The effect of Ag additions on the microstructure of aluminium–lithium alloys

Abstract

Minor quantities of Ag have been added to Al–Li–Cu–Mg–Zr alloys. Their microstructure has been studied by means of optical metallography, transmission electron microscopy and X-ray diffraction. In the high Li, low Cu : Mg ratio alloys the main phases found were δ′, β′, S′ and T₁, while fewer T₂ and Al₇Cu₂Fe precipitates were also observed. The addition of up to 0.5 wt% Ag diminishes the δ′ and T₁ precipitates size. This is attributed to a small increase of Li solubility in the matrix. In the low Li, high Cu : Mg ratio alloy the addition of 0.2 wt % Ag resulted in the precipitation of Ω phase simultaneously with δ′, β′, S′ and T₁ phases. Due to the low Li concentration an unusual growth of the δ′/β′ precipitates at the expense of the δ′ precipitates was also observed.