Abstract: X-ray method was used to investigate the effect of retrogression time on δ′ precipitation in an Al-9.74%Li alloy treated by retrog ression. The investigation results show that the hardness clearly drops in short retrogression time due to the dissolution of δ′ particles. A weak peak value of hardness was achieved and gradually dropped due to the δ′ particles repreci pitation and coarsening because of increasing retrogression time.

Key words: Al-Li alloy, retrogression, δ′ phase particles