Abstract
Combined with microstructure characterization and properties tests, the effects of Zn contents on the mechanical properties, corrosion behaviors, and microstructural evolution of extruded Al–Li–Cu–Mg–Ag alloys were investigated. The results show that the increase in Zn contents can accelerate hardening kinetics and improve the hardness of peak-aged alloys. The Zn-added alloys present non-recrystallization characteristics combined with partially small recrystallized grains along the grain boundaries, while the T1 phase with finer dimension and higher number density could explain the constantly increasing tensile strength. In addition, increasing Zn contents led to a lower corrosion current density and a shallower maximum intergranular corrosion depth, thus improving the corrosion resistance of the alloys. Zn addition, distributed in the central layer of T1 phases, not only facilitates the precipitation of more T1 phases but also reduces the corrosion potential difference between the T1 phase and the matrix. Therefore, adding 0.57 wt.% Zn to the alloy has an excellent combination of tensile strength and corrosion resistance. The properties induced by Zn under the T8 temper (solid solution treatment + water quenching + 5% pre-strain+ isothermal aging), however, are not as apparent as the T6 temper (solid solution treatment + water quenching + isothermal aging).
Highlights
Due to lower density, better specific strength, higher specific stiffness, and higher fatigue performance compared with conventional Al alloys [1], Al–Li alloys are appealing prospects for critical structures used in the aerospace and aircraft industries [2,3]
The results suggested that Zn was observable in the T1 phase and was more likely to replace Cu atoms
Zn is not predicted to integrate into other phases in competition with T1, such as θ’, which appears to be helpful in the formation of the T1 phase
Summary
Better specific strength, higher specific stiffness, and higher fatigue performance compared with conventional Al alloys [1], Al–Li alloys are appealing prospects for critical structures used in the aerospace and aircraft industries [2,3]. Li added to Al alloys simultaneously reduces the density and the stiffness of the alloys, while combining it with Cu enhances precipitation strengthening, resulting in a high level of strength [4]. Li addition promotes the formation of anodic precipitation phases such as T1 (Al2CuLi) and T2 (Al6CuLi3) at the grain boundaries, which causes the alloys to be more prone to intergranular corrosion (IGC) [5]. The combined addition of Mg and noble metal Ag that distributes in the interior of the T1 phase increases the properties of the alloy by promoting the precipitation kinetics of the T1 phase and increasing its nucleation efficiency [12]
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