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Hot-Dip Galvanizing

Electroplating & electroless plating · Dip / immersion

Hot-dip galvanizing immerses fabricated steel or hardware in molten zinc to form a thick sacrificial alloy coating.

Sheet metalStandard cost $$Conductive
Quote a part with Hot-dip zincCompare electroplating & electroless plating
Hot-Dip Galvanizing on a machined part

What is Hot-dip zinc?

ASTM A123 covers fabricated products and ASTM A153 covers hardware.

How it works

Steel is degreased, pickled, fluxed, dried, and immersed in molten zinc near 450 °C. Iron and zinc react to form alloy layers with an outer zinc layer. Withdrawal speed, drainage, steel chemistry, section thickness, and bath control determine coating mass and appearance. The process coats accessible inside and outside surfaces but leaves runs at drain points and adds far more thickness than electroplating.

Why specify it

  • Thick sacrificial protection for outdoor steel
  • Covers edges and accessible interiors
  • Metallurgically bonded iron-zinc alloy layers
  • Long life with little field maintenance

Where it falls short

  • Can fill threads and small holes
  • Heat can distort thin or asymmetric fabrications
  • Appearance includes runs, ash, and drainage marks
  • Not dimensionally precise

Hot-dip zinc at a glance

Hot-dip zinc is strongest on corrosion protection (90 of 100), at a standard cost.

Corrosion protectionExcellent90 / 100
Surface hardnessFair42 / 100
Cosmetic qualityLow32 / 100
LubricityLow22 / 100
Relative costStandard28 / 100
CorrosionHardnessCosmeticLubricityEconomy

Each score is 0–100 against every finish in this catalog. Corrosion comes from salt-spray life (ASTM B117, log scale) and hardness from the finish layer's Vickers or pencil hardness; cosmetic, lubricity and cost are FabDigit's engineering assessment. Economy on the radar is the inverse of cost.

Hot-dip zinc key numbers

Typical values from the governing specifications and shop practice; bars are this finish against the highest value among electroplating & electroless plating finishes.

Thickness45–100 µm1.8–3.9 mil
Hardness70–250 HV
Salt spray800–1,500 h
Max service temp.200 °C392 °F
Thickness
Approximately 45–100 µm depending on ASTM A123 material category and steel thickness
Hardness
70–250 HV — η (pure zinc) outer layer ≈ 70 HV; ζ/δ Fe-Zn alloy layers 180–250 HV — harder than the steel they protect. Alloy-layer hardness is not a drawing acceptance criterion.
Corrosion (salt spray)
800–1,500 h per ASTM B117 to red rust, typical for an ASTM A123 coating of ≈ 85 µm — B117 is known to understate zinc in service; galvanizing specifications control coating mass, not salt-spray hours.
Electrical
Conductive
Colours
  • silver gray
  • matte gray
Appearance
Bright spangled to matte gray, with visible drainage and handling marks accepted within the specification.

Where Hot-dip zinc sits among all finishes

Surface hardness (Vickers, log scale) against corrosion protection (salt-spray hours, log scale) for every coating FabDigit offers, one cloud per finish group. Hot-dip zinc is highlighted; hover a dot for its name or open the full map.

02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finisheshard, low corrosion protectionhard and protectiveprotective, softsoft, little protectionType II anodize — corrosion 71, hardness 54BSA anodize — corrosion 71, hardness 52Type I anodize — corrosion 71, hardness 49Hard anodize — corrosion 71, hardness 61PTFE hard anodize — corrosion 71, hardness 61Nitriding — corrosion 55, hardness 73PEO — corrosion 70, hardness 74Sherardizing — corrosion 83, hardness 56Brass plate — corrosion 35, hardness 44Bronze plate — corrosion 40, hardness 49Cadmium plate — corrosion 70, hardness 26Copper plate — corrosion 32, hardness 39Decorative chrome — corrosion 64, hardness 71Electroless copper — corrosion 20, hardness 41Electroless nickel — corrosion 70, hardness 68Nickel plate — corrosion 51, hardness 55Gold plate — corrosion 68, hardness 39Hard chrome — corrosion 40, hardness 73Nickel-PTFE — corrosion 72, hardness 57Silver plate — corrosion 55, hardness 39Solder plate — corrosion 42, hardness 9Tin plate — corrosion 34, hardness 0Zinc plate — corrosion 60, hardness 30Zinc-nickel — corrosion 86, hardness 60Cerakote — corrosion 83, hardness 27E-coat — corrosion 83, hardness 15Epoxy coat — corrosion 83, hardness 15Powder coat — corrosion 83, hardness 14Wet paint — corrosion 59, hardness 10AlCrN PVD — corrosion 58, hardness 93AlTiN PVD — corrosion 52, hardness 94CrN PVD — corrosion 62, hardness 83DLC — corrosion 55, hardness 93MoS2 PVD — corrosion 20, hardness 26TiAlN PVD — corrosion 50, hardness 93TiCN PVD — corrosion 40, hardness 92TiB2 PVD — corrosion 40, hardness 94TiN PVD — corrosion 45, hardness 87WC/C PVD — corrosion 48, hardness 77ZrN PVD — corrosion 52, hardness 90CVD alumina — corrosion 70, hardness 85CVD TiCN — corrosion 38, hardness 92CVD TiN — corrosion 45, hardness 87Multilayer CVD — corrosion 62, hardness 88HVOF coating — corrosion 78, hardness 77Plasma spray — corrosion 60, hardness 68Plastic chrome — corrosion 72, hardness 71Electroless plastic — corrosion 58, hardness 39Clear coat — corrosion 20, hardness 12Soft-touch — corrosion 20, hardness 5PLATINGHARD COATINGSANODIZE & CONVERSIONPAINT & POWDERZinc plateType II anodizePowder coatZinc-nickelHard chromeDLCTiN PVDTin plateCadmium plateE-coatCerakoteWet paintNitridingHVOF coatingHot-dip zinc — corrosion 90, hardness 42Hot-dip zinc
02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finishesType II anodize — corrosion 71, hardness 54BSA anodize — corrosion 71, hardness 52Type I anodize — corrosion 71, hardness 49Hard anodize — corrosion 71, hardness 61PTFE hard anodize — corrosion 71, hardness 61Nitriding — corrosion 55, hardness 73PEO — corrosion 70, hardness 74Sherardizing — corrosion 83, hardness 56Brass plate — corrosion 35, hardness 44Bronze plate — corrosion 40, hardness 49Cadmium plate — corrosion 70, hardness 26Copper plate — corrosion 32, hardness 39Decorative chrome — corrosion 64, hardness 71Electroless copper — corrosion 20, hardness 41Electroless nickel — corrosion 70, hardness 68Nickel plate — corrosion 51, hardness 55Gold plate — corrosion 68, hardness 39Hard chrome — corrosion 40, hardness 73Nickel-PTFE — corrosion 72, hardness 57Silver plate — corrosion 55, hardness 39Solder plate — corrosion 42, hardness 9Tin plate — corrosion 34, hardness 0Zinc plate — corrosion 60, hardness 30Zinc-nickel — corrosion 86, hardness 60Cerakote — corrosion 83, hardness 27E-coat — corrosion 83, hardness 15Epoxy coat — corrosion 83, hardness 15Powder coat — corrosion 83, hardness 14Wet paint — corrosion 59, hardness 10AlCrN PVD — corrosion 58, hardness 93AlTiN PVD — corrosion 52, hardness 94CrN PVD — corrosion 62, hardness 83DLC — corrosion 55, hardness 93MoS2 PVD — corrosion 20, hardness 26TiAlN PVD — corrosion 50, hardness 93TiCN PVD — corrosion 40, hardness 92TiB2 PVD — corrosion 40, hardness 94TiN PVD — corrosion 45, hardness 87WC/C PVD — corrosion 48, hardness 77ZrN PVD — corrosion 52, hardness 90CVD alumina — corrosion 70, hardness 85CVD TiCN — corrosion 38, hardness 92CVD TiN — corrosion 45, hardness 87Multilayer CVD — corrosion 62, hardness 88HVOF coating — corrosion 78, hardness 77Plasma spray — corrosion 60, hardness 68Plastic chrome — corrosion 72, hardness 71Electroless plastic — corrosion 58, hardness 39Clear coat — corrosion 20, hardness 12Soft-touch — corrosion 20, hardness 5PLATINGHARD COATINGSANODIZE & CONVERSIONPAINT & POWDERZinc platePowder coatHot-dip zinc — corrosion 90, hardness 42Hot-dip zinc
Anodize & conversionPlatingPaint & powderHard coatings

Specifications for Hot-dip zinc

The documents a drawing cites to define this finish, with the Type / Class rows that apply. Each links to a page explaining the standard.

StandardType / ClassThicknessRequirement / testStatus
ASTM A123
Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products · ASTM
Structural shapes45–100 µmGrades 45, 65, 75, 75, 100, and 100 across steel-thickness bands from <1.6 to ≥16 mm. · Grade number equals average thickness in µm. · Magnetic thickness or stripping mass.Active
Plate, strip, and bar45–100 µmGrades 45, 65, 75, 75, 75, and 100 across the six thickness bands. · Grade number equals average thickness in µm. · Magnetic thickness or stripping mass.
Pipe and tubing45–75 µmGrades 45, 45, 75, 75, 75, and 75 across the six thickness bands. · Grade number equals average thickness in µm. · Magnetic thickness or stripping mass.
Wire35–80 µmGrades 35, 50, 60, 65, 80, and 80 across the six thickness bands. · Grade number equals average thickness in µm. · Magnetic thickness or stripping mass.
Forgings and castings≥ 100 µmGrade 100 for applicable products at least 4.8 mm thick. · Approximately 705 g/m² at Grade 100. · Magnetic thickness or stripping mass.
ASTM A153
Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware · ASTM · alternative
Class A≥ 86 µmMalleable iron and steel castings. · 610 g/m² minimum average; 550 g/m² individual. · Average and individual thickness or mass.Active
Class B-1≥ 86 µmAt least 15.88 mm thick and over 381 mm long. · 610 g/m² minimum average; 550 g/m² individual. · Average and individual thickness or mass.
Class B-2≥ 66 µmUnder 15.88 mm thick and over 381 mm long. · 458 g/m² minimum average; 381 g/m² individual. · Average and individual thickness or mass.
Class B-3≥ 56 µmAny thickness and 381 mm or less long. · 397 g/m² minimum average; 336 g/m² individual. · Average and individual thickness or mass.
Class C≥ 53 µmFasteners over 9.52 mm diameter and washers at least 4.76 mm thick. · 381 g/m² minimum average; 305 g/m² individual. · Average and individual thickness or mass.
Class D≥ 43 µmFasteners 9.52 mm diameter and under, rivets, nails, and washers under 4.76 mm thick. · 305 g/m² minimum average; 259 g/m² individual. · Average and individual thickness or mass.

Drawing call-out

HOT-DIP GALVANIZE AFTER FABRICATION PER ASTM A123; PROVIDE VENT AND DRAIN HOLES; CHASE M12 THREADS AFTER GALVANIZING

Pattern: HOT-DIP GALVANIZE AFTER FABRICATION PER ASTM A123/A123M, MATERIAL CATEGORY <CATEGORY>, <MASKING AND REPAIR LIMITS>

Which materials take Hot-dip zinc?

Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library.

Material familyVerdictNotes
Steel
YesPrimary substrate for ASTM A123 and A153.
  • Silicon and phosphorus content affect coating growth and appearance.
Aluminum
NoHot-dip galvanizing is a steel process; aluminum would dissolve in the zinc bath.
Brass
NoBrass is not hot-dip galvanized.
Copper Alloy
NoCopper alloys are not hot-dip galvanized.
DMLS / SLM
NoPrecision AM parts are not hot-dip galvanized; the 450 °C bath and thick irregular coating destroy tolerances.
FDM
NoFused-filament polymers are incompatible with this process.
Magnesium Alloy
NoMagnesium is incompatible with molten zinc.
MJF
NoPolymer powder-bed prints are incompatible with this process.
Polymer
NoOrganic polymers cannot take this inorganic metal-finishing process.
SLA
NoPhotopolymer prints are incompatible with this process.
SLS
NoPolymer powder-bed prints are incompatible with this process.
Stainless Steel
NoNot a standard hot-dip galvanizing substrate.
Titanium
NoTitanium is incompatible with the molten-zinc bath.
Zinc Alloy
NoThe part is already zinc-based.

How Hot-dip zinc is applied, and what it does to the part

  1. 1Degrease
  2. 2Pickle
  3. 3Rinse
  4. 4Flux
  5. 5Dry
  6. 6Immerse in molten zinc
  7. 7Drain and quench
  8. 8Inspect coating mass and continuity
DimensionsExpect roughly 45–100 µm per side with local excess; oversize tapped and clearance holes and use galvanized-thread allowances.
Build-up per side45–100 µm — Irregular local buildup, especially at edges, threads, and drain points.
MaskingUsually needed. Keep weld zones, precision interfaces, and selected threads uncoated or plan post-galvanizing chase operations.
ElectricalConductive
Temperature limit200 °C (392 °F) continuous
AppearanceBright spangled to matte gray, with visible drainage and handling marks accepted within the specification.
Added lead time4–10 working days on top of the bare part

Design rules for Hot-dip zinc

What to decide on the drawing before the part goes to the finisher.

  1. Provide vent and drain holes.Closed cavities can explode and trapped zinc creates dangerous, defective work.
  2. Use symmetric sections and balanced welds.The 450 °C cycle can release stress and distort fabrications.
  3. Design threads for galvanizing.45–100 µm per side can prevent assembly.
  4. Galvanize after fabrication.Welding later destroys coating and releases zinc fumes.

Hot-dip zinc versus the alternatives

Finishes engineers weigh against Hot-dip zinc, and when each wins.

FinishCorrosionHardnessCosmeticCostThicknessChoose it when
Hot-dip zinc
this page
904232$$45–100 µm—
Zinc Plating
Hot-dip zinc vs Zinc Plating →
603055$5–25 µmwhen threads and precision dimensions require a 5–25 µm coating
Zinc-Flake Dip-Spin Coating
Hot-dip zinc vs Zinc-Flake Dip-Spin Coating →
85—35$$$6–15 µmwhen high-strength fasteners need thin non-electrolytic protection
CorrosionHardnessCosmeticLubricityEconomy
Hot-dip zincZinc Plating

The radar overlays Hot-dip zinc with Zinc Plating, its most common alternative — chosen when threads and precision dimensions require a 5–25 µm coating. Scores in the table are 0–100 across every finish in the catalog.

Cost, lead time and compliance

Relative cost

Hot-Dip Galvanizing is a standard-cost finish ($$): cheaper than about 69 % of the finishes FabDigit quotes.

Finishing is priced per part with a lot minimum, from FabDigit's own China-side rates cross-checked against US job-shop pricing. The exact figure appears on the instant quote once the part is uploaded.

Lead time and compliance

Added lead time4–10 working days
RoHSCompliant
NotesZinc is generally RoHS compatible; pickling acids, flux, zinc ash, and quench chemistry require industrial controls.

What Hot-dip zinc is used for

  • Outdoor structures
  • Highway hardware
  • Steel brackets
  • Guardrails
  • Fabricated frames

Hot-dip zinc — frequently asked

zinc plating vs galvanizing

Electroplated zinc is typically 5–25 µm and better for precision hardware. Hot-dip galvanizing is commonly about 45–100 µm and better for fabricated steel outdoors, but it can fill threads and distort thin work.

how thick is hot dip galvanizing

ASTM A123 requirements vary by product category and steel thickness, with practical coatings commonly around 45–100 µm. Local runs can be thicker than the average.

does hot dip galvanizing warp steel

It can because steel enters molten zinc near 450 °C and residual fabrication stress relaxes. Thin, asymmetric, or heavily welded assemblies need balanced design and consultation with the galvanizer.

can threaded parts be hot dip galvanized

Yes, ASTM A153 covers hardware, but mating threads need special allowances. A 45–100 µm coating on each flank can seize a standard unmodified thread.

how long does galvanized steel last

Life depends on zinc thickness and atmospheric corrosion rate, so one universal year value is not defensible. A 45–100 µm coating lasts much longer in dry rural exposure than in marine splash or acidic industrial service.