Transmission electron microscopy and X-ray diffraction study of T-1 and Omega precipitates in Al-Li alloys

Two Al-Li-Cu-Mg based alloys were studied by means of transmission electron microscopy and X-ray diffraction. Apart from the well known precipitation of delta', beta', S' and T-1 phases in both alloys, coprecipitation of the Omega phase was observed in the low Li, high Cu:Mg,Ag containing alloy. Sim ulation and experimental electron nanodiffraction and X-ray diffraction tec hniques were used in order to differentiate the T-1 From the Omega phase. T he Omega precipitates seem to nucleate preferentially on subgrain boundarie s, possibly due to the higher dislocation density at the boundaries compare d with that of the matrix inside the grains.