Steel is forgiving. Copper and aluminium are not. Both are perfectly weldable with a laser, but they punish assumptions carried over from steel work: the same settings, the same joint preparation, and the same expectations do not transfer.
Why these two metals are difficult
- High reflectivity. At the near-infrared wavelength used by most fiber lasers, copper in particular reflects a large part of the beam when cold. Coupling is poor until the surface starts to melt.
- Very high thermal conductivity. Heat leaves the weld zone almost as fast as it arrives, so the energy budget is tight and the process window narrow.
- Oxide layers. Aluminium forms a tenacious oxide that melts at a far higher temperature than the metal underneath.
- Dissimilar joints. Copper-to-aluminium is the classic case: the two melt at different temperatures and can form brittle intermetallic compounds if too much material is mixed.
What to change in practice
- Wavelength. Copper absorbs blue and green light far better than near-infrared. Where copper welding is the main job rather than an occasional one, a shorter-wavelength source is worth discussing.
- Beam oscillation (wobble). Spreading the beam over a small circle widens the melt pool, improves coupling and makes the seam far more tolerant of fit-up variation.
- Power and pulse shaping. Higher peak power helps break through the initial reflective phase; controlled ramp-up avoids spatter.
- Filler wire. For dissimilar joints or for bridging gaps, a suitable filler changes the joint metallurgy and reduces cracking.
- Shielding gas. Correct gas and flow protect the pool. On aluminium in particular, poor shielding shows up immediately as porosity and soot.
- Clean the oxide. For aluminium, removing the oxide immediately before welding — mechanically or chemically — is often the single biggest improvement.
- Tight fit-up and clamping. Because the heat input is small, the laser cannot bridge gaps the way a TIG torch can. Fixtures matter more here than in any other process.
Copper-to-aluminium joints
These can be produced, but the metallurgy needs respect. Keep the mixed zone as thin as possible, consider an interlayer, and qualify the joint by sectioning rather than by appearance alone — a joint can look clean on the surface and still be brittle inside.
How to judge the result
- Visual: smooth, regular seam, no spatter or soot, no undercut.
- Cross-section: penetration and, for dissimilar joints, the thickness of the intermetallic layer.
- Functional: pull or peel test on production-representative parts.
Because the process window is narrow, the sensible route is always a sample on your own material and joint geometry before committing the batch.
Have a specific part or material you are not sure about? Send us the details and we will tell you whether the process fits — or run a sample so you can see the result before you decide.