A NdFeB surface protective layer and preparation method thereof

Abstract

The present invention provides a NdFeB surface protective layer and a preparation method thereof, belonging to the technical field of rare earth permanent magnet materials. The present invention immerses a NdFeB magnet in a nickel plating solution for electroplating to form a Ni protective layer; the Ni protective layer is pressure-oriented to obtain the NdFeB surface protective layer, wherein the texture strength of the Ni close-packed (111) surface after the pressure orientation is 20-80%. The present invention pressure-orients the Ni protective layer, adjusts the arrangement direction of the grains, refines the grains, and optimizes the texture, so that the texture strength of the Ni close-packed (111) surface after the pressure orientation is 20-80%. The atomic arrangement of the (111) surface is more compact, the surface energy is lower, and the corrosive medium is more difficult to penetrate. That is, the corrosion resistance is improved by utilizing the (111) surface with high texture strength. At the same time, the pressure orientation technology can repair related defects such as pores and microcracks, further improving the corrosion resistance of the protective layer.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth permanent magnet materials, in particular to a neodymium iron boron surface protective layer and a preparation method thereof. Background Art

[0002] Neodymium iron boron magnets are widely used in electronics and electrical applications, such as hard drives, mobile phones, headphones, and battery-powered tools. However, neodymium iron boron magnets have poor corrosion resistance and typically require surface treatment. Among existing anti-corrosion treatment technologies, the most widely used methods include electrodeposition, electroless plating, and electrophoretic coating. Electrodeposition, a relatively mature method, can be applied using various methods, including nickel, copper, zinc, tin, and gold, depending on the surface coating material.

[0003] In the related art, by changing the formula design of the nickel electroplating solution, a pure nickel layer is formed on the surface of the NdFeB magnetic material, avoiding the phenomenon of hydrogen ion precipitation on the surface of the NdFeB magnetic material in the nickel-containing electroplating solution during the electrodeposition process, thereby ensuring the surface corrosion resistance of the NdFeB magnetic material. However, the problem of poor corrosion resistance of the magnet coating still exists. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a NdFeB surface protective layer and a preparation method thereof. The present invention pressure-orients the Ni protective layer to improve the corrosion resistance of the protective layer.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a surface protective layer of NdFeB, comprising the following steps:

[0007] Immersing the NdFeB magnet in a nickel plating solution for electroplating to form a Ni protective layer;

[0008] The Ni protective layer is pressure-oriented to obtain the NdFeB surface protective layer, and the texture intensity (MUD) of the close-packed (111) surface of Ni after the pressure orientation is 20-80%.

[0009] Preferably, the pressure orientation is rolling, the rolling pressure is 2-9 MPa, and the rolling passes are 1-3 times.

[0010] Preferably, the rolling method is unidirectional, reciprocating or multidirectional.

[0011] Preferably, the thickness of the Ni protective layer is 15-70 μm.

[0012] Preferably, the electroplating is carried out under conditions of a constant magnetic field and a variable frequency electric field, and the magnetic field strength of the constant magnetic field is 0.4-0.8T.

[0013] Preferably, the parameters of the variable frequency electric field include: forward current density of 6~10A / dm 2 , operating frequency is 400~800Hz, duty cycle is 40~80%; reverse current density is 0.2~1A / dm 2 , the operating frequency is 400~800Hz, and the duty cycle is 40~80%.

[0014] Preferably, the electroplating temperature is 45±5°C.

[0015] Preferably, the nickel plating solution comprises components with the following concentrations: 180-280 g / L of nickel sulfate, 20-40 g / L of nickel chloride, 30-40 g / L of boric acid, 0.6-1 g / L of o-benzoylsulfonimide, 0.2-0.5 g / L of 1,4-butynediol, 0.1-0.2 g / L of coumarin, 0.1-0.2 g / L of formaldehyde, and 0.05-0.1 g / L of sodium lauryl sulfate, and the pH value of the nickel plating solution is 2-6.

[0016] Preferably, the NdFeB magnet is activated before electroplating, and the activation agent is an acidic substance.

[0017] The present invention also provides a surface protective layer of NdFeB prepared by the preparation method described in the above technical solution.

[0018] The invention provides a method for preparing a surface protective layer of NdFeB, comprising the following steps: immersing a NdFeB magnet in a nickel plating solution for electroplating to form a Ni protective layer; and pressure-orienting the Ni protective layer to obtain the surface protective layer of NdFeB, wherein the texture strength of the close-packed (111) surface of Ni after the pressure orientation is 20-80%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention performs pressure orientation on the Ni protective layer, adjusts the arrangement direction of the grains, refines the grains, and optimizes the texture, so that the texture strength of the close-packed surface (111) of the Ni after rolling is 20-80%, the atomic arrangement of the (111) surface is tighter, the surface energy is lower, and the corrosive medium is more difficult to penetrate, that is, the corrosion resistance of the NdFeB surface protective layer is improved by utilizing the (111) surface with high texture strength. At the same time, the pressure orientation technology can repair related defects such as pores and microcracks, further improving the corrosion resistance of the NdFeB surface protective layer; and the pressure orientation can promote the interface bonding between the Ni protective layer and the NdFeB magnet matrix, increase the dislocation density, improve the shear resistance, and form a nano-scale diffusion layer at the interface between the Ni protective layer and the NdFeB magnet, thereby improving the bonding force of the NdFeB surface protective layer.

[0021] The data of the embodiment show that the corrosion current density of the NdFeB surface protective layer prepared by the present invention is as low as 1.9×10 - 6 A.cm -2 , the corrosion potential is as low as -480mV, and the salt spray corrosion time is as high as 72h. DETAILED DESCRIPTION

[0022] The present invention provides a method for preparing a surface protective layer of NdFeB, comprising the following steps:

[0023] Immersing the NdFeB magnet in a nickel plating solution for electroplating to form a Ni protective layer;

[0024] The Ni protective layer is pressure-oriented to obtain the NdFeB surface protective layer, and the texture strength of the close-packed (111) surface of Ni after the pressure orientation is 20-80%.

[0025] Unless otherwise specified, the raw materials used in the present invention are all commercially available products in the art.

[0026] The invention immerses the NdFeB magnet in a nickel plating solution for electroplating to form a Ni protective layer.

[0027] In the present invention, the thickness of the Ni protective layer is preferably 15-70 μm, specifically 15, 20, 30, 40, 50, 60 or 70 μm.

[0028] In the present invention, the electroplating is preferably carried out under the conditions of a constant magnetic field and a variable frequency electric field.

[0029] In the present invention, the magnetic field strength of the constant magnetic field is preferably 0.4-0.8T, specifically 0.4, 0.5, 0.6, 0.7 or 0.8T.

[0030] In the present invention, the parameters of the variable frequency electric field preferably include: forward current density of 6~10A / dm 2 , specifically 6, 7, 8, 9 or 10A / dm 2 The operating frequency is 400~800Hz, specifically 400, 500, 600, 700 or 800Hz; the duty cycle is 40~80%, specifically 40%, 50%, 60%, 70% or 80%; the reverse current density is 0.2~1A / dm 2 , specifically 0.2, 0.4, 0.6, 0.8 or 1A / dm 2 The operating frequency is 400~800Hz, specifically 400, 500, 600, 700 or 800Hz, and the duty cycle is 40~80%, specifically 40%, 50%, 60%, 70% or 80%.

[0031] The present invention adopts the synergistic effect of a constant magnetic field and a variable frequency electric field, which can regulate the composition and uniformity of the nickel plating solution, improve the quality of the plating layer, and optimize the magnetic properties.

[0032] In the present invention, the electroplating temperature is preferably 45±5°C, specifically 40, 45 or 50°C.

[0033] In the present invention, the nickel plating solution preferably includes components with the following concentrations: 180-280 g / L of nickel sulfate, 20-40 g / L of nickel chloride, 30-40 g / L of boric acid, 0.6-1 g / L of o-benzoylsulfonimide, 0.2-0.5 g / L of 1,4-butynediol, 0.1-0.2 g / L of coumarin, 0.1-0.2 g / L of formaldehyde, and 0.05-0.1 g / L of sodium lauryl sulfate. The pH value of the nickel plating solution is 2-6.

[0034] In the present invention, the concentration of nickel sulfate in the nickel plating solution can be specifically 180, 200, 220, 240, 260 or 280 g / L. Controlling the concentration of nickel sulfate within the above range can ensure that there is an appropriate amount of Ni in the plating solution. 2+ , maintaining a suitable deposition rate.

[0035] In the present invention, the concentration of nickel chloride in the nickel plating solution can specifically be 20, 25, 30, 35 or 40 g / L. Controlling the concentration of nickel chloride within the above range can adjust the anode dissolution efficiency and the conductivity of the plating solution.

[0036] In the present invention, the concentration of boric acid in the nickel plating solution can specifically be 30, 35 or 40 g / L. Controlling the concentration of boric acid within the above range can maintain a stable pH value of the plating solution, reduce cathode polarization, and improve deposition uniformity.

[0037] In the present invention, the concentration of o-benzoylsulfonyl imide in the nickel plating solution can specifically be 0.6, 0.8 or 1 g / L. Controlling the concentration of o-benzoylsulfonyl imide within the above range can act as a secondary brightener, refine grains, enhance ductility of the coating and improve leveling properties.

[0038] In the present invention, the concentration of 1,4-butynediol in the nickel plating solution can be specifically 0.2, 0.3, 0.4, or 0.5 g / L. Controlling the concentration of the 1,4-butynediol within the above range can act as a secondary brightener to improve the specular gloss of the coating and enhance the leveling property.

[0039] In the present invention, the concentration of coumarin in the nickel plating solution can be specifically 0.1, 0.15 or 0.2 g / L. Controlling the concentration of coumarin within the above range can refine the grains of the nickel plating layer and make the plating layer bright and smooth.

[0040] In the present invention, the concentration of formaldehyde in the nickel plating solution can specifically be 0.1, 0.15 or 0.2 g / L. Controlling the concentration of formaldehyde within the above range can accelerate the nickel ion reduction deposition rate and improve the cathode current efficiency.

[0041] In the present invention, the concentration of sodium lauryl sulfate in the nickel plating solution can specifically be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1 g / L. Controlling the concentration of sodium lauryl sulfate within the above range can reduce the surface tension of the plating solution and effectively prevent the generation of pinholes and pitting.

[0042] In the present invention, the solvent of the nickel plating solution is preferably water.

[0043] In the present invention, the pH value of the nickel plating solution can specifically be 2, 3, 4, 5 or 6.

[0044] The present invention preferably uses ammonia water to adjust the pH value of the nickel plating solution to 2-6. The present invention has no special limitation on the concentration and amount of the ammonia water, and a solution well known to those skilled in the art can be used.

[0045] In the present invention, the electroplating is preferably carried out under ultrasonic conditions, and the frequency of the ultrasound is preferably 20 to 60 Hz, specifically 20, 30, 40, 50 or 60 Hz.

[0046] In the present invention, the NdFeB magnet is preferably activated before electroplating, and the activation agent is preferably an acidic substance. The role of the activation is to form a rough surface.

[0047] In the present invention, the acidic substance preferably includes a nitric acid solution, the concentration of the nitric acid solution is preferably 10-40 g / L, specifically 10, 20, 30 or 40 g / L, and the activation time is preferably 3-5 min, specifically 3, 4 or 5 min.

[0048] In the present invention, the NdFeB magnet is preferably pre-cleaned to remove surface contaminants and metal oxides before the activation is performed.

[0049] In the present invention, the pre-cleaning preferably includes alkaline cleaning (for degreasing), acid cleaning, pre-activation (the acid cleaning and pre-activation are for removing surface pollutants and metal oxides) and ultrasonic cleaning (for surface cleaning) performed in sequence.

[0050] In the present invention, the alkaline washing solution used in the alkaline washing preferably includes the following components in concentrations: 5-10 g / L sodium hydroxide, 30-45 g / L sodium carbonate, 40-60 g / L sodium phosphate, 0.1-1 g / L OP-10 emulsifier, and 0.1-0.2 g / L sodium lauryl sulfate.

[0051] In the present invention, the pickling solution used in the pickling is preferably prepared from nitric acid solution, thiourea and water, the concentration of HNO3 in the pickling solution is 5wt%, and the concentration of thiourea in the pickling solution is preferably 0.5g / L.

[0052] In the present invention, the activation solution used in the pre-activation is preferably a 10 wt % H 2 SO 4 solution, and the pre-activation time is preferably 5 to 30 s, specifically 5, 10, 20 or 30 s.

[0053] In the present invention, the ultrasonic frequency of the ultrasonic cleaning is preferably 20-60 Hz, specifically 20, 30, 40, 50 or 60 Hz, and the time is preferably 5-30 s, specifically 5, 10, 20 or 30 s.

[0054] In the present invention, the pre-cleaned magnet is preferably immersed in the acidic substance for activation.

[0055] After forming the Ni protective layer, the present invention performs pressure orientation on the Ni protective layer to obtain the NdFeB surface protective layer. After the pressure orientation, the texture strength of the close-packed surface (111) of Ni is 20-80%, specifically 20%, 30%, 40%, 50%, 60%, 70% or 80%. The present invention improves the texture strength of the close-packed surface (111) of Ni by pressure orientation. The higher the texture strength of the close-packed surface (111), the tighter the atomic arrangement of the close-packed surface (111), the lower the surface energy, the more difficult it is for the corrosive medium to penetrate, and the better the corrosion resistance of the protective layer. At the same time, the pressure orientation technology can repair related defects such as pores and microcracks, further improving the corrosion resistance of the NdFeB surface protective layer. Moreover, the pressure orientation can promote the interface bonding between the Ni protective layer and the NdFeB magnet substrate, increase the dislocation density, improve the shear resistance, and form a nano-scale diffusion layer at the interface between the Ni protective layer and the NdFeB magnet, thereby improving the bonding force of the NdFeB surface protective layer.

[0056] In the present invention, the pressure orientation is preferably rolling, the rolling pressure is preferably 2~9MPa, specifically 2, 3, 4, 5, 6, 7, 8 or 9MPa, and the rolling passes are preferably 1~3 times, specifically 1, 2 or 3 times; the present invention controls the rolling parameters within the above range to optimize the corrosion resistance of the protective layer.

[0057] In the present invention, the rolling method is preferably unidirectional, reciprocating or multidirectional.

[0058] In the present invention, the rolling temperature is preferably room temperature, that is, no additional heating or cooling is required.

[0059] In the present invention, the Ni protective layer is preferably placed on a stainless steel roller for performing the rolling.

[0060] The present invention also provides a surface protective layer of NdFeB prepared by the preparation method described in the above technical solution.

[0061] The pressure orientation technology of the NdFeB surface protective layer of the present invention can improve the bonding force and corrosion resistance of the magnet coating.

[0062] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0063] Test methods in Examples and Comparative Examples

[0064] 1: Electrochemical testing (corrosion current density and corrosion potential)

[0065] The electrochemical performance of the coatings was tested using a Shanghai Chenhua CHI760E electrochemical workstation in a three-electrode system in a 3.5 wt% NaCl corrosion solution. First, the open-circuit potential (OCP) of the coating was measured for 1200 s until the OCP stabilized. The Tafel curve of the sample was then measured, with the measurement range near the OCP selected (initial potential: -0.25 V vs. OCP, final potential: +0.25 V vs. OCP) at a scan rate of 1 mV / s.

[0066] 2: Neutral salt spray test

[0067] GB / T 2423.17-2008 / IEC 60068-2-11:1981.

[0068] 3: Mechanical properties

[0069] Proceed in accordance with GB / T 39494-2020.

[0070] Example 1

[0071] (1) Pre-cleaning of NdFeB magnets: alkaline washing (the alkaline washing solution includes the following components: sodium hydroxide 10 g / L, sodium carbonate 45 g / L, sodium phosphate 60 g / L, OP-10 emulsifier 1 g / L, sodium lauryl sulfate 0.2 g / L) acid washing (the concentration of HNO3 in the acid washing solution is 5 wt%, and the concentration of thiourea is 0.5 g / L) + pre-activation (pre-activation in 10 wt% H2SO4 solution for 10 s) ultrasonic cleaning (ultrasonic frequency is 20 Hz, 10 s);

[0072] (2) Activate the pre-cleaned NdFeB magnetic material with 10g / L nitric acid solution for 3 minutes to obtain the magnet to be electroplated;

[0073] (3) Connect the magnet to be plated to a power source and immerse it in a nickel plating solution. Apply a constant magnetic field and a variable frequency electric field to the magnet to be plated. Electroplate the magnet to be plated using enhanced ion exchange deposition technology to prepare a Ni protective layer (thickness of 15 μm). The variable frequency electric field parameters are: forward current density of 6 A / dm 2 , reverse current density is 0.2A / dm 2 , the frequency is 800 Hz, the duty cycle is 40%, the electroplating temperature is 45°C, the magnetic field strength is 0.6 T, the nickel plating solution includes the following components in concentration: nickel sulfate 180 g / L, nickel chloride 20 g / L, boric acid 30 g / L, saccharin 0.6 g / L, 1,4-butynediol 0.2 g / L, coumarin 0.1 g / L, formaldehyde 0.1 g / L, sodium lauryl sulfate 0.05 g / L, the pH value is adjusted to 6 by ammonia water, the solvent of the nickel plating solution is water, and the electroplating is carried out under ultrasonic conditions with an ultrasonic frequency of 20 Hz;

[0074] (4) The Ni protective layer is placed on a stainless steel roller and rolled to obtain the NdFeB surface protective layer. The rolling is performed at room temperature, the rolling pressure is 3 MPa, the rolling pass is 1, and the rolling method is unidirectional.

[0075] Examples 2 to 7

[0076] The same as Example 1, the only difference is the rolling process. The specific parameters are shown in Table 1.

[0077] control group

[0078] The same as Example 1, except that no rolling is performed.

[0079] The corrosion resistance and mechanical property test results of the protective layers prepared in Examples 1 to 7 and the control group are shown in Table 1. It can be seen that the present invention rolls the Ni protective layer and uses pressure orientation technology to adjust the arrangement direction of the grains, refine the grains, and optimize the texture, so that the texture strength of the close-packed (111) surface of the Ni after rolling is 20-80%, the atomic arrangement of the (111) surface is tighter, the surface energy is lower, and the corrosive medium is more difficult to penetrate. At the same time, the pressure orientation technology can repair related defects such as pores and microcracks, and further improve the corrosion resistance of the protective layer; pressure orientation can promote the interface bonding between the Ni protective layer and the NdFeB magnet matrix, increase the dislocation density, improve the shear resistance, and form a nano-scale diffusion layer at the interface between the Ni protective layer and the NdFeB magnet, thereby improving the bonding force of the protective layer.

[0080] Table 1 Corrosion resistance and mechanical properties test results of the protective layers of Examples 1 to 7 and the control group

[0081]

[0082] Example 8

[0083] The same as Example 1, the only difference is that the thickness of the Ni protective layer obtained by electroplating is different. As shown in Table 2, the corrosion resistance and bonding strength of the coating show a non-monotonic correlation with the thickness of the Ni protective layer, which shows that the initial performance improves with the increase of the thickness of the Ni protective layer, and then decreases. Therefore, a certain thickness of the Ni protective layer should be maintained to achieve the best corrosion resistance and the maximum bonding strength.

[0084] Table 2 Performance test results of NdFeB surface protective layer obtained with different thickness of Ni protective layer

[0085]

[0086] Example 9

[0087] The same as Example 1, the only difference is the frequency of ultrasound, constant magnetic field and variable frequency electric field parameters during electroplating. See Table 3. It can be seen that the corrosion resistance and bonding strength of the NdFeB surface protective layer obtained with different magnetic field strengths, pulsed electric field parameters and ultrasonic frequencies are different.

[0088] Table 3 Corrosion resistance and mechanical properties test results of the NdFeB surface protective layer of Example 9

[0089]

[0090] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation thereto. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications shall also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a surface protective layer of NdFeB, characterized in that: It consists of the following steps: (1) Pre-cleaning of NdFeB magnets: alkaline washing, acid washing, pre-activation and ultrasonic cleaning are carried out in sequence. The alkaline washing solution includes the following components in concentration: sodium hydroxide 10g / L, sodium carbonate 45g / L, sodium phosphate 60g / L, OP-10 emulsifier 1g / L, sodium lauryl sulfate 0.2g / L; the concentration of HNO3 in the acid washing solution is 5wt%, and the concentration of thiourea is 0.5g / L; the pre-activation is pre-activated in 10wt% H2SO4 solution for 10s; the ultrasonic cleaning is performed at an ultrasonic frequency of 20Hz and a time of 10s; (2) Activate the pre-cleaned NdFeB magnetic material with 10g / L nitric acid solution for 3 minutes to obtain the magnet to be electroplated; (3) Connect the magnet to be plated to a power source and immerse it in a nickel plating solution. Apply a constant magnetic field and a variable frequency electric field to the magnet to be plated. Electroplate the magnet to be plated using enhanced ion exchange deposition technology to prepare a Ni protective layer with a thickness of 15 μm. The variable frequency electric field parameters are: forward current density of 6 A / dm 2 , reverse current density is 0.2A / dm 2 , the frequency is 800 Hz, the duty cycle is 40%, the electroplating temperature is 45°C, the magnetic field strength is 0.6 T, the nickel plating solution includes the following components in concentration: nickel sulfate 180 g / L, nickel chloride 20 g / L, boric acid 30 g / L, saccharin 0.6 g / L, 1,4-butynediol 0.2 g / L, coumarin 0.1 g / L, formaldehyde 0.1 g / L, sodium lauryl sulfate 0.05 g / L, the pH value is adjusted to 6 by ammonia water, the solvent of the nickel plating solution is water, and the electroplating is carried out under ultrasonic conditions with an ultrasonic frequency of 20 Hz; (4) The Ni protective layer is placed on a stainless steel roller and rolled to obtain the NdFeB surface protective layer. The rolling is performed at room temperature, the rolling pressure is 6 MPa, the rolling passes are 3 times, and the rolling method is unidirectional. After the rolling, the texture strength of the close-packed surface (111) of Ni is 80%.

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