Abstract
The interaction mechanisms between dislocations and semi-coherent, needle-shaped β′
precipitates in Al–Mg–Si alloys have been studied by High Resolution Transmission Electron
Microscopy (HRTEM). Dislocation loops appearing as broad contrast rings around the
precipitate cross-sections were identified in the Al matrix. A size dependency of the
interaction mechanism was observed; the precipitates were sheared when the longest
dimension of their cross-section was shorter than approximately 15 nm, and looped
otherwise. A more narrow ring located between the Al matrix and bulk β′ indicates the
presence of a transition interface layer. Together with the bulk β′ structure, this was further
investigated by High Angle Annular Dark Field Scanning TEM (HAADF-STEM). In the bulk β′
a higher intensity could be correlated with a third of the Si-columns, as predicted from the
published structure. The transition layer incorporates Si columns in the same arrangement
as in bulk β′, although it is structurally distinct from it. The Z-contrast information and
arrangement of these Si-columns demonstrate that they are an extension of the Si-network
known to structurally connect all the precipitate phases in the Al–Mg–Si(–Cu) system. The
width of the interface layer was estimated to about 1 nm.
precipitates in Al–Mg–Si alloys have been studied by High Resolution Transmission Electron
Microscopy (HRTEM). Dislocation loops appearing as broad contrast rings around the
precipitate cross-sections were identified in the Al matrix. A size dependency of the
interaction mechanism was observed; the precipitates were sheared when the longest
dimension of their cross-section was shorter than approximately 15 nm, and looped
otherwise. A more narrow ring located between the Al matrix and bulk β′ indicates the
presence of a transition interface layer. Together with the bulk β′ structure, this was further
investigated by High Angle Annular Dark Field Scanning TEM (HAADF-STEM). In the bulk β′
a higher intensity could be correlated with a third of the Si-columns, as predicted from the
published structure. The transition layer incorporates Si columns in the same arrangement
as in bulk β′, although it is structurally distinct from it. The Z-contrast information and
arrangement of these Si-columns demonstrate that they are an extension of the Si-network
known to structurally connect all the precipitate phases in the Al–Mg–Si(–Cu) system. The
width of the interface layer was estimated to about 1 nm.
