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 micr ostructure has been studied by means of optical metallography, transmission electron microscopy and X-ray diffraction. In the high Li, tow Cu: Mg rati o 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 attribute d to a small increase of Li solubility in the matrix. In the low Li, high C u:Mg ratio alloy the addition of 0.2 wt% Ag resulted in the precipitation o f Omega phase simultaneously with delta', beta', S' and T1 phases. Due to t he low Li concentration an unusual growth of the delta'/beta' precipitates at the expense of the delta' precipitates was also observed. (C) 1998 Kluwe r Academic Publishers.