1. Surface treatment of aluminum and its alloys

1.1 Notion of natural oxide

When aluminum comes into contact with the atmosphere, it is instantly covered by a thin oxide layer, the outer part of which is more or less hydrated, depending on the temperature and relative humidity conditions at the time of its formation. This layer, generally between 2 and 4 nm thick, plays an important role in the metal's corrosion resistance, as it renews itself spontaneously.

However, this "ideal" vision of the metal's protection by its oxide needs to be qualified, because in industrial reality, many factors modify the extreme surface structure of aluminum.

In the vast majority of cases, aluminum alloys are used, to which additive elements are added. These are found in the natural oxide layer, sometimes...