Filiform corrosion of aluminium sheet. I. Corrosion behaviour of painted material

Filiform corrosion (FFC) of cold rolled and painted aluminium substrates in the AA1000, 3000 and 8000 series, in various tempers and subjected to various pretreatments, were investigated by use of an accelerated laboratory test. Modifications in temper from the as-fabricated conditions were obtained by cold rolling and annealing in the laboratory. As a result of annealing, the surface was activated on alloys AA3005 and AA8006, giving rise to severe FFC. By removing or transforming the cuter surface by pretreatment prior to painting, such as by etching or anodising, the FFC resistivity of the annealed substrates was dramatically improved. The substrates from the AA1000 series were less affected by FFC, indicating a smaller effect of annealing. The FFC susceptibility of the AA1000 series substrates increased with increasing iron content. (C) 1998 Elsevier Science Ltd. All rights reserved