Study of the Evolution of the Phase Composition of Laser Welded Joints of Third-Generation Al–Li Alloys with the Use of Synchrotron Radiation

We studied the evolution of the phase composition of laser welded joints before and after heat treatment of 3rd generation Al–Li alloys using synchrotron radiation. The article demonstrates the fundamental role of the alloying elements of copper and lithium in formation of the phase composition of the fusion zone of the weld. It has been established that laser exposure changes the phase composition of the alloy. Namely, low copper contents mainly lead to formation of T₂(Al₆CuLi₃) and T₃(Al₅CuLi₃) phases, the average copper contents form T₁(Al₂CuLi), T₂(Al₆CuLi₃), T₃(Al₅CuLi₃) phases and the presence of high copper contents results in formation of T₁(Al₂CuLi) phase at the boundaries of dendrite. Post-heat treatment restores the initial phase composition in the fusion zone. As for the solid solution, the δ'(Al₃Li) phase is formed at low copper contents, the δ'(Al₃Li) and T₁(Al₂CuLi) phases are formed at average copper contents, and T₁(Al₂CuLi) phase is observed at high copper contents. Consequently, this makes it possible to improve the mechanical properties of weld joint specimens to match the numbers of the initial alloy.