ISO 10683 — non-electrolytic zinc flake coating systems for fasteners

Scope — and what it does not cover

ISO 10683 covers zinc flake (zinc lamellar) coating systems applied to fasteners by dip-spin or spray and cured with heat, including base coats, topcoats and integrated lubricants, with requirements for corrosion resistance, coefficient of friction and thickness. Because the coating is not deposited from an electrolytic bath, the process itself does not charge the steel with hydrogen — which is why it is the usual answer for very high-strength parts. It does NOT cover electroplated coatings (ISO 4042), hot dip galvanizing (ISO 10684) or mechanical properties, and it does not remove the need to control pre-treatment, since acid pickling before coating can still introduce hydrogen.

Standards are copyrighted documents. We explain scope, intent and practical application in our own words; obtain the current edition from ISO, ASTM, DIN or your national standards body.

What actually bites in production

• 1The reason to choose it is metallurgical, not commercial: no electrolytic hydrogen charging. For class 12.9, case-hardened parts and hard springs that is a design decision.
• 2Mechanical (blast) cleaning is preferred over acid pickling as pre-treatment on high-strength parts. If the parts are pickled, the embrittlement argument is weakened.
• 3Curing is typically in the 200–250 °C region — below the tempering temperature of a quenched and tempered fastener, but still worth checking against the part's temper.
• 4Thickness is typically 4–10 µm, so thread fit is far less constrained than with a thick electroplated deposit.
• 5The system is usually specified with a friction requirement as well as a corrosion requirement, because these coatings are used where torque-tension scatter matters. Friction is measured to ISO 16047.
• 6Corrosion requirements are commonly written as hours of ISO 9227 NSS to base-metal (red) corrosion; 240, 480 and 720 h are the classes seen most often on drawings.

What to write on the drawing or PO

• The coating system designation, base coat and topcoat, and whether an integrated lubricant is required.
• The corrosion requirement in hours, the test method (ISO 9227 NSS) and whether the criterion is base-metal corrosion or coating corrosion.
• The friction requirement (total coefficient of friction band) and the test method (ISO 16047), if the joint is torque-controlled.
• Any pre-treatment restriction for high-strength parts, for example "mechanical cleaning only, no acid pickling".
• Colour, electrical conductivity or rework restrictions, because zinc flake cannot be stripped and re-coated as freely as electroplate.

What goes wrong when it is cited loosely

• Assuming zinc flake makes embrittlement impossible. It removes the plating bath as a hydrogen source; pickling, hydrogen already in the steel and the service environment remain.
• Specifying zinc flake and an electroplated thickness class in the same callout.
• Ordering a corrosion class without a friction class on a torque-controlled joint, then finding the clamp load has moved.
• Expecting the same appearance and the same repair route as electroplated zinc.