The external corrosion of aluminum plate is caused by crevice corrosion. The mechanism of crevice corrosion is that there is an oxidation recovery reaction at the crevice. The conditions of crevice corrosion are as follows: ① the crevice width is in the range of 0.025 ~ 0. 1 mm; ② Poor fluidity of corrosive medium; (3) the same electrode potential difference. The corrosion resistance of any metal or alloy depends on the oxide film or passivation film, which leads to crevice corrosion, because this oxide film or passivation film is only destroyed by high concentration of chloride ions or hydrogen ions, and then the dissolution rate of metal is accelerated. Because this batch of anti-rust aluminum plates is selected in the dry season from the end of July to the beginning of August, the air humidity is high and the surface roughness of anti-rust aluminum plates is not high, so it is possible to leave a lot of water vapor on the surface. The water vapor adsorbed on the surface does not completely evaporate during the processing such as cleaning, but accumulates together after cutting, so there must be a gap of 0.025 ~ 0. 1 mm between plates, and the water vapor is difficult to evaporate due to the tight pressure between plates. In this case, crevice corrosion is likely to occur. Especially, Al(OH)3 is the main corrosion product of metals, and its corrosion resistance depends on the passivation film Al2O3. This corrosion will occur in almost all corrosive media (including fresh water). If the medium contains chloride ions, corrosion is more sensitive.
Another cause of appearance corrosion of antirust aluminum plate is pitting corrosion. Aluminum can form an amorphous oxide film with a thickness of about 65438±0nm in a boring atmosphere. The test results show that the corrosion products contain many ions, such as Cl-, (OH)- and impurity Fe3+ plasma. Cl- is an ion that destroys the passivation state. When it partially enters the external passivation film, the passivation film partially degenerates and Al3+ is generated. When Al3+ and (OH)- in water combine to form hydroxide, some pH values there will decrease and become acidic. When Al3+ is generated, the released electrons flow to another address and become H+, which is consumed by the cathode reaction of oxidant recovery. The growth condition of corrosion pit is the concentration of solution, which can be obtained in the production and storage environment of antirust aluminum plate analyzed in this paper. The accumulation of white crystalline hydroxide and the existence of iron impurities accelerate pitting corrosion.
White spots are produced in the early stage of corrosion, and black spots are the products of the middle and late stage of corrosion, so the elements are slender. Compared with the previous products, the middle and late products have more elements and more impurities.
These are some factors of aluminum corrosion. Please consult Changsheng Aluminum Sheng Yuan at telephone number15016941987. I hope I can help you.