Buyer's Guide

Laser Welding Galvanized Steel: Why the Zinc Fights You (2026 Guide)

October 22, 2026

Laser welding galvanized steel works fine on 0.8 to 3 mm sheet, but only if you plan around the coating. Zinc boils at 907 C, roughly 600 C below where steel melts, so it turns to vapor before the joint is even molten. That vapor is the whole problem. Give it a path out and you get fast, clean, low-distortion welds. Trap it and you get porosity that shows up at the leak test, not at the bench.

Why Zinc Changes the Process

Zinc melts at 419 C and boils at 907 C. Mild steel does not melt until somewhere around 1,450 to 1,520 C. That gap is the whole story: the coating is already a gas while the steel underneath is still solid.

A zinc coating is thin, usually 7 to 20 micrometres per side. That sounds harmless until you remember the volume. When that layer turns to vapor it expands by orders of magnitude, and it does it inside a keyhole that is only a fraction of a millimetre wide. Something has to give.

Heavier coatings make it worse. A Z275 sheet carries 275 g of zinc per square metre, both sides together, which is about 19 to 20 micrometres per face. That is HVAC and construction territory, and it is where most porosity complaints come from.

Coating	Zinc mass, both sides	Approx. per side	What it does at the weld
Z275 / G90	275 g/m2	19-20 um	Heaviest common coating. Most vapor, highest porosity risk, needs the widest gap.
Z180	180 g/m2	13 um	Typical for duct, enclosures and frames. Workable with a 0.1 mm gap.
Z120	120 g/m2	8-9 um	Easiest hot-dip grade. Little spatter, forgiving process window.
Electro-galvanized	20-60 g/m2	1-4 um	Appliance and automotive parts. Welds almost like bare steel.

Coating figures are typical values. Check the mill certificate, because a "galvanized" purchase order can land anything from Z100 to Z350.

The Three Defects You Will Actually See

Nine out of ten galvanized complaints come from three defects. Each one has a different fix, which is why random parameter changes rarely solve it.

Defect	What you see	Root cause	First change to make
Porosity	Gas pores on the cut face, failed leak test	Zinc vapor trapped in the joint, worst in tight laps	Open a 0.1-0.2 mm gap, then raise travel speed 10-20%
Spatter	Beads on the surface, dirty lens protection glass	Vapor erupting through the pool	Turn on wobble at 1.5-3 mm width, drop peak power
Uneven penetration	Undercut, thin spots, seam that wanders in depth	Zinc vapor collapsing the keyhole, unstable clamping	Steady CW mode, check focus and fixture pressure

One thing I notice on shop visits: porosity is almost never a gas-flow problem on galvanized work. It is a gap problem. Operators clamp the lap joint dead flat because that is what they were taught on bare steel, and that is exactly what traps the vapor.

Parameter Starting Points That Actually Run

These are starting points for a handheld laser welding machine in the 1.5 to 3 kW class, welding hot-dip galvanized sheet in overlap or edge configuration. Run them on scrap from the same coil before you touch a real part.

Sheet thickness	Power	Travel speed	Focus	Shielding gas
0.8 mm	600-800 W	25-35 mm/s	-1 to 0 mm	Argon, 10-14 L/min
1.0 mm	800-1,000 W	20-30 mm/s	-1 to 0 mm	Argon, 12-15 L/min
1.5 mm	1,200-1,500 W	up to 30 mm/s	0 mm	Argon, 14-18 L/min
2.0 mm	1,500-2,000 W	12-20 mm/s	0 to +1 mm	Argon, 15-20 L/min
3.0 mm	2,000-3,000 W	8-15 mm/s	0 to +2 mm	Argon, 18-20 L/min

Keep the laser in continuous wave mode. Pulsed mode looks cleaner on thin galvanized sheet for about ten seconds, then the seam consistency goes. Wobble at 1.5 to 3 mm width and 100 to 200 Hz widens the keyhole enough for vapor to escape without cutting your speed in half.

Two more settings matter more than people expect. First, gas flow: below 10 L/min you lose the vapor sweep, above 20 L/min you get turbulence that pulls air into the pool. Second, focus position: on galvanized work a focus set 1 mm into the surface gives a more stable keyhole than a perfect zero.

Joint Design Beats Parameter Tweaking

If you only change one thing after reading this, change the joint. Parameters buy you 20 percent. Joint design buys you the rest.

Lap joints. Leave a controlled gap of 0.1 to 0.2 mm. You can get it with embossed dimples, a shim at each end, or by not over-clamping. The gap lets zinc vapor escape sideways instead of through the pool.

Edge and flange joints. These are the friendliest for galvanized sheet. Vapor escapes upward with almost no resistance, so you can run faster and hotter without porosity.

Butt joints. A small root gap helps. Single pass, no weaving. If the part is a closed box, drill a 2 mm vent hole at each end of the seam and plug it afterwards.

What to avoid. A dead-flat double-sided lap on Z275 sheet is the worst case you can design. If the drawing forces it, switch to stitch welds with spot mode, or move the joint to a flange.

Wire and Gas: Two Cheap Wins

CuSi3 silicon bronze wire, 1.0 to 1.2 mm. Run it in brazing mode at 1,000 to 1,500 W and the steel never melts. The filler bonds at around 1,000 C, which is close to the zinc boiling point, so coating loss stays small. This is what automotive lines do on galvanized body panels, and it is the single best trick for visible galvanized parts.

308L Si stainless wire. Use it when the joint has to match base-metal strength. It handles zinc contamination better than plain carbon steel wire and keeps porosity down. Full details are in our wire filler selection guide.

On gas, argon at 12 to 18 L/min covers almost everything. An argon mix with 2 to 5 percent CO2 wets out better on carbon steel but oxidises slightly more, so keep it for parts that get painted. Helium is a waste of money below 3 kW.

Fume: The Cost Line Most Quotes Skip

Zinc oxide fume causes metal fume fever. It feels like flu, it arrives four to twelve hours after the shift, and it clears in a day. Welders learn to call it "Monday fever" and then stop mentioning it. That is not a control strategy.

General welding fume is capped at 5 mg/m3 as an 8-hour time-weighted average under the US OSHA PEL, and zinc oxide carries its own limit in most jurisdictions, typically 5 mg/m3 with some countries lower. Welding galvanized steel inside a tank or a closed frame without extraction will put you over that.

What works is extraction at the gun, or a downdraft table for bench work. A shop fan is not extraction. It moves the plume around the operator's face instead of away from it. Add the extractor, the ducting and the filter cost to your ROI sheet before you compare laser against MIG, because MIG needs the same treatment.

When Laser Is the Wrong Tool

Laser is not always the answer, and a supplier who says otherwise is selling, not advising.

Above 4 to 5 mm galvanized plate, especially structural work with multi-pass groove welds, MIG or laser-arc hybrid is more practical and more forgiving. Deep groove welds trap vapor no matter what you do with parameters.

Heavy structural joints that fall under a welding code also need procedure qualification, and a handheld unit is not the tool for that. And if the joint needs full coating integrity inside a lap, no laser process will give it to you without a gap or local zinc removal. Adhesive bonding or resistance spot welding may be cheaper than fighting the physics.

What to Test Before You Pay

Ask for a trial on your own material, not on the demo plate. Here is the list I give buyers:

Three thicknesses from your real production, both lap and edge joints.
Cut and bend test on the seam, plus a dye penetrant check on the weld face.
Leak test if the part holds air or water. This is where zinc porosity shows up.
Coating loss measured 10 mm either side of the seam, so you know how much touch-up is needed.
A run of at least 30 parts, to see whether the process drifts over a shift.
Written parameter sheet, spare parts price list and lens protection glass cost per 100 hours.

If a supplier cannot produce a parameter sheet for galvanized sheet, they have not welded much of it.

Frequently Asked Questions

Can you laser weld galvanized steel?

Yes. Laser welding galvanized steel works well on 0.8 to 3 mm sheet, and handheld units cover most duct, enclosure and frame work. The zinc coating does not stop the process, but it does change it. Zinc vaporizes at 907 C, well before the steel melts, so you have to give that vapor a way out of the joint. Our laser welding machine runs these settings daily on galvanized sheet.

What laser power do I need for 1 mm galvanized sheet?

About 600 to 1,000 W will weld 1 mm galvanized sheet at a usable speed. A 1,500 W machine covers 0.8 to 2 mm with headroom and still runs 3 mm at slower travel. Buy the power for the thickest joint you actually ship, not for the brochure maximum, because extra power on thin galvanized sheet just boils more zinc.

Why does laser welding galvanized steel cause porosity?

Because zinc vapor gets trapped. In a tight lap joint the vapor has nowhere to go, so it pushes through the molten pool or freezes inside it as gas pores. A controlled gap of 0.1 to 0.2 mm, a slightly faster travel speed and a wider wobble pattern remove most of it. If porosity survives those three changes, your fixture is clamping the gap shut.

Does laser welding burn off the zinc coating?

Locally, yes, within a few millimetres of the seam. The heat-affected zone is narrow, which is why laser damages far less coating than MIG or TIG. If the part needs full corrosion protection, run the joint in brazing mode with CuSi3 wire and lower heat input, then touch up the seam with a zinc-rich primer.

Is laser welding galvanized steel safe for the operator?

The weld itself is safe. The fume needs managing. Zinc oxide fume causes metal fume fever, a flu-like reaction that shows up hours after exposure. General welding fume is capped at 5 mg/m3 as an 8-hour average in the US, and zinc oxide has its own limit in most countries. Use extraction at the gun, not a shop fan.

Written by the FANY LASER team. Serving global industrial buyers since 2018. Connect on LinkedIn