HRTEM Observation of Intermediate Precipitates in Al-Mg-Si Alloys Containing Ag

This study uses high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy to identify the crystal structure of a metastable phase in a Ag-added Al-Mg-Si alloy, which we compared with the crystal structure of the β′-phase in Al-Mg-Si alloys without Ag. SAED patterns and HRTEM images of the β′-phase in the Ag-added Al-Mg-Si alloy were similar to those of the β′-phase in the Al-Mg-Si alloy without Ag. However, the lattice spacings were modified by the substitution of Ag into the β′-phase. Analyses of the obtained HRTEM images and SAED patterns revealed that the β′-phase has a more complex crystal lattice that consists of large (0.69 nm) and small (0.24 nm) hexagons. Discrete variational (DV-Xα) calculations were applied to the small cluster of the β′-phase. The results indicate that it should be possible to substitute silver in the β′-phase.