Complex Precipitation Sequences of Al-Cu-Li-(Mg) Alloys Characterized in Relation to Thermal Ageing Processes

Zhen Gao, Jiang-Hua Chen†, Shi-Yun Duan, Xiu-Bo Yang, Cui-Lan Wu

Fig.3 Microstructures of samples ageing at 200°C for various times: a-c 2, 12 and 72 h, respectively, viewed along <100>_Al. d δ′-θ′-δ′ composite phase as indicated by arrow in b. e, f 12 and 72 h, respectively, viewed along <011>_Al

Summarizing our observations and that reported for the samples aged at 180°C [6], the precipitation sequence in an Al-Cu-Li-Mg alloy treated with one-step artificial ageing at about 180-200°C can be considered as follows: SSSS → GPI + δ′-GPI-δ′ + GPB + T₁ → δ′-θ′-δ′ + GPB + T₁ + σ + S → GPB + T₁ + σ + S.