pressed at 50 MPa for 15 seconds to ensure a tight bond between the foamed copper-cobalt alloy foil and the sintered NdFeB magnet, thus obtaining the NdFeB magnet to be diffused.

[0135] The neodymium iron boron magnet to be diffused is placed in a vacuum sintering furnace, and the vacuum degree of the vacuum sintering furnace is 10. -3 Heating began at a certain temperature (Pa), with the temperature increased from room temperature to 770℃ at a rate of 10℃ / min, and heat-treated at 770℃ for 240 min. Heating continued, increasing the temperature to 910℃ at a rate of 10℃ / min, and heat-treated at 910℃ for 400 min. After heat treatment, the temperature was cooled to room temperature at a rate of 10℃ / min. The vacuum degree of the vacuum sintering furnace was 10... -3 Heating was restarted at Pa, and the temperature was increased from room temperature to 498℃ at a rate of 10℃ / min. The temperature was then heat-treated at 498℃ for 90 min. After the heat treatment, the temperature was rapidly cooled to room temperature to obtain the neodymium iron boron diffused magnet.

[0136] The magnetic properties of the neodymium iron boron diffused magnets are shown in Table 4. Compared with the initial magnet, the coercivity H of the neodymium iron boron diffused magnets prepared in Example 3 is significantly higher. cj The coercivity increased by 13.11 kOe to 25.64 kOe, representing a 104% increase, while the remanence decreased by only 0.21%. The grade of the neodymium iron boron diffused magnet was upgraded from the initial N50 grade to the N50UH grade.

[0137] Table 4

[0138]

[0139] Example 4

[0140] A foamed iron-silicon alloy foil was selected, in which iron accounted for 98.4 wt% and silicon accounted for 1.6 wt%. The main technical parameters of this foamed iron-silicon alloy foil are as follows: pore size of 0.1 mm, porosity of 96%, and bulk density of 0.32 g / cm³. 3 The thickness is 2mm. The foamed iron-silicon alloy foil is ultrasonically cleaned with anhydrous ethanol and then vacuum dried to obtain a clean and uncontaminated foamed iron-silicon alloy foil.

[0141] A coated foamed iron-silicon alloy foil was obtained by depositing a DyPrSn alloy thin film on one surface of a dried foamed iron-silicon alloy foil using magnetron sputtering. Specifically, a DC sputtering mode was used with a target sputtering power of 200W. The target material was a DyPrSn alloy with the following composition: Dy 51.3 wt%, Pr 30.8 wt%, and Sn 17.9 wt%. The thickness of the deposited DyPrSn alloy thin film was 35 μm. After deposition, a 0.8 μm thick AlMg alloy thin film was further magnetron sputtered onto the coated surface as an anti-oxidation protective layer. The AlMg alloy thin film contained 92.5 wt% Al, with the remainder being Mg. The coated foamed iron-silicon alloy foil was folded facet to bring the coated surfaces into contact, and then compressed using a roller press to a thickness of 75 μm to obtain a foamed iron-silicon alloy foil for grain boundary diffusion.

[0142] A sintered NdFeB magnet of grade N50 was selected as the initial magnet, with a length of 15 mm, a width of 12 mm, and a thickness of 6 mm. A 15 mm × 12 mm foamed iron-silicon alloy foil for grain boundary diffusion was applied to the upper and lower 15 mm × 12 mm surfaces of the sintered NdFeB magnet. At room temperature, the foil was pressed under 10 MPa for 60 seconds to ensure a tight bond between the foamed iron-silicon alloy foil and the sintered NdFeB magnet, thus obtaining the NdFeB magnet to be diffused.

[0143] The neodymium iron boron magnet to be diffused is placed in a vacuum sintering furnace, and the vacuum degree of the vacuum sintering furnace is 10. -3 Heating began at a certain temperature (Pa), with the temperature increased from room temperature to 770℃ at a rate of 10℃ / min, and heat-treated at 770℃ for 240 min. Heating continued, increasing the temperature to 910℃ at a rate of 10℃ / min, and heat-treated at 910℃ for 400 min. After heat treatment, the temperature was cooled to room temperature at a rate of 10℃ / min. The vacuum degree of the vacuum sintering furnace was 10... -3 Heating was restarted at Pa, and the temperature was increased from room temperature to 498℃ at a rate of 10℃ / min. The temperature was then heat-treated at 498℃ for 90 min. After the heat treatment, the temperature was rapidly cooled to room temperature to obtain the neodymium iron boron diffused magnet.

[0144] The magnetic properties of the neodymium iron boron diffused magnets are shown in Table 5. Compared with the initial magnet, the coercivity H of the neodymium iron boron diffused magnets prepared in Example 4 is significantly higher. cj The coercivity increased by 13.42 kOe to 25.95 kOe, representing a 107% increase, while the remanence decreased by only 0.14%. The grade of the neodymium iron boron diffused magnet was upgraded from the initial N50 grade to the N50UH grade.

[0145] Table 5

[0146]

[0147] Example 5

[0148] A foamed titanium alloy foil was selected. The titanium alloy is TC4 alloy, with aluminum accounting for 6.5 wt%, vanadium accounting for 4 wt%, and titanium as the balance. The main technical parameters of this foamed titanium alloy foil are as follows: pore size 0.2 mm, porosity 95%, and bulk density 0.23 g / cm³. 3 The thickness is 1 mm. The foamed titanium alloy foil is ultrasonically cleaned with anhydrous ethanol and then vacuum dried to obtain a clean and uncontaminated foamed titanium alloy foil.

[0149] A DyCuAl alloy film was deposited on one surface of a dried foamed titanium alloy foil using magnetron sputtering to obtain a coated foamed titanium alloy foil. Specifically, a DC sputtering mode was used with a target sputtering power of 200W. The target material was a DyCuAl alloy with the following composition: Dy 90wt%, Cu 7.6wt%, and Al 2.4wt%. The thickness of the deposited DyCuAl alloy film was 32.5μm. After the coating was completed, a 1.8μm thick AlCu alloy film was further magnetron sputtered on the coated surface as an anti-oxidation protective layer. In the AlCu alloy film, the Al content was 92.5wt%, and the remainder was Cu. The coated foamed titanium alloy foil was folded face to face so that the coated surfaces were in contact, and the folded coated foamed titanium alloy foil was compressed to a thickness of 68μm using a roller press to obtain a foamed titanium alloy foil for grain boundary diffusion.

[0150] A sintered NdFeB magnet of grade N38 was selected as the initial magnet, with a length, width, and thickness of 10 mm and 5.5 mm respectively. A 10 mm × 10 mm foamed titanium alloy foil for grain boundary diffusion was applied to the top and bottom 10 mm × 10 mm surfaces of the sintered NdFeB magnet. At room temperature, the foil was pressed under 20 MPa pressure for 45 seconds to ensure a tight bond between the foamed titanium alloy foil and the sintered NdFeB magnet, thus obtaining the NdFeB magnet to be diffused.

[0151] The neodymium iron boron magnet to be diffused is placed in a vacuum sintering furnace, and the vacuum degree of the vacuum sintering furnace is 10. -3 Heating began at a pressure of 10 Pa, increasing the temperature from room temperature to 844°C at a rate of 10°C / min, and heat-treated at 844°C for 240 min. Heating continued, increasing the temperature to 905°C at a rate of 10°C / min, and heat-treated at 905°C for 400 min. After heat treatment, the temperature was cooled to room temperature at a rate of 10°C / min. The vacuum degree of the vacuum sintering furnace was 10... -3 Heating was restarted at Pa, and the temperature was increased from room temperature to 640℃ at a rate of 10℃ / min. The temperature was then heat-treated at 640℃ for 75 min. After the heat treatment, the temperature was rapidly cooled to room temperature to obtain the neodymium iron boron diffused magnet.

[0152] The magnetic properties of the neodymium iron boron diffused magnets are shown in Table 6. Compared with the initial magnet, the coercivity H of the neodymium iron boron diffused magnets prepared in Example 5 is significantly higher. cj The coercivity was increased by 7.4 kOe to 19.84 kOe, representing a 59.5% increase, while the remanence decreased by only 0.32%. The grade of the neodymium iron boron diffused magnet was upgraded from the initial N38 grade to N380H.

[0153] Table 6

[0154]

[0155] 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. A method for preparing a foamed metal foil for grain boundary diffusion, comprising the following steps: 1) A rare earth alloy film is deposited on the surface of a foam metal foil to obtain a coated foam metal foil; 2) Fold the coated foam metal foil obtained in step 1) in half so that the coated surfaces are in contact, compress it to 10-100 μm after folding, and obtain the foam metal foil for grain boundary diffusion. The foamed metal foil has a porosity of over 90%, a pore size of 0.01–0.5 mm, and a thickness of 0.2–8 mm; the foamed metal foil is selected from at least one of Cu, Co, Ni, Fe, Ti, Zr, and Al, either as a metallic element or a metallic alloy. The rare earth element in the rare earth alloy film is selected from at least one of light rare earth elements and heavy rare earth elements, and must contain heavy rare earth elements; the thickness of the rare earth alloy film is 2 to 50 μm.

2. The preparation method according to claim 1, characterized in that, The light rare earth element is selected from at least one of Pr and Nd; the heavy rare earth element is selected from at least one of Dy and Tb. The rare earth alloy film also contains alloying elements, which are selected from at least one of Cu, Ga, Mg, Al, Mo, Fe, Zr, Nb, Sn, and Zn.

3. The preparation method according to claim 1, characterized in that, In step 1), the method for depositing rare earth alloy thin films is selected from at least one of vacuum evaporation coating, magnetron sputtering coating, and vacuum ion plating.

4. The preparation method according to claim 1, characterized in that, In step 2), the compression method is selected from at least one of rolling and pressing.

5. The preparation method according to claim 1, characterized in that, The preparation method further includes the step of depositing a protective layer on the obtained foam metal foil for grain boundary diffusion; wherein the protective layer is an aluminum alloy thin film with a thickness of 0.1 to 3 μm.

6. A foamed metal foil for grain boundary diffusion, characterized in that, The foamed metal foil is prepared by the preparation method according to any one of claims 1 to 5.

7. A method for preparing a neodymium iron boron diffused magnet, comprising the following steps: S1) Cover the surface of the NdFeB magnet with at least one layer of the foam metal foil for grain boundary diffusion as described in claim 6 to obtain the NdFeB magnet to be diffused; S2) The neodymium iron boron magnet to be diffused is subjected to vacuum heat treatment to obtain a neodymium iron boron diffused magnet.

8. The preparation method according to claim 7, characterized in that, The steps of vacuum heat treatment include: a) The neodymium iron boron magnet to be diffused is heat-treated under vacuum conditions at 500–850°C, and then heat-treated again at 880–950°C. After cooling, the heat-treated neodymium iron boron magnet is obtained. b) The heat-treated NdFeB magnets are further heat-treated under vacuum conditions at 400–660 °C to obtain NdFeB diffused magnets.

9. The preparation method according to claim 7, characterized in that, In step S1), the neodymium iron boron magnet covered with foam metal foil is processed using a press or ultrasonic welding machine to obtain the neodymium iron boron magnet to be diffused.

10. A neodymium iron boron diffused magnet, characterized in that, The neodymium iron boron diffused magnet is prepared by the preparation method according to any one of claims 7 to 9.

Images