Materials
How to weld aluminium
Quick answer
To weld aluminium: use AC TIG for quality, MIG with a spool gun for speed, 1.6 mm+ only, filler matched to the parent metal (ER4043 (general) or ER5356 (stronger, better on 5xxx alloys)), and prepare properly — stainless brush the oxide layer off right before welding — it reforms within hours. The key adjustment vs mild steel: more current per mm than steel (40–55 A/mm TIG) — aluminium dumps heat into the job.
Process and filler
Process: AC TIG for quality, MIG with a spool gun for speed, 1.6 mm+ only. Filler: ER4043 (general) or ER5356 (stronger, better on 5xxx alloys). Oxide melts at ~2000°C while the metal underneath melts at ~660°C — cleaning and AC balance are everything
Preparation
Stainless brush the oxide layer off right before welding — it reforms within hours. Fit-up matters more than most beginners expect: a gap you can see daylight through is a gap the filler has to fill, at the cost of heat control.
Amps and approach
Set current by thickness as you would for steel, then apply the adjustment: more current per mm than steel (40–55 A/mm TIG) — aluminium dumps heat into the job. Run test coupons first — every aluminium joint tells you loudly when the parameters are wrong.