How to weld aluminum with TIG?

TIG (GTAW) welding on aluminum requires a special technique because of aluminum oxide (Al₂O₃) which melts at 2,072°C, while aluminum melts at 660°C.

Preparation:

• Cleaning: Aluminum must be degreased and the oxide layer removed with a stainless steel brush (dedicated brush — never used on steel)
• Bevel: on thick pieces, a bevel prepared as the WPS specifies makes penetration easier

Settings:

• Current: AC (alternating current) — necessary to break the oxide in the positive half-cycle
• Frequency: a higher frequency concentrates the arc; the value is set according to the machine's data sheet
• AC balance: the setting splits the time between penetration and oxide cleaning; the value is on the machine's data sheet or in the WPS
• Tungsten: thoriated or ceriated, at the diameter suited to the thickness and current (manufacturer's data sheet)
• Gas: pure argon, at the flow rate set by the WPS

Filler metal:

• ER4043 (4043 alloys) or ER5356 (5356 alloys) rods
• Diameter: suited to the thickness and current, per the manufacturer's data sheet

Tip: The aluminum weld pool is very fluid and reflective. Travel speed depends on thickness, current and the welder's skill: it is set on the part, not from a number.