ANSI
View official documentation (opens in new tab)ANSI Z136.1 safe-use rules for all laser cleaning cells[1]
Ikmanda RoswatiPh.D.Indonesia
Ultrafast photonics and laser-matter interactionPublished
Jul 22, 2026
Galvanized Zinc Laser Cleaning
Galvanized zinc on steel comes off a weld land under pulsed light when the pulse reaches zinc's own boiling point near 907 degrees Celsius, well under the steel damage limits underneath it. Hot-dip and electroplated coatings do not clear the same way: a hot-dip stack carries bonded zinc intermetallic layers that need extra passes, while an electroplated deposit clears sooner because it carries no reaction layer at all. A copper sulfate spot test, not a visual check under shop lighting, is what confirms a weld land is actually zinc-free before the arc runs.
Fume limits, weld-prep clearance, and layer hardness for zinc removal
Why does removing galvanized zinc need active fume capture?
Zinc vaporizes into airborne oxide fume before the coating ablates as solid particulate, unlike a mechanical strip that sheds settled dust. OSHA caps that fume at 5 mg per cubic meter over an 8-hour shift, so extraction has to run for the whole pulse train, not only while visible coating is lifting.
Does laser cleaning meet AWS weld-prep zinc removal rules?
AWS D-19.0 requires zinc removed 1 to 4 inches from both sides of a weld joint before welding starts. A laser pass can clear that exact band without grinding marks or embedded abrasive on the zinc coating just outside it, and that matters because the surrounding coating still has to carry corrosion protection once the joint closes.
Are all galvanized zinc layers equally hard to strip?
Hot-dip galvanizing builds four Fe-Zn layers outward from the steel, gamma, delta, zeta, and an outer eta layer of pure zinc. Delta and zeta run roughly 180 to 250 DPH, harder than the ductile eta zinc sitting above them, while the gamma layer at the steel interface is under 1 μm[12] thick but metallurgically bonded rather than mechanically stacked, so it takes the highest fluence to clear. Electroplated zinc skips that intermetallic stack. It deposits.
Can a laser-stripped panel be re-galvanized afterward?
A fully stripped Galvanized Zinc coating can be replaced because the same reaction that first built it runs again on clean steel, whether that steel was cleared by acid pickling or by laser cleaning. Flash rust sets the real deadline, since bare steel picks up surface oxide within hours.
Sources(3 references)
- American Welding Society, "AWS D-19.0-72 — Welding Zinc-Coated Steel," 1972 pci.org (opens in new tab) — Supporting figure for this answer.
- Hot Dip Galvanizing, "High-Temperature Galvanizing (Delta Galvanizing): Process Characteristics and Standard Hot-Dip Galvanizing Alternatives," 2026 hotdipgalvanizing.com (opens in new tab) — Delta and zeta intermetallic layers run 180 to 250 DPH while the gamma layer at the steel interface is under 1 μm thick
- GalvInfo Center, "Galvanizing 2022," GalvInfo Note, 2022 galvinfo.com (opens in new tab) — Electroplated zinc deposits as a single 5 to 25 μm layer with no intermetallic bonding
Coating type sets the pass count before geometry sets the boundary
Classifying hot-dip versus electroplated coating comes before any energy setting, since the two coatings need a different number of passes to clear the same host steel. Marking the zinc-free zone geometry the weld needs, then proving the setting on scrap under live fume capture, is what keeps a production strip run inside the limits this page sets.
1Classify the coating before energy goes anywhere
- An unclassified coating cannot start under a single setting, since hot-dip and electroplated zinc clear at different pass counts on the same steel host.
- Mark the zinc-free zone the weld geometry requires on the part before the first production pulse.
2Prove the pass count on scrap under live capture
- Walk pulsed energy on labeled scrap until a copper sulfate spot test reads zinc-absent, using the cited coupon vaporization onset as a regime label rather than a fleet setting.
- Keep source capture live for the full pass, since fume generation continues after the visible coating is gone.
3Spot-test the production land, then release it
- Reject any land that still reacts on the copper sulfate spot test and add another pass before it moves forward.
- Send a cleared weld land to the arc only after it passes inspection, and route a full-panel strip toward re-galvanizing as its own separate job.
Sources(1 reference)
- American Galvanizers Association, "Stripping and Regalvanizing," KnowledgeBase Article, August 2014 galvanizeit.org (opens in new tab) — Industry guidance on stripping and regalvanizing treats full-panel coating removal as a distinct job from a spot-test weld-land pass
Weld-land strip and pre-plate removal are the covered jobs
This page covers laser strip of hot-dip and electroplated zinc on steel weld lands, repair zones, and full-panel removal ahead of re-galvanizing. That coverage stops at powder coat over galvanizing, mill scale, and field rust, which sit on their own contaminant pages instead. A published pre-weld surface-prep guide frames selective zinc removal as a defined step ahead of the arc, distinct from grinding an entire panel bare, which is the boundary this page follows for weld-prep work. Selective clearing along the weld-prep zone stays in scope whether the job is a repair patch or new fabrication.
Sources(1 reference)
- Laser Cleaning for Welding | Pre-Weld Surface Prep, JPT Laser jpt-laser.com (opens in new tab) — Pre-weld surface-prep guide on selective laser zinc removal ahead of the arc
A Bay Area particulate rule caps the vented cell, not just the fume PEL
Strip cells that vent outdoors cannot run past the Bay Area particulate ceiling just because the zinc oxide fume reading inside the room looks acceptable. That regional rule governs what leaves the exhaust stack, separate from the indoor exposure limit that governs the breathing zone at the bench. A shop running continuous strip on a large panel cannot treat an indoor-only reading as proof the job is compliant once ductwork carries fume outside. Thin-gauge coated sheet adds a second limit, since bulk heat that would otherwise warp the part has to stay low even while the surface zinc is leaving under the pulse.
Continuous vented strip on a large galvanized panel — Bay Area particulate rules cap what leaves the exhaust stack, a limit separate from the indoor zinc oxide fume exposure reading at the bench. Pre-treatment: Confirm outdoor particulate limits before scaling a coupon-proven setting to a full-panel vented strip run..
Sources(1 reference)
- BAAQMD Regulation 6 — Particulate Matter, Common Definitions and Test Methods baaqmd.gov (opens in new tab) — Bay Area particulate rules cap what leaves the exhaust stack on a vented strip cell, a limit separate from the indoor zinc oxide fume exposure reading
Immersion or plating decides whether an intermetallic stack forms
Two different processes put zinc on steel, and each one leaves a different bond behind. Molten immersion near 450 degrees Celsius grows a bonded intermetallic stack, while electroplating lays down pure zinc with no reaction layer underneath. That difference in bonding is why the two coating types do not behave the same way once a pulse hits them. Hot-dip work builds three to four iron-zinc layers at the steel interface, each one metallurgically locked to the surface, while an electroplated coat stays as a single soft layer with nothing bonded beneath it. Cited property tables put zinc's own melting point at 419.5 degrees Celsius and its boiling point at 907 degrees Celsius, the temperatures a pulse has to clear before the coating leaves the steel underneath it.
Sources(1 reference)
- PMC, "Evolution of the Laser-Induced Spallation Technique in Film Adhesion Measurement," Table 1 — Material Properties, PMC 8208493 pmc.ncbi.nlm.nih.gov (opens in new tab) — Zinc melts at 419.5 °C and boils at 907 °C on cited property tables
The pulse has to reach 907 degrees before zinc ever leaves the steel
A short pulse drives the coating past its own boiling point near 907 degrees Celsius, well under cited steel damage limits, so the metal underneath stays intact while the zinc vaporizes away from it. That vaporization removes the outer eta zinc first and, on hot-dip coatings, the harder intermetallic layers underneath once the pulse reaches them too. A coupon study on ultrashort-pulsed cleaning of zinc and galvanized steel places the vaporization onset near 2.1 J/cm² at 1030 nm, a labeled regime point from that specific pulse length rather than a universal figure for every pulsed source.
Sources(1 reference)
- Mustafa, H. et al., "Effect of surface roughness on the ultrashort pulsed laser ablation of zinc, galvanized steel, and forming steel," Applied Surface Science, 2019 ris.utwente.nl (opens in new tab) — A coupon study on ultrashort-pulsed ablation of zinc and galvanized steel places vaporization onset near 2.1 J/cm² at 1030 nm
Two coatings and two pulse regimes keep one band from fitting all
Peer-reviewed nanosecond floors for full hot-dip strip on production steel stay scarce, so this page does not carry one fleet band for every coating type. A mechanism study on oxide removal and plasma behavior during laser cleaning found that the removal mechanism itself, not just the energy level, shifts with the material's absorption and oxide structure, which is one reason a hot-dip intermetallic stack and a bare electroplated deposit do not share a single number. Picosecond coupon work places vaporization onset near 2.1 J/cm² at 1030 nm on galvanized steel, but that figure describes one specific pulse regime rather than a floor for nanosecond fleet sources. No published number covers a safe range across both coatings and both pulse regimes at once, so the floor and ceiling fields here stay empty until one does.
Sources(1 reference)
- Investigation on mechanism of oxide removal and plasma behavior during laser cleaning on aluminum alloy, Applied Surface Science, 2020 doi:10.1016/j.apsusc.2019.144428 (opens in new tab) — A mechanism study on oxide removal and plasma behavior during laser cleaning found the removal mechanism shifts with the material's absorption and oxide structure
Fume exposure, weld geometry, and laser-safety rules on strip cells
Galvanized zinc strip cells carry three separate duties at once. ANSI Z136.1 sets Class 4 laser safe-use rules for those cells regardless of what coating is coming off. OSHA Table Z-1 caps zinc oxide fume at 5 mg/m³ eight-hour time-weighted average with a 10 mg/m³ short-term limit, since the fume is respirable rather than settled dust. AWS D-19.0 sets the zinc-free weld geometry, requiring removal one to four inches from the weld zone on coated steel before the arc runs.
OSHA
View official documentation (opens in new tab)OSHA Table Z-1, zinc oxide fume 5 mg/m³ eight-hour TWA, 10 mg/m³ STEL[2]
AWS
View official documentation (opens in new tab)AWS D-19.0 weld-prep geometry, zinc-free zone one to four inches from the weld[3]
Sources(3 references)
- ANSI Z136.1 — Safe Use of Lasers webstore.ansi.org (opens in new tab) — ANSI Z136.1 Safe Use of Lasers
- 29 CFR 1910.1000 Table Z-1 — Limits for Air Contaminants osha.gov (opens in new tab) — 29 CFR 1910.1000 Table Z-1 zinc oxide fume row for galvanized strip cells
- American Welding Society, "AWS D-19.0-72 — Welding Zinc-Coated Steel," 1972 pci.org (opens in new tab) — AWS D-19.0 zinc-free zone geometry for weld-prep strip
The same plate carries two coatings with two different removal points
Host steel drives strip planning because hot-dip and electroplated coatings behave differently even on identical plate. A wavelength-dependence study on picosecond cleaning of hot-dip galvanized steel found the coating's removal point shifts with wavelength, which is why a setting proven at one wavelength does not transfer directly to a different pulsed source. Delta and zeta intermetallic layers in the hot-dip stack run harder than the outer eta zinc above them, so a hot-dip coat needs a multi-pass walk where an electroplated coat on the same host clears in fewer passes because it carries no bonded reaction layer at all.
| Substrate | Ablation threshold (J/cm²) | Substrate damage (J/cm²) | Process window | Regime |
|---|---|---|---|---|
| Hot-dip galvanized carbon steel | — | — | — | vaporization |
| Electroplated zinc on steel | — | — | — | vaporization |
Sources(1 reference)
- Wavelength dependence of picosecond-pulsed laser ablation of hot-dip galvanized steel, Applied Physics A, 2022 doi:10.1007/s00339-022-05393-4 (opens in new tab) — Picosecond HDG steel ablation dataset, 8-15 J/cm2 damage-threshold row
One number does not cover both coating types
Hot-dip galvanizing bonds to steel through an intermetallic layer that a single pass often leaves behind, while an electroplated coat sits as a thinner, unbonded deposit that clears sooner on the same setting. A broad review of laser-cleaning mechanisms across industrial contaminant types groups vaporization-driven coating removal like this under one mechanism family, even though the exact energy needed still depends on which of the two coatings is on the part.
| Parameter | Value |
|---|---|
| HDG intermetallic stack | Hot-dip galvanizing forms four Fe-Zn intermetallic layers; electroplated zinc is a pure deposit without that stack |
| ZnO fume exposure | OSHA Table Z-1 lists ZnO fume at 5 mg/m³ eight-hour time-weighted average with 10 mg/m³ short-term exposure limit |
| Picosecond coupon onset | Cited picosecond work places vaporization onset near 2.1 J/cm² on galvanized steel at 1030 nm |
Sources(1 reference)
- Zhu G. et al., "The Fundamental Mechanisms of Laser Cleaning Technology and Its Typical Applications in Industry", Processes (MDPI), 2023 mdpi.com (opens in new tab) — A broad review of laser-cleaning mechanisms across industrial contaminant types groups vaporization-driven coating removal under one mechanism family
A gray face can still hide bonded residue underneath it
Production strip on galvanized steel fails when a single pass thins the outer coating without clearing the bonded layer at the interface, when thin sheet overheats before the coating leaves, or when fume fills the cell without capture running. A general laser-cleaning mechanism study notes that stopping energy too early leaves a coating layer incomplete even when the visible surface looks finished, the same failure this page's spot test is built to catch.
| Condition | Consequence |
|---|---|
| A single pass thins outer eta zinc without clearing the bonded interface layer[1] | Weld-pool contamination risk remains even when the face looks gray under shop lighting. |
| Zinc strip runs without source capture on continuous weld-prep work[1] | Airborne zinc oxide fume fills the breathing zone above the OSHA and Cal/OSHA exposure rows. |
Sources(1 reference)
- Laser cleaning of slots of chrome-plated die sciencedirect.com (opens in new tab) — A general laser-cleaning mechanism study notes stopping energy too early leaves a coating layer incomplete even when the visible surface looks finished
A copper sulfate spot test catches what shop lighting misses
Inspection before strip records hot-dip versus electroplated coating and marks the zinc-free zone geometry the weld will need. A copper sulfate spot test after strip is the acceptance check that matters, since gamma intermetallic residue at the interface can stay invisible under shop lighting even when the surface looks fully gray. A published zinc coating specification for hot-dip work sets the coating-thickness basis a shop checks against before declaring a part fully stripped rather than partially thinned. Any land that still reacts on the spot test goes back for another pass before it reaches the arc.
- Pre-cleaning assessment: Record hot-dip versus electroplated coating and mark the zinc-free zone geometry before the first production pulse on labeled scrap.
- Copper sulfate spot test: Pass only when the weld land shows no pink reaction indicating residual zinc on the cleared face.
- Visual bare-steel check: Confirm gray bare metal under shop lighting, then spot-test because intermetallic residue may remain invisible to the eye.
Sources(1 reference)
- ASTM F2329 — Standard Specification for Zinc Coating, Hot-Dip, Requirements for Application to Carbon and Alloy Steel Bolts astm.org (opens in new tab) — ASTM F2329 zinc coating specification for hot-dip work
Vaporized zinc becomes a breathing-zone problem, not a floor sweep
A laser pass turns solid zinc coating into airborne oxide fume rather than leaving it as settled dust on the floor, so a shop cannot manage the byproduct with the same broom-and-bag routine that follows abrasive stripping. California's general air-contaminants table sets an eight-hour exposure figure for that airborne fume, a limit that governs the breathing zone at the bench regardless of whether the coating came off by grinding or by a beam. Source capture sized to the fume, not to the visible smoke plume, is what keeps a continuous strip run inside that table.
Sources(2 references)
- Cal/OSHA Title 8 §5155 — Airborne Contaminants (Table AC-1) dir.ca.gov (opens in new tab) — California's general air-contaminants table sets an eight-hour exposure figure for airborne zinc oxide fume at the bench
- OSHA, "Zinc Oxide, Dust & Fume — Chemical Data," Occupational Safety and Health Administration, 29 CFR 1910.1000 Table Z-1 osha.gov (opens in new tab) — OSHA zinc oxide fume PEL: 5 mg/m3 eight-hour TWA
Bare steel does not stay bare; it starts oxidizing on its own
A stripped weld land does not wait for the next process step; bare steel begins to re-oxidize in open air within hours of the zinc leaving, which is a different clock than the zinc-free-zone check that gates the weld itself. Re-galvanizing after a full-panel strip is a separate decision from a spot-test pass on a single weld land, and a shop moving a panel toward replating still needs to confirm the tool that stripped it meets the safety classification that governs any pulsed source through release into the next process. Neither step regrows the coating on its own; both need a deliberate next action once the beam stops.
- Recontamination susceptibility: Bare steel begins to re-oxidize in open air within hours of the zinc leaving; galvanizing itself does not regrow without a replating step.
- Post-removal surface readiness: Weld-ready lands pass copper sulfate spot test immediately; full-panel replating still needs a separate re-galvanizing pass, since neither happens on its own.
Sources(1 reference)
- IEC 60825 — Safety of Laser Products webstore.iec.ch (opens in new tab) — Laser product safety classification governs the tool that stripped a panel through release into the next process, whether that process is welding or replating
Substrates that carry galvanized zinc into a strip job
Steel
View details: Steel. Category: metal. Subcategory: Ferrous.Laser cleaning removes rust, mill scale, and weld discoloration from steel without media, holding fluence near a 1.5 J/cm² cleaning floor and stopping short of the 4.5 J/cm² mark that scars bare metal. Intact mill scale still needs mechanical pre-treatment under AMPP SP21511-1 first. Compare with [stainless steel](/materials/stainless-steel-laser-cleaning) or [cast iron](/materials/cast-iron-laser-cleaning) laser cleaning when the substrate is mixed, and see [weld prep](/applications/weld-prep-laser-cleaning-applications) for the fabrication step this feeds.
Zinc
View details: Zinc. Category: metal. Subcategory: Alloy.Zinc shows up as die-cast parts, rolled sheet, and galvanized coatings. A pulsed laser can take native oxide and white rust off the face when energy stays inside a gentle range for soft alloys and the job is scoped so the beam does not open bare steel under a coating. The zinc form decides the map. Zinc oxide fume needs capture at the head before weld prep or paint follows.
Stainless Steel
View details: Stainless Steel. Category: metal. Subcategory: Alloy.Stainless steel removes its chromium oxide passivation film starting near 0.41 J/cm² at 1064 nanometers, well below the 5 to 12 J/cm² range where the parent alloy takes thermal damage. That spacing gives shops room to clear [weld heat tint](/contaminants/weld-heat-tint-laser-cleaning) and mill scale without an acid pickle or a re-polish afterward. The same chromium content that resists corrosion also sets a tighter target: push fluence toward the high end of that band and the beam can disturb the passive layer the alloy depends on, so [weld passivation](/applications/stainless-steel-weld-passivation-laser-cleaning) work stays on the low side of the range rather than the high side. The usable spacing is not identical across grades either, since a [316 coupon](/materials/stainless-steel-316-laser-cleaning) often tolerates a different ceiling than 304 stock on the same chart.