Double-sided laser beam welded T-joints for aluminum aircraft fuselage panels: Process, microstructure, and mechanical properties

T-joints consisting of 1.8. mm thick AA6156-T6/AA6056-T4 aluminum alloys have been fabricated by double-sided laser beam welding using eutectic alloy AA4047 filler wire. The effects of the incident beam position, the incident beam angle, and the beam separation distance on the weld properties were investigated. The microstructure and mechanical properties were identified using optical microscopy, scanning electron microscopy, and tensile testing. The optimal incident beam position was determined to be 0.2. mm yielding a 40-50° seam angle. It was found that the weld penetration was increased significantly as the incident beam angle increased. The doubled-sided welds were not fused in a common molten pool and no longer symmetry when the beam separation distance exceeded to 1.5. mm. Five distinct zones were identified between the fusion zone center and the base material which consisted of: the cellular dendrite zone, parallel dendrite zone, partially melted zone, over-aged zone, and base material. The tensile strength depended on the weld penetration, and the failure originated at the weld toe on the skin side. The fracture mechanism of the head tensile test and hoop tensile test was found to be brittle fracture and ductile fracture, respectively.