Nano-indentation and in-situ investigations of double-sided laser beam welded 2060-T8/2099-T83 Al-Li alloys T-joints

Abstract 2060 and 2099 are both newly developed high-strength aluminum-lithium (Al-Li) alloys for fuselage panels of jetliners. In this work, double-sided laser beam welding of 2-mm-thick 2060-T8 and 2099-T83 Al-Li alloys was performed using AA4047 filler wire under optimized parameters. Weld zone microstructure and T-joint mechanical properties were investigated by means of scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), nano-indentation and in-situ tensile test. Experimental results indicated that the equiaxed grain zone (EQZ) featured by dense large-angle (θ＞10°) grain boundaries was observed in the weld zone along the fusion lines. Besides the softening problem found in the partially melted zone (PMZ), local softening phenomenon was detected in the local enrichment region of the EQZ. During in-situ tensile tests, the crack was initiated at the weld toe and then propagated alternately in the PMZ and EQZ's local enrichment regions. Micro-voids induced the localized softening problem and the crack's intergranular expansion in the EQZ. Localized absence of silicon was most likely to cause continuous micro-voids in the EQZ.