Study on shear buckling failure of laser-welded dissimilar aluminum alloy (Al-Li-2099/Al-Li-S4) stiffened panel

Laser welding of L-shaped aluminum alloy joints is of great significance in lightweight and efficient manufacturing of thin-wall reinforced aerospace structures. Shear performance is an important reference index for the structural design of aluminum alloy-reinforced panels. In this study, in-plane shear experiments of a continuous double-sided laser welded dissimilar Al-Li alloy (Al-Li-2099/Al-Li-S4) stiffened thin-walled panels were carried out. The deformation and buckling mode evolution of the stiffened panel were measured by the combination of fringe projection profilometry and strain gauge measurement. The results show that in the macroaspect, the stiffened panel first exhibits local skin buckling and then develops into overall buckling along the diagonal tensile direction. Finally, the stiffened panel shows weld desoldering failure. Metallographic examination and scanning electron microscopy were performed on the L-shaped joints at different positions of the stiffened panel. The microstructure observation shows that the weld was composed of a nondendritic equiaxed zone, a columnar dendritic zone, and an equiaxed dendritic zone. The failure mode of the weld is mainly brittle fracture with a small amount of shear dimples, indicating that the welded seam of the stiffened panel under the shear load is tensile shear coupling. After the force reaches material strength, the crack nucleates in the weld and extends along the weld until it penetrates the whole weld. This shows that the mechanical properties of the weld microstructure are closely related to the macroshear properties of the stiffened panel.