Corrosion-resistant neodymium-iron-boron material, slurry thereof and method for producing the same

Abstract

The present application belongs to the technical field of Nd-Fe-B permanent magnet material, and particularly relates to a corrosion-resistant Nd-Fe-B material, a slurry thereof and a preparation method thereof, wherein graphene oxide layers are arranged at grain boundaries on the surface of a Nd-Fe-B base material, the carbon content from the surface to the center of the Nd-Fe-B base material has a concentration gradient, and the carbon content concentration gradually decreases from the surface to the center. With the toughness of the multilayer two-dimensional graphene, the present application reduces the brittleness of sintered Nd-Fe-B material, thereby reducing the proportion of chipping and cracking; and the multilayer two-dimensional graphene infiltrated into the surface of the product improves the corrosion resistance of the sintered Nd-Fe-B permanent magnet material.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of corrosion-resistant neodymium iron boron material, its slurry and its preparation method, belong to neodymium iron boron permanent magnet material technical field. BACKGROUND

[0002] Neodymium iron boron permanent magnet is strong magnetic permanent magnet, in recent years the market demand of neodymium iron boron permanent magnet material and industry scale is rapidly developing, its application field covers new energy vehicle, wind power generation, energy-saving elevator, energy-saving household appliance, automation, intelligent consumer electronics and many other industries.

[0003] Neodymium iron boron permanent magnet is generally prepared by sintering, there is a large chemical potential difference between the phases of sintered neodymium iron boron material, and it is easy to form a corrosion cell in a humid environment, and it is easy to rust, and the rare earth in this material is expensive and very brittle, resulting in brittle sintered neodymium iron boron material, which is easy to break in the production process, resulting in loss of rare earth and increased production cost. The current method for preventing edge breakage is mainly to increase protection or reduce production efficiency during subsequent processing of sintered neodymium iron boron material to avoid edge breakage. The commonly used method for improving the corrosion resistance of sintered neodymium iron boron material is mainly to increase the plating layer (including phosphating, electroplating, epoxy, etc.), among which electroplating and epoxy are long-term corrosion protection, but there are certain environmental problems, electroplating will produce wastewater containing nickel, copper, zinc, etc., and epoxy will produce VOC. Phosphating is currently the mainstream short-term corrosion protection, but phosphating will also produce wastewater containing phosphorus.

[0004] Chinese invention patent with publication number CN103212714B discloses a method for preparing neodymium iron boron material, which mentions adding graphene powder to the primary crushed powder after hydrogen crushing, pressing and sintering to obtain neodymium iron boron magnetic material with added graphene powder. Since graphene has ultra-high strength, the compressive strength and toughness of neodymium iron boron magnetic material with added graphene powder will also be improved accordingly. Graphene is one of the materials with the highest strength, it is a single-layer sheet structure planar thin film material composed of sp & sp2 hybrid orbitals, its special two-dimensional crystal structure makes it have unusual properties, it has high electrical conductivity, and its breaking strength can be comparable to that of carbon nanotubes, it also has good toughness and can be bent, the theoretical Young's modulus of graphene is 1.0 TPa, and its inherent tensile strength is 130 GPa. Graphene is essentially a carbon element, and too high carbon content in sintered neodymium iron boron material will result in low coercivity, so the carbon content in sintered neodymium iron boron material should not be too high.

[0005] If graphene oxide is directly added to the formula or graphene is mixed with magnetic powder, graphene can be attached to the surface of the magnet grain to improve corrosion resistance, but it cannot realize synchronous diffusion of heavy rare earth into the grain boundary of the magnet, so as to further reduce the brittleness of the magnet.

[0006] In view of the above problems, it is urgent to improve the corrosion resistance and reduce the brittleness of sintered neodymium-iron-boron material. SUMMARY

[0007] In order to improve the problem of high brittleness and easy corrosion of sintered neodymium-iron-boron material, a corrosion-resistant neodymium-iron-boron material, its slurry and its preparation method are provided.

[0008] The technical solution of the present application to solve the above technical problems is as follows:

[0009] One of the purposes of the present application is to provide a corrosion-resistant neodymium-iron-boron material, which has a graphene oxide layer at the grain boundary of the surface of the neodymium-iron-boron substrate.

[0010] The neodymium-iron-boron substrate is sintered from the following components:

[0011] R1: 28wt%-33wt%;

[0012] T1: 63wt%-70wt%;

[0013] B: 0.94wt%-1.10wt%;

[0014] M1: 0-3wt%;

[0015] R1 is selected from Nd or a mixture of Nd and at least one of Pr, La, Ce, Dy, Tb, Ho, Gd;

[0016] T1 is Fe and / or Co;

[0017] M1 is at least one of Cu, Ga, Zr, Ti, Nb.

[0018] The surface of the neodymium-iron-boron substrate of the present application refers to the surface of the neodymium-iron-boron substrate to the center 200μm, more preferably, the surface of the neodymium-iron-boron substrate to the center 100μm, the grain boundary phase contains carbon-rich phase, in any cross section of the neodymium-iron-boron substrate, the carbon-rich phase accounts for 20-80% of the grain boundary phase, the graphene oxide with two-dimensional structure is aggregated on the grain boundary of the three-dimensional sintered neodymium-iron-boron substrate grain 1 to form a carbon-rich phase, and the carbon-rich phase exists in the form of multi-layer graphene 2 with two-dimensional sheet structure (see Figure 1 ); the carbon content of the carbon-rich phase is high on the surface of the neodymium-iron-boron substrate, and the carbon content of the carbon-rich phase is lower near the center of the sintered neodymium-iron-boron substrate. Not all of the two-dimensional structure of the graphene oxide is aggregated on the grain boundary of the three-dimensional neodymium-iron-boron material, and a part of it is attached to the surface of the sintered neodymium-iron-boron material in the form of sheet structure, thereby further improving the corrosion resistance of the sintered neodymium-iron-boron material.

[0019] On the basis of the above technical solution, the present application can also be improved as follows:

[0020] Further, the carbon content of the surface to the center of the Nd-Fe-B substrate has a concentration gradient, and the carbon content gradually decreases from the surface to the center; the carbon content of the surface of the Nd-Fe-B substrate is 7% or more than the carbon content of the center; the carbon content of the surface to the 200 μm position of the center of the Nd-Fe-B substrate is 3%-7% more than the carbon content of the center; and the carbon content of the surface to the 2 mm position of the center of the Nd-Fe-B substrate is 0.1%-3% more than the carbon content of the center.

[0021] The second object of the present application is to provide a slurry for the corrosion-resistant Nd-Fe-B material, comprising graphene and an organic solvent.

[0022] Further, the graphene is graphene oxide, and the mass ratio of the graphene oxide to the organic solvent is 1:2-20.

[0023] Further, the graphene oxide is prepared by the Hummer method.

[0024] Further, the preparation process of the slurry for the corrosion-resistant Nd-Fe-B material is as follows: the graphene oxide is mixed with the organic solvent, and then ultrasonic dispersion is performed to dissolve the graphene oxide in the organic solvent; the ultrasonic dispersion time is 60-300 s, and the ultrasonic frequency is 25-28 Hz; the graphene oxide and the organic solvent mixture are stirred for more than 10 min to achieve sufficient mixing, thereby obtaining the slurry for the corrosion-resistant Nd-Fe-B material.

[0025] Further, the slurry for the corrosion-resistant Nd-Fe-B material further comprises heavy rare earth metal powder, which is pure metal, metal oxide, fluoride or hydride of Dy and / or Tb.

[0026] Further, the preparation process of the slurry for the corrosion-resistant Nd-Fe-B material is as follows:

[0027] ① The graphene oxide is mixed with the organic solvent, and then ultrasonic dispersion is performed to dissolve the graphene oxide in the organic solvent; the ultrasonic dispersion time is 60-300 s, and the ultrasonic frequency is 25-28 Hz; the graphene oxide and the organic solvent mixture are stirred for more than 10 min to achieve sufficient mixing, thereby obtaining the mixture A;

[0028] ② The heavy rare earth metal powder, the antioxidant and the diluent are mixed, the weight ratio of the heavy rare earth metal powder is 40-70%, the weight ratio of the antioxidant is 15-30%, and the weight ratio of the diluent is 15-30%; the mixture is stirred for 1-4 h until uniform, thereby obtaining the mixture B; the mixture A obtained in the above step ① is added to the mixture B, and the mixture is stirred for more than 180 min to achieve sufficient mixing, thereby obtaining the slurry for the corrosion-resistant Nd-Fe-B material containing the graphene oxide and the intermediate metal powder.

[0029] Further, the volume of the mixture A accounts for 5-15% of the volume of the mixture B.

[0030] Further, the antioxidant is at least one of toluene, 4-hexylresorcinol and dibutyl hydroxytoluene; and the diluent is at least one of ethanol, benzyl alcohol and acetone.

[0031] A third object of the present application is to provide a preparation method of the corrosion-resistant neodymium iron boron material, which comprises the following steps: coating graphene oxide slurry to the surface of sintered neodymium iron boron, and inserting two-dimensional graphene oxide into three-dimensional neodymium iron boron structure through a permeation process.

[0032] (1) mixing all components and then placing them in a vacuum melting furnace for melting, and then pouring after cooling to obtain flakes;

[0033] (2) processing the flakes obtained in step (1) into magnetic powder;

[0034] (3) obtaining neodymium iron boron base material through forming, isostatic pressing and sintering process of the magnetic powder obtained in step (2);

[0035] (4) obtaining neodymium iron boron magnet base material black sheet through mechanical processing of the sintered neodymium iron boron base material obtained in step (3).

[0036] (5) removing the surface oxide layer through surface pretreatment of the neodymium iron boron magnet base material black sheet in step (4);

[0037] (6) coating the neodymium iron boron magnet base material black sheet with the removed oxide layer in step (5), wherein the coating material used for coating is graphene oxide slurry; placing the product to be coated on a tool, and arranging the coating material on the surface of the magnet, which can be sprayed onto the product by mechanical methods such as spray gun or manual coating, etc.

[0038] (7) placing the product coated in step (6) into a diffusion furnace for diffusion to obtain neodymium iron boron magnet diffusion product.

[0039] (8) cutting and processing the neodymium iron boron magnet diffusion product obtained in step (7) into neodymium iron boron magnet finished product.

[0040] Further, in step (2), the magnetic powder is obtained through hydrogen explosion and airflow milling;

[0041] Further, in the step (3), the magnetic powder is pressed into a compact under a magnetic field and is formed into an isostatic compact; after being degassed at 250-850 DEG C, being sintered at 1020-1120 DEG C and being aged at 400-600 DEG C, a sintered Nd-Fe-B substrate is formed.

[0042] Further, in the step (4), the oxide layer on the surface of the Nd-Fe-B magnet substrate black sheet is removed through ultrasonic oil removal, acid pickling and water washing.

[0043] Further, in the step (6), heating is started after the pressure is reduced to 100 Pa or below, the first stage diffusion temperature is 300-400 DEG C, the second stage diffusion temperature is 820-950 DEG C, the aging temperature is 400-600 DEG C, and the aging time is 3-5 h, so as to obtain a Nd-Fe-B magnet diffusion product.

[0044] The present application has the advantages that: the composite diffusion source containing graphene oxide and heavy rare earth metal powder is used, on the one hand, the toughness of the multilayer two-dimensional graphene existing on the surface grain boundary of the Nd-Fe-B substrate reduces the brittleness of the sintered Nd-Fe-B material, so as to reduce the proportion of edge chipping and cracking, and the heavy rare earth powder is sintered and diffused, so that the rare earth metal diffuses into the magnet, and the magnetic properties such as the coercive force are improved; on the other hand, the multilayer two-dimensional graphene on the surface of the product is infiltrated through the diffusion process, so as to improve the corrosion resistance of the sintered Nd-Fe-B permanent magnet material. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 It is a schematic diagram of the surface grain boundary structure of the Nd-Fe-B material of the present application.

[0046] The signs are recorded as follows: 1, grain; 2, multilayer graphene. DETAILED DESCRIPTION

[0047] The principles and characteristics of the present application are described below in combination with the drawings, and the examples are only used to explain the present application, and are not used to limit the scope of the present application.

[0048] Example 1:

[0049] (1) After 28% Nd, 2% Co, 1% B, 0.55% Dy, 0.2% Cu, 0.2% Ga and the balance of Fe and other metals are mixed, they are placed in a vacuum melting furnace surrounded by an argon atmosphere, melted at 1480 DEG C, and cooled to 1380 DEG C for casting, so as to obtain a flake.

[0050] (2) The flake obtained in the step (1) is broken by a hydrogen explosion furnace to obtain hydrogen explosion powder, and the hydrogen explosion powder is ground by an air flow mill device to obtain magnetic powder.

[0051] (3) The magnetic powder obtained in step (2) is pressed into a compact under a magnetic field and is formed into an isostatic compact by isostatic pressing; after degassing at 250-850°C, high-temperature holding sintering at 1060°C and aging treatment at 520°C, a sintered neodymium-iron-boron base material is formed.

[0052] (4) The sintered neodymium-iron-boron base material obtained in step (3) is subjected to primary processing by wire sawing and grinding, to obtain a neodymium-iron-boron magnet base material black sheet.

[0053] (5) The neodymium-iron-boron magnet base material black sheet in step (4) is subjected to ultrasonic oil removal, acid pickling and water washing to remove the oxide layer on the surface of the neodymium-iron-boron magnet base material black sheet.

[0054] (6) The neodymium-iron-boron magnet base material black sheet with the oxide layer removed in step (5) is coated, and the coating material used for the coating is a slurry containing 5% graphene oxide, wherein the graphene oxide is prepared by the Hummer method.

[0055] The preparation process of the coating material is as follows: the graphene oxide and anhydrous ethanol are mixed in a mass ratio of 1:19, ultrasonic dispersion is performed, the graphene oxide is dissolved in the anhydrous ethanol, the ultrasonic dispersion time is 120s, the ultrasonic frequency is 25Hz, the graphene oxide and anhydrous ethanol mixture is stirred for 15min to achieve full mixing, and the coating material is obtained.

[0056] The product to be coated is placed on a tooling, and the coating material is sprayed onto the product by a spray gun, and the thickness of the coating layer is 200μm.

[0057] (7) The product coated in step (6) is loaded into a diffusion furnace, heated after being pumped to below 100Pa, the first stage diffusion temperature is 380°C, the holding time is 3h, the second stage diffusion temperature is 870°C, the holding time is 12-15h, the aging treatment temperature is 520°C, and the time is 3-4h, and a neodymium-iron-boron magnet diffusion product is obtained.

[0058] (8) The neodymium-iron-boron magnet diffusion product obtained in step (7) is subjected to cutting processing to obtain a neodymium-iron-boron magnet finished product (M1).

[0059] Example 2:

[0060] (1) The neodymium-iron-boron magnet base material black sheet with the oxide layer removed is obtained according to steps (1)-(5) in Example 1.

[0061] (2) The neodymium-iron-boron magnet base material black sheet with the oxide layer removed in step (1) is coated, and the coating material used for the coating is a slurry containing 20% graphene oxide, wherein the graphene oxide is prepared by the Hummer method.

[0062] The preparation process of the coating material is as follows: the graphene oxide and anhydrous ethanol are mixed at a mass ratio of 1:4, the graphene oxide is dissolved in the anhydrous ethanol through ultrasonic dispersion, the ultrasonic dispersion time is 150 s, the ultrasonic frequency is 25 Hz, the graphene oxide and anhydrous ethanol mixture is stirred for 15 min to achieve full mixing, and the coating material is obtained.

[0063] (3) The product to be coated is placed on the tooling, the coating material is sprayed on the product by immersion spraying, and the thickness of the coating layer is 200 μm.

[0064] (4) The product coated in the above step (3) is loaded into a diffusion furnace, and heating is started after being pumped to below 100 Pa, the first-stage diffusion temperature is 380 ℃, the holding time is 3 h, the second-stage diffusion temperature is 870 ℃, the holding time is 10-12 h, the aging treatment temperature is 520 ℃, and the time is 3-4 h, and the neodymium-iron-boron magnet diffusion product is obtained at this time.

[0065] (5) The neodymium-iron-boron magnet diffusion product is cut and processed into a neodymium-iron-boron magnet finished product (M2).

[0066] Example 3:

[0067] (1) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed is obtained according to steps (1)-(5) in Example 1.

[0068] (2) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed in the above step (1) is coated, and the coating material used for the coating is: a slurry containing 30% modified graphene oxide, and the graphene oxide is prepared by the Hummer method.

[0069] The preparation process of the coating material is as follows: the graphene oxide and anhydrous ethanol are mixed at a mass ratio of 3:7, the graphene oxide is dissolved in the anhydrous ethanol through ultrasonic dispersion, the ultrasonic dispersion time is 180 s, the ultrasonic frequency is 25 Hz, the graphene oxide and anhydrous ethanol mixture is stirred for 15 min to achieve full mixing, and the coating material is obtained.

[0070] (3) The product to be coated is placed on the tooling, the coating material is sprayed on the product by immersion spraying, and the thickness of the coating layer is 200 μm.

[0071] (4) The product coated in the above step (3) is loaded into a diffusion furnace, and heating is started after being pumped to below 100 Pa, the first-stage diffusion temperature is 380 ℃, the holding time is 3 h, the second-stage diffusion temperature is 870 ℃, the holding time is 8-10 h, the aging treatment temperature is 520 ℃, and the time is 3-4 h, and the neodymium-iron-boron magnet diffusion product is obtained at this time.

[0072] (5) The neodymium-iron-boron magnet diffusion product is cut and processed into a neodymium-iron-boron magnet finished product (M3).

[0073] Example 4:

[0074] (1) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed was obtained according to steps (1)-(5) in Example 1.

[0075] (2) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed in step (1) above was coated, and the coating material used for the coating was: a slurry containing 50% modified graphene oxide, wherein the graphene oxide was prepared by the Hummer method.

[0076] The preparation process of the coating material is as follows: the modified graphene oxide prepared by the Hummer method and anhydrous ethanol were mixed in a mass ratio of 1:1, and the modified graphene oxide was dissolved in the anhydrous ethanol through ultrasonic dispersion, the ultrasonic dispersion time was 180 s, the ultrasonic frequency was 25 Hz, the modified graphene oxide and anhydrous ethanol mixture was stirred for 15 min to achieve full mixing, and the coating material was obtained.

[0077] (3) The product to be coated was placed on a tooling, and the coating material was sprayed onto the product by immersion spraying, and the thickness of the coating layer was 200 μm.

[0078] (4) The product coated in step (3) above was loaded into a diffusion furnace, and heating was started after the pressure was reduced to below 100 Pa, the first stage diffusion temperature was 380 °C, and the holding time was 3 h, the second stage diffusion temperature was 870 °C, and the holding time was 7-8 h; the aging treatment temperature was 520 °C, and the time was 3-4 h, and the neodymium-iron-boron magnet diffusion product was obtained at this time.

[0079] (5) The neodymium-iron-boron magnet diffusion product was cut and processed into a neodymium-iron-boron magnet finished product (M4).

[0080] Comparative Example 1

[0081] (1) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed was obtained according to steps (1)-(5) in Example 1.

[0082] (2) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed in step (1) above was cut and processed into a neodymium-iron-boron magnet finished product (M5)

[0083] Comparative Example 2

[0084] (1) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed was obtained according to steps (1)-(5) in Example 1.

[0085] (2) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed in step (1) above was coated, and the coating material used for the coating was: a slurry containing 60% graphene oxide, wherein the graphene oxide was prepared by the Hummer method.

[0086] The preparation process of the coating material is as follows: mixing graphene oxide and anhydrous ethanol according to a mass ratio of 3:2, ultrasonic dispersion, dissolving graphene oxide in anhydrous ethanol, ultrasonic dispersion time of 180 s, ultrasonic frequency of 25 Hz, mixing graphene oxide and anhydrous ethanol for 15 min of stirring to achieve sufficient mixing, and obtaining the coating material.

[0087] (3) Placing the product to be coated on a tool, spraying the coating material on the product by immersion spraying, and the thickness of the coating layer being 200 μm.

[0088] (4) Loading the product coated in the above step (3) into a diffusion furnace, starting heating after being pumped to below 100 Pa, the first stage diffusion temperature being 380 ℃, holding for 3 h, the second stage diffusion temperature being 870 ℃, holding for 7-8 h, and the aging treatment temperature being 520 ℃, the time being 3-4 h, thereby obtaining the Nd-Fe-B magnet diffusion product.

[0089] (5) Cutting the Nd-Fe-B magnet diffusion product to obtain the Nd-Fe-B magnet finished product (M6).

[0090] The wet heat, edge chipping and cracking ratio, and magnetic property of the Nd-Fe-B magnet finished products M1-M6 of the above examples 1-4 and comparative examples 1-2 are analyzed.

[0091] The detection method is as follows:

[0092] Wet heat: using a wet heat chamber, the test conditions being 85% RH and 85% ℃, and performing corrosion resistance test.

[0093] Edge chipping and cracking ratio: producing 10,000 pieces of products respectively, collecting edge chipping and cracking data, and calculating the proportion of edge chipping and cracking products.

[0094] Magnetic property: using a magnetic measuring instrument to measure the magnetic property.

[0095] The data are shown in Table 1.

[0096] Table 1 Product performance data table of examples 1-4 and comparative examples 1-2

[0097] Product Moist heat (corrosion resistance) Chipping and cracking ratio HCj (kA / m) Hk (kA / m) M1 60 min 2.2％ 1257 1229 M2 60 min 1.8％ 1246 1215 M3 90 min 1.5％ 1255 1219 M4 90 min 1.2％ 1247 1221 M5 30 min 3.5％ 1250 1220 M6 90 min 1.1％ 1190 1130

[0098] Through the comparison of the wet heat (corrosion resistance) and edge chipping and cracking ratio data of examples 1 (M1), 2 (M2), 3 (M3), 4 (M4) and comparative examples 1, 2 (M5, M6), the products coated and diffused with the graphene oxide slurry have obviously better corrosion resistance than the products without coating and diffusion of the graphene oxide slurry, and the edge chipping and cracking ratio is obviously lower than that of the products without coating and diffusion of the graphene oxide slurry. With the increase of the proportion of the modified graphene oxide slurry, the corrosion resistance gradually increases, and the edge chipping and cracking ratio gradually decreases.

[0099] However, when the proportion in the modified graphene slurry is increased to 50% or more, the corrosion resistance and the proportion of chipping and cracking are not reduced, but both HCj and Hk are significantly reduced. Microstructure analysis is performed on the finished neodymium-iron-boron magnets M1-M6 of Examples 1-4 and Comparative Examples 1-2,

[0100] The detection method is as follows:

[0101] Carbon content: The carbon content at the center position, 200 μm from the surface, and 2 mm from the surface is detected by using a spectrometer.

[0102] Carbon-rich phase proportion: The microstructure of the grain boundary phase at a distance of 200 μm from the surface is observed by using a scanning microscope.

[0103] The data are shown in Table 2:

[0104] Table 2 Carbon content and carbon-rich phase proportion of Examples 1-4 and Comparative Examples 1-2

[0105]

[0106] Through observation and analysis of the microstructure of the grain boundary of the products of Example 1 (M1), Example 2 (M2), Example 3 (M3), Example 4 (M4), and Comparative Examples 1-2 (M5, M6), it can be seen that the carbon content gradually decreases from the surface to the center, the carbon content at a position 200 μm from the surface is 3%-7% higher than that at the center, and the carbon content at a position 2 mm from the surface is 0.1%-3% higher than that at the center. The carbon-rich phase at a position 200 μm from the surface exists in a sheet structure. Figure 1 Although the proportion of the carbon-rich phase of Comparative Example 2 (M6) is higher, the magnetic performance is significantly lower than that of the products of Examples 1-4.

[0107] The grain boundary phase at a position 200 μm from the surface of the neodymium-iron-boron substrate of Examples 1-4 of the present application contains a carbon-rich phase, and the proportion of the carbon-rich phase is 10%-60%.

[0108] Example 5:

[0109] (1) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed is obtained according to steps (1)-(5) in Example 1.

[0110] (2) The neodymium-iron-boron magnet substrate black sheet with the oxide layer removed in step (1) is coated, and the coating material used for the coating is a mixed coating material containing mixed material A and mixed material B, wherein the mixed material A is a slurry containing 20% graphene oxide, and the mixed material B is a slurry containing 60% Dy.

[0111] The preparation process of the mixture A is as follows: the graphene oxide and the anhydrous ethanol are mixed in a mass ratio of 1:19, and the graphene oxide is dissolved in the anhydrous ethanol through ultrasonic dispersion, the ultrasonic dispersion time is 120 s, and the ultrasonic frequency is 25 Hz.

[0112] The preparation process of the mixture B is as follows: the Dy metal powder, the 4-hexylresorcinol and the ethanol are mixed in a ratio of 6:2:2, and stirred for 3 h to obtain the mixture B.

[0113] The mixture A is added to the mixture B, and the mixture A accounts for 5% of the mixture B. After stirring for more than 180 min, the mixture is fully mixed to obtain a slurry containing graphene oxide and Dy.

[0114] (3) The product to be coated is placed on a tooling, and the coating material is sprayed on the product by immersion spraying, and the thickness of the coating layer is 200 μm.

[0115] (4) The product coated in the above step (3) is loaded into a diffusion furnace, and is heated after being pumped to below 100 Pa, the first stage diffusion temperature is 380 ℃, and the holding time is 3 h, the second stage diffusion temperature is 870 ℃, and the holding time is 12-15 h; the aging treatment temperature is 520 ℃, and the time is 3-4 h, and the neodymium-iron-boron magnet diffusion product is obtained.

[0116] (5) The neodymium-iron-boron magnet diffusion product is cut and processed into a neodymium-iron-boron magnet finished product (M7).

[0117] Example 6:

[0118] The same process steps as (1)-(5) in Example 5 are adopted, and the only difference is that the mixture A accounts for 15% of the mixture B in step (2), and a neodymium-iron-boron magnet finished product (M8) is obtained.

[0119] Comparative Example 3:

[0120] (1) The metals of 28% Nd, 2% Co, 1% B, 0.55% Dy, 0.2% Cu, 0.2% Ga and the balance of Fe are mixed and placed in a vacuum melting furnace surrounded by an argon atmosphere, and are melted at 1480 ℃, and are cooled to 1380 ℃ for casting to obtain a flake.

[0121] (2) The flake obtained in step (1) is crushed by a hydrogen explosion furnace to obtain a hydrogen explosion powder, and the hydrogen explosion powder is ground by an air flow mill device to obtain a magnetic powder.

[0122] (3) The magnetic powder obtained in step (2) is pressed into a compact under a magnetic field, and is formed into an isostatic compact by isostatic pressing; the sintered neodymium-iron-boron base material is formed by degassing at 250-850°C, high-temperature sintering at 1060°C, and treatment at 520°C.

[0123] (4) The sintered neodymium-iron-boron base material obtained in step (3) is subjected to primary processing by wire sawing and grinding, to obtain a primary product, a neodymium-iron-boron magnet base material black sheet.

[0124] (5) The neodymium-iron-boron magnet base material black sheet in step (4) is subjected to ultrasonic oil removal, pickling, and water washing, to remove the oxide layer on the surface of the neodymium-iron-boron magnet base material black sheet.

[0125] (6) The neodymium-iron-boron magnet base material black sheet with the oxide layer removed in step (5) is coated, and the raw material used for the coating is: mixed material B. The product to be coated is placed on a jig, and the coating material is sprayed onto the product by immersion spraying.

[0126] The preparation process of the mixed material B is as follows: Dy metal powder, 4-hexylresorcinol, and ethanol are mixed in a ratio of 6:2:2, and stirred for 3 h to obtain the mixed material B.

[0127] (7) The product coated in step (6) is loaded into a diffusion furnace, and is heated after being pumped to below 100 Pa. The first-stage diffusion temperature is 380°C, and the holding time is 3 h. The second-stage diffusion temperature is 870°C, and the holding time is 12-15 h. The aging treatment temperature is 520°C, and the time is 3-4 h. The neodymium-iron-boron magnet diffusion product is obtained at this time.

[0128] (8) The neodymium-iron-boron magnet diffusion product is subjected to cutting processing to obtain a neodymium-iron-boron magnet finished product (M9).

[0129] The above examples 5-6 and comparative example 3 are each produced for 10,000 pieces, and the data of chipped edges and cracks are collected as shown in Table 1. Wet heat tests (test conditions: 85% RH, 85°C) and magnetic property analysis are performed, and the data are shown in Table 3.

[0130] Table 3 Product performance and chipped edge and crack ratio data of examples 5-6 and comparative example 3

[0131] Product Moist heat (corrosion resistance) Chipping and cracking ratio HCj (kA / m) Hk (kA / m) M7 60 min 3.2％ 1642 1582 M8 60 min 2.8％ 1657 1563 M9 30 min 5％ 1650 1570

[0132] By comparing Example 5 (M7), Example 6 (M8) with Comparative Example 3 (M9), the corrosion resistance data of the product with 5%-15% modified graphene oxide added in the diffusion Dy slurry is obviously better than that without the addition of graphene oxide, and the edge chipping and cracking ratio is significantly lower than that without the addition of graphene oxide, and with the increase of the proportion of graphene oxide (5%-15%), the edge chipping and cracking ratio gradually decreases. The addition of Dy slurry in the slurry is mainly to improve the magnetic properties of the product. Comparative Example 3 (M9) increases the Dy slurry compared with Comparative Example 1 (M5), and the magnetic properties (HCj and Hk) are higher than those of M5. The mixed slurry B containing Dy slurry can also be replaced by Tb slurry, and the corrosion resistance and edge chipping and cracking ratio of the obtained product are equivalent, but the magnetic property improvement is better.

[0133] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A corrosion-resistant neodymium iron boron material, characterized in that, The surface of the neodymium iron boron substrate has a graphene oxide layer at the grain boundaries; The carbon content of the NdFeB substrate has a concentration gradient from the surface to the center, and the carbon content concentration gradually decreases from the surface to the center; The carbon content on the surface of the NdFeB substrate is 7% or more higher than the carbon content at the center. The carbon content at a position 200 μm from the surface of the NdFeB substrate to the center is 3%-7% higher than that at the center. The carbon content at a depth of 2mm from the center of the NdFeB substrate surface is 0.1%-3% higher than that at the center. Its preparation method includes the following steps: (1) Mix all the components and melt them in a vacuum melting furnace. After cooling, cast the mixture to obtain flakes. (2) The scales obtained in step (1) are processed into magnetic powder by hydrogen explosion and air jet milling; (3) The magnetic powder obtained in step (2) is pressed into a compact under a magnetic field and then isostatically pressed to form an isostatic compact; after being degassed at 250℃-850℃, and then sintered at 1020-1120℃ and aged at 400-600℃, a sintered NdFeB substrate is formed. (4) The sintered NdFeB substrate obtained in step (3) is mechanically processed to obtain a black sheet of NdFeB magnet substrate; (5) The neodymium iron boron magnet substrate black sheet in step (4) undergoes surface pretreatment to remove the oxide layer on the surface; (6) Coating the black sheet of NdFeB magnet substrate with the oxide layer removed in step (5), placing the product to be coated on the tooling, and spraying the coating material onto the product; the coating material used for coating includes graphene, organic solvent and heavy rare earth metal powder; the graphene is graphene oxide, and the mass ratio of graphene oxide to organic solvent is 1:2-20; the heavy rare earth metal powder is pure metal, metal oxide, fluoride or hydride of Dy and / or Tb; (7) The coated product from step (6) is placed in a diffusion furnace for diffusion. The temperature is pumped down to below 100 Pa and then heated. The temperature of the first diffusion stage is 300-400℃ and held for 3-5 hours. The temperature of the second diffusion stage is 820-950℃ and held for 12-30 hours. The aging treatment temperature is 400-600℃ and the time is 3-5 hours to obtain the NdFeB magnet diffused product. (8) The neodymium iron boron magnet diffuser obtained in step (7) is cut and processed into a neodymium iron boron magnet finished product.

2. The corrosion-resistant NdFeB material according to claim 1, characterized in that, Neodymium iron boron substrates are formed by sintering raw materials with the following components: R1: 28%wt-33wt%; T1: 63wt%-70wt%; B: 0.94wt%-1.10wt%; M1: 0-3wt% Wherein, R1 is selected from Nd or a mixture of Nd with at least one of Pr, La, Ce, Dy, Tb, Ho, and Gd; T1 is Fe and / or Co; M1 is at least one of Cu, Ga, Zr, Ti, and Nb.

3. The corrosion-resistant NdFeB material according to claim 1, characterized in that, The preparation process of the coating material is as follows: ① Mix graphene oxide with an organic solvent and disperse it by ultrasonication. Dissolve the graphene oxide in the organic solvent. The ultrasonic dispersion time is 60-300s and the ultrasonic frequency is 25-28Hz. Stir the graphene oxide and organic solvent mixture for more than 10 minutes to achieve full mixing and obtain mixture A. ② Add antioxidant and diluent to heavy rare earth metal powder and mix. The weight ratio of heavy rare earth metal powder is 40-70%, the weight ratio of antioxidant is 15-30%, and the weight ratio of diluent is 15-30%. Stir for 1-4 hours until uniform to obtain mixture B. Add mixture A obtained in step ① to mixture B and stir for more than 180 minutes to achieve full mixing to obtain a coating material for corrosion-resistant NdFeB materials. The volume of mixture A accounts for 5-15% of the volume of mixture B; The antioxidant is at least one of toluene, 4-hexylresorcinol, and butylated hydroxytoluene; the diluent is at least one of ethanol, benzyl alcohol, and acetone.

4. The corrosion-resistant NdFeB material according to claim 1, characterized in that, In step (5), the oxide layer on the surface of the NdFeB magnet substrate black sheet is removed by ultrasonic degreasing, acid washing, and water washing.

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