Protective Coating on the Surface of NdFeB Permanent Magnet for Wind Power, Preparation Method and Permanent Magnet

Abstract

The present invention relates to a protective coating on the surface of a neodymium-iron-boron permanent magnet for wind power, a preparation method thereof, and a permanent magnet, belonging to the technical field of surface anti-corrosion coatings, and solves the problem of poor protective ability of the surface coating of the sintered neodymium-iron-boron permanent magnet used in existing wind turbines. The protective coating includes: along the direction of entering the neodymium-iron-boron matrix, the protective coating sequentially includes a surface co-permeation layer and an interface diffusion layer; the surface co-permeation layer is a metal layer composed of zinc element and cobalt element; the interface diffusion layer is a metal layer composed of zinc element, cobalt element and iron element. The technical solution provided by the present invention can improve the adhesion and corrosion resistance of the protective coating.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface anti-corrosion coatings, and particularly relates to a protective coating on the surface of a neodymium-iron-boron permanent magnet for wind power, a preparation method thereof, and a permanent magnet. Background Art

[0002] Wind energy is a renewable clean energy source. With the gradual maturity of technology, wind power generation has become the new energy power generation method with the largest application scale globally. By the end of 2020, the cumulative grid-connected installed capacity of wind power in China will exceed 210 million kilowatts, and the power generation cost is basically equivalent to that of coal-fired power, among which the grid-connected capacity of offshore wind power exceeds 5 million kilowatts. Sintered neodymium-iron-boron permanent magnets are important components in wind turbines.

[0003] The designed service life of a wind turbine is generally 20 years. The neodymium-iron-boron magnets in the unit are extremely vulnerable to corrosion in a humid environment. Compared with the land environment, the harsh environment in the offshore or marine areas poses higher requirements for the anti-corrosion project of offshore wind turbine equipment, especially bringing greater challenges to the anti-corrosion technology of neodymium-iron-boron permanent magnets in the unit. Therefore, the surface protection quality of neodymium-iron-boron permanent magnets becomes the key to the safe and stable operation of wind turbine units.

[0004] Common surface protection means for the surface of neodymium-iron-boron magnets include galvanizing, nickel plating, electrophoresis, coating with an organic coating, etc. These coatings cannot meet the anti-corrosion requirements of neodymium-iron-boron magnets used in offshore wind turbines. In view of the characteristics of the harsh working environment and long maintenance cycle of wind turbine units, researchers have studied the surface protection capabilities of coatings such as dacromet coatings, zinc + organic coatings, and vacuum aluminizing on permanent magnets. Although these coatings can extend the service life of the magnets, they cannot improve the disadvantage that the neodymium-iron-boron magnets start to corrode from the inside of the structure, resulting in coating peeling. In addition, the dacromet coating contains metallic chromium (Cr), which will pollute the environment. Therefore, it is urgent to develop a high-protection coating technology for the surface of magnets.

[0005] Although the vacuum powder zinc infiltration coating has more excellent corrosion resistance than electro-galvanizing and hot-dip galvanizing, compared with hot-dip galvanizing, the powder co-infiltration treatment has lower energy consumption and is a clean production process for energy conservation and emission reduction; at the same time, in order to further improve the corrosion resistance of the zinc infiltration layer, researchers have also developed multi-element alloy co-infiltration coatings such as zinc-aluminum-magnesium and zinc-nickel, and the alloy co-infiltration process has been used in anti-corrosion projects in fields such as railways, bridges, and highways. However, due to the cross-action of factors such as salts, ultraviolet radiation, temperature difference, and humidity in the marine environment, the corrosion resistance of existing multi-element co-infiltration coatings still cannot meet the protection requirements for the 20-year service life of unit equipment in the offshore wind power industry. Summary of the Invention

[0006] In view of the above analysis, the embodiment of the present invention aims to provide a protective coating on the surface of a neodymium iron boron permanent magnet for wind power, a preparation method thereof, and a permanent magnet, so as to solve the problem of poor surface coating protection ability of the sintered neodymium iron boron permanent magnet used in existing wind turbines, and provide a zinc cobalt co-deposited layer with strong adhesion and excellent corrosion resistance.

[0007] In the first aspect, the present invention provides a protective coating on the surface of a neodymium iron boron permanent magnet for wind power. Along the direction of entering the neodymium iron boron matrix, the protective coating sequentially includes a surface co-deposited layer and an interface diffusion layer;

[0008] The surface co-deposited layer is a metal layer composed of zinc element and cobalt element; the interface diffusion layer is a metal layer composed of zinc element, cobalt element and iron element.

[0009] Further, the protective coating is obtained by co-depositing zinc cobalt alloy powder, and the mass percentage content of metallic cobalt in the zinc cobalt alloy powder is 10wt%-13wt%.

[0010] Further, the thickness of the surface co-deposited layer is 5-10μm, and the thickness of the interface diffusion layer is 3μm-6μm.

[0011] Further, in the surface co-deposited layer, the content of zinc is 87-90wt%, and the content of cobalt is 10-13wt%; in the interface diffusion layer, the content of zinc is 83-87wt%, the content of cobalt is 8-10wt%, and the rest is iron.

[0012] Further, by mass, the co-depositing materials include: 42-44 parts of zinc cobalt alloy powder, 1-5 parts of activator, and 53-55 parts of inert medium.

[0013] In the second aspect, the embodiment of the present invention provides a preparation method of a protective coating on the surface of a neodymium iron boron permanent magnet for wind power. To prepare the protective coating on the surface of the neodymium iron boron permanent magnet for wind power according to any one of the first aspect, the method includes the following steps:

[0014] Step 1, weigh each raw material of the co-depositing materials and mix them evenly;

[0015] Step 2, clean the neodymium iron boron permanent magnet and set it aside after drying;

[0016] Step 3, sequentially load the co-depositing materials and the permanent magnet into the vacuum furnace inside the heat treatment furnace, close the hatch of the vacuum furnace; finally close the two symmetrically distributed left and right heating tanks on the outer layer.

[0017] Step 4, start the rotation of the vacuum furnace, and mix the co-depositing materials and the permanent magnet evenly;

[0018] Step 5: Evacuate the vacuum furnace. After the vacuum degree in the furnace is lower than 1.0×10-3Pa, inert gas is filled to keep the vacuum degree in the furnace at 1.0×10-3~2.0×10-2Pa;

[0019] Step 6: Start heating. After heating to the target temperature, keep it warm and maintain the vacuum degree at 1.0×10-3~2.0×10-2Pa;

[0020] Step 7: Stop heating, keep the pressure and cool to room temperature, then take out the permanent magnet.

[0021] Further, in the step 2, the neodymium iron boron permanent magnet is placed in a degreasing solution for cleaning, and the components of the degreasing solution include one or more of NaOH, Na3PO4, Na2CO3 and sodium dodecyl benzene sulfonate.

[0022] Further, in the step 3, the co-permeation materials include: zinc-cobalt alloy powder and quartz sand;

[0023] According to the preset thickness of the surface co-permeation layer, add the zinc-cobalt alloy powder. For every 1μm - 2μm increase in the thickness of the surface co-permeation layer, 1000g - 1100g of zinc-cobalt alloy powder needs to be added;

[0024] According to the number of the permanent magnets and the addition amount of the zinc-cobalt alloy powder, add quartz sand. For every additional permanent magnet, 1200g - 1300g of quartz sand is added.

[0025] Further, in the step 5, the vacuum pumping process includes: turn on the mechanical pump to pump vacuum. After the vacuum degree is lower than 5.0Pa, turn on the molecular pump to continue pumping vacuum. After the vacuum degree in the furnace is lower than 1.0×10-3Pa, fill in N2 gas to keep the vacuum degree in the furnace at 1.0×10-3~2.0×10-2Pa.

[0026] Further, in the step 6, the target temperature is 360℃~390℃, and the heat preservation time is 3~4h.

[0027] In the third aspect, an embodiment of the present invention provides a neodymium iron boron permanent magnet for wind power. The surface of the neodymium iron boron permanent magnet is provided with a protective coating, and the protective coating is the protective coating on the surface of the neodymium iron boron permanent magnet for wind power described in the first aspect or the protective coating prepared by the preparation method described in the second aspect.

[0028] Further, the components of the neodymium iron boron permanent magnet for wind power are composed by mass percentage, including: 22.0% - 32.0% Pr-Nd, 0% - 8.0% Nd, 0.3% - 2.4% B, 0% - 6.0% Dy, 0% - 5.0% Tb, 0% - 2.3% Al, 0% - 1.5% Cu, and the rest is Fe.

[0029] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0030] (1) The present invention uses the powder zinc-cobalt infiltration method to prepare a protective coating on the surface of the neodymium-iron-boron permanent magnet. The protective coating is metallurgically bonded to the substrate, and the diffusion layer between the coating and the substrate ensures the firm adhesion of the coating. The zinc-cobalt metal layer in the zinc-cobalt co-infiltration protective coating has more excellent corrosion resistance than the zinc-cobalt metal layer of electro-galvanizing, which can delay the corrosion of the permanent magnet in the marine climate and extend the service life of the device.

[0031] (2) During the thermal diffusion process, multi-metal atoms such as zinc and cobalt are evenly diffused on the surface of the neodymium-iron-boron permanent magnet to form an intermetallic compound composed of zinc, cobalt, and iron. The potential of this compound is higher than that of the zinc / iron compound produced by hot-dip galvanizing and also higher than that of the zinc / nickel / iron compound produced at the zinc-nickel co-infiltration interface, reducing the potential difference between the coating and the permanent magnet and lowering the corrosion driving force, thereby improving the protective ability of the coating.

[0032] (3) Before depositing the coating on the permanent magnet surface using the electro-galvanizing process, pickling of the permanent magnet is required. Since the interior of the neodymium-iron-boron permanent magnet has a loose and porous structure, it is inevitable that residual acid solution remains in the pores of its structure after pickling, which brings great hidden dangers to surface protection. However, the present invention does not require pickling of the permanent magnet, laying a foundation for forming a uniform, dense, and firmly adhered coating.

[0033] (4) According to the infiltration effect of the zinc-cobalt alloy powder and the physical and chemical properties of the neodymium-iron-boron used in the wind turbine generator, the addition amounts of the zinc-cobalt alloy powder and quartz sand corresponding to different thicknesses of the protective coating are determined to obtain quantitative process conditions, so as to improve the applicability of the technical solution provided by the present invention.

[0034] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained from the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals represent the same components.

[0036] Figure 1 It is a schematic structural diagram of a neodymium-iron-boron permanent magnet covered with a zinc-cobalt infiltration layer provided by an embodiment of the present invention;

[0037] Figure 2The physical corrosion morphology diagrams after testing the zinc-permeated NdFeB permanent magnet provided as a comparative example of the present invention and the zinc-cobalt-permeated layer NdFeB permanent magnet of the example by cyclic salt spray test to simulate the marine environmental atmosphere;

[0038] Figure 3 The Auger electron energy spectrum diagram of the NdFeB permanent magnet covered with a zinc-cobalt-permeated layer provided by the example of the present invention;

[0039] Figure 4 The cross-sectional morphology and EPMA micro-area composition diagram of the NdFeB permanent magnet covered with a zinc-cobalt-permeated layer provided by the example of the present invention.

[0040] Reference numerals:

[0041] 101 - Surface co-permeated layer; 102 - Interface diffusion layer; 103 - NdFeB matrix. Detailed implementation manners

[0042] The present invention uses zinc-cobalt alloy powder as a co-permeation material to prepare a protective coating on the surface of the permanent magnet that can resist corrosion in a marine climate, solving the problem of poor protective ability of the surface coating of the sintered NdFeB permanent magnet used in existing wind turbines. In the prior art, protective coatings on the surface of NdFeB permanent magnets, such as electroplated coatings, electrophoresis, organic coatings, and even dacromet coatings, cannot meet the corrosion resistance requirements under the harsh conditions of the marine environment. Powder co-permeation treatment has low energy consumption and is a clean production process for energy conservation and emission reduction. In order to further improve the corrosion resistance of the zinc-permeated layer, researchers have also developed multi-element alloy co-permeated coatings such as zinc-aluminum-magnesium and zinc-nickel. This coating can protect metal fittings from showing red rust in a neutral salt spray atmosphere for more than 700 h, far higher than the 300 - 400 h of the hot-dip galvanized layer. However, due to the cross-action of factors such as salt, ultraviolet radiation, temperature difference, and humidity in the marine environment, the corrosion resistance of the existing multi-element co-permeated coatings still cannot meet the protection requirements for the service life of 20 years of the unit equipment in the offshore wind power industry.

[0043] Metallic cobalt (Co) does not react with water at room temperature and is also very stable in humid air. Similar to chromium, after cobalt ions hydrolyze, a network-like passivation film will be formed, which has a self-healing effect. In the present invention, zinc-cobalt is used as a co-permeation material for co-permeation, which uniformly diffuses on the surface of the NdFeB permanent magnet to form an intermetallic compound composed of zinc, cobalt, and iron. The potential of this compound is higher than the potential of the zinc / iron compound produced by hot-dip galvanizing and also higher than the potential of the zinc / nickel / iron compound produced at the zinc-nickel co-permeation interface, reducing the potential difference between the coating and the permanent magnet and lowering the corrosion driving force, thereby improving the protection ability of the coating.

[0044] Specifically, the present invention provides a protective coating on the surface of a neodymium-iron-boron permanent magnet for wind power generation. Along the direction into the interior of the neodymium-iron-boron substrate, the protective coating sequentially includes a surface co-permeation layer and an interface diffusion layer; the surface co-permeation layer is a metal layer composed of zinc element and cobalt element; the interface diffusion layer is a metal layer composed of zinc element, cobalt element and iron element. Among them, the thickness of the surface co-permeation layer is 5μm - 10μm, and the thickness of the interface diffusion layer is 3μm - 6μm. In the surface co-permeation layer, the content of zinc is 87wt% - 90wt%, and the content of cobalt is 10wt% - 13wt%; in the interface diffusion layer, the content of zinc is 83wt% - 87wt%, the content of cobalt is 8wt% - 10wt%, and the rest is iron.

[0045] The protective coating is obtained by co-permeation of zinc-cobalt alloy powder. The melting point of the zinc-cobalt alloy powder increases with the increase of cobalt content, and at the same time, the thermal diffusion temperature of the zinc-cobalt alloy powder also increases, while high temperature will weaken the magnetic properties of the permanent magnet. Therefore, in the embodiment of the present invention, in the zinc-cobalt alloy powder, the cobalt content is 10 - 13wt% to control the diffusion temperature of the zinc-cobalt alloy powder to be 360°C - 390°C. Thermal diffusion within this temperature range will not cause hydrogen embrittlement problems in the substrate material. Therefore, preferably, the present invention uses zinc-cobalt alloy powder containing 12wt% cobalt as the co-permeation material.

[0046] In the embodiment of the present invention, by mass, the co-permeation material includes:

[0047] 42 - 44 parts of zinc-cobalt alloy powder, 1 - 5 parts of activator, and 53 - 55 parts of inert medium.

[0048] Among them, zinc-cobalt alloy powder is used as the zinc donor to ensure that both zinc element and cobalt element are evenly distributed in the obtained protective coating by infiltration plating. The activator includes ammonium chloride or aluminum chloride, which can decompose to produce trace amounts of hydrogen chloride gas within the co-permeation temperature range. This gas can keep the surface of the permanent magnet in an activated state, which helps the diffusion of metal atoms at the interface. The inert medium includes one or more of quartz sand, brown fused alumina sand, and ceramic sand. Since the neodymium-iron-boron for wind power generation is brittle and fragile, the inert medium is used to avoid the situation of bumps and corners during the tumbling process of the neodymium-iron-boron for wind power generation in the co-permeation furnace.

[0049] In the embodiments of the present invention, the particle size of the zinc-cobalt alloy powder is 10 - 30 μm (such as 15 μm, 20 μm, 25 μm), the particle size of ammonium chloride is 10 - 30 μm (such as 15 μm, 20 μm, 25 μm), and the particle size of quartz sand SiO₂ is 1 - 5 cm (such as 2 cm, 3 cm, 4 cm). Among them, the particle size of the zinc-cobalt alloy powder should not be too large or too small. If the particle size of the alloy powder is too large, the thermal diffusion rate of the alloy powder will decrease; if the particle size of the zinc-cobalt alloy powder is too small, the zinc-cobalt alloy powder is easily oxidized; the particle size of the quartz sand should be determined according to the size of the magnet. Generally, the larger the magnet, the more suitable it is to choose quartz sand with a larger particle size, so that the quartz sand can better ensure that the magnet is not easily chipped due to collision.

[0050] The present invention also provides a method for preparing a surface protection coating for a neodymium-iron-boron permanent magnet used in wind power generation, comprising the following steps:

[0051] Step 1: Weigh each raw material of the co-permeation material and mix them evenly;

[0052] Step 2: Clean the neodymium-iron-boron permanent magnet and set it aside after drying;

[0053] In the embodiments of the present invention, the neodymium-iron-boron permanent magnet is placed in a degreasing solution for cleaning, and the components of the degreasing solution include one or several of NaOH, Na₃PO₄, Na₂CO₃ and sodium dodecylbenzenesulfonate;

[0054] Step 3: Load the co-permeation material and the permanent magnet into the vacuum furnace in sequence, close the hatch of the vacuum furnace; finally, close the two symmetrically distributed left and right heating tanks on the outer layer;

[0055] During infiltration plating, usually only the co-infiltration materials need to cover the permanent magnets. However, wind turbine units are usually in relatively harsh conditions with high salt content, strong ultraviolet radiation, large temperature differences, and high humidity. Therefore, the surface co-infiltration layer needs to be thickened. There are usually two methods for the surface co-infiltration layer: the first is to increase the infiltration plating time, and the second is to increase the amount of zinc-cobalt alloy powder. However, as an important component of a wind power generating unit, it has relatively high requirements for magnetism. Increasing the infiltration plating time will greatly weaken the magnetism of the permanent magnets. Therefore, the second method is adopted in the present invention to increase the thickness of the surface co-infiltration layer. For the same problem, components of different types of wind power generating units or different components of the same wind power generating unit have different requirements for magnetism. For example, the rotors in different models of wind turbines. Therefore, it is necessary to precisely control the thickness of the surface co-infiltration layer on the permanent magnet to meet the magnetism of the permanent magnet in various application scenarios in the wind turbine unit. In the embodiment of the present invention, when the thickness of the surface co-infiltration layer of the permanent magnet increases by 1-2 μm each time, at least 1000 g of zinc-cobalt alloy powder needs to be added. It should be noted that the above quantitative relationship can be preferably selected when the following three conditions are met: first, use zinc-cobalt alloy powder with a cobalt content of 10-13%; second, adopt the infiltration plating method, and the infiltration plating temperature is 360°C to 390°C; third, the material of the permanent magnet is neodymium iron boron and is applied in a wind turbine unit. For example, the components of a neodymium iron boron permanent magnet for wind power are composed by mass percentage, including: 22.0%-32.0% Pr-Nd, 0%-8.0% Nd, 0.3%-2.4% B, 0%-6.0% Dy, 0%-5.0% Tb, 0%-2.3% Al, 0%-1.5% Cu, and the rest is Fe.

[0056] Since neodymium iron boron is brittle and fragile, during infiltration plating, if there are multiple permanent magnets, in order to ensure that the permanent magnets will not be damaged due to mutual collision during the infiltration plating process, it is necessary to control the addition amount of quartz sand. If the quartz sand is too little, the permanent magnets will be damaged mutually during the infiltration plating process. If the quartz sand is too much, the infiltration plating rate will be reduced. In the embodiment of the present invention, in combination with the number of permanent magnets and the addition amount of zinc-cobalt alloy powder, for each additional permanent magnet, 1200 g-1300 g of quartz sand is added. It can be understood that although the zinc-cobalt alloy powder is a zinc supplier, it can also prevent the permanent magnets from colliding with each other to a certain extent during the infiltration plating process. By the above method, it can be ensured that the permanent magnets will not collide with each other and the infiltration plating rate can be ensured. Similarly, the above quantitative relationship is preferably selected when the three conditions in the present invention are met: first, use zinc-cobalt alloy powder with a cobalt content of 10-13%; second, adopt the infiltration plating method, and the infiltration plating temperature is 360°C to 390°C; third, the material of the permanent magnet is neodymium iron boron and is applied in a wind turbine unit.

[0057] Step 4: The vacuum furnace starts to rotate, and the co-infiltration materials and the permanent magnets are mixed evenly;

[0058] Specifically, in step 4, the rotation speed of the heat treatment furnace is 10 - 20 r / min. Within this speed range, a uniform and consistent coating can be obtained quickly, and the permanent magnet is not easily damaged.

[0059] Step 5: Evacuate the vacuum furnace. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, fill it with N2 gas to keep the vacuum degree in the furnace at 1.0×10 -3 ~2.0×10 -2 Pa.

[0060] In the embodiment of the present invention, the vacuum evacuation process is specifically as follows: Start the mechanical pump to evacuate the vacuum. After the vacuum degree is lower than 5.0 Pa, start the molecular pump to continue evacuating the vacuum. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, fill it with N2 gas to keep the vacuum degree in the furnace at 1.0×10 -3 ~2.0×10 -2 Pa. The purpose is to reduce the oxygen content in the furnace atmosphere, slow down the oxidation of the zinc-cobalt alloy powder, and improve the diffusion rate between metal elements.

[0061] Step 6: Start heating. After heating to the target temperature, keep it warm while maintaining the vacuum degree at 1.0×10 -3 ~2.0×10 - 2 Pa.

[0062] In the embodiment of the present invention, the target temperature is 360 - 390 °C, and the heat preservation time is 3 - 4 h. Within this temperature range, the alloy powder will not melt, and the metal atoms can diffuse quickly without causing hydrogen embrittlement problems in the material. The heat preservation time has a direct relationship with the thickness of the co-permeation layer. Prolonging the heat preservation time can thicken the co-permeation layer. However, if the heat preservation time is too long, the interfacial diffusion layer will also thicken. At this time, the increase in the zinc content in the surface layer of the magnet will reduce the magnetic properties of the material, thereby affecting the use value of the magnet. In the embodiment of the present invention, the heating rate is 10 - 20 °C / min.

[0063] Step 7: Stop heating, keep the pressure and cool to room temperature, and take out the permanent magnet.

[0064] The present invention provides a neodymium iron boron permanent magnet for a wind turbine, which is prepared by using the above-mentioned preparation method of the surface protective coating for the neodymium iron boron permanent magnet for wind power generation.

[0065] The following further describes the specific implementation manners of the present invention with reference to embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can understand and utilize the present invention well. However, it should be understood that these descriptions are only exemplary and do not limit the scope of the present disclosure.

[0066] Example 1

[0067] In the neodymium iron boron magnet with dimensions of 80 (L) × 60 (W) × 30 (H) mm prepared in this example, the components are composed by mass percentage, including: 22.0 - 32.0% Pr-Nd, 0 - 8.0% Nd, 0.3 - 2.4% B, 0 - 6.0% Dy, 0 - 5.0% Tb, 0 - 2.3% Al, 0 - 1.5% Cu, and the rest is Fe. The steps are as follows:

[0068] 1) Weigh 2000 g of zinc-cobalt alloy powder with 12 wt% cobalt and a particle size of 10 - 30 μm, 47.6 g of ammonium chloride with a particle size of 10 μm, and 2620 g of quartz sand with a particle size of 1 cm, and mix them evenly to obtain the co-permeation material;

[0069] 2) Place the neodymium iron boron permanent magnet substrate in a degreasing solution composed of 3 - 5 g / L NaOH, 12 g / L Na2CO3, 1 g / L Na3PO4, and 0.3 ml / L sodium dodecyl benzene sulfonate, and ultrasonically wash for 5 minutes to remove dirt such as mineral oil used during machining on the magnet surface, otherwise it will affect the adhesion of the co-permeation layer. Then place it in an 80°C oven to dry for later use;

[0070] 3) Load the above co-permeation material into the vacuum furnace body, and then load 6 neodymium iron boron permanent magnet substrates, and close the heat treatment furnace hatch;

[0071] 4) Start the rotating device, and the heat treatment furnace starts to rotate, so that the co-permeation material and the permanent magnet are fully mixed for 10 minutes;

[0072] 5) Turn on the mechanical pump to pump vacuum. After the vacuum degree is lower than 5.0 Pa, turn on the molecular pump to continue pumping vacuum. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, fill in N2 to keep the vacuum degree in the furnace within the range of 1.0×10 -3 ~2.0×10 -2 Pa;

[0073] 6) Turn on the heating device to start heating the co-permeation material and the neodymium iron boron permanent magnet;

[0074] 7) Heat the heat treatment furnace to 360°C and keep it for 4 hours. During this period, continuously fill in N2 gas and keep the vacuum degree within the range, and the furnace body rotates at a constant speed with a rotation speed of 20 r / min;

[0075] 8) Stop heating, continuously introduce N2, keep the vacuum degree in the furnace within the range. Wait for the furnace temperature to drop to room temperature, turn off the rotating device; open the exhaust valve, increase the pressure in the furnace to atmospheric pressure, open the furnace door, separate the furnace materials, and take out the permanent magnet;

[0076] 9) Ultrasonically clean the permanent magnet in deionized water for 5 min to remove surface grit, and then place it in an oven at 80 °C for drying to prevent oxidation of the permanent magnet surface, obtaining a neodymium-iron-boron permanent magnet with a protective coating on its surface.

[0077] Repeat the implementation multiple times, extract 3 specimens for neutral salt spray test to evaluate the protective performance of the zinc-cobalt diffusion layer. The concentration of the NaCl solution in the neutral salt spray test is 5 wt%, the pH is 6.5 - 7.2, the test temperature is 35 ± 2 °C, and the sedimentation rate is 1 - 2 ml / 80 cm 2 ·h; Observe the appearance time and area of white rust and red rust on the magnet surface. The later the appearance time of rust and the smaller the area, the stronger the protective ability. The thickness of the surface co-deposited layer is 5 - 6 μm, and the thickness of the interface diffusion layer is 3.1 μm. In the surface co-deposited layer, the zinc content is 87.6 wt%, and the cobalt content is 10.5 wt%; in the interface diffusion layer, the zinc content is 83.2 wt%, and the cobalt content is 8.8 wt%, and the rest is iron. After 1200 h of neutral salt spray test, no red rust appears on the magnet surface, and no blistering or peeling occurs on the coating; under the same conditions (referring to the same coating thickness and salt spray test conditions), the surface of the permanent magnet with zinc electroplating shows white rust after 72 h of testing and red rust after 240 h of testing.

[0078] Example 2

[0079] This example is used to prepare the composition of each component in a neodymium-iron-boron magnet of 80 (L) × 60 (W) × 30 (H) mm by mass percentage, including: 22.0 - 32.0% Pr-Nd, 0 - 8.0% Nd, 0.3 - 2.4% B, 0 - 6.0% Dy, 0 - 5.0% Tb, 0 - 2.3% Al, 0 - 1.5% Cu, and the rest is Fe. It includes the following steps:

[0080] 1) Weigh 3000 g of zinc-cobalt alloy powder with 12 wt% cobalt having a particle size of 10 - 30 μm, 142.8 g of ammonium chloride with a particle size of 15 μm, and 2657.0 g of quartz sand with a particle size of 2 cm, and mix them evenly to obtain the co-deposition material;

[0081] 2) Place the neodymium-iron-boron permanent magnet substrate in a degreasing solution composed of 3 - 5 g / L NaOH, 12 g / L Na2CO3, 1 g / L Na3PO4, and 0.3 ml / L sodium dodecylbenzenesulfonate, ultrasonically wash for 5 min, and then place it in an oven at 80 °C for drying and standby;

[0082] 3) Load the above co-deposition material into the vacuum furnace body, and then load 6 neodymium-iron-boron permanent magnet substrates, and close the heat treatment furnace hatch;

[0083] 4) Start the rotating device, the heat treatment furnace starts to rotate, and the co-deposition material and the permanent magnet are fully mixed for 10 min;

[0084] 5) Start the mechanical pump to evacuate the air. After the vacuum degree is lower than 5.0 Pa, start the molecular pump to continue evacuating the air. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, charge N2 to keep the vacuum degree in the furnace within the range of 1.0×10 -3 ~2.0×10 -2 Pa;

[0085] 6) Start the heating device to raise the temperature of the co-permeation material and the NdFeB permanent magnet;

[0086] 7) Heat the heat treatment furnace to 360 °C and keep it for 4 h. During this period, always charge inert gas and keep the vacuum degree within the range. The furnace body rotates at a constant speed with a rotation speed of 18 r / min;

[0087] 8) Stop heating, continuously introduce N2, keep the vacuum degree in the furnace within the range. Wait for the furnace temperature to drop to room temperature, then turn off the rotating device; open the exhaust valve, raise the pressure in the furnace to atmospheric pressure, open the furnace door, separate the furnace charge, and take out the permanent magnet;

[0088] 9) Ultrasonically clean the permanent magnet in deionized water for 5 min to remove surface grit, and then place it in an oven at 80 °C to dry, obtaining a NdFeB permanent magnet with a protective coating on the surface.

[0089] Repeat Example 2 multiple times, extract 3 specimens for neutral salt spray test to evaluate the protective performance of the zinc-cobalt infiltration layer. The concentration of the NaCl solution in the neutral salt spray experiment is 5 wt%, the pH is 6.5 - 7.2, the test temperature is 35±2 °C, and the sedimentation rate is 1 - 2 ml / 80 cm 2 ·h; Observe the appearance time and area of white rust and red rust on the surface of the magnet. The later the appearance time of rust and the smaller the area, the stronger the protective ability. The thickness of the surface co-permeation layer is 7 - 8 μm, and the thickness of the interface diffusion layer is 3.2 μm. In the surface co-permeation layer, the zinc content is 88.2 wt%, and the cobalt content is 11.1 wt%; in the interface diffusion layer, the zinc content is 83.6 wt%, and the cobalt content is 9.1 wt%, and the rest is iron. After 1200 h of neutral salt spray test, no red rust appears on the surface of the magnet, and no blistering or peeling occurs on the coating; under the same conditions, after 72 h of testing, white rust appears on the surface of the permanent magnet with zinc electroplated on the surface, and red rust appears on the surface after 288 h.

[0090] Example 3

[0091] This embodiment is used for preparing a neodymium-iron-boron magnet with dimensions of 80 (L) × 60 (W) × 30 (H) mm, and the components are composed by mass percentage, including: 22.0 - 32.0% Pr-Nd, 0 - 8.0% Nd, 0.3 - 2.4% B, 0 - 6.0% Dy, 0 - 5.0% Tb, 0 - 2.3% Al, 0 - 1.5% Cu, and the balance is Fe. It includes the following steps:

[0092] 1) Weigh 4000 g of zinc-cobalt alloy powder with 12 wt% cobalt and a particle size of 10 - 30 μm, 279.0 g of ammonium chloride with a particle size of 20 μm, and 3863.2 g of quartz sand with a particle size of 3 cm, and mix them evenly to obtain the co-permeation material;

[0093] 2) Place the neodymium-iron-boron permanent magnet substrate in a degreasing solution composed of 3 - 5 g / L NaOH, 12 g / L Na2CO3, 1 g / L Na3PO4, and 0.3 ml / L sodium dodecylbenzenesulfonate, ultrasonically wash for 5 min, and then place it in an 80 °C oven to dry for later use;

[0094] 3) Load the above co-permeation material into the vacuum furnace body, and then load 7 neodymium-iron-boron permanent magnet substrates, and close the heat treatment furnace hatch;

[0095] 4) Start the rotating device, and the heat treatment furnace starts to rotate, so that the co-permeation material and the permanent magnet are fully mixed for 10 min;

[0096] 5) Then turn on the mechanical pump to evacuate the air. After the vacuum degree is lower than 5.0 Pa, turn on the molecular pump to continue evacuating the air. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, fill in nitrogen gas to keep the vacuum degree in the furnace within the range of 1.0×10 -3 ~2.0×10 -2 Pa;

[0097] 6) Turn on the heating device to start heating the co-permeation material and the neodymium-iron-boron permanent magnet;

[0098] 7) Heat the heat treatment furnace to 360 °C and keep it at this temperature for 4 h. During this period, always fill in nitrogen gas and keep the vacuum degree within the range, and the furnace body rotates at a constant speed with a rotation speed of 15 r / min;

[0099] 8) Stop heating, continuously introduce nitrogen gas, keep the vacuum degree in the furnace within the range. Wait until the furnace temperature drops to room temperature, then turn off the rotating device; open the exhaust valve, increase the pressure in the furnace to atmospheric pressure, open the furnace door, separate the furnace charge, and take out the permanent magnet;

[0100] 9) Ultrasonically clean the permanent magnet in deionized water for 5 min to remove the surface grit, and then place it in an 80 °C oven to dry, obtaining a neodymium-iron-boron permanent magnet with a protective coating on its surface.

[0101] Repeat Example 3 multiple times, extract 3 specimens for neutral salt spray test to evaluate the protective performance of the zinc-cobalt infiltrated layer. The concentration of the NaCl solution in the neutral salt spray experiment is 5wt%, the pH is 6.5 - 7.2, the test temperature is 35 ± 2°C, and the sedimentation rate is 1 - 2 ml / 80 cm 2 ·h; Observe the appearance time and area of white rust and red rust on the surface of the magnet. The later the appearance time of rust and the smaller the area, the stronger the protective ability. The thickness of the surface co-infiltrated layer is 8 - 9 μm, and the thickness of the interface diffusion layer is 3.3 μm. In the surface co-infiltrated layer, the zinc content is 88.5wt%, and the cobalt content is 11.5wt%; in the interface diffusion layer, the zinc content is 84.0wt%, the cobalt content is 9.3wt%, and the rest is iron. After 1200 h of neutral salt spray test, no red rust appears on the surface of the magnet, and no blistering or peeling occurs on the coating; under the same conditions, after 72 h of testing, white rust appears on the surface of the permanent magnet infiltrated with zinc on the surface, and red rust appears on the surface after 336 h.

[0102] Example 4

[0103] In this example, the mass percentage composition of each component in the NdFeB magnet with dimensions of 80(L)×60(W)×30(H) mm includes: 22.0 - 32.0% Pr-Nd, 0 - 8.0% Nd, 0.3 - 2.4% B, 0 - 6.0% Dy, 0 - 5.0% Tb, 0 - 2.3% Al, 0 - 1.5% Cu, and the rest is Fe. It includes the following steps:

[0104] 1) Weigh 5000 g of zinc-cobalt alloy powder with 12wt% cobalt having a particle size of 10 - 30 μm, 465.1 g of ammonium chloride with a particle size of 25 μm, and 3863.0 g of quartz sand with a particle size of 4 cm, and mix them evenly to obtain the co-infiltration material;

[0105] 2) Place the NdFeB permanent magnet substrate in a degreasing solution composed of 3 - 5 g / L NaOH, 12 g / L Na2CO3, 1 g / L Na3PO4, and 0.3 ml / L sodium dodecylbenzenesulfonate, ultrasonically wash for 5 min, and then place it in an 80°C oven to dry for later use;

[0106] 3) Load the above co-infiltration material into the vacuum furnace body, then load 7 NdFeB permanent magnet substrates, and close the heat treatment furnace hatch;

[0107] 4) Start the rotating device, the heat treatment furnace starts to rotate, and the co-infiltration material and the permanent magnet are fully mixed for 10 min;

[0108] 5) Then turn on the mechanical pump to evacuate. After the vacuum degree is lower than 5.0 Pa, turn on the molecular pump to continue evacuating. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, fill in nitrogen to keep the vacuum degree in the furnace at 1.0×10-3 ~2.0×10 -2 Pa range;

[0109] 6) Turn on the heating device to start heating the co-permeation material and the NdFeB permanent magnet;

[0110] 7) Heat the heat treatment furnace to 360 °C and hold for 4 h. During this period, nitrogen is always filled, and the vacuum degree is maintained within the range. The furnace body rotates at a constant speed, and the rotation speed is 12 r / min;

[0111] 8) Stop heating, continuously introduce nitrogen, maintain the vacuum degree in the furnace within the range. Wait until the furnace temperature drops to room temperature, then turn off the rotating device; open the exhaust valve, the pressure in the furnace rises to atmospheric pressure, open the furnace door, separate the furnace charge, and take out the permanent magnet;

[0112] 9) Ultrasonically clean the permanent magnet in deionized water for 5 min to remove surface grit, and then place it in an 80 °C oven to dry to obtain a NdFeB permanent magnet with a protective coating on the surface.

[0113] Repeat Example 4 multiple times, and extract 3 specimens for neutral salt spray test to evaluate the protective performance of the zinc-cobalt infiltration layer. The concentration of the NaCl solution in the neutral salt spray experiment is 5 wt%, the pH is 6.5 - 7.2, the test temperature is 35 ± 2 °C, and the sedimentation rate is 1 - 2 ml / 80 cm 2 ·h; Observe the appearance time and area of white rust and red rust on the surface of the magnet. The later the appearance time of rust and the smaller the area, the stronger the protection ability. The thickness of the surface co-permeation layer is 9 - 10 μm, and the thickness of the interface diffusion layer is 3.4 μm. In the surface co-permeation layer, the zinc content is 89.0 wt%, and the cobalt content is 11.8 wt%; in the interface diffusion layer, the zinc content is 84.3 wt%, and the cobalt content is 9.5 wt%, and the rest is iron. After 1200 h of neutral salt spray test, no red rust appears on the surface of the magnet, and no bubbling or peeling occurs on the coating; under the same conditions, the surface of the permanent magnet with zinc electroplating shows white rust after 72 h of testing and red rust after 360 h.

[0114] Example 5

[0115] This example is used to prepare a NdFeB magnet with dimensions of 80 (L) × 60 (W) × 30 (H) mm. The mass percentage composition of each component includes: 22.0 - 32.0% Pr-Nd, 0 - 8.0% Nd, 0.3 - 2.4% B, 0 - 6.0% Dy, 0 - 5.0% Tb, 0 - 2.3% Al, 0 - 1.5% Cu, and the rest is Fe. It includes the following steps:

[0116] 1) Weigh 5000 g of zinc-cobalt alloy powder with 12 wt% cobalt and a particle size of 10 - 30 μm, 465.1 g of ammonium chloride with a particle size of 25 μm, and 5075.0 g of quartz sand with a particle size of 5 cm, and mix them evenly to obtain the co-permeation material;

[0117] 2) Place the neodymium-iron-boron permanent magnet substrate in a degreasing solution composed of 3 - 5 g / L NaOH, 12 g / L Na2CO3, 1 g / L Na3PO4, and 0.3 ml / L sodium dodecylbenzenesulfonate, ultrasonically wash for 5 min, and then place it in an 80°C oven to dry for later use;

[0118] 3) Load the above co-permeation material into the vacuum furnace body, then load 8 neodymium-iron-boron permanent magnet substrates, and close the heat treatment furnace hatch;

[0119] 4) Start the rotating device, the heat treatment furnace starts to rotate, and the co-permeation material and the permanent magnet are fully mixed for 10 min;

[0120] 5) Then turn on the mechanical pump to pump vacuum. After the vacuum degree is lower than 5.0 Pa, turn on the molecular pump to continue pumping vacuum. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, fill in nitrogen gas to keep the vacuum degree in the furnace within the range of 1.0×10 -3 ~2.0×10 -2 Pa;

[0121] 6) Turn on the heating device to make the co-permeation material and the neodymium-iron-boron permanent magnet start to heat up;

[0122] 7) The heat treatment furnace is heated to 360°C and kept warm for 4 h. During this period, nitrogen gas is always filled in, and the vacuum degree is kept within the range. The furnace body rotates at a constant speed with a rotation speed of 10 r / min;

[0123] 8) Stop heating, continuously introduce nitrogen gas, keep the vacuum degree in the furnace within the range. Wait for the furnace temperature to drop to room temperature, turn off the rotating device; open the exhaust valve, the pressure in the furnace rises to atmospheric pressure, open the furnace door, separate the furnace charge, and take out the permanent magnet;

[0124] 9) Ultrasonically clean the permanent magnet in deionized water for 5 min to remove the surface grit, and then place it in an 80°C oven to dry to obtain a neodymium-iron-boron permanent magnet with a protective coating on the surface.

[0125] Repeat Example 5 multiple times, extract 3 specimens for neutral salt spray test to evaluate the protective performance of the zinc-cobalt infiltration layer. The concentration of the NaCl solution in the neutral salt spray experiment is 5 wt%, the pH is 6.5 - 7.2, the test temperature is 35 ± 2°C, and the sedimentation rate is 1 - 2 ml / 80 cm 2·h; Observe the appearance time and area of white rust and red rust on the magnet surface. The later the appearance time of rust and the smaller the area, the stronger the protection ability. The thickness of the surface co-permeation layer is 9 - 10 μm, and the thickness of the interface diffusion layer is 3.5 μm. In the surface co-permeation layer, the zinc content is 89.4 wt%, and the cobalt content is 12.3 wt%; in the interface diffusion layer, the zinc content is 84.6 wt%, the cobalt content is 9.7 wt%, and the rest is iron. After 1200 h of neutral salt spray test, no red rust appears on the magnet surface, and no blistering or peeling occurs on the coating; under the same conditions, after 72 h of testing, white rust appears on the surface of the permanent magnet with zinc electroplated on the surface, and red rust appears on the surface after 420 h.

[0126] The permanent magnet structures obtained in Examples 1 - 5 are as Figure 1 shown, including: a surface co-permeation layer 101, an interface diffusion layer 102, and a neodymium iron boron matrix 103. Among them, Figure 3 and Figure 4 can prove the above structure.

[0127] Specifically, use the Auger electron detection method to detect the distribution of each element in the neodymium iron boron matrix. Let the Auger electrons pass through the surface penetration layer 101, the boundary diffusion layer 102, and the neodymium iron boron matrix 103 in sequence. The detection results are as Figure 3 shown. At 100 min, the zinc content suddenly drops sharply, and the iron content rises sharply, indicating that the Auger electrons have penetrated the surface penetration layer, thus proving that the surface penetration layer indeed forms a layered structure on the surface of the neodymium iron boron matrix 103. At 120 min, the iron content is the largest, indicating that the Auger electrons have completely entered the neodymium iron boron matrix 103, and the cobalt content fluctuates continuously between 100 min - 120 min, indicating that cobalt forms an interface diffusion layer 102 between the surface penetration layer 101 and the neodymium iron boron matrix 103.

[0128] Figure 4 In, a is the overall image of the protective coating and the neodymium iron boron matrix in the sample, b is the distribution of metallic zinc in the corrosion-resistant coating in the sample, c is the distribution of metallic iron in the sample, and d is the distribution of metallic cobalt in the sample, where the sample is a neodymium iron boron permanent magnet coated with the protective coating provided in the embodiment of the present invention. It can be seen that in the technical solution of the present invention, metallic cobalt can indeed form a relatively thin interface diffusion layer in the neodymium iron boron matrix. At the same time, metallic cobalt also uses the interface diffusion layer as the demarcation line, and its distribution on the neodymium iron boron matrix side is significantly more than that on the surface co-permeation layer side. Since in the embodiment of the present invention, the potential of neodymium iron boron is the lowest, zinc element is the second, and cobalt element is the highest, the above method can make the mixed potential of neodymium iron boron and cobalt very close to the mixed potential of zinc element and cobalt element.

[0129] Example 6

[0130] The particle size of the zinc-cobalt alloy powder is 15 μm. The material components and process conditions are the same as those in Example 1, and the thickness of the obtained surface co-permeation layer is 5.9 μm.

[0131] Example 7

[0132] The particle size of the zinc-cobalt alloy powder is 20 μm. The material components and process conditions are the same as those in Example 1, and the thickness of the obtained surface co-permeation layer is 5.6 μm.

[0133] Example 8

[0134] The particle size of the zinc-cobalt alloy powder is 25 μm. The material components and process conditions are the same as those in Example 1, and the thickness of the obtained surface co-permeation layer is 5.0 μm.

[0135] It can be seen from Examples 6-8 that under the same process conditions, the smaller the particle size of the zinc-cobalt alloy powder, the thicker the surface co-permeation layer obtained by co-permeation. This means that reducing the powder particle size can improve the co-permeation rate, shorten the co-permeation treatment time, so as to improve production efficiency and reduce production costs. At the same time, the obtained coating is more uniform and dense, so as to enhance the protective performance of the coating. Therefore, on the premise of meeting the process technical requirements, using small particle size powder for co-permeation treatment not only has higher economic benefits, but also has higher corrosion resistance of the coating.

[0136] Comparative Example 1

[0137] The mass percentage composition of each component in the 80 (L) × 60 (W) × 30 (H) mm neodymium-iron-boron magnet prepared in this example includes: 22.0-32.0% Pr-Nd, 0-8.0% Nd, 0.3-2.4% B, 0-6.0% Dy, 0-5.0% Tb, 0-2.3% Al, 0-1.5% Cu, and the rest is Fe. It includes the following steps:

[0138] 1) Weigh 2000 g of zinc powder with a particle size of 10-30 μm, 47.6 g of ammonium chloride with a particle size of 10-30 μm, and 2620 g of quartz sand with a particle size of 1-2 cm, and mix them evenly to obtain the co-permeation material;

[0139] 2) Place the neodymium-iron-boron permanent magnet matrix in a degreasing solution composed of 3-5 g / L NaOH, 12 g / L Na2CO3, 1 g / L Na3PO4, and 0.3 ml / L sodium dodecylbenzenesulfonate, and ultrasonically wash for 5 minutes to remove dirt such as mineral oil used during machining on the magnet surface, otherwise it will affect the adhesion of the co-permeation layer, and then place it in an 80 °C oven to dry for later use;

[0140] 3) Load the above co-permeation material into the vacuum furnace body, and then load 6 neodymium-iron-boron permanent magnet matrices, and close the heat treatment furnace door;

[0141] 4) Start the rotating device, and the heat treatment furnace begins to rotate. The co-permeation materials and the permanent magnets are fully mixed for 10 minutes.

[0142] 5) Turn on the mechanical pump to evacuate. After the vacuum degree is lower than 5.0 Pa, turn on the molecular pump to continue evacuating. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, fill in N2 to keep the vacuum degree in the furnace within the range of 1.0×10 -3 ~2.0×10 -2 Pa.

[0143] 6) Turn on the heating device to start heating the co-permeation materials and the neodymium iron boron permanent magnets.

[0144] 7) Heat the heat treatment furnace to 360 °C and keep it warm for 4 hours. During this period, continuously fill in N2 gas and keep the vacuum degree within the range. The furnace body rotates at a constant speed, and the rotation speed is 20 r / min.

[0145] 8) Stop heating, continuously introduce N2, keep the vacuum degree in the furnace within the range. Wait for the furnace temperature to drop to room temperature, then turn off the rotating device; open the exhaust valve, increase the pressure in the furnace to atmospheric pressure, open the furnace door, separate the furnace charge, and take out the permanent magnets.

[0146] 9) Ultrasonically clean the permanent magnets in deionized water for 5 minutes to remove the surface grit, and then place them in an 80 °C oven to dry to prevent the surface of the permanent magnets from being oxidized, obtaining zinc-plated neodymium iron boron permanent magnets.

[0147] Figure 2 They are the corrosion morphologies (thickness is 20 μm) of the zinc-plated neodymium iron boron permanent magnet (a) and the zinc-cobalt permeation layer neodymium iron boron permanent magnet (b) in the embodiment of the present invention after neutral salt spray testing. From Figure 2 and Table 1, it can be seen that for the zinc-plated neodymium iron boron permanent magnets in the prior art, as the test time increases from 72 h to 480 h, the corrosion degree increases sharply. White rust appears on the surface of the magnet at 72 h, the area of white rust on the surface of the magnet further increases at 168 h, the surface of the magnet is covered with white rust at 480 h, and a large area of red rust appears, and the surface has been completely corroded. For the zinc-cobalt permeation layer neodymium iron boron permanent magnets of the present invention, as the test time increases from 72 h to 1200 h, no red rust appears on the surface of the magnet, and no blistering or peeling occurs on the coating.

[0148] Table 1 Comparison of corrosion resistance between Examples 1-5 and Comparative Examples

[0149]

[0150] In summary, the zinc-cobalt coating of the present invention and its preparation method can be applied to the surface protection process of NdFeB permanent magnets used in wind power, eliminating the pickling process in the pretreatment and obtaining a protective coating with excellent corrosion resistance. The coating significantly improves problems such as bubbling on the surface of NdFeB permanent magnets and poor protective ability, thereby improving the reliability of wind turbines and extending the maintenance cycle of the turbines.

[0151] The embodiments disclosed in the present invention have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should fall within the scope of the present disclosure.

Claims

1. A surface protection coating for a neodymium iron boron permanent magnet used in wind power, characterized in that, Along the direction into the interior of the NdFeB matrix, the protective coating sequentially includes a surface co-permeation layer and an interface diffusion layer; The surface co-permeation layer is a metal layer composed of zinc element and cobalt element; the interface diffusion layer is a metal layer composed of zinc element, cobalt element and iron element; The thickness of the surface co-permeation layer is 5 - 10 μm; The thickness of the interface diffusion layer is 3 μm - 6 μm; In the surface co-permeation layer, the content of zinc is 87wt% - 90wt%, and the content of cobalt is 10wt% - 13wt%; In the interface diffusion layer, the content of zinc is 83wt% - 87wt%, the content of cobalt is 8wt% - 10wt%, and the rest is iron; The protective coating is obtained by co-permeation of zinc-cobalt alloy powder. The mass percentage of metallic cobalt in the zinc-cobalt alloy powder is 10wt% - 13wt%. The diffusion temperature of the zinc-cobalt alloy powder is 360 - 390 °C; according to the preset thickness of the surface co-permeation layer, the zinc-cobalt alloy powder is added. For every 1 μm - 2 μm increase in the thickness of the surface co-permeation layer, 1000g - 1100g of zinc-cobalt alloy powder needs to be added.

2. The surface protection coating of the neodymium iron boron permanent magnet for wind power according to claim 1, characterized in that, By mass, the co-permeation materials include: 42 - 44 parts of zinc-cobalt alloy powder, 1 - 5 parts of activator, and 53 - 55 parts of inert medium.

3. A preparation method of a surface protective coating for a neodymium-iron-boron permanent magnet used in wind power generation, for preparing the surface protective coating for the neodymium-iron-boron permanent magnet used in wind power generation as described in claim 1 or 2, characterized in that, It includes the following steps: Step 1, Weigh each raw material of the co-permeation materials and mix them evenly; Step 2, Clean the NdFeB permanent magnet and set it aside after drying; Step 3, Load the co-permeation materials and the permanent magnet into the vacuum furnace in sequence, close the furnace door of the vacuum furnace; finally, close the two symmetrically distributed left and right heating tanks on the outer layer; Step 4, The vacuum furnace starts to rotate, and the co-permeation materials and the permanent magnet are mixed evenly; Step 5: Evacuate the vacuum furnace. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, inert gas is filled in to keep the vacuum degree in the furnace at 1.0×10 -3 ~2.0×10 -2 Pa; Step 6: Start heating up. After heating up to the target temperature, keep it insulated and maintain the vacuum degree at 1.0×10 -3 ~2.0×10 -2 Pa; Step 7, Stop heating, keep the pressure and cool to room temperature, and take out the permanent magnet.

4. The preparation method of the surface protective coating for the NdFeB permanent magnet used in wind power according to claim 3, wherein In Step 3, the co-permeation materials include: zinc-cobalt alloy powder and quartz sand; According to the preset thickness of the surface co-permeation layer, the zinc-cobalt alloy powder is added. For every 1 μm - 2 μm increase in the thickness of the surface co-permeation layer, 1000g - 1100g of zinc-cobalt alloy powder needs to be added; According to the number of the permanent magnets and the addition amount of the zinc-cobalt alloy powder, quartz sand is added. For every additional permanent magnet, 1200g - 1300g of quartz sand is added.

5. The preparation method of the surface protection coating for the NdFeB permanent magnet used in wind power according to claim 3, wherein, In the said step 5, the vacuum pumping process includes: starting the mechanical pump to pump vacuum. After the vacuum degree is lower than 5.0 Pa, start the molecular pump to continue pumping vacuum. After the vacuum degree in the furnace is lower than 1.0×10 -3 Pa, fill in N2 gas to keep the vacuum degree in the furnace at 1.0×10 -3 ~2.0×10 -2 Pa.

6. The preparation method of the surface protection coating for the NdFeB permanent magnet used in wind power according to claim 3, wherein, In Step 6, the target temperature is 360 °C - 390 °C, and the heat preservation time is 3 - 4 h.

7. A neodymium iron boron permanent magnet for wind power, characterized in that, The surface of the NdFeB permanent magnet contains a protective coating, and the protective coating is the protective coating for the surface of the NdFeB permanent magnet for wind power generation as described in Claim 1 or 2 or the protective coating prepared by the preparation method described in any one of Claims 3 to 6.

8. The neodymium iron boron permanent magnet for wind power according to claim 7, characterized in that, In the NdFeB permanent magnet for wind power generation, each component is composed by mass percentage, including: 22.0% - 32.0% Pr-Nd, 0% - 8.0% Nd, 0.3% - 2.4% B, 0% - 6.0% Dy, 0% - 5.0% Tb, 0% - 2.3% Al, 0% - 1.5% Cu, and the rest is Fe.

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