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Sherardized Zinc Coating

Anodizing & conversion coatings · Thermal

Sherardizing is a thermal-diffusion zinc treatment for steel fasteners and small components, standardized by ASTM A1059.

CNC machiningSheet metalPremium cost $$$Conductive
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Reference page — Sherardizing is not in the instant-quote configurator. Upload the part, name the finish in the notes, and an engineer quotes it with the part.

Sherardized Zinc Coating on a machined part

What is Sherardizing?

Zinc dust diffuses into steel in a rotating closed vessel to form a uniform 15–75 µm zinc-iron alloy coating.

How it works

Clean steel parts are tumbled with zinc dust and inert filler in a sealed drum below zinc's melting point, commonly around 320–500 °C. Zinc vapor and solid-state diffusion form zinc-iron intermetallic layers that follow threads and recesses without molten-zinc runs. A passivation or sealer may be added. The thermal cycle and coating growth must be checked for hardened fasteners.

Why specify it

  • Uniform 15–75 µm diffusion coating
  • Good thread and recess coverage
  • Sacrificial zinc corrosion protection
  • No liquid-metal drips or runs

Where it falls short

  • Batch process for suitably sized steel parts
  • Heat can affect high-strength fasteners
  • Grey matte appearance
  • Fewer suppliers than electroplating or galvanizing

Sherardizing at a glance

Sherardizing is strongest on corrosion protection (83 of 100), at a premium cost.

Corrosion protectionVery good83 / 100
Surface hardnessGood56 / 100
Cosmetic qualityLow30 / 100
LubricityLow30 / 100
Relative costPremium58 / 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.

Sherardizing key numbers

Typical values from the governing specifications and shop practice; bars are this finish against the highest value among anodizing & conversion coatings finishes.

Thickness15–75 µm0.59–3 mil
Hardness250–400 HV
Salt spray500–1,000 h
Max service temp.250 °C482 °F
Thickness
30–50 µm for general fastener service
Hardness
250–400 HV — Typical zinc-iron intermetallic range; delta and gamma phases differ and the substrate affects the reading.
Corrosion (salt spray)
500–1,000 h per ASTM B117 to red rust, typical for ISO 17668 Class 30–45 (30–45 µm) — Diffusion Zn-Fe layer; thickness class decides the result.
Electrical
Conductive
Colours
  • matte grey
Appearance
Uniform matte grey; post-passivation can alter tone slightly.

Where Sherardizing 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. Sherardizing 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 74Brass 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 73Hot-dip zinc — corrosion 90, hardness 42Nickel-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 plateHot-dip zincType II anodizePowder coatZinc-nickelHard chromeDLCTiN PVDTin plateCadmium plateE-coatCerakoteWet paintNitridingHVOF coatingSherardizing — corrosion 83, hardness 56Sherardizing
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 74Brass 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 73Hot-dip zinc — corrosion 90, hardness 42Nickel-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 plateHot-dip zincPowder coatSherardizing — corrosion 83, hardness 56Sherardizing
Anodize & conversionPlatingPaint & powderHard coatings

Specifications for Sherardizing

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

Drawing call-out

SHERARDIZE STEEL PARTS PER ASTM A1059, CLASS 30, 30 µm MINIMUM COATING THICKNESS; APPLY TRIVALENT PASSIVATION; THREADS SHALL ACCEPT GO GAUGE AFTER COATING

Which materials take Sherardizing?

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 fasteners and small parts.
  • Review temper of high-strength fasteners
DMLS / SLM
With careSteel AM fasteners or small parts only; confirm density and the 320–500 °C cycle against the build alloy.
Aluminum
NoNot compatible with the steel diffusion mechanism and heat cycle.
Brass
NoBrass is not sherardized.
Copper Alloy
NoSherardizing is a steel/iron zinc-diffusion process.
FDM
NoPolymers cannot be sherardized.
Magnesium Alloy
NoProcess temperature and chemistry are incompatible.
MJF
NoPolymers cannot be sherardized.
Polymer
NoProcess temperature is incompatible.
SLA
NoPolymers cannot be sherardized.
SLS
NoPolymers cannot be sherardized.
Stainless Steel
NoSacrificial zinc is not normally selected for stainless steel.
Titanium
NoTitanium is incompatible with this zinc-diffusion cycle.
Zinc Alloy
NoThe part is already a zinc alloy; this process is for steel.

How Sherardizing is applied, and what it does to the part

  1. 1Degrease and blast
  2. 2Load with zinc dust and filler
  3. 3Rotate and heat below zinc melting point
  4. 4Cool and separate media
  5. 5Passivate or seal if specified
  6. 6Inspect thickness
DimensionsAllow 15–75 µm per side on fits and threads; use oversize tapping or coating-compatible thread allowances.
Build-up per side15–75 µm — Allow coating growth on all exposed surfaces, including threads.
MaskingUsually needed. Mask precision fits, grounding areas if required, and threads without coating allowance.
ElectricalConductive
Temperature limit250 °C (482 °F) continuous
AppearanceUniform matte grey; post-passivation can alter tone slightly.
Added lead time7–15 working days on top of the bare part

Design rules for Sherardizing

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

  1. Specify ASTM A1059 coating class.The process name alone does not define thickness.
  2. Check thread allowance after coating.Diffusion zinc reaches thread flanks uniformly.
  3. Review high-strength steel temper.The 320–500 °C cycle can affect properties.
  4. State post-treatment.Passivation or sealing changes corrosion performance.

Sherardizing versus the alternatives

Finishes engineers weigh against Sherardizing, and when each wins.

FinishCorrosionHardnessCosmeticCostThicknessChoose it when
Sherardizing
this page
835630$$$15–75 µm—
Zinc Plating
Sherardizing vs Zinc Plating →
603055$5–25 µma thinner, widely available zinc finish is required
Hot-Dip Galvanizing
Sherardizing vs Hot-Dip Galvanizing →
904232$$45–100 µma thicker outdoor structural coating is acceptable
CorrosionHardnessCosmeticLubricityEconomy
SherardizingZinc Plating

The radar overlays Sherardizing with Zinc Plating, its most common alternative — chosen a thinner, widely available zinc finish is required. Scores in the table are 0–100 across every finish in the catalog.

Cost, lead time and compliance

Relative cost

Sherardized Zinc Coating is a premium-cost finish ($$$): more expensive than about 67 % of the finishes FabDigit quotes.

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

Lead time and compliance

Added lead time7–15 working days
RoHSCompliant
NotesTrivalent post-treatments can be RoHS-compliant; zinc dust handling and spent media require controls.

What Sherardizing is used for

  • Threaded fasteners
  • Washers
  • Chain components
  • Marine hardware

Sherardizing — frequently asked

What is sherardizing?

It is a zinc thermal-diffusion process performed in a rotating sealed vessel below zinc's melting point. It forms a zinc-iron alloy layer rather than a free zinc electroplate.

How thick is sherardized zinc?

ASTM A1059 systems commonly use classes within roughly 15–75 µm. A 30–50 µm requirement is typical for general fastener work.

Sherardizing vs hot-dip galvanizing: what is the difference?

Sherardizing diffuses zinc below its melting point and gives uniform thread coverage without drips. Hot-dip galvanizing immerses steel in molten zinc and is usually thicker.

Is sherardizing suitable for high-strength bolts?

It avoids electroplating hydrogen charging, but its 320–500 °C heat can affect temper. The fastener grade and thermal history must be approved.

What does ASTM A1059 cover?

ASTM A1059 specifies zinc-alloy thermo-diffusion coatings on iron and steel products. The drawing should state the required class, post-treatment, and thread acceptance.