ALUMINUM THEORY AND SETUP - GMAW
Aluminum can alloy with a number of other metals with the potential to customize alloys for the market;
alloys that have greater strength, better machinability, better weldability, better corrosion resistance, and
are designed for specific fabrication processes. In its pure form, aluminum is a rather weak metal. The
prime purpose of alloying aluminum with other metals is to strengthen aluminum.
Common Base Metals:
6061
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Heat treatable
Alloyed with silicon and magnesium
Most common base material in general fabrication
5052
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Hardened by coldworking
Alloyed with magnesium
*Silicon - Added for fluidity, improves crack sensitivity
*Magnesium - Increased strength, but harder to extrude
Common Filler Metals
ER4043
● More ductile than ER5356
● Higher tensile strength
● Better weldability
● Less WFS than 5xxx
● Cannot be used to weld 5052 base
● Can be used on 6061 base
ER5356
● More rigid than ER4043
● Higher shear strength
● Feeds better, but 25% more WFS needed ($).
● Less jamming and downtime refeeding wire
● Only ER5356 can be used on 5052 base
● Can also be used on 6061 base
There are certainly more grades than the few listed, but in general fabrication and maintenance these are
the most common ‘workhorse’ grades you will likely run into.
Note that unlike stainless, we can’t simply make filler that is the exact same chemistry as the base. By
adding enough filler metal with a different chemistry you change the chemistry of the solidifying weld
deposit so it’s not as crack-sensitive. Usually 4043—aluminum with 5 percent silicon added—or
5356—aluminum with 5 percent magnesium added—is used. By adding enough of either, the chemistry of
the weld now is crack-resistant.
Weldability of Aluminum Alloys
☑ 1XXX alloys. Essentially pure aluminum (99 percent pure) and used to carry electrical current or for
corrosion resistance in specific environments, these alloys are all readily weldable. The most common
filler metal is 1100.
☑ 3XXX alloys. This family comprises medium-strength alloys that are very formable. They often are
used for heat exchangers and air conditioners. All are readily weldable using either 4043 or 5356 filler
metal.
☑ 4XXX alloys. These usually are used as welding or brazing filler alloys. However, they are sometimes
used as base materials. If that is the case, they are readily welded with 4043 filler metal.
☑ 5XXX alloys. This is a family of high-strength sheet and plate alloys. All of them are easily welded
using 5356 filler metal, although 5183 or 5556 should be used for the stronger alloys, such as 5083.
☑ 6XXX alloys. These are primarily the extrusion alloys, although they are available in sheet and plate
as well. They are prone to be crack-sensitive. However, with the proper techniques, they can all be readily
welded using 4043 or 5356.
⛝ 2XXX alloys. These are high-strength aerospace alloys in sheet or plate form. Their chemistry makes
most of them unweldable using GTAW or GMAW because of hot cracking. The exceptions are 2219 and
2519, which are both readily welded using 2319 or 4043 filler metal. In any case, you should never weld
2024. It is very common and very high in strength, but it is extremely crack-sensitive.
⛝ 7XXX alloys. This too is a family of high-strength aerospace alloys. Like the 2XXX alloys, most of them
are unweldable using GTAW or GMAW because of hot-cracking and stress-corrosion concerns. The
exceptions are 7003 and 7005 extrusion alloys and 7039 plate alloys. All three of these are readily
weldable using 5356 filler. Never weld 7075.
POLARITIES AND PROCESSES
GMAW (MIG) SETUP
Works well on medium to thicker sized parts and for production welding. GMAW uses 100% argon gas, or
an Argon/Helium mix for increased penetration on thicker sections.
DC+ Reverse polarity is required.
With MIG welding you need a C.V power source and Reverse polarity.
U-Grooved drive rollers and plastic liners should be used.
Aluminum will most often require you to switch to a welding gun that is made specifically to handle an
aluminum setup.
CLEANING
Aluminum melts at about 1200°F but the oxide layer around it melts at approximately 3600°F. It is this
oxide film which prevents corrosion and also makes welding difficult.
Cleaning off the aluminum oxide layer before welding is of utmost importance either with a chemical
cleaner or stainless wire brush to remove the aluminum oxide layer. Special aluminum cutting and
grinding disks are also available.
Caution needs to be taken with using any type of solvent or chemical
on surfaces that are going to be
welded on - regardless of the material type. The ultraviolet radiation from welding can produce harmful
gases when it comes in contact with some solvents and cleaners like brake cleaner and chlorinated
bleach. This particular mixture produces deadly phosgene gas which has been known to cause
respiratory failure
Best practice is to only use cleaners that are known to be safe on weldable surfaces. Acetone is a safe
option provided it has time to evaporate, although it will only remove contaminants and not the oxide
layer. Other name brands such as Dynaflux and Ultra-Brite will remove oxides and are advertised as safe
provided they are thoroughly rinsed off before welding.