Anisotropic growth mechanism of octagonal plate-shaped β-phase in Al-Mg-Si alloys with and without Ag addition

This study investigates the anisotropic growth mechanism of plate-shaped β-phase precipitates in Al-Mg-Si alloys with and without Ag addition by using optical microscopy (OM), focused ion beam (FIB), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). In the Al-Mg-Si alloy, three distinct facets(001) Al //(001) β , (010) Al //(110) β , and (012) Al //(111) β were identified at the β-phase facet, indicating a complex faceted growth mechanism. In contrast, the β-phase in the Al-Mg-Si-Ag alloy exhibited only two primary facets: (001) Al //(001) β and (010) Al //(110) β . High-resolution transmission electron microscopy (HR-TEM) and energy-dispersive X-ray spectroscopy (EDS) showed Ag segregation at the β-phase/Al matrix facet in the Al-Mg-Si-Ag alloy, which is believed to influence facet formation and restrict the development of the third facet. These results provide new insights into the role of Ag in modifying the interfacial structure and growth behavior of β-phase precipitates, contributing to the fundamental understanding of microstructural evolution in 6xxx series aluminum alloys.