Influence of filler material on micro- and macro-mechanical behaviour of laser-beam-welded T-joint for aerospace applications

Abstract

3.2mm thick laminated skins of AA7475 alloy and 2.5mm thick extruded stringers of the alloy PA765 were T-jointed by laser beam welding. Two different joints were fabricated using identical welding parameters but two different alloys as welding wires, AA5356 and AA4047. The microstructure, the tensile, and the failure behaviours of the two welded joints are studied by means of optical and electronic microscope, micro-indentation, and tensile testing. Weld beads extension using AA5356 are larger than those using AA4047. Microstructure of the welded joints is quite similar: at the centre of the fusion zone, cellular dendrites are present; near the fusion line in the fusion region, a chill zone and parallel dendrite arms are found; and an evident heat-affected zone is observed between the fusion line and the parent material. Microhardness tests reveal that the partially melted zone is a weak band in the welded specimens. Indeed, for both joints, failure took place at the partially melted zone upon tensile loading. Hoop testing demonstrates that AA4047 joints present a lower yield stress than AA5356 joints although both joints show similar tensile strength and elongation at break. AA4047 joints show more strength than AA5356 joints upon T-pull testing.