Aluminium welding involves fundamentally different technical requirements from steel welding. The main challenges are its low melting point (660°C), high thermal conductivity, surface oxide layer (Al₂O₃, melting point ~2050°C) and hydrogen porosity sensitivity.
Among industrial aluminium alloys, the 5xxx series (5083, 5754 — Al-Mg) and 6xxx series (6061, 6082 — Al-Mg-Si) cover the most common welding applications. These two groups have different weldability characteristics and filler wire requirements.
Comparison of 5083 and 6061
| Property | EN AW-5083 (Al-Mg4.5Mn) | EN AW-6061-T6 (Al-Mg1Si) |
|---|---|---|
| Yield Strength | ~145 MPa (H111) | ~276 MPa (T6 temper) |
| Weldability | Excellent | Good (HAZ strength loss present) |
| HAZ Strength Loss | Minimal | Significant (up to 40%) |
| Cracking Susceptibility | Low | Higher hot cracking risk (reduced with ER4043) |
| Recommended Filler Wire | ER5356 | ER4043 or ER5356 |
| Typical Application | Marine structures, pressure vessels, cryo tanks | Structural profiles, machine parts, automotive |
Oxide Removal and Porosity Prevention
The Al₂O₃ layer on the aluminium surface melts at three times the melting point of the base metal. In TIG welding, AC current removes this layer through cathodic cleaning (cleaning action); in MIG welding, appropriate pre-weld mechanical or chemical cleaning is mandatory.
Main causes of porosity formation:
- Surface moisture and oil (acetone wipe before welding is mandatory)
- Shielding gas quality (Argon at 99.998% purity)
- Hydroxide residues on wire or surface
- High travel speed combined with inadequate gas protection
Critical precaution: Aluminium welding wire must be taken from its packaging immediately before use. Wire that has absorbed moisture in storage dramatically increases porosity risk.
TIG or MIG? Process Selection
Process selection for aluminium is based on thickness and appearance requirements:
- TIG (141) — Preferred: ≤ 6 mm, precision root passes, applications requiring aesthetic appearance, critical welds on pressure vessels. AC-TIG provides excellent weld quality through its surface cleaning action.
- MIG (131) — Preferred: > 6 mm, structural applications requiring high deposition rate, series production. Pulse-MIG minimises spatter.
Basic rule in filler wire selection: ER4043 (low melting point, good fluidity, low cracking — for 6xxx series) or ER5356 (higher strength, corrosion resistance — for 5xxx series and marine applications).
ArmaWeld Aluminium Welding Capability
ArmaWeld provides aluminium welding services with certified welders under EN ISO 9606-2 (material groups FM21 and FM22). Welding procedures are based on approved WPQRs under EN ISO 15614-2. For aluminium fabrication, a physically separated workshop section, separate tooling sets and colour-coded equipment are applied to reduce carbon steel contamination to zero. Acceptance criterion is EN ISO 10042 Class B.
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