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 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \left[ {\bar{1}06} \right]_{{\beta^{\prime \prime } }} , $$\end{document} 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.