Study on keyhole and melt flow behaviors of laser welding of aluminum under reduced ambient pressures

Laser welding of aluminum alloy under reduced ambient pressure can produce less porosity defects. In this paper, the effect of reduced ambient pressures on porosity was investigated by a combination of experimental and numerical method. A novel numerical model was proposed to describe the keyhole and melt flow behaviors under reduced ambient pressures. Numerical results showed that, compared with atmospheric pressure, reduced ambient pressure would produce a more stable keyhole. The vortex of melt flow in molten pool became unapparent and even disappeared under reduced ambient pressures. The flow velocity of the melt on the keyhole wall became faster under reduced ambient pressures. The difference between boiling point and melting point decreased under reduced ambient pressure, which made a contribution to the formation of a thinner keyhole wall and hence improved the stability of keyhole. Higher recoil pressure would be produced under reduced ambient pressures, which was responsible for the weakened vortex and enhanced melt flow velocity. The formation of porosity during laser welding process could be effectively inhibited based on the above combined effects.