Preparation method of graphene-quantum dot-metal composite anticorrosive coating of neodymium-iron-boron magnet

Abstract

The application discloses a preparation method of a graphene-quantum dot-metal composite anticorrosion coating of a neodymium-iron-boron magnet, and relates to the technical field of neodymium-iron-boron magnet anticorrosion coating, and aims at solving the problem that the corrosion resistance performance of the neodymium-iron-boron magnet needs to be further improved.The application comprises the following steps: preparing graphene sheets by adopting a chemical vapor deposition method; transferring the graphene to the surface of the neodymium-iron-boron metal after surface pretreatment of the neodymium-iron-boron; adding a salt solution of a metal to be plated into a quantum dot solution as an electroplating solution, and electrochemically pre-plating a neodymium-iron-boron material to obtain a neodymium-iron-boron graphene quantum dot composite material; taking the composite material as a cathode, taking the metal to be plated as an anode, electroplating and depositing a metal protective layer, and preparing the graphene-quantum dot-metal composite anticorrosion coating on the surface of the neodymium-iron-boron material; and the process is simple and easy to operate, the quantum dot intermediate layer after pre-plating can increase the adhesion of metal particles and graphene, is beneficial to the uniform growth of metal grains, and improves the corrosion resistance performance of the neodymium-iron-boron.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of corrosion-resistant coatings of neodymium-iron-boron magnets, in particular to a preparation method of a graphene-quantum dot-metal composite corrosion-resistant coating of a neodymium-iron-boron magnet. BACKGROUND

[0002] Neodymium-iron-boron magnets are widely used in the fields of motors, sensors, medical devices, etc. due to their excellent magnetic properties. However, in humid, acidic or alkaline environments, neodymium-iron-boron is prone to oxidation and electrochemical corrosion, leading to a decrease in magnetic properties and even failure. This is because neodymium-iron-boron magnets contain a large amount of iron, which reacts with water in a humid environment to form iron hydroxide, and then undergoes further oxidation. In addition, the neodymium element in neodymium-iron-boron will also rapidly oxidize in the air to form neodymium oxides, which not only destroy the surface integrity of the material, but also penetrate into the interior, accelerating the corrosion process of the entire magnet.

[0003] In order to improve the corrosion resistance of neodymium-iron-boron magnets, the following measures are currently used to improve the corrosion resistance of neodymium-iron-boron, one is alloying, adding other elements such as aluminum (Al), copper (Cu), nickel (Ni), etc. in neodymium-iron-boron, which can improve its microstructure and enhance the corrosion resistance of the magnet. The other is surface coating, by applying a corrosion-resistant protective coating on the surface of the neodymium-iron-boron magnet, such as zinc plating, nickel plating, epoxy resin, etc., which can effectively isolate the magnet from the corrosive medium, thereby improving its corrosion resistance. At the same time, special heat treatment processes can also be used to change the crystal structure of the neodymium-iron-boron magnet, reducing stress concentration at the grain boundaries, thereby improving its overall corrosion resistance.

[0004] Patent CN111128503B discloses a high-strength neodymium-iron-boron magnet and a preparation method thereof, which uses a neodymium-iron-boron magnet as a mother material substrate, and has a metal plating layer on the surface of the neodymium-iron-boron magnet, and a graphene film layer on the metal plating layer. Due to the high strength characteristics of graphene, the surface of the magnet has extremely high strength, and the reticular structure of the graphene film can reduce the shedding of the metal plating layer, thereby obtaining a high-strength and high-stability neodymium-iron-boron magnet. However, this method cannot improve the corrosion during the electroplating process of neodymium-iron-boron, and the in-situ growth of the graphene coating requires a high-quality magnetron sputtering equipment.

[0005] Patent CN109161941B discloses a method and product for improving the corrosion resistance of sintered Nd-Fe-B magnets by coating a copper composite graphene layer. The sintered Nd-Fe-B is subjected to surface oil removal and oxide removal treatment, and then the sample is placed in a graphene-containing alkaline cyanide-free copper plating solution to co-deposit a copper composite graphene plating layer of a certain thickness under the assistance of ultrasonic waves, thereby obtaining the product. By co-depositing copper and graphene under the assistance of ultrasonic waves, a copper plating layer with finer grains than a pure copper plating layer can be obtained, and the copper plating layer has hydrophobic characteristics, so that the sintered Nd-Fe-B magnet directly coated with the copper composite graphene composite plating layer has better corrosion resistance. However, this method has many limitations on the type of metal, and the interaction between graphene and copper is weak, so the corrosion resistance needs to be further improved. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of a graphene-quantum dot-metal composite corrosion-resistant coating for Nd-Fe-B magnets to solve the problem that the corrosion-resistant coating performance of Nd-Fe-B magnets needs to be further improved.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solution: a preparation method of a graphene-quantum dot-metal composite corrosion-resistant coating for Nd-Fe-B magnets, comprising the following specific steps:

[0008] S1. Preparing graphene sheets by chemical vapor deposition;

[0009] S2. Pre-treating the surface of Nd-Fe-B to ensure the flatness of the surface of Nd-Fe-B;

[0010] S3. Transferring graphene to the surface of the Nd-Fe-B metal, maintaining the integrity of the graphene structure during the transfer process, and repeating several times to obtain Nd-Fe-B material with several layers of graphene on the surface;

[0011] S4. Adding a salt solution of the metal to be plated to the quantum dot solution as an electroplating solution, and electrochemically pre-plating the Nd-Fe-B material obtained in step S3 to obtain a Nd-Fe-B graphene quantum dot composite material;

[0012] S5. Using the material obtained in step S4 as the cathode and the metal to be plated as the anode, electroplating a metal protective layer, and obtaining a graphene-quantum dot-metal composite corrosion-resistant coating on the surface of the Nd-Fe-B material.

[0013] Preferably, in step S1 above, the substrate of the chemical vapor deposition method includes copper or nickel, and the prepared graphene sheets are single-layer or multi-layer graphene.

[0014] Preferably, in step S2 above, the pre-treatment method is plasma treatment or / and acid treatment, and the surface treatment time is not more than 3 min.

[0015] Preferably, in the step S3, the transferring method is dry transferring or wet transferring, and the transferring is repeated 1 to 3 times to obtain the neodymium-iron-boron material with 1 to 3 layers of graphene on the surface.

[0016] Preferably, the wet transferring method comprises the following steps: firstly, spin coating a layer of transferring medium on the graphene surface; secondly, removing the substrate material under the graphene by chemical or physical method, and transferring the graphene-containing transferring medium layer to the pretreated neodymium-iron-boron material; and finally, removing the transferring medium to leave the graphene film.

[0017] Preferably, the dry transferring method comprises the following steps: using a polymer film heat release tape as the transferring medium, physically peeling the graphene from the original substrate and transferring the graphene to the heat release tape, then transferring the heat release tape to the pretreated neodymium-iron-boron material, and tearing off the heat release tape to leave the graphene.

[0018] Preferably, in the step S4, the concentration of the quantum dot solution is 0.1-50 mg / ml, and the concentration of the salt solution of the metal to be plated is 1-100 μg / ml.

[0019] Preferably, in the step S4, the treatment voltage of the electrochemical pre-plating is 0.01-5 V, and the electrochemical pre-plating treatment is performed under stirring for 20-120 min.

[0020] Preferably, the metal to be plated is nickel, zinc, magnesium, copper or silver.

[0021] Another technical solution provided by the present application is a graphene-quantum dot-metal composite corrosion-resistant coating arranged on the surface of a neodymium-iron-boron magnet by electrochemical treatment, which is prepared by the above method.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] The method for preparing the graphene-quantum dot-metal composite corrosion-resistant coating of the neodymium-iron-boron magnet is simple and easy to operate, and the graphene is transferred to the surface of the neodymium-iron-boron magnet without damage, thus retaining the good conductivity of the graphene. The graphene film has excellent acid and alkali resistance, and the corrosion resistance of the neodymium-iron-boron magnet is improved. Before the metal layer is electroplated, the quantum dots and the salt solution of the metal to be plated are pre-plated, which increases the adhesion between the metal particles of the electroplated metal layer and the graphene, and is beneficial to the uniform growth of the metal grains in the later stage, thus further improving the corrosion resistance of the neodymium-iron-boron magnet. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The figure is a process flow diagram of the present application. DETAILED DESCRIPTION

[0025] The method of the present application mainly comprises the following 5 steps:

[0026] S1. Preparing graphene sheets by chemical vapor deposition;

[0027] S2. Pre-treating the surface of Nd-Fe-B to ensure the flatness of the surface of Nd-Fe-B;

[0028] S3. Transferring graphene to the surface of Nd-Fe-B metal, keeping the integrity of the graphene structure during the transferring process, and repeating several times to obtain Nd-Fe-B material with several layers of graphene on the surface;

[0029] In a preferred embodiment, the transferring method is dry or wet transferring, and the transferring is repeated 1 to 3 times to obtain Nd-Fe-B material with 1 to 3 layers of graphene on the surface.

[0030] For reference, the steps of wet transferring include: first spin-coating a layer of transfer medium, such as polymethyl methacrylate (PMMA) or other polymer materials, on the surface of graphene, then removing the substrate material, such as copper or nickel, under the graphene by chemical or physical methods, transferring the graphene-containing transfer medium layer to the pre-treated Nd-Fe-B material, and finally removing the transfer medium to leave the graphene film; compared with wet transferring, dry transferring is a relatively new transferring technology, which does not rely on liquid medium, but transfers graphene from the original substrate to the target substrate by physical means; a common form of dry transferring is to use a polymer film, such as a thermal release tape, as a transfer medium, in the transferring process, graphene is physically peeled off from the original substrate and transferred to the thermal release tape, and then the thermal release tape is transferred to the pre-treated Nd-Fe-B material, and the thermal release tape is torn off to leave the graphene.

[0031] S4. Adding a salt solution of the metal to be plated into a quantum dot solution as an electroplating solution, and electrochemically pre-plating the Nd-Fe-B material obtained in step S3 to obtain a Nd-Fe-B graphene quantum dot composite material;

[0032] For convenience, the concentration of the quantum dot solution can be 0.1-50 mg / ml, the concentration of the salt solution of the metal to be plated can be 1-100 μg / ml, and in addition, the size of the graphene quantum dots can be further selected to be 2-50 nm.

[0033] In a preferred embodiment, the treatment voltage for electrochemical pre-plating is 0.01-5 V, and the electrochemical pre-plating treatment can be generally carried out under stirring conditions for 20-120 min, specifically under magnetic stirring conditions of 1000-2000 rpm, and other stirring methods can also be used.

[0034] S5. Using the material obtained in step S4 as a cathode and the metal to be plated as an anode to electroplate and deposit a metal protective layer, and obtaining a graphene-quantum dot-metal composite corrosion-resistant coating on the surface of the Nd-Fe-B material.

[0035] The specific operations in steps S1, S2 and S5 about graphene preparation, surface treatment and metal layer electroplating can be directly adopted from the existing technologies of graphene sheet preparation by chemical vapor deposition, neodymium-iron-boron magnet surface pretreatment and metal protective layer electroplating respectively; but preferably, the substrate for chemical vapor deposition includes copper or nickel, the prepared graphene sheet is single-layer or multi-layer graphene, the pretreatment method can be plasma treatment or / and acid treatment, the surface treatment time is preferably no more than 3 min, and the metal to be plated can be nickel, zinc, magnesium, copper or silver, and the current density range for electroplating deposition of the metal protective layer is 0.5 to 2 mA / cm 2 .

[0036] The application is further illustrated by the following examples. It should be understood that the following examples are only illustrative and explanatory of the application, and should not be interpreted as limiting the scope of protection of the application.

[0037] In the following examples, the neodymium-iron-boron product is selected from square neodymium-iron-boron magnets with a size of 40 mm x 20 mm x 20 mm.

[0038] Example 1

[0039] The preparation method of the graphene-quantum dot-metal composite coating as a neodymium-iron-boron magnet corrosion-resistant coating in this example includes the following steps:

[0040] S1. Continuous graphene is obtained by chemical vapor deposition (CVD) on the surface of a 20 μm thick copper foil.

[0041] S2. After the neodymium-iron-boron surface is degreased, it is treated under N2 plasma at a power of 100 W for 20 s.

[0042] S3. Graphene transfer: a layer of thermal release tape is covered on the copper-graphene surface using a roller press at a pressure of 0.2 MPa. The copper substrate is etched away using a 1 M ammonium persulfate aqueous solution, and cleaned with deionized water to obtain a single-layer graphene-thermal release tape structure. The single-layer graphene-thermal release tape and the treated neodymium-iron-boron are laminated using a roller press at a pressure of 0.2 MPa at 90°C. Finally, the thermal release tape is peeled off at room temperature to obtain a single-layer graphene-neodymium-iron-boron composite material. The same method is used to obtain a neodymium-iron-boron-double-layer graphene composite material.

[0043] S4. A quantum dot aqueous solution with a concentration of 5 mg / ml is selected, and 10 μg / ml of nickel chloride is added as an electroplating solution; the neodymium-iron-boron-double-layer graphene-quantum dot composite material is obtained by treating for 50 min under a voltage of 1 V and 2000 rpm magnetic stirring.

[0044] S5. With neodymium iron boron-double layer CVD graphene-quantum dots as the cathode, a nickel plate as the anode, and a nickel sulfate hexahydrate solution 340 g / L, a nickel chloride hexahydrate solution 45 g / L, boric acid 45 g / L, and a sodium dodecyl benzene sulfonate solution 0.1 g / L as the electroplating solution. A graphene-quantum dot-nickel plating layer composite material is obtained by electrodeposition at a current density of 2.5 A / dm 2 2.5 A / dm

[0045] Example 2

[0046] In this embodiment, a graphene-quantum dot-metal composite coating is used as a corrosion-resistant coating for a neodymium iron boron magnet. The preparation method comprises the following steps:

[0047] S1. Continuous graphene is grown on the surface of a 30-μm-thick copper foil by chemical vapor deposition (CVD).

[0048] S2. After the neodymium iron boron surface is degreased, it is treated in a N2 plasma at a power of 50 W for 30 s.

[0049] S3. Graphene transfer: A poly(methyl methacrylate) (PMMA) solution (solvent: chlorobenzene) is spin-coated on the surface of the graphene by a spin coater. After spin coating, the graphene coated with PMMA and the copper foil are placed on a heating table at 90°C for 20 min. Then, the graphene is etched in an FeCl3 solution and transferred to ultrapure water after etching. The graphene is further cleaned with a dilute hydrochloric acid solution. Finally, the graphene is transferred to the surface of the neodymium iron boron. The surface layer of PMMA is dissolved in isopropyl alcohol-acetone solvent to obtain a single-layer graphene-neodymium iron boron composite material.

[0050] S4. A quantum dot aqueous solution with a concentration of 0.1 mg / ml is selected, and 1 μg / ml of nickel chloride is added as an electroplating solution. The neodymium iron boron-single-layer graphene-quantum dot composite material is obtained by treating at a voltage of 0.7 V and a magnetic stirring speed of 1500 rpm for 120 min.

[0051] S5. With neodymium iron boron-single-layer graphene-quantum dots as the cathode, a nickel plate as the anode, and a nickel sulfate hexahydrate solution 340 g / L, a nickel chloride hexahydrate solution 45 g / L, and boric acid 45 g / L as the electroplating solution. A graphene-quantum dot-nickel plating layer composite material is obtained by electrodeposition at a current density of 2.5 A / dm 2 2.5 A / dm

[0052] Example 3

[0053] In this embodiment, a graphene-quantum dot-metal composite coating is used as a corrosion-resistant coating for a neodymium iron boron magnet. The preparation method comprises the following steps:

[0054] S1. Continuous graphene was grown on the surface of 20 μm-thick nickel foil by chemical vapor deposition (CVD).

[0055] S2. After the neodymium iron boron surface was degreased, it was treated in O2 plasma for 2 min at a power of 30 W.

[0056] S3. Transfer of graphene: A thermal release tape was covered on the nickel-graphene surface by using a roller press at a pressure of 0.5 MPa. The copper substrate was etched away by using a 0.5 M aqueous solution of ammonium persulfate, and then cleaned with deionized water to obtain a single-layer graphene-thermal release tape structure. The single-layer graphene-thermal release tape and the treated neodymium iron boron were laminated by using a roller press at a pressure of 0.5 MPa at 100 °C. Finally, the thermal release tape was peeled off at room temperature to obtain a graphene-neodymium iron boron composite material. A neodymium iron boron-double-layer graphene composite material was obtained by using the same method.

[0057] S4. A quantum dot aqueous solution with a concentration of 30 mg / ml was selected, and 15 μg / ml nickel sulfate was added as an electroplating solution; the neodymium iron boron-graphene-quantum dot composite material was obtained by treating for 60 min at a voltage of 1 V and a magnetic stirring speed of 1000 rpm.

[0058] S5. The neodymium iron boron-graphene-quantum dot was used as a cathode, and a nickel plate was used as an anode. A nickel sulfamate solution 300 g / L, a nickel chloride hexahydrate solution 20 g / L, a boric acid solution 40 g / L, and a sodium dodecyl benzene sulfonate (SDBS) solution 0.1 g / L were used as an electroplating solution. The graphene-quantum dot-nickel plating layer composite material was obtained by electrodeposition for 30 min at a pH of about 4, a temperature of 45 °C, and a current density of 2 A / dm 2

[0059] Example 4

[0060] The preparation method of the graphene-quantum dot-metal composite coating as a corrosion-resistant coating for a neodymium iron boron magnet in this example comprises the following steps:

[0061] S1. Continuous graphene was grown on the surface of 10 μm-thick copper foil by chemical vapor deposition (CVD).

[0062] S2. After the neodymium iron boron surface was degreased, it was treated in a 2% hydrochloric acid solution for 30 s.

[0063] ​S3. Transfer of graphene: A piece of thermal release tape was covered on the surface of nickel-graphene by using a roller press at a pressure of 1 MPa. The copper substrate was etched away by using 2 M ammonium persulfate aqueous solution and cleaned by deionized water to obtain a single-layer graphene-thermal release tape structure. The single-layer graphene-thermal release tape and the treated neodymium-iron-boron were laminated by using a roller press at a pressure of 2 MPa at 90 °C. Finally, the thermal release tape was peeled off at room temperature to obtain a graphene-neodymium-iron-boron composite material. The same method was used to obtain a neodymium-iron-boron-three-layer graphene composite material.

[0064] S4. A quantum dot aqueous solution with a concentration of 40 mg / ml was selected, and 100 μg / ml nickel sulfate was added as an electroplating solution; the neodymium-iron-boron-graphene-quantum dot composite material was obtained by processing for 20 min at a voltage of 1.3 V and under the condition of 1000 rpm magnetic stirring.

[0065] S5. The neodymium-iron-boron-graphene-quantum dot was used as a cathode, a nickel plate was used as an anode, and nickel sulfamate 320 g / L, nickel chloride hexahydrate 30 g / L, boric acid 45 g / L, and sodium dodecyl benzene sulfonate (SDBS) 0.2 g / L were used as an electroplating solution. A three-layer graphene-quantum dot-nickel plating composite material was obtained by electrodeposition for 20 min at a pH of about 5, a temperature of 50 °C, and a current density of 2.5 A / dm 2

[0066] Example 5

[0067] The preparation method of the graphene-quantum dot-metal composite coating as a neodymium-iron-boron magnet anticorrosive coating in this example comprises the following steps:

[0068] S1. Continuous graphene was obtained by chemical vapor deposition (CVD) on the surface of a 30 μm thick copper foil.

[0069] S2. After the neodymium-iron-boron surface was degreased, it was treated in 1% nitric acid solution for 30 s.

[0070] S3. Transfer of graphene: A piece of thermal release tape was covered on the surface of nickel-graphene by using a roller press at a pressure of 0.8 MPa. The copper substrate was etched away by using saturated ammonium persulfate aqueous solution and cleaned by deionized water to obtain a single-layer graphene-thermal release tape structure. The single-layer graphene-thermal release tape and the treated neodymium-iron-boron were laminated by using a roller press at a pressure of 0.8 MPa at 100 °C. Finally, the thermal release tape was peeled off at room temperature to obtain a CVD graphene-neodymium-iron-boron composite material. This was repeated to obtain a neodymium-iron-boron-three-layer CVD graphene composite material.

[0071] ​S4. Select the concentration of quantum dots aqueous solution of 50mg / ml, and add 50μg / ml nickel sulfate as the electroplating solution; under the condition of 0.01V voltage, 2000rpm magnetic stirring for 50min, to obtain Nd-Fe-B-three-layer graphene-quantum dot composite material.

[0072] S5. With Nd-Fe-B-three-layer graphene-quantum dot as cathode, nickel plate as anode, with 350g / L nickel sulfate hexahydrate, 50g / L nickel chloride hexahydrate, 40g / L boric acid as electroplating solution, 0.2g / L sodium dodecyl benzene sulfonate (SDBS) as electroplating solution. At pH≈4, temperature 50℃, current density 3A / dm 2 Under the condition of 20min electrodeposition, to obtain Nd-Fe-B-graphene-quantum dot-nickel plating layer composite material.

[0073] Example 6

[0074] The preparation method of the graphene-quantum dot-metal composite coating as the corrosion-resistant coating of Nd-Fe-B magnet in this embodiment comprises the following steps:

[0075] S1. Continuous graphene is obtained by chemical vapor deposition (CVD) on the surface of metal nickel.

[0076] S2. After the oil on the surface of Nd-Fe-B is removed, it is treated in 2% sulfuric acid solution for 30s.

[0077] S3. Transfer of graphene: spin-coat polymethyl methacrylate (PMMA, solvent chlorobenzene) on the surface of graphene by a spin coater, after spin-coating, place the graphene coated with PMMA together with metal nickel on a heating table and bake at 95℃ for 30min; and then etch in FeCl3 solution, after etching, transfer to ultrapure water for rinsing, and then further rinse with dilute hydrochloric acid solution. Finally, transfer the sample to the surface of Nd-Fe-B. Finally, dissolve the surface layer PMMA with isopropyl alcohol-acetone solvent to obtain single-layer graphene-Nd-Fe-B composite material. Repeat twice to obtain double-layer graphene-Nd-Fe-B composite material.

[0078] S4. Select the concentration of quantum dots aqueous solution of 20mg / ml, and add 10μg / ml zinc chloride as the electroplating solution; under the condition of 0.3V voltage, 2000rpm magnetic stirring for 20min, to obtain Nd-Fe-B-double-layer graphene-quantum dot composite material.

[0079] S5. With Nd-Fe-B-double-layer graphene-quantum dot as cathode, zinc sheet as anode, with 180g / L zinc sulfate, 30g / L sulfuric acid, 2g / L ammonium chloride, 5g / L sodium chloride, 5g / L sodium hydroxide. Temperature 30℃, current density 3A / dm 2The graphene-quantum dot-zinc plating layer composite material is obtained by electrodeposition for 40 min under the current density.

[0080] The square Nd-Fe-B magnets before plating and the materials after plating in each embodiment are subjected to electrochemical test, and the test conditions are as follows: a platinum sheet is used as an anode, the effective area is 1 cm 2 Different Nd-Fe-B samples are used as working electrodes, and a saturated calomel electrode (SCE) is used as a reference electrode, the polarization curve of the plating layer in a 3.5% NaCl solution at 25°C is determined, so as to obtain the corrosion voltage and the corrosion current, and the test results are shown in Table 1 below:

[0081] Table 1 Test results of corrosion resistance of blank samples and sample in each embodiment

[0082] Sample Corrosion voltage (V) Corrosion current (A / cm 2 ) Neodymium iron boron base -0.785 2.1*10 -5 ]]> Example 1 -0.371 1.9*10 -7 ]]> Example 2 -0.539 7.8*10 -6 ]]> Example 3 -0.452 3.2*10 -6 ]]> Example 4 -0.483 5.1*10 -6 ]]> Example 5 -0.511 6.9*10 -6 ]]> Example 6 -0.496 5.6*10 -6 ]]>

[0083] The above only describes preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be defined by the protection scope defined by the claims.

[0084] The parts not described in the present application are well-known technologies of the person skilled in the art.

Claims

1. A method for preparing a graphene-quantum dot-metal composite anti-corrosion coating for a neodymium iron boron magnet, characterized in that: The specific steps include: S1. Prepare graphene sheets using chemical vapor deposition; S2. NdFeB surface pretreatment to ensure the surface flatness of NdFeB; S3. The graphene is transferred to the surface of the NdFeB metal, and the integrity of the graphene structure is maintained during the transfer process. The process is repeated several times to obtain an NdFeB material having several layers of graphene on the surface. S4. Adding a salt solution of the metal to be plated as an electroplating solution to the quantum dot solution, electrochemically pre-plating the NdFeB material obtained in step S3 to obtain a NdFeB graphene quantum dot composite material; S5. Using the material obtained in step S4 as the cathode and the metal to be plated as the anode, a metal protective layer is deposited by electroplating to obtain a graphene - quantum dot - metal composite anti-corrosion coating on the surface of the NdFeB material; In step S3, the transfer method is dry transfer or wet transfer; The wet transfer step includes: firstly, spin coating a transfer medium on the graphene surface, then removing the substrate material under the graphene by chemical or physical methods, transferring the transfer medium layer containing graphene to the pretreated NdFeB material, and finally removing the transfer medium to leave the graphene film; The dry transfer step includes: using a polymer film thermal release tape as a transfer medium, the graphene is physically peeled off from the original substrate and transferred to the thermal release tape, then the thermal release tape is transferred to the pre-treated NdFeB material, and the thermal release tape is torn off to leave the graphene; In step S4, the concentration of the quantum dot solution is 0.1-50 mg / ml, and the concentration of the salt solution of the metal to be plated is 1-100 μg / ml.

2. The method for preparing a graphene-quantum dot-metal composite anti-corrosion coating for a NdFeB magnet according to claim 1, wherein: In step S1, the substrate of the chemical vapor deposition method is copper or nickel, and the graphene sheet obtained is a single layer or multilayer graphene.

3. The method for preparing a graphene-quantum dot-metal composite anti-corrosion coating for a NdFeB magnet according to claim 1, characterized in that: In step S2, the pretreatment method is plasma treatment and / or acid treatment, and the surface treatment time does not exceed 3 minutes.

4. The method for preparing a graphene-quantum dot-metal composite anti-corrosion coating for a NdFeB magnet according to claim 1, wherein: In step S3, the transfer is repeated 1 to 3 times to obtain a NdFeB material having 1 to 3 layers of graphene on the surface.

5. The method for preparing a graphene-quantum dot-metal composite anti-corrosion coating for a NdFeB magnet according to claim 1, characterized in that: In the step S4, the electrochemical pre-plating treatment voltage is 0.01 to 5 V, and the electrochemical pre-plating treatment is carried out for 20 to 120 minutes under stirring conditions.

6. The method for preparing a graphene-quantum dot-metal composite anti-corrosion coating for a NdFeB magnet according to claim 1, characterized in that: The metal to be plated is nickel, zinc, magnesium, copper or silver.

7. A graphene-quantum dot-metal composite anti-corrosion coating provided on the surface of a neodymium iron boron magnet by electrochemical treatment, characterized in that: The graphene-quantum dot-metal composite anti-corrosion coating is prepared by the preparation method according to any one of claims 1 to 6.

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