Zinc-nickel alloy electroplating process

Abstract

According to the zinc-nickel alloy electroplating process, 2-pyridylaldoxime is used as a main complexing agent, ascorbic acid is used as an auxiliary complexing agent, and compared with a traditional single complexing agent system, the obtained experimental result shows that the corrosion resistance of a prepared zinc-nickel alloy coating is remarkably improved, and the comprehensive performance of the coating is optimized.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment, specifically to a composite complexing agent electroplating process. Background Technology

[0002] With increasingly stringent requirements for material corrosion resistance, zinc-nickel alloy coatings have broad application prospects. Due to their superior corrosion resistance, high gloss, high hardness, and low hydrogen embrittlement, zinc-nickel alloy coatings have become ideal protective coatings for industries such as automotive, medical, aerospace, and electrical appliances. Their corrosion resistance is 8-10 times that of traditional zinc coatings, and they meet the standard requirements of GB / T 41950-2022 "Metallic Coatings - Electroplating of Zinc and Zinc Alloys on Steel without Hexavalent Chromium Treatment" for a nickel mass fraction of 8%-16% (commonly controlled at 10%-16% in production). In alkaline zinc-nickel alloy plating solutions, the potential difference and side reaction competition between zinc and nickel necessitate the use of complexing agents and other additives to regulate co-deposition. Complexing agents can form complexes with metal ions, improving the stability of metal ions under alkaline conditions and preventing Ni... 2+ Zn 2+ Premature precipitation into hydroxides improves the uniformity of the cathode deposition process. However, traditional zinc-nickel alloy electroplating processes can no longer meet the current market demand for high-performance protective and decorative coatings. The technical pain points are concentrated in the insufficient optimization of the complexing agent system: 1. Most current studies still rely on single or simple combinations of complexing agents. Organic amine complexing agents commonly used in alkaline processes can form coatings, but the nickel content in the coating fluctuates greatly, making it difficult to stably control the alloy composition ratio, thus affecting the core properties of the coating such as corrosion resistance; in the citric acid-triethanolamine complexing system, citric acid is easily oxidized and decomposed in a high pH environment, leading to accelerated aging of the plating solution; although single oxime complexing agents can form stable bidentate complexes with nickel ions, increase the γ phase content of the coating and refine the grains, they lack a synergistic regulation mechanism, resulting in limited overall coating performance. 2. Electroplating in industrial production often faces complex conditions such as high temperatures, and some complexing agents are prone to performance degradation under high-temperature environments. For example, organic amine complexing agents can significantly reduce the deep plating capability of the plating bath at high temperatures, resulting in uneven plating in areas such as deep holes and grooves on parts. Complexing agents are crucial for controlling the co-deposition behavior of alkaline zinc-nickel alloys, and their performance directly determines the stability of the plating bath and the quality of the coating. An ideal complexing agent system needs to simultaneously achieve multiple objectives, including stable metal ion coordination, uniform and controllable deposition process, and optimized coating microstructure. Therefore, developing a composite complexing agent electroplating process with a clear synergistic mechanism and excellent overall coating performance has significant industrial application value. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a zinc-nickel alloy electroplating process that uses 2-pyridinecarboxaldehyde oxime as the main complexing agent and ascorbic acid as the auxiliary complexing agent. Compared with traditional single complexing agent systems, the experimental results show that the corrosion resistance of the prepared zinc-nickel alloy coating is significantly improved, and the overall performance of the coating is optimized.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a zinc-nickel alloy electroplating process, characterized in that the plating solution formula includes: zinc oxide 8-12 g / L, sodium hydroxide 80-120 g / L, nickel sulfate hexahydrate 10-14 g / L, 2-pyridinecarboxaldehyde oxime 20-24 g / L, ascorbic acid 19-28 g / L, primary brightener 6-10 mL / L, and secondary brightener 6-10 mL / L; the electroplating process parameters are as follows: temperature 27-35 ℃, plating solution pH: 10, cathode current density 4 A / dm², activation time 30 s, and electroplating time 10 min; the plating solution preparation process is as follows: a. Add the weighed 2-pyridinecarboxaldehyde oxime and ascorbic acid to deionized water and stir until fully dissolved; b. Weigh out the amount of nickel sulfate hexahydrate, add it to deionized water, stir until fully dissolved, and then slowly add it to the solution obtained in a. c. Add the weighed sodium hydroxide to deionized water and dissolve, stirring until the solution is clear; d. Weigh out the zinc oxide and dissolve it in deionized water. Stir until it becomes a suspension, then add it to the sodium hydroxide solution obtained in c. Continue stirring until the solution becomes clear. e. Slowly add the mixture obtained in d to the nickel complex solution obtained in b, and add the primary brightener and secondary brightener, and stir the mixture until homogeneous.

[0005] The 2-pyridinecarboxaldehyde oxime can be obtained by oximation reaction of 2-pyridinecarboxaldehyde and hydroxylamine hydrochloride and other raw materials through a liquid-phase synthesis method.

[0006] Preferably, nickel sheets are used as the anode during electroplating.

[0007] Preferably, the primary brightener is DPE-Ⅲ alkaline zinc plating brightener.

[0008] Preferably, the secondary brightener is BH-336 alkaline zinc plating brightener.

[0009] Experimental comparisons showed that the coating with 2-pyridinecarboxaldehyde oxime at 20-24 g / L and ascorbic acid at 19-28 g / L exhibited the best corrosion resistance.

[0010] This invention combines 2-pyridinecarboxaldehyde oxime with ascorbic acid to improve the performance of zinc-nickel alloy electroplating. Infrared spectroscopy revealed that 2-pyridinecarboxaldehyde oxime, as the main complexing agent, and ascorbic acid, as the auxiliary complexing agent, are compatible. Comparison with pure 2-pyridinecarboxaldehyde oxime plating solutions and pure ascorbic acid plating solutions showed that when the two act synergistically, the infrared spectrum originally located at 3301 cm⁻¹... -1 The OH peak at 3274 cm⁻¹ has redshifted to 3274 cm⁻¹. -1 At this point, the peak width becomes wider, mainly because a hydrogen bond network is formed between the oxime group OH of 2-pyridinecarboxaldehyde oxime and the hydroxyl group of ascorbic acid, resulting in a wider peak width and a red shift. The original peak width was 1635 cm⁻¹. -1 The peak splits into 1693cm. -1 and 1635 cm -1 The peaks at C=N and C=O / C=N-Ni are mainly due to the fact that Ni... 2+ Simultaneously, it combines with 2-pyridinecarboxaldehyde oxime (oxime group) and ascorbic acid (enol), and 2-pyridinecarboxaldehyde oxime forms a strong hydrogen bond (OH⋯O=C) with ascorbic acid, which increases the electron density of the C=O bond of ascorbic acid and the vibrational wavenumber, thus causing the C=O position to redshift to 1635 cm⁻¹. -1 It is located at 487 cm. -1 The presence of peaks in the Ni-N metal coordination region, without the appearance of any new functional groups, indicates that the two components, 2-pyridinecarboxaldehyde oxime and ascorbic acid, are compatible. Ascorbic acid, as an auxiliary complexing agent, possesses a certain degree of bidentate coordination ability—forming complexes with metal ions through hydroxyl groups—but it exhibits weak coordination. At appropriate concentrations, it can play a certain auxiliary role. The addition of suitable amounts of ascorbic acid can improve the composition of the plating bath, but it will not replace the core role of the main complexing agent. Furthermore, ascorbic acid acts as a plating bath buffer, maintaining the stability of the plating bath and contributing to the coordination balance and deposition process of the entire system.

[0011] An invention patent (CN117210893A) discloses an electroplating process using three oxime complexing agents (salicylaldehyde oxime, 2-pyridinecarboxaldehyde oxime, and 2-acetylpyridinone oxime). The plating bath system relies entirely on a single strong chelating system formed by the strong coordination of multiple oximes, primarily improving the stability and smoothness of the coating through the combination of multiple oximes. However, in this system, all three oximes are strong bidentate ligands, resulting in a relatively rigid overall coordination environment and limited ability of the plating bath to regulate cathodic polarization. In contrast, the innovative electroplating process proposed in this invention employs a complexing system of 2-pyridinecarboxaldehyde oxime and ascorbic acid. Ascorbic acid is not a commonly used complexing agent in the traditional sense, but possesses multiple functions including weak coordination, anti-oxidation, buffering and stabilization, and inhibition of side reactions. Infrared characterization shows that ascorbic acid can form a stable hydrogen bond network with 2-pyridinecarboxaldehyde oxime and participate in Ni... 2+The synergistic coordination of metal ions in this invention enables them to maintain higher stability in alkaline systems. Unlike existing technologies that rely solely on strong oximes to form rigid coordination structures, the composite complex system developed in this invention can more effectively regulate deposition kinetics, significantly improving the density and compositional uniformity of the coating. This invention can achieve smooth, dense coatings with low porosity even at high current densities, exhibiting significantly better corrosion resistance and hardness than existing methods, thus further enhancing the overall performance of the coating.

[0012] Compared with existing technologies, this invention offers the following advantages: By employing a complexing strategy primarily based on oximes and supplemented by polyhydroxyl groups, replacing the traditional single complexing system, it effectively refines grains in zinc-nickel alloy electroplating, forming a dense and uniform microstructure and significantly improving corrosion resistance. The complexing agent enhances the coordination stability and migration efficiency of metal ions, improving the conductivity and uniformity of the plating solution, thereby increasing the composition and uniformity of the coating. Ultimately, this results in an overall leap in coating quality, including improved corrosion resistance and hardness, a significant reduction in porosity and defects, and more reliable protection of the substrate. Attached Figure Description

[0013] Figure 1 This is a 5,000x scanning electron microscope image of the morphology of Example 1.

[0014] Figure 2 This is a 5,000x scanning electron microscope image of the morphology of Comparative Example 1.

[0015] Figure 3 This is a 5,000x scanning electron microscope image of the comparative example. Detailed Implementation

[0016] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0017] A zinc-nickel alloy electroplating process, characterized in that the plating bath formula includes: zinc oxide 8-12 g / L, sodium hydroxide 80-120 g / L, nickel sulfate hexahydrate 10-14 g / L, 2-pyridinecarboxaldehyde oxime 20-24 g / L, ascorbic acid 19-28 g / L, primary brightener 6-10 mL / L, and secondary brightener 6-10 mL / L; the electroplating process parameters are as follows: temperature 27-35 ℃, plating bath pH: 10, cathode current density 4 A / dm², activation time 30 s, and electroplating time 10 min; the plating bath preparation process is as follows: a. Add the weighed 2-pyridinecarboxaldehyde oxime and ascorbic acid to deionized water and stir until fully dissolved; b. Weigh out the amount of nickel sulfate hexahydrate, add it to deionized water, stir until fully dissolved, and then slowly add it to the solution obtained in a. c. Add the weighed sodium hydroxide to deionized water and dissolve, stirring until the solution is clear; d. Weigh out the zinc oxide and dissolve it in deionized water. Stir until it becomes a suspension, then add it to the sodium hydroxide solution obtained in c. Continue stirring until the solution becomes clear. e. Slowly add the mixture obtained in d to the nickel complex solution obtained in b, and add the primary brightener and secondary brightener, and stir the mixture until homogeneous. Example

[0018] a. Take 20 g of 2-pyridinecarboxaldehyde oxime and 28 g of ascorbic acid, add them to 200 mL of deionized water, and stir to dissolve them completely; b. Take 12 g of nickel sulfate hexahydrate and add it to 100 mL of deionized water. Stir until it is fully dissolved, and then slowly add it to the solution obtained in a. c. Dissolve 100 g of sodium hydroxide in 500 mL of deionized water and stir until the solution is clear; d. Dissolve 12 g of zinc oxide in 100 mL of deionized water, stir until a suspension is formed, then add it to the sodium hydroxide solution obtained in c, and continue stirring until the solution is clear; e. Slowly add the mixture obtained in d to the nickel complex solution obtained in b, add 6 mL each of primary brightener and secondary brightener, and add deionized water to make up to 1 L. Stir the mixture thoroughly.

[0019] f. Take Q235 steel plate as cathode plate and nickel plate as anode plate. Perform pretreatment on Q235 steel plate according to the steps of degreasing → water washing → pickling and rust removal → water washing → grinding → water washing → activation. g. Take 250 mL of the plating solution obtained in e and add it to the rectangular tank. Electroplating time is 10 min, and electroplating is performed using a current density of 4 A / dm².

[0020] h. After electroplating is completed, remove the cathode sample, wash it with deionized water and blow dry the plating surface.

[0021] a. Take 20 g of 2-pyridinecarboxaldehyde oxime and add it to 200 mL of deionized water, stirring until it is fully dissolved; b. Take 12 g of nickel sulfate hexahydrate and add it to 100 mL of deionized water. Stir until it is fully dissolved, and then slowly add it to the solution obtained in a. c. Dissolve 100 g of sodium hydroxide in 500 mL of deionized water and stir until the solution is clear; d. Dissolve 12 g of zinc oxide in 100 mL of deionized water, stir until a suspension is formed, then add it to the sodium hydroxide solution obtained in c, and continue stirring until the solution is clear; e. Slowly add the mixture obtained in d to the nickel complex solution obtained in b, add 6 mL each of primary brightener and secondary brightener, and add deionized water to make up to 1 L. Stir the mixture thoroughly.

[0022] f. Take Q235 steel plate as cathode plate and nickel plate as anode plate. Perform pretreatment on Q235 steel plate according to the steps of degreasing → water washing → pickling and rust removal → water washing → grinding → water washing → activation. g. Take 250 mL of the plating solution obtained in e and add it to the rectangular tank. Electroplating time is 10 min, and electroplating is performed using a current density of 4 A / dm².

[0023] h. After electroplating is completed, remove the cathode sample, wash it with deionized water and blow dry the plating surface.

[0024] a. Take 28 g of ascorbic acid and add it to 200 mL of deionized water, stirring until fully dissolved; b. Take 12 g of nickel sulfate hexahydrate and add it to 100 mL of deionized water. Stir until it is fully dissolved, and then slowly add it to the solution obtained in a. c. Dissolve 100 g of sodium hydroxide in 500 mL of deionized water and stir until the solution is clear; d. Dissolve 12 g of zinc oxide in 100 mL of deionized water, stir until a suspension is formed, then add it to the sodium hydroxide solution obtained in c, and continue stirring until the solution is clear; e. Slowly add the mixture obtained in d to the nickel complex solution obtained in b, add 6 mL each of primary brightener and secondary brightener, and add deionized water to make up to 1 L. Stir the mixture thoroughly.

[0025] f. Take Q235 steel plate as cathode plate and nickel plate as anode plate. Perform pretreatment on Q235 steel plate according to the steps of degreasing → water washing → pickling and rust removal → water washing → grinding → water washing → activation. g. Take 250 mL of the plating solution obtained in e and add it to the rectangular tank. Electroplating time is 10 min, and electroplating is performed using a current density of 4 A / dm².

[0026] h. After electroplating is completed, remove the cathode sample, wash it with deionized water and blow dry the plating surface.

[0027] Compared to Comparative Example 1, Example 1 used a synergistic complexing agent system of oximes and ascorbic acid, employing a dual complexing agent system, while Comparative Example 1 only added an oxime complexing agent, employing a single complexing agent system. Compared to Comparative Example 2, Example 1 used a synergistic complexing agent system of oximes and ascorbic acid, employing a dual complexing agent system, while Comparative Example 2 only added a polyhydroxy complexing agent, employing a single complexing agent system. The comparisons were primarily conducted using four metrics: SEM (2 micrometers), neutral salt spray test, and average coating hardness.

[0028] Result comparison: SEM results showed that Example 1 was generally flat and dense, with a fine layered texture. Comparative Example 1 was scaly, with many pores and pits, and visible penetrating micro-scratches. Comparative Example 2 generally exhibited a uniform, fine, mound-like morphology with densely distributed micropores, but no penetrating cracks were observed; its density and uniformity were between those of Example 1 and Comparative Example 1. The neutral salt spray test is an effective method for testing the corrosion resistance of the coating; the longer the salt spray test is conducted, the better the corrosion resistance of the coating. According to GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", a salt spray test was conducted. The test was stopped after red rust appeared and spread on the coating. The industrial anti-rust coating is considered qualified if there is no obvious substrate rust or peeling after 240-1000 hours. The neutral salt spray test time of Example 1 reached 820 hours, far exceeding that of Comparative Example 1 and Comparative Example 2, and can meet the standard of industrial anti-rust coating. The hardness test by microhardness tester showed that the average hardness of the coating in Example 1 was higher than that of Comparative Example 1 and Comparative Example 2. This is largely due to its dense structure, which can effectively resist friction and wear. It is particularly suitable for engineering applications that require good wear resistance and can be widely used in automotive parts, electrical equipment and petrochemical fields.

Claims

1. A zinc-nickel alloy electroplating process, characterized in that, The plating solution formula includes: zinc oxide 8-12 g / L, sodium hydroxide 80-120 g / L, nickel sulfate hexahydrate 10-14 g / L, 2-pyridinecarboxaldehyde oxime 20-24 g / L, ascorbic acid 19-28 g / L, primary brightener 6-10 mL / L, and secondary brightener 6-10 mL / L; The electroplating process parameters are as follows: temperature 30-35 ℃, plating solution pH: 10, cathode current density 4 A / dm³ 2 Activation time: 30 s; Electroplating time: 10 min. The plating solution preparation process is as follows: a. Add a measured amount of 2-pyridinecarboxaldehyde oxime and ascorbic acid to deionized water and stir until fully dissolved; b. Add a measured amount of nickel sulfate hexahydrate to deionized water, stir until fully dissolved, and then slowly add it to the solution obtained in a. c. Dissolve a measured amount of sodium hydroxide in deionized water and stir until the solution is clear; d. Dissolve a measured amount of zinc oxide in deionized water, stir until a suspension is formed, then add it to the sodium hydroxide solution obtained in c, and continue stirring until the solution is clear; e. Slowly add the mixture obtained in d to the nickel complex solution obtained in b, and add the primary brightener and secondary brightener, and stir the mixture until homogeneous.

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