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Argon-8-12% 02
– 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 someinstances a higher alloyed wire will be necessary
to compensate for the reactive
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%
02 –
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. Rernoval of the slag/scale before subsequent
weld passes is recommended
to insure the best weld integrity. Argon-Carbon
Dioxide Mixtures The
argon-carbon dioxide mixtures are mainly used on carbon and low alloy steels and
limited application on
stainless steels. The argon additions to CO2
decrease the spatter levels usually experienced with pure
CO2
mixtures. Small CO2 additions to argon produce
the same spray arc characteristics as small 02
additions. The difference lies mostly
in the higher spray arc transition currents of argon - CO2
mixtures. In GMAW
welding with CO2 additions, a slightly higher
current level must be reached in order to establish and maintain
stable spray transfer of metal across the arc. Oxygen additions reduce the spray
transfer transition current.
Above approximately 20% CO2 spray transfer
becomes unstable and random short circuiting and globular
transfer occurs. Argon-3-10%
CO2 –
These mixtures are used for spray arc and short circuiting transfer on a variety
of carbon
steel thicknesses. Because the mixtures can successfully utilize both arc modes,
this gas has gained much
popularity as a versatile mixture. A 5% mixture is very
commonly used for pulsed GMAW of heavy section
low alloy steels being welding out-of-position. The welds are generally less oxidizing
than those with 98
Ar-2% 02. Improved penetration is achieved
with less porosity when using CO2 additions
as opposed to 02 additions.
In the case of bead wetting, it requires about twice as much CO2
to achieve the same wetting
