Effects of shielding gases on process stability of 10CrNi3MoV steel in hybrid laser-arc welding

Hybrid laser-arc welding (HLAW) of 10CrNi3MoV steel was carried out with different shielding gas mixtures including 100% Ar, 5% CO2 + Ar, 10% CO2 + Ar, 15% CO2 + Ar, 20% CO2 + Ar, 25% CO2 + Ar and 100% CO2. A CMOS high speed camera and real-time electric signal data were utilized to obtain the high-speed images (HSI) and electric signals of the droplet transfer and weld pool dynamics in real time during the HLAW process. The results showed that the increase of CO2 content increased the synergetic effect, especially the energy density of laser, and improved the penetration. The electric signal and HSI results revealed that, at low CO2 content (5% CO2 + Ar, 10% CO2 + Ar), the process was unstable with spatters and the metal transfer mode was globular mode. But at medium CO2 content (15% CO2 + Ar, 20% CO2 + Ar), the process was stable with less spatters and the metal transfer mode was spray mode. Stable process and accepted sound weld were obtained using 20% CO2 + Ar, which corresponded to the welding current 200 A and welding voltage 29 V. As CO2 content in the shielding gas increased, the increase in the weld current and welding voltage deteriorated the stability of the welding process, and the transfer mode shifted to repelled transfer, leading to the formation of large spatters.