Abstract:The precipitation of S' phase in an 8090 Al-Li alloy under various aging conditions was investigated by transmission electron microscopy. The results show that a small quantity of S' precipitates precipitated on the grain and subgrain boundaries for the specimens aged to peak hardness during single aging. Cold working prior to aging promoted the widespread precipitation of S' phase because of increasing dislocation density. In natural aging the vacancies bound by Li atoms were released and formed dislocation loops. S' precipitates preferentially nucleated and grew on the dislocation loops.

Key words: AI-Li alloys  S' phase  aging precipitation