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

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 delta', beta', S' and T-1, while fewer T-2 and Al7Cu2Fe precipitates were also observed. The addition of up to 0.5 wt % Ag diminishes the delta' and T-1 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 Omega phase simultaneously with delta', beta', S' and T-1 phases. Due to the low Li concentration an unusual growth of the delta'/beta' precipitates at the expense of the delta' precipitates was also observed. (C) 1998 Kluwer Academic Publishers.