Trivalent chromium blue-white passivation agent and passivation process thereof

Abstract

This invention relates to the field of passivating agent technology, and provides a trivalent chromium blue-white passivating agent and its passivation process. The trivalent chromium blue-white passivating agent comprises: trivalent chromium salt, carboxylic acid complexing agent, fluoride activator, nitrate, organic acid regulator, acidic silica sol, zirconium salt, rare earth salt, nonionic wetting agent, deionized water, and the balance. This invention regulates chromium content through the carboxylic acid complexing agent. 3 The release and hydrolysis deposition rate, combined with fluoride activators and nitrates, gently activate the surface of zinc or zinc alloys to promote trace dissolution and interfacial film formation on the metal surface; at the same time, acidic silica sol is introduced to form a transparent silicon-rich closed structure in the micropores and surface of the film layer, and zirconium salts and rare earth salts replace cobalt salts in the composite film formation, so that a composite inorganic structure is formed in the passivation film, thereby improving the film density and corrosion resistance without relying on cobalt salts.

Description

Technical Field

[0001] This invention relates to the field of passivating agent technology, and more specifically, to a trivalent chromium blue-white passivating agent and its passivation process. Background Technology

[0002] Trivalent chromium blue-white passivating agents are a type of metal surface treatment agent, mainly used to form a transparent, translucent, or light blue-white passivation film on metal surfaces to improve the corrosion resistance, appearance stability, and subsequent reliability of the metal surface. Trivalent chromium blue-white passivating agents are primarily used for passivation treatment of non-ferrous metal surfaces such as zinc, zinc alloys, aluminum, aluminum alloys, cadmium, and cadmium alloys. Among these, the application of trivalent chromium blue-white passivating agents is particularly widespread in the blue-white passivation treatment of zinc plating, zinc alloy plating, and zinc-nickel alloy plating.

[0003] Zinc and zinc alloy coatings are commonly used to protect steel substrates, improving the corrosion resistance of steel parts through sacrificial anode action. They are widely used in fasteners, hardware, automotive parts, electronic structural components, and building metal parts. However, zinc and zinc alloy coatings are prone to oxidation and corrosion in humid, salt spray, or chlorine-containing environments, forming white rust, which affects the appearance and corrosion resistance of the workpiece. Therefore, after zinc or zinc alloy coatings are formed, passivation treatment is usually required to form a passivation film on the coating surface, thereby reducing the contact between the zinc layer and moisture, oxygen, and corrosive ions, and improving the coating's resistance to white rust.

[0004] Trivalent chromium blue-white passivating agents typically use trivalent chromium salts as the main film-forming component. When treating zinc or zinc alloy coatings, the zinc surface undergoes slight dissolution in the acidic passivation solution, releasing Zn. 2 ⁺, and at the same time, the acidity near the interface changes, causing Cr to 3 ⁺ Hydrolysis and deposition occur, and together with zinc oxide and hydroxide, they form a composite passivation film containing elements such as chromium, zinc, and oxygen.

[0005] In existing trivalent chromium blue-white passivating agents, cobalt salts are often added as auxiliary film-forming components to improve the density and corrosion resistance of the passivation film. Cobalt salts can improve the film-forming stability, film uniformity, and salt spray resistance of trivalent chromium passivation films to a certain extent. However, the use of cobalt salts often faces pressure from environmental protection, occupational health, and regulatory compliance. Simply removing cobalt salts can easily lead to problems such as insufficient film formation, loose film layer, increased micropore defects, unstable blue-white appearance, and decreased resistance to white rust in the trivalent chromium blue-white passivation system. Especially for the blue-white passivation system, insufficient corrosion resistance cannot be compensated for simply by increasing the film thickness, because an excessively thick film layer can easily lead to a hazy, dark, or yellowish appearance, or even the loss of the decorative effect that the blue-white passivation film should have. Therefore, for trivalent chromium blue-white passivating agents, how to improve the density and corrosion resistance of the film layer without relying on cobalt salts, while maintaining the blue-white appearance of the passivation film, has always been a goal pursued by experts in this field. Summary of the Invention

[0006] The present invention aims to provide a trivalent chromium blue-white passivating agent and its passivation process.

[0007] To address the aforementioned problems, this invention provides a trivalent chromium blue-white passivating agent, comprising: trivalent chromium salt: 3.0-4.0 g / L, carboxylic acid complexing agent: 5.0-10.0 g / L, fluoride activator: 0.35-0.65 g / L, nitrate: 1.5-2.5 g / L, organic acid regulator: 0.3-1.0 g / L, acidic silica sol: 1.0-2.0 g / L, zirconium salt: 0.10-0.20 g / L, rare earth salt: 0.02-0.05 g / L, nonionic wetting agent: 0.02-0.1 g / L, deionized water, and the balance; wherein the pH of the trivalent chromium blue-white passivating agent is 2.0-2.2.

[0008] In the above technical solution, the trivalent chromium salt includes at least one or a combination of chromium sulfate, chromium nitrate, chromium chloride, basic chromium sulfate, and chromium acetate; and / or the carboxylic acid complexing agent includes malonic acid and citric acid; and / or the fluoride activator includes at least one or a combination of sodium fluoride, ammonium fluoride, ammonium hydrofluoride, fluoroborate, and fluorozirconate; and / or the nitrate includes at least one or a combination of sodium nitrate, potassium nitrate, ammonium nitrate, magnesium nitrate, and zinc nitrate; and / or the organic acid regulator includes formic acid, acetic acid, lactic acid, and glycolic acid. At least one or a combination thereof; and / or acidic silica sol including acidic nano silica sol; and / or zirconium salt including at least one or a combination thereof of zirconium nitrate, zirconium oxychloride, zirconium sulfate, fluorozirconic acid, ammonium fluorozirconate, potassium fluorozirconate; and / or rare earth salt including at least one or a combination thereof of cerium nitrate, lanthanum nitrate, cerium ammonium nitrate, cerium chloride, lanthanum chloride; and / or nonionic wetting agent selected from at least one or a combination thereof of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyether modified siloxane wetting agent, acetylenide diol wetting agent.

[0009] In any of the above technical solutions, the mass ratio of malonic acid to citric acid is (3-5):1; and / or the particle size of the acidic silica sol is 5-20 nm.

[0010] This invention also provides a passivation process for a trivalent chromium blue-white passivating agent, using any one of the trivalent chromium blue-white passivating agents described in the above technical solutions, comprising the following steps: S100. After washing the metal workpiece to be treated with water, it is placed in a slightly acidic preconditioning solution for preconditioning treatment to obtain the pretreated workpiece. S200: The pretreated workpiece is passivated using trivalent chromium blue-white passivating agent to obtain a wet film passivated workpiece. S300: The wet film passivated workpiece is subjected to light washing, liquid control and curing treatment in sequence to obtain the passivated metal workpiece.

[0011] In any of the above technical solutions, S200 includes: S210. The pretreated workpiece is placed in a trivalent chromium blue-white passivating agent for the first passivation treatment to obtain the first intermediate workpiece. S220. The first intermediate workpiece is removed from the trivalent chromium blue-white passivating agent and subjected to liquid separation treatment to obtain the second intermediate workpiece. S230. The second intermediate workpiece is placed in a trivalent chromium blue-white passivating agent for a second passivation treatment to obtain a wet film passivated workpiece.

[0012] In any of the above technical solutions, the first passivation treatment time is 12-20s; and / or the second passivation treatment time is 8-15s; and / or the liquid removal treatment is to stay in the air for 15-30s.

[0013] In any of the above technical solutions, the slightly acidic preconditioning solution includes: citric acid: 0.5-2.0 g / L, malonic acid: 0.3-1.5 g / L, sodium nitrate: 0.2-1.0 g / L, and deionized water: balance; wherein the pH of the slightly acidic preconditioning solution is 3.0-4.5; and the preconditioning treatment time is 5-20 s.

[0014] In any of the above technical solutions, the light washing treatment includes a primary light washing treatment and a secondary light washing treatment; the primary light washing treatment uses deionized water with a conductivity of <100μS / cm and a residence time of 15-30s; the secondary light washing treatment uses deionized water with a conductivity of <20μS / cm and a residence time of 10-20s.

[0015] In any of the above technical solutions, the liquid control treatment includes one or a combination of low-pressure air knife, centrifugal drying, tilting dripping, and slow rotational drainage.

[0016] In any of the above technical solutions, the curing process includes: pre-drying at 50-60℃ for 1-3 minutes, and then drying at 75-90℃ for 8-15 minutes.

[0017] Beneficial Effects: This invention provides a trivalent chromium blue-white passivating agent and its passivation process, using trivalent chromium salt as the main film-forming component, and regulating Cr through a carboxylic acid complexing agent. 3 The release and hydrolysis deposition rate, combined with fluoride and nitrate, gently activate the zinc or zinc alloy surface to promote trace dissolution and interfacial film formation. Acidic silica sol is introduced to construct a transparent silicon-rich closed structure in the micropores and surface of the film to reduce defects. At the same time, zirconium salt and rare earth salt replace cobalt salt to participate in the formation of a composite passivation film containing Cr, Zn, Si, Zr and rare earth elements, improving the film density and corrosion resistance without relying on cobalt. Micro-acid preconditioning is introduced in the passivation process to uniformly regulate surface activity. After the initial Cr-Zn hydration conversion film is formed by the first passivation, the thin liquid film on the surface is used for further gentle conversion to reduce over-corrosion. The second passivation is used to reinforce the thin film and uncovered areas. Then, low-disturbance light washing is used to replace free acid salts to protect the nascent film. Combined with liquid control and segmented curing, flow marks, salt spots and color differences are reduced, and the dehydration and densification of the passivation film are promoted. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, a detailed description of specific embodiments of the present invention will be provided below.

[0019] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available. Experimental methods in the following examples that do not specify particular conditions should be performed according to conventional methods and conditions, or as selected in the product instructions.

[0020] In trivalent chromium blue-white passivation systems, cobalt salts are typically added as auxiliary film-forming components to improve the density and corrosion resistance of the passivation film. Cobalt salts can optimize the film-forming stability, film uniformity, and salt spray resistance of trivalent chromium passivation films to some extent, but their use often faces pressure from environmental protection, occupational health, and regulatory compliance concerns. Simply removing cobalt salts can easily lead to insufficient film formation, loose film layers, increased micropore defects, fluctuating blue-white appearance, and decreased resistance to white rust in the trivalent chromium blue-white passivation system. Especially for blue-white passivation systems, simply thickening the film layer cannot compensate for the corrosion resistance deficiency: an excessively thick film layer can easily result in a hazy, dark, or yellowish appearance, and even the loss of the decorative characteristics that the blue-white passivation film should possess.

[0021] This invention provides a trivalent chromium blue-white passivating agent and its passivation process, using trivalent chromium salt as the main film-forming component and regulating Cr through a carboxylic acid complexing agent. 3The release and hydrolysis deposition rate, combined with fluoride activators and nitrates, gently activate the surface of zinc or zinc alloys to promote trace dissolution and interfacial film formation on the metal surface; at the same time, acidic silica sol is introduced to form a transparent silicon-rich closed structure in the micropores and surface of the film layer, and zirconium salts and rare earth salts replace cobalt salts in the composite film formation, so that the passivation film forms a composite inorganic structure containing Cr, Zn, Si, Zr and rare earth elements, thereby improving the film density and corrosion resistance without relying on cobalt salts.

[0022] Specifically, the present invention provides a trivalent chromium blue-white passivating agent, comprising: trivalent chromium salt: 3.0-4.0 g / L, carboxylic acid complexing agent: 5.0-10.0 g / L, fluoride activator: 0.35-0.65 g / L, nitrate: 1.5-2.5 g / L, organic acid regulator: 0.3-1.0 g / L, acidic silica sol: 1.0-2.0 g / L, zirconium salt: 0.10-0.20 g / L, rare earth salt: 0.02-0.05 g / L, nonionic wetting agent: 0.02-0.1 g / L, deionized water, and the balance; wherein the pH of the trivalent chromium blue-white passivating agent is 2.0-2.2.

[0023] Preferably, in the trivalent chromium blue-white passivating agent of the present invention, the trivalent chromium salt is in the form of Cr 3 The content of ⁺ is 3.0-4.0 g / L, and the Cr content is 4.0-4.0 g / L. 3 ⁺ is the main film-forming ion of the blue-white passivation film. During the passivation process, the zinc or zinc alloy surface undergoes trace dissolution in the acidic passivating agent, resulting in the formation of Zn at the interface. 2 ⁺ and accompanied by local acidity changes, Cr 3 ⁺ Under this interfacial environment, hydrolysis and deposition gradually occur, forming a conversion film mainly composed of hydrated chromium oxide, chromium hydroxide, and chromium-zinc composite oxides or hydroxides. If Cr 3 ⁺ If the concentration is too low, there are insufficient chromium-containing species available for deposition at the interface, resulting in poor continuity and corrosion resistance of the passivation film; if Cr 3 If the ⁺ concentration is too high, it can easily lead to excessively rapid hydrolysis, a rough film, a foggy appearance, or decreased stability of the bath solution. Adding Cr... 3 ⁺ Limiting the concentration within the above range is beneficial for forming a continuous chromium-containing conversion film while maintaining a blue-white transparent appearance. Trivalent chromium salts include at least one or a combination of chromium sulfate, chromium nitrate, chromium chloride, basic chromium sulfate, and chromium acetate. Chromium sulfate and basic chromium sulfate are stable in source and low in cost, making them suitable for forming relatively stable trivalent chromium complex systems. Chromium nitrate can simultaneously introduce nitrate ions, which is beneficial for assisting in the slight dissolution of the metal surface and the initiation of film formation. Chromium chloride has good solubility and is suitable for rapid preparation of working solutions. The acetate ions in chromium acetate have a certain buffering and weak complexing effect, which is beneficial for reducing the acidity fluctuation of the system. Those skilled in the art can select appropriate trivalent chromium salts according to the stability of the bath, the film formation speed, and the appearance requirements, without changing the role of trivalent chromium as the main film-forming component.

[0024] Preferably, the content of the carboxylic acid complexing agent is 5.0-10.0 g / L, used to regulate Cr. 3 ⁺ and the complexation state and release rate of some auxiliary metal ions. Cr 3 ⁺ It has a strong tendency to hydrolyze in acidic aqueous solutions. Without proper complexation control, chromium hydroxide precipitate can easily form prematurely in the bath solution, or deposit too quickly on the metal surface, resulting in a rough film and uneven color. Carboxylic acid complexing agents can react with Cr... 3 ⁺ Forms a stable but reactive complex state, allowing Cr to 3 ⁺ It maintains good stability in the bath and gradually releases and participates in film formation as the pH at the metal interface changes. The preferred carboxylic acid complexing agent is a combination of malonic acid and citric acid, with malonic acid being beneficial for controlling Cr. 3 The release of ⁺ at the interface, citric acid is beneficial to improve the stability of the bath solution and the compatibility with polyvalent metal ions; when the mass ratio of malonic acid to citric acid is (3-5):1, it can avoid the excessive hydrolysis of trivalent chromium and prevent the complexation from being too strong and inhibiting film formation.

[0025] Preferably, the fluoride activator is F - The content is calculated to be 0.35-0.65 g / L, F - It can mildly activate oxides, passive contamination layers, and localized inert regions on the surface of zinc or zinc alloys, enabling uniform, trace dissolution of the metal surface after entering the passivation stage, thus facilitating subsequent Cr... 3 ⁺ Hydrolysis deposition provides interfacial conditions, while simultaneously allowing Zn 2 ⁺ Participates in the formation of a zinc-containing conversion film. If F - If the content is too low, the surface activation is insufficient, which can easily lead to incomplete film formation or a lighter color in some areas; if F - Excessive content may cause over-etching of the zinc layer, resulting in a hazy, dark film or reduced corrosion resistance. Therefore, controlling the content of fluoride activator within the above range can maintain the activation process in a mild and controllable state, reducing damage to the blue-white appearance. Fluoride activators include at least one or a combination of sodium fluoride, ammonium fluoride, ammonium hydrofluoride, fluoroborate, and fluorozirconate. Sodium fluoride and ammonium fluoride can stably provide F⁻, facilitating the adjustment of activation intensity; ammonium hydrofluoride has strong surface activation ability, suitable for coatings where surface oxides are difficult to remove; fluoroborate and fluorozirconate can provide a milder fluorine source in the form of complexed fluorine, making the activation process more stable; fluorozirconate contains both fluorine and zirconium compounds, providing both the fluorine component required for activation and the zirconium component required for film formation.

[0026] Preferably, nitrate is in the form of NO3 - The content is estimated to be 1.5-2.5 g / L, NO3. -In acidic passivation systems, it can assist in the micro-dissolution of metal surfaces and interfacial redox processes, allowing the zinc surface to enter a more uniform film-forming state and promoting Cr... 3 ⁺ Transformation deposition occurs at the interface. Insufficient nitrate dosage results in slow film formation and inadequate film coverage; excessive dosage increases oxidizing properties and salt residue, easily leading to salt spots, white fog, or flow marks on the passivation film surface. Nitrates include at least one or a combination of sodium nitrate, potassium nitrate, ammonium nitrate, magnesium nitrate, and zinc nitrate. Sodium nitrate and potassium nitrate have good water solubility and formulation stability; ammonium nitrate can adjust the ionic environment and acidity buffering state of the system to a certain extent; magnesium nitrate can improve the ionic strength of the system and improve the uniformity of film deposition; zinc nitrate can pre-provide a small amount of Zn. 2 ⁺, which makes the formation of the Cr-Zn composite film at the interface more stable.

[0027] Preferably, the content of the organic acid regulator is 0.3-1.0 g / L. Since the blue-white passivation film is usually thin and sensitive to changes in acidity, excessively low acidity can lead to premature hydrolysis of metal ions in the bath, while excessively high acidity can cause continuous dissolution of the nascent film. By combining the organic acid regulator with a carboxylic acid complexing agent, the passivating agent can maintain a relatively stable film-forming rate within a pH range of 2.0-2.2, resulting in a more uniform blue-white appearance of the passivation film. The organic acid regulator includes at least one or a combination of formic acid, acetic acid, lactic acid, and glycolic acid. Formic acid has a small molecular weight and strong acidity, making it suitable for rapidly adjusting the acidity of the system; acetic acid has a milder acidity, which helps reduce the impact of acidity fluctuations on the blue-white appearance; lactic acid and glycolic acid contain hydroxyl structures, and in addition to adjusting acidity, they also have a certain weak complexing and wetting auxiliary effect.

[0028] Preferably, the acidic silica sol, calculated as SiO2, has a content of 1.0-2.0 g / L, and is preferably an acidic nano-silica sol with a particle size of 5-20 nm. This allows it to penetrate micropores, cracks, or low-coverage areas of the passivation film during formation, and subsequently form a transparent Si-O-Si network through Si-OH condensation during drying. This silicon-rich structure does not significantly obscure the silvery-white base color of the zinc plating layer, thus maintaining a bluish-white appearance, while reducing the possibility of water, oxygen, and chloride ions entering the metal surface through film defects. If the acidic silica sol content is too low, the sealing and reinforcing effects are insufficient; if the content is too high, the silica sol is prone to aggregate in the bath or form uneven deposition on the workpiece surface, causing fogging, whitening, or decreased film transparency.

[0029] Preferably, the zirconium salt, calculated as Zr, has a content of 0.10-0.20 g / L. Zirconium ions have a strong hydrolytic film-forming ability and can form hydrated oxides or hydroxides of zirconium during passivation, which can then undergo composite deposition with chromium- or zinc-containing hydrated films. The zirconium component can improve the degree of inorganic cross-linking and structural density of the film, compensating for the insufficient auxiliary film-forming ability in cobalt-free systems. The zirconium salt includes at least one or a combination of zirconium nitrate, zirconium oxychloride, zirconium sulfate, fluorozirconic acid, ammonium fluorozirconate, and potassium fluorozirconate. Zirconium nitrate, zirconium oxychloride, and zirconium sulfate can provide Zr as conventional zirconium sources. The zirconium in fluorozirconic acid and its ammonium and potassium salts exists in a fluorine complex state, exhibiting good stability in acidic systems and gradually participating in film formation during interfacial reactions.

[0030] Preferably, the rare earth salt, calculated as Ce and / or La, has a content of 0.02-0.05 g / L. Rare earth ions such as cerium and lanthanum are more prone to hydrolysis and deposition in areas with significant local pH changes on metal surfaces, forming localized reinforcing structures at weak points in the film. The addition of rare earth components is low, but it can improve the sealing properties at film defects, making the passivation film less prone to rapid failure from defects under corrosive media. If the rare earth salt content is too high, the film is prone to yellowing, fogging, or granular deposition; if the content is too low, the local repair and auxiliary sealing effects are not significant. The rare earth salt includes at least one or a combination of cerium nitrate, lanthanum nitrate, cerium ammonium nitrate, cerium chloride, and lanthanum chloride. A combination of cerium nitrate and lanthanum nitrate is preferred, with a mass ratio of cerium to lanthanum of (3-8):1. Cerium mainly plays a role in defect reinforcement, while lanthanum assists in improving deposition uniformity and appearance stability, thus enabling the rare earth components to exert a stable sealing and reinforcing effect even at low addition levels.

[0031] Preferably, the content of the nonionic wetting agent is 0.02-0.1 g / L, used to improve the spreadability and wetting uniformity of the passivating agent on the metal surface. Zinc-plated parts, zinc alloy parts, or zinc-nickel alloy parts often have edges, holes, threads, and localized rough areas. If the passivating agent does not wet sufficiently, air bubbles, localized film leakage, or color differences can easily occur. The nonionic wetting agent can reduce the surface tension of the liquid, allowing the passivating agent to contact the surface being treated more evenly, thereby improving the consistency of the film coverage. Its content should not be too high, otherwise organic residues may be generated in the film, affecting the appearance and corrosion resistance after drying. Controlling the nonionic wetting agent within a low range can improve spreadability while reducing interference from organic components on the formation of the inorganic passivation film. The nonionic wetting agent is selected from at least one or a combination of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyether-modified siloxane wetting agent, and acetylenic diol wetting agent. Fatty alcohol polyoxyethylene ether has good wetting and low foaming properties, making it suitable for conventional impregnation and passivation systems. Alkylphenol polyoxyethylene ether has strong wetting ability, but its use can be selected according to environmental protection requirements. Polyether-modified siloxane wetting agent can significantly reduce surface tension and improve the spreading properties at corners, holes, and threads. Acetylene diol wetting agent has good dynamic wetting properties, which is beneficial for quickly removing bubbles and forming a uniform liquid film during short-time passivation.

[0032] Preferably, when the pH of the trivalent chromium blue-white passivating agent is too low, the zinc surface dissolves too strongly, and the initial passivation film is easily dissolved by the acidic system, resulting in a thinner film, fogging, or a darker appearance; when the pH is too high, Cr... 3 ⁺、Zr 4 ⁺ and rare earth ions are prone to premature hydrolysis in the bath solution, leading to precipitation, bath solution turbidity, or rough film. When the pH of the trivalent chromium blue-white passivating agent is 2.0-2.2, the passivation solution remains stable in the bath solution, while local pH changes at the metal interface can trigger the film-forming reaction, thereby forming a relatively uniform blue-white composite passivation film.

[0033] Furthermore, the preparation method of the trivalent chromium blue-white passivating agent is as follows: First, add some deionized water to the preparation container, then add the trivalent chromium salt under stirring to completely dissolve it. Next, add the carboxylic acid complexing agent and stir at 55-70℃ for 60-120 minutes to allow the chromium to passivate. 3The trivalent chromium complex solution was obtained by fully complexing the zirconium salt with a carboxylic acid complexing agent. The system was then cooled to below 35°C, and a fluoride activator, nitrate, and organic acid regulator were added to ensure uniform dispersion of the activating and acidity-regulating components. Zirconium and rare earth salts were pre-dissolved in a small amount of deionized water and added slowly. If necessary, a small amount of carboxylic acid complexing agent could be added to assist stabilization and prevent premature hydrolysis of zirconium or rare earth ions due to excessively high local concentrations. Acidic silica sol was then slowly added at 20-30°C, with stirring maintained during the addition process to prevent aggregation of the silica sol due to sudden changes in local salt concentration. Finally, a nonionic wetting agent was added, and the volume was brought up to the target volume with deionized water. The pH was adjusted to 2.0-2.2, and after filtration and settling, the trivalent chromium blue-white passivating agent was obtained.

[0034] This invention also provides a passivation process for a trivalent chromium blue-white passivating agent, using any one of the trivalent chromium blue-white passivating agents described in the above technical solutions, comprising the following steps: S100. After washing the metal workpiece to be treated with water, it is placed in a slightly acidic preconditioning solution for preconditioning treatment to obtain the pretreated workpiece. S200: The pretreated workpiece is passivated using trivalent chromium blue-white passivating agent to obtain a wet film passivated workpiece. S300: The wet film passivated workpiece is subjected to light washing, liquid control and curing treatment in sequence to obtain the passivated metal workpiece.

[0035] Preferably, in step S100, the surface of the workpiece to be treated often contains residual electroplating solution, cleaning solution, salts, floating dust, and other soluble impurities. If these residues directly enter the passivation solution, they will change the local pH and ionic composition of the passivation solution and may form local contamination points on the workpiece surface, causing Cr... 3 ⁺ Uneven hydrolysis deposition. Water washing cleans the workpiece surface, reducing interference from residual impurities on the passivating agent's film-forming reaction and allowing the passivation film to grow from a more uniform surface. Zinc plating, zinc alloy plating, or other non-ferrous metal surfaces often contain slight oxides, alkaline residues, localized water spots, differences in edge activity, and coating roughness. If directly subjected to acidic trivalent chromium blue-white passivating agent, highly active areas tend to dissolve and deposit preferentially, forming thicker or rougher films, while low-activity areas may experience insufficient film formation. Pre-conditioning the washed metal workpiece in a slightly acidic pre-conditioning solution removes slight oxides and alkaline residues with a milder acidity, making the surface reactivity of edges, planes, holes, and locally rough areas more similar. This reduces the risk of localized over-corrosion, fogging, darkening, and uneven coloring during subsequent passivation. After preconditioning, minor oxides and contaminant residues on the metal surface are gradually removed, and the passivating agent can contact the surface to be treated more evenly, giving the film-forming components a more consistent reaction starting point on the metal surface.

[0036] Furthermore, the slightly acidic preconditioning solution comprises: citric acid: 0.5-2.0 g / L, malonic acid: 0.3-1.5 g / L, sodium nitrate: 0.2-1.0 g / L, and deionized water: balance. The combination of citric acid and malonic acid in the preconditioning solution provides a mild complexing, dissolving, and buffering effect on oxides and localized alkaline residues on the metal surface. Citric acid has a strong complexing ability, helping to remove trace amounts of metal oxides or alkaline residues from the coating surface and reducing the interference of surface contaminants on subsequent film formation. Malonic acid has a relatively moderate complexing effect, assisting in regulating the dissolution process of surface metal ions, preventing the preconditioning effect from becoming excessive. The addition of sodium nitrate to the preconditioning solution provides a small amount of nitrate ions, making the micro-dissolution and surface activation of the metal surface more uniform. By combining low-concentration sodium nitrate with citric acid and malonic acid, the reactivity of corners, holes, threads, and locally rough areas can be moderated and regulated, reducing the possibility of preferential over-reaction in these areas during subsequent passivation.

[0037] Preferably, the pH of the slightly acidic preconditioning solution is 3.0-4.5, which allows for gentle cleaning and surface homogenization during preconditioning, facilitating the formation of a uniform, fine, and transparent blue-white passivation film. The preconditioning treatment time is 5-20 seconds, which allows for surface homogenization without significant damage to the coating, providing more consistent interface conditions for the subsequent first passivation.

[0038] Preferably, in step S200, the pretreated metal surface undergoes controlled micro-dissolution in an acidic passivating agent, particularly the release of Zn from the zinc or zinc alloy surface. 2 ⁺, at the same time, the acidity and ion concentration near the interface change, causing Cr 3 ⁺ Gradually hydrolyzes and deposits chromium oxide, chromium hydroxide, and chromium-zinc composite oxide / hydroxide. This process transforms the metal surface from an active state to a passivated state covered by a chromium-containing composite film, thereby reducing the direct contact between the corrosive medium and the metal substrate.

[0039] Specifically, S200 includes: S210. The pretreated workpiece is placed in a trivalent chromium blue-white passivating agent for the first passivation treatment to obtain the first intermediate workpiece. S220. The first intermediate workpiece is removed from the trivalent chromium blue-white passivating agent and subjected to liquid separation treatment to obtain the second intermediate workpiece. S230. The second intermediate workpiece is placed in a trivalent chromium blue-white passivating agent for a second passivation treatment to obtain a wet film passivated workpiece.

[0040] Preferably, in step S210, the pretreated workpiece is placed in a trivalent chromium blue-white passivating agent for a first passivation treatment, mainly to initiate the conversion reaction on the metal surface. After micro-acid preconditioning, the metal surface has relatively uniform activity. Upon entering the passivating agent, controlled micro-dissolution occurs on the metal surface, especially the zinc or zinc alloy surface, releasing Zn. 2+ Simultaneously, changes in pH and ion concentration near the interface cause Cr to... 3 ⁺ Initial hydrolysis and deposition occur, forming an initial Cr-Zn hydration conversion film. Although this initial film is not yet fully dense, it can cover the main active areas of the metal surface, providing a basis for subsequent liquid-free reactions and a second film coating. The first passivation treatment takes 12-20 seconds, which allows for the formation of a uniform basic conversion film while reducing the continuous corrosion of the metal surface by the acidic system.

[0041] Preferably, in step S220, the first intermediate workpiece is removed from the trivalent chromium blue-white passivating agent and left in the air for 15-30 seconds for liquid removal treatment. After the workpiece leaves the passivating solution, a thin wet film of passivating solution remains on its surface, and this wet film contains Cr. 3 ⁺ complex, Zn 2+ The process involves acidic silica sol, zirconium ions, rare earth ions, and a small amount of activating components. At this stage, the workpiece is no longer continuously immersed in a large amount of acidic passivation solution. The continuous dissolution and scouring of the nascent film are significantly reduced, while the film-forming components in the thin liquid film on the surface can continue to undergo hydrolysis, deposition, and condensation reactions on the metal surface and in the micropores of the nascent film, allowing the initial hydrated film to continue homogenizing in a milder thin liquid film environment. Furthermore, during the first passivation treatment, the nascent film forms quickly in highly active areas, while areas with low activity may still have thin or insufficiently covered film layers. During the liquid removal process, metal ions and film-forming components in the thin liquid film on the surface continue to diffuse and react in localized areas, further enriching the Cr-Zn hydrated film, silicon-rich components, and zirconium / rare earth hydrolysis products in micropores and defects. Because there is no continuous replenishment of acidic activating components with fresh passivation solution at this stage, the film formation process is more focused on the continued transformation and local reinforcement of the nascent film, rather than continued intense etching of the metal surface.

[0042] Preferably, after the first passivation and liquid removal treatment, the workpiece surface already has an initial Cr-Zn composite conversion film. In step S230, the second intermediate workpiece is placed again in a trivalent chromium blue-white passivating agent for a second passivation treatment. At this time, the metal surface is not completely exposed, and the passivation reaction no longer exhibits a large-area restart, but rather tends to continue to replenish the film in thin film areas, microporous areas, and locally uncovered areas. The second passivation treatment lasts for 8-15 seconds, which can replenish the continuity and uniformity of the film layer, while preventing the already formed nascent film from being continuously dissolved by the acidic passivating agent, thus avoiding fogging or darkening.

[0043] Preferably, the newly formed trivalent chromium blue-white passivation film on the surface of the wet passivated workpiece after passivation treatment is not yet fully cured, and its surface still contains residual passivation solution, free acid, fluoride ions, nitrates, incompletely reacted chromium complexes, and incompletely condensed silica sol. In step S300, since the trivalent chromium blue-white passivation film is relatively thin and the film strength in the initial stage is limited, a low-flow-rate, low-impact light washing treatment can gradually reduce the concentration of residual ions on the surface, reduce the continued etching of the film by residual fluoride ions and acidic components, and avoid local damage to the film caused by strong spraying. After the light washing treatment, the free matter on the film surface is reduced, and it is less likely to form salt spots, white fog, or flow marks during subsequent drying, resulting in a more uniform film appearance. The light washing treatment includes a first-stage light washing treatment and a second-stage light washing treatment. The first-stage cleaning treatment uses the concentration difference in a low-disturbance water environment to reduce the residual H on the surface. + F - NO3 - As unbound metal complexes gradually diffuse into the aqueous phase, the first-stage light wash uses deionized water with a conductivity of <100μS / cm, which effectively reduces the residual ion concentration without causing drastic changes in ionic strength to the nascent hydrated film due to excessively pure water. The residence time is 15-30s, which allows the residual passivation solution to be fully replaced without prolonged soaking, which could lead to over-hydration of the film or loss of some soluble components. The second-stage light wash further reduces the residual ion content on the workpiece surface, making it less prone to salt concentration, white spots, and flow marks during subsequent drying. The second-stage light wash uses deionized water with a conductivity of <20μS / cm, with a residence time of 10-20s, which can complete surface cleaning while avoiding excessive washing that could remove too much of the unstable hydrated components in the film.

[0044] Preferably, a liquid control treatment is performed after the light washing process to reduce localized liquid accumulation on the workpiece surface, especially in holes, threads, corners, grooves, and overlapping areas. If the workpiece carries too much liquid or the local liquid film thickness is uneven, the different evaporation rates of water and the different migration paths of salts during the drying process can easily cause localized concentration, color differences, flow marks, or uneven film thickness. By using low-pressure air knives, centrifugal drying, tilted dripping, or slow-speed rotation for liquid drainage, residual water can be discharged evenly, reducing the impact of excessively thick localized liquid films on the blue-white appearance and film density; the air pressure of the low-pressure air knife is preferably 0.02-0.15 MPa.

[0045] Furthermore, the curing process can further dehydrate, condense, and densify the wet or hydrated passivation film. The Cr-Zn hydrated conversion film formed after passivation gradually loses some of its bound water during heating, and hydrated chromium oxide, chromium hydroxide, zinc oxide / hydroxides, as well as zirconium and rare earth hydrolysis deposits, gradually form a more stable composite inorganic film layer. The Si-OH groups in the acidic silica sol undergo condensation under drying conditions to form a transparent Si-O-Si network, further sealing the micropores of the film layer. The curing process begins with pre-drying at 50-60℃ for 1-3 minutes, which gently removes surface free water and allows the film to gradually transition from a wet state to a semi-dry state, reducing the disturbance to the nascent film structure caused by sudden temperature increases. Then, drying at 75-90℃ for 8-15 minutes further promotes the dehydration and densification of the hydrated chromium-zinc conversion film, and causes the Si-OH in the acidic silica sol to condense and form a Si-O-Si network. At the same time, the zirconium and rare earth hydrolysis deposits further combine with the chromium- and zinc-containing film layers, making the composite passivation film structure more stable.

[0046] Example 1

[0047] This embodiment provides a trivalent chromium blue-white passivating agent, comprising: chromium sulfate in Cr 3 ⁺ Total: 3.0 g / L, Carboxylic acid complexing agent: 5.0 g / L, Sodium fluoride as F - Calculated as: 0.35 g / L, ammonium nitrate as NO3 - Total: 1.5 g / L, formic acid: 0.3 g / L, acidic nano-silica sol with a particle size of 5 nm (as SiO2): 1.0 g / L, zirconium nitrate (as Zr): 0.10 g / L, cerium nitrate and lanthanum nitrate (as Ce and La): 0.02 g / L, fatty alcohol polyoxyethylene ether: 0.02 g / L, deionized water, balance; wherein, the carboxylic acid complexing agent includes malonic acid and citric acid in a mass ratio of 3:1; the mass ratio of cerium nitrate and lanthanum nitrate is 3:1; the pH of the trivalent chromium blue-white passivating agent is 2.2.

[0048] Example 2

[0049] This embodiment provides a trivalent chromium blue-white passivating agent, comprising: chromium nitrate in the form of Cr 3 ⁺ Total: 4.0 g / L, Carboxylic acid complexing agent: 10.0 g / L, Ammonium fluoride as F - Calculated: 0.65 g / L, potassium nitrate as NO3 -Total: 2.5 g / L, lactic acid: 1.0 g / L, acidic nano-silica sol with a particle size of 20 nm (SiO2): 2.0 g / L, zirconium sulfate (Zr): 0.20 g / L, cerium nitrate and lanthanum nitrate (Ce and La): 0.05 g / L, alkylphenol polyoxyethylene ether: 0.1 g / L, deionized water, balance; wherein, the carboxylic acid complexing agent includes malonic acid and citric acid in a mass ratio of 5:1; the mass ratio of cerium nitrate and lanthanum nitrate is 8:1; the pH of the trivalent chromium blue-white passivating agent is 2.0.

[0050] Example 3

[0051] This embodiment provides a trivalent chromium blue-white passivating agent, comprising: basic chromium sulfate in Cr 3 ⁺ Total: 3.5 g / L, Carboxylic acid complexing agent: 8.0 g / L, Ammonium fluoride as F - Calculated: 0.55 g / L, potassium nitrate as NO3 - Total: 2.0 g / L, acetic acid: 0.8 g / L, acidic nano-silica sol with a particle size of 10 nm (SiO2): 1.5 g / L, zirconium oxychloride (Zr): 0.15 g / L, cerium nitrate and lanthanum nitrate (Ce and La): 0.03 g / L, polyether-modified siloxane wetting agent: 0.08 g / L, deionized water, balance; wherein, the carboxylic acid complexing agent includes malonic acid and citric acid in a mass ratio of 4:1; the mass ratio of cerium nitrate and lanthanum nitrate is 5:1; the pH of the trivalent chromium blue-white passivating agent is 2.1.

[0052] Example 4

[0053] This embodiment provides a trivalent chromium blue-white passivating agent, comprising: chromium acetate in the form of Cr 3 ⁺ total: 3.6 g / L, carboxylic acid complexing agent: 8.0 g / L, sodium fluoride as F - Calculated as: 0.55 g / L, sodium nitrate as NO3 - Total: 2.0 g / L, acetic acid: 0.8 g / L, acidic nano-silica sol with a particle size of 10 nm (as SiO2): 1.5 g / L, zirconium nitrate (as Zr): 0.10 g / L, cerium nitrate and lanthanum nitrate (as Ce and La): 0.03 g / L, acetylenide diol wetting agent: 0.08 g / L, deionized water, balance; wherein, the carboxylic acid complexing agent includes malonic acid and citric acid in a mass ratio of 4:1; the mass ratio of cerium nitrate and lanthanum nitrate is 6:1; the pH of the trivalent chromium blue-white passivating agent is 2.1.

[0054] The appearance of the trivalent chromium blue-white passivating agents in Examples 1-4 was observed, the pH was measured, and after being sealed and placed at 25°C for 30 days, it was observed whether obvious precipitation, flocculation, stratification or gelation occurred. The results are shown in Table 1.

[0055] Table 1

[0056] As shown in Table 1, the trivalent chromium blue-white passivating agents obtained in Examples 1-4 were all uniform, transparent or nearly transparent aqueous working solutions with a stable pH range of 2.0-2.2. No obvious precipitation, stratification, or gelation occurred after 30 days of storage, indicating that the carboxylic acid complex system can stabilize Cr. 3 The acidic silica sol can maintain good dispersion stability in the system containing ⁺, Zr and rare earth components.

[0057] Example 5

[0058] This embodiment provides a passivation process using a trivalent chromium blue-white passivating agent, employing the trivalent chromium blue-white passivating agent from Example 1, and includes the following steps: S100. After washing the metal workpiece with water, place it in a slightly acidic preconditioning solution with a pH of 3.0 for 5 seconds to obtain the pretreated workpiece. S200: The pretreated workpiece is passivated using trivalent chromium blue-white passivating agent to obtain a wet film passivated workpiece. S300. The wet film passivated workpiece is subjected to a first-stage light wash with deionized water with a conductivity of <100μS / cm for 15s, followed by a second-stage light wash with deionized water with a conductivity of <20μS / cm for 10s. Then, a low-pressure air knife is used for liquid control treatment. Finally, it is pre-dried at 50℃ for 1min and then dried at 75℃ for 8min to obtain the passivated metal workpiece. The slightly acidic preconditioning solution includes: citric acid: 0.5 g / L, malonic acid: 0.3 g / L, sodium nitrate: 0.2 g / L, and deionized water: balance. S200 includes: S210. Place the pretreated workpiece in a trivalent chromium blue-white passivating agent for the first passivation treatment for 12 seconds to obtain the first intermediate workpiece. S220. Remove the first intermediate workpiece from the trivalent chromium blue-white passivating agent and leave it in the air for 15 seconds to obtain the second intermediate workpiece. S230. Place the second intermediate workpiece in a trivalent chromium blue-white passivating agent for a second passivation treatment for 8 seconds to obtain a wet film passivated workpiece.

[0059] Example 6

[0060] This embodiment provides a passivation process using a trivalent chromium blue-white passivating agent, employing the trivalent chromium blue-white passivating agent from Example 2, and includes the following steps: S100. After washing the metal workpiece with water, place it in a slightly acidic preconditioning solution with a pH of 4.5 for 20 seconds to obtain the pretreated workpiece. S200: The pretreated workpiece is passivated using trivalent chromium blue-white passivating agent to obtain a wet film passivated workpiece. S300. The wet film passivated workpiece is subjected to a first-stage light wash with deionized water with a conductivity of <100μS / cm for 30s, followed by a second-stage light wash with deionized water with a conductivity of <20μS / cm for 20s. Then, a low-pressure air knife is used for liquid control treatment. Finally, it is pre-dried at 60℃ for 3min and then dried at 90℃ for 15min to obtain the passivated metal workpiece. The slightly acidic preconditioning solution includes: citric acid: 2.0 g / L, malonic acid: 1.5 g / L, sodium nitrate: 1.0 g / L, and deionized water: balance. S200 includes: S210. Place the pretreated workpiece in a trivalent chromium blue-white passivating agent for a first passivation treatment of 20s to obtain the first intermediate workpiece. S220. Remove the first intermediate workpiece from the trivalent chromium blue-white passivating agent and leave it in the air for 30 seconds to obtain the second intermediate workpiece. S230. Place the second intermediate workpiece in a trivalent chromium blue-white passivating agent for a second passivation treatment for 15 seconds to obtain a wet film passivated workpiece.

[0061] Example 7

[0062] This embodiment provides a passivation process using a trivalent chromium blue-white passivating agent, employing the trivalent chromium blue-white passivating agent from Example 3, and includes the following steps: S100. After washing the metal workpiece with water, place it in a slightly acidic preconditioning solution with a pH of 4.0 for 10 seconds to obtain the pretreated workpiece. S200: The pretreated workpiece is passivated using trivalent chromium blue-white passivating agent to obtain a wet film passivated workpiece. S300. The wet film passivated workpiece is subjected to a first-stage light wash with deionized water with a conductivity of <100μS / cm for 20s, followed by a second-stage light wash with deionized water with a conductivity of <20μS / cm for 15s, then controlled liquid treatment with a low-pressure air knife, and finally pre-drying at 55℃ for 2min, and then drying at 80℃ for 10min to obtain the passivated metal workpiece. The slightly acidic preconditioning solution includes: citric acid: 1.0 g / L, malonic acid: 1.0 g / L, sodium nitrate: 0.8 g / L, and deionized water: balance. S200 includes: S210. Place the pretreated workpiece in a trivalent chromium blue-white passivating agent for the first passivation treatment for 15 seconds to obtain the first intermediate workpiece. S220. Remove the first intermediate workpiece from the trivalent chromium blue-white passivating agent and leave it in the air for 20 seconds to obtain the second intermediate workpiece. S230. Place the second intermediate workpiece in a trivalent chromium blue-white passivating agent for a second passivation treatment for 10 seconds to obtain a wet film passivated workpiece.

[0063] Example 8

[0064] This embodiment provides a passivation process using a trivalent chromium blue-white passivating agent, employing the trivalent chromium blue-white passivating agent from Example 4, and includes the following steps: S100. After washing the metal workpiece with water, place it in a slightly acidic preconditioning solution with a pH of 4.0 for 10 seconds to obtain the pretreated workpiece. S200: The pretreated workpiece is passivated using trivalent chromium blue-white passivating agent to obtain a wet film passivated workpiece. S300. The wet film passivated workpiece is subjected to a first-stage light wash with deionized water with a conductivity of <100μS / cm for 20s, followed by a second-stage light wash with deionized water with a conductivity of <20μS / cm for 15s, then controlled liquid treatment with a low-pressure air knife, and finally pre-drying at 55℃ for 2min, and then drying at 80℃ for 10min to obtain the passivated metal workpiece. The slightly acidic preconditioning solution includes: citric acid: 1.0 g / L, malonic acid: 1.0 g / L, sodium nitrate: 0.8 g / L, and deionized water: balance. S200 includes: S210. Place the pretreated workpiece in a trivalent chromium blue-white passivating agent for the first passivation treatment for 15 seconds to obtain the first intermediate workpiece. S220. Remove the first intermediate workpiece from the trivalent chromium blue-white passivating agent and leave it in the air for 20 seconds to obtain the second intermediate workpiece. S230. Place the second intermediate workpiece in a trivalent chromium blue-white passivating agent for a second passivation treatment for 10 seconds to obtain a wet film passivated workpiece.

[0065] Comparative Example 1 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The steps are the same as in Example 5, except that the trivalent chromium blue-white passivating agent used is a traditional cobalt-containing trivalent chromium blue-white passivating agent.

[0066] Comparative Example 2 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The steps are the same as in Example 5, except that the trivalent chromium blue-white passivating agent used is basically the same as that in Example 1, but does not contain acidic silica sol, zirconium salt, or rare earth salt.

[0067] Comparative Example 3 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The steps are the same as in Example 5, except that the trivalent chromium blue-white passivating agent used is basically the same as that in Example 1, but does not contain zirconium salts and rare earth salts.

[0068] Comparative Example 4 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The trivalent chromium blue-white passivating agent in Example 1 is used. The passivation process steps are the same as those in Example 5. The difference is that the trivalent chromium blue-white passivating agent used is basically the same as that in Example 1, but does not contain acidic silica sol.

[0069] Comparative Example 5 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The trivalent chromium blue-white passivating agent in Example 1 is used. The difference between the passivation process and that in Example 5 is that the preconditioning treatment in step S100 is not performed in the slightly acidic preconditioning solution, the passivation treatment in step S200 is performed only once for 25 seconds, and the conventional spray washing and drying treatment is performed in step S300.

[0070] Comparative Example 6 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent, using the trivalent chromium blue-white passivating agent in Example 1. The difference between the passivation process and Example 5 is that step S100 is performed in a slightly acidic preconditioning solution for preconditioning treatment, while the remaining steps are the same as in Example 5.

[0071] Comparative Example 7 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent, using the trivalent chromium blue-white passivating agent in Example 1. The difference between the passivation process and Example 5 is that step S220 is omitted.

[0072] Comparative Example 8 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent, using the trivalent chromium blue-white passivating agent in Example 1. The difference between the passivation process and Example 5 is that conventional spray washing treatment is used in step S300.

[0073] Comparative Example 9 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent, using the trivalent chromium blue-white passivating agent in Example 1. The difference between the passivation process and Example 5 is that the curing treatment in step S300 is directly dried at 85°C for 10 minutes.

[0074] Electro-galvanized steel sheets with dimensions of 50mm×100mm×1mm and a zinc coating thickness of 10μm were used as the substrate. All samples underwent the same degreasing, water washing and surface cleaning treatment before passivation, and were passivated using the passivation methods in Examples 5-8 and Comparative Examples 1-9, respectively.

[0075] The passivation film was visually evaluated for the presence of haze, darkening, yellow spots, white spots, flow marks, and local color difference. Color difference was tested using a colorimeter, and the appearance was scored (1-5 points, where 5 points indicates uniform blue-white color, brightness, and no obvious defects; 1 point indicates obvious haze, darkening, yellowing, or local film discontinuity). The results are shown in Table 2.

[0076] Table 2

[0077] As shown in Table 2, the passivation films obtained in Examples 5-8 all exhibit a light blue-white or blue-white appearance with good overall uniformity and an appearance grade of 4 or higher. Examples 7-8 show a uniform and bright blue-white appearance, indicating that the formulation and process of this invention can balance film transparency, deposition uniformity, and blue-white appearance stability. Comparative Example 1, while achieving a relatively uniform blue-white appearance, has a slightly darker color, demonstrating that this invention can still achieve an appearance no less than that of traditional cobalt-containing systems without using cobalt salts. Comparative Example 2 has a lighter color and localized whitening, indicating insufficient film formation with a simple cobalt-free trivalent chromium system. Comparative Examples 3-4 have poor appearances, indicating that zirconium salts, rare earth salts, and acidic silica sols all affect the film appearance. Comparative Examples 5-9 exhibit haze, color difference, watermarks, or flow marks, respectively, indicating that the passivation process of this invention helps improve the uniformity of the passivation film appearance and the stability of its blue-white appearance.

[0078] The neutral salt spray test was used for evaluation. The time of the first appearance of white rust and the proportion of white rust area after 96h, 120h and 168h were recorded. The results are shown in Table 3.

[0079] Table 3

[0080] As can be seen from Table 3, the salt spray resistance of Examples 5-8 is better than that of Comparative Examples 1-9. The first white rust time of Comparative Example 2 is only 48 hours, indicating that the corrosion resistance of the cobalt-free trivalent chromium blue-white film is significantly insufficient without the addition of acidic silica sol, zirconium salt, and rare earth salt. The salt spray resistance of Comparative Examples 3 and 4 is significantly lower than that of Example 7, indicating that zirconium salt, rare earth salt, and acidic silica sol all contribute to the white rust resistance. Although Comparative Examples 5-9 use the passivating agent of Example 1, their corrosion resistance is low due to the change in process steps, indicating that the passivation process of the present invention can further improve the integrity and corrosion resistance stability of the film.

[0081] The surface of the passivated film was observed and rated (1-5, where 5 indicates a continuous film with few cracks and pores, and 1 indicates a discontinuous film with many pores or cracks). The results are shown in Table 4.

[0082] Table 4

[0083] As can be seen from Table 4, the film integrity levels of Examples 5-8 are all relatively good, especially those of Examples 7-8. Although Comparative Example 1 has a certain degree of film integrity, it is still lower than that of Examples 7-8. The film integrity level of Comparative Example 2 is only level 2, indicating that the film continuity of the simple cobalt-free trivalent chromium system is insufficient. The integrity levels of Comparative Examples 3-4 are all level 3, indicating that the micropores and defects of the film are difficult to be fully improved when zirconium salt, rare earth salt and acidic silica sol are lacking. The film integrity of Comparative Examples 5-9 is lower than that of Example 5, indicating that a single soaking, omitting the micro-acid preconditioning, omitting the liquid separation treatment, strong water washing or direct drying will affect the continuity and density of the nascent film.

[0084] After passivation, the sample was soaked in deionized water for 10 minutes, then removed and dried. The appearance changes were observed and the ΔE change value was recorded. The results are shown in Table 5.

[0085] Table 5

[0086] As can be seen from Table 5, the appearance of Examples 5-8 remained basically unchanged after being soaked in deionized water for 10 minutes, indicating that the passivation film obtained by the present invention has good water wash resistance stability. The ΔE change values ​​of Comparative Examples 2-4 increased significantly, indicating that the stability of the film structure decreased when one or more of acidic silica sol, zirconium salt and rare earth salt were lacking. Comparative Examples 5-9 all showed varying degrees of fogging, color difference, shallow film expansion or white fog aggravation after soaking, indicating that the passivation process of the present invention helps to protect the nascent film and improve the appearance retention ability of the passivation film.

[0087] Comparative Example 10 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The steps are the same as in Example 5, except that the trivalent chromium blue-white passivating agent used is basically the same as that in Example 1, but does not contain zirconium salt.

[0088] Comparative Example 11 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The steps are the same as in Example 5, except that the trivalent chromium blue-white passivating agent used is basically the same as that in Example 1, but does not contain rare earth salts.

[0089] Comparative Example 12 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The steps are the same as in Example 5, except that the trivalent chromium blue-white passivating agent used is basically the same as that in Example 1, but only cerium nitrate is used as the rare earth salt.

[0090] Comparative Example 13 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The steps are the same as in Example 5, except that the trivalent chromium blue-white passivating agent used is basically the same as that in Example 1, but only lanthanum nitrate is used as the rare earth salt.

[0091] Comparative Example 14 This comparative example provides a passivation process for a trivalent chromium blue-white passivating agent. The steps are the same as in Example 5, except that the trivalent chromium blue-white passivating agent used is basically the same as that in Example 1, but the mass ratio of cerium nitrate to lanthanum nitrate in the rare earth salt is 12:1.

[0092] After passivation using the passivation process in Comparative Examples 10-14, tests were conducted, and the results are shown in Table 6.

[0093] Table 6

[0094] As shown in Table 6, compared with Comparative Examples 5-8, the white rust area of ​​Comparative Example 10 increased to 8% after 120 hours, and the film integrity level dropped to level 3, indicating that zirconium salt helps to improve the density and integrity of the film. The white rust area of ​​Comparative Example 11 was 6% after 120 hours, and the change value of ΔE before and after immersion increased to 1.1, indicating that rare earth salt helps to reinforce film defects and improve water washability. The corrosion resistance of Comparative Example 12 was improved compared with Comparative Example 11, but the appearance showed slight darkening and yellowing, indicating that Ce salt has a strong defect reinforcement effect, but its use alone can easily affect the blue-white appearance. The appearance of Comparative Example 13 was relatively light, but the white rust area was 5% after 120 hours, indicating that La salt deposition was milder and conducive to appearance stability, but the improvement in corrosion resistance was not as obvious as that of Ce salt. The appearance of Comparative Example 14 showed slight haziness, and the change value of ΔE before and after immersion increased, indicating that an excessively high Ce ratio is not conducive to the stability of the blue-white appearance.

[0095] In summary, zirconium salts primarily improve film density, while rare earth salts mainly reinforce film defects; Ce is more beneficial for improving corrosion resistance, and La is more beneficial for uniform appearance. When Ce and La are compounded in a ratio of (3-8):1, they can improve corrosion resistance and film stability while maintaining a blue-white appearance, indicating a synergistic effect between acidic silica sol, zirconium salts, and the Ce / La compounded rare earth salts. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of this invention; therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. A trivalent chromium blue-white passivating agent, characterized in that, The mixture comprises: trivalent chromium salt: 3.0-4.0 g / L, carboxylic acid complexing agent: 5.0-10.0 g / L, fluoride activator: 0.35-0.65 g / L, nitrate: 1.5-2.5 g / L, organic acid regulator: 0.3-1.0 g / L, acidic silica sol: 1.0-2.0 g / L, zirconium salt: 0.10-0.20 g / L, rare earth salt: 0.02-0.05 g / L, nonionic wetting agent: 0.02-0.1 g / L, deionized water, and the balance; wherein the pH of the trivalent chromium blue-white passivating agent is 2.0-2.

2.

2. The trivalent chromium blue-white passivating agent according to claim 1, characterized in that, The trivalent chromium salt includes at least one or a combination of chromium sulfate, chromium nitrate, chromium chloride, basic chromium sulfate, and chromium acetate; and / or The carboxylic acid complexing agent includes malonic acid and citric acid; and / or The fluoride activator includes at least one or a combination of sodium fluoride, ammonium fluoride, ammonium hydrofluoride, fluoroborate, and fluorozirconate; and / or The nitrate includes at least one or a combination of sodium nitrate, potassium nitrate, ammonium nitrate, magnesium nitrate, and zinc nitrate; and / or The organic acid regulator includes at least one or a combination of formic acid, acetic acid, lactic acid, and glycolic acid; and / or The acidic silica sol includes acidic nano-silica sol; and / or The zirconium salt includes at least one or a combination of zirconium nitrate, zirconium oxychloride, zirconium sulfate, fluorozirconic acid, ammonium fluorozirconate, and potassium fluorozirconate; and / or The rare earth salt includes at least one or a combination of cerium nitrate, lanthanum nitrate, cerium ammonium nitrate, cerium chloride, and lanthanum chloride; and / or The nonionic wetting agent is selected from at least one or a combination of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyether-modified siloxane wetting agent, and acetylenic diol wetting agent.

3. The trivalent chromium blue-white passivating agent according to claim 2, characterized in that, The mass ratio of malonic acid to citric acid is (3-5):1; and / or The particle size of the acidic silica sol is 5-20 nm.

4. A passivation process using a trivalent chromium blue-white passivating agent, employing the trivalent chromium blue-white passivating agent as described in any one of claims 1-3, characterized in that... Includes the following steps: S100. After washing the metal workpiece to be treated with water, it is placed in a slightly acidic preconditioning solution for preconditioning treatment to obtain the pretreated workpiece. S200. The pretreated workpiece is passivated using the trivalent chromium blue-white passivating agent to obtain a wet film passivated workpiece. S300. The wet film passivated workpiece is subjected to light washing, liquid control and curing treatment in sequence to obtain the passivated metal workpiece.

5. The passivation process according to claim 4, characterized in that, S200 includes: S210. The pretreated workpiece is placed in the trivalent chromium blue-white passivating agent for a first passivation treatment to obtain a first intermediate workpiece; S220. The first intermediate workpiece is removed from the trivalent chromium blue-white passivating agent and subjected to liquid separation treatment to obtain the second intermediate workpiece. S230. The second intermediate workpiece is placed in the trivalent chromium blue-white passivating agent for a second passivation treatment to obtain the wet film passivated workpiece.

6. The passivation process according to claim 5, characterized in that, The first passivation treatment lasts for 12-20 seconds; and / or The second passivation treatment takes 8-15 seconds; and / or The liquid separation process involves leaving the liquid in the air for 15-30 seconds.

7. The passivation process according to claim 4, characterized in that, The slightly acidic preconditioning solution comprises: citric acid: 0.5-2.0 g / L, malonic acid: 0.3-1.5 g / L, sodium nitrate: 0.2-1.0 g / L, and deionized water: balance; wherein the pH of the slightly acidic preconditioning solution is 3.0-4.5; and the preconditioning treatment time is 5-20 seconds.

8. The passivation process according to claim 4, characterized in that, The light wash treatment includes a primary light wash treatment and a secondary light wash treatment; the primary light wash treatment uses deionized water with a conductivity of <100μS / cm and a residence time of 15-30s; the secondary light wash treatment uses deionized water with a conductivity of <20μS / cm and a residence time of 10-20s.

9. The passivation process according to claim 4, characterized in that, The liquid control process includes one or a combination of low-pressure air knife, centrifugal drying, tilting dripping, and slow rotational drainage.

10. The passivation process according to claim 4, characterized in that, The curing process includes: pre-drying at 50-60℃ for 1-3 minutes, and then drying at 75-90℃ for 8-15 minutes.

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