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How to Weld Aluminum

Published October 3, 2026 · Built by Jeremy Panasuk

Aluminum welding on this site is two different jobs. One is which machine can reach the thickness, and that already lives on what size welder for aluminum. The other is what to do with the metal in front of you: get the oxide off, run AC so the arc can clean what the brush missed, and then read a published amperage row for the thickness you measured. At 125 mils the TIG tab returns Miller’s 1/8 inch 6061 butt-joint start. Other thicknesses use a published Lincoln row, or the nearest published row. The tab does not multiply the steel rule by 1.5, and it does not invent a window between chart rows.

The oxide melts hotter than the metal

Miller’s account of AC balance starts with the temperatures. Aluminum oxide typically melts at 3,600 degrees Fahrenheit. The aluminum under it melts at 1,200 degrees. Leave the oxide in place and it sits on top of a puddle that is already liquid, which is how you get a weld that looks closed and is not fused. The electrode-positive half of an AC cycle blasts at that oxide. The electrode-negative half puts heat into the work. Miller is explicit that those two halves add to 100 percent: more cleaning time means less penetration time.

That arc cleaning is the second step. The same article says to wipe off dust, debris, and oil first, because the oxide holds oil, and then to clean with acetone and a wire brush. Heavily oxidized parts, such as marine pieces that have sat in salt air, need a heavy file or a carbide burr. A light wipe is only for parts that are already free of grease and thick debris. Balance control does not replace that. On a clean part, Miller’s practice start is about 75 percent electrode negative. Dirtier aluminum may need a setting as low as 65 percent electrode negative, and a very clean part may allow something closer to 80 percent. If the puddle “peppers,” more cleaning (a lower electrode-negative share) is required, and if you would have to go below 60 percent, Miller says the part usually needs more mechanical cleaning instead.

A published start for 1/8 inch 6061

Miller’s gas-tungsten-arc guidelines include a table of inverter starting parameters for aluminum joints, all on 6061 that is 1/8 inch thick, with 1/8 inch 5356 filler, 3/32 inch 2 percent ceriated tungsten, and argon at 15–20 cubic feet per hour. The butt-joint row is 90–120 amps, 65–75 percent balance, and 60–120 Hz. The T-joint row is 100–125 amps, 70–75 percent, and 100–200 Hz. A lap joint is 90–110 amps. A corner joint is 80–90 amps. The joint changes the start. A corner is not a butt.

The same guide says to keep shielding gas flowing 10–15 seconds after the arc stops, described as one second for each 10 amps, so the tungsten does not oxidize while it cools. That is a post-flow instruction, not an amperage.

Worked example: 125 mils on the TIG tab

One-eighth inch is 125 thousandths. On the TIG tab, set thickness to 125 and material to aluminum. The function does not multiply by 1.5. It prints Miller’s butt-joint start: 90–120 amps. The other stats on that result are the rest of the same published row: a T-joint start of 100–125 amps, 3/32 inch 2 percent ceriated tungsten, 1/8 inch 5356 filler, and AC, with the butt-row balance of 65–75 percent. Lap and corner stay in the note, at 90–110 and 80–90 amps, because the result card has room for one joint in the headline.

Section 8-3 publishes those four starts for 1/8 inch only. A 62-mil piece is not given a scaled 90–120, and a 250-mil piece is not given a multiplied one. Those other thicknesses have their own published cells, below.

Other thicknesses: published rows, or the nearest one

Lincoln’s Square Wave TIG 200 quick reference, part L16988, has an Aluminum (AC) column. At 62 mils, which is the chart’s 1/16 inch (0.062 in) cell, the tab returns 75–85 amps, with 3/32 inch tungsten and 1/16 inch filler. That same column also covers 16 gauge (0.060 in). At 188 mils, this site’s marker for 3/16 inch, the tab returns 165–195 amps. L16988 prints that thickness as 3/16 inch (4.8 mm), with 3/32 inch tungsten and 1/8 inch filler. The Harris/Lincoln 4043 sheet lists 170–225 amps at 3/16 inch; the tab does not blend that with 165–195.

Three-thirty-seconds of an inch is about 94 mils, and 94 is not a thickness on either chart. The nearest published thickness is 0.090 inch on L16988, four mils away. That cell is 85–110 amps, with 3/32 inch tungsten and 3/32 inch filler. The result says “nearest published row.” Twelve gauge (0.105 in) shares that same 85–110 amp cell, but 94 is closer to 0.090 than to 0.105, so the label names 0.090 inch.

One-quarter inch is 250 mils. L16988 stops at 3/16 inch, so the tab uses the Harris/Lincoln 4043 GTAW (AC) sheet: 220–275 amps, 3/16 to 1/4 inch pure or zirconiated tungsten, 3/16 inch filler, a 1/2 inch cup, and argon at 30 CFH. The sheet calls those figures basic guidelines that vary with joint design and the number of passes.

Enter thisWhat the TIG tab printsWhy that window
62 mils (1/16 in)75–85 A, published rowLincoln L16988, Aluminum (AC)
94 mils (3/32 in)85–110 A, nearest published row: 0.090 inLincoln L16988. Not an interpolated 3/32 in window
125 mils (1/8 in)90–120 A buttMiller GTAW section 8-3. Lincoln’s 120–135 A cell is not used
188 mils (3/16 in)165–195 A, published rowLincoln L16988, 3/16 in (4.8 mm)
250 mils (1/4 in)220–275 A, published rowHarris/Lincoln 4043 GTAW sheet
For 1/8 in (125 mils) aluminumWhat it saysWhere it comes from
Butt joint, 606190–120 A, 65–75% balance, 60–120 Hz, 1/8 in 5356, 3/32 in ceriated, argon 15–20 CFHMiller GTAW guidelines
T-joint, 6061100–125 A, 70–75% balance, 100–200 HzMiller GTAW guidelines
This calculator, 125 mils, aluminum90–120 A butt, T-joint 100–125 A shown beside it, AC, 3/32 in 2% ceriated, 1/8 in 5356TIG function: Miller GTAW section 8-3, not a 1.5× factor

MIG with a spool gun is a different page

A Millermatic 211 spec sheet lists aluminum only with a spool gun: 18 gauge to 1/8 inch on 120 volts, and 18 gauge to 3/8 inch on 240 volts. That comparison, including the Handler 140’s .030 aluminum wire note, is the aluminum welder-size page. Miller’s 1 amp per .001 inch rule is a solid-wire steel example. It is not an aluminum TIG start, and this page does not apply it to the 6061 table.

Stick is a poor fit. The farm guide calls stick marginal for aluminum and lists TIG from 22 gauge up. If the only machine in the shop is a stick welder, the honest reading of that guide is that aluminum is the wrong job for it, not that a different rod diameter fixes the metal.

A common mistake

The mistake is treating “125 amps for 1/8 inch” as universal. That 125 amp figure is Miller’s solid-wire steel example at .125 inch. On aluminum, the same thickness is the butt-joint start of 90–120 amps, which is also what this TIG tab prints at 125 mils. A corner in the same table starts at 80–90 amps. Welding the steel number onto aluminum, or welding the butt row onto a corner, is how the puddle either sits cold on oxide or falls through.

Limits, and when to call a pro

These are starting points for practice on scrap of the same alloy and thickness, which is what Miller says to do before the real part. They are not a welding procedure specification, a code qualification, or a substitute for a joint that has to carry a load. If the part is structural, pressure-containing, or an alloy and temper you cannot identify, stop and use a qualified procedure. This site does not certify settings for a specific machine.

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MIG welder with spool gun for aluminum

Frequently asked questions

Why does aluminum need cleaning before the arc?

Miller states that aluminum oxide melts at 3,600 degrees Fahrenheit while aluminum melts at 1,200 degrees. The oxide has to come off, or it blocks fusion. Acetone and a wire brush are the manual clean Miller describes; AC balance is the second step, not the first.

What does Miller list as a starting point for 1/8 inch 6061?

For a butt joint, the GTAW guidelines list 90–120 amps, 65–75 percent balance, 60–120 Hz, 1/8 inch 5356 filler, 3/32 inch 2 percent ceriated tungsten, and argon at 15–20 CFH.

What does this site’s calculator return for 125 mils of aluminum?

Set thickness to 125 mils and material to aluminum. The TIG tab returns 90–120 amps for a 6061 butt joint, AC, 3/32 inch 2 percent ceriated tungsten, and 1/8 inch 5356 filler. The same Miller row lists a T-joint at 100–125 amps, a lap at 90–110, and a corner at 80–90. It does not multiply by 1.5.

What does this site’s calculator return for other aluminum thicknesses?

62 mils (1/16 inch) returns Lincoln L16988’s 75–85 A row. 94 mils (a 3/32 inch entry) is not a published row; the nearest is 0.090 inch, Lincoln L16988, 85–110 A, and the tab labels it as the nearest published row. 188 mils (3/16 inch) returns 165–195 A from that same Lincoln chart. 250 mils (1/4 inch) returns 220–275 A from the Harris/Lincoln 4043 GTAW sheet. None of those windows is interpolated.

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