Effect of shielding gas on laser-MAG arc hybrid welding results of thick high-tensile-strength steel plates

In this study, high-power disk laser-metal active gas arc hybrid welding was performed on thick plates of high-tensile-strength steel, HT780. The effect of shielding gas on the penetration, defects, and mechanical properties of the hybrid weld beads was investigated using either 80 % Ar-20% CO2 or 100 % CO2 shielding gas. The results showed that the process window of laser powers for the production of sound welds was wider in 100 % CO2 gas, although more spatters occurred. Besides, the optimization of the arc parameters could reduce spattering significantly by controlling the globular transfer mode to form a buried arc. The Vickers hardness test was performed to identify the levels of hardening and softening in the bead and HAZ, respectively. The tensile test results showed that the tensile strengths of the joints hybrid-welded in either 80 % Ar-20 % CO2 or 100 % CO2 gas were much higher than those of the HT780 base material. The Charpy V-notch test results revealed that the values of the hybrid-welded joints in 80 % Ar-20 % CO2 gas were higher than those in 100 % CO2 gas. The reduction in toughness was attributed to the increase in the oxygen content and the consequent formation of a higher number of oxides in a weld bead made in 100 % CO2 gas.