Nature of second phases present in an As-cast Al-Cu-Li-Mg-Ag-Zr alloy

An as-cast Al-Cu-Li-Mg-Ag-Zr alloy, having chemical composition close to th at of the Weldalite alloy, has been examined using a combination of X-ray d iffraction (X-RD), differential scanning calorimetry (DSC), scanning electr on microscopy (SEM) and electron probe microanalysis (EPMA). Four types of second phases were identified as products of solidification: T-1 (Al2CuLi), theta (Al2Cu), T-B (Al7Cu4Li) and S (Al2CuMg). The S phase is present in r ather small amounts, and, as a result, this phase could not be detected by XRD. The presence of S phase was detected, using DSC, through its associati on with a low-temperature eutectic in the constituent Al-Cu-Mg system. The detection of this eutectic contributes further towards the determination of the upper limit of temperatures for ingot homogenisation. DSC also detects the presence of a ternary eutectic in the constituent Al-Cu-Li system, and reconfirms the presence of the associated Li-bearing second phases in the alloy. Combinations of SEM and EPMA reveal that the S phase dissolves small amounts of Ag, and that the nature of association of both Ag and Mg with T -1 and theta phases during their evolutionary stages is similar.