Getting the right AC frequency on your TIG machine can feel like a secret code. One weld beads beautifully. The next weld wanders, soots up the tungsten, and leaves the aluminum looking like a zebra.
TIG AC frequency explained simply comes down to one dial that shapes your arc and your cleaning action. Get it right and the puddle does what you want. Get it wrong and you're chasing everything else.
Manufacturer specifications indicate that most modern inverter machines let you adjust from 20 to 250 Hz, and the sweet spot for general aluminum sits around 150 Hz. Slower is better for thick, dirty, or cracked-open joints, while faster works for thin, clean sheet. In our research, welders who understand this one setting fix more weld quality issues than any other adjustment.
If you're new to the process, start with the basics of TIG welding before touching the dials.
Quick Answer: The Frequency Range You’ll Use Most
Start at 150 Hz for most aluminum TIG jobs. Drop to 60-80 Hz for thick, dirty plate. Raise to 180-250 Hz for thin sheet and tight joints.
Adjust by 10-20 Hz until the arc feels crisp and the puddle wets out.
| Aluminum Thickness | Frequency Range | Cleaning Width |
|---|---|---|
| Under 1/16 inch | 180-250 Hz | Narrow |
| 1/16 to 1/4 inch | 120-180 Hz | Medium |
| Over 1/4 inch | 60-120 Hz | Wide |
Use the table as a starting point, not a rule. Every joint, filler rod, and tungsten prep shifts the ideal number. The key is to learn what each range feels like, then trust your own test welds.
Why Frequency Matters More Than Most Dial Settings
Here's what actually happens. In AC TIG, the current flips between electrode negative (EN) and electrode positive (EP). EN gives you penetration.
EP gives you cleaning action. Frequency controls how many times that flip happens every second.
At low frequency, the arc becomes soft and wide. The cleaning band spreads out like a paintbrush. That helps on dirty material but can make the puddle feel loose.
At high frequency, the arc snaps into a tight column. Think pencil point, not brush. You get focused heat, better penetration, and a narrower cleaning zone.
That's why TIG AC frequency matters so much. It's not just a technical spec. It's the difference between an arc that scrubs away oxide and one that cuts through thick plate like a laser.
Modern inverter welders from manufacturers like Miller give you full control of this dial, which is why they're so popular for aluminum. The weld quality difference between 60 Hz and 200 Hz is unmistakable once you see it.
The settings also interact with amperage and balance. You can't treat frequency like an island. But if you're only going to master one advanced setting, this is it.
The Variables That Change Your Frequency Choice
The right frequency depends on four main variables. Let's run through them.
Base Metal Thickness
Thickness is the first thing to check. Thin sheet conducts heat poorly, so you need a focused arc to avoid burn-through. Thick plate needs a broader arc to wet out into the joint.
That's why you'd never run the same frequency on both.
Dirty or Oxidized Metal
Oxide level decides how much cleaning you need. Heavy oxide likes a wide scrubbing band, which happens at low frequency. Clean, freshly brushed aluminum can handle a tighter arc at higher frequency.
Old castings are the worst, so give them extra room. Per American Welding Society guidelines, cleaning and fit-up are the two biggest contributors to aluminum weld quality. Frequency is the tool you use to respond to them.
You can reference those standards on the AWS site when you're setting up a procedure.
Tungsten Electrode Type and Condition
The electrode matters more than you'd think. Pure tungsten forms a clean ball at the tip, which helps at low frequencies. Ceriated and lanthanated tungsten hold up better at higher frequencies, but they need the right prep.
A sharp or ground tip won't form a proper ball, and that changes the arc shape. If you see the tungsten splitting or spraying, your frequency might be too high for the electrode size.
Joint Position and Fit-Up
Out-of-position welds call for a softer, wider arc. That means lower frequency. Tight, closed joints with good fit-up can handle a focused arc.
Gaps and sloppy fit-up need a wider arc to fill the space without cutting a keyhole. Think about the physical geometry before you dial anything in.
Decision Guide: Choosing Frequency by Situation
Here's the practical part. Use these starting points, then adjust based on real test welds. No two jobs are identical, but these base numbers get you close fast.
Thin Aluminum Sheet (Under 1/8")
If you're welding thin sheet, start at 180 to 250 Hz. The narrow arc keeps heat concentrated, so you move fast and avoid warping. If the bead looks too triangular or the puddle feels stiff, drop the frequency by 20 Hz.
If you're still blowing through, lower your amperage instead. For thin sheet, TIG is often the go-to approach for aluminum, but only if you set the arc correctly.
Thick Aluminum Plate (1/4" and Up)
On thick plate, you need a wider cleaning band. Run 60 to 100 Hz. The lower frequency spreads the arc, which preheats the base metal and wets the puddle out nicely.
You'll also get better oxide removal at the weld toes. If the arc feels too wide and you're getting a fat bead, bump it up slowly. For thick, open-root joints, TIG's superior control gives you penetration that other processes can't match.
Heavily Oxidized Castings
Castings store oil, dirt, and oxidation deep in the pores. Drop to 40 to 70 Hz. That slow, wide arc scrubs aggressively and gives the cleaning action time to work.
You'll still need to pre-clean with solvent or a wire brush. If the arc wanders, go up a touch but not past 90 Hz. The low frequency keeps the puddle fluid enough to flow into pits and imperfections.
TIG Welding Magnesium
Magnesium is similar to aluminum but runs hotter and faster. Start at 80 to 120 Hz. This keeps the puddle fluid without letting it run away.
You want enough cleaning power without overheating the part. Watch for dull, gray oxide reforming behind the arc. That's a sign you need a wider cleaning band, so drop your frequency slightly.
How to Set Frequency on Different Machines
Setting frequency depends on what machine you're using. Not every TIG welder gives you this control.
Inverter Welder with Digital Controls
Most modern inverters have a dedicated AC frequency knob or menu setting. Set your balance first, usually around 70% EN. Then set frequency to 150 Hz as a baseline.
Run a test bead and adjust in 10 Hz steps. Small changes make a visible difference, so don't jump 50 Hz at once. Some machines let you adjust frequency while welding, which is perfect for fine-tuning on a practice coupon.
Transformer Welder with Fixed Frequency
Older transformer machines run at line frequency. That's 60 Hz in North America and 50 Hz in most other countries. There's no adjustment knob.
You get a wide, soft arc, which is fine for thick aluminum but frustrating on thin sheet. If you're stuck with that, focus on amperage control and torch angle instead. You can compensate with faster travel speed and a tighter arc length.
Remember, the torch, cup size, and gas lens all change the way frequency behaves, so don't overlook the rest of your welding torch setup. A gas lens smooths out turbulence and lets the arc work the way your settings intend. Cup size also affects shielding gas coverage and arc characteristics.
Get those right and your frequency decisions will actually show up in the weld.
Step-by-Step: Dialing In AC Frequency from Scratch
Work on a scrap piece first. Match the thickness and surface condition of the real job. Clean it the same way you plan to clean the actual part.
Then walk through these steps.
- Set balance first. Use 70% EN for a solid baseline. Balance controls penetration versus cleaning.
- Pick a starting frequency. Refer to the thickness table from earlier. About 150 Hz is a solid middle ground.
- Run a test bead. Watch the arc shape, the puddle, and the silver frosted band beside the weld.
- Adjust in 10 Hz steps. Small changes are visible. Don't jump 50 Hz at once.
- Reset amperage if needed. A different frequency changes how the puddle feels. Your current may need a nudge.
The frosted cleaning band is your visual feedback. Too narrow at the weld toes? Drop frequency.
Too wide, or the arc wanders? Raise it. American Welding Society guidance emphasizes prep and heat control above all else for aluminum.
Frequency lets you fine-tune heat behavior for each joint.
As of 2026, even mid-range inverter welders include adjustable frequency. Budget machines from most major brands offer it. There's little reason to guess.
The Relationship Between Frequency, Balance, and Amperage
Frequency doesn't act alone. It works with balance and amperage as one system.
Balance sets the split between electrode negative (EN) and electrode positive (EP). EN drives penetration. EP drives cleaning action.
Frequency decides how fast the arc switches between them. Amperage controls overall heat input.
Here's the practical interaction. On thin sheet, raise frequency to tighten the arc. Then drop amperage slightly to prevent burn-through.
On thick dirty plate, lower frequency for a wider cleaning band and increase EN for penetration. That combination is why adjustable TIG handles aluminum better than most alternatives for welding aluminum.
If you make a big frequency change, recheck your balance. Also rethink travel speed. These three settings live together.
Common Mistakes to Avoid with AC Frequency
Running High Frequency on Thick Plate
High frequency creates a tight, focused arc. Thick, oxidized plate needs the opposite. Use 60 to 100 Hz for a broad scrubbing arc.
Running Low Frequency on Thin Sheet
Low frequency spreads heat. Thin sheet warps, burns through, and turns ugly fast. Keep it at 180 Hz or higher for clean material.
Ignoring Material Prep
No dial setting fixes dirty aluminum. Acetone and a clean stainless wire brush matter more than any frequency number. Good fit-up helps, too.
Twisting Multiple Settings at Once
Change frequency first. Watch the bead. Then adjust balance or amperage if the puddle still misbehaves.
Tweak one variable at a time.
Confusing AC Frequency with Pulse Frequency
AC frequency controls the arc's AC cycle. Pulse frequency controls a separate on-off current pulsing pattern. They do different things.
Pulse is great for heat management, but it doesn't change cleaning width.
Overlooking Machine Limits
Transformer welders run fixed at 50 or 60 Hz. You get one wide, soft arc. On thin aluminum, that's painful.
If you need a tighter arc for sheet metal, get an inverter machine. Or use a spool gun setup for speed instead, though weld quality will be lower.
Pro Tips for Getting the Best Arc and Cleaning Width
Match Tungsten to Frequency
Pure tungsten balls nicely at low frequencies. Ceriated or lanthanated tungsten holds up better at high frequencies. Use 2% ceriated for most sheet aluminum.
Read the Cleaning Band
The frosty silver band next to the weld is your feedback. Too narrow? Lower the frequency.
Too wide? Raise it. Trust what the arc tells you.
Use a Gas Lens
Gas lenses stabilize shielding gas flow. Less turbulence means the arc behaves closer to your settings. Try one before blaming other variables.
Test on a Coupon
Run a two-inch bead on scrap. Let it cool and inspect the surface. Tight puddle, clean toes, and a bright bead mean you're close.
Real Scenario Examples: What Frequency Works Where
Example 1: Thin Sheet Repair
Patching a 1/16-inch aluminum boat hull. Clean stock, tight fit-up. Run 200 Hz with 70% EN and low amperage.
The narrow arc keeps heat concentrated and prevents sagging.
Example 2: Dirty Aluminum Casting
A cracked manifold with years of oil and oxide. Wipe it down, wire brush it, then set frequency to 60 Hz. The wide scrubbing arc has time to clean as you weld.
Expect a slower travel speed and a fluid puddle.
Example 3: Magnesium Motorcycle Casing
Magnesium runs hot and oxidizes fast. Start at 100 Hz. Use a steady hand and push the puddle forward with filler rod.
The arc needs enough cleaning action without overheating the part.
Frequently Asked Questions
What Does AC Frequency Do on a TIG Welder?
AC frequency controls how many times per second the current switches between electrode negative and electrode positive. Higher frequency creates a tighter, more focused arc. Lower frequency widens the arc and spreads the cleaning action across a larger zone.
Every flip scrubs away oxide while balancing heat input.
What Is a Good Starting Frequency for Aluminum?
Start at 150 Hz for general purpose aluminum. Drop to 60 to 100 Hz for thick plate and heavy oxide. Raise to 180 to 250 Hz for thin sheet and tight joints.
Adjust in 10 Hz steps until the puddle wets out cleanly.
Does AC Frequency Affect Cleaning Action?
Yes, and that's one of its biggest roles. Lower frequency gives the electrode positive portion of the cycle more time to scrub oxidation. That widens the cleaning band.
Higher frequency reduces cleaning width and focuses the arc for deeper penetration. Visible surface and bead shape shift with each change.
Can I Weld Aluminum on a Machine with Fixed Frequency?
You can, but you're stuck with 50 or 60 Hz. That gives a wide, soft arc. Use it for thicker, dirtier aluminum.
For thin sheet and precision work, an inverter machine with adjustable frequency makes a visible difference.
Is AC Frequency the Same as Pulse Frequency?
No, they're separate settings entirely. AC frequency controls the alternating current cycling for aluminum. Pulse is a secondary feature that changes amperage in a square wave pattern.
Pulse controls heat input and puddle agitation, but not cleaning width. Many welders confuse the two because both appear in the advanced settings menu.
Final Recommendation: Your Starting Point and How to Adjust
If you remember nothing else, remember this. Start at 150 Hz for most aluminum. Use the cleaning band as your guide.
Adjust in small steps.
The process is simple. Set balance around 70% EN. Set frequency from the thickness table.
Run a test bead. Read the frosted band. Then adjust.
Here's the bottom line. TIG AC frequency is one of the few settings on your welder that shapes both the arc and the puddle. Learn it first and you'll master clean aluminum far sooner.
Write down what frequency works for each job. Tool, thickness, and material condition are the three things to note. Use your machine's digital readout to track settings.
After a few sessions you'll have a personal chart that beats any generic table.
Watch for hinge-point signals. If the arc wanders, slow the frequency down. If the bead goes narrow and tall, speed it up.
If you see soot on the tungsten, check your balance instead. The right number feels crisp and quiet.
Repetition builds instinct. Over time you'll hear the arc change before you even see the weld. That's when frequency stops being a mystery and becomes a tool.
