Discontinuities in the porous anodic film formed on AA2099-T8 aluminium alloy

The anodizing behaviour of constituent particles (Al–Fe–Mn–Cu) and dispersoids (Al–Cu–Mn–Li and β′(Al3Zr)) in AA2099-T8 has been investigated. Low-copper-containing Al–Fe–Mn–Cu particles anodized more slowly than the alloy matrix, forming a highly porous anodic oxide film. Medium- and high-copper-containing Al–Fe–Mn–Cu particles were rapidly dissolved, resulting in defects in the anodic film. The anodizing of Al–Cu–Mn–Li dispersoids is slightly slower than the alloy matrix, forming a less regular anodic oxide film. β′(Al3Zr) dispersoids anodized at a similar rate to the alloy matrix. Further, the potential impact of the discontinuities in the resultant anodic films on the performance of the filmed alloy is discussed.

► Low-copper-containing intermetallics anodized more slowly than the alloy matrix.
► Defects are generated due to the dissolution of Al–Fe–Mn–Cu particles.
► Al–Cu–Mn–Li dispersoids anodized slightly slower than the alloy matrix.
► β′(Al3Zr) dispersoids anodized at a similar rate to the alloy matrix.
► Morphological and compositional discontinuities are present in the film.