High-corrosion-resistance protective layer, preparation method thereof and neodymium-iron-boron permanent magnet comprising protective layer

Abstract

The invention provides a high-corrosion-resistance protective layer, a preparation method of the high-corrosion-resistance protective layer and a neodymium iron boron permanent magnet comprising the high-corrosion-resistance protective layer. The protective layer sequentially comprises a plating layer, a metal oxide layer and an organic coating layer, wherein the plating layer is positioned on the surface of the substrate. The protective layer is obtained on the neodymium-iron-boron permanent magnet substrate, so that the adhesive force, wear resistance and corrosion resistance of the protective layer are greatly improved, the stone impact resistance of the neodymium-iron-boron permanent magnet is improved, and the edge and crack situations of the permanent magnet are also improved.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology of neodymium iron boron permanent magnet materials, and particularly relates to a highly corrosion-resistant protective layer, its preparation method, and a neodymium iron boron permanent magnet including the protective coating. Background Technology

[0002] With the continuous development of sintered NdFeB materials, the requirements for the matrix protection performance of NdFeB permanent magnet materials are becoming increasingly stringent. While pursuing high corrosion resistance, the adhesion, stone impact resistance, and wear resistance of the surface coating of NdFeB magnets have become key areas of focus.

[0003] The preparation process of sintered NdFeB permanent magnets belongs to the field of powder metallurgy. The main steps include: first, preparing flakes, then crushing them into extremely fine powder, followed by pressing and sintering to obtain NdFeB magnet blanks, and finally processing and cutting to obtain finished magnets of suitable sizes. Due to the characteristics of this process, a neodymium-rich phase forms inside the blank, the grain boundaries are relatively active, and the magnet matrix is ​​brittle, making it prone to chipping and cracking. This makes coating protection for NdFeB magnets far more difficult than for their substrate. Current coating processes have many problems. For example, magnets produced by directly spraying an organic coating onto the magnet surface after polished phosphating are prone to chipping and cracking, and the coating has poor stone impact resistance and insufficient corrosion resistance. Magnets produced by polished nickel-copper plating followed by electrophoresis have hanging points on the surface, and these hanging points have relatively poor corrosion resistance. Furthermore, the process of using polished nickel-plated copper followed by roller-spraying of an organic coating is prone to substrate leakage at the edges due to impacts during the spraying process. Additionally, the adhesion between the organic coating and the smooth copper surface is relatively poor, leading to peeling. The industry often uses a diamond abrasive treatment to roughen the smooth copper-plated surface, increasing surface tension and improving adhesion. However, this process damages the copper-plated surface to some extent, affecting the coating's corrosion resistance. Moreover, the high roughness Ra after epoxy coating negatively impacts the product's appearance. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] A protective layer comprising, in sequence, a plating layer, a metal oxide layer, and an organic coating layer, wherein the plating layer is located on the surface of a substrate.

[0006] According to an embodiment of the present invention, the substrate is selected from neodymium iron boron or cerium iron boron permanent magnets known in the art, and the present invention does not specifically limit it. Preferably, the present invention uses a substrate with a unit weight greater than 2g, and the shape of the substrate can be a regular shape known in the art, such as a cube. The inventors have found that when the unit weight of the substrate is small or irregularly shaped, construction is more difficult when designing the protective layer, and the thickness uniformity of the protective layer is poor. For example, during spraying, the substrate is prone to displacement when the unit weight is small.

[0007] According to an embodiment of the present invention, the coating includes at least a first coating, and may further include a second coating between the first coating and the substrate.

[0008] Preferably, the materials of the first coating and the second coating can be the same or different, and are independently selected from Cu, Ni, etc. For example, the first coating is selected from copper, and the second coating is selected from nickel.

[0009] According to an embodiment of the present invention, the metal coating has metal ductility and stone impact resistance, and the metal oxide layer has a dense structure, which can improve the corrosion resistance of the protective layer and form high surface tension.

[0010] According to an embodiment of the present invention, the metal oxide layer is selected, for example, from copper oxide.

[0011] According to an embodiment of the present invention, the surface roughness Ra of the metal oxide layer is 0.3 to 0.8 μm.

[0012] According to an embodiment of the present invention, the thickness of the metal oxide layer is 0.2 to 1 μm.

[0013] According to a preferred embodiment of the present invention, the first plating layer is a copper plating layer, which includes a copper plating underlayer and a copper plating surface layer.

[0014] According to a preferred embodiment of the present invention, in the copper plating layer, the thickness ratio of the copper plating underlayer to the copper plating surface layer is 5-9:1-5, preferably 6-8:2-4, for example 6:4 or 8:2.

[0015] According to an embodiment of the present invention, the thickness of the organic coating is 15–20 μm.

[0016] According to embodiments of the present invention, the organic coating comprises at least an organic compound. Preferably, the organic coating is an epoxy coating, which comprises a leveling agent and an epoxy resin.

[0017] Preferably, the leveling agent is selected from leveling agents known in the art, such as a leveling agent including at least one of ethylene glycol butyl ether, ethylene glycol ethyl ether, propylene glycol butyl ether, ethylene glycol phenyl ether, etc., or, for example, BASF's SV08062A BUTYLGLYCOL.

[0018] Preferably, the epoxy resin paint is selected from Nippon Paint's EM2000 black epoxy coating.

[0019] According to an embodiment of the present invention, the protective layer has high adhesion, high corrosion resistance, and abrasion resistance.

[0020] According to an exemplary embodiment of the present invention, the protective layer sequentially comprises a second plating layer, a first plating layer, a metal oxide layer, and an organic coating layer, wherein the second plating layer is located between the substrate and the first plating layer; the second plating layer comprises nickel, the first plating layer comprises a copper-plated underlayer and a copper-plated surface layer, and the metal oxide layer comprises copper oxide.

[0021] According to an exemplary embodiment of the present invention, the protective layer sequentially comprises a second plating layer, a first plating layer, a metal oxide layer, and an organic coating layer, wherein the second plating layer comprises nickel, the first plating layer comprises copper, and the metal oxide layer comprises copper oxide.

[0022] According to an embodiment of the present invention, the protective layer simultaneously possesses at least three or more of the following properties:

[0023] (1) The number of grids is no greater than level 1, for example, level 0;

[0024] (2) Stone impact resistance is not greater than level 1, for example, level 0;

[0025] (3) The neutral salt spray duration is not less than 500 hours, for example, 510 hours, 550 hours, or 600 hours;

[0026] (4) The hardness is not less than grade 3, for example, grade 4;

[0027] (5) The shear strength is not less than 40MPa, for example, 41MPa or 42MPa.

[0028] Preferably, the protective layer has all of the above properties (1)-(5).

[0029] The present invention also provides a method for preparing the above-mentioned protective layer, the method comprising:

[0030] (1) A coating is prepared on the surface of a substrate by electroplating.

[0031] (2) The coating is subjected to surface oxidation treatment to obtain a metal oxide layer;

[0032] (3) After an organic coating is applied to the surface of the metal oxide layer, the protective layer is cured to obtain the protective layer.

[0033] According to an embodiment of the present invention, in step (1), the substrate and the coating have the meanings described above.

[0034] According to an embodiment of the present invention, in step (1), the preparation of the coating specifically includes: first obtaining a second coating on the surface of the substrate by electroplating, and then obtaining a first coating on the surface of the second coating.

[0035] According to an embodiment of the present invention, the thickness of the second coating is 3 to 5 μm, for example, 4 μm.

[0036] According to an embodiment of the present invention, the thickness of the first coating is 8 to 15 μm, for example, 10 μm.

[0037] According to a preferred embodiment of the present invention, the first plating layer is a copper plating layer, which includes a copper plating underlayer and a copper plating surface layer. The thickness ratio of the copper plating underlayer to the copper plating surface layer is 5-9:1-5, preferably 6-8:2-4, for example 6:4 or 8:2.

[0038] According to an embodiment of the present invention, the surface roughness Ra of the coating is 0.3-0.8 μm.

[0039] According to an exemplary embodiment of the present invention, the second plating layer is selected from a nickel plating layer, and the first plating layer is selected from a copper plating layer.

[0040] According to an embodiment of the present invention, the coating is prepared by an electroplating solution. Preferably, the electroplating solution comprises a soluble metal compound, an amino complexing agent, an additive, and a solvent. Further, the soluble metal compound is selected from compounds containing at least one of Cu, Ni, etc., such as nickel chloride, copper pyrophosphate, etc.; the amino complexing agent is selected from at least one of ammonia, ethylenediamine, ammonium acetate, etc.; the additive is selected from at least one of sodium sulfate, diammonium hydrogen citrate, boric acid, potassium pyrophosphate, etc.; and the solvent is selected from water or other known aqueous solvents.

[0041] According to an embodiment of the present invention, the electroplating solutions for preparing the first coating and the second coating can be the same or different, depending on the materials of the first coating and the second coating.

[0042] According to an embodiment of the present invention, the preparation conditions for the second coating are as follows: the substrate is immersed in a primer plating solution for primer treatment. Preferably, the primer treatment conditions include: an electroplating time of 3500–4500 seconds and a current density of 0.2–0.7 A / dm³. 2 The temperature of the base plating solution is 45-55℃, and the pH value is 4.5-5.5.

[0043] According to an embodiment of the present invention, before the base treatment, the substrate may also be polished and / or degreased and cleaned using methods known in the art.

[0044] According to an embodiment of the present invention, the base plating solution includes a soluble metal compound, an amino complexing agent, an additive, and a solvent, wherein the mass concentration of the soluble metal compound is 70-90 g / L, the volume concentration of the amino complexing agent is 20-60 ml / L, and the concentration of the additive is 290-450 g / L.

[0045] According to a preferred embodiment of the present invention, the second plating layer is a nickel plating layer, and the base plating solution is a nickel solution. Further, the nickel solution specifically comprises sodium sulfate, nickel chloride, diammonium hydrogen citrate, boric acid, an amino complexing agent, and water, wherein the mass-volume concentration of sodium sulfate is 200–250 g / L, the mass-volume concentration of nickel chloride is 70–90 g / L, the mass-volume concentration of boric acid is 30–50 g / L, the volume concentration of the amino complexing agent is 20–60 ml / L, and the mass-volume concentration of diammonium hydrogen citrate is 60–150 g / L.

[0046] According to an embodiment of the present invention, the preparation of the first coating specifically includes: using an underlayer electroplating solution, at a low current density (e.g., 1-3 A / dm³) 2 A metal electroplating underlayer is obtained under high current density (e.g., 4–6 A / dm²). Subsequently, a surface electroplating solution is used at high current density (e.g., 4–6 A / dm²). 2 A metal electroplated surface layer is obtained by means of a process whereby the concentration of the amino complexing agent in the surface electroplating solution is controlled to be 4–5 ml / L. Preferably, the concentration of the amino complexing agent in the bottom electroplating solution is 1–3 ml / L (volume concentration). Preferably, the concentration ratio of the amino complexing agent in the bottom electroplating solution and the surface electroplating solution is 1–3:4–5. Preferably, the metal electroplated bottom layer has a dense structure, and the metal electroplated surface layer has a high roughness, for example, 0.3–0.8 μm.

[0047] According to an embodiment of the present invention, the conditions for preparing the metal electroplating underlayer include: an electroplating underlayer treatment time of 3000–4000 s and a cathode current density of 1–3 A / dm². 2 The electroplating temperature is 40–50℃, and the pH value is 8.2–8.5.

[0048] According to an embodiment of the present invention, the conditions for preparing the metal electroplated surface layer include: a processing time of 1500–2000 s and a cathode current density of 4–6 A / dm². 2 The electroplating temperature is 45-55℃, and the pH value is 8.5-9.0.

[0049] According to an embodiment of the present invention, the bottom electroplating solution includes a soluble metal compound, an amino complexing agent, an additive, and a solvent, wherein the mass concentration of the soluble metal compound is 60-80 g / L, the volume concentration of the amino complexing agent is 1-3 ml / L, and the concentration of the additive is 230-280 g / L.

[0050] According to an embodiment of the present invention, the surface electroplating solution includes a soluble metal compound, an amino complexing agent, an additive, and a solvent, wherein the mass concentration of the soluble metal compound is 60-80 g / L, the volume concentration of the amino complexing agent is 4-5 ml / L, and the concentration of the additive is 230-280 g / L.

[0051] For example, the first plating layer is a copper plating layer, and its preparation method includes: obtaining a copper plating underlayer at a low current density, and then obtaining a copper plating surface layer at a higher current density; wherein the thickness ratio of the copper plating underlayer to the copper plating surface layer is 5-9:1-5, preferably 6-8:2-4, for example 6:4 or 8:2; and the surface roughness Ra of the copper plating surface layer is 0.3 to 0.8 μm.

[0052] For example, the underlying electroplating solution includes copper pyrophosphate, potassium pyrophosphate, PL copper pyrophosphate brightener, amino complexing agent and water, wherein the mass-volume concentration of copper pyrophosphate is 60-80 g / L, the mass-volume concentration of potassium pyrophosphate is 230-280 g / L, the volume concentration of PL copper pyrophosphate brightener is 2-4 mL / L, and the volume concentration of amino complexing agent is 1-3 mL / L.

[0053] For example, the surface electroplating solution includes copper pyrophosphate, potassium pyrophosphate, PL copper pyrophosphate brightener, amino complexing agent and water, wherein the mass-volume concentration of copper pyrophosphate is 60-80 g / L, the mass-volume concentration of potassium pyrophosphate is 230-280 g / L, the PL copper pyrophosphate brightener is 3-5 mL / L, and the volume concentration of amino complexing agent is 4-5 mL / L.

[0054] The inventors discovered that during the surface electroplating process, it is necessary to strictly control the current density to 4–6 A / dm³. 2 When the current density is too high, the electroplating speed is fast, resulting in a rough metal surface layer. The concentration of the amino complexing agent in the plating solution must be strictly controlled during the process, maintaining a volume concentration of 4–5 ml / L. During electroplating, the amino complexing agent, as a weakly alkaline complexing solution, can react with metal ions (such as copper ions) in the plating solution to generate stable metal-ammonia complexes (such as copper-ammonia complexes). These metal-ammonia complexes can alter the crystallization process of the coating. The inventors also discovered that during surface electroplating, both excessively high and low amino complexing agent concentrations affect the coating effect: excessively high concentrations result in a whitish coating with excessive roughness; while excessively low concentrations lead to uneven coloring, a mottled appearance, and insufficient roughness. This invention, by adjusting the current density and the concentration of the amino complexing agent in the plating solution during surface electroplating, can regulate the crystallization speed and morphology of the coating, thereby obtaining a coating with a roughness Ra of 0.3–0.8 μm.

[0055] According to an embodiment of the present invention, in step (2), the surface oxidation treatment includes: activating the coating with an activating solution, and then immersing it in a passivation solution for passivation at room temperature for 5 to 10 minutes.

[0056] According to an embodiment of the present invention, the surface roughness Ra of the metal oxide layer is 0.3 to 0.8 μm.

[0057] According to an embodiment of the present invention, the thickness of the metal oxide layer is 0.2 to 1 μm.

[0058] According to an embodiment of the present invention, the activating solution is selected from nitric acid solution, for example, a nitric acid solution with a volume concentration of 3%.

[0059] According to an embodiment of the present invention, the passivation solution is selected from hydrogen peroxide aqueous solution, for example, a hydrogen peroxide aqueous solution with a volume concentration of 5-10%.

[0060] The inventors discovered that, because the electroplated coating is a reactive metal layer, its adhesion to the epoxy coating is poor. To enhance the adhesion of the epoxy coating to the coating surface, this invention performs a surface oxidation treatment on the coating to form a dense metal oxide film (e.g., a copper oxide film) as a metal oxide layer. This not only enhances the corrosion resistance of the coating but also promotes the bonding of organic compounds in the organic coating with the metal oxide layer, thereby improving the adhesion of the organic coating.

[0061] According to an embodiment of the present invention, step (3), arranging the organic coating specifically includes: arranging the coating composition on the surface of the metal oxide layer.

[0062] According to an embodiment of the present invention, the thickness of the organic coating is 15-20 μm.

[0063] According to an embodiment of the present invention, the arrangement can be carried out using methods known in the art, such as spraying. Exemplarily, the spraying is air spraying, and the spraying conditions include: atomization pressure of 0.3–0.4 MPa, fan-shaped pressure of 0.3–0.4 MPa, and nozzle diameter of 1.0 mm.

[0064] According to an embodiment of the present invention, the coating composition includes an epoxy coating, a leveling agent, and a diluent.

[0065] According to an embodiment of the present invention, in the coating composition, the volume ratio of the leveling aid to the epoxy coating is 0.3% to 1%, for example, 0.5%.

[0066] According to an embodiment of the present invention, the viscosity of the coating composition is adjusted with a diluent to be no greater than 30S (Zane 3# cup), for example, 15-20S (Zane 3# cup).

[0067] According to an embodiment of the present invention, the organic coating is selected from epoxy coatings, such as Nippon EM2000 black epoxy coating, Nippon EP-5000 epoxy coating, and NPES-500 epoxy coating.

[0068] According to an embodiment of the present invention, the leveling agent is selected from alcohol ethers.

[0069] Preferably, the alcohol ether additive contains polar hydroxyl groups and nonpolar ether groups. The polar hydroxyl groups can bind to oxygen atoms in polar molecular metal oxides, and the nonpolar ether groups can bind to epoxy groups in epoxy coatings.

[0070] Preferably, the boiling point of the alcohol ether auxiliaries is greater than 120°C, more preferably greater than 120°C and less than 200°C, for example 171°C.

[0071] Preferably, the alcohol ether additive is selected from known alcohol ether additives, such as at least one of ethylene glycol butyl ether, ethylene glycol ethyl ether, propylene glycol butyl ether, ethylene glycol phenyl ether, etc.; for example, BASF SV08062A, which is commercially available, has ethylene glycol butyl ether as its main component.

[0072] The inventors discovered that by using high-boiling-point alcohol ethers as leveling agents, the present invention increases the leveling time of the coating composition after spraying, which is beneficial for removing air bubbles inside the coating and thus can improve the adhesion of the organic coating to the surface of the metal oxide layer.

[0073] According to an embodiment of the present invention, the diluent is selected from diluents known in the art, such as diluents purchased from Nippon Paint, or Nippon Paint's standard diluent PCD.

[0074] According to an exemplary embodiment of the present invention, the coating composition comprises Nippon EM2000 black epoxy coating and alcohol ether additive SV08062A.

[0075] According to an exemplary embodiment of the present invention, the organic coating comprises Nippon EM2000 black epoxy coating and Nippon standard diluent PCD, with alcohol ether additives (such as alcohol ether additive SV08062A) added to adjust the viscosity to 15-20S (Zei 3# cup).

[0076] According to an embodiment of the present invention, the curing conditions include: a curing temperature of 175–195°C (preferably 185–195°C) and a curing time of 30–60 min (preferably 40–60 min).

[0077] The inventors discovered that after curing at a temperature of 140–170°C for 30–40 minutes, microscopic observation revealed a loose and porous internal structure in the coating. However, when the curing temperature was increased to 175–195°C and the curing time was extended to 30–60 minutes, the coating developed a dense, void-free internal structure. This not only increased the density of the cured organic coating but also enhanced its corrosion resistance and abrasion resistance.

[0078] The present invention also provides the application of the above-mentioned protective layer in the preparation of neodymium iron boron permanent magnets.

[0079] The present invention also provides a neodymium iron boron permanent magnet, wherein the neodymium iron boron permanent magnet includes the above-mentioned protective layer; the protective layer includes, in sequence, a plating layer, a metal oxide layer, and an organic coating layer, wherein the plating layer is located on the surface of the substrate.

[0080] According to embodiments of the present invention, the coating, metal oxide layer, organic coating, and substrate have the meanings described above.

[0081] According to an embodiment of the present invention, the protective layer of the neodymium iron boron permanent magnet simultaneously possesses at least three or more of the following properties:

[0082] (1) The number of grids is no greater than level 1, for example, level 0;

[0083] (2) Stone impact resistance is not greater than level 1, for example, level 0;

[0084] (3) The neutral salt spray duration is not less than 500 hours, for example, 510 hours, 550 hours, or 600 hours;

[0085] (4) The hardness is not less than 3H, for example, 4H;

[0086] (5) The shear strength is not less than 40MPa, for example, 41MPa or 42MPa.

[0087] Preferably, the protective layer of the neodymium iron boron permanent magnet has the above-mentioned properties (1)-(5).

[0088] Beneficial effects:

[0089] The protective layer obtained on the NdFeB permanent magnet substrate by the preparation method of the present invention significantly improves the adhesion of the protective layer (e.g., cross-cut strength not greater than level 1, shear strength not less than 40MPa), improves the wear resistance (e.g., hardness not less than 3H), improves the corrosion resistance (e.g., neutral salt spray not less than 500h), and improves the product's stone impact resistance (e.g., stone impact resistance not greater than level 1). Attached Figure Description

[0090] Figure 1 This is a schematic diagram of the protective layer of the present invention.

[0091] Figure 2 The cross-cut test results for the permanent magnet before and after the improvement in Example 1 are shown, where a is the permanent magnet before the protective layer is applied, and b is the permanent magnet after the protective layer is applied.

[0092] Figure 3 The hardness test results for the permanent magnet in Example 1 before and after the improvement are shown in Figure 1. Here, a represents the hardness test result before the protective layer is applied, and b represents the hardness test result after the protective layer is applied.

[0093] Figure 4 The corrosion resistance test results of the permanent magnet before and after the improvement in Example 1 are shown in Figure 1. In Figure 1, a is the salt spray test result before the protective layer is applied, and b is the salt spray test result after the protective layer is applied.

[0094] Figure 5 The images show the stone impact resistance test results before and after the permanent magnet was improved in Example 1. In the images, a represents the stone impact resistance test results before the protective layer was applied, and b represents the stone impact resistance test results after the protective layer was applied. Detailed Implementation

[0095] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0096] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0097] Example 1

[0098] The preparation method of the protective layer of neodymium iron boron permanent magnet is as follows:

[0099] (1) Take a neodymium iron boron permanent magnet with a length-width-thickness of 29mm-7.8mm-1.9mm, first perform a polishing process using methods known in the art, and then perform the following electroplating process on its surface in sequence:

[0100] First, a nickel layer is electroplated using a nickel solution as a base coat under the following conditions: electroplating time of 3500 seconds and current density of 0.2–0.7 A / dm³. 2 The temperature of the base plating solution is 45-55℃, and the pH value is 4.5-5.5;

[0101] The nickel solution specifically includes sodium sulfate, nickel chloride, diammonium hydrogen citrate, boric acid, ammonia, and water. The mass-volume concentration of sodium sulfate is 200–250 g / L, the mass-volume concentration of nickel chloride is 70–90 g / L, the mass-volume concentration of boric acid is 30–50 g / L, the volume concentration of ammonia is 20–60 ml / L, and the mass-volume concentration of diammonium hydrogen citrate is 60–150 g / L.

[0102] Secondly, copper electroplating is performed in two plating tanks. First, a bottom plating solution is added to the first tank to prepare the copper underlayer. Then, a surface plating solution is added to the second tank to prepare the copper surface layer. During the preparation of the surface layer, ammonia water needs to be added to the surface plating solution in real time, and the ammonia water volume concentration of the copper plating solution is controlled at 4.5 ± 0.5 ml / L.

[0103] The underlying electroplating solution comprises copper pyrophosphate, potassium pyrophosphate, PL copper pyrophosphate brightener, ammonia, and water. The mass-volume concentration of copper pyrophosphate is 60–80 g / L, the mass-volume concentration of potassium pyrophosphate is 230–280 g / L, the volume concentration of PL copper pyrophosphate brightener is 2–4 mL / L, and the volume concentration of ammonia is 1–3 mL / L. The conditions for preparing the metal electroplating underlayer include: an electroplating underlayer treatment time of 3000–4000 s and a cathode current density of 1–3 A / dm³. 2 The electroplating temperature is 40–50℃, and the pH value is 8.2–8.5.

[0104] The surface electroplating solution comprises copper pyrophosphate, potassium pyrophosphate, PL copper pyrophosphate brightener, ammonia, and water. The mass-volume concentration of copper pyrophosphate is 60–80 g / L, the mass-volume concentration of potassium pyrophosphate is 230–280 g / L, the PL copper pyrophosphate brightener is 3–5 mL / L, and the volume concentration of ammonia is 4–5 mL / L. The conditions for preparing the metal electroplated surface layer include: a processing time of 1500 s and a cathode current density of 4–6 A / dm³. 2 The electroplating temperature is 45–55℃, and the pH value is 8.5–9.0.

[0105] The average surface roughness Ra of the coating prepared in this embodiment is 0.6 μm.

[0106] (2) The nickel-copper plating layer prepared in step (1) above is first activated with a 3% nitric acid solution, and then immersed in a passivation tank containing a 10% hydrogen peroxide passivation solution for passivation. 50 ml of 20% hydrogen peroxide is added every half hour, and the tank solution is changed every 8 hours. When it is found that the surface of the nickel-copper plating layer is unevenly oxidized, the 10% hydrogen peroxide passivation solution is replaced and passivation continues until a uniform copper oxide layer is obtained.

[0107] (3) An epoxy coating is obtained by spraying a coating composition onto the surface of the above-mentioned copper oxide layer. The spraying is air spraying, and the spraying conditions include: spraying atomization pressure of 0.3 to 0.4 MPa, fan-shaped pressure of 0.3 to 0.4 MPa, and spray gun nozzle diameter of 1.0 mm.

[0108] The coating composition includes 10 kg of Nippon EM2000 black epoxy coating, 0.05 kg of alcohol ether additive SV08062A, and 4 kg of Nippon standard diluent PCD, with a viscosity of 15-20 S (Zei 3# cup). When preparing the coating composition, mix all raw materials and stir for 30 minutes at a stirring speed of 200 rpm. The mixture is considered to be uniform when no bubbles are generated in the vortex during the stirring process.

[0109] (4) After spraying, the epoxy coating has a leveling time of 3 to 5 minutes, and then is cured under the following conditions: curing temperature 190℃, curing time 40 minutes.

[0110] In this embodiment, a protective layer for a neodymium iron boron permanent magnet was prepared. The thicknesses of the Ni plating layer, Cu plating layer, copper oxide layer, and epoxy coating were 4.5 μm, 9.8 μm, 0.5 μm, and 14.5 μm, respectively. The copper plating underlayer of the Cu plating layer was 6.2 μm, and the copper plating surface layer was 3.6 μm.

[0111] Example 2

[0112] The method for preparing a permanent magnet with a protective layer in this embodiment is basically the same as in Embodiment 1, except that there is only a first electroplating layer, that is, only a copper plating layer and no nickel plating layer.

[0113] In step (4), the curing temperature is 175℃ and the time is 60min.

[0114] In this embodiment, a protective layer for a neodymium iron boron permanent magnet was prepared. The thicknesses of the Cu plating layer, the copper oxide layer, and the epoxy coating were 14.6 μm, 0.5 μm, and 15.6 μm, respectively. The copper plating underlayer of the Cu plating layer was 9.6 μm, and the copper plating surface layer was 5.0 μm.

[0115] Comparative Example 1

[0116] The method for preparing a permanent magnet with a protective layer in this comparative example is basically the same as in Example 1, except that:

[0117] In step (2), during the copper electroplating process, only the bottom layer electroplating solution is used to prepare the copper plating bottom layer, and no surface layer electroplating solution is added to prepare the copper plating surface layer.

[0118] The protective layer of the neodymium iron boron permanent magnet was prepared in this comparative example, wherein the thicknesses of the Ni coating, Cu coating (only the copper plating underlayer), copper oxide layer and epoxy coating were 4.3 μm, 10.1 μm, 0.5 μm and 15.2 μm, respectively.

[0119] Comparative Example 2

[0120] The method for preparing a permanent magnet with a protective layer in this comparative example is basically the same as in Example 1, except that:

[0121] In step (2), during the copper plating process, the bottom layer of copper plating is not prepared by adding the bottom layer electroplating solution, and the top layer of copper plating is prepared directly by using the surface layer electroplating solution.

[0122] The protective layer of the neodymium iron boron permanent magnet was prepared in this comparative example, wherein the thicknesses of the Ni coating, Cu coating (only the copper surface layer), copper oxide layer and epoxy coating were 4.6 μm, 9.3 μm, 0.6 μm and 15.5 μm, respectively.

[0123] Comparative Example 3

[0124] The method for preparing a permanent magnet with a protective layer in this comparative example is basically the same as in Example 1, except that:

[0125] The oxidation treatment in step (2) is cancelled, that is, the nickel-copper plating layer prepared in step (1) is directly subjected to step (4), and an epoxy coating is obtained by spraying a coating composition on the surface of the nickel-copper plating layer.

[0126] The protective layer of the neodymium iron boron permanent magnet was prepared in this comparative example. The thicknesses of the Ni coating, Cu coating and epoxy coating were 4.4 μm, 9.6 μm and 15.2 μm, respectively. In the Cu coating, the copper underlayer was 6.1 μm and the copper surface layer was 3.5 μm.

[0127] Comparative Example 4

[0128] The method for preparing a permanent magnet with a protective layer in this comparative example is basically the same as in Example 1, except that:

[0129] In step (4), the curing temperature is 170℃ and the curing time is 50min.

[0130] In this comparative example, a protective layer for a neodymium iron boron permanent magnet was prepared. The thicknesses of the Ni coating, Cu coating, copper oxide layer, and epoxy coating were 4.6 μm, 10.1 μm, 0.5 μm, and 15.1 μm, respectively. The copper plating underlayer in the Cu coating was 6.6 μm, and the copper plating surface layer was 3.5 μm.

[0131] Test Example 1

[0132] The permanent magnets before the preparation of the protective layer in Example 1 (denoted as before improvement) and after the preparation of the protective layer (denoted as after improvement) were tested on their surfaces. The test methods and test results are shown in Table 1.

[0133] Among them, cross-cut test and shear strength characterize the adhesion of the protective layer, hardness characterizes the wear resistance of the protective layer, and salt spray characterizes the corrosion resistance of the protective layer.

[0134] Table 1. Test results of permanent magnets before and after preparation of the protective layer in Example 1.

[0135]

[0136] The surface protective layers of the permanent magnets with protective layers obtained in the above embodiments and comparative examples were tested as follows, and the test results are shown in Table 2.

[0137] Table 2 Performance test results of Examples 1-2 and Comparative Examples 1-4

[0138]

[0139] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A protective layer, characterized in that, The protective layer comprises, in sequence, a plating layer, a metal oxide layer, and an organic coating layer, wherein the plating layer is located on the surface of the substrate.

2. The protective layer according to claim 1, characterized in that, The coating includes at least a first coating, and may also include a second coating between the first coating and the substrate. Preferably, the materials of the first coating and the second coating can be the same or different, and can be independently selected from Cu or Ni. Preferably, the surface roughness Ra of the metal oxide layer is 0.3 to 0.8 μm. Preferably, the thickness of the metal oxide layer is 0.2 to 1 μm. Preferably, the thickness of the organic coating is 15–20 μm. Preferably, the organic coating comprises at least an organic compound. Preferably, the organic coating is an epoxy coating, which comprises a leveling agent and an epoxy resin. Preferably, the leveling agent is selected from at least one of ethylene glycol butyl ether, ethylene glycol ethyl ether, propylene glycol butyl ether, and ethylene glycol phenyl ether.

3. The protective layer according to claim 1 or 2, characterized in that, The first plating layer is a copper plating layer, which includes a copper-plated underlayer and a copper-plated surface layer. Preferably, in the copper plating layer, the thickness ratio of the copper plating underlayer to the copper plating surface layer is 5-9:1-5. Preferably, the protective layer simultaneously possesses at least three or more of the following properties: (1) The number of grids is no greater than level 1; (2) Stone impact resistance is not greater than level 1; (3) Neutral salt spray test not less than 500 hours; (4) The hardness is not less than 3H; (5) Shear strength not less than 40 MPa.

4. The method for preparing the protective layer according to any one of claims 1-3, characterized in that, The preparation method includes: (1) A coating is prepared on the surface of a substrate by electroplating. (2) The coating is subjected to surface oxidation treatment to obtain a metal oxide layer; (3) After an organic coating is applied to the surface of the metal oxide layer, the protective layer is cured to obtain the protective layer.

5. The preparation method according to claim 4, characterized in that, In step (1), the preparation of the coating specifically includes: first obtaining a second coating on the surface of the substrate by electroplating, and then obtaining a first coating on the surface of the second coating. Preferably, the thickness of the second coating is 3 to 5 μm. Preferably, the thickness of the first coating is 8–15 μm. According to a preferred embodiment of the present invention, the first plating layer is a copper plating layer, which includes a copper plating underlayer and a copper plating surface layer, wherein the thickness ratio of the copper plating underlayer to the copper plating surface layer is 5-9:1-5. Preferably, the surface roughness Ra of the coating is 0.3-0.8 μm. Preferably, the coating is prepared by an electroplating solution. Preferably, the electroplating solution comprises a soluble metal compound, an amino complexing agent, an additive, and a solvent. Further, the soluble metal compound is selected from compounds containing at least one of Cu and Ni; the amino complexing agent is selected from at least one of ammonia, ethylenediamine, and ammonium acetate; the additive is selected from at least one of sodium sulfate, diammonium hydrogen citrate, boric acid, and potassium pyrophosphate; and the solvent is selected from water or an aqueous solvent.

6. The preparation method according to claim 4 or 5, characterized in that, The preparation conditions for the second coating are as follows: the substrate is immersed in a primer plating solution for primer treatment; the primer treatment conditions include: plating time of 3500-4500 seconds and current density of 0.2-0.7 A / dm³. 2 The temperature of the base plating solution is 45-55℃, and the pH value is 4.5-5.

5. Preferably, the base plating solution comprises a soluble metal compound, an amino complexing agent, an additive, and a solvent, wherein the mass concentration of the soluble metal compound is 70–90 g / L, the volume concentration of the amino complexing agent is 20–60 ml / L, and the concentration of the additive is 290–450 g / L.

7. The preparation method according to any one of claims 4-6, characterized in that, The preparation of the first plating layer specifically includes: using a bottom plating solution to obtain a metal plating bottom layer at a low current density; subsequently using a top plating solution to obtain a metal plating surface layer at a high current density. During the preparation of the metal plating surface layer, the concentration of the amino complexing agent in the top plating solution is controlled to be 4-5 ml / L; the concentration of the amino complexing agent in the bottom plating solution is 1-3 ml / L (volume concentration). Preferably, the concentration ratio of the amino complexing agent in the bottom electroplating solution and the top electroplating solution is 1-3:4-5. Preferably, the conditions for preparing the metal electroplating underlayer include: an electroplating underlayer treatment time of 3000–4000 s and a cathode current density of 1–3 A / dm³. 2 The electroplating temperature is 40-50℃, and the pH value is 8.2-8.

5. Preferably, the conditions for preparing the metal electroplated surface layer include: a processing time of 1500–2000 s and a cathode current density of 4–6 A / dm³. 2 The electroplating temperature is 45-55℃, and the pH value is 8.5-9.

0. Preferably, the bottom electroplating solution includes a soluble metal compound, an amino complexing agent, an additive, and a solvent, wherein the mass concentration of the soluble metal compound is 60-80 g / L, the volume concentration of the amino complexing agent is 1-3 ml / L, and the concentration of the additive is 230-280 g / L. Preferably, the surface electroplating solution includes a soluble metal compound, an amino complexing agent, an additive, and a solvent, wherein the mass concentration of the soluble metal compound is 60-80 g / L, the volume concentration of the amino complexing agent is 4-5 ml / L, and the concentration of the additive is 230-280 g / L.

8. The preparation method according to any one of claims 4-7, characterized in that, In step (2), the surface oxidation treatment includes: activating the coating with an activating solution, and then immersing it in a passivation solution for passivation at room temperature for 5 to 10 minutes. Preferably, the surface roughness Ra of the metal oxide layer is 0.3 to 0.8 μm. Preferably, the thickness of the metal oxide layer is 0.2 to 1 μm. Preferably, the activating solution is selected from nitric acid solution. Preferably, the passivation solution is selected from hydrogen peroxide aqueous solution. Preferably, in step (3), the arrangement of the organic coating specifically includes: arranging the coating composition on the surface of the metal oxide layer. Preferably, the thickness of the organic coating is 15-20 μm. Preferably, the coating composition includes an epoxy coating, a leveling agent, and a diluent. Preferably, the curing conditions include: a curing temperature of 175–195°C and a curing time of 30–60 min.

9. The use of the protective layer according to any one of claims 1-3 in the preparation of neodymium iron boron permanent magnets.

10. A neodymium iron boron permanent magnet, the neodymium iron boron permanent magnet comprising the protective layer as described in any one of claims 1-3; the protective layer comprising, in sequence, a plating layer, a metal oxide layer, and an organic coating layer, the plating layer being located on the surface of a substrate.

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