Ag2Al plates in Al–Ag alloys

Abstract

Abstract The late stages of precipitation in aluminum-rich Al –Ag alloys with silver contents from 3 at.% to 22 at.% were studied with transmission electron microscopy. Shapes, sizes, and arrangements of plates of the stable hexagonal Ag2Al phase forming on {111} planes of the f.c.c. matrix were analysed. The high-angle annular dark-field contrast in scanning transmission electron microscopy is calibrated. This calibration allows for the quantitative measurement of plate thicknesses from high-angle annular dark-field scanning transmission electron micrographs of Ag2Al plates inclined to the electron beam. Results from these measurements are in good agreement with direct bright-field micrographs of plates viewed edge-on. For samples with silver contents above 12 at.% a parallel lamellar arrangement of fine γ-plates and Al-rich matrix is found after extended heat treatments.