An atomic-resolution investigation of precipitation evolution in Al-Mg-Ag alloys

Abstract The compositional and structural evolution of precipitates in Al-Mg-Ag alloy were investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The study suggests that Ag-addition promoted the formation of elliptical- shaped GP zones at the early-aged stage. Then the GP zones transformed to metastable MgAg phase and the orientation relationship between the precipitate and Al-matrix was (1 0 0) MgAg //(1 0 0) α . The equilibrium phase in Al-Mg-Ag alloy can be speculated as rod-like body-centered cubic T phase (Mg 32 (Al, Ag) 49 ) with the lattice parameter of a = 1.41 nm. The rod-like MgAg phase and T phase serve as the key strengthening mechanism of Al-Mg-Ag alloys at the peak-age stage. In addition, the role of GBPs in the strengthening effect of Al-Mg-Ag alloys was also discussed in detail.