Numerical and experimental study on keyhole dynamics and pore formation mechanisms during adjustable-ring-mode laser welding of medium-thick aluminum alloy

Keyhole induced-pore is one of the biggest challenges in laser welding of aluminum alloys. A shaped laser controlling strategy, ring-mode laser, has shown the possibility of reducing porosity in welding due to its potential to enlarge keyhole openings and improve the stability of the keyhole. However, few attempts have been made to reveal the influence of ring-mode laser on keyhole dynamics and pore formation. This paper quantitatively investigated porosity improvement during adjustable-ring-mode laser welding (ARM-LW) of aluminum alloys and analyzed keyhole dynamics and porosity formation mechanisms using a validated model. Experimental results indicate that porosity can be dramatically reduced when compounding a ring laser beam over the Gaussian beam. As the core/ring power ratio adjusts from 10:0 to 5:5, the porosity decreases significantly and remains lower (1.73%∼2.58%) while ensuring a similar melt depth (5∼6 mm). Simulation results demonstrate that two mechanisms work synergistically to suppress porosity: (1) The ring-mode laser contributes to decreasing keyhole collapse and regulating melt pool flow, hence reducing pores created at the Gas-Liquid interface (G/L-pore); (2) The ring-mode laser facilitates reducing the frequency and depth of keyhole into the melt pool, thus minimizing pores created at the Liquid-Solid interface (L/S-pore). This work can guide the porosity suppression during laser welding of aluminum alloys and is of significant theoretical meaning and application value.