What Pre-Treatment Is Needed When Welding Coated Materials with a Laser Welding Machine?

When using a laser welding machine on coated metals—like galvanized steel, painted aluminum, or anodized parts—the coating can interfere with weld quality if not properly managed. The right pre-treatment isn’t always full removal; it depends on the coating type, thickness, and joint design.

Understand the Coating Type

Zinc-based coatings (e.g., galvanized steel) vaporize at much lower temperatures than steel melts. During welding, this creates zinc vapor that can cause porosity or spatter. For thin zinc layers (<10 µm), some modern laser welding machines can handle it using high-speed keyhole welding or beam oscillation to let vapor escape. But for thicker coatings, mechanical removal (grinding, milling, or laser ablation) along the weld seam is usually necessary.

Paint, oil, or polymer films must be fully removed from the joint area. These organics burn during welding, producing gas inclusions and weak, brittle seams. Even fingerprint oils can affect consistency on stainless or aluminum.

Anodized aluminum presents another challenge: the oxide layer is electrically insulating and highly stable. While the laser can penetrate it, the resulting weld often contains oxides that reduce strength. Best practice is to remove the anodization within 2–3 mm of the joint using chemical etching or light abrasion.

Practical Approaches

Localized stripping: Only clean the immediate weld path, not the entire part—saves time and preserves corrosion protection elsewhere.

In-line cleaning: Some automated laser welding systems integrate a pre-weld cleaning station (brush, plasma, or low-power laser) to strip coatings just before welding.

Process tuning: If minimal residue remains, adjusting focus position, travel speed, or using wobble can help mitigate defects—but don’t rely on this as a fix for poor prep.

Bottom Line

Pre-treatment doesn’t have to be complicated, but skipping it almost always leads to rework. Assess your coating, test with real parts, and choose the simplest effective method. A clean joint isn’t optional—it’s the foundation of a reliable laser weld.

For consistent results on coated materials, Haiwei Laser’s welding systems offer integrated cleaning options, precise beam control, and proven process stability—helping you minimize defects without over-engineering your pre-treatment steps.