Microstructure Characterization of Friction Stir Welded 2099 Al-Li Alloy

The friction stir welded 2099-T83 extruded Al-Li alloy has been characterized in terms of microstructure and crystallographic texture. The optical microscopy, scanning electron microscopy, transmission electron microscopy and hardness tester were applied to investigate the microstructure and hardness. Hardness tests reveal that the hardness profile in the welded zone presents a "W" shape and reaches a minimum at thermo-mechanically affected zone. The base metal shows partial recrystallization with T1 phase and delta' phase at the grain and grain boundaries. The grain size of the welded zone is smaller than that of the base metal, and the precipitates observed in the base metal dissolve and transform into fine delta' phases in the welded zone. Furthermore, crystallographic texture analysis by electron backscatter diffraction indicates that the base metal has {112}< 111 > copper, {123}< 634 > S and {001}< 100 > cubic textures. The nugget zone presents a {001}< 110 > rotated-cube texture as it undergoes dynamic recrystallization. The thermo-mechanically affected zone and heat affected zone are dominated by {112}< 110 > and {112}< 111 > textures, respectively, and both of them have weak {001}< 120 > textures.