Shielding Gas for Aluminium Welding (Australia)

Aluminium welding has one non-negotiable rule: pure argon, no exceptions. This guide explains why, and covers the other factors that make aluminium welding different.

The One Rule

Never use CO2 or argon/CO2 mix on aluminium. CO2 is chemically reactive with molten aluminium — it produces a black, sooty weld with zero ductility. The weld will look terrible and fail structurally.

Pure argon (99.997%) is the only shielding gas for:

• Aluminium MIG welding
• Aluminium TIG welding (AC mode)
• Aluminium brazing

Why Argon Only?

Aluminium forms an oxide layer (Al2O3) that melts at 2,072°C — far above aluminium's own melting point of 660°C. Without gas shielding, you'd melt the aluminium but the oxide layer would remain as a solid film, preventing fusion.

argon's inert nature means:

CO2 and helium behave differently:

• No chemical reaction with molten aluminium
• The arc's cleaning action (in AC TIG) breaks through the oxide layer
• The weld pool stays clean and fluid
• CO2: Reactive — forms aluminium oxide and carbon monoxide. Produces black, porous welds.
• Helonium (Ar/He mix): Sometimes used for very thick aluminium (>12mm) — helium adds heat. But pure argon is correct for 95% of applications.

AC vs DC TIG for Aluminium

AC (Alternating Current) TIG is required for aluminium. Here's why:

DC TIG can't do both — DCEN gives penetration but no cleaning; DCEP gives cleaning but no penetration ( and destroys the tungsten). AC alternates between the two, doing both.

AC Balance control lets you adjust the ratio:

AC Frequency control focuses the arc:

This is why machines like the UNIMIG Envy Multi 250 AC/DC are specifically marketed for aluminium — the AC frequency and balance controls are the features that make aluminium TIG possible.

• Electrode positive (EP) half-cycle: Cleans the oxide layer off the aluminium surface
• Electrode negative (EN) half-cycle: Provides penetration and heat input into the work
• More EP (cleaning): For dirty or heavily oxidised aluminium
• More EN (penetration): For clean aluminium, faster welding, less tungsten erosion
• Lower frequency (50-80 Hz): Wider bead, more cleaning — for thicker material
• Higher frequency (150-300 Hz): Narrower, more focused arc — for thin material and precision work

MIG Welding Aluminium

Aluminium MIG is faster than TIG but harder to master:

• Wire: Must be aluminium-specific (ER4043 or ER5356). Never use steel wire.
• Liner: Use a Teflon or nylon liner (steel liners catch aluminium wire)
• Contact tips: Use oversized tips (0.9mm tip for 0.9mm wire) — aluminium expands more than steel
• Gas: Pure argon, 15-20 L/min (higher than steel MIG)
• Technique: Push (not drag), with the torch angled 10-15° from vertical

Flow Rates

Too much gas is as bad as too little. Excessive flow causes turbulence that draws air into the weld zone. Increase flow only if you're getting porosity with adequate coverage.

Common Problems

Black soot on welds: Caused by magnesium oxide (from the aluminium alloy). Clean with stainless brush. Indicates adequate heat, not a gas problem.

porosity: Caused by hydrogen contamination (moisture, oil, dirt on the aluminium). Clean thoroughly with acetone before welding. Increase gas flow if needed.

Weld won't pool: Insufficient heat or oxide layer too thick. Increase amperage or use more AC cleaning. File or brush the surface to remove thick oxide.

tungsten contaminates: Dipping the tungsten into the weld pool, or using DC instead of AC. Clean or replace the tungsten; confirm AC mode.

Australian Gas Supply

For pure argon in Australia:

See our live gas price tracker for current verified pricing across all suppliers.

• BOC FlexiGas Argon: D $108/yr, E $199/yr, G $219/yr
• Coregas (Bunnings) Trade N Go: D $118 swap, E $184 swap
• SpeedGas: D ~$115 swap

Frequently Asked Questions

Can I use the same argon bottle for steel and aluminium TIG?

Yes. Pure argon works for TIG on all materials. The bottle doesn't know what you're welding.

Can I MIG weld aluminium with my regular MIG welder?

Only if it supports aluminium wire (Teflon liner, U-groove feed rolls, and enough amperage). Most quality multi-process welders (UNIMIG Viper/Envy, Cigweld BlueVenom) can with the right setup.

Why does my aluminium weld look grey instead of shiny?

Grey indicates adequate (not perfect) shielding. The weld is structurally sound. Bright silver indicates optimal gas coverage. Black soot is normal for aluminium with magnesium content (5xxx series).

Do I need a spool gun for aluminium MIG?

A spool gun (feeds wire right at the torch) makes aluminium MIG much easier because the soft wire doesn't have to push through a long liner. Recommended for anything over occasional aluminium work.