THE EARLY STAGES OF PRECIPITATION IN AL-LI ALLOYS

The initial stages of precipitation in supersaturated binary Al - Li s olid solution alloys are discussed. Results of experimental investigat ions referring mostly to ageing at or near room temperature are review ed and compared with predictions of theoretical treatments. In alloys containing more than about 7 at.% Li a fast continuous ordering (spino dal ordering) takes place before the somewhat slower decomposition. Th ere are indications that the decomposition starts with a homogeneous n ucleation in the ordered matrix. In artificially aged samples further precipitation takes place during the subsequent room temperature stora ge by nucleation within the disordered matrix phase. The ordered natur e of the precipitates determines their interaction with dislocations a nd thereby their effect on the mechanical properties of the precipitat ion-hardened alloy.