Shape and depth of Penetration

The shape and depth of penetration of beads obtained with various shielding gases using DCEP polarity


Some shielding gas selections for GMAW of various metals


Metals Gases % Uses and results
Aluminum Ar





Good transfer, stable arc, little spatter, Removes oxides


Hot arc – 3/8” to 3/4” (10mm to 19mm) thickness, Remove oxides. Hot arc, less porosity, removes oxides – 1/2” to 1” (13mm to 25mm) Hotter, more gas; 1/2” (13mm) and up. Removes oxides.

Magnesium Ar


Good cleaning.

Hotter, less porosity, removes oxides.

Copper (deox.) 75He-25Ar


Preferred. Good wetting, hot. For thinner materials.
Carbon steel CO2


Ar-2 O2 Ar-5 O2



Short circuiting arc: high quality, low current, out-of-possition, medium spatter

Globular arc: fast, cheap, spattery, deep penetration.

Fast, stable, good bead shape, little undercut, fluid weld pool. Short circuiting arc: fast, no melt-throgh, little distortion and spatter. Short circuiting arc: deep penetration, low spatter.

Low-alloy steel Ar-2 O2 Removes oxides, eliminates undercut, good properties.
High-strength steels 60He-35Ar-5CO2



Short circuiting arc: stable arc, good wetting and bead contour, little spatter. Good impacts.

Short circuiting arc: same except low impact.

Stainless steel Ar-1 O2 Ar-5 O2

90He-7 1/2 Ar-2

1/2 CO2

No undercutting. Stable arc, fluid weld, good shape. More stable arc.

Short circuiting arc: small heat-affected zone, no undercut, little warping

Nickel, monel Ar Good wetting – decreases fluidity.
Inconel Ar-He Stable arc on thinner material.