A higher risk of porosity has been found to exist when a higher density gas is used, because the gas is more likely
of being trapped in the keyhole and the weld after solidification (Katayama et al. 2009). However, Chen et al. (Chen
et al. 2011) reported porosity and crack in the weld produced with double pass laser welding using either N2 or Ar gas,
without any obvious relation between the type of gas used and the porosity found in the weld samples, seen from Fig.
3