Overview
ISO 10683:2018 specifies requirements for non‑electrolytically applied zinc flake coating systems on steel fasteners. It covers coatings with or without hexavalent chromium (Cr(VI)), with or without top coats and lubricants, and applies to bolts, screws, studs, nuts (ISO and non‑ISO metric threads) and non‑threaded parts (washers, pins, clips). The standard excludes mechanically applied zinc coatings and does not set requirements for weldability or paintability. Annexes provide practical guidance on design, assembly, coating thickness and test evaluation.
Key topics and technical requirements
- Coating system types: base coat, base coat + lubricant, base coat + top coat, and base coat + top coat + lubricant.
- Corrosion testing: neutral salt spray (NSS) per ISO 9227 with defined test durations and reference coating thicknesses; sulfur dioxide (Kesternich) testing also referenced.
- Thickness and dimensional control: requirements for coating thickness, gaugeability and assemblability (specifics for ISO metric threads in Annex B). Measurement methods reference ISO 1463.
- Mechanical and physical properties: appearance, ductility, adhesion/cohesion, sacrificial cathodic protection performance, and torque/clamp force relationships (ISO 16047).
- Hydrogen embrittlement avoidance: preference for mechanical or alkaline/solvent cleaning to eliminate hydrogen generation; controlled acid pickling only with inhibitors and limited use (fasteners > 390 HV or class 12.9+ must not be acid cleaned). Zinc flake coatings allow outward diffusion of hydrogen during curing.
- Curing: curing temperatures can be up to 320 °C; processes must not degrade fastener mechanical properties or fatigue limits (warning for thread‑rolled after heat treatment).
- Testing and designation: mandatory lot tests, in‑process controls, and purchaser‑specified tests; designation and ordering rules ensure clear specification of composition and performance.
Applications and who uses it
- Manufacturers and coaters of high‑strength fasteners (≥ 1 000 MPa) seeking corrosion protection without risk of internal hydrogen embrittlement.
- Fastener designers and OEMs in automotive, construction, heavy equipment, and industrial machinery specifying reliable, thin, conductive coatings for cathodic protection.
- Quality and procurement teams requiring clear test criteria (NSS, Kesternich), coating thickness guidance, and assembly design considerations (Annex A).
Related standards
ISO 10683:2018 is a practical reference for specifying, testing and applying zinc flake coatings to steel fasteners where corrosion resistance and avoidance of hydrogen embrittlement are priorities.
