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A short history of welding aluminum
Q: What is the h istory behind the welding of aluminum? IsHeliarc welding
still a viable option for welding aluminum? Why do we not see much Gas
weldingor stick electrode weldingof aluminum in industry?
A:During my attempt to address these questions, I will also try to clarify some of the
terms an d definitions used.
Heliarc welding This is an old traditional name, sometimes still used
today, for the Gas Tungsten Arc Welding process (GTAW). This same
welding process is oft en referred to, p articularly in Europe, as the
Tungsten Inert Gas (TIG) welding process.
Th e GT AW process is quite oft en a viable option for welding aluminum. It was
developed in 1944 (see fig1), and is still exten sively used to successfully weld
aluminum alloys to day. Some o f th e highest quality welds used in critical applications,
such as full penet ration pipe welds on cryogenic pressure vessels, are almo st
exclusively made with th is welding process. Alternat ing current (AC) is used for most
applications, but direct current ( DC) power is employed for some specialized
applications. Th e GTAW process was developed earlier than th e Gas Metal Arc
Welding process, (GMAW) and for a time, was used to weld aluminum of all metal
thickn esses and joint types. Th e GT AW process has since been replaced by the gas
metal arc welding (GMAW) process for many aluminum welding applications,
primarily because of t he in creased speed of t he GMAW process t o weld th icker
sections. However, GTAW st ill has an import ant p lace in the aluminum welding
industry. GTAW , with alternat ing current (AC) and pure argon shielding gas, is now
most o ften used to weld thinner gauges of aluminum (up to inch) and also for
applications where aesthetics are most important . Alternat ing current (AC) is the
most popular met hod of gas tungsten arc welding aluminum. A balanced wave AC arc
provides cleaning act ion for most app lications an d divides the arc h eat about ev enly
between elec tro de and base mater ial. GTAW power sources for AC welding, which
allow for adjustment of the balance between polarities, enable the user to choose either
enhanced arc cleaning or greater penetrat ion capabilities. For more specialized
applications, we can find GTAW used in the direct current electrode negative mo de
(DCEN). This method provides arc concentration of about 80% of the heat at the
base mat erial an d about 20% at th e elect rode. This results in rela tively deep and
narrow weld penetrat ion, and very little, if any , significant arc cleaning during the
welding operat ion. Ty pically used with p ure helium shielding gas, this metho d of
welding is capable of welding much greater t hicknesses of mat erial (up to 1 inch) and is
most oft en used in automatic seam welding applications. Th e third mode of GTAW is
the direct current electro de positive (DCEP). With t his method, we have about 20%
of the heat generated at the base plate and 80% at the electrode. We create excellent
cleaning action but very shallow penet ration. Th is is probably the least used method
of GTAW.
Gas welding This is a nonstandard term for the oxyfuel gas welding
process (OFW). This was one of the earliest welding processes used for
welding aluminum. Fig 2 shows a USA Army water canteen. Welded by
the OFW process and dated 1918, this canteen was probably used in the
Great War (1stWorld War) and welded around 25 years prior to the
development of the inert gas welding processes (GT AW & GM AW).
Oxyfuel gas welding is a gas welding process. It ach ieves coalescence by using the heat
from an oxygen-fuel gas flame and, for aluminum, an active flux to remove the oxide
and shield the weld pool. Very t hick joints hav e been welded in the p ast with t his
process, but t he m ost comm on applicatio ns have been fo r sheet m eta l. One o f t he
problems with t his welding process is that the flux used during th e pr ocess is
hydroscopic, meaning it absorbs moisture from the surrounding atmosphere. When
moist, th e flux becomes corrosive to aluminum. Th erefore, after welding, the flux
must be removed to m inimize the chance fo r corrosion. Because it can be difficult to
be cert ain t hat all t races o f flux h ave been remov ed, it was often necessary to finish
the op eration with an acid dip, to neutralize any flux residue. Other disadvant ages of
using th is process for welding aluminum are, mechanical stren gths t end to be lower and
heat affect ed zones wider than with arc welding. Welding is only practical in t he flat
and vertical positions, and distortion can ten d to be extreme. Most of the problems
are caused by corrosive flux and excessive heat input associated with t his process. T he
oxyfuel gas welding process was widely used for welding aluminum prior to the
development of t he inert gas welding process, but has limited use to day.
Stick electrode welding This is a nonstandard term for Shielded
Metal Arc Welding (SMAW)
Prior to the development of the inert gas welding process (GTAW & GMAW) the arc
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welding of aluminum was mainly restrict ed to the Shielded Metal Arc P rocess (SMAW)
sometimes referred to as the Manual Metal Arc Process (MMA). Th is welding process
uses a flux-coat ed welding electrode. T he electr odes are straight length s of aluminum
rod, coated with flux. Th e flux acts to dissolve the aluminum oxide on both the base
alloy and th e rod during welding, which is necessary if coalescence is to occur. Some
of the flux components vaporize in the arc to form shielding gases that help to
stabilize the arc and shield both it and t he weld pool fro m t he surrounding
atmosph ere. One of t he main p roblems with t his welding process was corrosion caused
by flux en trapmen t, part icularly in fillet welds where t he f lux could be t rapp ed behind
the weld and promot e corrosion from th e back of the weld. Other pro blems were that
welds from th is process are prone t o gross porosity. Th ere are no electrodes available
for the high magnesium content base alloys and electrodes, once exposed to the air,
begin to absorb moisture in to th e flux, which event ually cor rodes t he a luminum core
and produces excessive porosity problems. It was soon found that this process was notthe most suited for welding aluminum. Current welding codes and standards for
aluminum structures do n ot recognize th is welding pro cess as being suitable for
production welding app licatio ns.
Conclusion:
Witho ut a doubt, the breakthrough for aluminum as a welded structural material
occurred with t he intro duction in t he 194 0s of the inert gas welding processes. With
the introduction of a welding process that used an inert gas to protect the molten
aluminum during welding, it became possible to make high quality, high strength welds
at h igh speeds and in all positions, without co rrosive fluxes.
Fig 1. 1944 -1 994 advertisement celebrating 50 years of Heliarc (T he trade name
used for th e GTAW/TIG welding process that is sometimes still used today). A major
breakt hro ugh for aluminum as a struct ural welded mat erial.
Fig 2. This USA Army water canteen welded with t he OFW p rocess and dated 1918
some 25 years prior to the development of the GMAW / MIG and GTAW / TIG inert
gas welding processes.
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