[China Aluminum Industry Network] The aluminum foil used for negative electrode of aluminum electrolytic capacitors (hereinafter referred to as "anode aluminum foil") is one of the key raw materials for capacitor manufacturing. The negative electrode aluminum foil is chemically or electrochemically etched in a professional factory to form a negative electrode foil of different sizes, and then is wound together with an anode electrode foil and other materials impregnated with an electrolyte to form an aluminum electrolytic capacitor. . The quality of the aluminum foil directly determines the reliability and stability of the capacitor quality. With respect to the negative-electrode aluminum foil, its chemical composition and processing quality greatly influence the quality level of the aluminum foil. The two aspects of industrial production technology and quality control will be briefly described.
1. The chemical composition and technical characteristics of aluminum foil of negative pole material A wide variety of aluminum alloys for producing aluminum foil of negative pole material are reported at home and abroad. Aluminum alloys used for industrial production can be mainly classified into four types: aluminum-copper and aluminum-manganese. Department, pure aluminum and multi-element mixed system. Different types of anode foils have different performance characteristics, and the applicable corrosion processes vary widely. Electrode foil made of negative pole aluminum foil is required to have the following main quality indicators: higher capacity, tensile strength, number of bends, and low surface chloride ion content.
1.1. Aluminum-Copper Foil The electrode foil made of aluminum-copper anode-negative aluminum foil has the characteristics of high capacitance, low surface light ash and medium strength, and is particularly suitable for varieties requiring high electric capacity. Electrode foils are usually produced by chemical etching using hard-state foils.
A portion of the copper in the aluminum-copper alloy is solid-dissolved in the aluminum matrix, and a part thereof is precipitated as an intermetallic compound CuAl2. The electrode potential of copper is higher than that of aluminum. Solid solution of copper and CuAl2 become the core of corrosion. Copper has a certain strengthening effect, but the copper content in the aluminum-copper anode negative aluminum foil is limited, so its contribution to strength is not great. If the content of copper is too low, the effect of increasing the electrostatic capacity of the aluminum foil is not significant; if the content of copper is too high, coarse etch pits will be generated and excess corrosion will be formed, which will reduce the electrostatic capacity. Copper content is generally selected within the range of 0.1% to 0.5%.
1.2. Aluminum-Manganese Foil The electrode foil made of aluminum-manganese anode material aluminum foil has the characteristics of medium capacity, dark surface, easy to produce powder, and high strength. It is especially suitable for requiring higher strength and thinner specifications. Variety. Electrode foils are usually produced by chemical etching using hard-state foils.
Aluminum-manganese alloys are non-heat-treatable alloys. Manganese has a certain strengthening effect. With the increase of manganese content, the strength of the alloy increases. The solubility of manganese in aluminum is small, mainly in the form of MnAln distributed in the aluminum matrix to form a corrosive core. If the manganese content is too low, the amount of precipitated compound MnAln is small, and sufficient etching pits cannot be obtained. If the manganese content is too high, a coarse MnAln phase will precipitate, resulting in non-uniform corrosion. The manganese content is generally controlled between 0.8% and 1.3%.
1.3, pure aluminum foil electrode foil made of pure aluminum negative electrode aluminum foil has the characteristics of medium capacity, less uniform surface ash powder, low strength, good flexibility, good anti-fade stability, etc., especially suitable for stable requirements Higher species. Electrode foils are usually produced by alternating current electrochemical etching using a soft state foil.
The corrosion mechanism of pure aluminum foil and aluminum-copper foil and aluminum-manganese foil is different. Since there is no deliberately added copper, manganese, etc. in the pure aluminum foil, it can form the corroded core of the intermetallic compound. Therefore, only pure aluminum is used. The unavoidable impurities, such as copper, iron, silicon, etc., form intermetallic compounds with a small number of corrosive cores. The main corrosion core is the intergranular defect produced during the cold-working process. Dislocations are formed on the surface of the aluminum foil and dislocations are exposed. The aluminum purity of such foils is generally between 99.7% and 99.95%. With the increase of the purity of aluminum, the corrosion resistance of aluminum foils is also correspondingly improved.
1.4, multi-element combination foil
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