With the rapid development of the electronics industry, the application of aluminum electrolytic capacitors has become more widespread, and the performance requirements are becoming increasingly stringent. Etched foil for aluminum electrolytic capacitors is a specialized electronic material for basic components in the electronic information industry, and the market demand for etched foil for medium-to-high-end medium- and high-voltage aluminum electrolytic capacitors exceeds supply. As etched foil for medium- and high-voltage electrolytic capacitors with rated voltages exceeding 200V, it has high quality requirements and is difficult to produce. Only a few manufacturers in China produce it, but the performance cannot meet user requirements. Therefore, there is an urgent need to continuously improve the specific capacitance while ensuring the bending strength of the etched aluminum foil. The specific capacitance of the etched foil used for the anode of high-voltage electrolytic capacitors is a key factor restricting the size of high-voltage, large-capacity electrolytic capacitors. Besides the quality of the foil itself, the etching process is a crucial step in obtaining high specific capacitance, high strength, and other excellent properties for aluminum foil used in aluminum electrolytic capacitors. Etching is a preliminary process in the manufacturing of the etched foil. The specific capacitance of the etched foil is the foundation and key to the specific capacitance of the etched foil. Various etching processes are used to obtain satisfactory performance, but some processes, while achieving excellent performance, introduce troublesome environmental problems (such as the chromic acid-hydrofluoric acid system). Therefore, people are committed to the development and research of high-performance and environmentally friendly corrosion processes. In recent years, domestic corrosion process systems represented by hydrochloric acid-sulfuric acid or hydrochloric acid-sulfuric acid-nitric acid have brought about a qualitative leap in the specific capacitance of corroded aluminum foil, and the performance has been greatly improved, opening up a broad road for the development of aluminum foil for capacitors in China. The author used the orthogonal experimental method to study the relevant process parameters and find the optimal process conditions. 1 Experiment 1.1 Corrosion Process Specifications The experiment used 110μm thick bright foil, which is high-purity aluminum with a purity of 99.99%. The sulfuric acid-hydrochloric acid corrosion system was used. The corrosion process was as follows (foil speed 100cm/min): 1.2 Performance Testing The specific capacitance of the corroded foil was measured according to the Japanese JCC2000 standard. The voltage was 600V. The bending strength of the corroded foil was measured using an aluminum foil bending tester. The corrosion morphology and cross-sectional morphology of the corroded foil were observed and analyzed using an H-8010 scanning electron microscope. After the resin adhesive filling the etched foil cured, the etched foil was removed by alkali dissolution, and the morphology of the etched pits was observed using a SEM-6480LV scanning electron microscope. 2. Results and Discussion The experimental results of changing the corrosion process specifications are shown in Table 2. Aluminum and its alloys are metals and alloys with self-purification properties, and electrochemical pitting corrosion occurs in certain acidic media (such as media containing Cl-). The pitting corrosion process includes: 1. nucleation on the pure metal surface; 2. pit growth. The old man's corrosion process controls these two processes. The experimental results in Table 2 show that by changing the levels of various factors, the aluminum foil corrosion process was optimized to obtain ideal results. As can be seen from Table 2, the influence of each factor on the experimental results is not entirely the same. According to range analysis, the composition of the corrosion solution, corrosion time, temperature, and corrosion voltage are significant factors affecting the specific volume of etched aluminum, while the composition of the corrosion solution, corrosion time, and temperature are important factors affecting the bending strength of the etched foil. 2.1 Effect of Corrosive Medium Ratio on Corrosion Foil Performance The effect of corrosion solution composition on corrosion foil performance is shown in Figure 1. As can be seen from Figure 1, with the increase of sulfuric acid component ratio, the specific volume of the corrosion foil reaches a maximum value, while the bending strength consistently decreases. Aluminum and its alloys suffer from pitting corrosion in halide-containing media. During anodizing, the presence of Cl- in the medium is sufficient to cause pitting corrosion, and the pitting potential decreases with the increase of Cl- concentration in the medium, making pitting corrosion easier to occur. According to the purification adsorption theory, pitting is caused by the adsorption of corrosive anions (Cl-) on the surface of the purification film, followed by the passage of ions through the purification film. Increasing the Cl- concentration is beneficial to increasing the nucleation rate of pitting corrosion on the aluminum foil surface. When the surface pits nucleate and continue to develop deeper, forming an alumina purification film on the pit wall, oxidizing acids play a key role. Therefore, increasing the sulfuric acid ratio is beneficial to film formation, and thus the corrosion foil exhibits the maximum specific volume when the solution composition is ψ(H2SO4:HCl) = 3:1. Figure 2 shows the surface pitting of corrosion foils obtained with different solution compositions. When the solution composition is ψ(H2SO4:HCl) = 3:1, the pore size of the etched foil is small and uniform, the total corrosion area increases, and the specific volume reaches its maximum. When the solution composition is ψ(H2SO4:HCl) = 4:1, the pore size of the etched foil is large and uneven, many pore walls collapse, the total corrosion area decreases, and the specific volume decreases rapidly. The bending strength of the etched foil depends on the thickness of the core layer (i.e., the thickness of the uncorroded portion of the aluminum foil) and the uniformity of the pores. The thicker the core layer, the more uniform the pores, and the higher the bending strength, but the lower the specific volume; the thinner the etched layer, the more uneven the pores, and the lower the bending strength. With the increase of the H2SO4 ratio in the etched solution, the extension of the corrosion time, the increase of the pore depth, the decrease of the remaining aluminum foil thickness, and the decreasing bending strength. Figure 3 shows the cross-sectional morphology of the etched foil. During the bending experiment of the etched foil, the alumina on the pore walls is a brittle material that is easily broken, and the main load-bearing component is the remaining aluminum material. 2.2 Effect of Corrosion Voltage on Electrode Foil Performance Figure 4 shows the changes in specific volume and flexural strength of the corroded foil with anodic oxidation voltage. There is an optimal value for specific volume, while the flexural strength decreases accordingly. According to the principle of electrochemical corrosion, the formation of pitting corrosion on the filter surface is related to the critical potential. Pitting corrosion can only occur when the electrode potential in a local area of ​​the metal surface reaches or exceeds the critical potential value (pitting corrosion potential). As the electrode potential increases, the sensitivity to pitting corrosion intensifies. Therefore, pitting corrosion is closely related to the electrode potential. During the anodizing process of aluminum foil, increasing the voltage promotes both the nucleation and growth of pits, but the magnitude of the effect differs. When the nucleation rate is higher than the growth rate, the specific volume of the corroded foil increases with increasing voltage. However, when the voltage can cause the adjacent pit walls to corrode and collapse, the specific volume of the corroded foil will decrease with increasing voltage. Increasing the voltage is beneficial for increasing the nucleation rate and achieving uniform corrosion, while the flexural strength of the corroded foil will decrease non-linearly. 2.3 Effects of Corrosion Temperature and Corrosion Time on the Performance of Corrosion Foil The effects of increasing the corrosion environment temperature and extending the corrosion time on the performance of aluminum foil are shown in Figure 5. As can be seen from Figure 5, with increasing temperature, the specific volume of the corrosion foil reaches an extreme value, while the bending strength decreases linearly. With prolonged corrosion time, the specific volume of the corrosion foil also reaches an extreme value, while the bending strength decreases almost linearly. After the nucleation of pinholes on the aluminum foil surface, further corrosion mainly occurs within the pinholes. This process is self-promoting; the rapid dissolution of the metal within the pinholes causes excessive cations to be generated. As a result, to maintain electroneutrality, anions (Cl-) migrate from outside the pinholes into the air, also increasing the Cl- concentration, thus forming a concentrated solution of metal chlorides within the pinholes. This concentrated solution helps maintain the active state of the metal surface within the pinholes. As the pitting corrosion deepens and corrosion products cover the pit opening, oxygen has difficulty diffusing into the pit, resulting in the deposition of corrosion products at the pit opening and the formation of a closed cell with the rust layer. After the formation of a closed cellular structure, the migration of substances inside and outside the pore becomes more difficult, leading to a greater concentration of metal chlorides within the pore. The hydrolysis of chlorides further increases the acidity of the medium, which in turn accelerates anodic dissolution within the pore, contributing to the deep-penetrating ability of the pore. The linear decrease in bending strength with increasing temperature and time is easily understood. In the corrosion process of all metallic materials, increasing the corrosion environment temperature and extending the corrosion time will intensify metal corrosion. As the surface corrosion depth of aluminum foil increases, the bending strength naturally decreases. However, when the temperature rises to a certain level, the pore becomes blocked, the reaction within the pore stops, and the bending strength does not change significantly. However, the specific volume of the corroded foil is directly proportional to the amount of alumina on the corroded surface. Increasing the corrosion temperature and extending the corrosion time intensifies the corrosion of the aluminum foil, increases the aluminum surface area, and increases the specific volume of the corrosion rate. As corrosion progresses further, the walls of the corrosion pores may collapse and connect, resulting in a slow increase or even a decrease in the specific volume of the corroded foil. This phenomenon can be seen in Figures 2 and 6. Furthermore, while the aluminum foil undergoes extensive chemical corrosion on its surface, its effective thickness also decreases due to erosion. Therefore, the total specific volume does not increase linearly with the increase of corrosion degree. The specific volume of the corrosion foil mainly depends on the area of ​​the alumina forming the porous layer. The area of ​​the porous layer is related to the number, size and depth of the pores, as well as the corrosion loss due to the erosion and collapse of the pore walls during the corrosion process. The significant factors affecting the specific volume of the corrosion foil are the composition of the corrosion solution, the corrosion voltage and charge, the reaction temperature and the treatment time. Optimizing the composition of the corrosion solution, the voltage and charge, the temperature and time will result in a high specific volume. The bending strength of the corrosion foil depends on the thickness of the aluminum core layer and the uniformity of the pores. The composition of the corrosion solution, the temperature and the corrosion time are important factors affecting the bending strength of the corrosion foil. 3 Conclusion (1) In the hydrochloric acid-sulfuric acid corrosion system, as the proportion of H2SO4 increases, the strength of the corrosion foil decreases, but its specific volume first increases and then decreases. The optimal value of ψ(H2SO4:HCl) is 3:1. (2) In the voltage range of 6 to 10V, the higher the anodic oxidation voltage, the higher the specific volume of the corrosion foil. However, the bending strength is highest at a voltage of 8V. (3) Increasing the corrosion temperature and extending the corrosion time will reduce the remaining aluminum foil thickness and decrease the bending strength. However, the effect on the specific volume of the corrosion foil is complex. The specific volume increases gradually with increasing corrosion temperature and extending corrosion time, and then begins to decrease after reaching a maximum value. The rate of decrease in specific volume is faster with extended corrosion time.