The chemical cleaning of 7075T651 aluminum plate and aluminum alloy usually adopts weak acid or weak alkaline solution, solvent and its vapor, surfactant and other solutions to remove surface grease and dirt. This treatment can adopt chemical or electrochemical methods, the former is called chemical cleaning, also called degreasing or degreasing; Electrochemical cleaning has not been widely used in surface treatment of aluminum. In order to thoroughly remove grease or pollutants, some processes use a cleaning solution with strong corrosiveness, together with an oxide film or a composite oxide film, to clean and remove the aluminum material, so that the aluminum material presents a clean surface with uniform wetting. Lubricant and rolling oil are used in the production of aluminum materials, polishing paste is used in mechanical polishing, and necessary grease such as antirust oil is used in the storage of semi-finished products; In addition, if aluminum is not paid attention to during operation and transportation, it is likely to stick to unnecessary pollutants such as lubricating grease, dust and impurity particles of mechanical equipment, which will pollute the surface of aluminum and seriously form dirt. After the surface of aluminum comes into contact with grease or pollutants, it will hinder the full contact between the surface and the treatment solution, and the evenly wetted surface cannot be obtained; If grease or pollutants are brought into the subsequent treatment bath, the composition of the bath will be destroyed. Therefore, in the process of aluminum surface treatment, chemical cleaning should be carried out first to remove grease, pollutants, dirt and aluminum oxide film on the surface, so that aluminum can obtain a clean surface with uniform wetting.

Surface oxide film of aluminum. Aluminum is a very active metal, and its standard electrode potential is very negative. However, the surface of aluminum in air is usually covered with a very thin oxide film formed in air, and its electrode potential moves forward at this time. The thickness of aluminum oxide film formed in air is about l ~ 3 nm. A high-temperature oxide film is formed on the surface of aluminum during heat treatment, and the thickness of the high-temperature oxide film is more than ten times that of the oxide film formed in air. In the conventional chemical cleaning process, it is difficult to remove this high-temperature oxide film of aluminum, especially for the high-temperature oxide film seriously polluted by oil or pollutants.

Most aluminum and aluminum alloys used in industry contain certain alloying elements. This means that the oxide film on the surface of aluminum alloy also contains more or less oxides of iron, magnesium, manganese, copper, zinc and so on. Usually, it is irrelevant that the oxide film of aluminum contains these oxides. The widely used building aluminum alloy 6063 contains 0.45% ~ 0.9% magnesium. In some aluminum alloys (such as 6061, 6070 and 6082), the upper limit of magnesium content is as high as 1.29/5. In 5000 series (Al-Mg series) aluminum alloys, the magnesium content is even higher, usually about 0.5% ~ 5%, and the magnesium content of 5A13 aluminum alloy is very high, ranging from 9.2% to 10.5%. This series of aluminum alloys are mainly processed into aluminum alloy plates and coils, or used for mechanical deep processing to form deep-processed products. 7000 series (Al-Zn-Mg series) aluminum alloy contains high zinc and magnesium, among which the typical high-strength aviation aluminum alloy 7075 contains 2.1% ~ 2.9% magnesium, 5.19/5 ~ 6.1% zinc and 1.2% ~ 2.0% copper. Therefore, the oxide film of this series of aluminum alloys is rich in oxides containing zinc and magnesium, and there may be deformation of aluminum oxide film.

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