Welding Aluminum

Aluminum demands a completely different approach from steel. It conducts heat 5 times faster, melts at roughly 1200F (no color change to warn you), and carries a tenacious oxide layer that melts at 3700F. Get the technique right and aluminum produces beautiful, lightweight welds. Get it wrong and you burn holes, trap oxide inclusions, or crack the joint during cooling.

TIG (GTAW) is the primary process for aluminum under 3/8 inch. Run AC polarity with 100% argon shielding at 20-25 CFH. The AC cycle does double duty: the EN (electrode negative) half provides penetration, and the EP (electrode positive) half blasts oxide off the surface through cathodic cleaning. Set AC balance to 65-75% EN on most inverters. Use a 2% lanthanated or pure tungsten, sized one step up from what you’d use on steel because AC generates more electrode heat.

MIG welding aluminum requires a spool gun or push-pull gun because soft aluminum wire birds-nests in standard MIG cable runs longer than 10 feet. Run 100% argon shielding at 25-30 CFH and spray transfer (higher voltage, higher wire speed). Short-circuit transfer on aluminum creates cold lap defects. Pulse MIG is the best option for thinner material if your machine supports it.

Filler selection splits two ways. ER4043 has 5% silicon, flows easily, and works on 6061, 6063, and most casting alloys. ER5356 has 5% magnesium, provides higher strength, better saltwater corrosion resistance, and proper color match after anodizing. For structural 5xxx-series alloys (5052, 5083, 5086), 5356 is the only correct choice.

Surface prep is non-negotiable. Scrub the oxide layer with a dedicated stainless brush (not one used on steel) immediately before welding. Degrease with acetone. Preheat thick sections to 200-300F to combat aluminum’s rapid heat dissipation. But don’t overheat, as some alloys (like 6061-T6) lose temper properties above 400F and won’t recover without full heat treatment.