Effects of small additions of Mg and Ag on precipitation process of Al-Cu-Li-(Mg)-(Ag)-Zr alloys

The effects of small Mg and Ag additions on precipitation process of Al-Cu-Li-(Mg)-(Ag)-Zr alloys were studied. The results show that the independent roles of Mg additions are to promote the precipitation of GP zones, theta' and T-1 phases; the independent roles of Ag additions are to retard the formation of GP zones, stimulate the T-1 precipitation; the combined additions of Mg and Ag increase and accelerate the precipitation of T-1 phases. It is suggested that the strong interaction of Mg with Ag may be favorable to the formation of stacking faults and acting as catalyst for linking Li and Cu atoms required for the T-1 precipitation. The potent role of independent Mg additions in promoting the precipitation of theta' is also effective in presence of Ag, but it is weakened due to the strong interaction of Mg with Ag.