AC Balance and AC Frequency for Aluminum TIG, Explained Simply
Buy an AC/DC inverter TIG welder and you'll see two settings older transformer machines didn't have: AC balance and AC frequency. They look intimidating, and many people leave them on default forever. That's fine to start, but understanding them gives you much more control over aluminum.
This guide explains what each does, how they interact, and how to use them to solve common aluminum problems like a dirty puddle, a wide bead, or excessive tungsten wear.
Why aluminum needs AC
Aluminum forms a thin, tough oxide layer on its surface almost instantly when exposed to air. That oxide melts at a much higher temperature than the aluminum underneath. If you don't break it up, the aluminum melts beneath a skin of oxide and the puddle doesn't flow or fuse properly.
AC TIG solves this by alternating between two polarities:
Electrode positive (EP)
The cleaning half. Breaks up the oxide layer on the surface. Puts more heat into the tungsten.
Electrode negative (EN)
The penetration half. Puts more heat into the work and less into the tungsten.
Older transformer machines gave a fixed, roughly even split between the two at the mains frequency. Inverters let you change both the split (balance) and the switching speed (frequency).
AC balance
AC balance sets the proportion of time in each half of the cycle.
| More cleaning (more EP) | More penetration (more EN) | |
|---|---|---|
| Oxide removal | Stronger, wider | Lighter, narrower |
| Etched (frosted) zone | Wider | Narrower |
| Tungsten heating | More; tip balls more | Less; tip holds shape |
| Penetration | Shallower | Deeper |
| Good for | Dirty or heavily oxidized material (after cleaning) | Clean material, thicker sections, faster travel |
Different manufacturers label balance differently. One machine's "70%" might mean 70% EN; another's might mean 70% EP. Some use a minus-to-plus dial. Before you change it, read the manual so you know which direction adds cleaning.
The etched zone is a useful visual clue. A narrow frosted band along each side of the bead tells you the cleaning action is working. If the frosted band is very wide, you're probably using more cleaning than you need, heating the tungsten unnecessarily.
AC frequency
AC frequency, measured in hertz (Hz), is how many times per second the current reverses. Transformer machines are fixed at the mains frequency (60 Hz in the US). Inverters let you adjust it over a much wider range.
| Lower frequency | Higher frequency | |
|---|---|---|
| Arc shape | Wider, softer cone | Narrower, more focused cone |
| Bead | Wider, flatter | Narrower |
| Directional control | Arc can wander more | Arc stays where you point it |
| Good for | Wide buildup, broad fillets on thicker material | Fillet roots, inside corners, thin material, tight joints |
| Sound | Lower buzz | Higher-pitched buzz |
Higher frequency is very helpful on fillet welds, where a wide arc tends to climb the walls of the joint instead of going into the root.
How they interact
Balance and frequency affect different things, but they combine:
- Balance changes how much cleaning versus penetration you get.
- Frequency changes the shape of the arc.
So if you raise frequency to tighten the arc, you might find you can reduce cleaning slightly because the arc's oxide removal is more concentrated. The best way to learn is to change one at a time on scrap and watch.
Diagnosing problems
| Symptom | Possible setting change | Also check |
|---|---|---|
| Dirty, peppered or scummy puddle | More cleaning | Clean and degrease material, dedicated stainless brush, gas coverage |
| Tungsten balls heavily or spits | Less cleaning | Larger tungsten diameter, tungsten type, amperage |
| Wide frosted zone along bead | Less cleaning | Nothing; this is cosmetic, not a defect |
| Arc climbs fillet walls | Higher frequency | Torch angle, tungsten stickout |
| Bead too narrow for the joint | Lower frequency | Amperage, travel speed |
| Arc wanders | Higher frequency | Sharper tungsten, contamination |
Practical setup tips
- Use the manual's starting values or the machine's default AC settings.
- Clean the aluminum: degrease with a suitable solvent, then brush with a stainless brush used only on aluminum. Let solvents fully evaporate before welding.
- Use a suitable tungsten. On inverters, 2% lanthanated or ceriated is common, ground to a point with a small truncated tip.
- Run beads on scrap, then adjust balance first, watching the puddle and tungsten.
- Adjust frequency to suit the joint: higher for fillets and corners, lower for wider beads.
- Record settings that work for each thickness and joint.
Common beginner mistakes
- Turning cleaning to maximum "just in case." It overheats the tungsten and widens the etch without making the weld stronger.
- Changing balance, frequency and amperage at once. You can't tell which change helped.
- Blaming settings for dirty metal. No balance setting fixes oil, heavy oxide or a contaminated filler rod.
- Using a brush that has touched steel. It can embed steel particles in the aluminum surface.
Advanced AC settings
Some machines go beyond balance and frequency with features like independent EN and EP amperage, or selectable AC waveforms (square, soft square, sine, triangular). These give further control over arc character and heat input. They're powerful, but they're also brand-specific, so learn them from your machine's manual and change them only after you're comfortable with balance and frequency.
Aluminum TIG reflects a lot of UV, so cover all skin and use the shade your helmet manual recommends for your amperage. Use local fume extraction, especially for longer welds. Check your machine's input requirements in the manual and confirm your circuit with an electrician before running at high AC amperage.
Verdict: Treat balance as the cleaning-versus-tungsten-heat dial and frequency as the arc-width dial. Start from the defaults, adjust one at a time, and let the puddle, the frosted band and your tungsten tell you which way to go.
FAQ
What AC balance should I use for aluminum TIG?
Start with your machine manual's recommended setting or its default. Many welders find they can use less cleaning than they'd expect on clean aluminum. Increase cleaning if the puddle looks dirty or peppered, and decrease it if the tungsten is balling excessively or the etched zone is wider than needed.
Why does my machine's AC balance scale look backward?
Brands use different conventions. Some machines show balance as the percentage of electrode-negative time; others show the percentage of electrode-positive (cleaning) time; others use a plus/minus scale. Read your manual to see which way yours works.
What does high AC frequency do in TIG welding?
Higher frequency produces a narrower, more focused arc that's easier to direct into tight corners and fillet roots, and it can help on thin material. Lower frequency produces a wider, softer arc and a wider bead.
Do I still need to clean aluminum if I use more cleaning action?
Yes. The arc's cleaning action removes the thin oxide layer, but it doesn't remove oil, dirt, heavy oxidation or contamination. Degrease and brush the joint with a dedicated stainless brush before welding.
Why is my tungsten balling up on aluminum?
A large ball usually means too much heat in the tungsten, often from too much cleaning (electrode-positive time), too much amperage for the tungsten diameter, or the wrong tungsten type. Reduce cleaning or move to a larger tungsten.
Putting it together
Start with your machine's defaults, then change one setting at a time based on what you see. Dirty puddle: more cleaning. Balled tungsten or wide etch: less cleaning. Arc too wide for a corner: raise frequency. Bead too narrow: lower frequency. With practice, you'll find a pair of settings you return to for most aluminum work.
Related reading: how to weld aluminum with MIG or TIG, dedicated TIG vs multi-process, and budget TIG welders.