How to weld aluminum: AC TIG, MIG and prep

Q: What gas do you use to weld aluminum?

Pure argon for both TIG and MIG. On thick aluminum, argon/helium mixes add heat and penetration.

Free guide · The Welder's Forge · updated September 2026

Aluminum fools you. It looks cold, it does not glow red like steel and then, all at once, it sags and drops a hole. There are two reasons: an oxide layer that melts at a much higher temperature than the metal, and how fast aluminum carries heat away. Once you understand both, aluminum stops being a mystery.

Quick answer

The reference process is AC TIG with pure argon: the AC half cycle that cleans breaks up the oxide and the other half melts the metal. For MIG, use pure argon and aluminum wire, ideally with a spool gun or push-pull gun. Either way, degrease and remove oxide just before you weld.

The oxide problem

Aluminum is always coated in a film of aluminum oxide (Al₂O₃). It melts at about 3,760 °F (2,072 °C), while the aluminum under it melts at only about 1,220 °F (660 °C). If the oxide is not removed, the metal beneath melts inside a skin that will not fuse. You get a puddle that will not wet, little balls of metal and lack of fusion.

Table 11.1 of the e-book rates aluminum as good (TIG/MIG) weldability with one key precaution: remove the oxide layer, and watch heat input.

Type	Carbon content	Weldability	Precautions
Low-carbon steel	0.05–0.30%	Excellent	Usually none
Aluminum	n/a	Good (TIG/MIG)	Remove the oxide layer; watch heat input

Table 11.1 of the e-book The Welder's Forge (excerpt).

AC TIG: the cleaning action

On aluminum, TIG runs on alternating current, which swaps polarity every cycle:

In the electrode-positive half cycle, ion bombardment breaks up the oxide. This is the cleaning action.
In the electrode-negative half cycle, heat concentrates in the work and melts the metal.

AC balances cleaning and penetration. On DCEN the oxide stays put and you will never get a clean puddle. On AC the tungsten tip is balled, and the ball should not exceed 1.5 times the electrode diameter. Which tungsten to use is covered in tungsten electrode colors; torch angles and rod rhythm are in TIG welding for beginners.

Processes and gases for aluminum

Process	Gas	Current	When to use it
TIG	Pure argon	AC	Thin to medium sheet, quality finish
TIG on thick parts	Argon/helium	AC	Helium adds heat and penetration
MIG	Pure argon	DCEP	Larger parts, more speed
MIG on thick parts	Argon/helium	DCEP	Thick aluminum
Pulsed MIG	Pure argon	Pulsed	All positions with a good finish

Chapters 4, 5 and 11 of the e-book The Welder's Forge.

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MIG on aluminum: the soft wire problem

MIG on aluminum takes pure argon, never the CO₂ mixes made for steel. The difficulty is feeding: aluminum wire is soft and kinks inside a long liner. Use a spool gun or a push-pull gun, a short gun lead and drive rolls made for soft wire. The differences between gases are in MIG welding gas compared.

Why aluminum "sags"

Aluminum conducts heat very fast. At the start, the heat runs off into the rest of the part and it seems nothing is happening. Then the whole part heats up and the puddle suddenly grows until it burns through.

At the start, you need more current to form the puddle.
As the part heats, take current away. This is where a TIG foot pedal earns its place.
Keep travel speed steady and never dwell in one spot with the arc on.

For a starting amperage, use the TIG welding amperage chart. Aluminum often wants somewhat more current than steel of the same thickness at the start; adjust by how the puddle behaves.

Cleaning before you weld

Degrease the area with a solvent and a clean rag.
Brush off the oxide with a stainless steel brush used only on aluminum.
Weld soon after: the oxide re-forms over time.
Clean the filler rod if it has dirt or oil on it.

Solvents and the arc

Never weld near parts still wet with chlorinated solvents, including some brake cleaners. The arc's UV light can turn the vapor into toxic gases. Let solvent dry fully, read the product label and work with ventilation. Aluminum welding fume also calls for good ventilation and a NIOSH-approved respirator with P100 filters or a PAPR if fume cannot be kept out of your breathing zone.

Start small

Practice on small scraps of the same alloy. Aluminum asks for more practice than any other common metal. If you cannot yet run a steady bead on steel, start there. No article replaces hands-on training with someone who can watch your technique.

Frequently asked questions

Why can't I weld aluminum?

Usually it is the oxide, which melts at about 3,760 °F (2,072 °C) while the aluminum melts at about 1,220 °F (660 °C). Use AC TIG, which breaks up the oxide, and clean the area just before welding.

What gas do you use to weld aluminum?

Pure argon for both TIG and MIG. On thick aluminum, argon/helium mixes add heat and penetration.

Can you TIG weld aluminum with DC?

Not for normal work. On DCEN the oxide stays and the puddle will not wet. Aluminum needs AC, which cleans and melts in the same cycle.

Can my MIG welder weld aluminum?

With pure argon and aluminum wire, yes, but the soft wire tangles easily. A spool gun or push-pull gun, drive rolls for soft wire and a short gun lead solve the feeding problems.

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