Optimization of gas shielding for the vacuum laser beam welding of Ti–6Al–4 V titanium alloy

Vacuum laser beam welding, also known as subatmospheric laser welding, is a promising welding process that simultaneously offers deep penetration and sound welding quality. It has both the welding quality of electron beam welding and the flexibility of laser welding. In this study, vacuum laser beam welding was applied to Ti–6Al–4 V alloy, which has strong affinity with oxygen and which is usually welded via arc welding under a strictly controlled atmosphere or by electron beam welding in a vacuum chamber. In low vacuum laser welding, the ambient pressure was maintained at about 1 kPa by a vacuum pump while supplying shielding gas. The effects of the type of shielding gas, the shielding gas flow rate, and the nozzle stand-off distance on the laser-induced plume generation, degree of weld bead oxidation, and bead cross sections were investigated. Helium shielding was found to lead to excellent suppression of plume generation and bead oxidation regardless of the stand-off distance. For argon shielding, a low stand-off distance of 10 mm is necessary to prevent plume generation and oxidation. The shielding gas flow rate was not a critical parameter, unlike the type of shielding gas used and nozzle stand-off distance in this study.