Studies of orientations of β'' precipitates in Al-Mg-Si-(Cu) alloys by electron diffraction and transition matrix analysis

Transition matrix, combine with high-resolution transmission electron microscopy (HRTEM) and stereographic projection, was used in this article to predict and characterize the orientations and electron diffraction patterns of β'' precipitates in Al-Mg-Si-(Cu) alloys. It was found that the β'' phases as the main strengthening precipitates had 12 variants with Al matrix, and the orientation relationships could be expressed as (010) _β''//{100}_Al, [001]_β''// <310>_Al, and [100]_β''// <230> _Al. Further, based on the C-centered monoclinic structure of β'' precipitate, a new diffraction patterns model under the [001]_Al zone axis could be established, which was in good agreement with the experiment date. Further, it could be used to explain reasonably some issues (for example, the ''cross-shaped'' diffraction streaks phenomenon). Simultaneously, we also found that the β'' precipitates had only three different zone axes, [010]_β'', [304]_β'', and [106] _β''; parallel to the [001]_Al direction when they were precipitated from the Al matrix, and the β'' precipitate might deviate 1.6 deg from its original orientation because of the lattice relaxation.