Atom probe tomography study of Mg-dependent precipitation of Ω phase in initial aged Al-Cu-Mg-Ag alloys

The association between Mg variations and the precipitation of Omega phase in Al-Cu-Mg-Ag alloys were investigated by transmission electron microscopy and quantitative atom probe tomography analysis. After aging at 165 degrees C for 2 h, the highest number density of a phase was revealed in 0.81Mg alloy, leading to the highest strength properties. The lowest strength properties of 0.39Mg alloy was related to the lowest precipitation kinetics of Omega phase. The parabolic change in the plate number density with increasing Mg highlighted the existence of a critical Mg content that contributed to the strongest precipitation kinetics of Omega phase. The number density of Mg-Ag co-clusters was not the sole factor in controlling the Omega precipitation. It was found that the precipitation of Omega phase was not only determined by initial Mg-Ag co-clustering but also related to the effective competition for solutes. In addition, the cluster-dominated microstructure facilitated the dense precipitation of Omega phase. (C) 2015 Elsevier B.V. All rights reserved.