Activated tungsten inert gas (TIG) welding, which involves the deposition of an inorganic powder on the metal surface prior welding, improves TIG welding performances in terms of weld bead penetration. Most common commercial fluxes contain halides and oxides. The present paper focuses on fluxes made of oxides. It appears that oxides have two different effects: one on the fusion zone chemistry and the other on the electric arc behaviour. First, oxygen reverses the Marangoni convection movements that become centripetal, contributing thus to increase 'D' penetration. On the other hand, oxides may cause an increase in the energy flux density transferred by the arc to the metal. The characterisation of the arc plasma by optical emission spectroscopy suggests that oxides do not increase the arc temperature. It is established that the oxide effects by Marangoni convection appear for a critical value of the welding energy, whereas the oxide effects on the electrical arc exist irrespective of the welding energy value.

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The mechanisms of the inorganic powders, named activating flux and used in ATIG welding process, are not well identified. Oxides and fluorides usually compose activating fluxes. The present paper studies the fluoride activating effect. The analysis of the arc energy influence on the weld bead geometry allows determining the mechanisms that occur during ATIG welding with fluorides. It seems that fluoride activating effect could depends on the fluoride lattice energy and/ or the ionic radius of the element. Fluorides act on the arc physics only. An arc energy densification is observed. Furthermore, an arc temperature increase, find out with optical emission spectrometry, characterises the fluoride activating effect. The fluorides do not affect the weld bead surface chemistry. Marangoni convection movements stay centrifugal as in TIG welding and do not favour a penetration increase.

The use of an inorganic powder, termed activating flux, is a technique that can be used to improve the tungsten inert gas welding process. The activated tunsten inert gas (ATIG) process greatly increases single pass depth penetration. In the present work the activating effect of different oxides on 304L stainless steel was studied, to determine the main relationships between the oxide propertie(s) and the weld bead geometry variation and consequently to determine the mechanism(s) occurring during the ATIG welding process. The results show that oxide melting point T m , the liquid state (T b 2T m ), the lattice energy E L , and the quantity of oxygen that can be liberated seem to play an important role, even though T m is the main property. Moreover, for some oxides, the hygrometry rate is another property that can increase the activating effect.

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