Combined nuclear microprobe and TEM study of corrosion pit nucleation by intermetallics in aerospace aluminium alloys

A microscopic study of the onset of pitting corrosion has been conducted on the important aerospace alloy AA2024-T3 with the aim of understanding the role of intermetallic particles in triggering the formation of deep pits in the corroding surface. By trace element and correlation mapping using a 3 MeV H+ microprobe, it has been shown that Cu-Fe-Mn-Al particles in conjunction with S-phase particles have a high correlation with pit nucleation. Al-Cu correlation diagrams can be used to show dealloying of S-phase particles (CuMgAl2). Transmission electron microscopy and elemental mapping were used to look at the distribution of elements, particularly Cu, within pits.