Generally speaking, the basic types of industrial aluminum profile
and aluminum alloy corrosion: pitting corrosion, galvanic corrosion crevice corrosion, intergranular corrosion, stress corrosion, exfoliation corrosion, fatigue corrosion, filamentous corrosion, etc., in this paper, only introduces the common corrosion phenomenon in the production and use of industrial aluminum profiles.
Pitting corrosion, also known as pore corrosion, is a very local corrosion form that produces needle-like, puncture-like and pore-like on metals. Pitting corrosion is a unique form of anodic reaction and an autocatalytic process. Aluminum in the atmosphere, fresh water, or neutral aqueous solution will occur pitting corrosion, serious can also lead to perforation, but the corrosion hole may eventually stop development, corrosion to maintain a limit. The ultimate degree of pitting corrosion is related to the medium alloy, such as chloride ion, fluoride ion and so on. There must also be substances that promote the cathodic reaction, such as dissolved oxygen in aqueous solution, copper ions, etc. From the industrial aluminum profile aluminum alloy fine, aluminum profile high purity aluminum is generally difficult to occur pitting corrosion, aluminum alloy containing copper pitting corrosion is the most obvious.
Galvanic corrosion is also a characteristic corrosion form of aluminum. The spontaneous potential of aluminum is very negative. When aluminum is in contact with other metals, aluminum is always in the anode to accelerate its corrosion. Galvanic corrosion is also known as bimetallic corrosion. The severity of galvanic corrosion is determined by the relative position of two metal potential sequences. The larger their potential difference, the more serious the galvanic corrosion, almost all aluminum alloy can not avoid galvanic corrosion.
Crevice corrosion, industrial aluminum profile aluminum itself or aluminum and other materials surface contact when there is a gap, due to the difference of the inflatable battery, the corrosion in the gap accelerated, and the gap has no effect. Crevice corrosion is not dependent on the type of alloy. Crevice corrosion can occur even in very corrosion-resistant alloys. In recent years, the mechanism of crevice corrosion has been studied more deeply, and the acidic environment at the crevice tip is the driving force of corrosion. Subsediment corrosion is a form of crevice corrosion.
The cause of intergranular corrosion is related to improper heat treatment. Alloying elements or intermetallic compounds precipitate along grain boundaries, which are anode to the grains and form the corrosion cell, resulting in accelerated intergranular corrosion.
Filamentous corrosion. Filamentous corrosion is a submembrane corrosion that develops under the membrane in a worm-like manner. This membrane can make the paint film, as well as other layers, do not normally occur under the anodized film. Filamentous corrosion was first discovered under the layer of aircraft, and has been reported in europe this year under the coating of aluminum profiles in the construction industry. Filamentous corrosion is related to alloy composition, pretreatment before aluminum profile coating and environmental factors such as humidity, temperature, chloride, etc.