POSITRON LIFETIME STUDY IN AL-LI ALLOYS

Light alloys such as Al-Li binary alloys are very important from the t echnological point of view due to their mechanical properties. The Al- rich side of the Al-Li binary alloy for Li concentrations between 5% a nd 25% atomic contains at room temperature a two-phase region formed b y the alpha terminal solid solution and the ordered metastable delta'- phase Al3Li. We present a systematic positron lifetime study for Li co ntent below and above 5at% (the appearance of delta'-phase) in the Al- rich side of the binary alloy to investigate the influence of Li conte nt and also the influence of Zr addition. We also present the study of the formation and dissolution of delta' precipitates, the recovery be haviour of an electron irradiated alloy, aging studies to monitor Li l osses, and the Li influence on the nucleation of defects in quenched a lloys. The technique has proved to be very sensitive to Li-rich zones in the alpha solid solution and to the growth and dissolution of delta ' precipitates due to the high positron affinity for Li in an Al matri x.