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At constant current, the arc voltage increases with increasing helium or CO 2 content. At constant wire feed speed and constant voltage, as the helium or CO 2 content increases, the welding current decreases. The arc length decreases significantly with the increase of CO 2 content and arc core expands with the increase of helium content. When the shielding gas composition changes, arc properties and wire melting characteristics both change and the arc works at a new equilibrium point to keep the wire melting rate equal to wire feed speed. Shielding gas with the addition of helium presents a bowl weld bead profile. The depth of sidewall fusion increases as helium content increases. The welding process and weld quality are good when the shielding gas is 80%Ar10%CO 2 10%He. [ABSTRACT FROM AUTHOR]