Independent and combined roles of trace Mg and Ag additions in properties precipitation process and precipitation kinetics of Al–Cu–Li–(Mg)–(Ag)–Zr–Ti alloys

The independent and combined roles of trace Mg and Ag additions in properties and precipitation of Al–Cu–Li–(Mg)–(Ag)–Zr–Ti alloys were studied. The independent roles of Mg additions are to promote the T 1 precipitation, decrease activation energy for the growth of θ′ plates and reduce lengthening rates of T 1 and θ′ plates. The independent roles of Ag additions are to retard GP-zone formation, stimulate the T 1 precipitation and enhance the lengthening rates of T 1 and θ′ plates. The combined additions of Mg and Ag augment and accelerate the nucleation of T 1 phases. The potent role of independent Mg additions in promoting the precipitation of θ′ is still effective in the presence of Ag, but it is weakened due to the strong interaction of Mg with Ag. The role of Ag as a stimulus in the lengthening of θ′ plates is diminished in the presence of Mg additions. The growth of T 1 is controlled by Cu solute diffusion along dislocations regardless of alloy contents of Mg and Ag. The growth of θ′ plates in the Ag-free alloy is controlled by vacancy-assisted diffusion of Cu.