Method for plating double-layer zinc on surface of neodymium-iron-boron permanent magnet material

Abstract

The application relates to a neodymium-iron-boron surface zinc plating technical field, in particular to a method for plating double-layer zinc on the surface of a neodymium-iron-boron permanent magnet material, which comprises the following steps: S1, pretreating the neodymium-iron-boron magnet; S2, placing the pretreated neodymium-iron-boron magnet in step S1 into a primary electroplating solution to perform primary zinc plating treatment; S3, placing the neodymium-iron-boron magnet subjected to the primary zinc plating treatment in step S2 into a nano-silicon dioxide suspension solution, and vacuum impregnating for 10-20 min; S4, placing the neodymium-iron-boron magnet subjected to the treatment in step S3 into a hydrochloric acid solution to perform treatment, and then washing with water; S5, placing the neodymium-iron-boron magnet subjected to the treatment in step S4 into a secondary electroplating solution to perform secondary zinc plating treatment; and S6, performing passivation on the surface of the neodymium-iron-boron magnet subjected to the treatment in step S5. The application can improve the compactness of the first zinc plating layer and effectively prolong the corrosion resistance time of the neodymium-iron-boron magnet.

Description

Technical Field

[0001] This invention relates to the field of zinc plating technology for neodymium iron boron (NdFeB) magnets, specifically a method for plating a double layer of zinc onto the surface of a NdFeB permanent magnet material. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets are intermetallic compounds composed of the rare earth elements neodymium (Nd), iron (Fe), and boron (B). They possess extremely high magnetic energy product and coercivity, and are widely used in modern industry and electronics. Their advantages include high energy density and good cost-effectiveness, but they also have disadvantages such as low Curie temperature and susceptibility to corrosion. Therefore, their performance needs to be improved by adjusting the chemical composition and surface treatment.

[0003] To improve the corrosion resistance of NdFeB magnets, plating a zinc layer on their surface is a common method. The plating solution typically uses zinc chloride or zinc sulfate. Zinc sulfate plating produces larger particles, a rougher surface, and easily forms a porous structure, offering limited improvement in the corrosion resistance of NdFeB magnets. Zinc chloride plating exhibits better bonding with NdFeB magnets; however, chloride ions easily corrode the NdFeB magnet surface during the plating process. Therefore, current methods generally involve first plating the NdFeB magnet surface with zinc sulfate, followed by a secondary plating with zinc chloride.

[0004] However, as Qianwen described, the first electroplating layer is more like a transition layer used for the second electroplating layer. If the outermost zinc layer is corroded, the neodymium iron boron magnet inside will also corrode quickly. To solve this problem, this invention proposes to seal the rough surface of the inner zinc plating layer, thereby extending the corrosion resistance time of the neodymium iron boron magnet. Summary of the Invention

[0005] The purpose of this invention is to provide a method for plating a double layer of zinc on the surface of neodymium iron boron permanent magnet materials, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material, the method comprising the following steps: S1. Pre-treat the neodymium iron boron magnet; S2. The neodymium iron boron magnet pretreated in step S1 is placed into a primary electroplating solution for a primary zinc plating process. S3. Place the neodymium iron boron magnets that have undergone the zinc plating treatment in step S2 into the nano silica suspension and vacuum immerse them for 10-20 minutes. S4. The neodymium iron boron magnets treated in step S3 are placed in hydrochloric acid solution for treatment, and then washed with water. S5. The neodymium iron boron magnets treated in step S4 are placed into a secondary electroplating solution for secondary zinc plating. S6. Passivate the surface of the neodymium iron boron magnet treated in step S5. The electroplating material used in the first electroplating solution in step S2 is zinc sulfate; The electroplating material used in the second electroplating solution in step S5 is zinc chloride; In step S3, the nano-silica in the nano-silica suspension has undergone pretreatment. The pretreatment of nano-silica includes the following steps: S101. Tetrabutylammonium bromide is added to a mixed solution of ammonia and ethanol to obtain a mixed solution. Then, nano-silica is ultrasonically dispersed into the mixed solution, followed by the addition of tetraethyl orthosilicate. The reaction is carried out continuously at 30-45℃ for 4-6 hours. S102. After the reaction in step S101 is completed, filter the product, wash the product with sufficient ethanol, and then vacuum dry it to constant weight at 30-45℃ to complete the pretreatment of nano-silica.

[0007] Furthermore, the pretreatment in step S1 includes acid washing, water washing, and activation.

[0008] Furthermore, the pickling in step S1 is carried out using 2-3 wt% nitric acid for 15-20 seconds; the activation in step S1 is carried out using 2-3 wt% hydrochloric acid for 5-10 seconds.

[0009] Furthermore, in step S2, the concentration of zinc sulfate in the primary electroplating solution is 300-450 g / L; the primary electroplating solution also contains boric acid and potassium sulfate, with the concentration of boric acid being 10-20 g / L and the concentration of potassium sulfate being 50-120 g / L; the pH of the first zinc plating treatment is 4-5.

[0010] Furthermore, in step S3, the concentration of nano-silica in the nano-silica suspension is 10-30 g / L.

[0011] Furthermore, in step S101, the concentration of tetrabutylammonium bromide in the mixed solution is 4-10 mmol / L, the concentration of ammonia is 25 wt%, and the mass ratio of ammonia, ethanol, nano silica and tetraethyl orthosilicate is (10-15):(60-100):1:(4-8).

[0012] Furthermore, the nano-silica suspension in step S3 also contains sodium hexadecyl sulfate and γ-aminopropyltriethoxysilane, with the concentration of sodium hexadecyl sulfate being 5-10 g / L and the concentration of γ-aminopropyltriethoxysilane being 2-4 g / L.

[0013] Furthermore, in step S4, the concentration of the hydrochloric acid solution is 4-6 wt%, and the NdFeB magnet treated in step S3 is treated in the hydrochloric acid solution for 4-8 seconds.

[0014] Furthermore, in step S5, the concentration of zinc chloride in the secondary electroplating solution is 40-60 g / L; the secondary electroplating solution also contains potassium chloride and boric acid, with the concentration of potassium chloride being 100-200 g / L and the concentration of boric acid being 10-20 g / L; the pH of the second electroplating treatment is 4-6.

[0015] Furthermore, in step S6, the passivation treatment uses a chromium nitrate solution with a pH of 1.5-2.5, a chromium nitrate concentration of 20-30 g / L, and a passivation time of 30-40 s.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, a double-layer zinc plating is performed. First, a zinc layer with larger particles is electroplated on the surface of the neodymium iron boron magnet using zinc sulfate. Then, through the vacuum immersion treatment in step S3, nano-silica can combine with the rough and porous surface of the first zinc plating layer, filling its surface and pores, improving the density of the first plating layer and improving its salt spray resistance. 2. In this invention, by pretreating the nano-silica, a rough surface layer is formed on the surface of the nano-silica. This rough surface layer is more likely to anchor and bond with the rough surface of the first zinc plating layer, which further improves the salt spray resistance of the zinc plating layer and extends its service life. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a process flow diagram of the nano-silica pretreatment in this invention; Figure 3 This is a photograph of the zinc-plated neodymium iron boron magnet prepared in Example 1 of this invention. Figure 4 This is a photograph of the zinc-plated NdFeB magnet prepared in Example 2 of this invention. Figure 5 This is a photograph of the zinc-plated neodymium iron boron magnet prepared in Example 3 of this invention. Figure 6 This is a 40x microscope image of the zinc-plated surface of the zinc-plated neodymium iron boron magnet prepared in Example 1 of this invention; Figure 7 This is a 500x scanning electron microscope backscattering image of the zinc-plated surface of the zinc-plated NdFeB magnet prepared in Example 1 of this invention; Figure 8 This is a secondary electron image of the zinc-plated surface of the zinc-plated neodymium iron boron magnet prepared in Example 1 of this invention, magnified by scanning electron microscopy at 500x. Figure 9 Backscattering image of the zinc-plated surface of the zinc-plated neodymium iron boron magnet prepared in Example 1 of this invention (1000x scanning electron microscope). Figure 10 This is a secondary electron image obtained by scanning electron microscopy at 1000x magnification of the zinc-plated surface of the zinc-plated neodymium iron boron magnet prepared in Example 1 of this invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figures 1 to 10 The present invention provides: Example 1 A method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material, the method comprising the following steps: S1. Pre-treat the neodymium iron boron magnet; The pretreatment in step S1 includes pickling, washing, and activation; The specific pickling process involves using 2.5 wt% nitric acid for 18 seconds, and the activation process involves using 2.5 wt% hydrochloric acid for 8 seconds. S2. The neodymium iron boron magnet pretreated in step S1 is placed into a primary electroplating solution for a primary zinc plating process. In step S2, the electroplating material used in the first electroplating solution is zinc sulfate, with a concentration of 400 g / L; the first electroplating solution also contains boric acid and potassium sulfate, with a boric acid concentration of 15 g / L and a potassium sulfate concentration of 80 g / L; the pH of the first zinc plating treatment is 4.5. S3. Place the neodymium iron boron magnet that has undergone the zinc plating treatment in step S2 into the nano silica suspension and vacuum immerse it for 16 minutes. The concentration of nano-silica in the nano-silica suspension is 18 g / L; the nano-silica suspension also contains sodium hexadecyl sulfate and γ-aminopropyltriethoxysilane, with the concentration of sodium hexadecyl sulfate being 8 g / L and the concentration of γ-aminopropyltriethoxysilane being 3 g / L. S4. The neodymium iron boron magnets treated in step S3 are placed in hydrochloric acid solution for treatment, and then washed with water. The concentration of the hydrochloric acid solution is 5 wt%, and the NdFeB magnet treated in step S3 is treated in the hydrochloric acid solution for 6 seconds. S5. The neodymium iron boron magnets treated in step S4 are placed into a secondary electroplating solution for secondary zinc plating. In step S5, the electroplating material used in the second electroplating solution is zinc chloride, with a concentration of 55 g / L; the second electroplating solution also contains potassium chloride and boric acid, with a potassium chloride concentration of 120 g / L and a boric acid concentration of 15 g / L; the pH of the second electroplating treatment is 5. S6. Passivate the surface of the NdFeB magnet treated in step S5. The resulting galvanized NdFeB magnet is shown in the image below. Figure 3 As shown; The passivation treatment used a chromium nitrate solution with a pH of 2, a chromium nitrate concentration of 25 g / L, and a passivation time of 35 s; The nano-silica in the nano-silica suspension in step S3 above has undergone pretreatment. The pretreatment of nano-silica includes the following steps: S101. Tetrabutylammonium bromide is added to a mixed solution of ammonia and ethanol to obtain a mixed solution. Then, nano-silica is ultrasonically dispersed into the mixed solution, followed by the addition of tetraethyl orthosilicate. The reaction is carried out continuously at 40°C for 5.5 hours. The concentration of tetrabutylammonium bromide in the mixed solution was 5 mmol / L, the concentration of ammonia was 25 wt%, and the mass ratio of ammonia, ethanol, nano silica and tetraethyl orthosilicate was 12:80:1:6. S102. After the reaction in step S101 is completed, filter the product, wash the product with sufficient ethanol, and then vacuum dry it to constant weight at 40°C to complete the pretreatment of nano-silica.

[0020] Example 2 A method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material, the method comprising the following steps: S1. Pre-treat the neodymium iron boron magnet; The pretreatment in step S1 includes pickling, washing, and activation; The specific pickling process involves using 2wt% nitric acid for 15 seconds; the activation process involves using 2wt% hydrochloric acid for 5 seconds. S2. The neodymium iron boron magnet pretreated in step S1 is placed into a primary electroplating solution for a primary zinc plating process. In step S2, the electroplating material used in the first electroplating solution is zinc sulfate, with a concentration of 300 g / L; the first electroplating solution also contains boric acid and potassium sulfate, with a boric acid concentration of 10 g / L and a potassium sulfate concentration of 50 g / L; the pH of the first zinc plating treatment is 4. S3. Place the neodymium iron boron magnet that has undergone the zinc plating treatment in step S2 into the nano silica suspension and vacuum immerse it for 10 minutes. The concentration of nano-silica in the nano-silica suspension is 10 g / L. The silica suspension also contains sodium hexadecyl sulfate and γ-aminopropyltriethoxysilane, with the concentrations of sodium hexadecyl sulfate being 5 g / L and γ-aminopropyltriethoxysilane being 4 g / L. S4. The neodymium iron boron magnets treated in step S3 are placed in hydrochloric acid solution for treatment, and then washed with water. The concentration of the hydrochloric acid solution is 4 wt%, and the neodymium iron boron magnet treated in step S3 is treated in the hydrochloric acid solution for 4 seconds. S5. The neodymium iron boron magnets treated in step S4 are placed into a secondary electroplating solution for secondary zinc plating. The electroplating material used in the second electroplating solution is zinc chloride, with a concentration of 40 g / L; the second electroplating solution also contains potassium chloride and boric acid, with a potassium chloride concentration of 100 g / L and a boric acid concentration of 10 g / L; the pH of the second electroplating treatment is 4. S6. Passivate the surface of the NdFeB magnet treated in step S5. The resulting galvanized NdFeB magnet is shown in the image below. Figure 4 As shown; The passivation treatment used a chromium nitrate solution with a pH of 1.5, a concentration of 20 g / L, and a passivation time of 30 s. The nano-silica in the nano-silica suspension in step S3 above has undergone pretreatment. The pretreatment of nano-silica includes the following steps: S101. Tetrabutylammonium bromide is added to a mixed solution of ammonia and ethanol to obtain a mixed solution. Then, nano-silica is ultrasonically dispersed into the mixed solution, followed by the addition of tetraethyl orthosilicate. The reaction is carried out continuously at 30°C for 3 hours. The concentration of tetrabutylammonium bromide in the mixed solution was 4 mmol / L, the concentration of ammonia was 25 wt%, and the mass ratio of ammonia, ethanol, nano silica and tetraethyl orthosilicate was 10:60:1:4. S102. After the reaction in step S101 is completed, filter the product, wash the product with sufficient ethanol, and then vacuum dry it to constant weight at 30°C to complete the pretreatment of nano-silica.

[0021] Example 3 A method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material, the method comprising the following steps: S1. Pre-treat the neodymium iron boron magnet; The pretreatment in step S1 includes pickling, washing, and activation; The specific pickling process involves using 3wt% nitric acid for 20 seconds; the activation process involves using 3wt% hydrochloric acid for 10 seconds. S2. The neodymium iron boron magnet pretreated in step S1 is placed into a primary electroplating solution for a primary zinc plating process. In step S2, the electroplating material used in the first electroplating solution is zinc sulfate, with a concentration of 450 g / L; the first electroplating solution also contains boric acid and potassium sulfate, with a boric acid concentration of 20 g / L and a potassium sulfate concentration of 120 g / L; the pH of the first zinc plating treatment is 5. S3. Place the neodymium iron boron magnet that has undergone the zinc plating treatment in step S2 into the nano silica suspension and vacuum immerse it for 20 minutes. The concentration of nano-silica in the nano-silica suspension is 30 g / L; The nano-silica suspension also contains sodium hexadecyl sulfate and γ-aminopropyltriethoxysilane, with the concentration of sodium hexadecyl sulfate being 10 g / L and the concentration of γ-aminopropyltriethoxysilane being 4 g / L. S4. The neodymium iron boron magnets treated in step S3 are placed in hydrochloric acid solution for treatment, and then washed with water. The concentration of the hydrochloric acid solution is 6 wt%, and the NdFeB magnet treated in step S3 is treated in the hydrochloric acid solution for 8 seconds. S5. The neodymium iron boron magnets treated in step S4 are placed into a secondary electroplating solution for secondary zinc plating. The electroplating material used in the second electroplating solution was zinc chloride, with a concentration of 60 g / L. The second electroplating solution also contained potassium chloride and boric acid, with potassium chloride concentrations of 200 g / L and boric acid concentrations of 20 g / L. The pH of the second electroplating treatment was 6. The resulting zinc-plated NdFeB magnet is shown in the image below. Figure 7 As shown; S6. Passivate the surface of the neodymium iron boron magnet treated in step S5. The passivation treatment used a chromium nitrate solution with a pH of 2.5, a chromium nitrate concentration of 30 g / L, and a passivation time of 40 s. The nano-silica in the nano-silica suspension in step S3 above has undergone pretreatment. The pretreatment of nano-silica includes the following steps: S101. Tetrabutylammonium bromide is added to a mixed solution of ammonia and ethanol to obtain a mixed solution. Then, nano-silica is ultrasonically dispersed into the mixed solution, followed by the addition of tetraethyl orthosilicate. The mixture is reacted continuously at 45°C for 6 hours. The concentration of tetrabutylammonium bromide in the mixed solution was 10 mmol / L, the concentration of ammonia was 25 wt%, and the mass ratio of ammonia, ethanol, nano silica and tetraethyl orthosilicate was 15:100:1:8. S102. After the reaction in step S101 is completed, filter the product, wash the product with sufficient ethanol, and then vacuum dry it to constant weight at 45°C to complete the pretreatment of nano-silica.

[0022] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the pretreatment step of nano-silica was omitted, while the remaining steps are exactly the same as in Example 1.

[0023] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the addition of nano-silica was completely eliminated in step S3 of the nano-silica suspension, while the remaining steps were exactly the same as in Example 1.

[0024] Salt spray resistance tests were conducted on the neodymium iron boron permanent magnet materials prepared in Examples 1-3 and Comparative Examples 1-2 according to the standard GB / T10125-2012, with observations every 24 hours.

[0025] Experimental results show that the NdFeB permanent magnet materials prepared in Examples 1-3 of this invention can withstand salt spray tests for more than 160 hours without developing white rust on the surface; the NdFeB permanent magnet materials prepared in Comparative Example 1 begin to develop white rust on the surface after 145 hours of salt spray tests; and the NdFeB permanent magnet materials prepared in Comparative Example 2 begin to develop white rust on the surface after 128 hours of salt spray tests.

[0026] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for plating a double layer of zinc onto the surface of a neodymium iron boron permanent magnet material, characterized in that, The method includes the following steps: S1. Pre-treat the neodymium iron boron magnet; S2. The neodymium iron boron magnet pretreated in step S1 is placed into a primary electroplating solution for a primary zinc plating process. S3. Place the neodymium iron boron magnets that have undergone the zinc plating treatment in step S2 into the nano silica suspension and vacuum immerse them for 10-20 minutes. S4. The neodymium iron boron magnets treated in step S3 are placed in hydrochloric acid solution for treatment, and then washed with water. S5. The neodymium iron boron magnets treated in step S4 are placed into a secondary electroplating solution for secondary zinc plating. S6. Passivate the surface of the neodymium iron boron magnet treated in step S5. The electroplating material used in the first electroplating solution in step S2 is zinc sulfate; The electroplating material used in the second electroplating solution in step S5 is zinc chloride; In step S3, the nano-silica in the nano-silica suspension has undergone pretreatment. The pretreatment of nano-silica includes the following steps: S101. Tetrabutylammonium bromide is added to a mixed solution of ammonia and ethanol to obtain a mixed solution. Then, nano-silica is ultrasonically dispersed into the mixed solution, followed by the addition of tetraethyl orthosilicate. The reaction is carried out continuously at 30-45℃ for 4-6 hours. S102. After the reaction in step S101 is completed, filter the product, wash the product with sufficient ethanol, and then vacuum dry it to constant weight at 30-45℃ to complete the pretreatment of nano-silica.

2. The method for plating a double layer of zinc onto the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, The pretreatment in step S1 includes acid washing, water washing, and activation.

3. The method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, The pickling in step S1 is carried out using 2-3 wt% nitric acid for 15-20 seconds; the activation in step S1 is carried out using 2-3 wt% hydrochloric acid for 5-10 seconds.

4. The method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step S2, the concentration of zinc sulfate in the primary electroplating solution is 300-450 g / L; the primary electroplating solution also contains boric acid and potassium sulfate, with the concentration of boric acid being 10-20 g / L and the concentration of potassium sulfate being 50-120 g / L; the pH of the first zinc plating treatment is 4-5.

5. The method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step S3, the concentration of nano-silica in the nano-silica suspension is 10-30 g / L.

6. The method for plating a double layer of zinc onto the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step S101, the concentration of tetrabutylammonium bromide in the mixed solution is 4-10 mmol / L, the concentration of ammonia is 25 wt%, and the mass ratio of ammonia, ethanol, nano silica and tetraethyl orthosilicate is (10-15):(60-100):1:(4-8).

7. The method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step S3, the nano-silica suspension also contains sodium hexadecyl sulfate and γ-aminopropyltriethoxysilane, with the concentration of sodium hexadecyl sulfate being 5-10 g / L and the concentration of γ-aminopropyltriethoxysilane being 2-4 g / L.

8. The method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step S4, the concentration of the hydrochloric acid solution is 4-6 wt%, and the neodymium iron boron magnet treated in step S3 is treated in the hydrochloric acid solution for 4-8 seconds.

9. The method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, The concentration of zinc chloride in the secondary electroplating solution in step S5 is 40-60 g / L; the secondary electroplating solution also contains potassium chloride and boric acid, with the concentration of potassium chloride being 100-200 g / L and the concentration of boric acid being 10-20 g / L; the pH of the second electroplating treatment is 4-6.

10. The method for plating a double layer of zinc on the surface of a neodymium iron boron permanent magnet material according to claim 1, characterized in that, In step S6, the passivation treatment uses a chromium nitrate solution with a pH of 1.5-2.5, a concentration of chromium nitrate of 20-30 g / L, and a passivation time of 30-40 s.

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