Improved arc stability in aluminium welding by oxygen doping of inert shielding gas

Abstract

Over the last few years, worldwide aluminium consumption has been constantly on the rise. Certainly the most important driving force in this development is the need for lightweight and fuel-efficient design in all fields of transportation. Consequently, the importance of successful and profitable processing of aluminium into serviceable products or components comes more and more into the focus of manufacturing industry. Unfortunately, this necessity is complicated by some of aluminium's material properties because they differ significantly from steel's properties, with which in most cases manufacturing experience has been gained; and by the fact that for an optimum lightweight design, a material mix of different alloys and semi-finished products (extrusion, forged, rolled, or cast parts) is necessary, creating a vast variety of different possible surface and material conditions. In terms of joining processes for aluminium, gas shielded arc welding is outstanding. But the above-mentioned material diversity, in combination with mass production requirements, results in a comparably small operating window for successful welding. This results in a significant reduction in profitability due to, for example reduced welding speed, excessive downtime of the production line, scraping, or reworking after welding. To explain how counteracting aluminium-related welding defects is possible by means of the shielding gas used, this paper will take a close look at the properties of different shielding gases: the column of the electric arc, the aluminium surface (oxide film), and surface transactions. It will also explain how a dose of active O2 in an inert shielding gas will contribute to an enlargement of the welding operating window, and, as such, how the choice of shielding gas can increase the profitability of the welding process.