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 theta' plates and reduce lengthening rates of T-1 and theta' 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 theta' 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 theta' 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 theta' 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 MB and Ag. The growth of theta' plates in the Ag-Free alloy is controlled by vacancy-assisted diffusion of Cu. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.