CN117542645A - Method for improving magnetic performance of rare earth permanent magnet - Google Patents

Method for improving magnetic performance of rare earth permanent magnet Download PDF

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Publication number
CN117542645A
CN117542645A CN202311567485.8A CN202311567485A CN117542645A CN 117542645 A CN117542645 A CN 117542645A CN 202311567485 A CN202311567485 A CN 202311567485A CN 117542645 A CN117542645 A CN 117542645A
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China
Prior art keywords
rare earth
permanent magnet
heavy rare
electroplating
earth permanent
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Inventor
周巧英
范璐
陈仁杰
郭帅
闫阿儒
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Ningbo Institute of Material Technology and Engineering of CAS
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Ningbo Institute of Material Technology and Engineering of CAS
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Priority to CN202311567485.8A priority Critical patent/CN117542645A/en
Publication of CN117542645A publication Critical patent/CN117542645A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus 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
    • H01F41/02—Apparatus 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
    • H01F41/0253—Apparatus 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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D7/00—Electroplating characterised by the article coated
    • C25D7/001—Magnets
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets 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
    • H01F1/04—Magnets 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
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus 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
    • H01F41/02—Apparatus 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
    • H01F41/0253—Apparatus 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
    • H01F41/0293—Apparatus 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)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing Cores, Coils, And Magnets (AREA)

Abstract

The invention discloses a method for improving the magnetic performance of a rare earth permanent magnet. The method comprises the following steps: placing the rare earth permanent magnet in an electrolyte molten salt system containing heavy rare earth salt, and electrifying to perform electroplating to obtain the rare earth permanent magnet with the surface covered with the heavy rare earth plating layer; and carrying out grain boundary diffusion and tempering treatment on the rare earth permanent magnet with the surface covered with the heavy rare earth plating layer, so that the magnetic performance of the rare earth permanent magnet is improved. The invention provides a method for electroplating a heavy rare earth coating on the surface of a sintered neodymium iron boron matrix in a room temperature molten salt system, and further realizes improvement of the magnetic property of a neodymium iron boron magnet by a heat treatment diffusion technology.

Description

Method for improving magnetic performance of rare earth permanent magnet
Technical Field
The invention belongs to the technical field of surface treatment of rare earth permanent magnet materials, and relates to a method for improving the magnetic performance of a rare earth permanent magnet.
Background
The sintered NdFeB permanent magnet material has super strong magnetic property and is widely applied to the fields of automobiles, wind power generation, medical treatment, traffic, communication and the like. However, when the neodymium-iron-boron magnet is in service for a long time under the high temperature condition, the magnetic property of the neodymium-iron-boron magnet is greatly reduced due to thermal demagnetization, the stability and the reliability of a magnetic device are reduced, and the service life of the magnetic device is seriously influenced, so that the application environment and the field of the neodymium-iron-boron magnet device are limited. Therefore, the sintered NdFeB greatly improves the coercive force of the magnet by adding heavy rare earth elements Dy and Tb in the preparation process of the material so as to meet the requirements of practical application. At present, most of industrial production adopts a surface coating and grain boundary diffusion process, namely, an alloy powder or compound coating of a small amount of heavy rare earth elements such as Dy, tb and the like is attached to the surface of a neodymium-iron-boron substrate, and then proper heat treatment is carried out to greatly improve the coercive force of the neodymium-iron-boron magnet.
At present, the method for attaching heavy rare earth elements to the surface of a neodymium iron boron matrix comprises the following steps: spray coating, dipping, physical vapor deposition and electroplating. Wherein, the spraying method has short operation flow, simple working procedures and wider application. However, the method has serious waste of heavy rare earth in the preparation process, and is generally suitable for workpieces with larger surface areas. The dipping method is to dip the magnet into the mixture of heavy rare earth compound and ethanol solution to obtain the heavy rare earth coating with uneven thickness and difficult regulation. The physical vapor deposition method can control the thickness of the plating layer by adjusting the deposition time, but has low working efficiency and expensive equipment, and can cause serious waste of raw materials in the deposition process. Electroplating technology is mature in industrial production, equipment and process are simple, and cost is low. However, rare earth elements are hardly prepared by electroplating due to the strong chemical activity thereof, which is affected by hydrogen precipitation in an aqueous solution or an acidic system. Meanwhile, the surface of the alloy material prepared by powder metallurgy such as neodymium iron boron is provided with a large number of pores, so that hydrogen in the solution can be easily adsorbed; the rare earth neodymium and the like on the surface of the magnet react with water and acid severely, which easily causes the corrosion of the matrix, thereby reducing the magnetic performance.
Therefore, how to find a more suitable way to solve the above technical problems existing in the electroplating process of the rare earth permanent magnet surface and to use the rare earth permanent magnet surface in the subsequent grain boundary diffusion process has become one of the focuses of many first-line researchers in the industry.
Disclosure of Invention
The invention mainly aims to provide a method for improving the magnetic performance of a rare earth permanent magnet, thereby overcoming the defects in the prior art.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
the embodiment of the invention provides a method for improving the magnetic performance of a rare earth permanent magnet, which comprises the following steps:
placing the rare earth permanent magnet in an electrolyte molten salt system containing heavy rare earth salt, and electrifying to perform electroplating to obtain the rare earth permanent magnet with the surface covered with the heavy rare earth plating layer;
and carrying out grain boundary diffusion and tempering treatment on the rare earth permanent magnet with the surface covered with the heavy rare earth plating layer, so that the magnetic performance of the rare earth permanent magnet is improved.
In some preferred embodiments, the heavy rare earth salt-containing electrolyte molten salt system further comprises a metal salt and/or an additive.
In some preferred embodiments, the potential of the plating is-0.1 to-3V.
In some preferred embodiments, the temperature of the grain boundary diffusion is 600 to 1000 ℃ and the time of the grain boundary diffusion is 4 to 10 hours.
In some preferred embodiments, the tempering treatment is performed at a temperature of 300 to 500 ℃ for a time of 2 to 6 hours.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method for electroplating a heavy rare earth coating on the surface of a sintered neodymium iron boron matrix in a room temperature molten salt system, and further realizes improvement of the magnetic property of a neodymium iron boron magnet by a heat treatment diffusion technology.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a cross-sectional thickness test chart of a heavy rare earth coating prepared in example 2 of the present invention;
FIG. 2 is a graph showing the bonding force test of the heavy rare earth plating layer prepared in example 2 of the present invention;
FIG. 3 is a surface topography of a heavy rare earth coating prepared in example 6 of the present invention;
FIG. 4 is a cross-sectional thickness test chart of the heavy rare earth coating prepared in example 6 of the present invention;
fig. 5 is a graph showing demagnetization of the heavy rare earth plating layers prepared in example 2 and example 6 according to the present invention after the diffusion treatment of the magnet grain boundaries.
Detailed Description
In view of the shortcomings in the prior art, the inventor of the present invention has long studied and practiced in a large number of ways to propose the technical scheme of the present invention. The invention aims to provide a method for improving the magnetic performance of a rare earth permanent magnet, in particular to a method for improving the magnetic performance of a neodymium-iron-boron magnet by electroplating a heavy rare earth coating on the surface of a sintered neodymium-iron-boron matrix in a room temperature molten salt system and further adopting a heat treatment diffusion technology.
For further understanding of the present invention, the technical scheme, its implementation process and principle, etc. will be further explained as follows. It should be understood that the description is only intended to further illustrate the features and advantages of the invention, and not to limit the invention to the claims.
Another aspect of the embodiment of the present invention provides a method for improving magnetic properties of a rare earth permanent magnet, including:
placing the rare earth permanent magnet in an electrolyte molten salt system containing heavy rare earth salt, and electrifying to perform electroplating to obtain the rare earth permanent magnet with the surface covered with the heavy rare earth plating layer;
and carrying out grain boundary diffusion and tempering treatment on the rare earth permanent magnet with the surface covered with the heavy rare earth plating layer, so that the magnetic performance of the rare earth permanent magnet is improved.
In some preferred embodiments of the present invention, the rare earth permanent magnet preferably comprises a sintered rare earth permanent magnet, wherein the rare earth permanent magnet has the general formula RE-Fe-B, wherein RE comprises any one or a combination of two or more of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, yttrium, and the like, more preferably lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, or yttrium, but is not limited thereto.
In the present invention, the rare earth permanent magnet may be a sintered blank of the rare earth permanent magnet.
In some embodiments, the rare earth permanent magnet includes a neodymium-based rare earth permanent magnet, and in particular, the neodymium-based rare earth permanent magnet may include any one or a combination of two or more of neodymium-iron-boron, neodymium-cerium-iron-boron, neodymium-yttrium-iron-boron, and the like, but is not limited thereto.
In the invention, the rare earth permanent magnet preferably comprises a sintered rare earth permanent magnet obtained by one or more steps of smelting, rapid hardening, crushing, hydrogen crushing and oriented compression molding of raw material powder and sintering.
In some embodiments, the electroplating process employs a three-electrode system or a two-electrode system, preferably a three-electrode system. Specifically, the electroplating method adopts a three-electrode system, the sintered rare earth permanent magnet is preferably used as a working electrode, and more preferably, the method comprises multiple steps of smelting, casting, crushing, hydrogen crushing and orientation press forming.
In some embodiments, the electrolyte molten salt system is used as an electrolyte, the rare earth permanent magnet is used as a working electrode, and a counter electrode is used to be arranged parallel to the surface of the rare earth permanent magnet.
In the present invention, the counter electrode is preferably disposed parallel to the rare earth permanent magnet surface. Specifically, the two counter electrodes are respectively parallel to the opposite two surfaces of the heavy rare earth composite coating to be plated of the sintered rare earth permanent magnet, and the electrodes are preferably arranged opposite to the heavy rare earth composite coating to be plated.
In some preferred embodiments of the invention, the plating employs more than two counter electrodes, preferably two counter electrodes.
In some preferred embodiments of the invention, the method further comprises: the rare earth permanent magnet is pretreated and then placed in an electrolyte molten salt system containing heavy rare earth salt.
In the present invention, the pretreatment preferably includes any one or a combination of two or more of acid washing, organic solution washing, electrochemical activation, deionized water washing, ultrasonic washing, and the like, more preferably acid washing, organic solution washing, electrochemical activation, deionized water washing, or ultrasonic washing. Alternatively, the pretreatment may include any one or a combination of two or more of polishing, electropolishing, acid washing, alkali washing, oil removal, deionized water washing, and absolute ethanol ultrasonic washing, but is not limited thereto.
Among these, as a more preferable aspect of the present application, a method for improving magnetic properties of a rare earth permanent magnet includes the steps of:
1) Placing the pretreated rare earth permanent magnet into an electrolyte molten salt solution containing heavy rare earth salt, and electrifying to perform electroplating to obtain the rare earth permanent magnet with the surface covered with the heavy rare earth composite coating;
the electroplating is an electroplating method adopting an electrolyte molten salt system containing heavy rare earth elements;
two or more counter electrodes are adopted in the electroplating method;
2) And carrying out grain boundary diffusion and tempering treatment on the rare earth permanent magnet with the surface covered with the heavy rare earth composite coating.
In some preferred embodiments of the present invention, the electrolyte molten salt system preferably comprises: one or more of 1-ethyl-3-methylimidazole tetrafluoroborate, trimethyl phosphate and 1-butyl-1-methylpyrrolidine triflate, more preferably 1-ethyl-3-methylimidazole tetrafluoroborate, trimethyl phosphate or 1-butyl-1-methylpyrrolidine triflate.
In some preferred embodiments of the present invention, the electroplating process may be performed directly at room temperature without heating, and the electrolyte molten salt solution containing the heavy rare earth salt is in a liquid state at room temperature. Specifically, the room temperature may be 10 to 40 ℃, more preferably 15 to 35 ℃, and still more preferably 20 to 30 ℃.
In the invention, the electrolyte molten salt is in a liquid molten state at room temperature, and does not need to be melted, and the electroplating process is used for adjusting the temperature, so that the conductivity of the electrolyte molten salt system is improved, the solubility of heavy rare earth salt in the system is improved, and the electrochemical reaction rate is accelerated.
In the present invention, the heavy rare earth salt and the solvent are preferably included in the electrolyte molten salt solution containing the heavy rare earth salt.
In the present invention, the heavy rare earth salt preferably includes a heavy rare earth element-containing chloride, a heavy rare earth element-containing fluoroborate, and a heavy rare earth element-containing trifluoromethanesulfonate (e.g., dy (OTf) 3 ) Any one or a combination of two or more of these, and more preferably chloride, fluoroborate or triflate, but not limited thereto.
In the present invention, the solvent preferably includes a commercial room temperature electrolyte molten salt, preferably includes any one or a combination of two or more of 1-ethyl-3-methylimidazolium tetrafluoroborate, trimethyl phosphate, 1-butyl-1-methylpyrrolidine triflate, etc., more preferably 1-ethyl-3-methylimidazolium tetrafluoroborate, trimethyl phosphate, or 1-butyl-1-methylpyrrolidine triflate, but is not limited thereto.
In some preferred embodiments of the present invention, the concentration of the heavy rare earth salt in the heavy rare earth salt-containing electrolyte molten salt system is 0.1 to 10.0mol/L, preferably 0.1 to 5.0mol/L, more preferably 0.1 to 2.0mol/L.
In some preferred embodiments of the present invention, the heavy rare earth elements contained in the heavy rare earth salt-containing electrolyte molten salt system include Dy and/or Tb, more preferably Dy or Tb.
In some preferred embodiments of the present invention, a metal salt and/or an additive, more preferably a metal salt or an additive, is also preferably included in the heavy rare earth salt-containing electrolyte molten salt system. Namely, the electroplating method can adopt an electrolyte molten salt system containing both heavy rare earth elements and metal elements to obtain the heavy rare earth composite plating layer containing the heavy rare earth elements and the metal elements.
In the present invention, the metal salt preferably includes a chloride containing a metal element, a fluoroborate containing a metal element, and a trifluoromethane sulfonate containing a metal element (e.g., cu (OTf) 2 ) Any one or a combination of two or more of these, and more preferably chloride, fluoroborate or triflate, but not limited thereto.
In the present invention, the metal element contained in the metal salt includes any one or a combination of two or more of Ti, cr, cu, al, pr, nd, ga, ni, zr, nb, hf, W and V, etc., but is not limited thereto.
In the invention, the concentration of the metal salt in the electrolyte molten salt system containing the heavy rare earth salt is 0.01-0.5 mol/L.
Further, the additive includes an alcohol additive and/or lithium chloride.
In the present invention, the additive is preferably any one or a combination of two or more of absolute ethanol, ethylene glycol, lithium chloride, and the like, and more preferably absolute ethanol, ethylene glycol, or lithium chloride. Specifically, the volume ratio of the alcohol additive in the whole electrolyte solution can be 10% -50%, and the concentration of lithium chloride can be 0.05-1.0 mol/L. Wherein, the additive has the following functions: the solubility of the heavy rare earth salt in a room temperature electrolyte molten salt system is improved, the concentration of heavy rare earth ions is improved, the stability of a solution system is improved, and additives can be adopted or not adopted.
Further, the concentration of lithium chloride in the electrolyte molten salt system containing the heavy rare earth salt is 0.05-1.0 mol/L.
Further, the volume ratio of the alcohol additive in the electrolyte molten salt system containing the heavy rare earth salt is 10-50%.
In some preferred embodiments of the present invention, the plating method preferably includes any one of direct current constant potential plating, alternating current plating or pulse plating, and the electrochemical parameter of the plating may be a constant voltage or constant current mode.
In the present invention, the potential of the plating is in the range of-0.1 to-3V, preferably-0.5 to-2.5V, and more preferably-1 to-2V.
In the present invention, the plating is performed at a temperature of 20 to 80 ℃, preferably 20 to 70 ℃, more preferably 20 to 40 ℃, and particularly at room temperature.
In the present invention, the duration of the plating process is 0.5 to 20 hours, preferably 3 to 18 hours, more preferably 5 to 15 hours, and particularly may be 5 hours.
In the present invention, the oxygen content in the plating process is controlled to be 0 to 50ppm, preferably 10 to 40ppm, more preferably 20 to 30ppm. In particular, the electroplating process of the invention has no oxygen better, but the existence of a small amount of oxygen has no obvious influence on experiments.
In the present invention, the water content in the plating process is controlled to be 10 to 100ppm, preferably 30 to 80ppm, more preferably 50 to 60ppm.
In some preferred embodiments of the invention, the heavy rare earth coating has a thickness of 100nm to 50. Mu.m, preferably 900nm to 30. Mu.m, more preferably 2 μm to 11. Mu.m, particularly preferably 3 μm to 8. Mu.m.
In the present invention, the heavy rare earth plating layer preferably includes a heavy rare earth element, or a heavy rare earth element and a metal element (i.e., a heavy rare earth composite plating layer).
In the present invention, the heavy rare earth element preferably includes Dy and/or Tb, more preferably Dy or Tb.
In the present invention, the metal element preferably includes one or more of Ti, cr, cu, al, pr, nd, ga, zr, nb, hf, W and V, more preferably Ti, cr, cu, al, pr, nd, ga, zr, nb, hf, W or V.
In some preferred embodiments of the invention, the temperature of the grain boundary diffusion is 600 to 1000 ℃, preferably 650 to 950 ℃, more preferably 700 to 900 ℃, more preferably 750 to 850 ℃.
In the present invention, the time for the grain boundary diffusion is preferably 4 to 10 hours, more preferably 5 to 9 hours, and still more preferably 6 to 8 hours.
In the present invention, the tempering treatment is performed at a temperature of 300 to 500 ℃, preferably 350 to 450 ℃.
In the present invention, the tempering treatment is performed for 2 to 6 hours, preferably 4 to 5 hours.
The invention relates to a complete and refined whole technical scheme, which better improves the electroplating effect, further improves the uniformity and the density of a heavy rare earth coating on the surface of a rare earth permanent magnet, and a method for improving the magnetic performance of the magnet comprises the following steps:
pre-treating the surface of the sintered NdFeB magnet before electroplating;
electroplating the sintered NdFeB matrix to obtain a sintered NdFeB magnet attached with a heavy rare earth element plating layer;
and carrying out heat treatment and grain boundary diffusion process treatment on the magnet attached with the heavy rare earth element coating to obtain the high-coercivity neodymium-iron-boron magnet.
Specifically, the pretreatment of the surface of the magnet comprises the following steps: polishing, electropolishing, acid cleaning, alkali cleaning, oil removing, deionized water cleaning and absolute ethyl alcohol ultrasonic cleaning.
Specifically, the electroplating process comprises the following steps: the three-electrode system based on the electrochemical workstation, wherein the electroplating mode can be one of direct current constant potential electroplating, alternating current electroplating and pulse electroplating, and the electrochemical parameters of electroplating can be constant voltage and constant current modes.
Specifically, the heavy rare earth salt comprises: one or more of Dy, tb chloride, fluoroborate and triflate, and the concentration in the room temperature molten salt system is as follows: 0.1mol/L to 10.0mol/L.
Specifically, the room temperature molten salt system additive comprises: ti, cr, cu, al, pr, nd, ga, ni, zr, nb, hf, W and V, and the concentration is 0.01-0.5 mol/L, and the heavy rare earth salt can be used for assisting the dissolution of the heavy rare earth salt or promoting the electroplating of the heavy rare earth, and can be non-rare earth metal inorganic salt.
The matrix in the invention can be a neodymium-based rare earth permanent magnet (such as neodymium-iron-boron, neodymium-cerium-iron-boron, neodymium-yttrium-iron-boron and the like). Firstly, the surface of a magnet is pretreated by adopting a specific solution system: and finally, carrying out post-treatment cleaning on the plating layer, thereby obtaining the plating layer with controllable thickness, in particular being capable of preparing the plating layer with thin thickness, and the plating layer has higher compactness and binding force, and simultaneously the heavy rare earth content in the plating layer is controllable.
The invention provides a method for improving the magnetic performance of a rare earth permanent magnet, which is based on electroplating a heavy rare earth coating on the surface of a sintered NdFeB matrix in a room temperature molten salt system, and further realizes the improvement of the magnetic performance of the NdFeB magnet by a heat treatment diffusion technology. The method has simple preparation process, is green and environment-friendly, can prepare the heavy rare earth plating layer with controllable thickness and better binding force on the magnet piece with complex shape, and has remarkable industrialized application prospect.
The method utilizes the electroplating method to co-deposit the heavy rare earth and the non-rare earth alloy on the surface of the sintered neodymium-iron-boron magnet, can reduce the melting point of the heavy rare earth compound, improve the diffusion depth of the heavy rare earth element, improve the coercive force of the magnet, can effectively regulate and control the thickness and uniformity of the heavy rare earth plating layer in the electroplating process, can recycle the heavy rare earth salt dissolved in a room-temperature molten salt system, reduces the waste of heavy rare earth resources, is not limited by the volume and the shape of the sintered neodymium-iron-boron magnet in the preparation process, and can obtain the heavy rare earth plating layer with excellent morphology and binding force.
The method for electroplating the heavy rare earth composite plating layer on the surface of the rare earth permanent magnet can electroplate rare earth elements on the surface of neodymium iron boron, and the electroplating solution system is uniform and reusable, has stable electroplating process, is not volatilized and has no corrosion to a matrix. The method can reduce the rare earth element with larger negative potential at room temperature, can electroplate the rare earth element on the surface of the sintered neodymium-iron-boron, has high chemical stability in the electroplating process, can reduce the rare earth element with larger negative potential at room temperature, has no corrosion to a matrix, and can plate the surface of the sintered neodymium-iron-boron magnet with complex shape; the electroplating solution system uses room temperature molten salt as electrolyte, the system is stable, the solution is not volatilized, the environment is protected, the electroplating solution can be reused, and the waste of rare earth resources caused by the traditional coating method is avoided.
The invention provides a method for preparing a heavy rare earth composite coating on the surface of a sintered NdFeB magnet, which comprises the steps of surface pretreatment of the magnet, solution system composition and coating preparation process. The used room temperature molten salt is composed of organic cations and inorganic or organic anions, is insensitive to water and environment, has high chemical stability and does not directly react with the neodymium-iron-boron magnet. The method provided by the invention has the advantages of simple process equipment and low cost, and can prepare the heavy rare earth composite coating with controllable thickness and good binding force on the complex finished product, and the magnetic properties of the electroplated neodymium-iron-boron magnet are increased to different degrees through heat treatment.
In summary, the invention provides a method for electroplating a heavy rare earth coating on the surface of a sintered neodymium-iron-boron matrix in a room temperature molten salt system, and further improving the magnetic performance of the neodymium-iron-boron magnet by a heat treatment diffusion technology. The method has simple preparation process, is green and environment-friendly, can prepare the heavy rare earth plating layer with controllable thickness and better binding force on the magnet piece with complex shape, and has remarkable industrialized application prospect.
For further explanation of the present invention, the application of the plating method provided by the present invention to plating heavy rare earth composite coating on the surface of rare earth permanent magnet and a method for plating heavy rare earth composite coating on the surface of rare earth permanent magnet will be described in detail with reference to the following examples, but it should be understood that these examples are implemented on the premise of the technical scheme of the present invention, and detailed implementation and specific operation procedures are given only for further explanation of the features and advantages of the present invention, and not for limitation of the claims of the present invention, and the scope of protection of the present invention is not limited to the following examples.
All the raw materials of the present invention are not particularly limited in their sources, and may be purchased on the market or prepared according to conventional methods well known to those skilled in the art.
All the raw materials of the invention are not particularly limited in purity, and the invention preferably adopts the conventional purity used in the field of preparing the surface plating layer of the industrial pure or neodymium-iron-boron magnet.
All raw materials of the invention, the brands and abbreviations of which belong to the conventional brands and abbreviations in the field of the related application are clear and definite, and the person skilled in the art can purchase from the market or prepare by the conventional method according to the brands, abbreviations and the corresponding application.
All processes and equipment of the present invention are well known in the art, and each is well known and understood in the art for its associated use, and from the names, one skilled in the art can understand the steps of the process and the corresponding equipment used.
Example 1
(1) Pretreatment of sintered NdFeB magnet surfaces
Commercial magnets with the brand number of N48 are washed with nitric acid and deionized water for two times by using an ultrasonic cleaner according to the volume ratio of 1:15-1:28, and then are dried after being washed by absolute ethyl alcohol.
(2) Electroplating process
The three-electrode system based on an electrochemical workstation is used, and the three-electrode system is performed in a direct-current constant-potential electroplating mode. The counter electrode is a platinum sheet electrode with the thickness of 20mm multiplied by 20mm and the thickness of 1mm, the reference electrode is an Ag/AgCl electrode with a salt bridge, the sintered NdFeB is a working electrode, and the surface is directly electroplated. The electrolyte is a triflate system based on a 1-ethyl-3-methylimidazole tetrafluoroborate solvent, 0.15mol/LDy (OTf) is added to 50mLTMP 3 And 0.03mol/LCu (OTf) 2 And 1mL of 1-butyl-1-methylpyrrolidinone triflate, and stirring the mixture by using a magnetic stirrer until the mixture is completely dissolved. The electroplating potential is-1.5V, the temperature during electroplating is room temperature, and the electroplating time is 3h. All the above experiments were performed in an argon filled acrylic glove box (controlling oxygen content below 50ppm and placing a desiccant to control water content).
(3) Grain boundary diffusion process
Washing the electroplated magnet with absolute ethyl alcohol, drying, and putting into a vacuum high-temperature sintering furnace to perform diffusion at 600 ℃ for 8h and tempering heat treatment at 300 ℃ for 2h under the condition of not contacting oxygen.
(4) Plating and magnet performance detection
The thickness and binding force of the plating layer obtained after electroplating are detected, and the magnetic performance and corrosion resistance of the neodymium-iron-boron magnet after diffusion are detected, and the test results are shown in table 1.
Example 2
The electrolyte solvent was replaced with TMP (trimethyl phosphate) in example 1, and the other conditions were unchanged. The thickness and binding force of the plating layer obtained after electroplating are detected, see fig. 1 and 2, and the magnetic performance and corrosion resistance of the neodymium-iron-boron magnet after diffusion are detected, and the test results are shown in table 1. The demagnetizing curve chart after the grain boundary diffusion treatment of the heavy rare earth plating magnet is shown in fig. 5.
Example 3
The counter electrode in example 2 was replaced with two platinum sheet electrodes, the counter electrode was disposed parallel to the surface of the rare earth permanent magnet, the thickness and area of the electrode were unchanged, and the added solute content was changed to 0.3mol/L Dy (OTf) 3 And 0.05mol/L Cu (OTf) 2 The plating potential is-1.8V, the plating time is 5 hours, the magnet after plating is put into a vacuum high-temperature sintering furnace to be subjected to diffusion at 900 ℃ for 8 hours and tempering heat treatment at 500 ℃ for 4 hours, the corrosion resistance of the plating layer and the magnet is detected as in example 1, and the test results are shown in table 1.
Example 4
The solute content added in example 3 was changed to 0.5mol/L Dy (OTf) 3 And 0.1mol/L Cu (OTf) 2 Other conditions are unchanged, and the magnet after electroplating is put into a vacuum high-temperature sintering furnace to be carried out at 900 ℃ for 8hDiffusion and tempering heat treatment at 500 ℃ for 6 hours. The corrosion resistance of the plating and the magnet is detected as in example 1, and the test results are shown in Table 1.
Example 5
The plating time in example 4 was prolonged to 10 hours, and the magnet after plating was put into a vacuum high-temperature sintering furnace to be subjected to diffusion at 1000 ℃ for 5 hours and tempering heat treatment at 400 ℃ for 6 hours. The corrosion resistance of the plating and the magnet is detected as in example 1, and the test results are shown in Table 1.
Example 6
The solute content added in example 5 was changed to lmol/L Dy (OTf) 3 And 0.2mol/L Cu (OTf) 2 The electroplating potential is-2V, the electroplating time is 10 hours, other conditions are unchanged, and the magnet after electroplating is put into a vacuum high-temperature sintering furnace to be subjected to diffusion at 850 ℃ for 10 hours and tempering heat treatment at 500 ℃ for 4 hours. The corrosion resistance of the plating and the magnet is detected as in example 1, and the test results are shown in Table 1. The surface morphology graph of the heavy rare earth plating layer is shown in fig. 3, and the cross section thickness test graph of the plating layer is shown in fig. 4. The demagnetizing curve chart after the grain boundary diffusion treatment of the heavy rare earth plating magnet is shown in fig. 5.
Example 7
The plating time in example 6 was prolonged to 15 hours, and the magnet after plating was put into a vacuum high-temperature sintering furnace to be subjected to diffusion at 850 ℃ for 10 hours and tempering heat treatment at 500 ℃ for 6 hours. The corrosion resistance of the plating and the magnet is detected as in example 1, and the test results are shown in Table 1.
Example 8
The solute content added in example 7 was changed to 2mol/L Dy (OTf) 3 And 0.5mol/L Cu (OTf) 2 The electroplating potential is-3V, the electroplating time is 18h, other conditions are unchanged, and the magnet after electroplating is put into a vacuum high-temperature sintering furnace to be subjected to diffusion at 900 ℃ for 8h and tempering heat treatment at 500 ℃ for 6h. The corrosion resistance of the plating and the magnet is detected as in example 1, and the test results are shown in Table 1.
Example 9
The electrolyte solvent was changed to 1-butyl-1-methylpyrrolidine triflate in example 7, with the other conditions unchanged. The thickness and binding force of the plating layer obtained after electroplating are detected, and the magnetic performance and corrosion resistance of the neodymium-iron-boron magnet after diffusion are detected, and the test results are shown in table 1.
Example 10
The solute content added in example 2 was changed to 0.1mol/L Dy (OTf) 3 And 0.01mol/L Cu (OTf) 2 The electroplating potential is-0.1V, the electroplating time is 0.5h, the magnet after electroplating is put into a vacuum high-temperature sintering furnace to be subjected to 950 ℃ multiplied by 4h diffusion and 450 ℃ multiplied by 5h tempering heat treatment, the corrosion resistance of the plating layer and the magnet is detected as in example 1, and the test results are shown in table 1.
Example 11
The solute content added in example 2 was changed to 10.0mol/L Dy (OTf) 3 And 0.2mol/L Cu (OTf) 2 The plating potential is-2.5V, the plating time is 20h, the magnet after plating is put into a vacuum high-temperature sintering furnace to be subjected to 650 ℃ multiplied by 6h diffusion and 350 ℃ multiplied by 6h tempering heat treatment, the corrosion resistance of the plating layer and the magnet is detected as in example 1, and the test results are shown in table 1.
Comparative example 1
This comparative example differs from example 5 in that: TMP (trimethyl phosphate) was changed to an aqueous solution as a solvent, and the other conditions were unchanged. The electroplating process solution has a large amount of bubbles, the surface of the magnet is severely corroded, magnet particles fall off, and Dy and Cu elements are not reduced. The magnetic properties and corrosion resistance of the magnet after deposition were measured as in example 1, and the test results are shown in table 1.
Comparative example 2
This comparative example differs from example 6 in that: the deposition potential was 2V. Other conditions were unchanged. The electroplating process reacts vigorously, the solution system becomes reddish brown rapidly, a large number of bubbles are generated, large magnet particles fall off, and Dy and Cu elements are not reduced. The magnetic properties and corrosion resistance of the magnet after deposition were measured as in example 1, and the test results are shown in table 1.
Comparative example 3
This comparative example differs from example 7 in that: the deposited magnet did not undergo grain boundary diffusion, and other conditions were unchanged. The thickness and binding force of the plating layer obtained after electroplating are detected, and the magnetic performance and corrosion resistance of the neodymium-iron-boron magnet after diffusion are detected, and the test results are shown in table 1.
Comparative example 4
This comparative example differs from example 8 in that: the difference is that: after the diffusion of the grain boundary, the magnet is not tempered, and other conditions are unchanged. The thickness and binding force of the plating layer obtained after electroplating are detected, and the magnetic performance and corrosion resistance of the neodymium-iron-boron magnet after diffusion are detected, and the test results are shown in table 1.
TABLE 1 detection of Corrosion resistance of coatings and magnets in the examples above
In addition, the inventors have conducted experiments with other materials, process operations, and process conditions as described in this specification with reference to the foregoing examples, and have all obtained desirable results.
While the foregoing has described in some detail the principles and embodiments of the present invention with specific examples provided herein, the foregoing examples are provided to aid in the understanding of the principles and embodiments of the present invention, including the best mode, and to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. It should be noted that it will be apparent to those skilled in the art that various modifications and adaptations of the invention can be made without departing from the principles of the invention and these modifications and adaptations are intended to be within the scope of the invention as defined in the following claims. The scope of the patent protection is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims (10)

1. A method for improving the magnetic properties of a rare earth permanent magnet, comprising:
placing the rare earth permanent magnet in an electrolyte molten salt system containing heavy rare earth salt, and electrifying to perform electroplating to obtain the rare earth permanent magnet with the surface covered with the heavy rare earth plating layer;
and carrying out grain boundary diffusion and tempering treatment on the rare earth permanent magnet with the surface covered with the heavy rare earth plating layer, so that the magnetic performance of the rare earth permanent magnet is improved.
2. The method according to claim 1, characterized in that: the general formula of the rare earth permanent magnet is RE-Fe-B, wherein RE comprises any one or more than two of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium;
preferably, the rare earth permanent magnet comprises a sintered blank;
preferably, the rare earth permanent magnet comprises a neodymium-based rare earth permanent magnet, and the neodymium-based rare earth permanent magnet comprises any one or more than two of neodymium-iron-boron, neodymium-cerium-iron-boron and neodymium-yttrium-iron-boron;
preferably, the rare earth permanent magnet comprises a sintered rare earth permanent magnet obtained by one or more steps of raw material powder smelting, rapid hardening, crushing, hydrogen crushing and orientation compression molding and sintering.
3. The method according to claim 1, characterized in that: the electroplating adopts a three-electrode system or a two-electrode system, preferably adopts a three-electrode system, the electrolyte molten salt system is used as electrolyte, the rare earth permanent magnet is used as a working electrode, and the adopted counter electrode is arranged parallel to the surface of the rare earth permanent magnet;
preferably, the plating uses more than two counter electrodes, preferably two counter electrodes.
4. The method as recited in claim 1, further comprising: firstly, pretreating a rare earth permanent magnet, and then placing the rare earth permanent magnet in an electrolyte molten salt system containing heavy rare earth salt; wherein the pretreatment comprises any one or more than two of acid washing, organic solution washing, electrochemical activation, deionized water washing and ultrasonic washing, or any one or more than two of polishing and grinding, electrolytic polishing, acid washing, alkali washing and degreasing, deionized water washing and absolute ethyl alcohol ultrasonic washing.
5. The method according to claim 1, characterized in that: the electrolyte molten salt system containing the heavy rare earth salt is in a liquid state at room temperature, wherein the temperature of the room temperature is 10-40 ℃, preferably 15-35 ℃, and more preferably 20-30 ℃;
and/or the electrolyte molten salt system containing the heavy rare earth salt comprises the heavy rare earth salt and a solvent;
preferably, the heavy rare earth salt comprises any one or more than two of heavy rare earth element-containing chloride, heavy rare earth element-containing fluoroborate and heavy rare earth element-containing trifluoromethane sulfonate;
preferably, the solvent comprises an electrolyte molten salt, preferably comprising any one or a combination of more than two of 1-ethyl-3-methylimidazole tetrafluoroborate, trimethyl phosphate and 1-butyl-1-methylpyrrolidine triflate;
and/or the concentration of the heavy rare earth salt in the electrolyte molten salt system containing the heavy rare earth salt is 0.1-10.0 mol/L, preferably 0.1-5.0 mol/L, more preferably 0.1-2.0 mol/L;
and/or the heavy rare earth elements contained in the electrolyte molten salt system containing the heavy rare earth salt comprise Dy and/or Tb.
6. The method according to claim 5, wherein: the electrolyte molten salt system containing the heavy rare earth salt further comprises a metal salt and/or an additive; preferably, the electroplating adopts an electrolyte molten salt system containing heavy rare earth elements and metal elements at the same time to obtain a heavy rare earth composite plating layer containing the heavy rare earth elements and the metal elements;
preferably, the metal salt includes any one or a combination of two or more of a chloride containing a metal element, a fluoroborate containing a metal element, and a trifluoromethanesulfonate containing a metal element;
preferably, the metal element contained in the metal salt comprises any one or a combination of more than two of Ti, cr, cu, al, pr, nd, ga, zr, nb, hf, W and V;
preferably, the concentration of the metal salt in the electrolyte molten salt system containing the heavy rare earth salt is 0.01-0.5 mol/L;
preferably, the additive comprises an alcohol additive and/or lithium chloride;
preferably, the additive comprises any one or more than two of absolute ethyl alcohol, ethylene glycol and lithium chloride;
preferably, the concentration of lithium chloride in the electrolyte molten salt system containing the heavy rare earth salt is 0.05-1 mol/L;
preferably, the volume ratio of the alcohol additive in the electrolyte molten salt system containing the heavy rare earth salt is 10-50%.
7. The method according to claim 1, characterized in that: the electroplating mode comprises any one of direct-current constant-potential electroplating, alternating-current electroplating or pulse electroplating;
and/or the electric potential of the electroplating is-0.1 to-3V, preferably-0.5 to-2.5V, and more preferably-1 to-2V;
and/or the temperature used for the electroplating is 20-80 ℃, preferably 20-70 ℃, more preferably 20-40 ℃;
preferably, the duration of the electroplating is 30min to 20h, preferably 3 to 18h, more preferably 5 to 15h;
preferably, the oxygen content in the electroplating process is 0-50 ppm, preferably 10-40 ppm, more preferably 20-30 ppm;
preferably, the water content in the electroplating process is 10 to 100ppm, preferably 30 to 80ppm, more preferably 50 to 60ppm.
8. The method according to claim 1, characterized in that: the thickness of the heavy rare earth plating layer is 100nm to 50. Mu.m, preferably 900nm to 30. Mu.m, more preferably 2 μm to 11. Mu.m, particularly preferably 3 μm to 8. Mu.m.
9. The method according to claim 1, characterized in that: the temperature of the grain boundary diffusion is 600-1000 ℃, preferably 650-950 ℃, more preferably 700-900 ℃, and more preferably 750-850 ℃; and/or the time for the grain boundary diffusion is 4 to 10 hours, preferably 5 to 9 hours, more preferably 6 to 8 hours.
10. The method according to claim 1, characterized in that: the tempering treatment temperature is 300-500 ℃, preferably 350-450 ℃; and/or the tempering treatment is carried out for 2 to 6 hours, preferably 4 to 5 hours.
CN202311567485.8A 2023-11-22 2023-11-22 Method for improving magnetic performance of rare earth permanent magnet Pending CN117542645A (en)

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