Ionic liquid aluminum plating method

Abstract

The invention relates to the technical field of electroplating, in particular to an ionic liquid aluminum plating method. The invention discloses an ionic liquid aluminum plating method. The frequency lt is adopted; and carrying out electroplating treatment by using a 50Hz pulsed power supply, wherein an electroplating solution is a chloroaluminate system ionic liquid. According to the ionic liquid aluminum plating method, the frequency lt is adopted; according to the invention, electroplating is carried out by using a pulse power supply with the frequency of 50 Hz, and aluminum ions can obtain sufficient growth time after nucleation and form a stable and compact crystal structure in cooperation with the chloroaluminate system ionic liquid, so that the problems of poor compactness, easy formation of loose dendritic crystals and weak leveling performance of an existing ionic liquid aluminum plating layer are effectively solved. And the prepared pure aluminum coating is flat and compact in surface, has no obvious defects, and is obviously superior to a coating prepared in the prior art.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, and more particularly to an ionic liquid aluminum plating method. Background Technology

[0002] Metallic aluminum possesses low density, good ductility, and metallic luster, and its surface readily forms a uniform and dense passivation film, thus exhibiting excellent corrosion resistance. It is widely used as a surface protective coating for various materials. Furthermore, pure aluminum coatings can be anodized and colored to create a brightly colored, metallic-lustered, and highly hard and wear-resistant surface structure, making it extremely valuable for applications in automotive parts, electronic components, and mechanical parts. It is a coating material with immense development potential.

[0003] Currently, methods for preparing aluminum coatings mainly include hot-dip galvanizing, physical vapor deposition, chemical vapor deposition, and electroplating. Among these, electroplating aluminum technology shows significant development potential in large-scale industrial production due to its mild reaction conditions, high purity of the resulting coating, good thickness uniformity, and applicability to surface treatment of workpieces with various complex shapes. However, aluminum is a chemically highly reactive metal with a standard electrode potential of -1.66V, making electrodeposition impossible in aqueous solutions of aluminum salts. Therefore, existing electroplating aluminum technologies all use non-aqueous systems, mainly classified into three categories: organic solvent systems, inorganic molten salt systems, and ionic liquid systems. Compared to the volatility and toxicity of organic solvent systems and the high-temperature requirements and safety hazards of inorganic molten salt systems, ionic liquid systems, as a novel type of electroplating solution, offer significant advantages such as no risk of combustion or explosion, low corrosiveness to equipment, and a green and environmentally friendly electroplating process, making them one of the core research directions in electroplating aluminum technology.

[0004] In electroplating, the frequency of the pulse power supply is a key parameter affecting the nucleation and growth process of the coating, directly determining its microstructure and macroscopic properties. In the traditional electroplating industry, the frequency of pulse power supplies is typically divided into three levels: high frequency (>5000Hz), mostly used for fine electroplating of precision electronic components; medium frequency (500Hz~5000Hz), suitable for the preparation of conventional coatings such as zinc and nickel plating; and low frequency (50Hz~500Hz), commonly used in the production of wear-resistant coatings such as hard chrome plating on automotive piston rings. For the ultra-low frequency range (<50Hz), due to the lack of relevant application requirements in traditional electroplating scenarios, related technical research is rarely reported.

[0005] Despite the numerous advantages of ionic liquid electroplating for aluminum, as an emerging technology, it still faces key technical bottlenecks that urgently need to be addressed: insufficient coating density, easy formation of loose dendrites on the surface, and weak leveling performance. These defects severely affect the protective performance and appearance quality of the aluminum coating, limiting its application in high-end products. To improve these issues, some studies have attempted to use high-frequency pulse schemes for ionic liquid electroplating of aluminum. However, practice has shown that under high-frequency pulses, the nucleation rate of aluminum ions is too fast, and the time for atomic diffusion and orderly arrangement is insufficient, making it difficult to form a stable and dense crystal structure, thus limiting the improvement in coating quality.

[0006] The pulse frequency directly regulates the nucleation rate of aluminum ions and the crystal growth mode, which is a core factor determining the microstructure and macroscopic properties of aluminum coatings. Therefore, developing ultra-low frequency pulse application technology adapted to ionic liquid aluminum plating systems is key to overcoming existing technological bottlenecks and preparing high-quality aluminum coatings. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing an ionic liquid aluminum plating method. By employing a pulsed power supply with a frequency <50Hz for electroplating, combined with a chloroaluminate ionic liquid system, aluminum ions are given sufficient growth time after nucleation, forming a stable and dense crystal structure. This effectively solves the problems of poor density, easy formation of loose dendrites, and weak leveling performance in existing ionic liquid aluminum plating coatings. The prepared pure aluminum coating has a smooth, dense surface without obvious defects, significantly superior to coatings prepared by existing technologies.

[0008] Therefore, the purpose of this invention is to provide an ionic liquid aluminum plating method.

[0009] To achieve the objective of this invention, the technical solution of this invention provides an ionic liquid aluminum plating method, which uses a pulse power supply with a frequency of <50Hz for electroplating treatment, and the electroplating solution is an ionic liquid based on aluminochloride system.

[0010] Compared with existing technologies, the technical effects achieved by this solution are as follows: This invention uses a pulsed power supply with a frequency of <50Hz for electroplating, which extends the pulse cycle time, allowing aluminum complex ions in the chloroaluminate ionic liquid system sufficient stable growth time after nucleation. This results in the formation of a regular and dense crystal structure, effectively solving the problem of insufficient coating density and the formation of loose dendrites in existing ionic liquid aluminum plating technologies, and significantly improving the density of the coating. The chloroaluminate ionic liquid system poses no risk of combustion or explosion, has low equipment requirements, and the electroplating process is environmentally friendly. When used with an ultra-low frequency pulsed power supply, it provides a stable and suitable chemical environment for the electrodeposition of aluminum ions, avoiding the volatile toxicity of traditional organic solvent systems and the high-temperature safety hazards of inorganic molten salt systems, thus balancing the environmental friendliness and safety of the process. The application of the ultra-low frequency pulsed power supply synergistically with the characteristics of the chloroaluminate ionic liquid system not only optimizes the nucleation and growth process of the aluminum layer but also improves the leveling performance of the coating, making the surface of the prepared pure aluminum coating smoother and more uniform, meeting the requirements of subsequent anodizing and coloring processes, and expanding the application scenarios of the coating. This technical solution requires no complex equipment modification, the pulse power supply parameters and ionic liquid system are easy to control, the process has high stability and good repeatability, and it is suitable for large-scale production of workpieces with various complex shapes. It reduces the cost of industrial applications while ensuring the consistency of coating quality.

[0011] In one technical solution of the present invention, the pulse power supply output waveform is a square wave, a double-pulse square wave, or a sawtooth wave.

[0012] Compared with existing technologies, the technical effects achieved by this solution are as follows: The pulsed power supply output square wave waveform features steep rising and falling edges, concentrated energy, and stable parameters. This enables aluminum complex ions in the chloroaluminate ionic liquid system to obtain a uniform and stable electric field environment on the cathode surface, ensuring the synchronization of nucleation and growth processes, and further improving the density and thickness uniformity of the coating. The dual-pulse square wave, through the synergistic effect of two pulses with different parameters, can provide sufficient deposition energy during the conduction period while using interval pulses to adjust the ion concentration distribution on the cathode surface, avoiding coating defects caused by excessive local ion consumption and effectively suppressing the formation of loose dendrites. The sawtooth wave enables a smooth and gradual change in current, adapting to the diffusion rate of aluminum complex ions, reducing the interference of sudden current changes on crystal growth, helping to form a well-organized crystal structure, enhancing the leveling performance of the coating, and making the coating surface smoother. The selectable design of multiple waveforms allows this method to be flexibly adjusted according to different substrate materials and coating thickness requirements, adapting to the aluminum plating needs of various substrates such as die-cast aluminum alloys, broadening the application range of the technical solution, and improving the practicality and flexibility of the process.

[0013] In one embodiment of the present invention, the chloroaluminate system ionic liquid includes 1-methyl-3-ethylimidazole chloride and aluminum chloride.

[0014] Compared with existing technologies, the technical advantages achieved by this solution are as follows: 1-Methyl-3-ethylimidazole chloride, as the cation source of the ionic liquid, possesses excellent chemical stability and conductivity. When combined with aluminum chloride, it forms a chloroaluminate ionic liquid system that provides a stable environment for the dissolution and complexation of aluminum ions, promoting the formation of electrodepositable species such as Al₂Cl₇⁻ and ensuring the efficient and orderly conduction of the electroplating reaction. The combination of aluminum chloride and 1-methyl-3-ethylimidazole chloride can optimize the plating solution performance by adjusting the molar ratio, giving the solution suitable viscosity and conductivity. This facilitates the diffusion of aluminum complex ions while avoiding coating defects caused by poor solution flowability. The chloroaluminate ionic liquid system formed by 1-methyl-3-ethylimidazole chloride and aluminum chloride is chemically stable and does not easily decompose or deteriorate under the long-cycle conditions of ultra-low frequency pulse electroplating. It can maintain stable plating solution performance over a long period, ensuring consistent coating quality and process repeatability, making it suitable for large-scale industrial production.

[0015] In one technical solution of the present invention, the process parameters for electroplating specifically include: a duty cycle of 5% to 30%, an average current density of 10 mA / cm² to 30 mA / cm², and a time of 40 min to 60 min.

[0016] Compared with existing technologies, the technical effects achieved by this solution are as follows: The duty cycle is controlled within a reasonable range of 5% to 30%, enabling a scientific ratio of pulse on / off time. This ensures that aluminum complex ions obtain sufficient electrons to complete reduction during the on-time, while providing time for ion diffusion and orderly crystal growth during the off-time. This effectively avoids localized over-deposition due to excessive on-time or crystal growth disorder due to insufficient off-time, thus improving coating density. The average current density is set at 10 mA / cm² to 30 mA / cm², meeting the requirements for efficient aluminum coating deposition while avoiding low deposition efficiency due to excessively low current density. It also prevents defects such as increased coating porosity and dendrite formation caused by excessively high current density, ensuring a balance between coating growth rate and crystal regularity. Electroplating time is controlled between 40 and 60 minutes to ensure the plating thickness reaches the required range for practical use. This avoids insufficient plating thickness due to too short a time, which would compromise protective performance, while preventing stress buildup and peeling due to too long a time, thus guaranteeing stable plating quality. The process parameters work synergistically to suit the characteristics of pulsed power supplies with frequencies below 50 Hz and aluminochloride ionic liquid systems. The parameters have a wide range and are easily adjustable, adapting to different substrates and plating requirements. This improves process stability and repeatability, making it suitable for large-scale industrial production and ensuring consistent plating quality across batches. In one technical solution of the present invention, the substrate is activated before electroplating. The current density of the activation treatment is 50mA / cm²~100mA / cm², and the activation time is 20s~50s.

[0017] Compared with existing technologies, the technical effects achieved by this solution are as follows: Pre-electroplating activation of the substrate with a controlled activation current density of 50 mA / cm²~100 mA / cm² effectively removes oxide films and oil stains from the substrate surface, preventing these impurities from affecting the adsorption and deposition of aluminum complex ions. Simultaneously, it avoids excessive corrosion of the substrate surface due to excessively high current density, creating a clean and stable interface for the subsequent bonding of the plating layer and the substrate. The activation time is set to 20s~50s, ensuring sufficient dissolution of the oxide film and thorough removal of surface impurities while preventing excessively long activation times that could lead to abnormally increased surface roughness or performance degradation, ensuring the substrate surface maintains a suitable active state. These activation parameters are compatible with chloroaluminate ionic liquid systems and ultra-low frequency pulse electroplating processes. The activated substrate surface exhibits uniform activity, promoting uniform nucleation of aluminum complex ions on the cathode surface, reducing localized porosity or uneven thickness of the plating layer caused by differences in surface activity, and further improving the density and smoothness of the plating layer. A reasonable combination of activation current density and time can enhance the adhesion between the coating and the substrate, prevent coating peeling and flaking during subsequent use, and extend the service life of the coating. At the same time, the activation process is simple to operate and easy to control, which is suitable for the needs of large-scale industrial production and ensures the consistency of the substrate surface after batch processing. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be discussed below. Obviously, the technical solutions described in conjunction with the accompanying drawings are only some embodiments of the present invention. For those skilled in the art, other embodiments and their accompanying drawings can be obtained based on the embodiments shown in these drawings without creative effort.

[0019] Figure 1 This is a metallographic image of the aluminum coating under a 500x magnifying glass in Embodiment 1 of the present invention; Figure 2 This is a metallographic image of the aluminum coating in Comparative Example 1 of this invention under a 500x magnifying glass. Detailed Implementation

[0020] The technical solutions of various 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 described in 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.

[0021]

Example 1

[0022] Test results: Coating thickness 20μm, surface roughness Ra=0.18μm.

[0023]

Example 2

[0024]

Example 3

[0025]

Example 4

[0026]

Example 5

[0027]

Example 6

[0028] Comparative Example 1 The preparation method in this embodiment is the same as in Example 1, except that a pulse power supply with a frequency of 60Hz is used (beyond the range of <50Hz). Test results: Coating thickness 21μm, surface roughness Ra=0.55μm.

[0029] Comparative Example 2 The preparation method in this embodiment is the same as in Example 1, except that a high-frequency pulse power supply with a frequency of 5000Hz is used. Test results: Coating thickness 20.5μm, surface roughness Ra=0.62μm.

[0030] Comparative Example 3 The preparation method in this embodiment is the same as in Example 1, except that the plating solution is a traditional organic solvent system (anhydrous ethanol + AlCl3); the test results are: the coating thickness is 19.2 μm and the surface roughness Ra = 0.58 μm.

[0031] Based on the test results of the above embodiments and comparative examples, it can be seen that the pure aluminum coating thickness provided in Examples 1-6 is stable at 19μm~20.3μm, and the surface roughness Ra is only 0.18μm~0.23μm. Overall, it exhibits excellent characteristics of uniform thickness and smooth surface, fully verifying the reliability and superiority of the technical solution of this invention. A comparison of Examples 1-3 shows that when the pulse power supply frequency is adjusted within the ultra-low frequency range of <50Hz, the surface roughness Ra of the coating is consistently controlled below 0.23μm, and the thickness fluctuation is small. The coating smoothness is optimal at a frequency of 5Hz. This indicates that the ultra-low frequency pulse can provide sufficient nucleation and growth time for aluminum complex ions in the chloroaluminate ionic liquid system, promoting the formation of a regular and dense crystal structure. Furthermore, this frequency range has strong process adaptability and can stably achieve the preparation of high-quality coatings. A comparison of Examples 1 and 4 shows that when the pulse power supply output waveform is a single-pulse square wave or a double-pulse square wave, the surface roughness Ra of the coating is 0.18 μm and 0.19 μm, respectively, with minimal performance difference. This indicates that both waveforms can work synergistically with ultra-low frequency conditions to provide a stable electric field environment for aluminum ion deposition, further broadening the range of process options and improving the practicality of the technical solution. A comparison of Examples 1 and 5 shows that when the molar ratio of AlCl3-EMIC ionic liquid is between 1.5:1 and 1.8:1, the coating thickness and surface roughness remain within the ideal range. The coating smoothness is better at a molar ratio of 1.8:1, demonstrating that the composition ratio of this ionic liquid system has good controllability and can provide a stable environment for the dissolution, complexation, and deposition of aluminum ions within a reasonable range, ensuring coating quality. A comparison between Example 1 and Example 6 shows that when the activation current density and time are adjusted within the limited range of 50mA / cm²~80mA / cm² and 20s~50s, the surface roughness Ra of the coating only changes from 0.18μm to 0.23μm, and the thickness remains basically stable. This indicates that the activation process parameter range is scientifically reasonable. It can effectively remove the oxide film and impurities on the substrate surface, creating good interface conditions for coating deposition, and will not cause a significant decrease in coating performance due to parameter fluctuations. This is beneficial for process control in industrial production.

[0032] A comparison of Examples 1-6 and Comparative Examples 1-2 clearly demonstrates that whether the pulse frequency meets the requirement of <50Hz is a key factor determining the smoothness of the coating. Comparative Example 1 used a 60Hz pulse power supply (exceeding the ultra-low frequency range), resulting in a coating Ra=0.55μm; Comparative Example 2 used a 5000Hz high-frequency pulse power supply, resulting in a coating Ra=0.62μm, both significantly higher than the surface roughness values ​​of the examples. This is because the period of high-frequency or non-ultra-low frequency pulses is too short, leaving insufficient growth time for aluminum complex ions after nucleation, easily leading to the formation of loose dendrites and resulting in an uneven coating surface. This fully demonstrates the core technological value of the ultra-low frequency pulse power supply used in this invention. (Refer to...) Figure 1 and Figure 2 As shown, in Example 1, the aluminum coating area on the substrate surface has a relatively uniform texture distribution, and the coating as a whole presents a relatively flat state without obvious concavity or convexity defects; in Comparative Example 1, the coating edge presents an irregular wavy structure, the coating area has a texture distribution, and fine concavity or convexity or impurity points can be seen locally, and the overall flatness is poor.

[0033] The comparison between Example 1 and Comparative Example 3 shows that, compared with the traditional organic solvent system (anhydrous ethanol + AlCl3), the surface roughness of the coating using the chloroaluminate ionic liquid system (AlCl3-EMIC) decreased from 0.58 μm to 0.18 μm, and the smoothness was significantly improved. This is because the chloroaluminate ionic liquid system has advantages such as non-volatile, high chemical stability, and suitable conductivity, which can provide a more stable chemical environment for ultra-low frequency pulse electroplating. It avoids the coating defects caused by the volatility and poor stability of the traditional organic solvent system, demonstrating the technical advantages of this plating solution system.

[0034] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention is defined by the appended claims, not by the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0035] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for aluminum plating with ionic liquids, characterized in that, Electroplating was performed using a pulsed power supply with a frequency of <50Hz, and the electroplating solution was an ionic liquid based on aluminochloride.

2. The ionic liquid aluminum plating method according to claim 1, characterized in that, The pulse power supply output waveform is a square wave, a double-pulse square wave, or a sawtooth wave.

3. The ionic liquid aluminum plating method according to claim 1, characterized in that, The chloroaluminate system ionic liquid includes 1-methyl-3-ethylimidazolium chloride and aluminum chloride.

4. The ionic liquid aluminum plating method according to claim 1, characterized in that, The specific process parameters for the electroplating treatment include: duty cycle of 5% to 30%, average current density of 10 mA / cm² to 30 mA / cm², and time of 40 min to 60 min.

5. The ionic liquid aluminum plating method according to claim 1, characterized in that, Before electroplating, the substrate is activated by a current density of 50 mA / cm² to 100 mA / cm² and an activation time of 20 s to 50 s.

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