Argon / Oxygen Mix
Overview
The addition of small amounts of 02 to argon greatly stabilizes the weld arc, increases the filler metal droplet rate, lowers the spray arc transition current, and improves wetting and bead shape. The weld puddle is more fluid and stays molten longer allowing the metal to flow out towards the toe of the weld. This reduces undercutting and helps flatten the weld bead. Occasionally, small oxygen additions are used on non- ferrous applications. For example, it’s been reported by NASA that .1% oxygen has been useful for arc stabilization when welding very clean aluminum plate.
Gas Blends
Argon-1% Oxygen
This mixture is primarily used for spray transfer on stainless steels. One percent oxygen is usually sufficient to stabilize the arc, improve the droplet rate, provide coalescence and improve appearance
Argon-2% Oxygen
This mixture is used for spray arc welding on carbon steels, low alloy steels and stainless steels. It provides additional wetting action over the 1% 02 mixture. Mechanical properties and corrosion resistance of welds made in the 1 and 2% 02 additions are equivalent.
Argon-5% Oxygen
This mixture provides a more fluid but controllable weld pool. It is the most commonly used argon-oxygen mixture for general carbon steel welding. The additional oxygen also permits higher travel speeds.
Argon-8-12% Oxygen
Originally popularized in Germany, this mixture has recently surfaced in the U.S. in both the 8% and 12% types. The main application is single pass welds but some multi-pass applications have been reported. The higher oxidizing potential of these gases must be taken into consideration with respect to the wire alloy chemistry. In some instances a higher alloyed wire will be necessary to compensate for there active nature of the shielding gas. The higher puddle fluidity and lower spray arc transition current of these mixtures could have some advantage on some weld applications.
Argon-12-25% Oxygen
Mixtures with very high 02 levels have been used on a limited basis but the benefits of 25% 02 versus 12% 02 are debatable. Extreme puddle fluidity is characteristic of this gas. A heavy slag/scale layer over the bead surface can be expected which is difficult to remove. Sound welds can be made at the 25% 02 level with little or no porosity. Removal of the slag/scale before subsequent weld passes is recommended to insure the best weld integrity.