Exfoliation

Exfoliation corrosion is considered a form of intergranular corrosion that attacks metals which have been mechanically deformed, primarily by extrusion or rolling, producing elongated grains directionally aligned. Most often, the attack is initiated at exposed endgrains, as has been the case with aircraft skins around fasteners see Figure 22. This form of corrosion is most evident in some of the aluminum alloys and is shown in Figure 23. Metals susceptible to exfoliation corrosion are aggressively attacked in environments corrosive to that particular metal. As an example, AA 2024-T4 is known to perform well in urban type environments,
but is severely attacked in marine environments.

Managing Exfoliation Corrosion

As with intergranular corrosion, the proper selection of alloy and heat treatment to avoid precipitation at grain boundaries is the primary method to combat exfoliation. Reducing the area of endgrain surfaces will limit the initiation of attack, as well as the use of barrier coatings.