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3.5 Shielding Gas Selection
Brass
With argon, the arc is stable and there is little smoke.
Cobalt-based alloys
Argon provides a stable, easy-to-control arc.
Copper nickel (Monel)
Argon gives a stable, easy-to-control arc. Also used for welding copper nickel
to steel.
Deoxidised copper
Helium is preferred as it helps greatly in counteracting thermal conductivity of
copper. A mixture of 75% helium and 25% argon (Alushield Heavy) produces a
stable arc, less heat than an arc produced with helium alone.
Nickel alloys
(Inconel)
Argon produces a very stable arc. Helium is recommended for automatic welding
at high speeds.
Mild steel
For manual welding, argon is recommended. Successful welding depends on the
skill of the welder. Helium is preferred for:
• high speed automatic welding
• where deeper penetration than with argon is required
• small HAZ
Magnesium alloys
Argon recommended with continuous high frequency AC. Produces good arc
stability and good cleaning action
0.5% Molybdenum
Pure argon or helium is recommended. For good welding ductility, welding must
be carried out in a draught-free area.
Silicon bronze
Argon decreases internal tension in base metal and in the weld since there is less
penetration with this gas compared to helium.
Stainless steel
Argon is the most commonly used gas for stainless steel. Helium can be used if
better penetration is required.
Titanium alloys
Argon produces a stable arc. Helium is recommended for high speed welding.