Welding aluminium with a standard MIG welder is possible, but your machine and setup will need some important modifications before you strike an arc. Aluminium behaves very differently from mild steel, and using the wrong consumables or settings can lead to poor welds, wire feed jams, or even dangerous situations. Here's what you need to know before you fire up the welder in your home workshop.
Why Aluminium Is Trickier Than Steel
Aluminium has a much lower melting point than steel (around 660°C versus over 1,400°C for mild steel), yet it conducts heat away very quickly. It also has a tough oxide layer on its surface that melts at a much higher temperature than the base metal itself. These properties mean:
- Heat input needs to be carefully controlled to avoid burn-through
- The oxide layer must be cleaned off before welding
- Wire feed issues are far more common because aluminium wire is soft and prone to birdnesting
- Porosity (gas pockets in the weld) is a common problem if moisture or contamination is present
What Your MIG Welder Needs to Handle Aluminium
Not every MIG welder is up to the job. Here's what to check and change:
1. Machine Capacity
You'll generally need a MIG welder rated at 150 amps or more for aluminium work on material thicker than about 2–3 mm. Smaller hobby machines often struggle to deliver consistent enough power.
2. Aluminium Wire
Swap out your steel wire for aluminium MIG wire — typically ER4043 or ER5356 alloy, depending on the base material. These are available from welding suppliers around NZ. Use the smallest diameter that suits your machine (0.9 mm is common for lighter work).
3. Pure Argon Shielding Gas
Aluminium must be welded with 100% pure argon shielding gas. The CO₂ or argon/CO₂ mix you use for steel will cause a contaminated, porous weld on aluminium. You'll need to swap your gas bottle — pure argon is widely available from NZ gas suppliers.
4. Teflon or Nylon Liner
Replace the standard steel liner in your MIG torch with a Teflon (PTFE) or nylon liner. Steel liners cause too much friction for soft aluminium wire, leading to the dreaded birdnest jam inside the torch.
5. U-Groove Drive Rolls
Standard V-groove drive rolls will crush soft aluminium wire. Fit U-groove drive rolls sized to match your wire diameter.
6. Spool Gun (Recommended)
For home use, a spool gun is the most reliable solution. It mounts a small spool of wire right at the torch, eliminating the long feed path where jams occur. Many mid-range MIG welders sold at Bunnings or Mitre 10 are compatible with aftermarket spool guns — check your welder's manual or manufacturer's website first.
Preparing the Aluminium
Preparation is critical with aluminium:
- Clean thoroughly with acetone or a dedicated aluminium degreaser to remove oil and moisture
- Remove the oxide layer by scrubbing with a clean stainless steel wire brush (dedicated to aluminium only — never use a brush that's touched steel)
- Weld as soon as possible after cleaning, as the oxide layer reforms quickly
- Store aluminium in a dry area — moisture causes porosity
MIG Settings for Aluminium
Aluminium is typically welded using DCEP (Direct Current Electrode Positive) polarity, which is standard for MIG. Use a push technique (pushing the torch away from the weld pool) rather than the drag technique used for steel. Travel speed needs to be faster than with steel to avoid burn-through.
| Parameter | Mild Steel (typical) | Aluminium (typical) |
|---|---|---|
| Shielding gas | Argon/CO₂ mix | 100% pure argon |
| Wire type | ER70S-6 | ER4043 or ER5356 |
| Liner | Steel | Teflon/nylon |
| Drive rolls | V-groove | U-groove |
| Technique | Push or drag | Push only |
Safety in the Home Workshop
Aluminium welding produces intense UV light and fumes — always wear an auto-darkening welding helmet with the correct shade (shade 10–13 is typical for MIG), leather gloves, and a welding jacket. Ensure your workspace is well ventilated; aluminium fumes can be harmful with prolonged exposure. Keep a fire extinguisher nearby and work away from flammable materials.
For general workshop safety guidance, WorkSafe NZ has useful resources on hazardous substances and safe work practices.
Is a Building Consent Required?
For most home hobby welding projects (garden furniture, trailers, brackets), no building consent is needed. However, if your welding forms part of a structural element of a building or a regulated item such as a gas fitting or pressure vessel, different rules apply. Always check with your local council if you're unsure. The MBIE Building Performance website is a good starting point for understanding consent requirements.
When to Call a Professional
Some aluminium welding jobs are best left to a qualified tradesperson:
- Structural or load-bearing fabrication — boats, trailers, vehicle chassis, or building structures where weld integrity is safety-critical
- Pressure vessels or gas-related components — these involve restricted work under NZ regulations
- Thin-gauge aluminium (under 2 mm) — very easy to burn through without experience
- TIG welding — for high-quality, precise aluminium work, TIG is often preferred and requires significant skill
If the job needs to be right first time, or involves safety-critical components, find a qualified local welder on tradedirectory.co.nz who has the right equipment and experience for aluminium fabrication.
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