Microstructure and mechanical properties of Mg, Ag and Zn multi-microalloyed Al–(3.2–3.8)Cu–(1.0–1.4)Li alloys

To develop super-high strength Al–Li alloy, the microstructures and mechanical properties of Mg, Ag and Zn micro-alloyed Al–(3.2–3.8)Cu–(1.0–1.4)Li alloys (mass fraction) with T8 temper were studied. The results showed that 1% of lower Li content restricted the strengthening effect of increasing Cu content, while simultaneous increase in Cu and Li contents contributed effectively to the enhancement of strength. The alloys were mainly strengthened by plenty of fine and well dispersed T1(Al2CuLi) precipitates. There were also some minor precipitates of θ ′(Al2Cu) and δ′(Al3Li), which became less in number density, even disappeared during the aging process. Meanwhile, higher Li content favored the formation θ ′ and δ ′ and a small amount of S′(Al2CuMg) phases. In addition, strengthening effect and microstructure variation were analyzed through total non-solution mole fraction of Cu and Li and their mole ratio. To obtain Al–Li alloy with super-high strength, the total mole fractions of Cu and Li should be increased, and their mole ratios should also be kept at a certain high level.