a short history of welding aluminum

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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 Th e GT AW process has since been replaced by the gas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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a short history of welding aluminum

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