MIG Welding Explained: the Process for Aluminium and Non-Ferrous Metals
Knowledge · Welding in contract manufacturing
How does MIG welding work?
A wire feeder delivers the electrode continuously to the torch, the arc melts the wire into the joint. The gas is inert, meaning it does not react with the pool: argon, or argon-helium mixtures for thick aluminium sections, which burn hotter and penetrate deeper. Modern power sources weld aluminium almost always in pulsed arc mode: controlled current pulses detach the droplets cleanly, reduce spatter and keep heat input under control.
Why does aluminium need inert gas?
Because of its oxide skin and reactivity. Aluminium instantly forms a hard oxide layer that melts above 2,000 °C while the base metal liquefies at 660 °C. Active, CO₂-bearing gas would oxidise the pool and create porosity. Under pure argon the pool stays clean and the arc breaks up the oxide. Add aluminium\u2019s high thermal conductivity, and MIG\u2019s high power density beats TIG on thicker sections.
What matters in preparation?
Cleanliness, more than in any steel process. Three shop rules: remove the oxide layer immediately before welding with a stainless brush reserved for aluminium; work free of grease and moisture, because hydrogen is the main cause of porosity; and let cold material acclimatise, since condensation on cold aluminium ruins seams. A practical tip for designers: state the alloy completely (EN AW-5083, EN AW-6082 T6). Age-hardened alloys lose strength in the heat-affected zone, and the design calculation needs to know that before welding.
MIG or MAG, MIG or TIG?
Against MAG the split is simple: steel runs under MAG with active gas, non-ferrous metals under MIG with inert gas; the equipment is nearly identical. Against TIG, economics decide: TIG gives the cleaner seams on aluminium but is far slower. From medium thicknesses and long seams on frames and housings MIG is the economical choice, while visible seams and thin sheet stay with TIG or the hand-held laser. The full picture is in the process comparison.
MIG at a glance
| Feature | Value / classification |
|---|---|
| Process number (EN ISO 4063) | 131 |
| Shielding gas | argon or argon-helium (inert) |
| Materials | aluminium, copper, brass, other non-ferrous |
| Arc mode | predominantly pulsed arc |
| Strengths | speed on non-ferrous metals, stable mechanisable seams |
| Limits | pointless on steel, sensitive to poor preparation |
Frequently asked questions
What is the difference between MIG and MAG?
Only the shielding gas and therefore the application: MIG uses inert argon for non-ferrous metals like aluminium, MAG uses active CO₂-bearing gas for steel. Equipment and principle are identical.
Can steel be MIG-welded?
Technically possible, practically unusual: under pure argon the arc on steel becomes unstable and penetration poor. MAG with mixed gas is better in every respect for steel.
Why does porosity occur when welding aluminium?
Almost always hydrogen: moisture, grease, release agents or condensation on cold material. Clean oxide removal, dry acclimatised material and clean wire are the effective remedies.
Does aluminium lose strength when welded?
Age-hardened alloys such as EN AW-6082 T6 do, sometimes considerably, in the heat-affected zone. That is metallurgy, not poor workmanship, and must be considered in design. Strain-hardened alloys like EN AW-5083 are less sensitive.