Fibre laser welding of aluminium alloy

The objectives of this research are to investigate the effects of various welding conditions on penetration and defect formation, to clarify their welding phenomena and to develop the procedure of reduction of the defect. Fibre laser bead-on-plate welding was performed on several aluminium alloys, in particular A5083, at the power of 6 or 10 kW and several power densities from 0.4 kW/mm². It was found that the weld beads were narrower and deeper with an increase in the laser power density. For example, fully penetrated weld beads in 10 mm thick plates were produced at the laser power density of 640 kW/mm² and the welding speed of 10 m/min. However, convex–concave bead surfaces were formed. Moreover, in the case of the high power density, no porosity and many pores were present at high and low welding speeds, respectively. On the other hand, in the case of the ultra-high power density, few pores were generated in high speed welding. These reasons were interpreted by observing keyhole behaviour, bubble formation and the molten pool geometry during high power fibre laser welding with a high-speed video camera and microfocused X-ray transmission in situ observation method. Moreover, the porosity in the weld bead was reduced and prevented by the utilization of nitrogen gas instead of Ar gas, or the forward inclination angle of 40° (50° from the right angle) in Ar shielding gas.