Microstructural analysis of the anode in gas metal arc welding
Résumé
The nature of the applied shielding gas has a strong influence on arc stability and transfer metal mode of the welding process. In particular, increase of the percentage of carbon dioxide in argon induces the increase of the transition current value from the globular to spray metal transfer mode. This work shows that these effects are linked to the chemical and microstructural modifications of the anode tip during the gas metal arc welding process. The microstructure of the anode is investigated for various experimental conditions. Transition between the two transfer modes is linked to the existence and disappearance of a rather insulating oxide "gangue" at the wire extremity whose nature depends of the shielding gas. Chemical reactions at high temperature such as oxidation-reduction reactions between shielding gas and melted metal govern the transition of the spray-arc to globular transfer mode.