Marangoni convection and weld shape variation in A-TIG welding process

The flux effect on TIG weld shape variations is investigated by application of the heat transfer and fluid flow model. The simulation makes use of Nimonic 263 alloy, TiO, TiO2 and Ti2O3 as the flux. The arc constriction and the reversed Marangoni convection are considered to be the two main factors for increasing penetration of A-TIG weld pool. And the simulated results show that the latter is the main factor for changing weld shapes. The surface tension temperature coefficient is sensitive to the active elements and affects the pattern of the fluid flow. By controlling the category and quantity of the active elements, different kinds of the weld shapes are obtained. The experimental result shows that increase of active flux on the weld bead tends to increase the penetration of the weld pool at first and then decreases steeply. This does not coincide with the simulated results. It is probably because part of the oxide in the flux is not totally decomposed when the flux reaches a critical value. The solid oxide particles in the weld pool act as the obstacles of the fluid flow and reduce the velocity of the flow.