The Influence of the type and pressure of shielding gas on the porosity formation for CO_2 Laser Welding of TA15

摘要

Many studies have shown that during laser welding, shielding gases play a key role in many aspects. In this paper, a series of contrast experiments about CO_2 laser welding of TA15 TI-alloy were completed by using He and Ar as shielding for different pressure, respectively. The experiments results reveal that the porosities in the weld have strong relation with weld penetration, and the shielding gas have great influences on the weld penetration. So the porosities mainly form in the center of welds which are under critical penetration and lack of penetration, and have no direct relation with the type and pressure of shielding gas. From the contrast images of penetrating process, it is known that when He as shielding gas, the sizes of keyholes on the back welds are quite larger than the sizes when Ar. This means more vapor erupting from bottom keyhole and porosities not easy to form. At the same pressure, the opening times of keyholes when He as shielding gas are longer than the times when Ar. Long opening times of keyholes make the shielding gas within keyhole not easy to be involved into the molten pool and form the porosities.