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AC balance is the welder’s main control for shaping the cleaning action and penetration when TIG welding aluminum. Many machines also offer AC frequency, measured in hertz (Hz). Frequency changes how tightly the arc is focused and how it behaves; it does not replace correct balance, amperage, torch technique, or joint preparation.
For most work, start near 100 Hz, then adjust in small steps while watching the puddle. The useful range depends on the machine, material thickness, joint, and torch setup. A high-frequency setting is not automatically better, and some entry-level welders offer only a fixed frequency.
What AC frequency changes
AC alternates between electrode-negative (EN) and electrode-positive (EP) portions of the cycle. EN supplies most of the heating that melts the work. EP helps break up the aluminum oxide at the surface. AC frequency sets how many times that cycle repeats each second.
At lower frequency, typically around 60–80 Hz, the arc tends to spread wider and feel softer. That can make it easier to cover a broad area or control a puddle on thicker plate, but the arc may wander more and heat a larger zone. At higher frequency, roughly 120–200 Hz, the arc generally becomes narrower and more directional. This can help with tight joints, corners, and thin material, though it may feel sharper and less forgiving.
These are starting ranges, not guarantees. Arc behavior varies by power source and setup. Follow the machine manual, particularly if its frequency control works differently from the common adjustment described here.
Practical starting settings
Begin around 100 Hz if your machine lets you set frequency. Set AC balance according to the manual, clean the aluminum, and establish a stable arc before judging frequency. Make short practice beads on scrap of the same alloy and thickness as the job. Change one control at a time so you can tell what helped.
| Work or symptom | Frequency to try | What to watch |
|---|---|---|
| General-purpose plate or tubing | About 80–120 Hz | Steady arc, even bead, adequate fusion |
| Thin material or a tight joint | About 120–180 Hz | Whether the arc stays focused without burning through |
| Wide bead on heavier material | About 60–100 Hz | Whether the puddle wets both sides of the joint |
| Arc wanders or feels difficult to direct | Try increasing frequency in small steps | Whether control improves without a harsh, noisy arc |
Keep the torch close enough for a short arc, hold a consistent angle, and use filler suited to the base metal and service conditions. Frequency cannot compensate for a long arc, dirty filler, poor fit-up, or insufficient amperage. For equipment selection, an AC/DC TIG welder with adjustable AC frequency is useful when you regularly move between thin, tight work and wider joints. If you weld occasional repairs, a fixed-frequency machine may be adequate.
A simple adjustment process
Set up a clean coupon, ideally the same thickness as your work. Mark several short sections. Weld the first at the machine’s default or around 100 Hz. On the next, raise frequency by 20–30 Hz; on another, lower it by the same amount. Keep balance, amperage, travel speed, and torch position as consistent as you can.
Compare bead shape, puddle control, and fusion at the toes. If the arc is spreading too broadly or tending to wander, a modest increase may help. If it feels excessively sharp, the puddle is difficult to control, or the bead is narrow without sound fusion, return toward the middle of the range. Inspect the back or cut and etch a sample if the joint’s strength matters; appearance alone cannot confirm penetration.
Symptoms and misadjustments
A broad arc is not proof that frequency is too low: excessive arc length, a dull or contaminated tungsten, and torch angle can also spread the arc. A sharp arc is not proof that frequency is too high either; excessive amperage or a very short arc can produce similar behavior.
Black smut or heavy oxide near the bead often points to contamination, poor cleaning, or an unsuitable balance setting—not simply the wrong frequency. Clean the material with a stainless-steel brush reserved for aluminum, remove oil and paint, and check your machine’s balance instructions. Too much cleaning action can overheat the tungsten and widen the etched area; too little can leave oxide that interferes with wetting.
Burn-through on thin sheet is usually addressed first by reducing amperage, improving fit-up, using a backing bar where appropriate, or moving faster. Raising frequency may tighten the arc, but it does not reduce the total heat required to melt the metal. If you are fighting heat input, practice pulse settings or use a thinner filler technique before relying on frequency alone.
Machine controls and tungsten
Not every TIG welder provides adjustable frequency. A basic AC machine with a fixed value can still weld aluminum well; spend the difference on reliable output, foot-pedal control, and suitable consumables if those matter more to your work. Adjustable frequency is a convenience and control option, not a measure of weld quality by itself.
Higher frequency can make a pointed tungsten more practical for a focused arc, but tungsten selection depends on the machine, current, and manufacturer guidance. Use the electrode type and diameter recommended for your setup, prepare it as directed, and avoid copying a sharpened-electrode setup from a different welder without checking the manual. A stable, clean arc matters more than chasing the highest frequency setting.
What to buy for the job
If you are choosing a machine, compare its usable AC frequency range, balance adjustment, maximum output, duty cycle, and whether it includes a foot pedal. For bench work on mixed aluminum thicknesses, frequency adjustment is worthwhile. For occasional brackets or repairs at one thickness, a lower-cost AC/DC TIG machine with a fixed frequency can be a sensible choice.
Budget for safety and preparation as well as the power source. A suitable TIG-capable auto-darkening helmet should reliably detect the lower currents used for TIG, and clean aluminum is easier to weld consistently. Choose settings by testing on representative scrap, then record the frequency and balance that work for each material thickness.