Zinc Coating Weight Explained: Z60 to Z275 — What to Order for Automotive Parts
If you buy hot-dip galvanized steel for stamped parts, the single most common quality dispute is not about the steel itself — it is about the zinc coating. Too little zinc and the part rusts in the field; too much and you pay for metal you don't need, and welding or forming can suffer. This guide explains how coating weight is designated, what each level is actually used for, and how to write it on a purchase order so you get what you paid for.
How coating weight is designated
Under EN 10346, the zinc coating is expressed as the total mass of zinc on both surfaces, in grams per square metre (g/m²). The letter Z followed by a number is the shorthand buyers and mills use: Z100 means roughly 100 g/m² total (about 50 g/m² per side). JIS G 3317 uses the same logic with designations like Z08, Z12, Z18, Z27 — where the number times 10 approximates the g/m² value, so JIS Z12 is about the same as EN Z120.
| EN 10346 | JIS G 3317 | Approx. g/m² total | Typical automotive / industrial use |
|---|---|---|---|
| Z60 | Z06 | 60 | Interior, non-exposed brackets; indoor parts. Not for corrosive environments. |
| Z100 | Z10 | 100 | Inner structures, under-hood brackets with e-coat protection, shallow-form indoor components. |
| Z140 | Z14 | 140 | The workhorse: outer-panel sub-parts, chassis components, appliance housings, HVAC ducting. |
| Z180 | Z18 | 180 | Exposed body areas, wheel-house panels, parts with stone-chip exposure, outdoor enclosures. |
| Z275 | Z27 | 275 | Underbody, brackets near road-salt exposure, heavy equipment, long-life outdoor structures. |
What buyers get wrong
First, coating class is not the same as coating thickness. A Z140 designation is a mass guarantee, measured by X-ray fluorescence or weight-loss test — if your incoming inspection only measures with a magnetic gauge, calibrate it against the mass equivalent, or you will reject good coil and accept marginal coil.
Second, higher zinc is not automatically better for welding. Zinc vaporizes around 900°C; spot-welding through thick coatings increases electrode tip wear, spatter and expulsion. For parts that will be resistance-welded in your press line, talk to your mill about whether a thinner coating plus e-coat is the smarter system design.
Third, remember the difference between regular-spangle, mini-spangle and spangle-free surfaces. If your part is visible or painted, spangle control matters for paint appearance — specify it explicitly (e.g. Z140, spangle-free, skin-passed FS).
How to write it on a purchase order
A complete, dispute-proof callout looks like this: EN 10346 / DX53D+Z / Z140 MA / spangle-free / skin-pass FS / oiled, anti-finger print optional. MA confirms the minimum-alloy zinc bath chemistry used for formable grades; oiled protects during shipping and storage. If you are buying to JIS (e.g. SGC400), state the JIS designation plus the g/m² you expect, because JIS letters alone are coarse.
Sourcing note for importers
Chinese mills export all of the above classes to automotive supply chains, but documentation style varies by mill. Before your first order, ask for the mill certificate (MTC 3.1) template and confirm that coating mass, spangle class and surface finish appear as separate fields — an MTC that only says galvanized is not enough for PPAP-grade programs. If you would like our team to check a specification against what the mills can actually deliver, send us your drawing or spec sheet.
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