Effect of Filler Wire on Mechanical Properties, Microstructure and Natural Aging Behavior of 2A55 Al-Li Alloy TIG Welded Joint

2A55 Al-Li alloy is considered to have potential applications in the manufacture of fuel tanks for aerospace vehicles. However, the composition design of filler wires for 2A55 Al-Li alloy TIG welding has not been fully studied. This work focuses on the mechanical properties and microstructure of 2A55 Al-Li alloy TIG welded joints obtained using 2A55 alloy and Al-8Cu filler wire that was designed for this work, as well as the effects brought about by natural aging on them. When filler wire with higher Zr and Ti content was used, the weld grain was significantly refined. Due to the difference in the Cu content of filler wire, the formed Cu-rich phases in welds are significantly different, showing a grid-like distribution in the Al-8Cu weld compared to the dispersed distribution in the 2A55 weld. After welding, the lack of dominant strengthening precipitates caused a sharp softening of the welds. However, Li and Cu atoms dissolved in the Al matrix can precipitate fine and dispersed Al3Li particles and GPZs by natural aging to strengthen the welds. After natural aging, the yield strength (YS) of the 2A55 joint increased by 24.1% compared with the 14.7% improvement of the Al-8Cu joint.