A method for plating cadmium on the surface of a screw pile and the prepared cadmium-plated screw pile

Abstract

The present application relates to the field of metal surface treatment, and specifically discloses a method for cadmium plating on the surface of a screw pile and a cadmium-plated screw pile obtained. The cadmium plating method comprises the following steps: S1, pre-treating the steel screw pile to obtain a pre-treated substrate; S2, electroplating the pre-treated substrate in a pre-plating solution containing Zn ions and In ions to form a Zn-In alloy pre-plating layer, and obtaining a pre-plated substrate; S3, drying the pre-plated substrate after cleaning the pre-plated substrate to obtain a substrate to be plated; S4, electroplating the substrate to be plated in a cyanide-free plating solution, and then cleaning and passivating to obtain a cadmium-plated screw pile; The present application also discloses a cadmium-plated screw pile obtained by the above method. The present application has the characteristics of improving the quality of the cadmium plating layer on the surface of the screw pile, further improving its corrosion resistance, and being more energy-saving and environmentally friendly.

Description

Technical Field

[0001] The present application relates to the field of metal surface treatment, and more specifically, to a method for cadmium plating on the surface of a screw pile and the prepared cadmium-plated screw pile. Background Art

[0002] Screw piles are widely used in the aerospace field, mainly used to connect various components to ensure the stability and reliability of the overall structure. For example, in aircraft engines, screw piles are used to connect key components such as compressor wheels and turbine blades. In structures such as fuselages and wings, screw piles are used to connect components such as frames. The quality and performance of screw piles are directly related to the overall performance and safety performance of aircraft, so there are strict requirements on the materials, structures and surface treatment of screw piles.

[0003] The aerospace field has extremely high requirements for the corrosion resistance of screw piles, because aircraft will be exposed to harsh environments such as high temperature, high pressure, high humidity, salt spray, etc. during flight. The cadmium plating layer can effectively improve the corrosion resistance of the bolts and extend their service life; the cadmium plating layer can also improve the lubrication performance of the bolts, reduce friction and wear during the connection process, and improve the connection efficiency; under certain conditions, the appearance of the cadmium plating layer is more beautiful than the zinc plating layer, and it is suitable for aerospace components with high requirements for surface quality.

[0004] At present, there are three main methods for electroplating cadmium: acid cadmium plating, cyanide cadmium plating and cyanide-free cadmium plating. Acid cadmium plating has low cost and simple operation, but poor all-plating ability and deep plating ability. It is only suitable for electroplating parts with simple shapes, and the electroplating effect is general. Although cyanide cadmium plating has good electroplating effect and is suitable for parts with complex shapes, the cadmium plating solution contains cyanide, which poses a great threat to the environment and human health. The waste gas and wastewater generated in the process need to be strictly treated, which increases the cost and difficulty of treatment. Cyanide-free cadmium plating eliminates the use of cyanide in traditional plating solutions, reduces environmental pollution and health risks, is more environmentally friendly, and is more suitable for screw pile applications in the aerospace field.

[0005] However, since aircraft will be exposed to harsh environments such as high temperature, high pressure, high humidity, salt spray, etc. during flight, higher requirements are placed on the quality of the coating, and a more uniform, dense, and corrosion-resistant coating needs to be obtained. Although there are some studies on cyanide-free cadmium plating, and compared with the traditional cyanide-containing cadmium plating process, the hydrogen embrittlement sensitivity of cyanide-free cadmium plating is usually lower. However, the diffusion and aggregation of cadmium atoms in the screw steel parts will change the internal structure of the steel, leading to brittle cracking and cadmium embrittlement. Therefore, it is necessary to further improve the coating quality, obtain better corrosion resistance and reduce cadmium embrittlement while being more environmentally friendly. Summary of the invention

[0006] In order to improve the quality of the cadmium plating layer on the surface of the screw pile, further improve its corrosion resistance, and at the same time be more energy-saving and environmentally friendly, the present application provides a method for cadmium plating on the surface of a screw pile and the prepared cadmium-plated screw pile.

[0007] In the first aspect, the present application provides a method for cadmium plating on the surface of a screw pile, which adopts the following technical solution:

[0008] A method for plating cadmium on the surface of a screw pile comprises the following steps:

[0009] S1. Pre-treating the steel screw pile to obtain a pre-treated substrate;

[0010] S2, electroplating the pretreated substrate in a preplating solution containing Zn ions and In ions to form a Zn-In alloy preplating layer to obtain a preplated substrate;

[0011] S3, cleaning the pre-plated substrate, activating it, and then drying it to obtain the substrate to be plated;

[0012] S4, electroplating cadmium on the substrate to be plated in a cyanide-free plating solution, and then cleaning and passivating the substrate to obtain a cadmium-plated screw pile.

[0013] By adopting the above technical scheme, in the present application, the bolts are first pre-plated to form a Zn-In alloy pre-plating layer before cadmium plating. On the one hand, as an intermediate layer, it has better chemical and physical compatibility with the steel screw pile substrate and the cadmium plating layer, and can form a close bond, thereby enhancing the adhesion between the cadmium plating layer and the steel substrate. In addition, during the electroplating of cadmium, the Zn-In alloy pre-plating layer can serve as a "skeleton" to make the cadmium plating layer more evenly deposited on the surface of the substrate, thereby improving the uniformity and density of the cadmium plating layer and reducing the formation of pores and defects. In addition, the Zn-In alloy pre-plating itself has high corrosion resistance and can serve as a barrier layer to protect the substrate from corrosion by corrosive media. In addition, the alloying effect of Zn and In can also improve the chemical stability of the coating, further improve the quality of the coating, and enhance its corrosion resistance.

[0014] On the other hand, since cadmium is a low-melting-point metal with a low diffusion activation energy, when the temperature exceeds three-quarters of the cadmium melting point of 322°C, the cadmium element penetrates into the grain boundaries of the steel by self-diffusion. The diffusion and aggregation of cadmium atoms in the steel will change the internal structure of the steel, making the screw pile more susceptible to brittle fracture when subjected to external forces, resulting in cadmium brittleness. The Zn-In alloy pre-plating layer in this application acts as a buffer layer, which can reduce the direct interaction between the cadmium plating layer and the steel screw pile substrate, reduce the diffusion and penetration of cadmium elements in the screw pile, and help reduce the risk of stress concentration and crack formation between the cadmium plating layer and the base layer. In addition, the Zn-In alloy pre-plating layer also has certain toughness and plasticity, which can absorb and disperse the stress inside the plating layer, further reduce the occurrence of cadmium brittleness, and ultimately improve the quality of the plating layer.

[0015] In addition, the pre-plating layer in the present application is also activated after being formed, which can further promote the bonding between the cadmium plating layer and the pre-plating substrate, and help to improve the bonding strength and corrosion resistance of the overall plating layer. The selection of cyanide-free plating solution in the present application can avoid the environmental pollution and safety impact caused by traditional cyanide-containing plating solutions, and the cyanide-free plating solution can also improve the uniformity and glossiness of the plating layer, improve the quality of the plating layer, and after the cadmium plating layer is formed, a passivation treatment is also performed to form a dense passivation film to improve the corrosion resistance and wear resistance of the plating layer.

[0016] Optionally, the pre-plating solution in step S2 includes the following raw materials:

[0017] 30-40 g / L zinc salt, 3-8 g / L indium salt, 20-30 g / L organic acid, 5-15 g / L ammonium borate, 0.05-0.1 g / L thiourea, 0.1-0.3 g / L sodium dodecyl sulfate and 0.2-0.5 g / L polyethylene glycol octylphenyl ether.

[0018] By adopting the above technical scheme, the above organic acid is used as an electrolyte and a buffer, so that the solution is more stable and the coating performance is improved. Ammonium borate is used as a conductive salt to improve the conductivity of the solution, which is more conducive to electroplating. Thiourea is used as an inhibitor to control the growth rate of the coating and improve the uniformity of the coating, which helps to obtain a uniform and dense coating. Moreover, as a stress reliever, it also helps to reduce the stress of the coating, improve the toughness of the coating and improve the cadmium brittleness. The addition of sodium dodecyl sulfate helps to improve the dispersibility and wettability of the plating solution and helps to obtain a uniform coating. The addition of polyethylene glycol octylphenyl ether can not only improve the uniformity of the current density distribution and help to obtain a coating with stable quality, but also inhibit the generation of hydrogen, reduce hydrogen bubbling, improve the quality of the coating, and change the crystal plane orientation of the coating to enhance the bonding force between the coating and the substrate.

[0019] Optionally, the pre-plating solution in step S2 is prepared by the following method:

[0020] The zinc salt and the indium salt are dissolved in water, and then organic acid, ammonium borate, sodium dodecyl sulfate and thiourea are added, and the pH value is adjusted to 4.5-5.5 to prepare a pre-plating solution.

[0021] Optionally, the organic acid is one or two of acetic acid, citric acid and tartaric acid.

[0022] By adopting the above technical scheme, the zinc salt in the above pre-plating solution provides zinc ions, the indium salt provides indium ions, and the alloying of Zn and In can form a tight bonding interface, improve the adhesion of the pre-plating layer, and help to improve the bonding with the substrate and the cadmium plating layer. In addition, the pre-plating layer formed is a Zn-In alloy, which has better chemical and physical compatibility with the substrate and the cadmium plating layer, and can form a tighter bonding interface.

[0023] Optionally, during the electroplating process in step S2, the electroplating temperature is 35-45° C., and the current density during electroplating is 1-2 A / dm².

[0024] Optionally, the specific operation of the activation treatment in step S3 is:

[0025] First, the pre-plated substrate in step S2 is immersed in a dilute sulfuric acid solution with a mass concentration of 5-10wt% for 60-90s and then dried to obtain an activated substrate;

[0026] Then the activated substrate is treated in a phosphating solution for 3-5 minutes at a treatment temperature of 35-45° C. The phosphating solution is prepared from the following raw materials in mass percentage: 10-20% zinc nitrate, 5-10% manganese nitrate, 25-40% phosphoric acid, 5-10% zinc oxide and the balance water.

[0027] By adopting the above technical scheme, in the present application, the pre-plated substrate is first treated in a dilute sulfuric acid solution to remove oxides and impurities on the surface of the pre-plated layer, while increasing the surface roughness and activity, and then it is subjected to phosphating treatment. The phosphating solution forms a dense protective film on the surface of the activated substrate, which can effectively prevent the direct contact between the corrosive medium and the metal matrix, thereby slowing down or preventing the occurrence of corrosion reactions. More importantly, a strong chemical bond and physical adsorption can be formed between the phosphoric acid film and the Zn-In alloy pre-plated layer, and the coordination between the phosphate ions and the indium ions forms a tighter bond. The formation of zinc phosphate and manganese phosphate in the phosphoric acid film can form a chemical reaction between zinc and cadmium and between phosphoric acid and cadmium in the subsequent cadmium electroplating process, thereby improving their binding ability, thereby improving the binding force between the cadmium plating layer and the substrate.

[0028] Optionally, when the activated substrate is treated in the phosphating solution, nitrogen gas is introduced into the phosphating solution, and the nitrogen gas introduction flow rate is 0.5-1 L / min.

[0029] By adopting the above technical scheme, when an inert gas is introduced into the phosphating solution, it is possible to effectively prevent the oxidation reaction between oxygen in the phosphating solution and the metal, thereby maintaining the stability of the phosphating solution, helping to reduce side reactions during the phosphating process, making the phosphating film formation more uniform and stable, and also helping the reaction in the phosphating solution and the effect on the substrate, reducing defects and impurities in the phosphating film, helping to regulate the microstructure of the phosphating film, thereby enhancing the bonding performance between the phosphating film and the substrate and the cadmium plating layer, and further improving the corrosion resistance of the coating.

[0030] Optionally, the cyanide-free plating solution in step S4 includes the following raw materials:

[0031] 35-50g / L cadmium chloride, 3-5g / L sodium stannate, 5-10g / L complexing agent, 3-8g / L brightener, 10-15g / L ammonium chloride, 10-20g / L sodium acetate.

[0032] By adopting the above technical scheme, cadmium chloride is used as the main element in the cyanide-free plating solution to provide cadmium ions required for electrodeposition. During the electroplating process, cadmium chloride ionizes cadmium ions in the aqueous solution. These ions move toward the cathode under the action of the electric field and are reduced and deposited on the cathode surface to form a coating. The addition of sodium stannate introduces the tin element, which can form an alloy coating with cadmium. The introduction of tin changes the preferred orientation and deposition type of the coating, which is beneficial to the release of hydrogen, further reduces hydrogen embrittlement, and further improves the cadmium embrittlement phenomenon. The addition of the complexing agent forms a stable complex with the cadmium ions to prevent the cadmium ions from being precipitated prematurely in the plating solution. The formed complex gradually releases cadmium ions during the electroplating process for reduction and deposition at the cathode.

[0033] The addition of brightener makes the coating brighter and smoother. The addition of ammonium chloride as a conductive salt improves the conductivity of the plating solution and promotes the electroplating process. Sodium acetate acts as a buffer to maintain the stability of the plating solution. The introduction of tin in the plating solution may form physical and chemical reactions with the phosphate film formed after phosphoric acid activation treatment. Combined with the electroplating parameter gap, it not only helps to improve the adhesion and durability of the coating, but also helps to disperse the stress in the coating, reduce the intergranular slip and dislocation of cadmium atoms, alleviate cadmium brittleness, and improve the quality of the coating.

[0034] Optionally, the complexing agent is one or more of nitrilotriacetic acid, ethylenediaminetetraacetic acid, citric acid, tartaric acid and 8-hydroxyquinoline.

[0035] Optionally, the complexing agent is selected from nitrilotriacetic acid, citric acid and 8-hydroxyquinoline in a mass ratio of 1: (0.2-0.3): (0.4-0.5).

[0036] Optionally, the cadmium electroplating operation in step S4 is specifically as follows:

[0037] The substrate to be plated obtained after the activation treatment in step S3 is first electroplated in a cyanide-free plating solution at a current density of 0.8-1 A / dm² and a plating tank temperature of 15-25°C for 20-30 minutes;

[0038] Then take it out and wash it in hot water at 50-60℃ for 1-2 minutes and dry it. Then continue to enter the cyanide-free plating solution for the second electroplating. The second electroplating current density is 1.2-1.5 A / dm², and the plating tank temperature is 25-35℃ for 10-20 minutes.

[0039] Then take it out and wash it in room temperature water for 1-2 minutes and then dry it. Then continue to electroplate it in the cyanide-free plating solution for the third time. During the third electroplating, add cadmium chloride to the cyanide-free plating solution to a concentration of 60-70g / L and sodium stannate to 8-12g / L. Then treat it at a current density of 0.8-1 A / dm² and a plating tank temperature of 20-30℃.

[0040] Then, the cadmium-plated screw pile is prepared by washing at 50-80°C for 1-3 minutes and then washing in room temperature water for 1-3 minutes, and then drying and passivation treatment are performed.

[0041] By adopting the above technical scheme, multiple electroplating is adopted when electroplating cadmium in the present application, and the electroplating current density, time and temperature are controlled during the process, so that the cadmium layer is deposited more evenly, and pores and defects are reduced. Compared with the pores and defects formed by a single electroplating that become the starting point of corrosion, the multiple cadmium plating in the present application improves the overall plating quality and further improves the corrosion resistance. In addition, the multiple electroplating in the present application can disperse the stress generated by a single electroplating and reduce the cadmium embrittlement caused by stress concentration. In addition, the cleaning and drying treatment after each electroplating helps to reduce the residual hydrogen in the coating, further reducing the cadmium embrittlement.

[0042] In a second aspect, the present application provides a cadmium-plated screw pile, which adopts the following technical solution:

[0043] A cadmium-plated screw pile is prepared by the method for plating cadmium on the surface of a screw pile.

[0044] By adopting the above-mentioned technical scheme, the coating of the cadmium-plated screw pile obtained by the method in the present application is denser and more uniform, the coating quality is better, and it has better corrosion resistance, which can meet the requirements of harsh environments such as high temperature, high pressure, high humidity, salt spray, etc. encountered during the flight of the aircraft. In addition, the cadmium embrittlement phenomenon will cause the toughness of the cadmium-plated screw pile to be significantly reduced, causing the screw pile to undergo brittle fracture when subjected to external force, especially in key components or components subjected to greater stress. Cadmium embrittlement will cause the screw pile to suddenly fail and cause safety accidents. The cadmium embrittlement phenomenon of the cadmium-plated screw pile obtained in the present application is significantly improved, thereby improving the reliability of the screw pile.

[0045] In summary, this application has the following beneficial effects:

[0046] 1. In the present application, before cadmium plating the bolts, the bolts are first pre-plated to form a Zn-In alloy pre-plating layer. On the one hand, as an intermediate layer, it has better chemical and physical compatibility with the steel screw pile substrate and the cadmium plating layer, and can form a close bond, thereby enhancing the adhesion between the cadmium plating layer and the steel substrate. In addition, during the electroplating of cadmium, the Zn-In alloy pre-plating layer can serve as a "skeleton" to make the cadmium plating layer more evenly deposited on the surface of the substrate, thereby improving the uniformity and density of the cadmium plating layer and reducing the formation of pores and defects. In addition, the Zn-In alloy pre-plating itself has high corrosion resistance and can serve as a barrier layer to protect the substrate from corrosion by corrosive media. In addition, the alloying effect of Zn and In can also improve the chemical stability of the coating, further improve the quality of the coating, and enhance its corrosion resistance.

[0047] 2. The Zn-In alloy pre-plating layer in the present application acts as a buffer layer, which can reduce the direct interaction between the cadmium plating layer and the steel screw pile substrate, reduce the diffusion and penetration of cadmium elements in the screw pile, and help reduce the risk of stress concentration and crack formation between the cadmium plating layer and the base layer. In addition, the Zn-In alloy pre-plating layer also has certain toughness and plasticity, which can absorb and disperse the stress inside the plating layer, further reduce the occurrence of cadmium embrittlement, and ultimately improve the quality of the plating layer;

[0048] 3. After the pre-plating layer is formed in the present application, it is also subjected to activation treatment, which can further promote the bonding between the cadmium plating layer and the pre-plating substrate, and help to improve the bonding strength and corrosion resistance of the overall plating layer. The selection of the cyanide-free plating solution in the present application can avoid the environmental pollution and safety impact caused by the traditional cyanide-containing plating solution, and the cyanide-free plating solution can also improve the uniformity and glossiness of the plating layer, improve the quality of the plating layer, and after the cadmium plating layer is formed, the passivation treatment is also performed to form a dense passivation film to improve the corrosion resistance and wear resistance of the plating layer.

[0049] 4. In the present application, multiple electroplating is adopted when electroplating cadmium, and the electroplating current density, time and temperature are controlled during the process, so that the cadmium layer is deposited more evenly, and pores and defects are reduced. Compared with the pores and defects formed by a single electroplating that become the starting point of corrosion, the multiple cadmium plating in the present application improves the overall coating quality and further improves the corrosion resistance. In addition, the multiple electroplating in the present application can disperse the stress generated by a single electroplating and reduce the cadmium embrittlement caused by stress concentration. In addition, the cleaning and drying treatment after each electroplating helps to reduce the residual hydrogen in the coating and further reduce the cadmium embrittlement. DETAILED DESCRIPTION

[0050] The present application is further described in detail below in conjunction with the examples. It is particularly noted that if no specific conditions are specified in the following examples, the experiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0051] The screw piles in the following embodiments are made of 30CrMnSiA alloy steel.

[0052] Example 1

[0053] 1. A method for plating cadmium on the surface of a screw pile, comprising the following steps:

[0054] S1. The steel screw pile is first preliminarily cleaned with deionized water to remove surface dust and impurities, and then degreased, washed and dried to obtain a pretreated substrate;

[0055] S2. Dissolve zinc sulfate and indium sulfate in water, then add acetic acid, ammonium borate and sodium dodecyl sulfate as well as thiourea and polyethylene glycol octylphenyl ether, adjust the pH value to 5, and prepare a pre-plating solution. The above raw materials are added in the following amounts:

[0056] 35 g / L zinc sulfate, 5 g / L indium sulfate, 25 g / L acetic acid, 10 g / L ammonium borate, 0.08 g / L thiourea, 0.2 g / L sodium dodecyl sulfate and 0.3 g / L polyethylene glycol octylphenyl ether;

[0057] Then, the pretreated substrate prepared in step S1 is electroplated in the preplating solution prepared above to form a Zn-In alloy preplating layer (the anode is a zinc plate with a zinc content of ≥99% and an indium content of ≥0.8%, and the anode and cathode area ratio is 1:2), the aqueduct temperature is 40°C, the current density during electroplating is 1A / dm², and a Zn-In alloy preplating layer with a thickness of 2μm is formed to obtain a preplated substrate;

[0058] S3, soaking the pre-plated substrate in a dilute sulfuric acid solution with a mass concentration of 8wt% for 75s and then drying to obtain an activated substrate;

[0059] The activated substrate is treated in a phosphating solution for 4 minutes at a treatment temperature of 40° C., and then the phosphating substrate is dried to obtain a substrate to be plated;

[0060] The phosphating solution is prepared from the following raw materials in percentage by weight: 15% zinc nitrate, 8% manganese nitrate, 30% phosphoric acid, 8% zinc oxide and the balance water;

[0061] S4, adding water to the aqueduct, and then preparing a cyanide-free plating solution according to the addition amount of 40g / L cadmium chloride, 4g / L sodium stannate, 8g / L complexing agent, 5g / L brightener, 12g / L ammonium chloride, and 15g / L sodium acetate, and finally adjusting the pH value of the cyanide-free plating solution to 6 by adding ammonium acetate, wherein the complexing agent is selected from nitrilotriacetic acid, citric acid and 8-hydroxyquinoline in a mass ratio of 1:0.2:0.4, and the brightener is selected from sodium methane disulfonate;

[0062] The substrate to be plated prepared in step S3 is first electroplated in a cyanide-free plating solution at a current density of 0.9 A / dm² and a plating bath temperature of 20° C. for 25 min;

[0063] Then take it out and wash it in hot water at 55℃ for 1min and then dry it. Then continue to enter the cyanide-free plating solution for the second electroplating. The second electroplating current density is 1.3 A / dm² and the plating tank temperature is 30℃ for 15min.

[0064] Then take it out and wash it in room temperature water for 1 minute and then dry it. Then continue to electroplate it for the third time in the cyanide-free plating solution. During the third electroplating, add cadmium chloride to the cyanide-free plating solution to a concentration of 65g / L and sodium stannate to 10g / L. Then treat it at a current density of 0.9A / dm² and a plating tank temperature of 25℃ to form a cadmium plating layer with a thickness of 9μm (total thickness after three electroplatings).

[0065] Then, the cadmium-plated screw pile is first cleaned at 65°C for 2 minutes and then cleaned in water at room temperature for 2 minutes, and then dried and passivated to obtain the cadmium-plated screw pile.

[0066] Example 2

[0067] 1. A method for plating cadmium on the surface of a screw pile, comprising the following steps:

[0068] S1. The steel screw pile is first preliminarily cleaned with deionized water to remove surface dust and impurities, and then degreased, washed and dried to obtain a pretreated substrate;

[0069] S2. Dissolve zinc sulfate and indium sulfate in water, then add acetic acid, ammonium borate and sodium dodecyl sulfate, thiourea and polyethylene glycol octylphenyl ether, adjust the pH value to 4.5, and prepare a pre-plating solution. The above raw materials are added in the following amounts:

[0070] 30 g / L zinc sulfate, 3 g / L indium sulfate, 20 g / L acetic acid, 5 g / L ammonium borate, 0.05 g / L thiourea, 0.1 g / L sodium dodecyl sulfate and 0.2 g / L polyethylene glycol octylphenyl ether;

[0071] Then, the pretreated substrate prepared in step S1 is electroplated in the pre-plating solution prepared above to form a Zn-In alloy pre-plating layer (the anode is a zinc plate with a zinc content of ≥99% and an indium content of ≥0.8%, and the anode and cathode area ratio is 1:2), the aqueduct temperature is 35°C, the current density during electroplating is 1A / dm², and a Zn-In alloy pre-plating layer with a thickness of 2μm is formed to obtain a pre-plated substrate;

[0072] S3, soaking the pre-plated substrate in a dilute sulfuric acid solution with a mass concentration of 5wt% for 90s and then drying to obtain an activated substrate;

[0073] Treat the activated substrate in a phosphating solution for 3 minutes at a temperature of 45°C, and then dry the phosphating substrate to obtain a substrate to be plated;

[0074] The phosphating solution is prepared from the following raw materials in percentage by weight: 10% zinc nitrate, 5% manganese nitrate, 25% phosphoric acid, 5% zinc oxide and the balance water;

[0075] S4, adding water to the aqueduct, and then preparing a cyanide-free plating solution according to the addition amount of 35g / L cadmium chloride, 3g / L sodium stannate, 5g / L complexing agent, 3g / L brightener, 10g / L ammonium chloride, and 10g / L sodium acetate, and finally adjusting the pH value of the cyanide-free plating solution to 6 by adding ammonium acetate, wherein the complexing agent is selected from nitrilotriacetic acid, citric acid and 8-hydroxyquinoline in a mass ratio of 1:0.2:0.4, and the brightener is selected from sodium methane disulfonate;

[0076] The substrate to be plated prepared in step S3 is first electroplated in a cyanide-free plating solution at a current density of 0.8 A / dm² and a plating bath temperature of 15° C. for 30 minutes;

[0077] Then take it out and wash it in hot water at 50℃ for 2 minutes and then dry it. Then continue to enter the cyanide-free plating solution for the second electroplating. The second electroplating current density is 1.2 A / dm² and the plating tank temperature is 25℃ for 20 minutes.

[0078] Then take it out and wash it in room temperature water for 1 minute and then dry it. Then continue to electroplate it for the third time in the cyanide-free plating solution. During the third electroplating, add cadmium chloride to the cyanide-free plating solution to a concentration of 60g / L and sodium stannate to 8g / L. Then treat it at a current density of 0.8A / dm² and a plating tank temperature of 20℃ to form a cadmium plating layer with a thickness of 8μm (total thickness after three electroplatings).

[0079] Then, the cadmium-plated screw pile is first cleaned at 50°C for 3 minutes and then cleaned in room temperature water for 1 minute, and then dried and passivated to obtain the cadmium-plated screw pile.

[0080] Example 3

[0081] 1. A method for plating cadmium on the surface of a screw pile, comprising the following steps:

[0082] S1. The steel screw pile is first preliminarily cleaned with deionized water to remove surface dust and impurities, and then degreased, washed and dried to obtain a pretreated substrate;

[0083] S2. Dissolve zinc sulfate and indium sulfate in water, then add acetic acid, ammonium borate, sodium dodecyl sulfate, thiourea and polyethylene glycol octylphenyl ether, adjust the pH value to 5.5, and prepare a pre-plating solution. The above raw materials are added in the following amounts:

[0084] 40 g / L zinc sulfate, 8 g / L indium sulfate, 30 g / L acetic acid, 15 g / L ammonium borate, 0.1 g / L thiourea, 0.3 g / L sodium dodecyl sulfate and 0.5 g / L polyethylene glycol octylphenyl ether;

[0085] Then, the pretreated substrate prepared in step S1 is electroplated in the preplating solution prepared above to form a Zn-In alloy preplating layer (the anode is a zinc plate with a zinc content of ≥99% and an indium content of ≥0.8%, and the anode and cathode area ratio is 1:2), the aqueduct temperature is 45°C, the current density during electroplating is 2A / dm², and a Zn-In alloy preplating layer with a thickness of 3μm is formed to obtain a preplated substrate;

[0086] S3, soaking the pre-plated substrate in a dilute sulfuric acid solution with a mass concentration of 10wt% for 90s and then drying to obtain an activated substrate;

[0087] Treat the activated substrate in a phosphating solution for 5 minutes at a temperature of 35° C., and then dry the phosphating substrate to obtain a substrate to be plated;

[0088] The phosphating solution is prepared from the following raw materials in percentage by weight: 20% zinc nitrate, 10% manganese nitrate, 40% phosphoric acid, 10% zinc oxide and the balance water;

[0089] S4, adding water to the aqueduct, and then preparing a cyanide-free plating solution according to the addition amount of 50g / L cadmium chloride, 5g / L sodium stannate, 10g / L complexing agent, 8g / L brightener, 15g / L ammonium chloride, and 20g / L sodium acetate, and finally adjusting the pH value of the cyanide-free plating solution to 7 by adding ammonium acetate, wherein the complexing agent is selected from nitrilotriacetic acid, citric acid and 8-hydroxyquinoline in a mass ratio of 1:0.3:0.5, and the brightener is selected from sodium methane disulfonate;

[0090] The substrate to be plated prepared in step S3 is first electroplated in a cyanide-free plating solution at a current density of 1 A / dm² and a plating bath temperature of 25° C. for 20 min;

[0091] Then take it out and wash it in hot water at 60℃ for 1min and then dry it. Then continue to enter the cyanide-free plating solution for the second electroplating. The second electroplating current density is 1.5 A / dm² and the plating tank temperature is 35℃ for 10min.

[0092] Then take it out and wash it in room temperature water for 2 minutes and then dry it. Then continue to electroplate it for the third time in the cyanide-free plating solution. During the third electroplating, add cadmium chloride to the cyanide-free plating solution to a concentration of 70g / L and sodium stannate to 12g / L. Then treat it at a current density of 1 A / dm² and a plating tank temperature of 30°C to form a cadmium plating layer with a thickness of 10μm (total thickness after three electroplatings).

[0093] Then, the cadmium-plated screw pile is first cleaned at 80°C for 1 minute and then cleaned in room temperature water for 3 minutes, and then dried and passivated to obtain the cadmium-plated screw pile.

[0094] Example 4

[0095] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that, when the activated substrate is treated in a phosphating solution in step S3, nitrogen is introduced into the phosphating solution at a flow rate of 0.8 L / min.

[0096] Example 5

[0097] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that, when the activated substrate is treated in a phosphating solution in step S3, nitrogen is introduced into the phosphating solution at a flow rate of 0.5 L / min.

[0098] Example 6

[0099] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that, when the activated substrate is treated in a phosphating solution in step S3, nitrogen is introduced into the phosphating solution at a flow rate of 1 L / min.

[0100] Example 7

[0101] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that no phosphating treatment is performed in step S3, and the activated substrate after activation treatment with dilute sulfuric acid is directly used as the substrate to be plated and step S4 is performed.

[0102] Example 8

[0103] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that sodium stannate is not added in step S4.

[0104] Example 9

[0105] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that an equal amount of sodium stannate in step S4 is replaced by titanium salt-titanyl sulfate.

[0106] Example 10

[0107] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that in step S4, the electroplating of the substrate to be plated in a cyanide-free plating solution is a one-time electroplating treatment, the electroplating density is 1 A / dm², the aqueduct temperature is 25°C, and the electroplating is performed until a cadmium plating layer with a thickness of 9 μm is formed, and then the substrate is first cleaned at 65°C for 2 minutes and then cleaned in room temperature water for 2 minutes, and then dried and passivated to obtain a cadmium-plated screw pile.

[0108] Embodiment 11

[0109] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that no manganese nitrate is added to the phosphating solution in step S3.

[0110] Example 12

[0111] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that in step S2, an equal amount of polyethylene glycol octylphenyl ether in the pre-plating solution is replaced by sodium dodecyl sulfate.

[0112] Comparative Example 1

[0113] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that steps S2 and S3 are not performed, and the pretreated substrate in step S1 is directly subjected to the cadmium electroplating operation in step S4.

[0114] Comparative Example 2

[0115] A method for plating cadmium on the surface of a screw pile is carried out according to the method in Example 1, except that indium sulfate is not added to the pre-plating solution in step S2.

[0116] Comparative Example 3

[0117] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that in step S2, an equal amount of indium sulfate in the pre-plating solution is replaced with nickel sulfate.

[0118] Comparative Example 4

[0119] A method for cadmium plating on the surface of a screw pile is carried out according to the method in Example 1, except that step S3 is not carried out, and the pre-plated substrate obtained in step S2 is directly subjected to step S4.

[0120] Performance Testing

[0121] The cadmium-plated screw piles prepared in the embodiment and the comparative example were subjected to a neutral salt spray test according to GB / T 10125-1997 "Artificial atmosphere corrosion test salt spray test" to detect the time for the cadmium plating layer to generate white rust or red corrosion products. In addition, with reference to JB2111-1977 "Test method for bonding strength of metal covering layer", the bonding strength of the coating was determined by a thermal shock test method. The plated parts were placed in a heating furnace and heated to 190°C, taken out and quenched in water at room temperature, and the coating was observed for bubbles and shedding. The above operation was repeated, and the number of cycles in which bubbles or shedding of the coating appeared was counted, and the bonding strength of the coating was observed. The test results are shown in Table 1 below.

[0122] Table 1:

[0123]

[0124] Referring to the test results in Table 1 above, the bonding force between the coating of the cadmium-plated screw piles prepared in the embodiment of the present application and the screw pile substrate is excellent. Referring to the test results of Examples 1 and 4-6, in Example 4, when the aeration treatment is performed during the phosphating treatment, the corrosion resistance of the cadmium-plated screw piles is improved, and its bonding force is further improved. The introduction of inert gas is helpful for the uniform stability of the phosphating film and the adjustment of the microstructure, and can serve as a better transition connection layer; combined with the test results of Example 7, in step S3, when the pre-plated substrate is only activated by sulfuric acid without phosphating treatment, the bonding force of the coating is reduced, and the corrosion resistance is also reduced. Referring to the test results in Examples 8 and 9, when tin or other elements are not introduced during cadmium electroplating, Due to the existence of cadmium embrittlement and hydrogen embrittlement, its corrosion resistance and bonding strength are also reduced; referring to the test results of Example 10, when the cadmium electroplating in Example 10 adopts a one-time electroplating, the quality of the coating is further reduced, thereby affecting its bonding strength and corrosion resistance. Combined with the test results of Example 12, when the polyethylene glycol octylphenyl ether in the pre-plating solution in step S2 is replaced with other surfactants, the penetration and electroplating performance of the pre-plating solution and the substrate are affected, and finally the bonding strength of the overall coating is reduced, and its corrosion resistance is also reduced. Referring to the test results of Example 11, when manganese nitrate is not added to the phosphating solution, the bonding force between the manganese element and the pre-plating layer and the cadmium plating layer is affected, and finally the bonding strength of the coating is reduced, and the corrosion resistance is also reduced.

[0125] Referring to the test results of Example 1 and Comparative Example 1, when the pre-plating and activation treatment are not performed, due to the cadmium embrittlement phenomenon, the bonding strength and corrosion resistance are significantly reduced. Combined with the test results of Comparative Example 2, when the indium element is not added to the pre-plating layer, the bonding strength and corrosion resistance are also low. Combined with the test results of Comparative Example 3, when the indium in the pre-plating layer is replaced with nickel, the corrosion resistance and bonding strength are improved compared with Comparative Example 2, but it is still weaker than Example 1. It may be due to the different effects of the above elements on the cadmium embrittlement phenomenon, which ultimately affects the quality of the coating. Combined with the test results of Comparative Example 4, the pre-plated substrate is directly subjected to cadmium electroplating without activation treatment, and its bonding strength and corrosion resistance are also significantly reduced.

[0126] In addition, the cadmium-plated screw piles in Example 1, Examples 8-10 and Comparative Examples 1-3 were used as test screw piles, and a universal testing machine was used to perform a tensile test on the cadmium-plated test screw piles and the untreated steel screw piles in step S1 as blank controls, and the breaking strength and elongation mechanical properties were tested. The test results are shown in Table 2 below.

[0127] Table 2:

[0128]

[0129] Referring to the test results in Table 2 above, the fracture strength of the cadmium-plated screw pile is significantly lower than that of the non-cadmium-plated screw pile, and the elongation is significantly reduced, so the surface cadmium-plated screw pile has a certain cadmium brittle phenomenon. Especially in Comparative Example 1 and Comparative Example 2, its brittle fracture can be observed, and the fracture presents a river-patterned mixed morphology. A large amount of metal cadmium can be observed along the crystal fracture zone at the edge of the fracture, and it has cadmium brittleness. When no tin element is added in Examples 8 and 9, and when a single electroplating method is used in Example 10, it can also be observed that there is a phenomenon of metal cadmium aggregation along the crystal fracture zone at the edge of the fracture, which is weakened compared to Comparative Example 1. It also has cadmium brittleness, but it is less severe than Comparative Example 1. It can be seen that the use of multiple electroplating and the introduction of indium and tin elements in this application helps to improve the cadmium brittleness phenomenon.

[0130] The cadmium content at the fracture is high and unevenly distributed, and there is an obvious interface between the fracture and the base metal. The surface cadmium element has penetrated into the base metal, which may cause cadmium embrittlement.

[0131] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for cadmium plating on the surface of a screw pile, characterized in that: The following steps are involved: S1. Cleaning, degreasing, washing and drying the steel screw piles to achieve pretreatment, thereby obtaining a pretreated substrate; S2, electroplating the pretreated substrate in a preplating solution containing Zn ions and In ions to form a Zn-In alloy preplating layer to obtain a preplated substrate; S3, cleaning the pre-plated substrate, activating it, and then drying it to obtain the substrate to be plated; S4, electroplating the substrate to be plated with cadmium in a cyanide-free plating solution, and then cleaning and passivating the substrate to obtain a cadmium-plated screw pile; The pre-plating solution in step S2 includes the following raw materials: 30-40 g / L zinc salt, 3-8 g / L indium salt, 20-30 g / L organic acid, 5-15 g / L ammonium borate, 0.05-0.1 g / L thiourea, 0.1-0.3 g / L sodium dodecyl sulfate and 0.2-0.5 g / L polyethylene glycol octylphenyl ether, the zinc salt is zinc sulfate, and the indium salt is indium sulfate; The specific operation of the activation treatment in step S3 is: First, the pre-plated substrate in step S2 is immersed in a dilute sulfuric acid solution with a mass concentration of 5-10wt% for 60-90s and then dried to obtain an activated substrate; Then the activated substrate is treated in a phosphating solution for 3-5 minutes at a treatment temperature of 35-45° C. The phosphating solution is prepared from the following raw materials in mass percentage: 10-20% zinc nitrate, 5-10% manganese nitrate, 25-40% phosphoric acid, 5-10% zinc oxide and the balance water; The cyanide-free plating solution in step S4 includes the following raw materials: 35-50g / L cadmium chloride, 3-5g / L sodium stannate, 5-10g / L complexing agent, 3-8g / L brightener, 10-15g / L ammonium chloride, 10-20g / L sodium acetate.

2. The method for cadmium plating on the surface of a screw pile according to claim 1, characterized in that: In step S2, the pre-plating solution is prepared by the following method: The zinc salt and the indium salt are dissolved in water, and then organic acid, ammonium borate, sodium dodecyl sulfate, thiourea and polyethylene glycol octylphenyl ether are added, and the pH value is adjusted to 4.5-5.5 to prepare a pre-plating solution.

3. The method for cadmium plating on the surface of a screw pile according to claim 1, characterized in that: The organic acid is selected from one or two of acetic acid, citric acid and tartaric acid.

4. The method for cadmium plating on the surface of a screw pile according to claim 1, characterized in that: During the electroplating process in step S2, the electroplating temperature is 35-45°C, and the electroplating is performed until a Zn-In alloy pre-plating layer with a thickness of 2 μm is formed. The current density during the electroplating is 1-2 A / dm².

5. The method for cadmium plating on the surface of a screw pile according to claim 1, characterized in that: The complexing agent is selected from one or more of nitrilotriacetic acid, ethylenediaminetetraacetic acid, citric acid, tartaric acid and 8-hydroxyquinoline.

6. The method for cadmium plating on the surface of a screw pile according to claim 1, characterized in that: The cadmium electroplating operation in step S4 is specifically as follows: The substrate to be plated obtained after the activation treatment in step S3 is first electroplated in a cyanide-free plating solution at a current density of 0.8-1 A / dm² and a plating tank temperature of 15-25°C for 20-30 minutes; Then take it out and wash it in hot water at 50-60℃ for 1-2 minutes and dry it. Then continue to enter the cyanide-free plating solution for the second electroplating. The second electroplating current density is 1.2-1.5 A / dm², and the plating tank temperature is 25-35℃ for 10-20 minutes. Then take it out and wash it in room temperature water for 1-2 minutes and then dry it, and then continue to electroplate it for the third time in the cyanide-free plating solution, and during the third electroplating, add cadmium chloride to the cyanide-free plating solution to a concentration of 60-70g / L, add sodium stannate to 8-12g / L, and then process it at a current density of 0.8-1 A / dm² and a plating tank temperature of 20-30℃ to form a cadmium plating layer with a total thickness of 8-10μm; Then, the cadmium-plated screw pile is prepared by washing at 50-80°C for 1-3 minutes, then washing at room temperature for 1-3 minutes, and then drying.

7. A cadmium-plated screw pile, characterized in that: The invention is prepared by the method for cadmium plating on the surface of a screw pile as claimed in any one of claims 1 to 6.

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