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CN118155968A - Regenerated sintered NdFeB magnet and preparation method thereof - Google Patents

Regenerated sintered NdFeB magnet and preparation method thereof Download PDF

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Publication number
CN118155968A
CN118155968A CN202410282052.6A CN202410282052A CN118155968A CN 118155968 A CN118155968 A CN 118155968A CN 202410282052 A CN202410282052 A CN 202410282052A CN 118155968 A CN118155968 A CN 118155968A
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magnet
content
powder
shell
regenerated
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徐吉元
熊晏秋
李靖
史荣莹
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Beijing Jingci Electrical Technology Co ltd
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Beijing Jingci Electrical Technology Co ltd
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047Alloys characterised by their composition
    • H01F1/053Alloys characterised by their composition containing rare earth metals
    • H01F1/055Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0577Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047Alloys characterised by their composition
    • H01F1/053Alloys characterised by their composition containing rare earth metals
    • H01F1/055Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0576Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together pressed, e.g. hot working
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/0266Moulding; Pressing
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/0293Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Hard Magnetic Materials (AREA)

Abstract

The invention discloses a regenerated sintered NdFeB magnet and a preparation method thereof, wherein the regenerated sintered NdFeB magnet comprises the following components in percentage by mass :RE1 aRE2 bCocCudMeFebalBfCgOh,24≤a≤31,0≤b≤8,0≤c≤5,0≤d≤0.8,0≤e≤3,0.85≤f≤1.2,28.5≤a+b≤35,0<g≤0.15,0<h≤0.10,bal as the rest; wherein RE 1 is one or a combination of a plurality of Pr, nd, la, ce, Y, RE 2 is one or a combination of a plurality of heavy rare earth Gd, ho, dy, tb, and M is one or a combination of a plurality of Al, cr, nb, zr, ga, ti, zn, V, mo, mn; the microstructure of the regenerated sintered NdFeB magnet consists of a grain boundary phase and two main phases, wherein the first main phase has a double-shell structure, and the second main phase has a single-shell structure. The invention effectively solves the problems of serious environmental pollution caused by waste recycling and low performance of the waste regenerated magnet, and the preparation method of the regenerated sintered NdFeB magnet is an environment-friendly method for high-value utilization of waste.

Description

Regenerated sintered NdFeB magnet and preparation method thereof
Technical Field
The invention relates to the technical field of rare earth permanent magnet material recycling. More particularly, the invention relates to a regenerated sintered neodymium-iron-boron magnet and a preparation method thereof.
Background
The rare earth permanent magnetic material is the permanent magnetic material with the highest coercive force Hcj and the largest magnetic energy product (BH) max, and is an important and emerging strategic material in China. Sintered NdFeB is used as a rare earth permanent magnet material with best comprehensive magnetic performance and highest cost performance at present, and has been widely applied to the fields of automobiles, electronics, electric power, energy sources, medical treatment, information technology and the like since the coming out of 1983, and is called as 'magnetic king'. According to incomplete statistics, the annual output of sintered NdFeB in China exceeds 20 ten thousand tons, and meanwhile, the annual output is kept at a high speed of 5-10%. Along with the increase of the output and the consumption of the sintered NdFeB magnet, the resource supply of the waste magnet is also increased, and the supply of the waste magnet is expected to reach 2.7-5.4 ten thousand tons in 2030. The sources of the waste magnets mainly have two approaches: firstly, in the production and manufacturing process of neodymium iron boron, defective products can be produced in each working procedure, and particularly, a large amount of leftover materials can be produced in a processing link; secondly, after the permanent magnet device is used for a certain period of time, the whole device is retired and scrapped along with the retirement of the magnetic steel. Under the large background of rare earth resource shortage and double carbon, how to realize the efficient recycling of neodymium iron boron waste resources has become an important subject of sustainable development in the rare earth permanent magnet industry.
At present, two methods for recycling neodymium iron boron waste materials are mainly applied in the industry. Firstly, purifying and separating a magnet by a chemical method to obtain simple substance elements with higher purity, such as praseodymium, neodymium and the like. The rare earth elements in the NdFeB waste can be reused by adopting a chemical purification separation method, but the technology is complex, the cost is high, and the purification purity of other elements is not high after the rare earth is purified, so that the rare earth elements are difficult to reuse. For example, chinese patent CN116377521a discloses a method for recovering mixed rare earth from neodymium iron boron waste, firstly mixing the waste with chlorinating agent and roasting, then soaking the roasted product in water to obtain chloride solution, then adding precipitant into the solution, and calcining the precipitate to obtain mixed rare earth oxide, then electrolyzing the rare earth oxide molten salt, and extracting mixed rare earth. If a sintered magnet is to be produced, conventional steps such as batch smelting, powder preparation, profiling, sintering heat treatment and the like are required to be performed again. The patent shows that the recovery process by the chemical method is complicated, the process difficulty is high, a large amount of chemical reagents such as strong acid, strong alkali and the like are used, and the environmental pollution is high. Secondly, a powder preparation adding method is adopted, waste materials are pickled to remove surface oxide skin, then the waste materials are put into a hydrogen crushing furnace to be crushed, and then the crushed waste materials are mixed with alloy powder of other components according to requirements, and a regenerated magnet is obtained through air flow grinding, profiling, sintering and tempering. Chinese patent CN115954202a discloses a process method for obtaining sintered neodymium-iron-boron magnet by re-air grinding waste magnet, mixing air grinding powder with rare earth powder and liquid phase powder uniformly, then performing magnetic field orientation, press forming, sintering, tempering and cooling. The waste powder prepared by the method inevitably contains more impurity elements, and the impurities are inherited into the regenerated magnet, so that the mechanical property of the regenerated magnet is poor, the permeation and diffusion are difficult to carry out, the service application of the regenerated magnet is influenced, and the magnet obtained by the method is generally used in the middle-low end field at present.
Disclosure of Invention
The invention aims to provide a regenerated sintered neodymium-iron-boron magnet and a preparation method thereof, which effectively solve the problem of low performance of waste regenerated magnets.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a regenerated sintered neodymium-iron-boron magnet having a composition of :RE1 aRE2 bCocCudMeFebalBfCgOh,24≤a≤31,0≤b≤8,0≤c≤5,0≤d≤0.8,0≤e≤3,0.85≤f≤1.2,28.5≤a+b≤35,0<g≤0.15,0<h≤0.10,bal by mass as a balance; wherein RE 1 is one or a combination of a plurality of Pr, nd, la, ce, Y, RE 2 is one or a combination of a plurality of heavy rare earth Gd, ho, dy, tb, M is one or a combination of a plurality of Al, cr, nb, zr, ga, ti, zn, V, mo, mn, and the microstructure of the regenerated sintered NdFeB magnet consists of a grain boundary phase and two main phases;
The first main phase has a double-shell structure, and comprises a first core, a first shell a and a first shell b from inside to outside, wherein the first core is formed by a neodymium-iron-boron waste magnet, the first shell a is formed by a new-born magnet alloy powder particle after being swallowed by the neodymium-iron-boron waste magnet alloy powder particle when being sintered at a high temperature, and the first shell b is a heavy rare earth shell formed by grain boundary diffusion;
The second main phase has a single-shell structure, and is provided with a second core and a second shell from inside to outside, wherein the second core is a new-born magnet, the second shell is a heavy rare earth shell formed after grain boundary diffusion, the second shell has the same components as the first shell b, and the new-born magnet has the same components as the neodymium-iron-boron waste magnet.
Preferably, the volume fraction of the first main phase accounts for 90-99% of the sum of the volume fractions of the two main phases, wherein the content of C element and the content of O element of the first core are higher than the content of C element and the content of O element of the first shell layer a, and the difference between the content of C element and the content of O element of the first shell layer a and the content of O element of the first shell layer b is less than or equal to 50ppm.
Preferably, the content of C element in the first core is 50-200 ppm higher than that of C element in the first shell layer a, and the content of O element is 150-400 ppm higher.
Preferably, the difference between the content of C element and the content of O element in the second core and the content of C element and the content of O element in the second shell is less than or equal to 50ppm.
The invention also provides a preparation method of the regenerated sintered NdFeB magnet, which comprises the following steps:
Demagnetizing, cleaning and drying the neodymium iron boron waste magnet, and then smelting and throwing the alloy throwing piece, wherein the smelting and casting temperature is 1400-1500 ℃, the content of C element in the alloy throwing piece is less than or equal to 400ppm, the content of O element in the alloy throwing piece is less than or equal to 500ppm, the average thickness of the alloy throwing piece is 0.25-0.50 mm, and the average size of columnar crystals of the alloy throwing piece is 3.5-5.5 mu m;
Step two, carrying out hydrogen crushing on the alloy throwing piece obtained in the step one to obtain hydrogen crushing powder with the granularity of 500-1000 mu m and the H element content less than or equal to 1500ppm, and grinding the hydrogen crushing powder to obtain waste magnet alloy powder with the average granularity of 4.0-5.5 mu m;
Mixing the waste magnet alloy powder obtained in the step two with new magnet alloy powder with the same components as the neodymium-iron-boron waste magnet, wherein the mixing ratio of the new magnet alloy powder and the new magnet alloy powder is 99:1-50:50, the granularity of the new magnet alloy powder is 0.5-3.9 mu m, 0.05-0.2% of lubricant is added during mixing, the carbon content of the mixed powder is 600-950 ppm, the mixed powder is subjected to magnetic field forming and isostatic pressing to obtain a pressed compact, and the pressed compact is subjected to hot sintering treatment and cooling to obtain a sintered magnet;
And fourthly, slicing the sintered magnet obtained in the third step, decontaminating the surface, wherein the thickness of the slice is 1-8 mm, uniformly coating slurry containing heavy rare earth elements on the surface of the slice, carrying out heat treatment after the coated slurry is air-dried, wherein the primary heat treatment temperature is 800-950 ℃, the heat preservation time is 8-40 h, the secondary heat treatment temperature is 450-650 ℃, the heat preservation time is 4-8 h, and after the heat preservation is finished, filling argon gas and cooling, and discharging from the furnace after cooling to 70 ℃ to obtain the regenerated sintered neodymium-iron-boron magnet.
Preferably, the specific hydrogen crushing process in the second step is as follows: loading the alloy throwing piece into a hydrogen crushing furnace, vacuumizing to below 10Pa, heating to 350-500 ℃ for activation for 1.5-3 h, stopping heating when the vacuum degree is reduced to below 10Pa again, charging hydrogen to 0.1-0.2 MPa to enable the alloy throwing piece to fully absorb hydrogen, stopping charging hydrogen after the hydrogen absorption is saturated, vacuumizing and heating to 450-570 ℃ for dehydrogenation for 2-5 h, and cooling to normal temperature.
Preferably, the specific process of grinding the hydrogen-broken powder in the second step is as follows: adding about 0.05-0.15% of lubricant into the hydrogen broken powder, fully and uniformly mixing, grinding by using an air flow grinding device to prepare powder, wherein the grinding pressure is 0.35-0.65 MPa, and supplementing oxygen to reduce the powder activity during grinding, the oxygen supplementing amount is 30-50 ppm, and the rotating speed of a grading wheel of the air flow grinding device is 2000-5000 r/min.
Preferably, the specific process of the magnetic field forming, isostatic pressing and hot sintering treatment in the third step is as follows: placing the mixed powder into a die of a fully-sealed molding press, controlling the oxygen content in the press to be 100-500 ppm, orienting and pressing the powder into a molding under an orientation magnetic field with the magnetic field strength of 1.4-2.0T, placing the powder into an isostatic press for further densification, and setting the isostatic pressure to be 180-250 MPa to obtain a pressed compact, placing the pressed compact into a vacuum sintering furnace with the temperature of 1000-1060 ℃ for sintering for 2-10 h, and quenching the pressed compact to room temperature by inert gas to obtain the sintered state magnet.
The invention at least comprises the following beneficial effects:
1) Compared with the chemical method for recycling rare earth metals, the method omits the high-pollution and high-energy processes such as strong acid and alkali treatment, oxidative roasting, reduction treatment and the like, and has the remarkable advantages of short flow and environmental friendliness; compared with the direct regeneration of the crushed waste magnet, the magnet obtained by the invention has the characteristics of excellent tissue structure, low content of C, O and other impurity elements, and the like, and has great improvement on the processing performance, grain boundary diffusion performance, mechanical strength and the like of the regenerated magnet.
2) The regenerated magnet obtained by the method has excellent microstructure through the component control and tissue control technology. The beneficial effects of this tissue structure are mainly the following. Firstly, the regenerated magnet has two main phases with different structures, the magnetocrystalline anisotropy fields H A of the two main phases are different, and when the demagnetizing domain is nucleated, the energy difference between the different main phases needs to be overcome, so that the reverse domain expansion is difficult, and the magnet has higher demagnetizing resistance. On the other hand, as the particle size of the waste magnet powder is large, the particle size of the new-born magnet powder is small and the activity is high, when the two kinds of powder are mixed and sintered at a high temperature, the large particles spontaneously engulf the small particles, and finally, a shell layer mainly containing the new-born magnet particles is formed on the periphery of the waste magnet particles.
3) The regenerated magnet provided by the invention has good grain boundary diffusion performance, and realizes high-value utilization of the waste magnet. Conventional regenerated magnets have been difficult to apply to high-end fields, especially grain boundary diffusion products, due to their high impurity element content and poor microstructure. According to the regenerated magnet disclosed by the invention, the impurity element content in the grain boundary is low, so that on one hand, a heavy rare earth diffusion source can reach a deeper position of the magnet along the grain boundary, on the other hand, the impurity content of a new magnet shell layer at the periphery of a main phase of a waste magnet is very low, the energy required by replacing PrNd element in the main phase by the heavy rare earth element is reduced, the formed heavy rare earth shell layer is more complete, the main phase crystal grain has higher anti-demagnetizing capability, and the coercivity improvement amplitude caused by diffusion is greatly improved compared with that of a traditional method. Meanwhile, the main phase has the characteristics of complete heavy rare earth shell layers and low impurity element content in the grain boundaries, so that the diffused regenerated magnet has excellent bending resistance, corrosion resistance and demagnetizing resistance.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
FIG. 1 is a schematic view of microstructure of a regenerated sintered NdFeB magnet according to the present invention;
FIG. 2 is a flow chart of the preparation of a regenerated sintered NdFeB magnet according to example 1 of the present invention;
FIG. 3 is a microstructure of the S2 step alloy fling sheet of example 1 of the present invention;
Fig. 4 is a scanning electron microscope picture of a fracture of a regenerated sintered neodymium-iron-boron magnet in example 1 of the present invention.
Detailed Description
The present invention is described in further detail below with reference to the drawings and detailed description so as to enable those skilled in the art to practice the invention by referring to the description.
It will be understood that terms, such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
It should be noted that the experimental methods described in the following embodiments, unless otherwise specified, are all conventional methods, and the reagents and materials, unless otherwise specified, are all commercially available; in the description of the present invention, it should be noted that, unless explicitly stated and limited otherwise, the terms "mounted," "connected," and "disposed" are to be construed broadly, and may be fixedly connected, disposed, or detachably connected, disposed, or integrally connected, disposed, for example. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art. The terms "transverse," "longitudinal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used for convenience in describing and simplifying the description of the present invention based on the orientation or positional relationship shown in the drawings, and do not denote or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus are not to be construed as limiting the present invention.
The invention provides a regenerated sintered NdFeB magnet, which comprises the following components in percentage by mass :RE1 aRE2 bCocCudMeFebalBfCgOh,24≤a≤31,0≤b≤8,0≤c≤5,0≤d≤0.8,0≤e≤3,0.85≤f≤1.2,28.5≤a+b≤35,0<g≤0.15,0<h≤0.10,bal as the rest; wherein RE 1 is one or a combination of a plurality of Pr, nd, la, ce, Y, RE 2 is one or a combination of a plurality of heavy rare earth Gd, ho, dy, tb, M is one or a combination of a plurality of Al, cr, nb, zr, ga, ti, zn, V, mo, mn, and the microstructure (shown in figure 1) of the regenerated sintered NdFeB magnet consists of a grain boundary phase 300 and two main phases;
the first main phase 100 has a double-shell structure, and comprises a first core, a first shell a 101 and a first shell b 102 from inside to outside, wherein the first core is formed by neodymium-iron-boron waste magnets, the first shell a 101 is formed by swallowing new magnet alloy powder particles when neodymium-iron-boron waste magnet alloy powder particles are sintered at a high temperature, and the first shell b 102 is a heavy rare earth shell formed by grain boundary diffusion;
the second main phase 200 has a single-shell structure, and is provided with a second core and a second shell from inside to outside, wherein the second core is a new-born magnet, the second shell is a heavy rare earth shell formed after grain boundary diffusion, the second shell has the same components as the first shell b, and the new-born magnet has the same components as the neodymium-iron-boron waste magnet.
In another technical scheme, the volume fraction of the first main phase accounts for 90-99% of the sum of the volume fractions of the two main phases, wherein the content of C element and the content of O element of the first core are higher than the content of C element and the content of O element of the first shell layer a, and the difference between the content of C element and the content of O element of the first shell layer a and the content of O element of the first shell layer b is less than or equal to 50ppm.
In another technical scheme, the content of C element of the first core is 50-200 ppm higher than that of C element of the first shell layer a, and the content of O element is 150-400 ppm higher.
In another technical scheme, the difference between the content of C element and the content of O element in the second core and the content of C element and the content of O element in the second shell is less than or equal to 50ppm.
The invention also provides a preparation method of the regenerated sintered NdFeB magnet, and the preparation method is specifically shown in the following examples.
Example 1
The method selects the neodymium-iron-boron waste magnet with the brand number of 52M for recycling, and comprises the following specific steps (the flow chart is shown in figure 2):
S1, pretreatment of waste magnets: the neodymium iron boron waste magnets produced in the production process are collected and mainly comprise scraps and unqualified waste materials of sizes of products in various links, and the waste materials are classified according to the grades of the waste materials and whether the waste materials are magnetized. Firstly, carrying out demagnetization treatment on the 52M neodymium-iron-boron waste magnet with magnetism, wherein the demagnetization temperature is 350 ℃, and the heat preservation time is 0.5 hour. Then placing the nonmagnetic 52M neodymium-iron-boron waste magnet into a decontamination agent solution for degreasing treatment, ultrasonically cleaning for 3 hours, then cleaning for 2 times by using clear water, and placing into a baking oven at 150 ℃ for baking for 2 hours;
S2, smelting waste magnets: 600Kg of waste 52M brand neodymium iron boron waste magnets are put into a rapid hardening furnace for smelting and throwing. And loading small scraps into the lower layer of the crucible during loading, and loading large scraps into the upper layer of the crucible. The smelting casting temperature is 1450+/-10 ℃. The content of C element in the melted alloy throwing piece is 110ppm, and the content of O element is 200ppm. 100 alloy throwing pieces are taken, the thickness is measured by a micrometer, and the average thickness of the throwing pieces is 0.50mm. Microscopic observation of the microstructure was performed using a scanning microscope, and as shown in FIG. 3, the average size of the columnar crystals was 5.5. Mu.m. The cast piece component test is carried out by using ICP, and the cast piece component of the batch of waste alloy is (PrNd) 29.7Al0.18Cu0.23Co1.21Ga0.23Zr0.15FebalB0.9, compared with the design component of the brand new magnet, the PrNd in the waste alloy is 0.35 percent less, the Al is about 0.1 percent higher, the C content is equivalent, and the O content is about 100ppm higher. For convenience of distinction, the scrap alloy is named alloy I, and the 52M brand of new magnet alloy is named alloy II;
S3, hydrogen crushing: and (3) loading the waste alloy throwing pieces obtained in the step (S2) into a rotary hydrogen crushing furnace, vacuumizing to below 10Pa, heating to 500 ℃ for activation for 3 hours, stopping heating and charging hydrogen to 0.2MPa when the vacuum degree is reduced to below 10Pa again, fully absorbing hydrogen by the alloy throwing pieces, stopping charging hydrogen after saturation of hydrogen absorption, vacuumizing and heating to 450 ℃ for dehydrogenation for 5 hours, and cooling to normal temperature. The particle size of the obtained powder after hydrogen breaking is 1000 mu m, and the hydrogen content in the powder is 1500ppm;
S4, air flow grinding: and (3) adding 0.05% of lubricant into the hydrogen-broken powder obtained in the step S3, and fully and uniformly mixing. And then grinding into powder by using an air flow grinding device. The grinding pressure was 0.35MPa. Oxygen was properly supplied during grinding to reduce the powder activity, with an oxygen supply of 30ppm. The classifier wheel speed was adjusted to 2200 rpm. Powder particle size testing was performed using a laser particle sizer with an average particle size of 5.5 μm;
S5, mixing powder: and (3) uniformly mixing the waste magnet alloy powder I obtained in the step S4 with the new magnet alloy powder II according to the proportion of 99:1 for 5 hours. The average particle size of alloy powder II was 2. Mu.m. The lubricant is added during powder mixing, and the adding proportion is 0.2%. The carbon content of the powder after uniform mixing is 950ppm;
S6, magnetic field forming and isostatic pressing: and (3) putting the mixed powder in the step (S5) into a die of a fully-sealed molding press, wherein the oxygen content in the press is controlled below 500 ppm. Orienting and press forming under an orientation magnetic field with the magnetic field strength of 1.5T to obtain a pressed compact; placing the pressed compact into an isostatic press for further densification, wherein the isostatic pressure is 180MPa;
S7, sintering heat treatment: and removing the outer bag of the green body in a sealed glove box, controlling the oxygen content in the glove box to be less than 300ppm, and then placing the green body in an graphite box, and scattering a small amount of alumina powder in the graphite box to prevent the blank from adhering. Placing the green body in a vacuum sintering furnace with the temperature set at 1060 ℃ for sintering for 10 hours, and quenching to room temperature by using inert gas to obtain a sintered magnet;
S8, grain boundary diffusion: the sintered magnet obtained in S7 was subjected to slicing processing, and the sample size was 30mm×20mm×1mm, with the 1mm direction being the orientation direction. Degreasing the surface of a magnet sheet, uniformly coating slurry containing heavy rare earth Tb elements on the surface of the magnet, wherein the weight ratio of Tb coating is 0.4%, performing heat treatment after the coated slurry is air-dried, wherein the primary heat treatment temperature is 910 ℃, the heat preservation time is 8h, the secondary heat treatment temperature is 450 ℃, and the heat preservation time is 4h;
s9, cooling and discharging to obtain a regenerated magnet: and after the heat treatment and heat preservation are finished, filling argon into the furnace, starting a fan for cooling, and discharging the furnace when the furnace is cooled to about 70 ℃ to obtain the regenerated sintered NdFeB magnet.
Example 2
The method comprises the steps of preparing N38-grade Ce-containing neodymium-iron-boron waste magnet, regenerating the magnet according to the steps in the embodiment 1, preparing a cast piece from the waste magnet through the step S2, and testing (PrNd)22.1Ce10Al0.17Cu0.15Co1.00Ga0.22Zr0.17FebalB0.92. -grade waste magnet alloy serving as a new magnet alloy with a test component of (PrNd)21.8Ce9.9Al0.21Cu0.15Co1.01Ga0.20Zr0.15Feba lB0.92. and a grade, wherein the new magnet alloy is named A. Uniformly mixing waste magnet alloy A powder and new magnet alloy B powder according to the proportions of 50:50, 60:40, 70:30, 80:20 and 90:10 respectively, wherein the average particle size of the alloy A powder is 4.0 microns, and the average particle size of the alloy B powder is 0.5 microns. The sintering temperature of the regenerated magnet is 1010-1040 ℃. The sintered magnet was then processed into a sheet of 50X 25X 3 mm. And then, according to the step S8, dy+Tb heavy rare earth slurry coating is carried out, wherein the weight ratio is 0.35 percent Dy+0.30 percent Tb.
Example 3
The unknown grade neodymium iron boron waste magnet is pretreated according to the step S1 in the embodiment 1, then the waste alloy smelting and throwing piece is carried out according to the step S2, and the component of the waste alloy throwing piece A is (PrNd) 31Dy0.15Gd1Al0.65Cu0.15FebalB0.91 through ICP test. According to the components of the waste alloy A, preparing a new magnet alloy B, wherein the components of the alloy B are designed to be (PrNd) 31.3Dy0.15Gd1Al0.55Cu0.15FebalB0.91, and the design thought is that about 0.3% of rare earth burning loss exists in the smelting of the waste alloy, and the characteristic that 0.1% of Al rises exists at the same time. Then, the subsequent processes were performed according to steps S3 to S9 in example 1. Wherein the mixing ratio of A and B was 97:3, a mixed powder sample was obtained, the size of the sliced sample at the time of grain boundary diffusion was 35X 25X (1-8) mm, and the samples were named as h=1 to h=8, respectively, depending on the thickness of the sliced sample. The thickness direction of the sample is the magnetizing direction. The main components of the sample coating slurry comprise Tb, dy and Ho rare earth elements, and the weight gain ratio of the sample is 0.4 percent Dy+0.5 percent Tb+0.3 percent Ho.
Comparative example 1
For comparative analysis with the conventional method of adding the powder of the waste, 52M waste was obtained in exactly the same manner as in step S1 of example 1, and the waste composition test was performed, and it was found that the waste was almost identical to the composition of the nascent magnet. Then the magnet is regenerated through the steps S3 to S9. The particle size of the obtained waste alloy powder in the step S4 of the method is 4.2 mu m as the S2 smelting step is not carried out. S5, obtaining 1850ppm of C in the mixed powder.
Comparative example 2
The newly produced 52M brand of magnet is selected for grain boundary diffusion, and the technological parameters are exactly the same as the steps S8-S9 in the example 1.
Comparative example 3
The difference with example 2 is that the regenerated magnet A of the pulverizing method is obtained by directly crushing N38 brand Ce-containing NdFeB waste magnet without smelting and then carrying out an air flow grinding-pressing-sintering-grain boundary diffusion method.
Comparative example 4
The difference from example 2 is that a new magnet B blank of N38 brand was taken as a comparative sample for grain boundary diffusion treatment.
Comparative example 5
The mixed powder sample used in example 3 was subjected to sintering and secondary heat treatment only, without coating with heavy rare earth elements, and finally a regenerated magnet was obtained.
< Test of magnet Performance >
The regenerated sintered neodymium-iron-boron magnets prepared in example 1 and comparative examples 1 to 2 were subjected to magnetic property tests, and at least 9 samples (corresponding to 9 points in the furnace) were tested for average values of demagnetization curve tests (room temperature 23.+ -. 2 ℃ C., B r,Hcj,(BH)max,Hk/Hcj), weight loss tests (WH, 120 ℃ C., 100% RH,96 h), thermal demagnetization tests (h irr, 130 ℃ C..times.3 h,1.5mm iron plate) and bending strength (R bb, 15mm in three-point bending span) in each group of tests, and the results are shown in Table 1.
Table 1 results of magnet performance test
The results showed that the regenerated sintered neodymium-iron-boron magnet obtained in example 1 of the present invention was almost equivalent to the magnetic properties index (B r,Hcj and (BH) max) of the new magnet in comparative example 2, in which the coercive force index (H cj) was about 1.8kOe higher than that of the magnet added by the pulverizing method in comparative example 1. The higher the coercivity of the magnet means the stronger the demagnetizing resistance of the magnet, the higher the service temperature of the magnet. It can also be seen from the thermal demagnetization (h irr) data of the magnet that the thermal demagnetization of example 1 of the present invention is only-0.25% under the same experimental conditions of heat preservation at 130 ℃ for 3h, which is equivalent to the nascent magnet of comparative example 2, whereas the regenerated magnet of comparative example 1 has reached-6.82%. When the thermal demagnetization is greater than 5% as specified in the national standard GB/T13560, it has been shown that the magnet cannot be used at this temperature.
When the magnet is used in service, the magnetic reliability is considered first, but the corrosion resistance and the mechanical property are also very important indexes. As can be seen from table 1, the regenerated sintered neodymium-iron-boron magnet prepared in example 1 of the present invention has a flexural strength R bb of 225MPa, which is almost identical to the regenerated magnet of comparative example 2, whereas the regenerated magnet of comparative example 1 is only 186MPa; similarly, the weight loss of the regenerated sintered NdFeB magnet prepared in example 1 of the present invention is only 0.08mg/cm 2, while the regenerated magnet in comparative example 1 reaches 0.27mg/cm 2, which is more than 3 times that of example 1 of the present invention.
< Magnet component and impurity element test >
The chemical composition and impurity element content of the regenerated sintered neodymium-iron-boron magnets prepared in example 1 and comparative examples 1 to 2 were measured using an ICP and C/O/N analyzer, and the results are shown in table 2.
TABLE 2 testing of the compositions and impurity elements of magnets (mass percent,%)
PrNd Tb Al Cu Ga Zr B C O
Example 1 29.66 0.34 0.21 0.23 0.21 0.15 0.899 0.10 0.05
Comparative example 1 29.82 0.31 0.16 0.25 0.21 0.15 0.901 0.18 0.11
Comparative example 2 30.11 0.32 0.15 0.24 0.22 0.15 0.901 0.09 0.04
The results showed that the regenerated sintered neodymium-iron-boron magnet obtained in example 1 of the present invention was very close to the metal element composition of the magnets of comparative examples 1 and 2, but the C and O impurity elements were significantly different. The C content of the present invention was 0.10% (i.e., 1000 ppm), the O content was 0.05% (i.e., 500 ppm), and the level was lower than that of the regenerated magnet of comparative example 1. Because the C and O elements in the magnet are controlled at a lower level, the regenerated sintered NdFeB magnet obtained in the embodiment 1 of the invention is ensured to have higher mechanical properties, because the sintered NdFeB belongs to a brittle material, the magnet starts to fracture along a grain boundary when fracture occurs, and when the grain boundary is doped with more C and O element impurities, the probability of occurrence of stress concentration is increased, so that the strength is reduced. The fracture of the regenerated sintered NdFeB magnet obtained in the embodiment 1 of the invention is shown in fig. 4, and the fracture of the magnet is relatively flush, the grain size is uniform, the fracture morphology has typical crystal-along fracture characteristics, so that the regenerated magnet is ensured to have higher bending strength.
< Test of magnet Performance at different mixing ratios >
The regenerated magnets obtained in example 2 and comparative examples 3 to 4 were subjected to magnetic properties, thermal demagnetization (120 ℃ C. For 2 hours, 1.5mm iron plate), flexural strength (three-point bending, span 15 mm), weight loss properties and impurity element contents, and the test results are shown in Table 3.
TABLE 3 test results for magnets of different mixing ratios
The results showed that the powder process regenerated magnet A of comparative example 3 had a low coercive force Hcj and a large thermal demagnetization, and that the C and O impurity elements in the magnet were numerous, reaching 2500ppm (0.25%) and 1800ppm (0.18%). This is because the regenerated magnet produced by the powder process leaves behind impurities from the previous process, and the re-introduction of impurity elements is unavoidable during regeneration, resulting in poor performance of the magnet. The regenerated sintered NdFeB magnets prepared in the embodiment 2 of the invention have the characteristics of high coercive force, low thermal demagnetization and high bending strength, and under the condition of adding 10% of the new magnet powder, the performances of the regenerated sintered NdFeB magnets are still equivalent to those of the new magnet B in the comparative example 4, and the regenerated sintered NdFeB magnets have good service characteristics.
< Test of magnetic Properties and impurity element content of regenerated magnets produced from sliced samples of different thicknesses >
The regenerated magnets obtained in example 3 and comparative example 5 were subjected to magnetic properties and impurity element content tests, and the test results are shown in table 4.
TABLE 4 magnetic properties and impurity element contents of regenerated magnets
The result shows that the invention is still applicable to the mixed waste magnet with unknown brands, and after the waste magnet is subjected to smelting and throwing, the components of the magnet can be determined on one hand, and C, O and other impurities existing in the waste magnet can be removed on the other hand, so that the alloy purifying effect is achieved. In the embodiment 3, a small amount of new magnet alloy is prepared according to the components of the waste magnet throwing pieces, so that the preparation of the regenerated magnet can be realized. After grain boundary diffusion, the regenerated magnet is provided with a new magnet shell layer, meanwhile, the content of C, O impurity elements in the shell layer is very low, heavy rare earth elements can replace light rare earth elements in a main phase relatively easily, a second shell layer with a higher magnetocrystalline anisotropy field is formed, and the coercive force of the magnet is greatly improved. After the magnet thickness is gradually increased from 1mm to 8mm, the magnet coercivity is only reduced from 9.01 to 8.66, and the reduction range is only about 3.8%, which shows that the regenerated magnet has good grain boundary diffusion characteristics.
Although embodiments of the present invention have been disclosed above, it is not limited to the details and embodiments shown and described, it is well suited to various fields of use for which the invention would be readily apparent to those skilled in the art, and accordingly, the invention is not limited to the specific details and illustrations shown and described herein, without departing from the general concepts defined in the claims and their equivalents.

Claims (8)

1. The regenerated sintered NdFeB magnet is characterized in that the regenerated sintered NdFeB magnet comprises the following components in percentage by mass :RE1 aRE2 bCocCudMeFebalBfCgOh,24≤a≤31,0≤b≤8,0≤c≤5,0≤d≤0.8,0≤e≤3,0.85≤f≤1.2,28.5≤a+b≤35,0<g≤0.15,0<h≤0.10,bal as the rest; wherein RE 1 is one or a combination of a plurality of Pr, nd, la, ce, Y, RE 2 is one or a combination of a plurality of heavy rare earth Gd, ho, dy, tb, M is one or a combination of a plurality of Al, cr, nb, zr, ga, ti, zn, V, mo, mn, and the microstructure of the regenerated sintered NdFeB magnet consists of a grain boundary phase and two main phases;
The first main phase has a double-shell structure, and comprises a first core, a first shell a and a first shell b from inside to outside, wherein the first core is formed by a neodymium-iron-boron waste magnet, the first shell a is formed by a new-born magnet alloy powder particle after being swallowed by the neodymium-iron-boron waste magnet alloy powder particle when being sintered at a high temperature, and the first shell b is a heavy rare earth shell formed by grain boundary diffusion;
The second main phase has a single-shell structure, and is provided with a second core and a second shell from inside to outside, wherein the second core is a new-born magnet, the second shell is a heavy rare earth shell formed after grain boundary diffusion, the second shell has the same components as the first shell b, and the new-born magnet has the same components as the neodymium-iron-boron waste magnet.
2. The regenerated sintered neodymium-iron-boron magnet according to claim 1, wherein the volume fraction of the first main phase is 90-99% of the sum of the volume fractions of the two main phases, wherein the content of C element and the content of O element in the first core are higher than the content of C element and the content of O element in the first shell layer a, and the difference between the content of C element and the content of O element in the first shell layer a and the content of O element in the first shell layer b is less than or equal to 50ppm.
3. The regenerated sintered neodymium-iron-boron magnet according to claim 2, wherein the C element content of the first core is 50-200 ppm higher than the C element content of the first shell layer a, and the o element content is 150-400 ppm higher.
4. The regenerated sintered neodymium-iron-boron magnet according to claim 2, wherein the difference between the content of C element and the content of O element in the second core and the content of C element and the content of O element in the second shell is less than or equal to 50ppm.
5. The method for producing a regenerated sintered neodymium-iron-boron magnet according to any one of claims 1 to 4, comprising the steps of:
Demagnetizing, cleaning and drying the neodymium iron boron waste magnet, and then smelting and throwing the alloy throwing piece, wherein the smelting and casting temperature is 1400-1500 ℃, the content of C element in the alloy throwing piece is less than or equal to 400ppm, the content of O element in the alloy throwing piece is less than or equal to 500ppm, the average thickness of the alloy throwing piece is 0.25-0.50 mm, and the average size of columnar crystals of the alloy throwing piece is 3.5-5.5 mu m;
Step two, carrying out hydrogen crushing on the alloy throwing piece obtained in the step one to obtain hydrogen crushing powder with the granularity of 500-1000 mu m and the H element content less than or equal to 1500ppm, and grinding the hydrogen crushing powder to obtain waste magnet alloy powder with the average granularity of 4.0-5.5 mu m;
Mixing the waste magnet alloy powder obtained in the step two with new magnet alloy powder with the same components as the neodymium-iron-boron waste magnet, wherein the mixing ratio of the new magnet alloy powder and the new magnet alloy powder is 99:1-50:50, the granularity of the new magnet alloy powder is 0.5-3.9 mu m, 0.05-0.2% of lubricant is added during mixing, the carbon content of the mixed powder is 600-950 ppm, the mixed powder is subjected to magnetic field forming and isostatic pressing to obtain a pressed compact, and the pressed compact is subjected to hot sintering treatment and cooling to obtain a sintered magnet;
And fourthly, slicing the sintered magnet obtained in the third step, decontaminating the surface, wherein the thickness of the slice is 1-8 mm, uniformly coating slurry containing heavy rare earth elements on the surface of the slice, carrying out heat treatment after the coated slurry is air-dried, wherein the primary heat treatment temperature is 800-950 ℃, the heat preservation time is 8-40 h, the secondary heat treatment temperature is 450-650 ℃, the heat preservation time is 4-8 h, and after the heat preservation is finished, filling argon gas and cooling, and discharging from the furnace after cooling to 70 ℃ to obtain the regenerated sintered neodymium-iron-boron magnet.
6. The method for preparing a regenerated sintered neodymium-iron-boron magnet according to claim 5, wherein the specific hydrogen crushing process in the second step is as follows: loading the alloy throwing piece into a hydrogen crushing furnace, vacuumizing to below 10Pa, heating to 350-500 ℃ for activation for 1.5-3 h, stopping heating when the vacuum degree is reduced to below 10Pa again, charging hydrogen to 0.1-0.2 MPa to enable the alloy throwing piece to fully absorb hydrogen, stopping charging hydrogen after the hydrogen absorption is saturated, vacuumizing and heating to 450-570 ℃ for dehydrogenation for 2-5 h, and cooling to normal temperature.
7. The method for preparing a regenerated sintered neodymium-iron-boron magnet according to claim 5, wherein the specific process of grinding the hydrogen-broken powder in the second step is as follows: adding about 0.05-0.15% of lubricant into the hydrogen broken powder, fully and uniformly mixing, grinding by using an air flow grinding device to prepare powder, wherein the grinding pressure is 0.35-0.65 MPa, and supplementing oxygen to reduce the powder activity during grinding, the oxygen supplementing amount is 30-50 ppm, and the rotating speed of a grading wheel of the air flow grinding device is 2000-5000 r/min.
8. The method for preparing a regenerated sintered neodymium-iron-boron magnet according to claim 5, wherein the specific process of magnetic field forming, isostatic pressing and thermal sintering treatment in the third step is as follows: placing the mixed powder into a die of a fully-sealed molding press, controlling the oxygen content in the press to be 100-500 ppm, orienting and pressing the powder into a molding under an orientation magnetic field with the magnetic field strength of 1.4-2.0T, placing the powder into an isostatic press for further densification, and setting the isostatic pressure to be 180-250 MPa to obtain a pressed compact, placing the pressed compact into a vacuum sintering furnace with the temperature of 1000-1060 ℃ for sintering for 2-10 h, and quenching the pressed compact to room temperature by inert gas to obtain the sintered state magnet.
CN202410282052.6A 2024-03-12 2024-03-12 Regenerated sintered NdFeB magnet and preparation method thereof Pending CN118155968A (en)

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