An environmentally friendly and low-toxicity copper plating technology for surface treatment of different metals

Abstract

This invention discloses an environmentally friendly and low-toxicity copper plating technology for different metal surface treatments, belonging to the field of metal surface treatment and electroplating engineering technology. This invention constructs an environmentally friendly composite plating solution system – differentiated cyanide-free pretreatment – ​​intelligent online control – pulse-coated synergistic electroplating process, completely replacing traditional highly toxic cyanide-based copper plating. It is applicable to three major metal substrates: aluminum alloys, copper alloys, and steel parts. The entire process is cyanide-free and environmentally friendly, significantly improving plating solution stability, resulting in excellent coating performance and wide substrate compatibility: a single process adapts to three major substrates—aluminum alloys, copper alloys, and steel parts—offering strong versatility and fully replacing cyanide-based copper plating.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment and electroplating engineering technology, specifically relating to an environmentally friendly and low-toxicity copper plating technology for different metal surface treatments. Background Technology

[0002] Cyanide copper plating has long been used as a base plating process for various metal substrates due to its good coating adhesion and stable plating solution. However, cyanide is a highly toxic substance, and the production process generates highly toxic waste gas and wastewater, which seriously threatens occupational health and the ecological environment.

[0003] Existing cyanide-free copper plating processes generally suffer from problems such as poor plating bath stability, low impurity tolerance, insufficient coating adhesion, and poor deep plating capability, and cannot completely replace cyanide copper plating. Although the polymeric thiocyanate copper plating technology proposed in the reference document achieves a low-toxicity alternative, it still has drawbacks such as short plating bath life, potential cyanide risks in pretreatment, and reliance on manual process control.

[0004] Based on this, the present invention provides an environmentally friendly and low-toxicity technology for applying a copper plating layer as a base layer on different metal surfaces. Summary of the Invention

[0005] The purpose of this invention is to provide an environmentally friendly and low-toxicity copper plating technology for the entire process, characterized by cyanide-free plating, high solution stability, excellent plating performance, and intelligent control. This technology completely solves the problem of the high toxicity of cyanide copper plating and overcomes the core defects of existing cyanide-free copper plating, thus achieving a complete replacement for traditional cyanide copper plating.

[0006] The technical solution adopted by this invention to solve its technical problem is: an environmentally friendly and low-toxicity copper plating technology for different metal surface treatments, which constructs an environmentally friendly composite plating solution system - differentiated cyanide-free pretreatment - intelligent online control - pulse synergistic electroplating full-process cyanide-free copper plating process, completely replacing the traditional highly toxic cyanide-based copper plating, and is suitable for three major types of metal substrates: aluminum alloys, copper alloys, and steel parts, specifically including: The environmentally friendly and low-toxicity polymeric thiocyanate composite plating solution uses polymeric thiocyanate as the main complexing agent, combined with a double copper salt system, composite stabilizer and environmentally friendly brightener. The plating solution has a stability of ≥6 months and an impurity tolerance that is more than 3 times higher. The differentiated cyanide-free pretreatment unit develops exclusive pretreatment processes for different metal matrices. Among them, aluminum alloys use a cyanide-free secondary zinc plating process, while copper alloys and steel parts use an environmentally friendly activation process, with no cyanide added throughout the entire process. The intelligent online control unit for plating solution monitors the copper ion concentration, pH value, temperature, and complexing agent ratio of the plating solution in real time, and automatically completes the replenishment of reagents, online filtration, and impurity purification to achieve dynamic stability of the plating solution composition. The pulse-coordinated electroplating execution unit adopts a composite pulse electroplating process of forward pulse + reverse pulse to refine the coating grains and improve the coating adhesion and density. The copper plating layer prepared by the aforementioned technology has fine crystal structure, a porosity of ≤0.5%, and an adhesion to the substrate that meets GB / T9286-1998 standard level 0. It also has a neutral salt spray resistance of ≥72h, fully meeting the requirements for subsequent plating.

[0007] Preferably, the components and contents of the environmentally friendly and low-toxicity polymeric thiocyanate composite plating solution are as follows: 140-160 g / L of polymeric potassium thiocyanate complexing agent, 25-27 g / L of polymeric cuprous thiocyanate, 14-16 g / L of potassium sodium copper tartrate, 8-12 g / L of composite stabilizer, 2.5-3.5 ml / L of environmentally friendly brightener, 1-2 ml / L of leveling agent, and the balance being pure water; The composite stabilizer is a composite of sodium sulfite and sodium thiosulfate in a mass ratio of 2:1; the environmentally friendly brightener is a composite of polyethylene glycol and 2-mercaptobenzimidazole in a mass ratio of 5:1.

[0008] Preferably, the process of the differentiated cyanide-free pretreatment unit is as follows: (1) Pretreatment of aluminum alloy: ultrasonic degreasing → alkaline washing to remove oxidation → nitric acid brightening → cyanide-free primary zinc precipitation → nitric acid zinc stripping → cyanide-free secondary zinc precipitation → alkaline pre-plating of nickel; the components of the cyanide-free zinc precipitation solution are: zinc sulfate 30~40g / L, sodium hydroxide 120~150g / L, potassium sodium tartrate 80~100g / L, bismuth nitrate 1~2g / L, and zinc precipitation time 20~30s; (2) Copper alloy pretreatment: ultrasonic degreasing → 1:1 hydrochloric acid activation for 30~60s → pure water rinsing; (3) Pretreatment of steel parts: ultrasonic degreasing → 1:1 hydrochloric acid activation for 1~2 min → pure water rinsing.

[0009] Preferably, the intelligent online control unit for the plating solution includes: The multi-parameter online monitoring module collects data on copper ion concentration, pH value, temperature, and conductivity of the plating solution in real time, with a collection frequency of once every 10 minutes. The automatic reagent replenishment module automatically calculates and replenishes complexing agents, copper salts, and brighteners based on monitoring data, maintaining the complexing agent and Cu... + The molar ratio (P ratio) is between 8.5 and 9.5; The online circulating purification module uses a composite purification method of precision filtration and activated carbon adsorption to continuously filter the plating solution and automatically perform activated carbon adsorption treatment every 7 days to remove organic and metallic impurities.

[0010] Preferably, the parameters of the pulse-coated electroplating process are: temperature 52~58℃, pH value 12.2~12.8, average cathode current density 0.8~1.2A / dm², pulse frequency 500~1000Hz, duty cycle 30%~50%, reverse pulse current density is 1 / 3~1 / 2 of the forward pulse, reverse time 1~2ms, and the electroplating time is adjusted according to the coating thickness requirements.

[0011] Preferably, the preparation method of the environmentally friendly, low-toxicity polymeric thiocyanate composite plating solution includes the following steps: S1. Pour 50% of the volume of pure water into the plating tank, heat to 55°C, add the calculated amount of polymeric potassium thiocyanate complexing agent, and stir until completely dissolved. S2 mixes polymerized cuprous thiocyanate and potassium sodium copper tartrate with a small amount of pure water to form a paste, slowly adds it to the plating bath, stirs until completely dissolved, and keeps it at the temperature for 5 hours to fully complex. Add the composite stabilizer to S3 and stir for 30 minutes until dissolved; add pure water to the working liquid level and start the circulating filtration system. S4. Use an electroplating solution with a current density of 0.18 A / dm² for 4 hours to remove impurities; S5. Add diluted environmentally friendly brightener and leveling agent, stir evenly, and then perform trial plating.

[0012] Preferably, the maintenance method for the plating solution is as follows: The plating solution composition was analyzed every 24 hours, and the pH ratio was adjusted to 8.5-9.5; the pH value was adjusted to 12.2-12.8 using potassium hydroxide. The plating solution is continuously filtered with a filtration accuracy of 5μm; activated carbon adsorption treatment is performed every 7 days, with an activated carbon dosage of 1~2g / L. A major treatment is performed every 3 months to remove accumulated impurities, and the service life of the plating solution is ≥6 months.

[0013] Preferably, the performance indicators of the base copper plating layer are: Appearance: Uniform and glossy, free from burrs, pinholes, and peeling defects; Bonding strength: Grade 0 in cross-cut test, no detachment in file test, no cracking in 180° bending test; Porosity: ≤0.5 particles / dm² (measured by filter paper method); Corrosion resistance: No rust was observed after 72 hours of neutral salt spray testing; Deep plating capability: ≥90% in Hall effect cell test.

[0014] Preferably, a method for preparing an environmentally friendly, low-toxicity copper plating base layer based on the technology described in any one of claims 1 to 8 is characterized by comprising the following steps: S1 plating solution preparation: Prepare the polymeric thiocyanate composite plating solution according to the formula, and complete the electrolytic purification and debugging; S2 matrix pretreatment: Depending on the type of metal matrix, a corresponding differentiated cyanide-free pretreatment process is performed; S3 Pulse Electroplating: The treated substrate is placed into the plating tank, the intelligent control system is started, and electroplating is carried out according to the set pulse process parameters; S4 Post-treatment: After electroplating, the workpiece is cleaned with pure water and dried with hot air to obtain a base copper plating layer. S5 plating solution maintenance: The intelligent control unit automatically monitors the plating solution composition, replenishes chemicals, and performs online purification to maintain the stability of the plating solution.

[0015] The advantages of this invention are: 1. Cyanide-free and environmentally friendly throughout the entire process: Completely eliminates the use of cyanide, the plating solution components are low in toxicity, wastewater is easy to treat, and occupational health and environmental risks are significantly reduced. Significantly improved plating solution stability: Composite stabilizers increase the plating solution's impurity tolerance by 3 times, extend its lifespan to over 6 months, and reduce maintenance costs by 40%. Superior plating performance: Pulse electroplating results in finely crystallized plating layers with a bonding strength of Grade 0, salt spray resistance for 72 hours, and a deep plating capability of ≥90%, fully achieving the level of cyanide copper plating.

[0016] 2. Intelligent Management and Control: Online monitoring and automatic replenishment enable unmanned management, improving process stability and achieving a product qualification rate of over 99.5%. Wide Substrate Compatibility: One process is compatible with three major substrate types: aluminum alloy, copper alloy, and steel parts, offering strong versatility and fully replacing cyanide copper plating as a base. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the entire process of the environmentally friendly and low-toxicity copper plating technology for the base coat of this invention. Figure 2 This is an architectural diagram of the intelligent online control unit for plating solution of the present invention; Figure 3 The images show a comparison of the SEM morphology of the coatings in Example 1 and the comparative example. Figure 4 This is a comparison chart of the adhesion test results between the coatings in Example 1 and the comparative example. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0020] Based on the polymer thiocyanate plating solution system in the reference document, this invention innovates from four dimensions: plating solution formulation optimization, cyanide-free pretreatment, intelligent process control, and electroplating process upgrade, to construct a closed-loop environmentally friendly copper electroplating technology system.

[0021] 1. Environmentally friendly, low-toxicity polymeric thiocyanate composite plating solution system Based on the reference document, this invention optimizes the plating solution formula and introduces composite stabilizers and environmentally friendly brighteners to solve the problems of poor plating solution stability and sensitivity to impurities in the reference document.

[0022] Optimization of the dual copper salt system: The dual copper salt system of polymeric cuprous thiocyanate and potassium sodium copper tartrate is retained, and the content of polymeric cuprous thiocyanate is precisely controlled at 25~27g / L and potassium sodium copper tartrate at 15g / L. This ensures a stable copper ion concentration while improving the deep plating capability of the plating solution.

[0023] Innovation in composite stabilizers: For the first time, a composite stabilizer composed of sodium sulfite and sodium thiosulfate in a 2:1 ratio is introduced. Sodium sulfite can prevent Cu... + Oxidized to Cu 2+ Sodium thiosulfate can complex metal impurities such as iron and nickel in the plating solution, increasing the impurity tolerance of the plating solution from 50 ppm in the reference document to 150 ppm, and extending the life of the plating solution from 3 months to more than 6 months.

[0024] Environmentally friendly brightener and leveling agent: The environmentally friendly brightener is a composite of polyethylene glycol and 2-mercaptobenzimidazole, which replaces the traditional sulfur-containing organic brightener. It does not release any toxic or harmful substances and can refine the coating grains, making the coating crystals fine and bright. The addition of polyether leveling agent improves the dispersion ability and deep plating ability of the plating solution. The deep plating ability of the Hall tank is ≥90%.

[0025] pH and P ratio control of plating solution: Strictly control the pH value of the plating solution between 12.2 and 12.8, and the ratio of complexing agent to Cu... + The molar ratio (P ratio) is between 8.5 and 9.5 to ensure that the complexation reaction proceeds fully and to avoid copper salt precipitation.

[0026] 2. Cyanide-free differentiated pretreatment process throughout the entire process In the pretreatment process described in the reference document, there may still be a risk of cyanide residue in the zinc plating process of aluminum alloys. This invention develops a cyanide-free pretreatment process that is designed with specific processes for different metal matrices to completely eliminate cyanide from the source.

[0027] Aluminum Alloy Cyanide-Free Secondary Zinc Immersion Process: A cyanide-free zinc immersion solution was developed, using zinc sulfate as the main salt, sodium hydroxide as the complexing agent, and potassium sodium tartrate and bismuth nitrate as grain refiners, replacing the traditional cyanide-containing zinc immersion solution. The zinc immersion solution formula is: zinc sulfate 35g / L, sodium hydroxide 135g / L, potassium sodium tartrate 90g / L, and bismuth nitrate 1.5g / L. The process flow is as follows: ultrasonic degreasing (50℃, 10min) → alkaline washing to remove oxidation (50g / L NaOH, 50℃, 15s) → nitric acid brightening (300ml / L HNO3, room temperature, 25s) → cyanide-free primary zinc immersion (room temperature, 25s) → nitric acid zinc stripping (500ml / L HNO3, room temperature, 55s) → cyanide-free secondary zinc immersion (room temperature, 25s) → alkaline pre-plating nickel (55℃, 10min). The zinc layer formed by this process is uniform and dense, with excellent adhesion to the aluminum alloy substrate, providing a good foundation for subsequent copper plating.

[0028] Environmentally friendly activation process for copper alloys and steel parts: Copper alloys are activated with 1:1 hydrochloric acid at room temperature for 45 seconds to remove the surface oxide film; steel parts are activated with 1:1 hydrochloric acid at room temperature for 1.5 minutes to remove rust and oxide scale. After activation, they are rinsed three times with pure water to prevent residual acid from being carried into the plating tank.

[0029] 3. Intelligent online control unit for plating solution The plating solution maintenance described in the reference documents relies on manual analysis and replenishment, which is prone to errors and inefficient. This invention develops an intelligent online control unit to achieve real-time monitoring and automatic regulation of the plating solution composition, ensuring long-term stability of the plating solution.

[0030] Multi-parameter online monitoring module: integrates copper ion selective electrode, pH sensor, temperature sensor and conductivity sensor, to collect the core parameters of the plating solution in real time, with a collection frequency of 1 time / 10min, and data accuracy: copper ion concentration ±0.1g / L, pH value ±0.05, temperature ±0.5℃.

[0031] Automatic reagent replenishment module: Built-in expert control system automatically calculates reagent consumption based on monitoring data, and automatically replenishes complexing agent, copper salt, brightener and pH adjuster through high-precision metering pump to maintain the pH ratio between 8.5 and 9.5 with replenishment accuracy of ±1%.

[0032] Online circulating purification module: The plating solution is continuously filtered using a 5μm precision filter to remove solid impurities; the activated carbon adsorption device is automatically activated every 7 days, with an activated carbon dosage of 1.5g / L and an adsorption time of 2h, to remove organic and metallic impurities and keep the plating solution clean.

[0033] 4. Upgrade of pulse-coordinated electroplating process The reference document uses DC electroplating, which results in a coating with coarse grains and high porosity. This invention introduces a composite pulse electroplating process to further improve the coating performance.

[0034] Composite pulse parameter design: A composite mode of forward pulse + reverse pulse is adopted. The forward pulse provides the main deposition current, and the reverse pulse dissolves the protrusions in the coating and refines the grains. The optimized parameters are: average current density 1.0A / dm², pulse frequency 800Hz, duty cycle 40%, reverse current density is 1 / 3 of the forward current, and reverse time 1.5ms.

[0035] Process advantages: Compared with DC electroplating, pulse electroplating refines the grain size of the coating from 500nm to 200nm, reduces the porosity from 2% to below 0.5%, improves the adhesion by 15%, and improves the corrosion resistance by 50%.

[0036] Figure 3 SEM morphology comparison images The pulse electroplating coating of this invention has uniform and fine grains, approximately 200 nm in size, with no obvious pores; Reference document: DC electroplating coating: grains are relatively coarse, with a size of about 500nm, and a small number of pores exist; (c) Traditional cyanide copper plating: grain size is about 300nm, with good density.

[0037] Figure 4 Comparison chart of bonding strength test The coating of this invention: grade 0 in cross-cut test, no peeling; Reference document coating: Cross-cut test grade 1, minor edge peeling; (c) Traditional cyanide copper plating: Cross-cut test grade 0, no peeling. The technical solution of the present invention will be further described in detail below with reference to specific embodiments and comparative examples. The described embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0038] Example 1: Copper plating on an aluminum alloy substrate 1. Plating solution preparation Prepare 100L of polymeric thiocyanate composite plating solution according to the following formula: Polymerized potassium thiocyanate: 15kg (150g / L) Polymeric cuprous thiocyanate: 2.6 kg (26 g / L) Potassium sodium copper tartrate: 1.5 kg (15 g / L) Composite stabilizer (sodium sulfite: sodium thiosulfate = 2:1): 1 kg (10 g / L) Environmentally friendly brightener: 300ml (3ml / L) Displacement agent: 150ml (1.5ml / L) Pure water: Balance Preparation steps: Pour 50L of pure water into the plating tank, heat to 55℃, add polythiocyanate, and stir for 30 minutes until completely dissolved; Polymeric cuprous thiocyanate and potassium sodium copper tartrate were mixed into a paste with 5L of pure water, and slowly added to the plating tank. The mixture was stirred for 1 hour until completely dissolved, and then kept at the temperature for 5 hours to perform complexation. Add the composite stabilizer and stir for 30 minutes; add pure water to 100L and start the circulating filtration system. Impurities were removed by electrolysis at a current density of 0.18 A / dm² for 4 hours. Add the diluted brightener and leveling agent, stir well, and the plating solution is ready.

[0039] 2. Aluminum Alloy Pretreatment Using 6061 aluminum alloy test pieces, measuring 100mm × 50mm × 1mm, the following cyanide-free pretreatment process was performed: Ultrasonic degreasing: Soak in a degreasing powder solution at 50℃ for 10 minutes to remove cutting fluid and oil stains; Alkaline washing to remove oxidation: Immerse in 50g / L NaOH solution at 50℃ for 15s to remove the surface oxide film; Nitric acid brightening: Immerse in 300ml / L HNO3 solution at room temperature for 25s to remove the alkaline washing black film; Cyanide-free primary zinc precipitation: Cyanide-free zinc precipitation solution (zinc sulfate 35g / L, NaOH 135g / L, potassium sodium tartrate 90g / L, bismuth nitrate 1.5g / L), immersion at room temperature for 25s; Zinc removal with nitric acid: Immerse in 500 ml / L HNO3 solution at room temperature for 55 seconds to remove the zinc layer once; Cyanide-free secondary zinc precipitation: Immerse in the same zinc precipitation solution at room temperature for 25 seconds; Alkaline pre-plating of nickel: Pre-plating in an alkaline nickel plating solution at 55℃ for 10 minutes, with a thickness of approximately 2μm.

[0040] 3. Pulse electroplating The treated aluminum alloy sample was placed in the plating bath and electroplated using the following pulse process parameters: Temperature: 55℃ pH value: 12.5 Average current density: 1.0 A / dm² Pulse frequency: 800Hz Duty cycle: 40% Reverse current density: 0.33 A / dm² Reverse time: 1.5ms Electroplating time: 20 min, coating thickness approximately 10 μm.

[0041] 4. Post-processing After electroplating, the sample was rinsed three times with pure water and dried with hot air at 80°C to obtain a base copper plating layer.

[0042] Example 2: Copper alloy substrate electroplating H62 copper alloy specimens were used. The pretreatment process was as follows: ultrasonic degreasing for 10 min → 1:1 hydrochloric acid activation at room temperature for 45 s → rinsing with pure water 3 times. The plating solution formula and electroplating process were the same as in Example 1, the electroplating time was 15 min, and the plating thickness was approximately 8 μm.

[0043] Example 3: Copper plating on steel substrate Q235 steel specimens were used. The pretreatment process was as follows: ultrasonic degreasing for 10 min → 1:1 hydrochloric acid activation at room temperature for 1.5 min → rinsing with pure water 3 times. The plating solution formula and electroplating process were the same as in Example 1, the electroplating time was 15 min, and the coating thickness was approximately 8 μm.

[0044] Comparative Example 1 Reference Document Process The plating solution was prepared according to the formula and process in the reference document. Direct current electroplating was used with a current density of 1.0 A / dm², a temperature of 55°C, and a pH of 12.5. The aluminum alloy pretreatment adopted the traditional zinc immersion process in the reference document, and the remaining steps were the same as in Example 1.

[0045] Comparative Example 2: Traditional Cyanide Copper Plating Process The standard cyanide copper plating solution used was: 50 g / L cuprous cyanide, 70 g / L sodium cyanide, and 30 g / L sodium potassium tartrate. The temperature was 55℃, the current density was 1.0 A / dm², and the plating time was 20 min.

[0046] Performance Testing and Comparative Analysis The performance of the coatings from Examples 1-3 and Comparative Examples 1-2 was tested, and the results are shown in the table below:

[0047] Test results show that: The coating prepared by this invention has better adhesion, porosity, corrosion resistance, and deep plating capability than the process in the reference document, reaching or even exceeding the level of traditional cyanide copper plating. The plating solution life has been increased from 2.8 months in the reference document to 6.5 months, the impurity tolerance has been greatly improved, and the maintenance cost has been significantly reduced; The intelligent control system has increased the product qualification rate from 92.3% to over 99.5%, and significantly enhanced process stability.

[0048] Plating solution stability verification The plating solution of Example 1 was continuously operated for 6 months, and the performance of the plating solution and the quality of the coating were tested monthly. The results showed that the copper ion concentration of the plating solution fluctuated by ≤±0.2g / L, the P ratio was stable between 8.5 and 9.5, the appearance and performance of the coating showed no significant changes, and there was no copper salt precipitation or impurity accumulation, which verified the long-term stability of the plating solution.

[0049] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A low-toxicity environmentally friendly technology for treating different metal surfaces and electroplating a copper layer, characterized in that, This system constructs an environmentally friendly composite plating bath system, employing differentiated cyanide-free pretreatment, intelligent online control, and pulse-coordinated electroplating to achieve a complete cyanide-free copper plating process, entirely replacing traditional highly toxic cyanide-based copper plating. It is suitable for three major metal substrates: aluminum alloys, copper alloys, and steel parts. Specifically, it includes: The environmentally friendly and low-toxicity polymeric thiocyanate composite plating solution uses polymeric thiocyanate as the main complexing agent, combined with a double copper salt system, composite stabilizer and environmentally friendly brightener. The plating solution has a stability of ≥6 months and an impurity tolerance that is more than 3 times higher. The differentiated cyanide-free pretreatment unit develops exclusive pretreatment processes for different metal matrices. Among them, aluminum alloys use a cyanide-free secondary zinc plating process, while copper alloys and steel parts use an environmentally friendly activation process, with no cyanide added throughout the entire process. The intelligent online control unit for plating solution monitors the copper ion concentration, pH value, temperature, and complexing agent ratio of the plating solution in real time, and automatically completes the replenishment of reagents, online filtration, and impurity purification to achieve dynamic stability of the plating solution composition. The pulse-coordinated electroplating execution unit adopts a composite pulse electroplating process of forward pulse + reverse pulse to refine the coating grains and improve the coating adhesion and density. The copper plating layer prepared by the aforementioned technology has fine crystal structure, a porosity of ≤0.5%, and an adhesion to the substrate that meets GB / T9286-1998 standard level 0. It also has a neutral salt spray resistance of ≥72h, fully meeting the requirements for subsequent plating.

2. The technology according to claim 1, characterized in that, The components and contents of the environmentally friendly and low-toxicity polymeric thiocyanate composite plating solution are as follows: 140-160 g / L of polymeric potassium thiocyanate complexing agent, 25-27 g / L of polymeric cuprous thiocyanate, 14-16 g / L of potassium sodium copper tartrate, 8-12 g / L of composite stabilizer, 2.5-3.5 ml / L of environmentally friendly brightener, 1-2 ml / L of leveling agent, and the balance being pure water; The composite stabilizer is a composite of sodium sulfite and sodium thiosulfate in a mass ratio of 2:1; the environmentally friendly brightener is a composite of polyethylene glycol and 2-mercaptobenzimidazole in a mass ratio of 5:

1.

3. The technology according to claim 1, characterized in that, The process of the differentiated cyanide-free pretreatment unit is as follows: (1) Pretreatment of aluminum alloy: ultrasonic degreasing → alkaline washing to remove oxidation → nitric acid brightening → cyanide-free primary zinc precipitation → nitric acid zinc stripping → cyanide-free secondary zinc precipitation → alkaline pre-plating of nickel; the components of the cyanide-free zinc precipitation solution are: zinc sulfate 30~40g / L, sodium hydroxide 120~150g / L, potassium sodium tartrate 80~100g / L, bismuth nitrate 1~2g / L, and zinc precipitation time 20~30s; (2) Copper alloy pretreatment: ultrasonic degreasing → 1:1 hydrochloric acid activation for 30~60s → pure water rinsing; (3) Pretreatment of steel parts: ultrasonic degreasing → 1:1 hydrochloric acid activation for 1~2 min → pure water rinsing.

4. The technology according to claim 1, characterized in that, The intelligent online management and control unit for the plating solution includes: The multi-parameter online monitoring module collects data on copper ion concentration, pH value, temperature, and conductivity of the plating solution in real time, with a collection frequency of once per 10 minutes. The automatic medicament supplementing module automatically calculates and supplements complexing agent, copper salt and brightener according to monitoring data, maintains the molar ratio (P ratio) of the complexing agent and Cu + between 8.5~9.5; The online circulating purification module uses a composite purification method of precision filtration and activated carbon adsorption to continuously filter the plating solution and automatically perform activated carbon adsorption treatment every 7 days to remove organic and metallic impurities.

5. The technology according to claim 1, characterized in that, The parameters of the pulse-coated electroplating process are: temperature 52~58℃, pH value 12.2~12.8, average cathode current density 0.8~1.2A / dm², pulse frequency 500~1000Hz, duty cycle 30%~50%, reverse pulse current density is 1 / 3~1 / 2 of the forward pulse, reverse time 1~2ms, and the electroplating time is adjusted according to the coating thickness requirements.

6. The technology according to claim 1, characterized in that, The preparation method of the environmentally friendly and low-toxicity polymeric thiocyanate composite plating solution includes the following steps: S1. Pour 50% of the volume of pure water into the plating tank, heat to 55°C, add the calculated amount of polymeric potassium thiocyanate complexing agent, and stir until completely dissolved. S2 mixes polymerized cuprous thiocyanate and potassium sodium copper tartrate with a small amount of pure water to form a paste, slowly adds it to the plating bath, stirs until completely dissolved, and keeps it at the temperature for 5 hours to fully complex. Add the composite stabilizer to S3 and stir for 30 minutes until dissolved; add pure water to the working liquid level and start the circulating filtration system. S4. Use an electroplating solution with a current density of 0.18 A / dm² for 4 hours to remove impurities; S5. Add diluted environmentally friendly brightener and leveling agent, stir evenly, and then perform trial plating.

7. The technology according to claim 1, characterized in that, The maintenance method for the plating solution is as follows: The plating solution composition was analyzed every 24 hours, and the pH ratio was adjusted to 8.5-9.5; the pH value was adjusted to 12.2-12.8 using potassium hydroxide. The plating solution is continuously filtered with a filtration accuracy of 5μm; activated carbon adsorption treatment is performed every 7 days, with an activated carbon dosage of 1~2g / L. A major treatment is performed every 3 months to remove accumulated impurities, and the service life of the plating solution is ≥6 months.

8. The technology according to claim 1, characterized in that, The performance indicators of the underlying copper plating layer are as follows: Appearance: Uniform and glossy, free from burrs, pinholes, and peeling defects; Bonding strength: Grade 0 in cross-cut test, no detachment in file test, no cracking in 180° bending test; Porosity: ≤0.5 particles / dm² (measured by filter paper method); Corrosion resistance: No rust was observed after 72 hours of neutral salt spray testing; Deep plating capability: ≥90% in Hall effect cell test.

9. A method for preparing an environmentally friendly and low-toxicity strike plating copper layer based on the technology according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1 plating solution preparation: Prepare the polymeric thiocyanate composite plating solution according to the formula, and complete the electrolytic purification and debugging; S2 matrix pretreatment: Depending on the type of metal matrix, a corresponding differentiated cyanide-free pretreatment process is performed; S3 Pulse Electroplating: The treated substrate is placed into the plating tank, the intelligent control system is started, and electroplating is carried out according to the set pulse process parameters; S4 Post-treatment: After electroplating, the workpiece is cleaned with pure water and dried with hot air to obtain a base copper plating layer. S5 plating solution maintenance: The intelligent control unit automatically monitors the plating solution composition, replenishes chemicals, and performs online purification to maintain the stability of the plating solution.

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