Autogenous double-sided T-joint welding on aluminum alloys using low power fiber laser

In this study, a successive double sided laser beam welding process was used to join dissimilar aluminum alloys, AA2024-O and AA7075-T6 using a low power Yb-fiber laser in a T-joint configuration without additions of filler materials. The influence of welding speeds and focal distances were evaluated. First, the welding speeds were varied from 12 mm/s to 21 mm/s at a constant laser power of 270W. Optical microscopic observations have shown that the minimum gap line of 0.8mm was obtained at a laser welding speed of 12mm/s, while the maximum gap line of 1.8mm was obtained at a laser welding speed of 21mm/s. The focal distance with offsets of -1, 0 and +1 at welding speed 18mm/s were evaluated, showing variations in the gap line. Vickers microhardness evaluation across the welding region showed the hardness values at the fusion and heat affected zones were lower than those of the base metals when welding speed varied. Meanwhile, the Vickers microhardness increases when focal distance is defocused +1. The pull test showed the force needed to fracture the welded specimens increased from 101N to 427N as the welding speed decreased from 21mm/s to 12mm/s. For constant welding speed and laser power, the fracture force increased from 100N to 400N as the focal distance changes from -1 to +1. It was observed that a lower welding speed and positive offset value of focal distance will result in deeper penetration, leading to better weld quality between alloys AA2xxx and AA7xxx.