The corrosion resistance of aluminum alloy depends on the stability of oxide film in different environments. In a dry atmosphere, the passivating film is not easy to be damaged, is stable. Local pitting will occur when exposed to an outdoor atmosphere for a long time. This is mainly because after the dust ions are deposited on the surface, the metal surface in the water film under the dust ions forms an anoxic zone, which leads to the destruction of the passivation film and the decline of self-passivation ability. In the industrial atmosphere, the protective film is vulnerable to damage, and the corrosion resistance decreases, especially in the area polluted by acid rain of sulfur oxides. The aluminum surface generally black, black or gray-black spots. In the ocean-atmosphere, CL – has a strong destructive effect on the passivating film.
The blunt state of aluminum alloy in seawater is unstable, and the local corrosion is its main form of corrosion. The common local corrosion is hole corrosion and crevice corrosion. Pure aluminum will not produce intercrystalline corrosion, aluminum alloy has a greater intercrystalline corrosion sensitivity. Stress corrosion mainly occurs in high-strength aluminum alloy after heat treatment, and they are all intercrystalline cracking type.
When aluminum alloys come into contact with most metals in seawater, they are anodized and corrosion is accelerated. Aluminum alloy is said to be the most corrosive, splashing area is the lightest, the range of the middle. In the full immersion or tidal range, the surface of the Marine biological pollution than other metals, which can aggravate the partial corrosion of aluminum alloy.
In the industrial environment, the average corrosion rate of aluminum alloy for 20 years is about 1 carbon m/a. In different corrosion environments, the average point corrosion degree of aluminum alloy in 20 years is much more serious. Urban environment Marine environment 85~260
Aluminum is at risk of galvanic corrosion when it is in contact with metals such as steel, copper and stainless steel. Therefore, aluminum and these metals are insulated from each other.
Aluminum alloys containing 4.5% magnesium and 1% manganese, called seawater aluminum alloys, have good corrosion resistance in the Marine Environment. This kind of aluminum alloy is used more at the antifouling paint that does not contain cuprous oxide. Because the antifouling paint with cuprous oxide as the main antifouling agent is in contact with the aluminum hull, the corrosion of the hull is caused by the galvanic action