Brake caliper surface treatment method

Abstract

The invention relates to the field of metal workpiece treatment, and relates to a metal surface treatment method, in particular to a brake caliper surface treatment method. A compact zinc-nickel alloy layer with high corrosion resistance can be formed on the surface of the brake caliper through oil removal treatment, electroplating treatment and passivation treatment, and in the treatment process, an environment-friendly oil removal cleaning agent and a trivalent chromium passivation solution are introduced, so that the problems of high environmental pollution and toxicity caused by traditional electroplating treatment are solved; and by optimizing the trivalent chromium passivation solution, the problem of poor corrosion resistance effect of a passivation film formed by the trivalent chromium passivation solution in the prior art is solved, so that the environmental protection effect is improved on the basis of ensuring the quality of the passivation film.

Description

Technical Field

[0001] This invention relates to the field of metal workpiece processing, and specifically to a metal surface treatment method, and more particularly to a brake caliper surface treatment method. Background Technology

[0002] As a core component of a vehicle's braking system, the brake caliper plays a crucial role in the vehicle's safety and reliability. As a key component of the braking system, the brake caliper has a decisive influence on the system's operating condition and lifespan. With the increasing sophistication of vehicle powertrains, especially the rise of high-torque electric vehicles, the challenges to brake calipers are becoming increasingly severe. Particularly under extreme conditions such as high humidity and high temperature, and high loads, the surface of the brake caliper is highly susceptible to corrosion and wear, leading to reduced lifespan and decreased braking performance. Summary of the Invention

[0003] To address the above problems, this invention provides a method for surface treatment of brake calipers, which forms a high-brightness and highly flat zinc-nickel alloy layer on the surface of the brake caliper through electroplating. This layer has high hardness, high temperature resistance, and is suitable for humid and hot environments.

[0004] To achieve the above objectives, the technical solution adopted in this invention application is as follows:

[0005] This invention provides a method for surface treatment of brake calipers, comprising: immersing the brake caliper to be treated in a cleaning solution for 2-5 minutes to remove oil, obtaining an initial brake caliper; the cleaning solution comprising an active ingredient and an aqueous solution, wherein the volume ratio of the active ingredient to the aqueous solution is 1:9; placing the initial brake caliper in a single-anode electroplating device containing an electroplating solution, and performing electroplating treatment on the brake caliper surface using the single-anode electroplating device to form a zinc-nickel alloy layer, obtaining an intermediate brake caliper; the single-anode electroplating device comprising a power source, an anode, and a cathode, wherein the anode is zinc. The plate, wherein the cathode is the brake caliper to be treated; the current density of the electroplating treatment is 3~6A / dm2, the electroplating temperature is 10~40℃, and the electroplating time is 30min; the intermediate brake caliper after electroplating treatment is placed in a passivation solution and passivated at 35℃ for 40s to obtain the target brake caliper; the passivation solution includes a base passivation solution and a complexing agent, wherein the base passivation solution is a mixed solution of trivalent chromium passivation solution and anionic solution, and the complexing agent is based on oxalic acid, and malonic acid and oxalic acid are mixed in a 1:2 ratio to form a composite complexing agent.

[0006] In some specific implementations, the active ingredients include surfactants, detergent builders, and neutralizing fillers. The surfactants are mainly composed of a mixture of multi-branched isomeric tridecyl alcohol polyoxyethylene ether at a concentration of 2-4 g / L, a wetting agent at a concentration of 3-5 g / L, and sodium dodecylbenzenesulfonate at a concentration of 5-7 g / L.

[0007] In some specific implementations, the detergent is mainly composed of a mixture of layered sodium metasilicate at a concentration of 2-5 g / L, sodium gluconate at a concentration of 1-3 g / L, and N,N-dicarboxymethylalanine at a concentration of 3-7 g / L.

[0008] In some specific implementations, the neutralizing filler comprises Na2CO3 with a concentration of 22-30 g / L and Na2SO4 with a concentration of 2-4 g / L.

[0009] In some specific implementations, the wetting agent is obtained by mixing tung oil acid and acetylenic diol polyoxyethylene ether at a molar ratio of 0.5 to 2:1 and reacting them under catalytic conditions and an inert atmosphere for 4 to 6 hours.

[0010] In some specific implementations, the catalyst is p-toluenesulfonic acid, which accounts for 2% of the total mass of the reaction system.

[0011] In some specific implementations, the basic passivation solution is Cr(NO3)3·9H2O with a concentration of 30~35 g / L; the anion solution includes CoSO4 with a concentration of 1~3 g / L, NaNO3 with a concentration of 2~7 g / L, and Na2SO4 with a concentration of 10~14 g / L.

[0012] In some specific implementations, the basic passivation solution includes Cr(NO3)3·9H2O with a concentration of 30~35 g / L, and also includes YbCl3·6H2O with a concentration of 0.3~3.0 g / L or SmCl3·6H2O with a concentration of 0.3~2.8 g / L added to Cr(NO3)3·9H2O.

[0013] In some specific implementations, the electroplating solution is mainly composed of zinc chloride with a concentration of 45~55g / L, nickel chloride hexahydrate with a concentration of 120~135g / L, potassium chloride with a concentration of 180~210g / L, and potassium acetate with a concentration of 35~45g / L.

[0014] In some specific implementations, the method further includes pre-plating the initial brake caliper before the electroplating process, specifically including: placing the initial brake caliper in a pre-plating solution at an electroplating temperature of 55°C, an electroplating time of 10 minutes, and an electroplating rate of 3 A / dm. 2Electroplating is performed under current density conditions, and the pre-plating solution includes 150 g / L nickel sulfate, 40 g / L ammonium sulfate, 30 g / L nickel chloride, and 140 g / L sodium citrate.

[0015] The technical solution provided in this application provides a method for surface treatment of brake calipers. Through degreasing, electroplating, and passivation, a dense and highly corrosion-resistant zinc-nickel alloy layer can be formed on the surface of the brake caliper. In addition, by introducing environmentally friendly degreasing and cleaning agents and trivalent chromium passivation solution during the treatment process, the high pollution and toxicity of traditional electroplating treatment are reduced. Furthermore, by optimizing the trivalent chromium passivation solution, the problem of poor corrosion resistance of the passivation film formed by the trivalent chromium passivation solution in the prior art is solved, thereby improving the environmental protection effect while ensuring the quality of the passivation film. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a brake caliper surface treatment method provided in an embodiment of this application.

[0018] Figure 2 This is a schematic diagram of the single-anode electroplating apparatus provided in the embodiments of this application.

[0019] Figure 3 This is a flowchart of another brake caliper surface treatment method provided in the embodiments of this application.

[0020] Figure 4 This is a schematic diagram of an SEM image result provided in an embodiment of this application.

[0021] Figure 5 This is a schematic diagram of another brake caliper SEM image result provided in an embodiment of this application;

[0022] Among them, 5(a) is a schematic diagram of the SEM image results of the brake caliper corresponding to Example 1; Figure 5 (b) is a schematic diagram of the SEM image results of the brake caliper corresponding to Example 2; Figure 5 (c) is a schematic diagram of the SEM image results of the brake caliper corresponding to Example 3; Figure 5 (d) is a schematic diagram of the SEM image results of the brake caliper corresponding to Example 4.

[0023] Figure 6This is a schematic diagram of EDS analysis results for another brake caliper passivation film provided in an embodiment of this application;

[0024] in, Figure 6 (a) is a schematic diagram of the EDS analysis results of the passivation film of the brake caliper corresponding to Example 1; Figure 6 (b) is a schematic diagram of the EDS analysis results of the brake caliper passivation film corresponding to Example 2; Figure 6 (c) is a schematic diagram of the EDS analysis results of the brake caliper passivation film corresponding to Example 3; Figure 6 (d) is a schematic diagram of the EDS analysis results of the brake caliper passivation film corresponding to Example 4.

[0025] Figure 7 This is a schematic diagram of another brake caliper SEM image result provided in an embodiment of this application;

[0026] in, Figure 7 (a) is a schematic diagram of the SEM image results of the brake caliper corresponding to Example 6; Figure 7 (b) is a schematic diagram of the SEM image results of the brake caliper corresponding to Example 7; Figure 7 (c) is a schematic diagram of the SEM image results of the brake caliper corresponding to Example 8; Figure 7 (d) is a schematic diagram of the SEM image results of the brake caliper corresponding to Example 9.

[0027] Figure 8 This is a schematic diagram of another brake caliper EDS analysis result provided in an embodiment of this application;

[0028] in, Figure 8 (a) is a schematic diagram of the EDS analysis results of the brake caliper passivation film corresponding to Example 6; Figure 8 (b) is a schematic diagram of the EDS analysis results of the passivation film of the brake caliper corresponding to Example 7; Figure 8 (c) is a schematic diagram of the EDS analysis results of the brake caliper passivation film corresponding to Example 8; Figure 8 (d) is a schematic diagram of the EDS analysis results of the brake caliper passivation film corresponding to Example 9.

[0029] Figure 9 This is a schematic diagram of the corrosion resistance test results of the brake caliper provided in the embodiments of this application.

[0030] Figure 10 This is a schematic diagram of the SEM image results of the pre-nickel plating layer of the brake caliper provided in the embodiments of this application.

[0031] Figure 11 This is a schematic diagram showing the comparison of corrosion resistance test results between the brake caliper provided in this application embodiment and the prior art.

[0032] Illustration:

[0033] 10-Electroplating equipment; 11-Zinc plate; 12-Brake caliper; 13-Power supply. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. The embodiments described below are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art in conjunction with the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] In one specific embodiment of the present invention, a surface treatment method for brake calipers is provided. This method involves electroplating the surface of the brake caliper to form a zinc-nickel alloy layer, which protects the base material of the brake caliper and reduces wear and tear on the base material under external environmental conditions and high-frequency operating conditions. The base material of the brake caliper is generally ductile iron. Due to the material characteristics of ductile iron brake calipers, there are issues such as easy carbon deposition, poor plating filling of small sand holes in cast iron parts, and plating deposition in areas where shot blasting is incomplete. This embodiment addresses these issues through three processes: pretreatment, electroplating, and passivation post-treatment. By using appropriate solvents in each process, the final zinc-nickel alloy layer exhibits high hardness, high temperature resistance, and high corrosion resistance.

[0036] For details, please refer to Figure 1 The surface treatment method for the brake caliper in this embodiment includes the following steps:

[0037] Step S11. Soak the brake caliper to be processed in cleaning fluid for 2-5 minutes to remove oil and obtain the initial brake caliper.

[0038] In this embodiment, the base material of the brake caliper is cast iron. During the refining, storage, and transportation of cast iron, it inevitably becomes contaminated with oil. This oil affects the quality of subsequent electroplating and easily adsorbs insoluble particulate matter. These particulates are typically acidic, leading to corrosion and aging of the steel material. Furthermore, these particulates can directly abrade the surface of the brake caliper, reducing its surface performance. Therefore, the brake caliper needs to be degreased before electroplating to ensure the adhesion between the electroplated layer and the base metal, the smoothness of the electroplating process, the quality requirements of the base metal, and the quality and durability of the final plating layer. The oil on the surface of the cast iron typically includes mostly mineral oil, a small amount of animal and vegetable oil, and a small amount of soluble metal ions and insoluble particulate matter.

[0039] In this embodiment, the surface degreasing treatment of the brake caliper is performed using a cleaning solution. Specifically, the cleaning solution includes an active ingredient and an aqueous solution, with a volume ratio of active ingredient to aqueous solution of 1:9.

[0040] Furthermore, the active ingredients in this embodiment include surfactants, detergent builders, and composite fillers. Surfactants are the core component of the cleaning solution; however, a single surfactant cannot achieve the desired degreasing effect. In this embodiment, a multi-component compounding method is used to induce mutual adsorption between the various substances in the cleaning solution, thereby promoting micelle formation. This results in more amphiphilic molecules adsorbed on the oil film interface per unit area, thus improving the treatment of oil stains. The main function of the surfactant is to remove oil stains, especially mineral oil, from the brake caliper surface through emulsification. The detergent builder, acting as a metal ion exchanger, removes metal ions from the oil stains to decompose them. It can minimize the hardness of the degreasing solution water, act as a pH buffer, prevent redeposition of dirt, and synergistically enhance the effect with the surfactant. The neutralizing filler provides a certain alkalinity for the degreasing process, allowing the cleaning solution to operate in an optimal pH environment. It can also saponify small amounts of animal and vegetable oils.

[0041] In this context, surfactants are used to oriented and closely align at the interface between a solution and air, or between two immiscible liquids, thereby increasing the interfacial strength and reducing the surface tension at the interface. As a core component of the cleaning fluid, surfactants can wet, penetrate, and emulsify oil stains during the degreasing process, reducing the interfacial energy between the oil-matrix surface and the oil-water clean surface, and peeling off oil stains in the form of dispersed phase particles. Therefore, the surfactant used in this embodiment should possess good performance in terms of wettability, penetration, and emulsification.

[0042] Furthermore, the surfactant in this embodiment is mainly composed of a penetrant with a concentration of 2-4 g / L, a wetting agent with a concentration of 3-5 g / L, and an emulsifier with a concentration of 5-7 g / L.

[0043] The main function of wetting agents is to significantly reduce the surface tension of liquids, thereby enhancing the spreadability and penetration of surfactant liquids on the substrate surface, giving the surfactants good wetting properties. Wetting agents not only improve the dispersibility and adhesion of surfactants but also effectively enhance application efficiency and product performance. However, while commonly used wetting agents in existing technologies can meet the aforementioned process requirements, many suffer from high foaming, high environmental toxicity, and poor biodegradability. These problems not only affect the toxicity of the electroplating environment but also result in the presence of harmful substances in the treated water. Therefore, to address these technical issues, this embodiment uses a Gemini-type wetting agent with a superior structure, which offers advantages such as low toxicity, environmental friendliness, and biodegradability. Furthermore, its low-foaming properties make it particularly suitable for the brake caliper product in this embodiment.

[0044] Specifically, in this embodiment, the wetting agent is obtained by mixing tung oil acid and acetylenic glycol polyoxyethylene ether in a molar ratio of 0.5 to 2:1 and reacting under an inert atmosphere for 4 to 6 hours under catalytic conditions. The acetylenic glycol polyoxyethylene ether has two lipophilic and two hydrophilic groups, classifying it as a nonionic wetting agent that can be directly used for dynamic wetting and defoaming. However, acetylenic glycol polyoxyethylene ether still presents some challenges, such as how to improve the wetting effect while maintaining low foaming performance. For the application scenario in this embodiment, the surfactant itself needs to have low foaming properties. Therefore, to address this issue, in this embodiment, tung oil acid and acetylenic glycol polyoxyethylene ether are mixed to synthesize a wetting agent with low foaming properties and high wetting properties. The tung oil acid used is α-tung oil acid, which has a high proportion in the chemical composition of tung oil. It is worth noting that tung oil acid itself is not directly used as a wetting agent, but its derivatives, such as monoglycerides, possess surfactant properties. For example, tung oil monoglycerides can effectively reduce the surface tension of water, thereby increasing the oil / water interfacial tension, and have significant potential applications in improving wetting and dispersing performance. Furthermore, the conjugated double bond structure of α-keto acids gives them a unique advantage in the synthesis of geminal wetting agents; their conjugated double bonds can enhance surface activity by altering the molecular arrangement at the interface. Therefore, synthesizing tung oil acid with acetylenic glycol polyoxyethylene ether can reduce the high foaming properties of the wetting agent while improving the wetting and dispersing effect.

[0045] Tung oil acid cannot be obtained directly, so in this embodiment, it is synthesized from tung oil. Specifically, tung oil acid is obtained by using tung oil as the basic raw material, mixing it with potassium hydroxide dissolved in methanol solution, wherein the molar ratio of tung oil to potassium hydroxide is 1:3~5; heating to 70℃~80℃ and refluxing for 1.5h~2.0h, then adjusting the pH to 3 with an acid solution, stirring and allowing it to stand for separation, taking the upper organic phase and washing it with an alkaline solution and then washing it a second time with deionized water, finally removing water with anhydrous CaCl2 to obtain tung oil acid. The acid solution used is a 98% H2SO4 solution, and the alkaline solution is a 10% NaCl solution. The tung oil acid obtained through the above treatment has a high yield, which is 98.5±0.5%. For the tung oil acid obtained above, tung oil acid and acetylacetonate diol polyoxyethylene ether were mixed in a molar ratio of 0.5 to 2:1, and p-toluenesulfonic acid was added as a catalyst at 2% of the total mass of the wetting agent synthesis system. Cyclohexane was then added as a reaction medium to promote the removal of moisture. Nitrogen gas was purged throughout the reaction as an inert atmosphere to prevent oxygen interference or side reactions. This reaction system was connected to a water separator filled with cyclohexane and refluxed at 80°C for 5 hours. After the reaction, the reaction mixture was rotary evaporated at 0.1 MPa and 40°C to obtain the residue, which is the wetting agent in this embodiment.

[0046] Penetrants are used to achieve high penetration of surfactants. For high penetration based on the cast iron characteristics of brake calipers, the penetrant needs to penetrate the oil film, enter the grease, and ultimately reach the interface between the oil film and the substrate surface to be cleaned. The combined addition of penetrants and wetting agents works synergistically. Stronger penetration performance means a shorter penetration and wetting time for the surfactant, faster emulsification of the oil, and a larger effective cleaning area. Therefore, when selecting surfactants, substances with strong penetration should be prioritized as their main components. Furthermore, just as wetting agents have environmentally friendly requirements, penetrants also need to have excellent environmental performance and be easily biodegradable. Specifically, based on the above requirements, in this embodiment, multi-branched isomeric tridecyl alcohol polyoxyethylene ether is preferred as the penetrant. Multi-branched isomeric tridecyl alcohol polyoxyethylene ether belongs to the isomeric alcohol ether type surfactant, which has significant low-foaming characteristics and defoaming ability, and high penetration.

[0047] Furthermore, since the oil adhering to the brake caliper surface is mainly mineral oil, the emulsifier is the primary mechanism by which surfactants remove mineral oil. Therefore, the better the emulsification, the stronger the adsorption of oil at the water-oil interface and the brake caliper-oil interface, and the stronger the mutual repulsion between dispersed phase particles, thus increasing the limit of emulsion formation. Therefore, the surfactant should possess strong emulsifying properties. In this embodiment, sodium dodecylbenzenesulfonate is preferentially used as the emulsifier, as it has good emulsifying properties, is biodegradable, and will not pollute the environment.

[0048] In this embodiment, the final surfactant is obtained by mixing the three reagents. The functions of the three reagents influence each other, and all of them have high environmental protection effects. The combined use of the three reagents can improve the oil stain removal effect on the surface of brake calipers.

[0049] However, it is worth noting that the degreasing effect cannot be achieved solely by the aforementioned composite surfactant. Therefore, in this embodiment, a detergent builder is also included in the cleaning solution. This detergent builder removes calcium and magnesium ions from the solution through chelation or ion exchange during the degreasing process, thereby reducing solution hardness and providing a favorable working medium environment for the surfactant. Simultaneously, by removing metal ions from the oil, it can structure the oil, accelerating the adsorption and penetration process of the surfactant. Furthermore, the detergent builder can adjust the pH of the cleaning solution, allowing the surfactant to operate under optimal pH conditions. Since most oil is acidic, pH adjustment helps maintain stability during cleaning, thus extending the service life of the cleaning solution. Additionally, the detergent builder improves the miscibility of multiple reagents in the composite surfactant, rapidly forming micelles. These micelle particles can be more stably adsorbed at the oil-water and oil-casting interfaces, thereby enhancing surface activity.

[0050] Specifically, the detergent builder is mainly composed of layered sodium metasilicate at a concentration of 2-5 g / L, sodium gluconate at a concentration of 1-3 g / L, and N,N-dicarboxymethylalanine at a concentration of 3-7 g / L.

[0051] For the neutralizing fillers, Na2CO3 with a concentration of 22~30 g / L and Na2SO4 with a concentration of 2~4 g / L were selected.

[0052] Step S12. Place the initial brake caliper in a single-anode electroplating device containing electroplating solution, and perform electroplating treatment based on the single-anode electroplating device to form a zinc-nickel alloy layer on the surface of the brake caliper to obtain an intermediate brake caliper.

[0053] See Figure 2In this embodiment, the process is an electroplating process used to form a zinc-nickel alloy layer on the brake caliper, and the electroplating is achieved using a single-anode electroplating device. The single-anode electroplating device includes a DC power supply, an anode, and a cathode. The anode is a nickel plate, and the cathode is the brake caliper to be processed.

[0054] The electroplating solution mainly consists of zinc oxide (45-55 g / L), nickel chloride hexahydrate (120-135 g / L), potassium chloride (180-210 g / L), and potassium acetate (35-45 g / L). The electroplating process conditions are: plating density of 3-6 A / dm², plating temperature of 20℃, and plating time of 30 min.

[0055] Nickel chloride hexahydrate is used to provide Ni 2+ The main salt, zinc chloride, is used to provide Zn. 2+ The main salt content is crucial; too low a main salt content can easily lead to concentration polarization, thus lowering the upper limit of the allowable current density of the electroplating solution. In high current density areas, the coating is prone to scorching. Conversely, a higher main salt content increases the number of metal ions available for reduction around the substrate. These metal ions can reach the brake caliper substrate surface for reduction simply through short-layer diffusion, thereby accelerating the deposition rate. Furthermore, with the increase in Zn content in the plating solution... 2+ Ni 2+ As the total concentration increases, the current efficiency also increases. And for Zn in the electroplating solution... 2+ Ni 2+ The total concentration affects the corrosion resistance of the coating as Zn increases. 2+ Ni 2+ With increasing total concentration, the corrosion current density of the electroplated layer first decreases and then increases, while when Zn 2 + Ni 2+ The lowest corrosion current density at a total concentration of 0.9 mol / L means that the coating obtained at this concentration has the best corrosion resistance.

[0056] Specifically, the contents of zinc chloride and nickel chloride hexahydrate in the electroplating solution are determined based on the aforementioned optimal total concentration. Firstly, regarding Ni... 2+ In low concentrations of Ni 2+ Under these conditions, the amount of Ni deposited in the coating with a more positive standard electrode potential is less than that of Zn with a more negative standard electrode potential. This indicates that the Zn-Ni alloy electroplated by this solution is an abnormal process. The hydrogen evolution reaction on the cathode surface causes a sharp increase in the interfacial pH, thereby promoting the deposition of Zn. 2+ A colloidal Zn(OH)2 adsorption layer is formed, which inhibits Ni. 2+ The movement towards the cathode surface leads to anomalous co-deposition. And with the Ni in the plating bath... 2+With increasing concentration, the Ni content in the coating continuously rises. And with increasing Ni... 2+ As the concentration increases, the current efficiency of the electroplating solution gradually decreases. This change is due to the exacerbation of the hydrogen evolution side reaction caused by excessive Ni content. Therefore, in this embodiment, the Ni content is... 2+ The concentration should not be too high. Furthermore, with the increase of Ni... 2+ With increasing Ni concentration, the corrosion current density of the coating first decreases and then increases, and when Ni... 2+ At a concentration of 0.5 mol / L, the corrosion current density is the lowest, thus exhibiting superior corrosion resistance. Therefore, for Ni in electroplating solutions... 2+ The preferred concentration is 0.5 mol / L, corresponding to Zn 2+ The preferred concentration is 0.4 mol / L. Correspondingly, the optimal concentrations for zinc chloride and nickel chloride hexahydrate are 55 g / L and 130 g / L, respectively.

[0057] The current density in this embodiment is in the range of 3~6 A / dm. 2 The current density directly affects the Ni content and corrosivity of the coating. When the current density is too low, the zinc-nickel alloy coating exhibits canonical co-deposition, with nickel preferentially depositing before zinc, resulting in a high nickel content and poor corrosivity. The minimum acceptable current density for electroplating should be 3 A / dm³. 2 As the current density continues to increase, concentration polarization intensifies, thus affecting Zn. 2+ with Ni 2+ The concentration of Zn decreases near the cathode. 2+ For Ni 2+ The reduced inhibition effect on deposition favors nickel deposition, while the decrease in Ni content on the electrode surface leads to a decrease in Ni deposition, creating a dynamic equilibrium. This results in a stable but slow fluctuation in the Ni content of the coating. Compared to the change in Ni content, the corresponding current efficiency at a current density of 3 A / dm³... 2 The optimal time is when the current density is 3A / dm. 2 The initial current densities were all relatively high. Furthermore, as the current density increased, the corrosion current density of the coating initially decreased and then increased, reaching a maximum at a current density of 4 A / dm³. 2 At this point, the corrosion current density is minimum, resulting in the best corrosion resistance of the coating. Considering the above three aspects, in this embodiment, a current density of 4 A / dm is preferably used. 2 .

[0058] In this embodiment, the electroplating temperature ranges from 10 to 40°C, with 10°C serving as the base electroplating temperature. The Ni content in the coating increases with increasing temperature, but exceeds 20% above 45°C. This is because the exchange current density between Zn and Ni increases with temperature. However, since the exchange current density of Zn is much greater than that of Ni, the effect of temperature on the exchange current density of Ni is more significant, resulting in a significant increase in the partial current density of deposited Ni in the cathode current density, thus leading to an increase in the Ni content in the coating. The current efficiency fluctuates between 90-95% with increasing temperature, with higher efficiency between 20°C and 40°C. When the electroplating temperature reaches 45°C, the excessively high temperature leads to poor coating quality and localized defects. Therefore, for both the Ni content and current efficiency in the coating, an electroplating temperature of 20°C to 40°C is preferred. Regarding the impact on coating corrosion, the corrosion current density of the coating first decreases and then increases with increasing electroplating temperature, reaching its minimum at 20°C, indicating the best corrosion resistance at this temperature. Therefore, based on the coating's Ni content, current efficiency, and corrosion resistance, 20°C is preferentially selected as the optimal electroplating temperature in this embodiment.

[0059] In summary, the optimal process conditions for the electroplating process in this embodiment are a current density of 4 A / dm³. 2 The plating temperature is 20℃ and the plating time is 10min.

[0060] Step S13. Place the electroplated intermediate brake caliper in a passivation solution and passivate it at 35°C for 40 seconds to obtain the target brake caliper.

[0061] Step S12 forms a zinc-nickel alloy layer on the brake caliper surface. However, zinc-nickel alloys are typically reactive metals, prone to corrosion in humid environments, leading to the appearance of a white powdery substance, commonly known as white rust, on the coating surface. This process accelerates the exposure of the base metal. Therefore, in industrial applications, a surface passivation process is required for brake calipers. This process involves constructing a dense passivation film on the alloy coating surface through chemical or electrochemical methods. This film provides both physical barrier and chemical protection.

[0062] In existing technologies, chromate passivation films are commonly used for passivation, with hexavalent chromium passivation films, known for their high corrosion resistance, being particularly popular. However, while hexavalent chromium passivation films offer significant advantages, they also pose substantial potential hazards. For instance, hexavalent chromium is highly toxic, and long-term exposure can lead to cancer. Furthermore, the anti-corrosion effect of hexavalent chromium passivation films is greatly reduced after annealing above 60°C. Hexavalent chromium passivation films exhibit good drainage and stability below 60°C; however, after heat treatment or prolonged exposure to high temperatures, hexavalent chromium dehydrates to form trivalent chromium compounds. Therefore, to reduce the potential harm of hexavalent chromium passivation films to the human body, the selection of passivation films is increasingly biased towards trivalent chromium passivation films.

[0063] However, while trivalent chromium passivation films offer better environmental friendliness compared to hexavalent chromium passivation films, their corrosion resistance still lags behind in current technologies. This is primarily because the trivalent chromium passivation film lacks hexavalent chromium filling, resulting in high porosity, poor density, and a lack of self-healing properties. Once damaged, the passivation film is highly susceptible to corrosion. Therefore, the application of trivalent chromium passivation films faces numerous technical challenges in current technologies.

[0064] To address this technical problem, embodiments of this application provide a passivation solution and a corresponding passivation treatment method, which can ensure that the passivation film formed on the surface of the zinc-nickel alloy layer has high corrosion resistance while reducing environmental damage.

[0065] Specifically, the passivation process in this embodiment employs a chemical passivation method, whereby the brake caliper with a zinc-nickel alloy layer on its surface is placed in a passivation solution for chemical passivation treatment. The passivation solution includes a base passivation solution and a complexing agent. The base passivation solution is the supply solution for the target film ultimately formed on the zinc-nickel alloy layer surface, and includes a trivalent chromium passivation solution. The complexing agent is a ligand for the passivation solution, and the ligand plays a crucial role in the passivation film formation rate and the stability of the passivation solution. Specifically, the complex electronic structure is 3d... 5 4s 1 Therefore, Cr 3+ Chromium ions have a small ionic radius but a large charge. In water, chromium ions react with water to form chromium hexahydrate, which is sp... 3 d 2 The hybrid form results in a symmetrical octahedral structure with equal hexagonal sides. This structure is extremely stable, and the water molecules within it are not easily dissociated. To break this stable state and promote the formation of a more reactive intermediate, ligands need to be introduced to replace some of the water molecules, thus forming a mixed ligand complex with lower stability. The complexing agent is a composite complexing agent, based on oxalic acid and mixed with malonic acid.

[0066] In this embodiment, a Cr(NO3)3·9H2O solution with a concentration of 30-35 g / L is used for the trivalent chromium passivation solution. A composite complexing agent is used, specifically a mixture of oxalic acid as the base complexing agent and malonic acid. In this embodiment, the use of oxalic acid and malonic acid as a composite complexing agent provides a high pH buffer range, maintaining a locally higher pH area. This also facilitates the complexation of the insoluble zinc, making it easier to form a stable passivation film, thus obtaining a trivalent chromium passivation film with good corrosion resistance. The molar ratio of oxalic acid to malonic acid is 0.5-3:1, with the preferred optimal mixing ratio being H2C2O4 / C3H4O4 = 2:1.

[0067] Furthermore, in this embodiment, to improve the passivation effect, in addition to the trivalent chromium passivation solution mentioned above, an anionic solution is also added to the passivation solution. This can be understood as the preferred passivation solution in this embodiment being a mixture of the trivalent chromium passivation solution and the anionic solution. Specifically, the anionic solution in this embodiment includes CoSO4 at a concentration of 1-3 g / L, NaNO3 at a concentration of 2-7 g / L, and Na2SO4 at a concentration of 10-14 g / L. Preferably, the optimal concentrations of the anionic solution are: CoSO4: 2 g / L, NaNO3: 5 g / L, and Na2SO4: 12.8 g / L.

[0068] In this embodiment, the passivation solution at 35°C, pH 3.5 and a passivation time of 40 seconds can form a highly corrosion-resistant, bluish-white, bright trivalent chromium passivation film on the zinc-nickel alloy layer surface of the brake caliper.

[0069] Furthermore, to enhance the passivation effect, another feasible implementation method is provided. In this implementation, in addition to the passivation solution, the passivation solution is also doped. Specifically, by introducing highly active rare earth ions into the passivation solution, the adhesion and chemical stability of the passivation film are improved, thereby further enhancing the corrosion resistance of the zinc-nickel alloy layer.

[0070] In this embodiment, the rare earth ions are Sm ions or Yb ions, and the above two ions are provided by introducing YbCl3·6H2O with a concentration of 0.3~3.0 g / L or SmCl3·6H2O with a concentration of 0.3~2.8 g / L.

[0071] During the formation of the trivalent chromium passivation film, Zn and H in the zinc-nickel alloy layer +The reaction causes the pH of the passivation solution near the plating layer to rise. Cr, Ni, and Sm ions in the passivation solution form hydroxides or oxides, which deposit on the surface of the zinc-nickel alloy layer to form a passivation film. Because the rare earth element Sm is more chemically reactive, the rapidly formed oxides or hydroxides accelerate the film formation rate of trivalent chromium. Furthermore, the higher the Sm concentration, the more film-forming nuclei there are, the higher the film formation rate, and the smaller and denser the film grains. Moreover, with increasing Sm... 3+ The addition of [a specific ingredient] first forms a complex with the components in the passivation solution. This complexation reaction leads to localized pH changes, and pH plays a crucial role in the passivation process of zinc-nickel alloys. As shown in the previous embodiment, under appropriate pH conditions, the passivation film formed on the metal surface is more uniform and dense. Furthermore, this uniform and dense film formation process is related to intermediates or other stabilizing compounds induced by complexation. These intermediates or stabilizers can provide a more uniform growth environment for the film, resulting in lower internal stress in the formed passivation film. Due to the uniformity of the film and lower internal stress, the interfacial adhesion between the film and the substrate is enhanced, reducing crack formation caused by stress accumulation. Moreover, for Sm [a specific ingredient]... 3+ The Sm2O3 formed naturally can play a "filling" and "repairing" role in the film layer, thereby making the film layer more complete. Therefore, in this embodiment, by adding Sm 3+ It can promote the formation of a more uniform, crack-free passivation film in trivalent chromium passivation solution by adjusting pH, forming stable complexes, and reducing internal and interfacial stresses of the film.

[0072] Regarding Yb doping 3+ Ions can act as catalysts in the passivation reaction, thereby accelerating the formation rate of the passivation film, and the added Yb 3+ Ions can increase the surface hydrophobicity of the zinc-nickel alloy layer, changing the surface energy of the passivation film and thus affecting the adsorption behavior during the passivation film growth process. This change helps to form a more uniform and smooth film layer.

[0073] In summary, the passivation liquid in this embodiment can be divided into a first passivation liquid and a second passivation liquid according to the doping composition. The first passivation liquid is a passivation liquid doped with Sm, and the second passivation liquid is a passivation liquid doped with Yb. The optimal composition for the first passivation solution is: Cr(NO3)3·9H2O: 32 g / L, H2C2O4: 9.6 g / L, C3H4O4: 5.5 g / L, CoSO4: 2 g / L, NaNO3: 5 g / L, Na2SO4: 12.8 g / L, SmCl3·6H2O: 1.5 g / L. The optimal composition for the second passivation solution is: Cr(NO3)3·9H2O: 32 g / L, H2C2O4: 9.6 g / L, C3H4O4: 5.5 g / L, CoSO4: 2 g / L, NaNO3: 5 g / L, Na2SO4: 12.8 g / L, YbCl3·6H2O: 0.8 g / L. The first and second passivation solutions can be selected according to the actual situation. The passivation process parameters are the same for both, namely, pH value of 3.5, passivation temperature of 35℃, and passivation time of 40s.

[0074] This application provides a method for surface treatment of brake calipers. Through degreasing, electroplating, and passivation, a dense and highly corrosion-resistant zinc-nickel alloy layer can be formed on the surface of the brake caliper. In addition, by introducing environmentally friendly degreasing and cleaning agents and trivalent chromium passivation solution during the treatment process, the high pollution and toxicity of traditional electroplating treatment are reduced. Furthermore, by optimizing the trivalent chromium passivation solution, the problem of poor corrosion resistance of the passivation film formed by the trivalent chromium passivation solution in the prior art is solved, thereby improving the environmental protection effect while ensuring the quality of the passivation film.

[0075] In addition to the above-described embodiments, to improve the adhesion of the zinc-nickel alloy coating, please refer to... Figure 3 Another possible implementation method is provided, in which a pre-plating treatment is performed before electroplating. This pre-plating treatment is used to form a nickel plating layer of uniform thickness and low porosity on the initial brake caliper surface before electroplating. The formed nickel plating layer has good adhesion to the brake caliper substrate and possesses excellent corrosion resistance to protect the substrate. This possible implementation method specifically includes the following steps:

[0076] Step S31. Soak the brake caliper to be processed in the cleaning fluid for 2-5 minutes to remove oil and obtain the initial brake caliper.

[0077] Step S32. Place the initial brake caliper in the pre-plating solution and perform electroplating at a temperature of 55°C, a plating time of 10 minutes, and a plating rate of 3A / dm. 2 Electroplating is performed under current density conditions.

[0078] In this embodiment, the pre-plating solution includes 150 g / L nickel sulfate, 40 g / L ammonium sulfate, 30 g / L nickel chloride, and 140 g / L sodium citrate.

[0079] Step S33. Place the initial brake caliper in a single-anode electroplating device containing electroplating solution, and perform electroplating treatment based on the single-anode electroplating device to form a zinc-nickel alloy layer on the surface of the brake caliper to obtain an intermediate brake caliper.

[0080] Step S34. Place the electroplated intermediate brake caliper in a passivation solution and passivate it at 35°C for 40 seconds to obtain the target brake caliper.

[0081] Example 1

[0082] This application provides a brake caliper with a zinc-nickel alloy layer on its surface, and a surface treatment method for this brake caliper, the method comprising the following steps:

[0083] Preparation of the wetting agent: Tung oil and potassium hydroxide were mixed at a molar ratio of 1:3 and reacted. The mixture was heated to 70℃ and refluxed for 1.5 h. The pH was adjusted to 3 with a 98% H2SO4 solution, and the mixture was stirred and allowed to stand for separation. The upper organic phase was collected and washed with a 10% NaCl solution, followed by a second wash with deionized water. Finally, anhydrous CaCl2 was used to remove water to obtain tung oil acid. The prepared tung oil acid was then mixed with acetylacetonate diol polyoxyethylene ether at a molar ratio of 0.5:1. 2% (by mass) of p-toluenesulfonic acid was added as a catalyst to form a reaction solution. Cyclohexane was added to the reaction solution as a reaction medium, and the reaction vessel was purged with nitrogen using a vacuum pump. The reaction vessel was connected to a water separator and refluxed at 80℃ for 4 h to obtain a reaction mixture. The reaction mixture was then subjected to rotary evaporation at 0.1 MPa and 40℃ until no more liquid was removed, yielding the wetting agent.

[0084] Step S21. The brake caliper to be treated is immersed in a cleaning solution consisting of 2 g / L multi-branched isomeric tridecyl alcohol polyoxyethylene ether, 3 g / L wetting agent, 5 g / L sodium dodecylbenzenesulfonate, 2 g / L layered sodium metasilicate, 1 g / L sodium gluconate, 3 g / L N,N-dicarboxymethyl alanine, 22 g / L Na2CO3 and 2 g / L Na2SO4 for 2 minutes to remove oil, thus obtaining the initial brake caliper.

[0085] Step S22. Place the initial brake caliper in a single-anode electroplating apparatus containing a mixed solution of zinc oxide (45 g / L), nickel chloride hexahydrate (120 g / L), potassium chloride (180 g / L), and boric acid (3 g / L), and apply the plating using the single-anode electroplating apparatus at a current density of 5 A / dm². 2 The electroplating process is carried out at a temperature of 20℃ for 20 minutes to form a zinc-nickel alloy layer on the surface of the brake caliper, thus obtaining the intermediate brake caliper.

[0086] Step S23. Place the electroplated intermediate brake caliper in a passivation solution containing Cr(NO3)3·9H2O (30 g / L), H2C2O4 (2.5 g / L), C3H4O4 (5 g / L), CoSO4 (1 g / L), NaNO3 (2 g / L), Na2SO4 (10 g / L), and SmCl3·6H2O (0.3 g / L), and passivate it at 35°C for 40 seconds to form a passivation film on the zinc-nickel alloy layer surface to obtain the target brake caliper.

[0087] Example 2

[0088] This application provides a brake caliper with a zinc-nickel alloy layer on its surface, and a surface treatment method for this brake caliper, the method comprising the following steps:

[0089] Preparation of the wetting agent: Tung oil and potassium hydroxide were mixed at a molar ratio of 1:4 and reacted. The mixture was heated to 75℃ and refluxed for 2 hours. The pH was adjusted to 3 using a 98% H2SO4 solution, and the mixture was stirred and allowed to stand for separation. The upper organic phase was collected and washed with a 10% NaCl solution, followed by a second wash with deionized water. Finally, water was removed using wastewater CaCl2 to obtain tung oil acid. Tung oil acid and acetylacetonate polyoxyethylene ether were mixed at a molar ratio of 1:1, and p-toluenesulfonic acid (2% by mass of the total reaction system) was added as a catalyst to form a reaction solution. Cyclohexane was added to the reaction solution as a reaction medium, and the reaction vessel was purged with nitrogen using a vacuum pump. The reaction vessel was connected to a water separator and refluxed at 80℃ for 4 hours to obtain a reaction mixture. The reaction mixture was then subjected to rotary evaporation at 0.1 MPa and 40℃ until no more liquid was removed, yielding the wetting agent.

[0090] Step S21. The brake caliper to be treated is immersed in a cleaning solution consisting of 3 g / L multi-branched isomeric tridecyl alcohol polyoxyethylene ether, 4 g / L wetting agent, 6 g / L sodium dodecylbenzenesulfonate, 3 g / L layered sodium metasilicate, 2 g / L sodium gluconate, 5 g / L N,N-dicarboxymethyl alanine, 25 g / L Na2CO3 and 3 g / L Na2SO4 for 2 minutes to remove oil, thus obtaining the initial brake caliper.

[0091] Step S22. Place the initial brake caliper in a single-anode electroplating apparatus containing a mixed solution of zinc oxide (50 g / L), nickel chloride hexahydrate (127 g / L), potassium chloride (190 g / L), and boric acid (38 g / L), and apply the plating using the single-anode electroplating apparatus at a current density of 6 A / dm². 2 The electroplating process is carried out at a temperature of 20℃ for 20 minutes to form a zinc-nickel alloy layer on the surface of the brake caliper, thus obtaining the intermediate brake caliper.

[0092] Step S23. Place the electroplated intermediate brake caliper in a passivation solution containing Cr(NO3)3·9H2O (32 g / L), H2C2O4 (9.6 g / L), C3H4O4 (5.5 g / L), CoSO4 (2 g / L), NaNO3 (5 g / L), Na2SO4 (12.8 g / L), and SmCl3·6H2O (1.5 g / L). Perform passivation treatment for 40 seconds at a passivation temperature of 35°C and a pH of 3.5 to form a passivation film on the surface of the zinc-nickel alloy layer, thus obtaining the target brake caliper.

[0093] Example 3

[0094] This application provides a brake caliper with a zinc-nickel alloy layer on its surface, and a surface treatment method for this brake caliper, the method comprising the following steps:

[0095] Preparation of the wetting agent: Tung oil and potassium hydroxide were mixed at a molar ratio of 1:5 and reacted. The mixture was heated to 80℃ and refluxed for 2 hours. The pH was adjusted to 3 using a 98% H2SO4 solution, and the mixture was stirred and allowed to stand for separation. The upper organic phase was collected and washed with a 10% NaCl solution, followed by a second wash with deionized water. Finally, anhydrous CaCl2 was used to remove water, yielding tung oil acid. Tung oil acid and acetylacetonate diol polyoxyethylene ether were mixed at a molar ratio of 1.5:1, and p-toluenesulfonic acid (2% by mass of the total reaction system) was added as a catalyst to form a reaction solution. Cyclohexane was added to the reaction solution as a reaction medium, and the reaction vessel was purged with nitrogen using a vacuum pump. The reaction vessel was connected to a water separator and refluxed at 80℃ for 4 hours to obtain a reaction mixture. The reaction mixture was then subjected to rotary evaporation at 0.1 MPa and 40℃ until no more liquid was removed, yielding the wetting agent.

[0096] Step S21. The brake caliper to be treated is immersed in a cleaning solution consisting of 4 g / L multi-branched isomeric tridecyl alcohol polyoxyethylene ether, 5 g / L wetting agent, 7 g / L sodium dodecylbenzenesulfonate, 5 g / L layered sodium metasilicate, 3 g / L sodium gluconate, 7 g / L N,N-dicarboxymethyl alanine, 30 g / L Na2CO3 and 4 g / L Na2SO4 for 2 minutes to remove oil, thus obtaining the initial brake caliper.

[0097] Step S22. Place the initial brake caliper in a single-anode electroplating apparatus containing a mixed solution of zinc oxide (55 g / L), nickel chloride hexahydrate (135 g / L), potassium chloride (210 g / L), and boric acid (45 g / L), and apply the plating using the single-anode electroplating apparatus at a current density of 4 A / dm². 2 The electroplating process is carried out at a temperature of 20℃ for 20 minutes to form a zinc-nickel alloy layer on the surface of the brake caliper, thus obtaining the intermediate brake caliper.

[0098] Step S23. Place the electroplated intermediate brake caliper in a passivation solution containing Cr(NO3)3·9H2O (35 g / L), H2C2O4 (13 g / L), C3H4O4 (5.5 g / L), CoSO4 (3 g / L), NaNO3 (6 g / L), Na2SO4 (14 g / L), and SmCl3·6H2O (2.2 g / L), and passivate it at 35°C for 40 seconds to form a passivation film on the zinc-nickel alloy layer surface to obtain the target brake caliper.

[0099] Example 4

[0100] This application provides a brake caliper with a zinc-nickel alloy layer on its surface, and a surface treatment method for this brake caliper, the method comprising the following steps:

[0101] Preparation of the wetting agent: Tung oil and potassium hydroxide were mixed at a molar ratio of 1:5 and reacted. The mixture was heated to 70℃ and refluxed for 2 hours. The pH was adjusted to 3 using a 98% H2SO4 solution, and the mixture was stirred and allowed to stand for separation. The upper organic phase was collected and washed with a 10% NaCl solution, followed by a second wash with deionized water. Finally, anhydrous CaCl2 was used to remove water, yielding tung oil acid. Tung oil acid and acetylacetonate diol polyoxyethylene ether were mixed at a molar ratio of 2:1, and p-toluenesulfonic acid (2% by mass of the total reaction system) was added as a catalyst to form a reaction solution. Cyclohexane was added to the reaction solution as a reaction medium, and the reaction vessel was purged with nitrogen using a vacuum pump. The reaction vessel was connected to a water separator and refluxed at 80℃ for 4 hours to obtain a reaction mixture. The reaction mixture was then subjected to rotary evaporation at 0.1 MPa and 40℃ until no more liquid was removed, yielding the wetting agent.

[0102] Step S21. The brake caliper to be treated is immersed in a cleaning solution consisting of 3 g / L multi-branched isomeric tridecyl alcohol polyoxyethylene ether, 4 g / L wetting agent, 6 g / L sodium dodecylbenzenesulfonate, 4 g / L layered sodium metasilicate, 2 g / L sodium gluconate, 5 g / L N,N-dicarboxymethyl alanine, 25 g / L Na2CO3 and 3 g / L Na2SO4 for 2 minutes to remove oil, thus obtaining the initial brake caliper.

[0103] Step S22. Place the initial brake caliper in a single-anode electroplating apparatus containing a mixed solution of zinc oxide (50 g / L), nickel chloride hexahydrate (130 g / L), potassium chloride (200 g / L), and boric acid (40 g / L), and apply the plating using the single-anode electroplating apparatus at a current density of 3 A / dm². 2 The electroplating process is carried out at a temperature of 20℃ for 20 minutes to form a zinc-nickel alloy layer on the surface of the brake caliper, thus obtaining the intermediate brake caliper.

[0104] Step S23. Place the electroplated intermediate brake caliper in a passivation solution containing Cr(NO3)3·9H2O (33 g / L), H2C2O4 (5 g / L), C3H4O4 (5.5 g / L), CoSO4 (2 g / L), NaNO3 (5 g / L), Na2SO4 (10-14 g / L), and SmCl3·6H2O (1.7 g / L), and passivate it at 35°C for 40 seconds to form a passivation film on the zinc-nickel alloy layer surface to obtain the target brake caliper.

[0105] Example 5

[0106] The difference between this embodiment and Embodiment 1 is that the passivation solution in this embodiment is composed of Cr(NO3)3·9H2O with a concentration of 33 g / L, H2C2O4 with a concentration of 2.5 g / L, C3H4O4 with a concentration of 5 g / L, CoSO4 with a concentration of 1 g / L, NaNO3 with a concentration of 2 g / L, and Na2SO4 with a concentration of 10 g / L.

[0107] Example 6

[0108] The difference between this embodiment and Embodiment 1 is that the passivation solution in this embodiment is composed of Cr(NO3)3·9H2O with a concentration of 30 g / L, H2C2O4 with a concentration of 2.5 g / L, C3H4O4 with a concentration of 5 g / L, CoSO4 with a concentration of 1 g / L, NaNO3 with a concentration of 2 g / L, Na2SO4 with a concentration of 10 g / L, and YbCl3·6H2O with a concentration of 0.3 g / L.

[0109] Example 7

[0110] The difference between this embodiment and Embodiment 2 is that the passivation solution in this embodiment is composed of Cr(NO3)3·9H2O with a concentration of 32 g / L, H2C2O4 with a concentration of 9.6 g / L, C3H4O4 with a concentration of 5.5 g / L, CoSO4 with a concentration of 2 g / L, NaNO3 with a concentration of 5 g / L, Na2SO4 with a concentration of 12.8 g / L, and YbCl3·6H2O with a concentration of 0.8 g / L.

[0111] Example 8

[0112] The difference between this embodiment and Embodiment 4 is that the passivation solution in this embodiment is composed of Cr(NO3)3·9H2O with a concentration of 35 g / L, H2C2O4 with a concentration of 13 g / L, C3H4O4 with a concentration of 5.5 g / L, CoSO4 with a concentration of 3 g / L, NaNO3 with a concentration of 6 g / L, Na2SO4 with a concentration of 14 g / L, and YbCl3·6H2O with a concentration of 1.5 g / L.

[0113] Example 9

[0114] The difference between this embodiment and Embodiment 4 is that the passivation solution in this embodiment is composed of Cr(NO3)3·9H2O with a concentration of 33 g / L, H2C2O4 with a concentration of 5 g / L, C3H4O4 with a concentration of 5.5 g / L, CoSO4 with a concentration of 2 g / L, NaNO3 with a concentration of 5 g / L, Na2SO4 with a concentration of 10~14 g / L, and YbCl3·6H2O with a concentration of 2.9 g / L.

[0115] Experimental Example 1

[0116] The surface morphology of the brake calipers corresponding to Examples 1-9 was scanned by electron microscopy to obtain the SEM images corresponding to the above examples. For the image results, please refer to [reference needed]. Figure 4 , Figure 5 and Figure 6 As shown, where Figure 4 The results are from Example 5. Figure 5 These are SEM images of the brake caliper surface morphology from Examples 1-4. Figure 5 (a) Figure 5 (b) Figure 5 (c) and Figure 5 (d) Results corresponding to Examples 1, 2, 3 and 4 respectively.

[0117] Figure 4 This is a SEM image of the undoped passivation film. Figure 5 (a)- Figure 5 (d) SEM images of passivation films doped with different amounts of Sm. Figure 4 It can be seen that a coating can be formed on the zinc-nickel alloy layer of the brake caliper using the passivation solution. However, this coating exhibits a cracked state, with wide crack gaps and slight protrusions. This is mainly due to the large amount of crystal water in the trivalent chromium passivation film. When the passivation film is baked at high temperature, the film layer dehydrates, generating internal stress, which leads to cracking of the film layer. In contrast... Figure 5 (a)- Figure 5 (d) The passivation film is also made with the same passivation solution, but due to the doping of SmCl3 in the passivation solution, a significant difference can be seen compared to the previous film. Figure 4 The passivation film layer exhibits fewer through-cracks and greater integrity compared to the unadded passivation film. Furthermore, the variations in crack size and the surface morphology of the passivation film differ depending on the degree of doping. Figure 5 (a) This image shows the passivation film morphology corresponding to Example 1 and the resulting doping concentration. It can be seen from this image that the number of through cracks decreases, the number of microcracks increases, and the crack spacing decreases. Furthermore, with increasing doping concentration, as... Figure 5As shown in (b), the film has begun to exhibit a more compact structure, with a significant reduction in crack size and number, resulting in a more complete film. With increasing doping concentration, an optimal result is reached. Figure 5 (c) As shown in the image, the passivation film under these conditions shows no obvious cracks and has relatively fine grains. This is because during the formation of the trivalent chromium passivation film, Zn, Ni, and Sm plasmas form hydroxides, which are deposited on the surface of the conductive layer to form the passivation film. Since the rare earth element Sm has stronger chemical reactivity, the rapidly formed hydroxides accelerate the trivalent chromium film formation rate. The higher the Sm concentration, the more film-forming nuclei there are, the faster the film formation rate, the finer the film grains, and the denser the film. However, it is worth noting that if the Sm concentration is too high, the hydroxides can agglomerate, exacerbating the internal stress of the film and causing cracks to reappear. This result is as follows: Figure 5 As shown in (d), fine cracks appear when the Sm concentration is continuously increased. EDS analysis was performed on the passivation films corresponding to Examples 1-4 to determine the composition of the particles in the passivation films. The analytical results are provided by [Source Name]. Figure 6 As shown. Among them, Figure 6 (a) Figure 6 (b) Figure 6 (c) and Figure 6 (d) EDS analysis results corresponding to Examples 1, 2, 3, and 4, respectively. Through... Figure 6 It can be seen that the various elements in the passivation film are generally evenly distributed, and the Cr content in the passivation film reaches the highest value in Example 3.

[0118] in, Figure 7 These are SEM images of the brake caliper surface morphology from Examples 6-9. Figure 7 (a) Figure 7 (b) Figure 7 (c) and Figure 7 (d) Results corresponding to Examples 6, 7, 8 and 9 respectively.

[0119] pass Figure 7 (a)-(d) and Figure 4 The differences between the passivation films are clearly discernible. With the addition of YbCl3 to the passivation solution, the film surface remains intact, and sparse, tiny white particles are distributed on the surface. Then, EDS analysis was performed on the passivation films corresponding to Examples 6-9 to determine the composition of the particles in the passivation films. The analytical results are provided by [the relevant authority / organization]. Figure 8 As shown. Among them, Figure 8 (a) Figure 8 (b) Figure 8 (c) and Figure 8(d) EDS analysis results corresponding to Examples 6, 7, 8, and 9, respectively. Through... Figure 8 It can be seen that the various elements in the passivation film are generally evenly distributed, and the Cr content in the passivation film reaches the highest value in Example 8.

[0120] Experimental Example 2

[0121] The brake calipers of Examples 1-4 and Examples 6-8 were subjected to corrosion resistance tests, and the polarization curves corresponding to each example were obtained as follows: Figure 9 As shown. (Through) Figure 9 It can be seen that, under the change of current density, the corrosion current density of the brake caliper first decreases and then increases. When the current density is 4A / dm³, the corrosion effect is most pronounced. 2 At this time, the corrosion current density is the lowest, at 6.09 × 10⁻⁶. -5 A / cm 2 The coating obtained at this current density exhibits the best corrosion resistance. When the electrode potential reaches approximately -1.0V, the corrosion current density of the coating shows a rapid increase to varying degrees, which is likely due to pitting corrosion in the coating.

[0122] In summary, the optimal embodiments of the brake caliper surface treatment method provided in this application are Embodiment 3 and Embodiment 8.

[0123] Example 10

[0124] This embodiment provides another embodiment based on Embodiment 3. The difference from Embodiment 3 is that, in this embodiment, before electroplating, the initial brake caliper is placed in an electroplating solution composed of 150 g / L nickel sulfate, 40 g / L ammonium sulfate, 30 g / L nickel chloride, and 140 g / L sodium citrate. The electroplating temperature is 50°C, the electroplating time is 10 minutes, and the electroplating rate is 3 A / dm². 2 Electroplating is performed under current density conditions to form a pre-plated nickel layer on the surface of the initial brake caliper.

[0125] Experimental Example 3

[0126] SEM images of the pre-plated nickel layer in Example 10 were acquired; for details, please refer to [link to relevant documentation]. Figure 10 As shown, through Figure 10 As can be seen, the surface of the pre-plated nickel layer is uniform and smooth, with no obvious voids or defects in its microstructure, meeting the requirements for a pre-plated layer. However, it is worth noting that pre-plating treatment incurs a higher cost compared to direct electroplating. Therefore, when performing surface treatment using Examples 1-4 and Examples 6-9, pre-plating nickel can be selectively performed on the surface of the initial brake caliper.

[0127] Comparative Example

[0128] A commercially available military-green Cd coating was used to compare its corrosion resistance with that of a zinc-nickel alloy coating prepared under the conditions of Example 3. The polarization curves were obtained and are shown below. Figure 11 As shown. (Through) Figure 11 It can be seen that the corrosion current density of the zinc-nickel alloy coating is slightly lower than that of the Cd coating, which means that the zinc-nickel alloy coating has better corrosion resistance than the Cd coating.

[0129] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for surface treatment of brake calipers, characterized in that, include: The brake caliper to be treated is immersed in the cleaning solution for 2-5 minutes to remove oil, and an initial brake caliper is obtained; the cleaning solution includes active ingredients and an aqueous solution, and the volume ratio of the active ingredients to the aqueous solution is 1:9; The initial brake caliper is placed in a single-anode electroplating device containing an electroplating solution, and an electroplating process is performed on the single-anode electroplating device to form a zinc-nickel alloy layer on the surface of the brake caliper, resulting in an intermediate brake caliper. The single-anode electroplating device includes a power supply, an anode, and a cathode. The anode is a zinc plate, and the cathode is the initial brake caliper. The current density of the electroplating process is 3~6A / dm2, the electroplating temperature is 10~40℃, and the electroplating time is 30min. The intermediate brake caliper after electroplating is placed in a passivation solution and passivated at 35°C for 40 seconds to obtain the target brake caliper. The passivation solution includes a base passivation solution and a complexing agent. The base passivation solution is a mixture of trivalent chromium passivation solution and anionic solution. The complexing agent is based on oxalic acid, and malonic acid and oxalic acid are mixed in a 1:2 ratio to form a composite complexing agent.

2. The brake caliper surface treatment method according to claim 1, characterized in that, The active ingredients include surfactants, detergent builders, and neutralizing fillers. The surfactants are mainly composed of a mixture of multi-branched isomeric tridecyl alcohol polyoxyethylene ether at a concentration of 2-4 g / L, a wetting agent at a concentration of 3-5 g / L, and sodium dodecylbenzenesulfonate at a concentration of 5-7 g / L.

3. The brake caliper surface treatment method according to claim 2, characterized in that, The detergent builder is mainly composed of a mixture of layered sodium metasilicate at a concentration of 2-5 g / L, sodium gluconate at a concentration of 1-3 g / L, and N,N-dicarboxymethylalanine at a concentration of 3-7 g / L.

4. The brake caliper surface treatment method according to claim 2, characterized in that, The neutralizing filler comprises Na2CO3 with a concentration of 22-30 g / L and Na2SO4 with a concentration of 2-4 g / L.

5. The brake caliper surface treatment method according to claim 2, characterized in that, The wetting agent is obtained by mixing tung oil acid and acetylenic diol polyoxyethylene ether at a molar ratio of 0.5 to 2:1 and reacting them under catalytic conditions and an inert atmosphere for 4 to 6 hours.

6. The brake caliper surface treatment method according to claim 5, characterized in that, The catalyst is p-toluenesulfonic acid, which accounts for 2% of the total mass of the catalytic reaction system.

7. The brake caliper surface treatment method according to claim 1, characterized in that, The basic passivation solution is Cr(NO3)3·9H2O with a concentration of 30~35 g / L; the anion solution includes CoSO4 with a concentration of 1~3 g / L, NaNO3 with a concentration of 2~7 g / L and Na2SO4 with a concentration of 10~14 g / L.

8. The brake caliper surface treatment method according to claim 7, characterized in that, The basic passivation solution includes Cr(NO3)3·9H2O with a concentration of 30~35 g / L, and also includes YbCl3·6H2O with a concentration of 0.3~3.0 g / L or SmCl3·6H2O with a concentration of 0.3~2.8 g / L added to Cr(NO3)3·9H2O.

9. The brake caliper surface treatment method according to claim 1, characterized in that, The electroplating solution is mainly composed of zinc chloride with a concentration of 45-55 g / L, nickel chloride hexahydrate with a concentration of 120-135 g / L, potassium chloride with a concentration of 180-210 g / L, and potassium acetate with a concentration of 35-45 g / L.

10. The brake caliper surface treatment method according to claim 1, characterized in that, The method further includes pre-plating the initial brake caliper before performing the electroplating process, specifically including: placing the initial brake caliper in a pre-plating solution at an electroplating temperature of 55°C, an electroplating time of 10 minutes, and an electroplating rate of 3A / dm. 2 Electroplating is performed under current density conditions, and the pre-plating solution includes 150 g / L nickel sulfate, 40 g / L ammonium sulfate, 30 g / L nickel chloride, and 140 g / L sodium citrate.

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