What's inside
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Porosity in an aluminum TIG weld shows up as small holes, pinholes, or cavities in the bead. A few surface pores can point to contamination; a cluster or a pore that opens up during machining may mean gas was trapped deeper in the weld. The fix is usually not a higher amperage setting. Start with the work area, filler, and shielding gas, then check your technique and equipment.
Identify the problem before changing settings
Let the weld cool, then inspect the bead under bright light. Porosity can look like scattered pinholes or a rough, peppered surface. If the weld will be machined, cut, or ground, surface appearance alone is not enough: a pore can be hidden below the bead. For pressure-containing or structural parts, follow the applicable inspection requirements rather than assuming a clean-looking bead is sound.
Note when the pores appear. A sudden change after switching filler rods, cleaning a joint, or moving outdoors often points to contamination or shielding. Porosity that occurs in one spot may indicate a local problem, such as a dirty edge or a gap. Pores along the whole bead suggest a process issue, poor gas coverage, or contaminated material.
Clean the aluminum and filler
Aluminum quickly forms an oxide layer, and it can also carry oil, marker ink, adhesive, and moisture. Remove grease first with a clean, residue-free solvent suited to the material and your shop’s safety rules. Use a dedicated stainless-steel brush on the joint after degreasing; a brush previously used on steel can transfer contamination. Brush just before welding, since the oxide reforms.
Do not use chlorinated brake cleaner or an unknown solvent near an arc. Heat and arc radiation can produce hazardous decomposition products. Keep solvents away from sparks, let the surface dry completely, and follow the product label.
Clean the filler rod, too. Store it in a closed container, handle it with clean gloves, and discard rods with oily or visibly dirty surfaces. If a fresh section still produces pores, test a new filler batch. For occasional repairs, a small, properly stored supply is often enough; a dedicated rod holder is useful when rods are exposed to shop dust or moved between jobs.
Check shielding gas and coverage
Use clean argon for most aluminum TIG work. A common starting point is about 15–20 cubic feet per hour (CFH) with a standard cup, but the right flow depends on cup size, torch setup, and drafts. More gas is not automatically better: excessive flow can become turbulent and pull air into the shielding envelope. A large cup or gas lens may allow broader coverage at a lower, steadier flow.
Check that the cylinder is not nearly empty, the regulator is working, and the hose and torch connections are leak-free. Look for a cracked hose, loose fitting, damaged cup, blocked gas lens, or clogged nozzle. Let post-flow protect the hot crater; a starting range of roughly 5–10 seconds is often adequate, adjusted for heat and electrode size.
Welding outdoors or under a fan can disrupt shielding even when the flow meter looks right. Put up a windbreak, but do not create a confined space or block required ventilation. If the weld improves when the draft is stopped, changing the machine settings was not the fix.
Compare the likely causes
| What you see | Likely cause | First check |
|---|---|---|
| Pores across most of the bead | Dirty material, filler, or poor shielding | Degrease, brush, and inspect gas delivery |
| Pores near the start or end | Insufficient pre-flow or crater protection | Check pre-flow, post-flow, and start technique |
| Pores on the side facing a draft | Shielding gas being blown away | Block drafts and keep the torch close |
| Pores after increasing gas flow | Turbulence or air entrainment | Return to a moderate flow and inspect the cup |
| One localized cluster | Local oil, oxide, gap, or trapped contamination | Reclean the joint and check fit-up |
Adjust technique and fit-up
Keep a steady arc length and hold the torch so the cup shields the molten pool. A long arc spreads the gas coverage and can expose the puddle to air. A very steep torch angle can also leave part of the pool unprotected. Use enough travel speed to avoid overheating the puddle, but do not race past the joint before the filler is incorporated.
For butt joints, remove dirt and oxide from both edges and make sure the parts fit consistently. A wide gap can make it harder to maintain a stable puddle and adequate shielding. On thicker aluminum, remove heavy oxide and contamination from the joint faces; do not rely on AC cleaning action to burn through oil or grime.
Keep the tungsten out of the puddle. If it touches the aluminum or filler, stop and regrind the contaminated tip before continuing. Tungsten contamination may cause an unstable arc and make the bead harder to control, even if it is not the original source of porosity.
Change one variable at a time
Run a short test bead on clean scrap of the same alloy and similar thickness. Keep the gas, cup, filler, and travel technique steady while changing just one factor. For example, compare a bead before and after replacing a suspect hose, rather than raising flow, changing cups, and adjusting balance all at once. Record the settings so you can identify which change helped.
A reliable TIG argon flow meter can help verify flow at the torch instead of relying only on a regulator reading. A dedicated stainless-steel brush is an inexpensive way to avoid carrying steel debris onto aluminum. For occasional shop work, basic tools are usually sufficient; a gas lens or larger cup is worth considering when coverage remains inconsistent after the joint and gas system are clean and sound.
Know when to rework the weld
Do not weld over visible pores and assume they will disappear. Remove the affected section to clean, sound metal, then clean the joint again before rewelding. If pores keep returning, stop and verify the gas supply, torch parts, material condition, and draft protection. On a critical part, use the specified inspection and repair procedure; surface grinding cannot confirm that internal porosity is gone.