Mig welding aluminum can be just as simple as mig welding steel, if you
understand the fundamental mig process and the alloy differences between steel
and aluminum. Typical weld characteristics of steel or stainless don't apply to
mig welding aluminum. Aluminum has higher thermal conductivity and lower melting
temperatures, both factors will influence weld solidification, weld burn through
potential and warp problems.
Why MIG welding aluminum is done...
The reason why aluminum is specified for so many welded jobs is that it
provides unique physical properties: Aluminum Weight. Aluminum is three
times lighter than steel and it's stronger when alloyed with specific elements.
Aluminum's Conductivity. It conducts electricity six times better than
steel. The high electrical conductivity makes the effect of electrical wire
stick-out in MIG welding less of a concern when compared to steel MIG welding.
Since aluminum is non-magnetic, arc blow is not a problem during aluminum
welding. Thermal Conductivity. With a thermal conductivity rate that is
five times higher than steel and the aluminum welds being more sluggish and less
fluid, aluminum can be welded in all positions with relative ease. In contrast
to steel the high conductivity of aluminum acts as a heat sink making weld
fusion and weld penetration more difficult to achieve.
MIG welding aluminum requires different techniques than MIG welding mild
Material thickness that can be welded with Mig process on aluminum are 14
Ga. and heavier. (How heavy depends on the output capacity of the welder being
used.) To MIG weld aluminum thinner than 14 Ga. (.074") either specialized
pulsed MIG or AC TIG welding equipment may be necessary.
The removal of lubricants from the aluminum base material may be necessary.
This is best done with solvents. Consult with your local Miller Welding
Distributor for their recommendation. Oxide removal should be done after
degreasing. This should be done with a stainless wire brush. This can be done
with a hand wire brush or with a cup wire brush. If a power wire brush is used
keep the RPM'S and pressures low to reduce smearing the surface of the material,
which could entrap oxides and impurities under the surface. Always use a wire
brush that is used on aluminum only, to keep from contaminating the base
Contact your local welding distributor or aluminum filler metal
representative for recommendations on wire alloys that fit your application.
Know the alloy of your base aluminum and what conditions the finished part will
be subjected to. The 2 most readily available aluminum filler wires are ER4043
Mig Welding Techniques
- Hook spoolgun to the positive stud on the power supply.
- For MIG welding aluminum you need to use a 10 to 15 degree push travel angle
(tip and nozzle pointed in the direction of travel). (See Figure 1)
- Pulling or using a drag angle will produce porous, dirty welds because of lack
of gas coverage.
- Spray transfer is the desired mode of metal transfer for welding aluminum. The
spray transfer is a very smooth transfer of molten metal droplets from the end
of the electrode to the molten pool. The droplets crossing the arc are smaller
in diameter than the electrode. There is no short-circuiting in spray transfer.
With spray transfer the deposition rate and efficiency is relatively high. The
arc is very smooth, stable, and stiff and the weld bead has a nice appearance
and a good wash into the sides. In the spray transfer a large amount of heat is
involved which creates a large weld pool with good penetration that can be
difficult to control and can not be used on materials thinner than 14 Ga. This
transfer will produce a hissing sound, and no spatter.
- The short arc transfer on aluminum produces poor cleaning action, poor tie in
at the edges of the weld, and large amounts of spatter and smoke.
- Maintain a tip to work distance, and have the contact tip recessed
approximately 1/8" inside the nozzle if possible. (See Figure 2)
- The reflective heat and weld puddle that is present when MIG welding aluminum
is very hot. Holding the tip closer than this could lead to the wire burning
back to the contact tip and other feeding problems.
- The most common shielding gas for MIG welding aluminum is 100 % argon. Flow
rates of 20 to 30 CFH (cubic feet per hour) are acceptable. C25 or argon Co2
mixes are not acceptable.
- Avoid large weave beads on aluminum. If larger fillet welds are needed
multiple pass straight beads will provide better appearance and have less chance
of cold lapping, burn through, and other weld defects.
- It will be necessary to increase torch travel speed as the base material
becomes heated during the weld.
- The skill level of the operator, joint types, fit up, and positions, as well
as the welding power supply will all have great influence on the weldability of
the aluminum and your success.
Common Mig Welding Problems/Troubleshooting
Burn-Through (Melt Through) Caused by Over Heating the Base Material
1. Increase travel speed. Make shorter welds.
2. Move around on part, spreading out the heat.
3. Use thicker material or change joint design or welding process to AC TIG.
4. Eliminate/Reduce gaps
1. Use push angle instead of drag technique.
2. Increase voltage to get into spray transfer.
3. Use proper base metal cleaning techniques (Stainless Steel Brush).
4. Check for proper shielding gas and wire alloy type.
Cannot Get Mig Welding Machine Set Correct
1. Check inside cover of Millermatic welders for good starting setting and
fine tune for you needs.
2. Order Millermatic MIG Calculator Part # 086446 for good starting settings.
Wire burns back to contact tip during or at the end of the weld
1. Maintain a tip to work distance.
2. Check to make sure the contact tip size, drive rolls and gun liner match the
wire diameter that you are using.
Wire 'Bird Nests' (piles up) in Front of Inlet Guide on Gun
1. Check and adjust drive roll tension.
2. Check to make sure drive rolls match wire diameter
3. Replace contact tip if fouled up
4. Check pressure adjustment on Aluminum spoolgun hub.