Method for improving mechanical properties of neodymium-iron-boron magnets and neodymium-iron-boron magnet

Abstract

The application provides a method for improving the mechanical properties of a neodymium-iron-boron magnet and the neodymium-iron-boron magnet. When the alloy components are proportioned, the proportion of amorphous particles is increased, the cooling process in the vacuum rapid solidification process and the tempering process is improved, the conversion of the rare earth-rich phase into the amorphous phase is promoted by using the cooling process control means, and the amorphous state particle additive of inorganic non-metal is added. Through the synergistic effect of the amorphous phase and the amorphous state particle additive, the proportion of the amorphous phase in the grain boundary phase of the neodymium-iron-boron magnet is increased, the aggregation and transmission of cracks in the material are weakened, the toughness of the magnet is enhanced, and the mechanical properties of the material are greatly improved. The bending strength, tensile strength, compressive strength and hardness parameters of the neodymium-iron-boron magnet can be effectively improved by the simple process means. The process means adopted by the application is simple and efficient, and the upgrading and reconstruction can be realized by simply replacing the hot medium on the basis of the original sintered neodymium-iron-boron production equipment. The reconstruction cost is low, and the application is easy to popularize and use on a large scale.

Description

Technical Field

[0001] This application relates to the field of rare earth permanent magnet materials technology, and more specifically to a method for improving the mechanical properties of neodymium iron boron magnets and neodymium iron boron magnets. Background Technology

[0002] Sintered NdFeB magnets, known as the "King of Magnets" due to their excellent magnetic properties, are widely used in aerospace, wind power generation, energy-saving home appliances, electronics, and new energy vehicles. However, with current technology, sintered NdFeB magnets have relatively poor strength and toughness, making them prone to breakage and surface peeling during production and processing, exhibiting poor brittleness.

[0003] The main reason for the poor brittleness of existing sintered NdFeB magnets is that, due to the intrinsic characteristics of multiphase materials, the grain boundary phase in the material, acting as a grain boundary weakening phase, greatly reduces the strength of the magnet. This leads to the accumulation and propagation of cracks in the grain boundary phase, making the material extremely prone to brittle fracture. Consequently, existing sintered NdFeB magnets have poor stability and safety during service, severely limiting their application in high-intensity working environments. Summary of the Invention

[0004] This application addresses the shortcomings of existing technologies by providing a method for improving the mechanical properties of NdFeB magnets and an NdFeB magnet itself. This application, through the synergistic effect of cooling process control and the addition of inorganic non-metallic amorphous particles, further increases the proportion of amorphous phase in the grain boundary phase of the NdFeB magnet by directly adding amorphous substances to the material, building upon the process-driven transformation of rare-earth-rich phases into amorphous phases. This weakens crack aggregation and propagation within the material, significantly enhancing its mechanical properties. The specific technical solution adopted in this application is as follows.

[0005] First, to achieve the above objectives, a method for improving the mechanical properties of NdFeB magnets is proposed, comprising the following steps: proportioning alloy components and smelting to prepare an alloy melt; subjecting the alloy melt to vacuum rapid solidification treatment to obtain rapidly solidified alloy flakes, and subjecting the rapidly solidified alloy flakes to hydrogen crushing treatment to obtain coarse powder with a particle size not exceeding 8 μm; subjecting the coarse powder to hydrogen crushing and high-energy air jet milling treatment to obtain fine powder with a particle size distribution range between 1-6 μm; subjecting the fine powder to magnetic field orientation pressing and cold isostatic pressing treatment to obtain a green compact; subjecting the green compact to high-temperature sintering and tempering processes to obtain NdFeB magnets; wherein, high-specific-heat medium is used for high-speed cooling in the vacuum rapid solidification treatment and / or tempering process.

[0006] Optionally, as described in any of the above methods, the alloy composition includes: adding 0.1%-1.0% by mass of inorganic non-metallic amorphous particles during the neodymium iron boron magnet smelting stage, wherein the particle size of the inorganic non-metallic amorphous particles ranges from 100 nm to 2 μm.

[0007] Optionally, as described in any of the above methods, the amorphous particles of the inorganic nonmetallic material include: oxides, carbides, nitrides, halogen compounds, borides, and any one or a combination of silicates, aluminates, phosphates, borates, and perovskites.

[0008] Optionally, as described in any of the above methods, the vacuum rapid solidification process specifically employs the following method for high-speed cooling: an oil cooling pipe is added to the cooling copper rod used in the vacuum rapid solidification, and helium, liquid ammonia, and / or ammonia are introduced into the oil cooling pipe as a high specific heat medium to rapidly cool the alloy melt for vacuum rapid solidification, thereby obtaining alloy rapid solidification sheets.

[0009] Optionally, as described in any of the above methods, the tempering process specifically employs the following steps: the sintered magnet is taken out and placed in an atmosphere furnace and held at 900°C for 4-6 hours, then rapidly cooled to room temperature using a helium-ammonia mixed gas medium for secondary tempering, held at 480-520°C for 2-4 hours, and then quickly taken out and placed in a quenching oil tank for rapid cooling.

[0010] Optionally, as described in any of the above methods, the helium-ammonia ratio in the medium used during the cooling process is set in the range of 2:1 to 4:1.

[0011] Optionally, as described in any of the above methods, the high-temperature sintering and tempering process specifically adopts the following steps: sintering the green embryo at 1080~1120℃ for 4-6 hours, then holding it at 900℃ for 3-5 hours for primary tempering, and then holding it at 500℃ for 2-4 hours for secondary tempering.

[0012] In addition, to achieve the above objectives, this application also provides a neodymium iron boron magnet, which is prepared by any of the methods described above.

[0013] Optionally, in any of the neodymium iron boron magnets described above, the mass percentage of the amorphous phase in the neodymium iron boron magnet is not less than 0.1%.

[0014] Optionally, in any of the neodymium iron boron magnets described above, the amorphous phase includes: any one or a mixture of amorphous particles of oxides, carbides, nitrides, halogen compounds, borides, silicates, aluminates, phosphates, borates, and perovskites.

[0015] Beneficial effects

[0016] This application provides a method for improving the mechanical properties of NdFeB magnets and a NdFeB magnet itself. In the alloy composition, this application increases the proportion of amorphous particles and, in conjunction with improvements to the cooling process in vacuum rapid solidification and tempering, utilizes controlled cooling techniques to promote the transformation of rare-earth-rich phases into amorphous phases. This, combined with inorganic non-metallic amorphous particle additives, increases the proportion of amorphous phase in the grain boundary phase of the NdFeB magnet through the synergistic effect of the amorphous phase and the additives. This weakens crack aggregation and propagation in the material, enhances the magnet's toughness, and significantly improves the material's mechanical properties. This application can effectively improve the bending strength, tensile strength, compressive strength, and hardness parameters of NdFeB magnets through simple process methods. The process methods employed are simple and efficient, and can be easily upgraded by simply replacing the specific heat medium in existing sintered NdFeB production equipment. The upgrade cost is low, and it is easy to promote and use on a large scale.

[0017] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing this application. Detailed Implementation

[0018] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0019] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0020] This application discloses a method for preparing neodymium iron boron magnets to improve their mechanical properties. The method described herein can be implemented using the following steps based on existing sintering processes:

[0021] (1) Composition ratio: The alloy composition is proportioned. During the proportioning process, amorphous substances can be added to the existing nominal composition of NdFeB alloy, and alloy melt containing more amorphous components can be prepared by melting.

[0022] (2) Vacuum rapid solidification: The alloy melt is subjected to vacuum rapid solidification treatment to obtain alloy rapid solidification flakes, and the alloy rapid solidification flakes are subjected to hydrogen crushing treatment to obtain coarse powder with a particle size not exceeding 8μm.

[0023] (3) Hydrogen crushing and air jet milling: The coarse powder is subjected to hydrogen crushing and high-energy air jet milling to obtain fine powder with a particle size distribution range of 1-6 μm;

[0024] (4) Pressing and molding: The fine powder is subjected to magnetic field orientation pressing and molding, and cold isostatic pressing to obtain a green embryo;

[0025] (5) High-temperature sintering and tempering: The green blank is subjected to high-temperature sintering and tempering processes to obtain neodymium iron boron magnets;

[0026] In the above steps, (2) vacuum rapid solidification treatment and / or (5) tempering process, a high specific heat medium can be used to promote the transformation of rare earth-rich phase into amorphous phase by high-speed cooling, thereby increasing the proportion of amorphous phase in grain boundary phase.

[0027] In practical applications, considering that sintered Nd-Fe-B magnets are ferromagnetic materials, the proportion of impurity phases (paramagnetic or antiferromagnetic) should not be too high, otherwise it will damage the structure of the ferromagnetic phase and deteriorate the magnetic properties. Therefore, this application can specifically increase the proportion of amorphous NdFeB by rapidly cooling the alloy at a specific temperature during melting, sintering, or tempering stages, based on the existing NdFeB alloy composition. Furthermore, by adding inorganic non-metallic amorphous particles with a mass percentage between 0.1% and 1.0%, the amorphous characteristics of ensuring that the liquid grain boundary phase in the magnet remains in amorphous state are further enhanced.

[0028] The effects of different addition ratios of inorganic nonmetallic amorphous particles on the mechanical properties of the magnet are as follows:

[0029] 1. Table 1 Mechanical Properties

[0030]

[0031] In practical applications, considering that existing production equipment can only prepare magnetic powder with a particle size between 1-6 μm, and that the NdFeB particles in the pressed green powder are distributed between 1-6 μm, the particle size of the paramagnetic nanorod-shaped refractory particles should be smaller than that of the magnetic powder. Preferably, the particle size range of the inorganic non-metallic amorphous particles can be controlled between 100 nm and 2 μm to avoid the problems of excessively small particle size making it difficult to fill the grain boundary phase, or excessively large particle size damaging the main phase structure. The inorganic non-metallic amorphous particles added in this application can be selected from: oxides, carbides, nitrides, halogen compounds, borides, and any one or any combination of silicates, aluminates, phosphates, borates, and perovskites. These substances are inorganic non-metallic materials with completely different microstructures from traditional metals; the two are incompatible and will promote the formation of the amorphous phase.

[0032] The following examples illustrate the rapid cooling technology used in this application during the melting, sintering, or tempering stages.

[0033] Example 1:

[0034] (1) Composition ratio (addition of amorphous materials): 0.1%-1.0% (mass ratio) of inorganic non-metallic amorphous particles are added during the smelting stage of NdFeB magnets; (wherein inorganic non-metals include oxides, carbides, nitrides, halogen compounds, borides, as well as silicates, aluminates, phosphates, borates, perovskites and other amorphous particles), wherein the particle size range of the additives is 100nm-2μm.

[0035] (2) Vacuum rapid solidification: After vacuum rapid solidification, alloy rapid solidification sheets are obtained. The rapid solidification sheets are then subjected to hydrogen crushing treatment to obtain coarse powder with a particle size of ~8μm.

[0036] (3) Hydrogen crushing and air jet milling: By hydrogen crushing and high-energy air jet milling of the coarse powder in step (2), fine powder with a particle size distribution range of 1-6 μm is obtained;

[0037] (4) Pressing and molding: The neodymium iron boron alloy powder is magnetically oriented and pressed into shape, and then cold isostatically pressed to obtain a green blank;

[0038] (5) High-temperature sintering and tempering: The green blank is subjected to traditional sintering and tempering processes. The sintering and tempering process is sintering at 1080~1120℃ for 4-6 hours, the first-stage tempering is held at 900℃ for 3-5 hours, and the second-stage tempering is held at 500℃ for 2-4 hours to obtain sintered NdFeB magnets with high mechanical properties.

[0039] Table 1 Mechanical Properties

[0040]

[0041] Example 2:

[0042] (1) Composition and Rapid Solidification: The alloy is proportioned according to its nominal composition. During vacuum rapid solidification, high-speed cooling technology is used to obtain rapidly solidified alloy flakes. The rapidly solidified flakes are then subjected to hydrogen crushing treatment to obtain coarse powder with a particle size of ~8μm. In this embodiment, during high-speed cooling, an oil cooling pipe is added to the cooling copper rod used for vacuum rapid solidification. Helium, liquid ammonia, and / or ammonia are introduced into the oil cooling pipe as a high specific heat medium to rapidly cool the alloy melt for vacuum rapid solidification treatment, thereby obtaining rapidly solidified alloy flakes. The high specific heat medium composed of helium, liquid ammonia, and / or ammonia in the oil cooling pipe can have its helium-ammonia ratio set in the range of 2:1 to 4:1 to significantly increase the cooling efficiency by mixing an appropriate amount of ammonia into the cooling gas. However, considering that ammonia expands when heated, it will increase the cavity pressure and obstruct air circulation. Therefore, it is generally necessary to control its ratio within a certain range to obtain an extremely fast cooling rate and ensure the formation of the amorphous phase.

[0043] (2) Hydrogen crushing and air jet milling: By hydrogen crushing and high-energy air jet milling of the coarse powder in step (1), fine powder with a particle size distribution range of 1-6 μm is obtained;

[0044] (3) Pressing and molding: The neodymium iron boron alloy powder is magnetically oriented and pressed into shape, and then cold isostatically pressed to obtain a green blank;

[0045] (4) High-temperature sintering and tempering: Neodymium iron boron magnets are obtained by processing the green blanks through traditional sintering and tempering processes. The processing is as follows: the sintering and tempering process is to sinter at 1080~1120℃ for 4-6 hours, then to perform a first-stage tempering at 900℃ for 3-5 hours, and then to perform a second-stage tempering at 500℃ for 2-4 hours, to obtain sintered neodymium iron boron magnets with high mechanical properties and an amorphous phase mass ratio of not less than 0.1%;

[0046] Table 2 Mechanical Properties

[0047]

[0048] Example 3:

[0049] (1) Composition ratio and rapid solidification: The alloy is proportioned according to the nominal composition. During vacuum rapid solidification, high-speed cooling technology is used to obtain alloy rapid solidification flakes. The rapid solidification flakes are then subjected to hydrogen crushing treatment to obtain coarse powder with a particle size of ~8μm. (During the high-speed cooling process, the following can be done: 1. Add oil cooling pipes to the cooling copper rod; 2. Introduce an appropriate amount of high specific heat medium such as helium or liquid ammonia during cooling).

[0050] (2) Hydrogen crushing and air jet milling: By hydrogen crushing and high-energy air jet milling of the coarse powder in step (1), fine powder with a particle size distribution range of 1-6 μm is obtained;

[0051] (3) Pressing and molding: The neodymium iron boron alloy powder is magnetically oriented and pressed into shape, and then cold isostatically pressed to obtain a green blank;

[0052] (4) High-temperature sintering: The green embryo is subjected to traditional sintering and tempering processes, wherein the sintering and tempering process is sintering at 1080~1120℃ for 4-6 hours;

[0053] (5) Tempering and rapid cooling: After the sintered magnet is taken out, it is placed in an atmosphere furnace at 900°C for 4-6 hours and then cooled using rapid cooling technology. The rapid cooling technology used in this embodiment can be achieved by using a mixture of helium and ammonia: After the magnet is taken out and kept at 900°C for 4-6 hours in the atmosphere furnace, it is placed in a cooling environment with a helium-ammonia ratio of 2:1 to 4:1. The magnet is rapidly cooled to room temperature using a helium-ammonia mixed gas medium and then tempered for two stages. After that, it is kept at 480-520°C for 2-4 hours and then quickly taken out and placed in a quenching oil tank for rapid cooling to obtain a high-performance sintered NdFeB magnet.

[0054] Table 3 Mechanical Properties

[0055]

[0056] Example 4:

[0057] (1) Composition ratio (addition of amorphous materials): 0.1%-1.0% (mass ratio) of inorganic non-metallic amorphous particles are added during the smelting stage of NdFeB magnets; (wherein inorganic non-metals include oxides, carbides, nitrides, halogen compounds, borides, as well as silicates, aluminates, phosphates, borates, perovskites and other amorphous particles), wherein the particle size range of the additives is 100nm-2μm.

[0058] (2) Vacuum rapid solidification: After vacuum rapid solidification, alloy rapid solidification sheets are obtained. The rapid solidification sheets are then subjected to hydrogen crushing treatment to obtain coarse powder with a particle size of ~8μm.

[0059] (3) Hydrogen crushing and air jet milling: By hydrogen crushing and high-energy air jet milling of the coarse powder in step (2), fine powder with a particle size distribution range of 1-6 μm is obtained;

[0060] (4) Pressing and molding: The neodymium iron boron alloy powder is magnetically oriented and pressed into shape, and then cold isostatically pressed to obtain a green blank;

[0061] (5) High-temperature sintering: The green embryo is subjected to traditional sintering and tempering processes, wherein the sintering and tempering process is sintering at 1080~1120℃ for 4-6 hours;

[0062] (6) Tempering and rapid cooling: After the sintered magnet is taken out, it is placed in an atmosphere furnace at 900℃ for 4-6 hours. The magnet is cooled by rapid cooling technology. A mixture of helium and ammonia is used for rapid cooling, with the ratio of helium to ammonia in the range of 2:1 to 4:1. After cooling to room temperature, a second tempering is performed, which is held at 480-520℃ for 2-4 hours. Then, it is quickly taken out and placed in a quenching oil tank for rapid cooling to obtain a high mechanical property sintered NdFeB magnet.

[0063] Table 4 Mechanical Properties

[0064]

[0065] In summary, compared with the prior art, the beneficial effects of this application are as follows:

[0066] (1) Adding trace amounts of amorphous material to the alloy smelting composition, taking advantage of its amorphous structure, changes the microstructure of the original sintered NdFeB magnet, increases the proportion of amorphous phase at grain boundaries, enhances the toughness of the magnet, and prepares a magnet with high mechanical properties;

[0067] (2) Based on the addition of amorphous materials, rapid cooling technology is introduced to cause the alloy to be rapidly cooled at specific temperatures during the melting, sintering and tempering stages, so as to ensure that the liquid grain boundary phase in the magnet retains the characteristics of the amorphous state and greatly enhances the toughness of the grain boundary phase.

[0068] (3) The process of this invention is simple and efficient, and can be completed by modifying the existing sintered NdFeB production equipment, and has the prospect of large-scale promotion and use.

[0069] The above are merely embodiments of this application, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application.

Claims

1. A method for improving the mechanical properties of neodymium iron boron magnets, characterized in that the steps include... include: Formulate alloy components and smelt to prepare alloy melt; The alloy melt was subjected to vacuum rapid solidification treatment to obtain rapidly solidified alloy flakes, and the rapidly solidified alloy flakes were subjected to hydrogen crushing treatment to obtain coarse powder with a particle size not exceeding 8μm. The coarse powder was subjected to hydrogen crushing and high-energy air jet milling to obtain fine powder with a particle size distribution range of 1-6 μm; Fine powder is subjected to magnetic field orientation pressing and cold isostatic pressing to obtain a green embryo; Neodymium iron boron magnets are obtained by subjecting the green blanks to high-temperature sintering and tempering processes. Among them, medium cooling is used in vacuum rapid solidification and / or tempering processes; The alloy composition includes: 0.1%-1.0% by mass of inorganic non-metallic amorphous particles added during the neodymium iron boron magnet smelting stage, wherein the particle size of the inorganic non-metallic amorphous particles ranges from 100nm to 2μm; The inorganic non-metallic amorphous particles include: oxides, carbides, nitrides, halogen compounds, borides, and any one or a combination of silicates, aluminates, phosphates, borates, and perovskites; The vacuum rapid solidification process specifically employs the following method for high-speed cooling: An oil cooling pipe is added to the cooling copper rod used in vacuum rapid solidification. Helium, liquid ammonia and / or ammonia are introduced into the oil cooling pipe as a high specific heat medium to rapidly cool the alloy melt for vacuum rapid solidification treatment, thereby obtaining alloy rapid solidification sheet. The tempering process specifically employs the following steps: The sintered magnets are taken out and placed in an atmosphere furnace and held at 900℃ for 4-6 hours. Then, they are rapidly cooled to room temperature using a helium-ammonia mixed gas medium and subjected to secondary tempering at 480-520℃ for 2-4 hours. After that, they are quickly taken out and placed in a quenching oil tank for rapid cooling. The helium-ammonia ratio in the medium used during the cooling process is set within the range of 2:1 to 4:1; The specific steps involved in the high-temperature sintering and tempering process are as follows: The green embryo is sintered at 1080~1120℃ for 4-6 hours, then tempered at 900℃ for 3-5 hours for the first stage, and then tempered at 500℃ for 2-4 hours for the second stage.

2. A neodymium iron boron magnet, characterized in that, Prepared by the method described in claim 1.

3. The neodymium iron boron magnet as described in claim 2, characterized in that, The amorphous phase content in the neodymium iron boron magnet is not less than 0.1%.

4. The neodymium iron boron magnet as described in claim 3, characterized in that, The amorphous phase includes: any one or a mixture of oxides, carbides, nitrides, halogen compounds, borides, silicates, aluminates, phosphates, borates, and perovskites.

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