6
broader and more shallow penetration
pattern. Aluminum welding with pure helium does not give the
cleaning action that pure argon experiences
but is beneficial and sometimes recommended for welding thick
aluminum. The helium arc column is wider
than argon which reduces current density. The higher voltage
gradient causes increased heat inputs
over argon thus promoting higher puddle fluidity and subsequent
bead wetting. This is an advantage when
welding aluminum, magnesium and copper alloys. Helium
is often mixed with various percentages of argon to take advantage of the good
characteristics of both
gases. The argon improves arc stability and cleaning action, in the case of aluminum
and magnesiurn, while
the helium improves wetting and weld metal coalescence.
