Overview
ISO 9717:2017 - Metallic and other inorganic coatings - Phosphate conversion coating of metals - specifies how to confirm requirements for phosphate conversion coatings typically applied to ferrous materials, zinc, cadmium and their alloys. The third edition (2017) updates scope, terminology and requirements, shifts corrosion-resistance statements into Annex A, and revises guidance on coating properties and testing. The standard is intended for use in procurement, production control and conformity assessment of phosphate (phosphating) treatments.
Key topics and technical requirements
- Coating types and designation: Defines common phosphate coating types (e.g., Feph, Mnph, Znph, ZnCaph) and prescribes a structured designation format including base material, coating type, function (r = adhesion/corrosion protection, z = cold-forming, g = friction reduction, e = electrical insulation) and surface-related mass.
- Information to be supplied by purchaser: Requires purchasers to specify coating designation, surface treatment, appearance, corrosion-resistance requirements, sampling procedures and measures for minimizing hydrogen embrittlement on high-strength steel (≥ 1 000 MPa).
- Appearance and coating mass: Coatings must evenly cover surfaces without stains or fingerprints. Coating mass per unit area is measured according to ISO 3892 (gravimetric method); an illustrative example in the standard uses 3 g/m² ± 0.9 g/m².
- Post-treatments (sealants/finishes): Untreated phosphate coatings are porous; post-treatments include varnishes (T1), inorganic or non-film-forming sealants (T2), dyes (T4), oils/greases (T5), etc. Corrosion resistance of after-treated components must be verified per customer test or the neutral salt spray (NSS) method.
- Corrosion testing: Annex A normatively specifies NSS testing in line with ISO 9227, including use of original components or representative test panels (150 × 100 mm with drilled holes for suspension).
- Thickness measurement methods: Correlation between coating thickness and mass can be determined by magnetic inductive (ISO 2178), dissolving (ISO 2177) or X‑ray (ISO 3497).
- Heat treatment: Not recommended above 120 °C as phosphate layers can be damaged.
Practical applications
- Improves corrosion resistance, paint adhesion, cold-forming performance and frictional properties of metal parts
- Commonly applied in automotive components, fasteners, wire drawing, electroplated substrates, and general metal finishing operations
- Used where a conversion layer is required as an intermediate or final finish prior to painting, sealing or lubrication
Who should use this standard
- Coating processors and surface-treatment shops
- Original equipment manufacturers (OEMs) and purchasers specifying phosphating requirements
- Quality and inspection engineers, corrosion specialists and testing laboratories
- Suppliers of sealants, primers and lubricants that interact with phosphate layers
Related standards
Keywords: ISO 9717:2017, phosphate conversion coating, phosphating, corrosion resistance, neutral salt spray, coating mass, zinc phosphate, manganese phosphate, surface treatment.
