Anodic undermining aluminum

Aluminum substrates are particularly prone to anodic undermining, whereas on steel this form of corrosion usually occurs under an applied potential [88]. Under conditions of free corrosion potential. 

Coated aluminum is very sensitive to anodic undermining while steel is more sensitive to cathodic delamination. 

This form of corrosion is more prevalent under organic coatings on aluminum than on other metallic surfaces, being a special form of anodic undermining. 

Anodic undermining is mainly reported on aluminum, which forms only Al + ions and porous corrosion products. Especially in the presence of chlorides, the natural oxide is easily attacked. Similarly to cathodic delamination, in this case also the anions and cations are separated leading to the formation of an HCl solution at the delamination front. 

A specific t) e of delamination that is also driven by a differential aeration cell is filiform corrosion [5,6,62,63]. In most cases it is related to anodic undermining, especially because it occurs mainly on aluminum alloys. Filiform corrosion is a specific t5 e of delamination that occurs only under atmospheric condition with relative humidity between qjproximately 50 and 90%. Small threadlike delamination tracks are formed that in general follow irregularities on the surface (either rolling or grinding marks). New interest in this special form of corrosion was stimulated by many practical cases along the coastal areas in Europe. It may be expected that new mechanistic information will become available within the next 2 years. 

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