Abstract: Two heat-treated 2219 aluminum alloys were welded by two-pass TIG welding. DC TIG was used for first pass, AC TIG for cover pass. The micro-structure, phase composition and mechanical properties under room and cryogenictemperaturesof welded joint were tested. The results show that the micro-structures of base metals are α(Al) with Al₂Cu strengthening phase, while 2219 C10S has a lath-like micro-structure along the rolling direction, 2219 CYS has a coarse irregular polygon micro-structure. α+θ eutectic phases distribute on grain boundary and matrix in weld and partial meltedzone.Solid solution of Cu in the matrix is in-homogeneous. Coarse grain, grain orientation and grain boundary segregation could be the causes of fracture initiation from partial melted zone of 2219CYS.