Single pass laser cold-wire welding of thick section AA6061-T6 aluminum alloy

Extending applications of thick section aluminum alloy plates in various industrial market segments such as ground transportation, railcar, and aerospace necessitates the development of advanced welding technologies to ensure high integrity welds for a successful joining of components. Conventional arc welding processes of thick aluminum plates are associated with large groove preparation, multi-pass welding, and high heat input. Therefore, developing high energy density process, such as laser welding for joining of thick aluminum plates, can increase weld penetration depth and production rate, while reducing the heat input and eliminating large groove preparation. In the present work, single pass laser cold-wire welding of 4.8 mm thick AA6061-T6 aluminum plates was carried out in the butt joint configuration using a disk laser with a maximum output power of 10 kW. The effect of laser welding parameters such as welding speed, continuous-wave (CW) and pulse-wave (PW) modes on weld integrity, microstructure, hardness, and tensile properties was evaluated. Porosity, underfill, and excessive penetration were observed as the main imperfections in the fusion zone (FZ). However, the underfill depth and excessive penetration height in the joints manufactured at different welding conditions met the specifications of ISO 13919 standard which sets production guidelines. Increasing the welding speed from 3 to 4.5 m/min leads to less porosity, as detected by radiography, possibly due to the stability of the keyhole at a higher welding speed. Less softening in the fusion zone was observed in PW mode compared to CW mode welds which can be due to less specific point energy in PW mode and consequently less metal evaporation from FZ during laser welding. The transverse tensile test was also performed and fracture surface analysis indicated the fracture path outside the fusion zone close to the fusion line.