Effects of CrxMo(0.2-x) addition on the dispersoids evolution and mechanical properties of Al–Cu–Mg–Ag–Mn alloy

Abstract

Unlike the rod-like T–Al20Cu2Mn3 dispersoids, the spherical Al7(Cr, Mn) and Al6(Fe, Mn, Mo) precipitated in Al–Cu–Mg–Ag–Mn alloys with CrxMo(0.2-x) addition, retained the deformed substructure, and acted as a dispersion reinforcement. In this study, the precipitation behavior of dispersoids in Al–Cu–Mg–Ag–Mn alloys with various CrxMo(0.2-x) (x = 0.15, 0.10, 0.05 wt.%) at 400 °C/12 h + 515 °C/24 h homogenization was investigated. The compositional and structural evolution of dispersoids in Al–Cu–Mg–Ag–Mn alloys were investigated by optical microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The effects of CrxMo(0.2-x) addition on morphology, size and number density of dispersoids inhibited the recrystallization behavior and improved the mechanical properties of alloys in varying degrees. When x = 0.15 in CrxMo(0.2-x), the large amount of Al7(Cr, Mn) precipitates to refine the T–Al20Cu2Mn3, and dispersoid-free zones (DFZ) significantly decreases. As x decreases to 0.05, the homogeneous Al6(Fe, Mn, Mo) dispersoids present the opposite precipitation trend of T–Al20Cu2Mn3 to compensate for the DFZ. During the deformation and subsequent heat treatment, the Al–Cu–Mg–Ag–Mn alloy with Cr0.05Mo0.15 addition maintains the highest substructure and dislocation density owing to the highest number density of spherical dispersoids, demonstrating excellent mechanical properties at ambient and elevated temperatures.