Effects of keyhole status on melt flow and flow-induced porosity formation during double-sided laser welding of AA6056/AA6156 aluminium alloy T-joint

Effects of the keyhole status on the melt flow during the double-sided laser welding of aluminium alloy T-joint were numerically investigated. And the influencing mechanisms of the flow-induced porosity formation and evolution were also discussed. When the keyhole status changed from complete connection to complete separation, the convection above the keyhole disappeared and vortex flow was formed. Meanwhile, the vortex flow below the keyhole became more complex. As the beam separation distance increased, the vortex flow near the keyhole opening position emerged and became more and more violent, and two vortexes were formed between both sides of the keyhole. The gradually weakened keyhole connectivity and symmetry reduced the pore evolution efficiency dramatically, and subsequently formed porosity defects in the weld seam. The distribution characteristics of the flow-induced porosity defects were found to be in good agreement with the simulation results under the experimental conditions examined.