The age-hardening behavior and precipitation microstructures of Al–Li–Cu–Zr alloys containing various additional elements (Ag, Ge, Zn, Si, Mg and Mg+Ag) were investigated using hardness measurement and transmission electron microscopy. The experimental results indicate that the addition of Mg has a pronounced effect to produce a high density of T
1 (Al
2CuLi) phase at aging temperatures above ~400 K, resulting in the increased hardness of the alloys. In contrast, the additions of Ag, Ge, Zn and Si to the quaternary alloy exerts no marked influence on the precipitation kinetics. Difference in quenching condition, W.Q. (water-quench), D.Q. (direct-quench) or S.Q. (step-quench), strongly affects the precipitation microstructures and hardness of the alloys. This is well explained by taking into account the effects of both the quenched-in excess vacancies and Mg atoms. The proposed mechanism is that the excess vacancies aggregate together with Mg and Cu atoms to form Mg/Cu/Vacancy complexes which play an important role in the enhanced nucleation of the T
1 phase (Mg/Cu/Vacancy complex mechanism).
抄録全体を表示