CN103451693A - Pulse electroplating method for alkaline zinc-nickel alloy with stable nickel content - Google Patents

Abstract

The invention belongs to the technical field of zinc-nickel alloy electroplating, and in particular relates to a zinc-nickel alloy pulse electroplating method with stable nickel content. The alkaline zinc-nickel alloy pulse electroplating method with stable nickel content of the present invention comprises the following steps: (1) preparing an alkaline zinc-nickel alloy electroplating solution, (2) substrate pretreatment, (3) pulse alkaline zinc-nickel alloy electroplating, (4) Wastewater recycling and cleaning coating. Compared with DC electroplating zinc-nickel alloy, pulse electroplating has the characteristics of fine crystallization of coating, stable nickel content, low stress, low porosity, excellent corrosion resistance, etc., and achieves true alloy electroplating.

Description

A kind of alkaline zinc-nickel alloy pulse electroplating method with stable nickel content

technical field

The invention belongs to the technical field of zinc-nickel alloy electroplating, and in particular relates to a zinc-nickel alloy pulse electroplating method with stable nickel content. the

Background technique

Electroplating zinc-nickel alloy is an anode-type protective coating on steel substrates that emerged in the 1980s. It usually refers to low-nickel-content alloys with a nickel content of less than 20%. Such alloy coatings not only have corrosion resistance 7-10 times higher than galvanized coatings, but also have low hydrogen embrittlement, good paintability, weldability and Formability, so it is widely used in steel protection such as automobiles, aerospace, light industry, and home appliances. As far as automotive components using zinc-nickel alloy plating are concerned, they have been standardized in the design drawings of some European and American countries, and their application range is wider in Japan. However, our country started relatively late, and relevant research reports were only available in the 1990s. It was only in recent years that it was put into production, and problems continued to appear in the production process. a major obstacle to development.

At present, the types of zinc-nickel alloy plating solutions are mainly divided into acidic and alkaline systems.

The current efficiency of acid zinc-nickel alloy electroplating is over 90%, the deposition speed of the coating is fast, up to over 1μm/min, the production and operation costs are low, and the color is bright. However, the throwing ability of the plating solution is poor, the thickness distribution is uneven, and the nickel content in the coating in the high and low current density areas of the workpiece varies greatly; the composition of the plating solution changes greatly, and the components need to be analyzed and adjusted at any time, especially the solution. acidity. Among them, patents CN201110362502.5 , CN200910094368.8 , and CN200680028815.4 involve the formulation and process of acidic zinc-nickel alloy electroplating, and the power sources used are DC.

Alkaline zinc-nickel alloy electroplating has the advantages of good throwing ability, relatively uniform coating thickness distribution, relatively uniform alloy coating in a large current density range, and easy process operation. As this process can ensure uniform nickel content in different current density areas in the initial stage of use, but with the continuous extension of the production cycle, the nickel content in the alloy coating shows a downward trend, and there is only zinc in the final deposited layer, which restricts zinc and nickel. Alloy electroplating can continue to develop and the main problem of large-scale industrialization. To solve this problem, the current main research focus is on the optimization of the formula components of the alkaline plating solution, among which patents CN94100815.0, CN02142485.3, CN200510086235.8, CN200810120050.8, CN201010501430.3, CN201110424916.6, CN201210109208 .8 It involves the formula of alkaline zinc-nickel alloy electroplating solution, and the process adopted is direct current electroplating.

Compared with DC electroplating, pulse electroplating has many advantages. Through the adjustment of pulse parameters such as pulse width, period and duty cycle, low porosity, fine crystallization, low stress, low hydrogen embrittlement, good coating adhesion and corrosion resistance can be obtained. Electrodeposited layer with excellent properties, and pulse electroplating can also reduce concentration polarization and increase the current density of the cathode, thereby achieving the effect of increasing the plating speed. Pulse electroplating has long been used in precious metals. In recent years, it has also been widely used in acid copper plating. However, there are few reports on zinc-nickel alloy electrodeposition technology, and there are no patent reports on zinc-nickel alloy pulse plating.

Contents of the invention

The object of the present invention is to utilize the advantages of the pulse electroplating technology to provide a method for pulse electroplating a zinc-nickel alloy in an alkaline system. Solve the problem of unstable nickel content in the coating, and at the same time achieve grain refinement, reduce the stress of the coating, and improve the corrosion resistance of the coating. The method belongs to the field of pulse electroplating, adopts single pulse electroplating technology, and realizes the above object by changing various process parameters of pulse electroplating.

The present invention is achieved through the following technical solutions:

A kind of alkaline zinc-nickel alloy pulse electroplating method with stable nickel content comprises the following steps:

(1) Preparation of alkaline zinc-nickel alloy electroplating solution: The composition of the prepared alkaline zinc-nickel alloy electroplating solution is as follows: 10g zinc oxide, 80g sodium hydroxide, 15g nickel sulfate hexahydrate, 15ml ethylene glycol Amine, 10ml tetraethylenepentamine, 30g sodium potassium tartrate, 10g sodium citrate, 40ml triethanolamine, 1.5 ml OP-10, 0.5 g vanillin;

(2) Substrate pretreatment: first, immerse and derust the substrate, and then electrolytically degrease the substrate until it is completely removed; after the degreasing is completed, wash it with hot water at 50~60°C, and then clean it with flowing pure water; Finally, impregnate and activate the substrate with 3-5% hydrochloric acid solution at room temperature. The activation time is 30-60s. After the activation is completed, it is washed with pure water to complete the pretreatment;

(3) Pulse alkaline zinc-nickel alloy electroplating: first add the alkaline zinc-nickel alloy electroplating solution prepared in step (1) into the electroplating tank, then connect the pretreated substrate to the cathode of the pulse power supply, and the anode is made of stainless steel plate , and then put it into the electroplating tank as a whole, and conduct pulse alloy electroplating at room temperature, wherein the pulse process conditions are: average current density 0.72~5.45A/dm ² , pulse width 100~1000μs, cycle 1000~9000μs;

(4) Waste water recycling and cleaning of the coating: After step (3) is completed, the alkaline plating solution is recycled for wastewater, and the coating is cleaned with distilled water to obtain the product.

OP-10 is a nonionic surfactant, a kind of alkylphenol polyoxyethylene ether.

The above-mentioned alkaline zinc-nickel alloy pulse electroplating method with stable nickel content, the specific steps of preparing the alkaline zinc-nickel alloy electroplating solution in the step (1) are as follows: firstly stir the weighed sodium hydroxide and zinc oxide evenly , add 1/5 of the total volume of the plating solution in distilled water to dissolve, and fully stir to dissolve until the solution is clear and transparent, then dilute to 1/3 of the total volume, this solution is the No. 1 solution; then add the weighed nickel sulfate hexahydrate Dissolve with potassium sodium tartrate and sodium citrate respectively, then mix, stir thoroughly, then add weighed ethylenediamine, tetraethylenepentamine and triethanolamine, stir and mix evenly, this solution is No. 2 solution, and finally No. 2 Slowly add the solution to No. 1 solution, stir while adding, then add vanillin and OP-10 until the plating solution is uniform and transparent blue-purple, dilute to the total volume and set aside.

In the above-mentioned alkaline zinc-nickel alloy pulse electroplating method with stable nickel content, the base material described in step (2) is a component that is not easy to evolve hydrogen, and the step of dipping and derusting is to use pickling at a temperature of 30-40°C After the rust is removed, it is washed with 2 cold waters; then the substrate is electrolytically degreased, and degreased with a degreasing agent at a temperature of 70-80°C, with a current density of 5-10A/dm ^2. The ratio of degreasing time between cathode and anode is 20:1 until it is completely removed.

Parts that are not prone to hydrogen evolution refer to parts with uniform metallographic structure, smooth surface, no oil stains, and easy to apply metal coating. Common parts that are not easy to evolve hydrogen are usually made of high hydrogen evolution overpotential metals (such as Pb, Cd, Zn, Sn) or as parts of the surface layer, and steel parts made of low carbon steel and low alloy steel are compared with other components As far as steel is concerned, it can be considered as a component that is not prone to hydrogen evolution.

In the above-mentioned alkaline zinc-nickel alloy pulse electroplating method with stable nickel content, the base material described in step (2) is a hydrogen-evolving component, and the step of dipping and derusting is to use a pickling agent at a temperature of 30-40°C Carry out corrosion and derusting, after the rust is removed, wash it with 2 cold waters; then conduct electrolytic degreasing on the substrate, degreasing with a degreasing agent at a temperature of 70-80°C, with a current density of 5-10A/dm ² , only anode degreasing is carried out until it is completely removed.

Parts prone to hydrogen evolution refer to parts with uneven metallographic structure, rough surface, high stress or oily surface, such as spring steel (high carbon steel), high alloy steel, welded parts, riveted parts, cast iron, thin-walled parts, etc.

In the above-mentioned alkaline zinc-nickel alloy pulse plating method with stable nickel content, the pickling agent in step (2) includes hydrochloric acid solution with a mass concentration of 15% to 20%, and 0.5 to 5 g/L urotropine.

In the above-mentioned alkaline zinc-nickel alloy pulse electroplating method with stable nickel content, the degreasing agent described in step (2) includes 20 g of sodium hydroxide, 20 g of sodium carbonate, 20 g of sodium phosphate, and 3 g of sodium silicate per liter of the degreasing agent. , and the balance is water.

Preferably, in the above-mentioned alkaline zinc-nickel alloy pulse plating method with stable nickel content, the pulse process conditions in step (3) are: average current density 1~3A/dm ² , pulse width 100~500μs, period 1000μs~5000μs .

More preferably, in the above-mentioned alkaline zinc-nickel alloy pulse plating method with stable nickel content, the pulse process conditions in step (3) are: average current density 2~2.5A/dm ² , pulse width 100~300μs, cycle 1000μs ~3000μs.

The beneficial effects of the present invention are: compared with direct current zinc-nickel alloy plating, pulse electroplating has the characteristics of fine crystallization of the coating, stable nickel content, low stress, low porosity, and excellent corrosion resistance, so as to achieve real alloy electroplating, Provide technical support for the sustainable development of zinc-nickel alloy electroplating industrial production.

The following will describe in detail by comparing the specific experimental results of the pulse electroplating method of the present invention and the direct current electroplating method.

When adopting the pulse process conditions of the zinc-nickel alloy electroplating method of the present invention, the average current density is 2.5A/ ^dm2 , the pulse width is 100μs, and the cycle is 1000μs, and the alloy coating obtained after electroplating at room temperature for 10min and the cathodic current density under DC conditions are 2.5A/dm ^2. The comparison of the alloy coatings obtained by electroplating at room temperature for 10 minutes is shown in Table 1 below.

Table 1: Comparison of Results

project Average porosity (pcs/cm ² ) Plating adhesion Microscopic morphology Self-corrosion potential (V) Pulse Plating 0 meet the requirements fine grains, uniform -0.765 DC plating 11 slight peeling Larger grains with cracks -0.816

The scanning electron microscope pictures of the zinc-nickel alloy plating layer under pulse and direct current plating are shown in Figure 1-2, where Figure 1 is the SEM morphology of the pulse plating layer surface, and Figure 2 is the SEM morphology of the DC plating layer surface,

From the comparison of Figure 1 and Figure 2, it can be seen that the crystals obtained under the pulse condition are finer, the crystal distribution is uniform, and there is no crack, which is the main reason for its enhanced corrosion resistance. However, the grains of the coating obtained under DC electroplating are relatively coarse, the distribution is relatively uneven, and there are obvious cracks and transgranular fractures, indicating that the coating stress under DC electroplating is greater, which is the reason for the decline in its corrosion resistance.

An alkaline zinc-nickel alloy pulse electroplating method with stable nickel content of the present invention belongs to zinc-nickel alloy electroplating. The present invention changes the traditional direct current electroplating method and adopts single pulse technology to realize co-deposition of zinc-nickel alloy by changing the pulse power supply A series of parameters are used to obtain a zinc-nickel alloy coating with good bonding force, low stress, low porosity, and fine crystallization. Replacing DC electroplating with pulse electroplating has obvious advantages in improving coating performance.

Description of drawings

Fig. 1 is the surface morphology of zinc-nickel alloy coating under scanning electron microscope in the specific embodiment of the present invention;

Figure 2 is the surface morphology of the direct current electroplated zinc-nickel alloy coating under a scanning electron microscope.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited thereby.

Example 1

(1) Preparation of alkaline zinc-nickel alloy plating solution: First, weigh 10g of zinc oxide, 80g of sodium hydroxide, 15g of nickel sulfate hexahydrate, 15ml of ethylenediamine, 10ml of tetraethylenepentamine, 30g of potassium sodium tartrate, and 10g of lemon sodium nitrate, 40ml triethanolamine, 1.5ml nonionic surfactant, 0.5g vanillin. Stir the weighed sodium hydroxide and zinc oxide evenly, add 1/5 of the total volume of the plating solution in distilled water to dissolve, and stir to dissolve until the solution is clear and transparent, then dilute to 1/3 of the total volume, this solution is 1 No. solution; then dissolve the weighed nickel sulfate hexahydrate, potassium sodium tartrate, and sodium citrate respectively, then mix and stir thoroughly, then add the weighed ethylenediamine, tetraethylenepentamine and triethanolamine, stir and mix Evenly, this solution is No. 2 solution. Finally, slowly add No. 2 solution into No. 1 solution, stir while adding, then add vanillin and non-ionic surfactant OP-10, until the plating solution is uniform and transparent blue-purple , diluted to the total volume for later use;

(2) Substrate pretreatment: The substrate material is low-carbon steel. Firstly, the substrate is dipped and derusted, and then etched and derusted with pickling agent at a temperature of 30-40°C. The pickling agent used includes 20% (mass fraction) Hydrochloric acid solution, 0.5g/L urotropine, after the rust is removed, it is washed with 2 cold waters; then the substrate is electrolytically degreased, and degreased with a degreasing agent at a temperature of 70-80°C. The degreasing agent per liter includes 20g of sodium hydroxide, 20g of sodium carbonate, 20g of sodium phosphate, and 3g of sodium silicate. The current density is 5~10A/dm ² . So far, after the degreasing is completed, wash it with hot water at 50~60℃, and then wash it with flowing pure water; finally, use 3% (mass fraction) hydrochloric acid solution at room temperature to impregnate and activate the substrate, and the activation time is 30~60s. After the activation is completed, wash with water, and the pretreatment is completed;

(3) Pulse alkaline zinc-nickel alloy electroplating: first add the alkaline electrolyte prepared in step (1) into the electroplating tank, then connect the pretreated substrate to the cathode of the pulse power supply, and use a stainless steel plate as the anode. Then the whole is put into the electroplating tank, and the pulse alloy electroplating is carried out at room temperature. The pulse process conditions are: average current density 2.5A/dm ² , pulse width 100μs, period 1000μs, electroplating 10min.

(4) Waste water recycling and cleaning of the coating: After step (3) is completed, the alkaline plating solution is recycled for wastewater, and the coating is cleaned with distilled water to obtain the product.

Example 2

(1) Preparation of alkaline zinc-nickel alloy plating solution: First, weigh 10g of zinc oxide, 80g of sodium hydroxide, 15g of nickel sulfate hexahydrate, 15ml of ethylenediamine, 10ml of tetraethylenepentamine, 30g of potassium sodium tartrate, and 10g of lemon sodium nitrate, 40ml triethanolamine, 1.5ml nonionic surfactant, 0.5g vanillin. Stir the weighed sodium hydroxide and zinc oxide evenly, add 1/5 of the total volume of the plating solution in distilled water to dissolve, and stir to dissolve until the solution is clear and transparent, then dilute to 1/3 of the total volume, this solution is 1 No. solution; then dissolve the weighed nickel sulfate hexahydrate, potassium sodium tartrate, and sodium citrate respectively, then mix and stir thoroughly, then add the weighed ethylenediamine, tetraethylenepentamine and triethanolamine, stir and mix Evenly, this solution is No. 2 solution. Finally, slowly add No. 2 solution into No. 1 solution, stir while adding, then add vanillin and non-ionic surfactant OP-10, until the plating solution is uniform and transparent blue-purple , diluted to the total volume for later use;

(2) Substrate pretreatment: The substrate material is spring steel. Firstly, impregnate and derust the substrate, and then use pickling agent to etch and remove rust at a temperature of 30-40°C. The pickling agent used includes 15% (mass fraction) hydrochloric acid Solution, 5g/L urotropine, after the rust is removed, it is washed with 2 cold waters; then the substrate is electrolytically degreased, and degreased with a degreasing agent at a temperature of 70-80°C. The degreasing agent used is Each liter of degreasing agent includes 20g of sodium hydroxide, 20g of sodium carbonate, 20g of sodium phosphate, and 3g of sodium silicate. The current density is 5~10A/dm ² . First wash with hot water at 50~60℃, and then wash with flowing pure water; finally, impregnate and activate the substrate with 5% (mass fraction) hydrochloric acid solution at room temperature, the activation time is 30~60s, wash with water after activation, and pretreat Finish;

(3) Pulse alkaline zinc-nickel alloy electroplating: first add the alkaline electrolyte prepared in step (1) into the electroplating tank, then connect the pretreated substrate to the cathode of the pulse power supply, and use a stainless steel plate as the anode. Then the whole is put into the electroplating tank, and the pulse alloy electroplating is carried out at room temperature. The pulse process conditions are: average current density 2A/dm ² , pulse width 100μs, cycle 1000μs, electroplating 15min;

(4) Waste water recycling and cleaning of the coating: After step (3) is completed, the alkaline plating solution is recycled for wastewater, and the coating is cleaned with distilled water to obtain the product.

Example 3

(1) Preparation of alkaline zinc-nickel alloy plating solution: First, weigh 10g of zinc oxide, 80g of sodium hydroxide, 15g of nickel sulfate hexahydrate, 15ml of ethylenediamine, 10ml of tetraethylenepentamine, 30g of potassium sodium tartrate, and 10g of lemon sodium nitrate, 40ml triethanolamine, 1.5ml nonionic surfactant, 0.5g vanillin. Stir the weighed sodium hydroxide and zinc oxide evenly, add 1/5 of the total volume of the plating solution in distilled water to dissolve, and stir to dissolve until the solution is clear and transparent, then dilute to 1/3 of the total volume, this solution is 1 No. solution; then dissolve the weighed nickel sulfate hexahydrate, potassium sodium tartrate, and sodium citrate respectively, then mix and stir thoroughly, then add the weighed ethylenediamine, tetraethylenepentamine and triethanolamine, stir and mix Evenly, this solution is No. 2 solution. Finally, slowly add No. 2 solution into No. 1 solution, stir while adding, then add vanillin and non-ionic surfactant OP-10, until the plating solution is uniform and transparent blue-purple , diluted to the total volume for later use;

(2) Substrate pretreatment: The substrate material is a thin-walled part. Firstly, the substrate is dipped and derusted, and the pickling agent is used for etching and derusting at a temperature of 30-40°C. The pickling agent used includes 18% (mass fraction) Hydrochloric acid solution, 2.5g/L urotropine, after the rust is removed, it is washed with 2 cold waters; then the substrate is electrolytically degreased, and degreased with a degreasing agent at a temperature of 70-80°C. The degreasing agent per liter includes 20g of sodium hydroxide, 20g of sodium carbonate, 20g of sodium phosphate, and 3g of sodium silicate. The current density is 5~10A/dm ² . After completion, wash with hot water first, and then wash with flowing pure water; finally, impregnate and activate the substrate with 4% (mass fraction) hydrochloric acid solution at room temperature, the activation time is 30-60s, wash with water after activation, and the pretreatment is complete;

(3) Pulse alkaline zinc-nickel alloy electroplating: first add the alkaline electrolyte prepared in step (1) into the electroplating tank, then connect the pretreated substrate to the cathode of the pulse power supply, and use a stainless steel plate as the anode. Then the whole is put into the electroplating tank, and the pulse alloy electroplating is carried out at room temperature. The pulse process conditions are: average current density 2.5A/dm ² , pulse width 200μs, cycle 2000μs, electroplating 10min;

(4) Waste water recycling and cleaning of the coating: After step (3) is completed, the alkaline plating solution is recycled for wastewater, and the coating is cleaned with distilled water to obtain the product.

Example 4

Steps The pulse process conditions in pulse alkaline zinc-nickel alloy electroplating are: average current density 2A/dm ² , pulse width 200μs, cycle 2000μs, electroplating 15min. Other steps are identical with embodiment 1.

Example 5

Steps The pulse process conditions in pulse alkaline zinc-nickel alloy electroplating are: average current density 2.5A/dm ² , pulse width 300μs, cycle 3000μs, electroplating 10min. Other steps are identical with embodiment 1.

Example 6

Steps The pulse process conditions in pulse alkaline zinc-nickel alloy electroplating are: average current density 2A/dm ² , pulse width 300μs, cycle 3000μs, electroplating 15min. Other steps are identical with embodiment 1.

Example 7

Steps The pulse process conditions in pulse alkaline zinc-nickel alloy electroplating are: average current density 0.7A/dm ² , pulse width 1000μs, period 9000μs, electroplating 15min. Other steps are identical with embodiment 1.

Example 8

Steps The pulse process conditions in pulse alkaline zinc-nickel alloy electroplating are: average current density 5A/dm ² , pulse width 100μs, cycle 1000μs, electroplating 15min. Other steps are identical with embodiment 1.

Example 9

Steps The pulse process conditions in pulse alkaline zinc-nickel alloy electroplating are: average current density 3A/dm ² , pulse width 500μs, cycle 5000μs, electroplating 15min. Other steps are identical with embodiment 1.

Example 10

Steps The pulse process conditions in pulse alkaline zinc-nickel alloy electroplating are: average current density 4A/dm ² , pulse width 700μs, cycle 7000μs, electroplating 15min. Other steps are identical with embodiment 1.

The above method changes the structure of the coating to make the coating smooth, fine and bright; reduces the porosity and stress of the coating and realizes the stability of nickel content.

Although the specific implementation of the present invention has been described above, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art can do it without creative work. Various modifications or deformations are still within the protection scope of the present invention.

Claims (8)

1. an alkaline zinc-nickel alloy pulse electroplating method with stable nickel content, comprising the following steps: (1) Preparation of alkaline zinc-nickel alloy electroplating solution: The composition of the prepared alkaline zinc-nickel alloy electroplating solution is as follows: 10g zinc oxide, 80g sodium hydroxide, 15g nickel sulfate hexahydrate, 15ml ethylene glycol Amine, 10ml tetraethylenepentamine, 30g sodium potassium tartrate, 10g sodium citrate, 40ml triethanolamine, 1.5 ml OP-10, 0.5 g vanillin; (2) Substrate pretreatment: first, immerse and derust the substrate, and then electrolytically degrease the substrate until it is completely removed; after the degreasing is completed, wash it with hot water at 50~60°C, and then clean it with flowing pure water; Finally, impregnate and activate the substrate with 3-5% hydrochloric acid solution at room temperature. The activation time is 30-60s. After the activation is completed, it is washed with pure water to complete the pretreatment; (3) Pulse alkaline zinc-nickel alloy electroplating: first add the alkaline zinc-nickel alloy electroplating solution prepared in step (1) into the electroplating tank, then connect the pretreated substrate to the cathode of the pulse power supply, and the anode is made of stainless steel plate , and then put it into the electroplating tank as a whole, and conduct pulse alloy electroplating at room temperature, wherein the pulse process conditions are: average current density 0.72~5.45A/dm ² , pulse width 100~1000μs, cycle 1000~9000μs; (4) Waste water recycling and cleaning of the coating: After step (3) is completed, the alkaline plating solution is recycled for wastewater, and the coating is cleaned with distilled water to obtain the product. 2. the alkaline zinc-nickel alloy pulse electroplating method with stable nickel content according to claim 1, characterized in that, the specific steps of preparing the alkaline zinc-nickel alloy electroplating solution in the step (1) are as follows: first weigh the Stir the well-measured sodium hydroxide and zinc oxide evenly, add 1/5 of the total volume of the plating solution in distilled water to dissolve, and stir to dissolve until the solution is clear and transparent, then dilute to 1/3 of the total volume, this solution is No. 1 solution Dissolve the weighed nickel sulfate hexahydrate, potassium sodium tartrate and sodium citrate respectively, then mix and fully stir, then add the weighed ethylenediamine, tetraethylenepentamine and triethanolamine, stir and mix evenly, This solution is No. 2 solution. Finally, slowly add No. 2 solution into No. 1 solution, stir while adding, then add vanillin and OP-10, until the plating solution is uniform and transparent blue-purple, dilute to the total volume stand-by. 3. The alkaline zinc-nickel alloy pulse electroplating method with stable nickel content according to claim 2, characterized in that the base material described in step (2) is a component that is not prone to hydrogen evolution, and the step of dipping and derusting is: Use pickling agent to etch and remove rust at a temperature of 30-40°C, and wash it with 2 passes of cold water after the rust is removed; For oil, the current density is 5~10A/dm ² , and the time ratio of cathode and anode degreasing is 20:1 until it is completely removed. 4. The alkaline zinc-nickel alloy pulse electroplating method with stable nickel content according to claim 2, characterized in that the base material described in step (2) is a hydrogen-evolving component, and the step of dipping and derusting is, Use pickling agent to etch and remove rust at a temperature of 30-40°C, and wash it with 2 passes of cold water after the rust is removed; For oil, the current density is 5~10A/dm ² , only the anode degreasing is performed until it is completely removed. 5. The alkaline zinc-nickel alloy pulse electroplating method with stable nickel content according to claim 1, characterized in that the pickling agent in step (2) includes hydrochloric acid solution with a mass concentration of 15% to 20%, 0.5 ~5g/L urotropine. 6. The alkaline zinc-nickel alloy pulse electroplating method with stable nickel content according to claim 1, characterized in that the degreasing agent in step (2) includes 20 g of sodium hydroxide per liter of degreasing agent, sodium carbonate 20g, sodium phosphate 20g, sodium silicate 3g, and the balance is water. 7. The alkaline zinc-nickel alloy pulse plating method with stable nickel content according to claim 1, characterized in that the pulse process conditions in step (3) are: average current density 1~3A/dm ² , pulse width 100 ~500μs, cycle 1000μs~5000μs. 8. The alkaline zinc-nickel alloy pulse plating method with stable nickel content according to claim 5, characterized in that the pulse process conditions in step (3) are: average current density 2~2.5A/dm ² , pulse width 100~300μs, cycle 1000μs~3000μs.

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