TIG aluminum burn through is one of the most frustrating problems you'll face in welding. One second you're laying a clean, controlled bead. The next, you've blown a molten hole straight through your workpiece.
Aluminum doesn't give you the visual warnings that steel does, and that's what makes it so unforgiving.
Aluminum melts at approximately 1,220°F (660°C), while its oxide layer doesn't break down until around 3,700°F (2,000°C). That massive gap creates a deceptively narrow working window where things go wrong fast. Per AWS D1.2 structural welding code guidelines, controlling heat input is the most critical factor when welding aluminum with GTAW.
Let's break down exactly why this happens and how to fix it.
Quick Answer
TIG aluminum burn through happens when excessive heat input melts through the base metal before a stable weld pool forms. The main causes are amperage set too high, insufficient filler metal, poor arc length control, and dirty surfaces. Pulse TIG settings and proper material preparation prevent most burn-through on thin aluminum.
Start with lower amperage than you expect, add filler consistently, and always clean the metal before striking an arc.
TIG Burn-Through Hurts More on Aluminum Than Any Other Metal
Burn-through is a problem in any welding process. But on aluminum, it's a different animal entirely. The margin between a good puddle and a catastrophic hole is razor thin.
And once you're through, there's no welding it back.
Here's why aluminum is so much worse. It conducts heat roughly four times faster than mild steel. That sounds helpful, but it actually works against you.
Heat spreads outward from the arc so quickly that the area around your puddle is already near its melting point. You don't get the gradual buildup that steel gives you. On steel, the metal darkens, glows red, and softens slowly.
Aluminum stays bright and shiny right up until it collapses.
Steel changes color as it heats. You see it go from dull red to bright orange, giving you a visual roadmap of temperature. Aluminum does none of that.
It reflects light at room temperature and it reflects light at 600°F. There's no color shift to tell you you're running too hot.
The oxide layer makes it worse. Aluminum oxide forms almost instantly on any exposed surface. It melts at 3,700°F, which is three times hotter than the base metal.
You're essentially welding through a crust that behaves completely differently than the aluminum underneath. This layer traps heat, causes erratic arc behavior, and contributes to sudden blow-through.
For anyone learning to weld aluminum, this combination of fast heat spread, zero visual warning, and a tricky oxide layer means burn-through happens faster and more often than on any other common material. If you're still building foundational skills, our overview of what TIG welding involves covers the core mechanics before you tackle aluminum.
Why Aluminum Burns Through So Fast (And Why It Catches You Off Guard)
The physics behind aluminum burn-through come down to three things: conductivity, the oxide layer, and how the arc behaves on AC current.
Thermal Conductivity Works Against You
Aluminum's thermal conductivity sits at about 205 W/m·K. Mild steel is roughly 50 W/m·K. When you apply the arc to aluminum, heat doesn't stay put.
It races outward in every direction. By the time your puddle looks right, the surrounding metal is already saturated with heat. Add a few more seconds and the entire section softens at once.
This is why thin aluminum is so unforgiving. A piece of 1/16-inch steel tolerates a surprising amount of heat before failing. The same thickness in aluminum can blow through in a heartbeat.
The Oxide Layer Creates a Hidden Trap
Aluminum oxide forms within seconds of air exposure and melts near 3,700°F. Your AC TIG arc cleans this layer during the positive half of the cycle. But if your AC balance is off or the surface is heavily oxidized, that cleaning action can't keep up.
The result is an unpredictable puddle that surges and collapses without warning.
Per NIST materials data, the thermal properties of aluminum alloys vary by series. Alloy 6061, the most common fabrication grade, is particularly prone to hot cracking when overheated. That adds crater cracking on top of burn-through as a compounding risk.
No Color Warning
On steel, a welder reads temperature by color. Red means warm. Orange means hot.
White means you're in trouble. Aluminum skips all of that. It stays bright and reflective from room temperature all the way through its melting range.
Your only real indicators are puddle size, fluidity, and arc sound.
Welders trained on steel rely on color cues that simply don't exist on aluminum. Building those new instincts takes deliberate practice. This same heat sensitivity shows up in gas welding aluminum applications, where torch control matters just as much.
Understanding these physics helps you anticipate burn-through before it happens.
The Four Variables That Control Whether You Burn Through
Burn-through isn't random. It follows predictable patterns driven by four controllable variables. Master these and you'll dramatically reduce your failure rate.
Variable 1: Amperage
This is the biggest factor. Too much amperage overwhelms the metal's ability to dissipate heat. A common starting rule is two amps per 0.001 inch of material thickness.
For 1/8-inch aluminum, that puts you at 250 amps theoretically. In practice, you'll want significantly less because that formula assumes full-penetration welds, not thin sheet.
For aluminum under 1/8 inch, start between 40 and 80 amps and adjust downward. Always begin conservatively. You can always add heat.
You can't take it back.
Variable 2: Filler Metal Feed Rate
Without enough filler, your puddle grows with no reinforcement to absorb heat. Consistent, rhythmic dipping keeps the puddle sized correctly and adds material that carries energy away from the base metal. If you're seeing a large, fluid puddle expanding despite steady travel speed, you're underfeeding.
Variable 3: Arc Length and Torch Distance
A long arc spreads heat over a wider area and raises total heat input. A short, tight arc concentrates the beam and gives you more precise puddle control. The ideal arc length roughly equals your tungsten diameter.
For most aluminum work with a 1/16-inch tungsten, that means staying about 1/16 inch from the work surface. Make sure your torch is properly configured with the right cup and gas lens before you start.
Variable 4: Surface Preparation
Contaminated aluminum causes erratic arc behavior and unpredictable heat spikes. Oxides, oil, and moisture all contribute. Acetone degreasing followed by a dedicated stainless wire brush is the minimum standard.
Never use a brush that's touched steel. Cross-contamination introduces iron particles that compromise the weld.
Amperage Settings by Thickness
| Material Thickness | Starting Amperage Range |
|---|---|
| 0.5mm (0.020") | 20–35A |
| 1.0mm (0.040") | 30–50A |
| 1.5mm (0.060") | 40–70A |
| 3.0mm (1/8") | 80–120A |
| 6.0mm (1/4") | 150–250A |
These are starting points. Joint type, filler diameter, and travel speed all shift the numbers. If you've been comparing MIG and TIG processes, you'll notice TIG gives you more granular control over each of these variables.
Step-by-Step: Diagnosing Your Burn-Through Problem
When burn-through happens, most welders reach for the amperage knob first. That's often correct, but not always. Here's a diagnostic workflow to pinpoint the actual cause before you start changing settings.
Step 1: Look at the Hole
Was it a clean, round blow-through with minimal surrounding weld metal? That's thermal overload. You put too much heat into a spot that couldn't handle it.
Was it a large, sagging puddle that eventually collapsed? That points to insufficient filler combined with excessive dwell time. The shape of the failure tells you which direction to go.
Step 2: Check Your Amperage
If the hole formed quickly and cleanly, your amperage is almost certainly too high. Drop by 10 to 15 amps and retry. On thin material, even 5 amps can be the difference between a clean bead and a blown hole.
Step 3: Evaluate Your Filler Technique
If the puddle grew uncontrollably before failing, you're not adding enough filler. The puddle should stay roughly the same size from start to finish. If it's expanding, increase your dip frequency or step up to a slightly larger filler diameter.
Step 4: Inspect Your Arc Length
Hold a practice piece and gauge the distance between your tungsten tip and the work surface. If you can see more than a few millimeters of arc gap, you're running long. Tighten it up and maintain that distance consistently.
Step 5: Check Your Prep
Look at the area around the failure. Heavy discoloration, black residue, or pitting suggests oxide contamination. The AC cleaning cycle isn't keeping up.
Increase your AC balance toward more cleaning, or prep the surface more aggressively before your next pass.
Step 6: Consider Pulse Settings
If you've addressed all four variables and still struggle, pulse welding is your next move. The best technique for aluminum on thin sheet almost always involves some form of pulsing to manage heat input.
Pulse TIG vs Constant Amperage: Which Prevents Burn-Through on Thin Aluminum
Pulse wins on thin aluminum. But understanding why helps you use both techniques more effectively.
How Pulse TIG Works
Pulse TIG alternates between a high amperage (peak) that melts the metal and forms the puddle, and a low amperage (background) that lets it cool slightly. The background setting stays just high enough to keep the arc lit. This cycling gives the aluminum brief cooling windows that prevent heat from building to the burn-through threshold.
A typical pulse frequency for thin aluminum is 1 to 5 Hz. That means one to five cycles per second. Each cycle deposits a small amount of heat, then backs off.
The result is a more controlled puddle with less total energy input.
When Constant Amperage Works Fine
For thicker aluminum over 1/4 inch, constant amperage is perfectly acceptable and often preferred. The extra mass absorbs heat better. There's enough material to handle sustained energy input.
Constant amperage also produces a smoother, more continuous bead appearance.
The trade-off is simplicity. You manage everything manually with your foot pedal. On thick material, that works well.
On thin material, the learning curve is steep and the margin for error approaches zero.
Side-by-Side Comparison
| Factor | Pulse TIG | Constant Amperage TIG |
|---|---|---|
| Thin material (<3mm) | Excellent | Risky |
| Heat input control | Built-in cycling | Manual only |
| Skill required | Moderate | High on thin stock |
| Bead appearance | Rippled texture | Smooth and continuous |
| Machine requirements | Pulse-capable inverter | Basic TIG setup |
| Amperage settings | Peak and background separate | Single value |
As of 2026, most mid-range inverter TIG machines include pulse capability as a standard feature. For anyone welding thin aluminum regularly, that's a worthwhile investment. It won't replace skill, but it gives you a mechanical advantage against burn-through.
If you're considering whether a spool gun MIG setup might be simpler for your aluminum work, pulse TIG still offers superior heat control on material under 3mm.
Frequently Asked Questions
Can you repair a burn-through hole in aluminum?
It depends on the hole size and material thickness. Small holes in thick material can sometimes be bridged by tacking a filler rod across the gap and welding over it. Large holes in thin sheet are usually not repairable.
The surrounding metal is already heat-compromised. Cut it out and start with fresh material.
What filler rod reduces burn-through risk on aluminum?
ER4043 has a lower melting point than ER5356, which gives you a slightly wider working window. For thin sheet where burn-through is a concern, ER4043 is generally the more forgiving choice. ER5356 offers higher strength but demands more heat to flow properly.
Does argon flow rate affect burn-through?
Indirectly, yes. Too little flow allows atmospheric contamination that destabilizes the arc and causes erratic heat spikes. Too much flow creates turbulence that pulls oxygen into the weld zone.
The standard range is 15 to 20 CFH for most TIG aluminum work.
Is burn-through more likely on AC or DC?
Aluminum is almost always welded on AC. DC electrode negative skips the oxide-cleaning half cycle, making puddle control even harder. Burn-through risk actually increases on DC because you can't read the puddle as reliably.
Our guide to sheet metal welding methods covers why process selection matters across different gauges.
How do I prevent crater cracks at the end of a weld?
Pause at the end of the bead and continue feeding filler metal until the crater fills completely. Some welders use a foot pedal to ramp down amperage gradually while still adding filler. The goal is to reduce heat slowly while filling the depression.
