Influence of Aging Precipitation Kinetics on Mechanical Properties and Corrosion Behavior of the Al-1.1Cu-2.4Li-X Alloy

The mechanical properties, intergranular corrosion, and exfoliation corrosion of T6- and T8-aged Al–1.1Cu–2.4Li–X alloys (high Li content, Cu/Li ratio ≈ 0.46) were systematically examined. Microstructural analysis shows that T8 aging produces a higher number density of T1 (Al2CuLi) precipitates and a higher number density, as well as a finer and more uniform distribution of δ′ (Al3Li) compared to T6 aging. This results in yield and tensile strengths that are 90 MPa and 40 MPa higher, respectively, for the T8 condition. In terms of corrosion, the T6-aged alloy displays intergranular corrosion depths of 176.5–210.1 μm, while the T8-aged alloy exhibits much shallower depths of 67.2–95.8 μm. The inferior resistance to intergranular and exfoliation corrosion in the T6 temper is attributed to precipitation-free zones (PFZs) and secondary-phase particles at grain boundaries. Increasing T6’s aging time reduces the PFZ width and thus improves corrosion resistance. Conversely, prolonged T8 aging causes a gradual decrease in corrosion potential and an increase in corrosion current density, linked to a higher density of T1 precipitates, which signifies increased corrosion susceptibility. These findings provide a reference for understanding corrosion mechanisms and improving the corrosion resistance of high-Li Al–Li alloys.