Specific precipitates in Al-Mg₂Si alloys aged after deformation

Precipitation behavior in Al-Mg-Si alloy artificially aged after mechanical deformation, was investigated by high resolution transmission electron microscopy (HRTEM ). Small particles ≃1.0 nm in diameter were observed together with dislocation lines after short aging treatment. They were arranged along the dislocation like a string of beads. The precipitates which appeared after peak aging, were lath-shaped and their longitudinal orientations were parallel to the [001] of the Al-matrix. Cross sectional observation revealed that the transverse orientation of the precipitate was deviated 10 degree from the [100] or [010] orientation of the Al-matrix. These specific precipitates were only observed in Al-Mg₂Si specimen annealed after deformation, but not in the specimen simply annealed. With the aging time, the specific precipitates disappeared and β phase particles became dominant.