Welding aluminum: can your machine do it, what to add, and what changes from steel
Aluminum takes AC tig or mig with the spool gun your machine's maker names. Which gun fits which welder, 4043 vs 5356, pure argon, and cleaning the oxide.
Aluminum looks like an easy step from steel and is not. It conducts heat away fast, it carries a skin of oxide that melts at three times the temperature of the metal under it, and its soft wire buckles in a normal mig gun. Your machine either has a route through that or it does not.
There are two routes: AC tig on an AC/DC tig machine, or mig with the spool gun your machine’s maker names for it. Flux core and DC-only tig are not routes. Then use 100 percent argon, 4043 filler for most repairs, and remove the oxide with a stainless brush used only on aluminum, after degreasing.
Does your machine have a route?
| Your machine | Aluminum route | What to add |
|---|---|---|
| Flux core only | None | A different machine |
| Mig with a spool gun port | Mig with the maker’s named spool gun | Spool gun, argon cylinder and regulator, aluminum wire |
| DC-only tig or multiprocess | Mig only, if it has a spool gun port | As above |
| AC/DC tig | AC tig | Argon, aluminum filler rod, suitable tungsten |
Tig machines are explained in tig welders, and which tungsten suits AC in tungsten electrodes.
Which spool gun fits which welder
Buy the gun your machine’s maker names, not a generic one. From each maker’s spec sheet, manual or guide, checked 2026-10-15:
| Machine | Spool gun the maker names | Wire | Aluminum thickness as published |
|---|---|---|---|
| Millermatic 142 or 211, Multimatic 220 AC/DC | Spoolmate 100 or Spoolmate 150 (not the 200) | .030 or .035 | Multimatic 220: 18 gauge to 3/8 in |
| Hobart Handler 140EZ | SpoolRunner 150 | .030 to .035 | 18 to 14 gauge |
| Hobart Handler 210MVP or 210i | SpoolRunner 100 | .030 to .035 | 210MVP: 18 gauge to 1/4 in |
| Lincoln POWER MIG 211i | Magnum PRO 100SG | .030 or .035 | Not published |
| Eastwood MIG 180 | Eastwood #20172 | Not published | Not published |
One detail catches people out: Miller’s Spoolmate 100 takes 4043 wire only, while the Spoolmate 150 takes 4000 and 5000 series. Miller also says the smaller Millermatics are optimized for 4043.
Why a spool gun at all? Miller: the gun carries a 1 lb, 4 inch spool so the soft wire is pushed only a few inches, instead of 10 or 15 feet through a normal gun. Lincoln adds that spool guns are for light duty work. For heavier work, Lincoln points to push-pull feeders, which feed aluminum wire up to 50 feet.
Sources: Miller, mig aluminum for DIY; Multimatic 220 spec sheet; Lincoln aluminum mig guide C8.100. Brand by brand: Miller, Hobart, Lincoln, Eastwood.
What changes from your steel setup
Lincoln’s guide lists the parts that do not carry over to aluminum:
- Drive rolls: polished U-groove, not the steel V-groove.
- Liner: plastic, such as Teflon or nylon.
- Contact tips: tips for steel are not suitable.
- Gas: argon or argon and helium only. Lincoln says oxygen, hydrogen or CO2 should never be used for aluminum mig, so your 75/25 cylinder is out.
A spool gun carries its own drive and tip, which is why it skips most of this list. Eastwood and Hobart both say to push the gun, not drag it, on aluminum.
Gas: pure argon
Lincoln recommends 100 percent argon up to about 1/2 inch thick, with argon and helium mixes above that, at 30 to 100 cubic feet per hour. Hobart’s Handler 210i manual gives 35 to 45 for aluminum with the spool gun. Eastwood specifies 100 percent argon. The same argon cylinder serves tig. Buying and handling cylinders is in mig welding gas.
Filler: 4043 or 5356
From Lincoln’s guide: 4043 is easier to use, flows better and is more crack resistant. 5356 feeds better and makes stronger, more ductile welds, and anodizes to a better color match, where 4043 anodizes dark grey. Miller says 4043 will work best for most DIYers.
| Base metal | Lincoln says |
|---|---|
| 3003 | Easily welded with either 4043 or 5356 |
| 5052 | Usually 5356; its magnesium is low enough that 4043 also works |
| Other 5000 series | Not with 4000 series filler |
| 6061 and other 6000 series | Readily welded with either; always add filler, since welds without it will almost always crack |
| 6000 series joined to 5000 series | 5356 |
Miller also warns that aluminum wire oxidizes once opened: do not unwrap a spool until you are ready to use it.
Cleaning: degrease, then brush
Both makers put cleaning ahead of any setting. Lincoln’s order: degrease first with a clean rag and solvent, then remove oxide with a stainless steel brush that has never touched anything but aluminum, using light pressure. Brushing first just spreads the oil. Miller suggests acetone and a wire brush, and says parts left in salt water and air for years, like a boat bracket, may need a heavy file or carbide burr. Fit the joint up and weld as soon as you can after cleaning.
AC tig: balance and frequency
On an AC/DC tig machine, two settings matter most. From Lincoln’s Square Wave TIG 200 sheet: a lower balance (percent electrode negative) gives more cleaning action, and a higher balance more penetration; a lower AC frequency gives a wider bead and a higher one a more focused bead. Miller gives 75 percent EN as a typical starting balance, going lower if the weld peppers with oxide, with a minimum around 60 percent. Below that, Miller says, the part needs more mechanical cleaning.
Source: Miller, AC balance for tig aluminum.
Fume and ozone
Lincoln lists gas-shielded arcs as the most severe for arc rays and says not to weld unless ventilation is adequate. Its aluminum guide also discusses gas additions that reduce ozone, which the aluminum arc produces, so keep air moving across the work. Respirators are compared in welding respirators.
Stainless has its own filler and gas rules; see welding stainless steel.
A boat bracket, trailer part or anything that carries a load belongs to a certified welder if it fails in a way that hurts someone. This page explains the process; it cannot tell you a weld will hold.
Frequently asked questions
Can I weld aluminum with a flux core welder?
No maker document we read lists a flux cored aluminum wire. Lincoln's aluminum mig guide covers solid 4043 and 5356 wire only, and says shielding gas for aluminum must be argon or argon and helium. A flux core only machine has no gas path, so it cannot run aluminum.
Can a 120 volt welder weld aluminum?
Some can, thinly. Hobart rates the Handler 140EZ with its spool gun for 18 to 14 gauge aluminum. Miller recommends a welder capable of 230 volt input for aluminum, saying 115 volt welders generally lack the power to overcome aluminum's heat conduction and oxide, which leads to poor fusion.
Should I use 4043 or 5356 filler?
Lincoln says 4043 is easier to use, flows better and is more crack resistant, while 5356 feeds better and gives stronger, more ductile welds. Miller says 4043 will work best for most DIYers. Use 5356 for 6000 series to 5000 series joints, per Lincoln, or when the part will be anodized and color match matters.
Why does aluminum need AC for tig?
Miller explains that the electrode positive half of the AC cycle removes surface oxide, and the electrode negative half melts the base metal and gives penetration. Aluminum oxide melts at about 3,600 F while aluminum melts at about 1,200 F, so the oxide has to be broken up for the weld to fuse.