Blue-white passivation solution for neodymium iron boron electrogalvanizing and passivation method

Abstract

The invention discloses a blue-white passivation solution for neodymium iron boron electrogalvanizing and a passivation method, and belongs to the technical field of electroplating processes. The passivation solution comprises the following raw materials: 3-6 g / L of a trivalent chromium compound, 3-6 g / L of soluble cerium salt, 1-2 g / L of soluble titanium salt, 3-5 g / L of phosphomolybdic acid, 2-4 g / L of polyaspartic acid, 0.5-1 g / L of cobalt nitrate, 0.3-0.6 g / L of benzotriazole, 1.5-2.5 g / L of sodium silicate, 4-6 g / L of sodium nitrate, 1-5 g / L of organic carboxylic acid, 1.5-3 g / L of ascorbic acid, 0.05-0.1 g / L of a nonionic surfactant and water as a solvent, and the pH is adjusted to 2.5-3.5 by a pH regulator. The neodymium iron boron material subjected to electrogalvanizing is subjected to dipping passivation treatment, tetravalent cerium formed through cerium salt oxidation in a passivation solution is deposited on a film layer under the strong chelation effect of polyaspartic acid, and a passivation film has the self-repairing capacity and is high in corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of electroplating technology, specifically relating to a blue-white passivation solution and passivation method for NdFeB electroplating zinc. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnets are widely used in new energy vehicles, consumer electronics, medical devices, aerospace, and industrial motors. However, a potential difference exists between the neodymium-rich and boron-rich phases in the material and the main phase of the magnet alloy, which easily forms a galvanic cell, causing electrochemical corrosion on the material surface. Therefore, NdFeB permanent magnets require anti-corrosion treatment, and electroplating with zinc is currently widely used.

[0003] However, the zinc plating layer on its surface is prone to oxidation and white rust in humid or corrosive environments. To improve its corrosion resistance, the zinc plating layer needs to undergo passivation treatment. Traditional passivation solutions often contain hexavalent chromium (Cr). 6+ While possessing excellent anti-corrosion properties, it is highly toxic and does not meet environmental protection requirements. Developing an environmentally friendly blue-white passivation solution to replace traditional hexavalent chromium-containing passivation solutions is an urgent need for the industry's green transformation.

[0004] The most commonly used passivation solution on the market is trivalent chromium passivation solution. Although the trivalent chromium in this passivation solution is less toxic than hexavalent chromium, it cannot achieve the corrosion resistance of hexavalent chromate passivation. Chromium-free passivation solutions have not been widely used due to their high cost and low reliability. Summary of the Invention

[0005] This invention provides a blue-white passivation solution and passivation method for NdFeB electroplating zinc, which can solve the problems of high toxicity and weak corrosion resistance of existing passivation solutions for NdFeB electroplating zinc.

[0006] The objective of this invention can be achieved through the following technical solutions: A blue-white passivation solution for NdFeB electroplating zinc comprises the following raw materials: The following ingredients are used: 3-6 g / L trivalent chromium compounds, 3-6 g / L soluble cerium salts, 1-2 g / L soluble titanium salts, 3-5 g / L phosphomolybdic acid, 2-4 g / L polyaspartic acid, 0.5-1 g / L cobalt nitrate, 0.3-0.6 g / L benzotriazole, 1.5-2.5 g / L sodium silicate, 4-6 g / L sodium nitrate, 1-5 g / L organic carboxylic acids, 1.5-3 g / L ascorbic acid, and 0.05-0.1 g / L nonionic surfactant. Water is used as the solvent, and the pH is adjusted to 2.5-3.5 with a pH adjuster.

[0007] In traditional passivation solutions, hexavalent chromium is the main component for oxide film formation. In hexavalent chromium passivation solutions, hexavalent chromium mainly exists as Cr2O7. 2- It exists in the form of zinc, and it reacts chemically with the zinc coating, causing the zinc to be oxidized into Zn. 2+Meanwhile, Cr(VI) is reduced to Cr(III) and forms a colloidal film containing hydrated zinc chromate, chromium hydroxide, and zinc and other metal oxides near the zinc coating surface. When the passivation film is scratched or damaged by external force, the hexavalent chromium compound dissolves in water and reacts with the exposed zinc layer in humid air to regenerate the passivation film. Trivalent chromium forms the framework of the passivation film, while hexavalent chromium fills the trivalent chromium framework through adsorption, inclusion and chemical bonding, thereby achieving self-repair.

[0008] In the formulation of trivalent chromium passivation solutions, trivalent chromium compounds are the main oxidizing film-forming components. Under acidic conditions, trivalent chromium reacts with a zinc layer to form chromium-zinc oxide, which deposits on the surface to form a corrosion-resistant film. Unlike hexavalent chromium, although trivalent chromium is less toxic, the trivalent chromium passivation film does not contain hexavalent chromium (Cr). 6+ It lacks self-healing capabilities. This means that once the passivation film is mechanically damaged or corroded, it cannot restore its integrity through its own repair mechanism, thus accelerating the corrosion process and resulting in poor corrosion resistance.

[0009] In contrast, trivalent chromium passivation films have poor corrosion resistance, mainly due to insufficient film density and self-healing ability. Trivalent chromium passivation films are usually thinner, and due to possible inhomogeneities during film formation, microcracks or pores may appear in the film. These defects can become channels for corrosive media, thereby reducing the overall corrosion resistance.

[0010] In the above passivation solution formulation, soluble cerium salts and soluble titanium salts are added to assist film formation in the presence of trivalent chromium compounds. Under acidic conditions, the trivalent cerium ions in the soluble cerium salt are oxidized to tetravalent cerium. At this point, due to the chelating effect of polyaspartic acid, premature precipitation of the generated CeO2 is prevented, stabilizing the passivation solution. At the film-forming interface, this promotes the orderly release and deposition of tetravalent cerium. CeO2 embeds into the trivalent chromium film layer, effectively filling the pores and forming a more uniform, dense, and smooth passivation film, improving the film's coverage of the substrate and reducing defects. Tetravalent cerium, possessing zinc oxide, also enhances the self-healing ability of the passivation film. Even when the passivation film is damaged, it can oxidize the exposed zinc layer and form a new passivation film with trivalent chromium, inhibiting corrosion. Soluble titanium salts hydrolyze to generate titanium hydroxide or oxide hydrates. These substances also deposit in the film layer, synergistically increasing the film's density and wear resistance, and improving the adhesion between the film layer and the substrate. Sodium silicate hydrolysis can form silica sol or gel, which can be deposited in the pores of the film to seal defects, increase density, and improve corrosion resistance and wear resistance. The Ti-OH of the hydrolysis products of soluble titanium salt condenses with the Si-OH of the hydrolysis products of sodium silicate to form Ti-O-Si bonds, forming a network structure and increasing the film density.

[0011] In addition, phosphomolybdic acid and sodium nitrate can be used as oxidants. Phospholybdic acid has a strong oxidizing effect, accelerating the dissolution of zinc in acid, significantly accelerating the film formation process, and can form heteropolyacid complexes with zinc ions, improving the color uniformity of the film and effectively inhibiting Cl. - This causes pitting corrosion. Sodium nitrate can provide nitrate ions to participate in the oxidation reaction.

[0012] Iron boron magnets often contain copper. Benzotriazole can specifically adsorb copper ions to form a complex. When doped into the film, it can prevent copper-induced galvanic corrosion or rust discoloration and ensure the corrosion resistance of the passivation film.

[0013] Ascorbic acid is an organic reducing agent that can inhibit the formation of hexavalent chromium in the passivation solution and maintain a low content of hexavalent chromium in the passivation solution.

[0014] Furthermore, the trivalent chromium compound is one of chromium nitrate and chromium sulfate.

[0015] Furthermore, the soluble cerium salt is one of cerium sulfate, cerium nitrate, and cerium acetate.

[0016] Furthermore, the soluble titanium salt is one of titanium sulfate and titanium oxysulfate.

[0017] Furthermore, the organic carboxylic acid is one of citric acid and tartaric acid.

[0018] Citric acid or tartaric acid, with their multiple carboxyl groups, effectively buffer the pH of the passivation solution, stabilizing it within a specified range. This is crucial for the rate of film formation and the quality of the film. They can also gently complex metal ions in the solution, preventing precipitation caused by localized pH increases, stabilizing the solution, and promoting uniform film formation.

[0019] Furthermore, the pH adjuster is either sulfuric acid or nitric acid.

[0020] Furthermore, the nonionic surfactant is one of alkyl glycosides, sorbitol esters, and polyethylene glycol. As a lubricant, the nonionic surfactant reduces the surface tension of the passivation solution, improves its wetting and spreading ability on the zinc layer surface, and allows the solution to quickly and uniformly cover the entire NdFeB material, preventing the formation of bubbles, watermarks, or unplated spots, thereby obtaining a uniform blue-white passivation film.

[0021] Furthermore, the preparation steps of the blue-white passivation solution for NdFeB electroplating zinc are as follows: Step 1: Add trivalent chromium compound, soluble cerium salt, soluble titanium salt and cobalt nitrate to water in sequence, stir to dissolve, then add other raw materials except pH adjuster and stir to mix well. Step 2: While stirring, add pH adjuster to adjust the pH to 2.5-3.5.

[0022] This invention also provides a passivation method, which uses the blue-white passivation solution for NdFeB electroplating zinc as described above to passivate the NdFeB material with zinc electroplating on its surface, including the following steps: S1. Wash the electroplated zinc-coated NdFeB material with water to remove surface impurities; S2. Immerse the material washed in S1 into the passivation solution for passivation, then take it out, wash it with water and dry it. A passivation film is formed on the surface of the electroplated zinc layer.

[0023] Furthermore, the passivation temperature is 20-40℃, the passivation time is 10-30s, and the thickness of the passivation film is 0.2-0.5μm.

[0024] The beneficial effects of this invention are: (1) In the passivation solution of the present invention, cerium salt is added on the basis of trivalent chromium salt. The tetravalent cerium formed by the oxidation of cerium salt is deposited on the film layer under the strong chelation of polyaspartic acid, replacing the original hexavalent chromium oxidation. After the passivation film is damaged, it has the ability to repair itself by self-oxidation to form a passivation film, inhibiting corrosion after damage and improving the corrosion resistance of the passivation film.

[0025] (2) When trivalent chromium salts are present in the passivation solution, the passivation film has poor density when formed alone. The hydrolysis products of titanium salts and sodium silicate are deposited in the pores of the film to seal the defects, increase the density, and improve the corrosion resistance and wear resistance.

[0026] (3) The oxidants in the passivation solution are mainly sodium nitrate and phosphomolybdic acid. Phospholybdic acid has strong oxidizing properties, which accelerates the formation of the passivation film. Sodium nitrate can assist in oxidation by releasing nitrate ions, thus avoiding unevenness of the film layer caused by localized violent reactions. Compared with the traditional hydrogen peroxide oxidant, phosphomolybdic acid can act as both an oxidant and participate in the formation of the film layer, forming a heteropolyacid complex with zinc to improve the corrosion resistance of the passivation film. Hydrogen peroxide decomposes under acidic conditions to produce oxygen, which will destroy the stability of the passivation solution and form pores on the surface of the passivation film, thus destroying the compactness of the passivation film. Sodium nitrate and phosphomolybdic acid do not form pores, have good compatibility with other components in the passivation solution, and will not cause side reactions or component consumption.

[0027] (4) Use organic reducing agent ascorbic acid to inhibit the oxidation of trivalent chromium to form hexavalent chromium, reduce the content of hexavalent chromium in the passivation solution, and ensure the low toxicity of the passivation solution. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 A blue-white passivation solution for NdFeB electroplating zinc comprises the following raw materials: Chromium nitrate 5g / L, cerium sulfate 4g / L, titanium sulfate 1.5g / L, phosphomolybdic acid 4g / L, polyaspartic acid 3g / L, cobalt nitrate 0.8g / L, benzotriazole 0.5g / L, sodium silicate 2.0g / L, sodium nitrate 5g / L, citric acid 3g / L, ascorbic acid 2g / L, polyethylene glycol 0.07g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0030] The passivation solution is prepared as follows: Step 1: Add chromium nitrate, cerium sulfate, titanium sulfate and cobalt nitrate to water in sequence, stir to dissolve, then add the other raw materials except concentrated sulfuric acid and stir to mix well, and make up to 5L. Step 2: While stirring, add concentrated sulfuric acid to adjust the pH to 3.0.

[0031] A passivation method, the specific steps of which are as follows: S1. Wash the electroplated zinc-coated NdFeB material with water to remove surface impurities; S2. Immerse the material washed in S1 into the passivation solution for passivation. Set the passivation temperature to 30℃ and the passivation time to 20s. After taking it out, wash it with water and dry it. A passivation film is formed on the surface of the electroplated zinc layer.

[0032] Example 2 The only difference from Example 1 is the ratio of raw materials in the passivation solution; the concentrations of cerium sulfate and polyaspartic acid are reduced. All other conditions and steps are the same as in Example 1, with the specific ratio as follows: Chromium nitrate 5 g / L, cerium sulfate 3 g / L, titanium sulfate 1.5 g / L, phosphomolybdic acid 4 g / L, polyaspartic acid 2 g / L, cobalt nitrate 0.8 g / L, benzotriazole 0.5 g / L, sodium silicate 2.0 g / L, sodium nitrate 5 g / L, citric acid 3 g / L, ascorbic acid 2 g / L, polyethylene glycol 0.07 g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0033] Example 3 The only difference from Example 1 is the ratio of raw materials in the passivation solution; the concentrations of cerium sulfate and polyaspartic acid are increased. All other conditions and steps are the same as in Example 1, with the specific ratio as follows: Chromium nitrate 5 g / L, cerium sulfate 6 g / L, titanium sulfate 1.5 g / L, phosphomolybdic acid 4 g / L, polyaspartic acid 4 g / L, cobalt nitrate 0.8 g / L, benzotriazole 0.5 g / L, sodium silicate 2.0 g / L, sodium nitrate 5 g / L, citric acid 3 g / L, ascorbic acid 2 g / L, polyethylene glycol 0.07 g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0034] Example 4 The only difference from Example 1 is the ratio of raw materials in the passivation solution; the concentrations of titanium sulfate and sodium silicate are reduced. All other conditions and steps are the same as in Example 1, with the specific ratio as follows: Chromium nitrate 5g / L, cerium sulfate 4g / L, titanium sulfate 1.0g / L, phosphomolybdic acid 4g / L, polyaspartic acid 3g / L, cobalt nitrate 0.8g / L, benzotriazole 0.5g / L, sodium silicate 1.5g / L, sodium nitrate 5g / L, citric acid 3g / L, ascorbic acid 2g / L, polyethylene glycol 0.07g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0035] Example 5 The only difference from Example 1 is the ratio of raw materials in the passivation solution; the concentrations of titanium sulfate and sodium silicate are increased. All other conditions and steps are the same as in Example 1, with the specific ratio as follows: Chromium nitrate 5 g / L, cerium sulfate 4 g / L, titanium sulfate 2.0 g / L, phosphomolybdic acid 4 g / L, polyaspartic acid 3 g / L, cobalt nitrate 0.8 g / L, benzotriazole 0.5 g / L, sodium silicate 2.5 g / L, sodium nitrate 5 g / L, citric acid 3 g / L, ascorbic acid 2 g / L, polyethylene glycol 0.07 g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0036] Example 6 The only difference from Example 1 is the ratio of raw materials in the passivation solution; the concentrations of phosphomolybdic acid and sodium nitrate are reduced. All other conditions and steps are the same as in Example 1, with the specific ratio as follows: Chromium nitrate 5 g / L, cerium sulfate 4 g / L, titanium sulfate 1.5 g / L, phosphomolybdic acid 3 g / L, polyaspartic acid 3 g / L, cobalt nitrate 0.8 g / L, benzotriazole 0.5 g / L, sodium silicate 2.0 g / L, sodium nitrate 4 g / L, citric acid 3 g / L, ascorbic acid 2 g / L, polyethylene glycol 0.07 g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0037] Example 7 The only difference from Example 1 is the ratio of raw materials in the passivation solution; the concentrations of phosphomolybdic acid and sodium nitrate are increased. All other conditions and steps are the same as in Example 1. The specific ratio is as follows: Chromium nitrate 5g / L, cerium sulfate 4g / L, titanium sulfate 1.5g / L, phosphomolybdic acid 5g / L, polyaspartic acid 3g / L, cobalt nitrate 0.8g / L, benzotriazole 0.5g / L, sodium silicate 2.0g / L, sodium nitrate 6g / L, citric acid 3g / L, ascorbic acid 2g / L, polyethylene glycol 0.07g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0038] Example 8 The only difference from Example 1 is the ratio of raw materials in the passivation solution, which is different, and the concentration of ascorbic acid is reduced. All other conditions and steps are the same as in Example 1, with the specific ratio as follows: Chromium nitrate 5 g / L, cerium sulfate 4 g / L, titanium sulfate 1.5 g / L, phosphomolybdic acid 4 g / L, polyaspartic acid 3 g / L, cobalt nitrate 0.8 g / L, benzotriazole 0.5 g / L, sodium silicate 2.0 g / L, sodium nitrate 5 g / L, citric acid 3 g / L, ascorbic acid 1.5 g / L, polyethylene glycol 0.07 g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0039] Example 9 The only difference from Example 1 is the ratio of raw materials in the passivation solution; the concentration of ascorbic acid is increased. All other conditions and steps are the same as in Example 1, with the specific ratio as follows: Chromium nitrate 5g / L, cerium sulfate 4g / L, titanium sulfate 1.5g / L, phosphomolybdic acid 4g / L, polyaspartic acid 3g / L, cobalt nitrate 0.8g / L, benzotriazole 0.5g / L, sodium silicate 2.0g / L, sodium nitrate 5g / L, citric acid 3g / L, ascorbic acid 3.0g / L, polyethylene glycol 0.07g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0040] Comparative Example 1 The only difference from Example 1 is the ratio of raw materials in the passivation solution; citric acid is used to replace polyaspartic acid in equal mass. All other conditions and steps are the same as in Example 1. The specific ratio is as follows: Chromium nitrate 5g / L, cerium sulfate 4g / L, titanium sulfate 1.5g / L, phosphomolybdic acid 4g / L, cobalt nitrate 0.8g / L, benzotriazole 0.5g / L, sodium silicate 2.0g / L, sodium nitrate 5g / L, citric acid 6g / L, ascorbic acid 2g / L, polyethylene glycol 0.07g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0041] Comparative Example 2 The only difference from Example 1 is the ratio of raw materials in the passivation solution; sodium silicate is used instead of titanium sulfate by an equal mass. All other conditions and steps are the same as in Example 1. The specific ratio is as follows: Chromium nitrate 5g / L, cerium sulfate 4g / L, phosphomolybdic acid 4g / L, polyaspartic acid 3g / L, cobalt nitrate 0.8g / L, benzotriazole 0.5g / L, sodium silicate 3.5g / L, sodium nitrate 5g / L, citric acid 3g / L, ascorbic acid 2g / L, polyethylene glycol 0.07g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0042] Comparative Example 3 The only difference from Example 1 is the ratio of raw materials in the passivation solution; sodium nitrate is used instead of phosphomolybdic acid by an equal mass. All other conditions and steps are the same as in Example 1. The specific ratio is as follows: Chromium nitrate 5g / L, cerium sulfate 4g / L, titanium sulfate 1.5g / L, polyaspartic acid 3g / L, cobalt nitrate 0.8g / L, benzotriazole 0.5g / L, sodium silicate 2.0g / L, sodium nitrate 9g / L, citric acid 3g / L, ascorbic acid 2g / L, polyethylene glycol 0.07g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0043] Comparative Example 4 The only difference from Example 1 is that the raw material ratio in the passivation solution is different, and ascorbic acid is not added. All other conditions and steps are the same as in Example 1, with the specific ratio as follows: Chromium nitrate 5g / L, cerium sulfate 4g / L, titanium sulfate 1.5g / L, phosphomolybdic acid 4g / L, polyaspartic acid 3g / L, cobalt nitrate 0.8g / L, benzotriazole 0.5g / L, sodium silicate 2.0g / L, sodium nitrate 5g / L, citric acid 3g / L, polyethylene glycol 0.07g / L, appropriate amount of water, and concentrated sulfuric acid to adjust the pH to 3.0.

[0044] Performance tests were conducted on Examples 1-9 and Comparative Examples 1-3, and the results are shown in Table 1.

[0045] Passivation film thickness: The thickness difference is calculated by detecting the thickness of the NdFeB material before and after passivation.

[0046] Salt spray rusting time: The passivated NdFeB material was subjected to a neutral salt spray test, and the test was set up in accordance with the standard GB / T 10125-2021 Artificial Atmosphere Corrosion Test Salt Spray Test.

[0047] Table 1

[0048] As shown in Table 1, among Examples 1-3, the raw material ratio in Example 1 was optimal. Reducing the concentrations of cerium sulfate and polyaspartic acid weakened the repair ability of cerium salts, thus reducing corrosion resistance. Excessive concentrations caused the tetravalent cerium compounds deposited in the pores after chelation to accumulate, increasing surface roughness, forming easily corroded defect areas, and further reducing corrosion resistance. Based on Example 1, Examples 4 and 5 adjusted the concentrations of titanium sulfate and sodium silicate. The concentrations of titanium sulfate and sodium silicate affected the density and adhesion of the film. Compared to Examples 1 and 5, the passivation film of Example 1 exhibited a longer corrosion resistance time in the neutral salt spray test. In Examples 6 and 7, the adjustment of the concentrations of phosphomolybdic acid and sodium nitrate significantly affected the passivation film performance. Compared to Example 1, the lower concentrations of phosphomolybdic acid and sodium nitrate in the passivation solution of Example 6 resulted in the inability to rapidly oxidize the zinc plating layer to form a passivation film within the passivation time, leading to a thinner film and rusting after 72 hours in the neutral salt spray test. In Example 7, the high concentration of oxidant caused over-oxidation, resulting in a loose passivation film structure and poor corrosion resistance. The organic reducing agent ascorbic acid can inhibit the oxidation of trivalent chromium in the passivation solution. The concentration of ascorbic acid in the passivation solution of Example 8 was 1.5 g / L, indicating a weaker inhibitory effect at lower concentrations. Compared to Example 1, the hexavalent chromium content in the passivation solution of Example 8 was significantly higher.

[0049] Combining Comparative Example 1 and Example 1, it can be seen that, unlike the effects of citric acid and other organic carboxylic acids, polyaspartic acid exhibits better chelating properties under acidic conditions, and can synergistically enhance the corrosion resistance of the passivation film with cerium salt. Compared to Example 1, in the absence of the combined effect of sodium silicate and titanium sulfate, the passivation film formed after treatment with the passivation solution in Comparative Example 2 has good density but insufficient adhesion, and the gaps between the film layers will accelerate corrosion. Compared to Example 1, Comparative Example 3 lacks phosphomolybdic acid, and the oxidation effect of high-concentration sodium nitrate is not as good as the combined oxidation effect of phosphomolybdic acid and sodium nitrate; it rusted after 62 hours in the neutral salt spray test.

[0050] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0051] 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 blue-white passivation solution for NdFeB electroplating zinc, characterized in that, Including the following raw materials: The following ingredients are used: 3-6 g / L trivalent chromium compounds, 3-6 g / L soluble cerium salts, 1-2 g / L soluble titanium salts, 3-5 g / L phosphomolybdic acid, 2-4 g / L polyaspartic acid, 0.5-1 g / L cobalt nitrate, 0.3-0.6 g / L benzotriazole, 1.5-2.5 g / L sodium silicate, 4-6 g / L sodium nitrate, 1-5 g / L organic carboxylic acids, 1.5-3 g / L ascorbic acid, and 0.05-0.1 g / L nonionic surfactant. Water is used as the solvent, and the pH is adjusted to 2.5-3.5 with a pH adjuster.

2. The blue-white passivation solution for NdFeB electroplating zinc according to claim 1, characterized in that, The trivalent chromium compound is one of chromium nitrate and chromium sulfate.

3. The blue-white passivation solution for NdFeB electroplating zinc according to claim 1, characterized in that, The soluble cerium salt is one of cerium sulfate, cerium nitrate, and cerium acetate.

4. The blue-white passivation solution for NdFeB electroplating zinc according to claim 1, characterized in that, The soluble titanium salt is one of titanium sulfate and titanium oxysulfate.

5. The blue-white passivation solution for NdFeB electroplating zinc according to claim 1, characterized in that, The organic carboxylic acid is one of citric acid and tartaric acid.

6. The blue-white passivation solution for NdFeB electroplating zinc according to claim 1, characterized in that, The pH adjuster is either sulfuric acid or nitric acid.

7. The blue-white passivation solution for NdFeB electroplating zinc according to claim 1, characterized in that, The nonionic surfactant is one of alkyl glycosides, sorbitol esters, and polyethylene glycol.

8. The blue-white passivation solution for NdFeB electroplating zinc according to claim 1, characterized in that, The preparation steps of the blue-white passivation solution for NdFeB electroplating zinc are as follows: Step 1: Add trivalent chromium compound, soluble cerium salt, soluble titanium salt and cobalt nitrate to water in sequence, stir to dissolve, then add other raw materials except pH adjuster and stir to mix well. Step 2: While stirring, add pH adjuster to adjust the pH to 2.5-3.

5.

9. A passivation method, characterized in that, The passivation treatment of NdFeB material with zinc plating surface using the blue-white passivation solution for NdFeB electroplating as described in any one of claims 1-8 includes the following steps: S1. Wash the electroplated zinc-coated NdFeB material with water to remove surface impurities; S2. Immerse the material washed in S1 into the passivation solution for passivation, then take it out, wash it with water and dry it. A passivation film is formed on the surface of the electroplated zinc layer.

10. A passivation method according to claim 9, characterized in that, The passivation temperature is 20-40℃, the passivation time is 10-30s, and the thickness of the passivation film is 0.2-0.5μm.

Images