Effect of aging temperature on microstructure and mechanical properties of different rolling orientations in novel Al-Li alloy

Microstructure and properties of different rolling orientation with aging temperature varying in a newly developed Al-Li alloy was investigated by transmission electron microscopy (TEM) analysis. Sheets of experimental Al-Li alloy were solution treated at 510°C for 2 h. Predeformation of ~3% was stretched in the 0 and 90° angle with respect to the original rolling orientation before aging treatment. All specimens were aged for 35 h at 138, 143, 148, 153, 158 and 163°C respectively. Tensile specimens were stretched along the previous orientation of predeformation. The results showed that the main strengthening phases in the alloy were δ' (Al₃Li), θ' (Al₂Cu)/θ'' (Guinier-Preston || zone), δ'/β' (Al₃Zr) and T₁ (Al₂CuLi) phase. Among the phases above, the strengthening effect of T₁ phase surpassed the others. Moreover, very little of cubic σ (Al ₅Cu₆Mg₂) phase was observed in the alloy. The microstructure evolution was similar via comparing sheets in different stretched directions. At initial stage of aging, a large amount of fine T₁, δ', δ'/β' and θ'/θ'' phases uniformly distributed in Al matrix with the aging temperature increasing. Subsequently, the quantity and size of T₁ phase increased gradually. In the middle and later period, T₁ phase was the main phase that grew at the cost of other phases. The peak aged temperature was 158°C with yield strength of 540 MPa when stretched at 0° angle to the original rolling orientation and 501 MPa when at 90° angle to the rolling direction. Meanwhile, the elongations were 9·5 and 10·9% respectively, which indicated that the anisotropy of the alloy was not obvious.