Formation of multiple orientation relationships of Q precipitates in Al–Mg–Si–Cu alloys

Precipitation of Q laths/rods in some age-hardenable aluminium alloys has been traditionally accepted to occur with a single orientation relationship with the α-Al matrix. In this study, the orientation relationships of Q precipitates are characterized by atomic resolution high-angle annular dark-field scanning transmission electron microscopy. Contrary to the long-standing view, multiple orientation relationships are found between Q precipitates and the α-Al matrix. These orientations are correlated by rigid-body rotations about the long axes of the Q laths/rods.