Stimulated Pulse Keyhole Behavior in Double-Pulsed VPTIG Welding of AA2219 High Strength Aluminum Alloy

Keyhole tungsten inert gas (K-TIG) welding is a variant of TIG welding, which can largely improve the weld penetration depth by forming keyholes inside the molten pool during welding. However, K-TIG welding is generally considered unsuitable for aluminum alloys due to their high thermal conductivity. A novel double-pulsed variable polarity TIG (DP-VPTIG) welding process was employed and the stable full penetration keyhole welding of 7 mm-thick AA2219 aluminum alloy was achieved. Keyhole dynamic evolution for DP-VPTIG was investigated based on visual sensing technology. Results indicate that in low-pulsed peak stage of DP-VPTIG process, the keyhole forms under the dominant role of the downward arc pressure against the upward surface tension and hydrostatic pressure acting on the surface of the molten pool, while the keyhole is closed as the upward surface tension and hydrostatic pressure become the dominant role in low-pulsed base stage. The periodic variation of low-frequency pulse in DP-VPTIG process stimulates a periodic keyhole behavior of opening and closing in the molten pool. The formation of keyhole is beneficial to the increase of weld penetration depth as the arc moves downwards along the keyhole and directly heats the solid metal under the molten pool. The keyhole size decreases with the increase of low-pulsed frequency.

Automated summary

Keyhole tungsten inert gas (K-TIG) welding is an improved variant of TIG welding that can significantly improve the weld penetration depth by forming keyholes inside the molten pool. However, it is generally not suitable for aluminum alloys due to their high thermal conductivity. In this study, a novel double-pulsed variable polarity TIG (DP-VPTIG) welding process was used to achieve stable full penetration keyhole welding of the AA2219 aluminum alloy. The keyhole dynamic evolution of DP-VPTIG was investigated and it was found that the keyhole is formed under the dominant role of arc pressure in the low-pulsed peak stage, while it is closed in the low-pulsed base stage. The periodic variation of low-frequency pulse stimulates a periodic keyhole behavior of opening and closing in the molten pool.