| Abstract Scope |
Emerging beam deflection technologies are pursued to mitigate and eliminate defects that form due to keyhole collapse during the laser welding of aluminum alloys. The application of circular beam deflection has been utilized and correlated with minimizing and, in some cases, completely mitigating the formation of this persistent defect in a range of alloy systems. However, there is little underlying knowledge of the roles that changes in the diameter or amplitude of the circle deflection, the frequency at which the beam is rotated, beam diameter, and travel speed play in mitigating the formation of these defects. By performing a series of laser welds on joints consisting of a combination of AA6061 and AA4047 alloys, the effects of these changes in welding parameters on the resulting defect size, morphology, and distribution have been quantified. When operating in the keyhole mode, no combination of beam deflection parameters completely mitigated the formation of these keyhole collapse defects, but trends were observed in the number, size, and shape of defects with changes in beam oscillation parameters. Across all conditions, small spherical pores were primarily located near the weld root region. Of the various parameters explored, decrease in travel speed had the biggest impact on the measured porosity levels. For example, porosity reached a volume fraction of 0.38% at a travel speed of 21 mm/s with a deflection amplitude of 0.8mm, and a frequency of 475 Hz. Further evaluation of the beam oscillation conditions and the corresponding defect structures observed in the welds highlighted the important role that the ratio between the laser beam diameter and oscillation amplitude played. Increases in beam overlapping during oscillation were driven by a combination of the beam diameter and oscillation amplitude and frequency, with higher beam diameters and slower travel speeds appearing to be more impactful on defect formation. |