Environment-friendly de-zincing agent for aluminum alloy electroplating and de-zincing process

Abstract

The present application relates to the technical field of aluminum alloy surface treatment, and particularly relates to an environmentally-friendly zinc removal agent for aluminum alloy electroplating and a zinc removal process, wherein the zinc removal agent comprises a zinc removal main agent and an acidity regulator; the zinc removal main agent does not contain ammonium salt, nitrate, chloride ion and fluoride ion, and can selectively dissolve the zinc layer on the surface of the aluminum alloy. The zinc removal process comprises the steps of pretreatment, micro-current assisted environmentally-friendly zinc removal and post-treatment. The zinc removal agent of the present application does not contain the four harmful ions of ammonium salt, nitrate, chloride ion and fluoride ion, so that no toxic and harmful gas is generated during use, the workshop operation environment is greatly improved, and the health of the operators is protected. Meanwhile, the waste liquid has simple components, is free of phosphorus, fluoride and strong oxidizing pollutants, the difficulty and cost of waste water treatment are significantly reduced, and the present application has good environmental protection performance.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy surface treatment technology, and in particular to an environmentally friendly zinc stripping agent and zinc stripping process for aluminum alloy electroplating. Background Technology

[0002] Aluminum alloys possess advantages such as light weight, excellent electrical and thermal conductivity, and ease of forming, making them widely used in various hardware and electronic component fields. However, aluminum alloy surfaces readily form a dense oxide film, which can lead to poor adhesion, peeling, and flaking when directly electroplated. Therefore, the industry commonly employs a pretreatment process involving two stages of zinc plating and dezincification: first, a first zinc layer is deposited on the aluminum alloy surface, then this zinc layer is removed through a dezincification process, followed by a second zinc plating stage. This process yields a thin and uniform zinc substrate, ensuring the adhesion of subsequent copper, silver, and other plating layers.

[0003] Currently, most traditional zinc removal agents on the market contain components such as ammonium salts, nitrates, chloride ions, and fluoride ions, which have significant drawbacks.

[0004] First, the use of the agent will release toxic and harmful gases, polluting the production environment and endangering the health of the operators;

[0005] Secondly, the treatment of waste liquid containing fluorine and nitrate is difficult and costly, which does not meet the requirements of environmentally friendly production.

[0006] Third, some traditional zinc stripping solutions have poor corrosion stability, which can easily lead to over-corrosion of the aluminum alloy substrate and surface discoloration, affecting the quality of subsequent zinc immersion and electroplating.

[0007] In view of this, based on the existing overall process flow for copper plating of aluminum alloys, the present invention provides an environmentally friendly zinc stripping agent and zinc stripping process for aluminum alloy electroplating to solve the above problems. Summary of the Invention

[0008] To achieve the above objectives, the present invention provides the following technical solution: an environmentally friendly zinc stripping agent for aluminum alloy electroplating, comprising a zinc stripping agent and an acidity regulator; the zinc stripping agent is free of ammonium salts, nitrates, chloride ions and fluoride ions, and can selectively dissolve the zinc layer on the surface of aluminum alloys.

[0009] Preferably, the zinc removal agent is a zinc precipitation activator with a concentration of 40~60g / L, and its composition by mass percentage is: sodium citrate 35%~45%, potassium sodium tartrate 5%~10%, anhydrous sodium sulfate 25%~35%, sodium carbonate 5%~10%, fatty alcohol polyoxyethylene ether 3%~6%, benzotriazole 0.5%~2%, and the balance being deionized water;

[0010] The acidity regulator is sulfuric acid with a concentration of 15~25 ml / L.

[0011] A zinc removal process using an environmentally friendly zinc removal agent for aluminum alloy electroplating, comprising the following steps:

[0012] S1 Pretreatment: The aluminum alloy workpiece is subjected to hot dipping degreasing, first water washing, alkaline micro-etching, second water washing, descaling, third water washing, first zinc immersion and fourth water washing in sequence.

[0013] S2 Environmentally Friendly Zinc Removal: Immerse the workpiece that has undergone one zinc deposit into the environmentally friendly zinc removal agent and treat it at 20~30℃ for 30~120s;

[0014] S3 post-treatment: The dezincified workpiece is subjected to a fifth water wash, a second zinc immersion, and a sixth water wash in sequence.

[0015] Preferably, the hot immersion degreasing uses a universal degreasing agent with a concentration of 30~60g / L, a treatment temperature of 30~60℃, and a treatment time of 3~10min.

[0016] Preferably, the alkaline micro-etching uses an alkaline micro-etching agent with a concentration of 30~70g / L, a treatment temperature of 30~50℃, and a treatment time of 0.5~3min.

[0017] Preferably, the descaling process uses an acidic descaling agent or an environmentally friendly descaling agent. When using an acidic descaling agent, its concentration is 200~250 ml / L, with the addition of 250~300 ml / L nitric acid, 380~400 ml / L phosphoric acid, and 30~50 ml / L hydrofluoric acid, and the treatment is carried out at room temperature for 0.5~1 min. When using an environmentally friendly descaling agent, its concentration is 300~500 g / L, with the addition of 100~200 ml / L 50% hydrogen peroxide, and the treatment is carried out at 20~40℃ for 10~120 s.

[0018] Preferably, both the primary and secondary zinc precipitation use cyanide-free or cyanide-containing zinc precipitation agents. When using a cyanide-free zinc precipitation agent, its concentration is 200-400 ml / L, and the treatment is carried out at 20-40°C for 20-120 seconds. When using a cyanide-containing zinc precipitation agent, its concentration is 500-600 ml / L, the pH value is 12.8-13.6, and the treatment is carried out at 15-30°C for 20-120 seconds.

[0019] Preferably, the S2 environmentally friendly dezincification process further includes micro-current assisted dezincification: the workpiece that has undergone one zinc deposit is connected to the anode of a DC rectifier, the stainless steel cathode plate is connected to the cathode of the rectifier, and it is immersed in the environmentally friendly dezincification agent, and treated for 15 to 60 seconds at a current density of 0.05~0.2A / dm² and a temperature of 20~30℃.

[0020] When using the microcurrent-assisted zinc removal method, the environmentally friendly zinc removal agent also contains a conductive salt, a corrosion inhibitor, and an activating complexing agent. The conductive salt is anhydrous sodium sulfate; the corrosion inhibitor is phytic acid; and the activating complexing agent is sodium gluconate. The concentrations of each component are: anhydrous sodium sulfate 10~20 g / L, phytic acid 2~5 g / L, and sodium gluconate 5~10 g / L.

[0021] The beneficial effects of this invention are:

[0022] 1. The zinc stripping agent of this invention is completely free of four harmful ions: ammonium salt, nitrate, chloride, and fluoride. It does not produce any toxic or harmful gases during use, which greatly improves the workshop working environment and protects the health of operators. At the same time, the waste liquid has a simple composition, free of phosphorus, fluoride, and strong oxidizing pollutants, which significantly reduces the difficulty and cost of wastewater treatment and has good environmental performance.

[0023] 2. The zinc stripping agent of this invention can precisely and selectively dissolve the zinc layer without corroding the aluminum alloy substrate. It effectively solves problems such as surface discoloration, color difference, and over-corrosion of the substrate in traditional processes, ensuring the smoothness and gloss of the workpiece surface. While removing the zinc layer, the zinc stripping agent can gently activate the surface of the aluminum alloy substrate, making the secondary zinc plating layer thinner, more uniform, and denser. This significantly improves the adhesion of subsequent copper and silver plating layers and effectively reduces the defect rate of plating peeling, flaking, and blistering.

[0024] 3. By applying a weak anodic current, the zinc layer undergoes an anodic oxidation reaction (Zn-2e). - =Zn² + The current works synergistically with the chemical dissolution reaction to significantly increase the zinc removal speed; at the same time, the current can penetrate into deep holes, blind holes and other parts that are difficult to reach by pure chemical zinc removal, so as to achieve uniform zinc removal on the entire surface. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] This embodiment provides an environmentally friendly zinc stripping agent and zinc stripping process for aluminum alloy electroplating, as detailed below:

[0028] Zinc removal agent formulation: 50g / L zinc precipitation activator, 20ml / L sulfuric acid, and the balance being deionized water. The 50g / L zinc precipitation activator consists of the following components by mass percentage: 35%~45% sodium citrate, 5%~10% potassium sodium tartrate, 25%~35% anhydrous sodium sulfate, 5%~10% sodium carbonate, 3%~6% fatty alcohol polyoxyethylene ether, 0.5%~2% benzotriazole, and the balance being deionized water. Sodium citrate is the core chelating agent, forming a stable five-membered ring chelate with zinc ions, and is the main effective component for zinc removal; potassium sodium tartrate is an auxiliary chelating agent, which, when combined with sodium citrate, enhances the chelating ability and broadens the applicable pH range; anhydrous sodium sulfate is used to stabilize the solution system and improve the uniformity of zinc removal; sodium carbonate is used to maintain the weakly alkaline environment of the solution and prevent the chelating agent from failing; fatty alcohol polyoxyethylene ether is used to reduce surface tension and improve wettability on complex workpieces; benzotriazole is an organic corrosion inhibitor that can selectively adsorb onto the aluminum alloy surface and inhibit the corrosion of the aluminum matrix.

[0029] Zinc removal process: (1) Hot immersion degreasing: Use a universal degreasing agent with a concentration of 45g / L and a temperature of 45℃. Immerse the aluminum alloy workpiece completely in the degreasing solution for 6 minutes to remove oil, dust, and organic impurities from the workpiece surface. The agent is mild and will not damage the aluminum alloy substrate. It is suitable for both rack plating and barrel plating. It ensures the cleanliness of the workpiece surface and avoids the oil affecting the subsequent corrosion and zinc deposition effects. (2) First water wash: The workpiece passes through three clean water tanks in sequence. Each water wash lasts for 1 minute to thoroughly remove the residual degreasing agent solution from the workpiece surface and prevent the alkaline degreasing solution from being carried into the next alkaline micro-etching process. The composition of the finished product solution is disordered and the process fails; (3) Alkaline micro-etching: use alkaline micro-etching agent, concentration 50g / L, temperature 40℃, immerse the workpiece in micro-etching solution for weak corrosion treatment for 1.5min to remove inorganic impurities and thin oxide film on the surface of aluminum alloy; at the same time, form a fine and uniform rough surface on the substrate surface, increase the contact area between the substrate and the subsequent coating, and improve the coating adhesion; (4) Second water washing: same as step (2); (5) Descaling: use environmentally friendly descaling agent 400g / L + 50% hydrogen peroxide 150ml / L, temperature 30℃, treatment time 60s to thoroughly remove the insoluble substances on the surface of the workpiece after micro-etching. (6) Third wash: same as step (2); (7) First zinc immersion: using 300ml / L of cyanide-free zinc immersion agent at 30℃, immerse the workpiece in the zinc immersion solution for 60s to deposit the first zinc layer on the surface to isolate the air and prevent the clean aluminum alloy substrate from oxidizing again; initially form a zinc metal transition layer to provide a treatment object for the dezincification process; (8) Fourth wash: same as step (2); (9) Environmentally friendly dezincification: immerse the workpiece in the above dezincification agent at 25℃ for 60s to completely and uniformly remove the first zinc layer from the surface of the workpiece. A layer of zinc plating, with no zinc residue; the solution contains no ammonium salts, nitrates, chloride ions, or fluoride ions, and the treatment process does not produce toxic or harmful gases; it gently activates the surface of the aluminum alloy substrate, keeping the substrate highly active and laying the foundation for secondary zinc plating; at the same time, it can prevent defects such as over-corrosion, surface mottled appearance, and color difference in the aluminum alloy substrate; (10) Fifth water wash: same as step (2); (11) Secondary zinc plating: same as step (7), to form a thin, flat, dense, and uniform secondary zinc layer on the activated aluminum alloy surface. This transition layer is the key to ensuring the high adhesion of subsequent copper and silver plating layers; (12) Sixth water wash: same as step (2).

[0030] It should be noted that the aluminum alloy workpiece used in this embodiment is a high-silicon cast aluminum alloy, and has a blind hole with a diameter of 2mm and a depth of 10mm.

[0031] Example 2

[0032] This embodiment provides an environmentally friendly zinc stripping agent and zinc stripping process for aluminum alloy electroplating, which differs from Embodiment 1 in that:

[0033] Zinc removal agent formula: 40g / L zinc precipitation activator, 15ml / L sulfuric acid, and the remainder is deionized water.

[0034] Zinc removal process: The environmentally friendly zinc removal process is carried out at a temperature of 20℃ for 120 seconds. Descaling process: Acidic descaling agent (225ml / L) + nitric acid (275ml / L) + phosphoric acid (390ml / L) + hydrofluoric acid (40ml / L) is used, and the process is carried out at room temperature for 45 seconds. Primary and secondary zinc precipitation: A cyanide-containing zinc precipitation agent (550ml / L) is used at a pH of 13.2, a temperature of 22℃, and a processing time of 90 seconds.

[0035] The rest is the same as in Example 1.

[0036] Example 3

[0037] This embodiment provides an environmentally friendly zinc stripping agent and zinc stripping process for aluminum alloy electroplating, which differs from Embodiment 1 in that:

[0038] Zinc removal agent formula: 60g / L zinc precipitation activator, 25ml / L sulfuric acid, and the remainder is deionized water.

[0039] Zinc removal process: The environmentally friendly zinc removal process has a temperature of 30℃ and a processing time of 30 seconds.

[0040] The rest is the same as in Example 1.

[0041] Comparative Example 1

[0042] This comparative example uses a traditional zinc removal agent and process containing nitric acid and hydrofluoric acid, as detailed below:

[0043] Zinc removal agent formula: 300ml / L nitric acid, 50ml / L hydrofluoric acid, and the remainder is deionized water.

[0044] Zinc removal process: Except for the zinc removal process, the other steps are the same as in Example 1; the zinc removal process is carried out at room temperature for 30 seconds.

[0045] The aluminum alloy workpiece used in this comparative example is the same as that in Example 1.

[0046] Comparative Example 2

[0047] This comparative example uses a traditional zinc stripping agent and process containing ammonium salts, as detailed below:

[0048] Zinc removal agent formula: ammonium chloride 100g / L, sodium nitrate 50g / L, balance deionized water.

[0049] Zinc removal process: Except for the zinc removal process, the other steps are the same as in Example 1; the zinc removal process temperature is 30℃ and the processing time is 60s.

[0050] The aluminum alloy workpiece used in this comparative example is the same as that in Example 1.

[0051] Performance Testing and Comparison

[0052] The workpieces prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests. The test items and methods are shown in Table 1 below:

[0053] Completeness of zinc removal: The zinc residue on the workpiece surface is detected by X-ray fluorescence spectrometry (XRF). The absence of zinc residue is considered as complete zinc removal.

[0054] Matrix corrosion: The mass change of the workpiece before and after dezincification was measured by the weight loss method, and the corrosion rate was calculated; at the same time, the surface morphology of the workpiece was observed by scanning electron microscopy (SEM).

[0055] Uniformity of the secondary zinc plating layer: The cross-sectional morphology of the secondary zinc plating layer was observed using a metallographic microscope, the thickness of the zinc layer at different locations was measured, and the thickness deviation rate was calculated.

[0056] Coating adhesion: The cross-cut adhesion test is conducted according to GB / T9286-1998 "Cross-cut test of paint and varnish film". The rating is divided into 0-5 levels, with 0 being the best and 5 being the worst.

[0057] Waste gas generation: The concentrations of nitrogen oxides, hydrogen fluoride, and ammonia were measured 10 cm above the zinc stripping process using a portable gas detector.

[0058]

[0059] Table 1

[0060] The test results above show that the zinc stripping agents of Examples 1-3 of this invention can completely remove the zinc layer from the aluminum alloy surface, and the substrate corrosion rate is extremely low, far lower than that of Comparative Example 1 and Comparative Example 2. This indicates that the zinc stripping agent of this invention has excellent zinc stripping selectivity and will not cause corrosion to the aluminum alloy substrate. The thickness deviation rate of the secondary zinc plating layer in Examples 1-3 of this invention is all below 7%, and the coating adhesion is all grade 0, which is significantly better than that of Comparative Example 1 and Comparative Example 2. This indicates that the zinc stripping process of this invention can obtain a uniform and dense secondary zinc plating layer, thereby greatly improving the adhesion of subsequent coatings.

[0061] Example 4

[0062] Based on the pure chemical zinc stripping agent and process of Examples 1-3 above, this embodiment further adopts "micro-current assisted chemical zinc stripping and phytic acid-sodium gluconate composite corrosion inhibition and activation". While fully retaining the environmentally friendly characteristics of "no ammonium salt, no nitrate, no chloride ion, and no fluoride ion", it accelerates the zinc layer dissolution through a weak electric field. Combined with the composite corrosion inhibitor and activator, it can effectively solve the problems of uneven zinc stripping of high silicon aluminum alloys, incomplete zinc stripping of deep holes / blind holes in complex workpieces, and limited zinc stripping speed.

[0063] Its difference from Examples 1-3 lies only in:

[0064] Zinc removal agent formula: 45g / L zinc precipitation activator, 17ml / L sulfuric acid, 15g / L anhydrous sodium sulfate, 3.5g / L phytic acid, 7.5g / L sodium gluconate, and the balance is deionized water.

[0065] Zinc Removal Process: The environmentally friendly zinc removal process utilizes micro-current assisted zinc removal. Specifically: A zinc removal tank made of PP material is prepared, with 316L stainless steel cathode plates (area to workpiece anode area ratio of 2:1) placed on both sides of the tank. An external 0~5V low-power DC rectifier is connected. The zinc removal agent is added to the tank and stirred evenly, maintaining a temperature of 20~30℃. The aluminum alloy workpiece on the hanger is connected to the rectifier anode, and the stainless steel plate to the cathode. The rectifier is turned on, and the current density is adjusted to 0.05~0.2A / dm². The workpiece is completely immersed in the zinc removal agent for 15~60 seconds. After treatment, the rectifier is turned off first, and then the workpiece is removed. This process utilizes micro-current acceleration, which can directionally accelerate the dissolution of the zinc layer (Zn-2e) through the anodic oxidation reaction. - =Zn² + First, the current can reach areas that are difficult to penetrate with pure chemical dezincification, such as deep holes, blind holes, and gaps, thus solving the problem of incomplete dezincification of complex workpieces. Second, phytic acid forms a protective film on the surface of the aluminum substrate, and sodium gluconate complexes zinc ions and activates the silicon phase, achieving dezincification without corroding the substrate and no zinc residue in the silicon phase.

[0066] It should be noted that the current density must not exceed 0.2 A / dm², otherwise it will cause anodizing of the aluminum substrate;

[0067] The workpiece must be completely submerged and kept 5-10 cm away from the cathode plate to avoid excessive local current. For barrel plating workpieces, it is necessary to ensure good conductivity of the barrel and control the rotation speed at 3-5 r / min.

[0068] Example 5

[0069] This embodiment provides an environmentally friendly zinc stripping agent and zinc stripping process for aluminum alloy electroplating, which differs from Embodiment 4 only in that:

[0070] Zinc removal agent formula: 35g / L zinc precipitation activator, 12ml / L sulfuric acid, 10g / L anhydrous sodium sulfate, 2g / L phytic acid, 5g / L sodium gluconate, and the balance is deionized water.

[0071] Zinc removal process: Environmentally friendly zinc removal process with a current density of 0.05A / dm², a temperature of 20℃, and a processing time of 60s.

[0072] Performance Testing and Comparison

[0073] Performance tests were conducted on Examples 4-5 and Example 1, and the test results are shown in Table 2 below:

[0074] Silicon phase residue: The zinc layer residue around the silicon phase on the surface of ADC12 aluminum alloy was observed using scanning electron microscopy (SEM). The residue area was divided into grade 0 (no residue), grade 1 (<5%), grade 2 (5%~20%), and grade 3 (>20%) according to the percentage of residual area.

[0075]

[0076] Table 2

[0077] The test results above show that: the zinc removal at the bottom of the blind hole in Examples 4 and 5 of this invention is complete, while zinc residue remains at the bottom of the blind hole in Example 1. This indicates that microcurrent assistance can effectively solve the problem of incomplete zinc removal inside complex workpieces, and at the same time, the zinc removal time is greatly reduced, significantly improving the zinc removal efficiency. There is no silicon phase residue on the aluminum alloy surface in Examples 4 and 5, while the silicon phase residue level in Example 1 is level 2. This indicates that sodium gluconate can effectively activate the silicon phase and solve the problem of uneven zinc removal in high-silicon aluminum alloys. At the same time, the substrate corrosion rate in Examples 4 and 5 is much lower than that in Example 1, indicating that phytic acid corrosion inhibitor can effectively protect the aluminum alloy substrate and avoid over-corrosion.

[0078] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An environmentally friendly zinc stripping agent for aluminum alloy electroplating, characterized in that, The components include a dezincification agent and an acidity regulator; the dezincification agent is free of ammonium salts, nitrates, chloride ions, and fluoride ions, and can selectively dissolve the zinc layer on the surface of aluminum alloys.

2. The environmentally friendly zinc stripping agent for aluminum alloy electroplating as described in claim 1, characterized in that: The zinc removal agent is a zinc precipitation activator with a concentration of 40~60g / L, and its composition by mass percentage is: sodium citrate 35%~45%, potassium sodium tartrate 5%~10%, anhydrous sodium sulfate 25%~35%, sodium carbonate 5%~10%, fatty alcohol polyoxyethylene ether 3%~6%, benzotriazole 0.5%~2%, and the balance being deionized water; The acidity regulator is sulfuric acid with a concentration of 15~25 ml / L.

3. A zinc removal process based on the environmentally friendly zinc removal agent for aluminum alloy electroplating according to any one of claims 1-2, characterized in that, Includes the following steps: S1 Pretreatment: The aluminum alloy workpiece is subjected to hot dipping degreasing, first water washing, alkaline micro-etching, second water washing, descaling, third water washing, first zinc immersion and fourth water washing in sequence. S2 Environmentally Friendly Zinc Removal: Immerse the workpiece that has undergone one zinc deposit into the environmentally friendly zinc removal agent and treat it at 20~30℃ for 30~120s; S3 post-treatment: The dezincified workpiece is subjected to a fifth water wash, a second zinc immersion, and a sixth water wash in sequence.

4. The zinc removal process as described in claim 3, characterized in that: The hot-dip degreasing process uses a universal degreasing agent with a concentration of 30-60 g / L, a treatment temperature of 30-60℃, and a treatment time of 3-10 min.

5. The zinc removal process as described in claim 1, characterized in that: The alkaline micro-etching process uses an alkaline micro-etching agent with a concentration of 30~70 g / L, a treatment temperature of 30~50℃, and a treatment time of 0.5~3 min.

6. The zinc removal process as described in claim 3, characterized in that: The descaling process uses an acidic descaling agent or an environmentally friendly descaling agent. When using an acidic descaling agent, its concentration is 200~250ml / L, with the addition of 250~300ml / L nitric acid, 380~400ml / L phosphoric acid, and 30~50ml / L hydrofluoric acid, and the treatment is carried out at room temperature for 0.5~1min. When using an environmentally friendly descaling agent, its concentration is 300~500g / L, with the addition of 100~200ml / L 50% hydrogen peroxide, and the treatment is carried out at 20~40℃ for 10~120s.

7. The zinc removal process as described in claim 3, characterized in that: Both the primary and secondary zinc precipitation processes use either cyanide-free or cyanide-containing zinc precipitation agents. When using a cyanide-free zinc precipitation agent, its concentration is 200-400 ml / L, and the treatment is carried out at 20-40°C for 20-120 seconds. When using a cyanide-containing zinc precipitation agent, its concentration is 500-600 ml / L, the pH value is 12.8-13.6, and the treatment is carried out at 15-30°C for 20-120 seconds.

8. The zinc removal process as described in claim 3, characterized in that: The S2 environmentally friendly zinc removal process also includes micro-current assisted zinc removal: the workpiece that has undergone one zinc deposit is connected to the anode of a DC rectifier, the stainless steel cathode plate is connected to the cathode of the rectifier, and it is immersed in the environmentally friendly zinc removal agent, and treated for 15~60s at a current density of 0.05~0.2A / dm² and a temperature of 20~30℃.

9. The zinc removal process as described in claim 8, characterized in that: In the microcurrent-assisted zinc removal process, the environmentally friendly zinc removal agent also contains a conductive salt, a corrosion inhibitor, and an activating complexing agent. The conductive salt is anhydrous sodium sulfate; the corrosion inhibitor is phytic acid; and the activating complexing agent is sodium gluconate. The concentrations of each component are: anhydrous sodium sulfate 10~20 g / L, phytic acid 2~5 g / L, and sodium gluconate 5~10 g / L.

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