DIN 50942 and ISO 9717 — phosphate conversion coatings on metals
How phosphate coatings are actually specified: coating mass in g/m² rather than colour, zinc versus manganese, the role of the supplementary oil, and what to write on the drawing.
| Related service | Phosphate Coating |
|---|---|
| Phosphate conversion coating | DIN 50942 / ISO 9717 |
| Also written as | DIN 50942, ISO 9717, EN ISO 9717, TT-C-490 (US paint pretreatment) |
| Updated |
Scope — and what it does not cover
ISO 9717 — with DIN 50942 as the long-standing German document behind much of the same practice — covers phosphate conversion coatings on metals: the coating types (zinc, manganese, iron phosphate), how the requirement is expressed (coating mass per unit area, appearance, supplementary treatment) and the test methods. Performance comes from the phosphate PLUS the supplementary oil, wax or paint; the phosphate on its own is a porous crystal layer, not a corrosion barrier. It does NOT specify a colour, does not cover electroplated coatings, and does not define a service life.
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
- 1Coating mass in g/m², not colour, is the measurable requirement. Two identically grey-black parts can differ by a factor of five in coating mass.
- 2Zinc and manganese phosphate do different jobs: fine zinc phosphate is a paint base, heavier zinc phosphate with oil is a corrosion system, manganese phosphate is a wear, run-in and anti-scuffing layer.
- 3The supplementary treatment is part of the specification. "Phosphate + oil" and "phosphate, no oil" are different products with completely different salt-spray behaviour.
- 4Phosphate crystals grow both into and out of the surface, so there is a small dimensional effect on threads. On fine-pitch small fasteners that is agreed in advance, not discovered later.
- 5Coating mass is verified by stripping and weighing a known area, which is destructive — so sampling and the reference sample matter.
- 6On high-strength parts the pickling step deserves the same hydrogen discipline as plating, even though phosphating itself is a low-temperature process.
Reference tables
Scroll the table sideways on a narrow screen.
Phosphate types, function and typical coating mass
| Coating type / function | Typical coating mass (g/m²) |
|---|---|
| Iron phosphate — paint pre-treatment | 0.2–1.0 |
| Zinc phosphate, fine — paint base | 1.5–4.5 |
| Zinc phosphate, heavy + oil — corrosion | 7.5–30 |
| Manganese phosphate — wear / run-in | 5–30 |
Typical ranges. Coating mass is the measurable requirement — colour is not.
Values on this page are typical industry figures that depend on the part, the coating system and the governing specification. They are not guarantees. Always confirm against the edition in force and the customer drawing — this page does not replace either.
What to write on the drawing or PO
- Phosphate type (zinc, manganese or iron) and the intended function: paint base, corrosion with oil, or wear and run-in.
- Coating mass range in g/m², or an approved reference sample if mass is not being controlled.
- The supplementary treatment by name — oil, wax, sealer, or the paint system that follows — and who applies it.
- The significant surfaces and any areas that must stay free of coating.
- The test requirement, if any: coating mass, appearance, or a corrosion test with method, hours and criterion.
What goes wrong when it is cited loosely
- Ordering "black phosphate" and judging the result by shade. Colour comes from the crystal and the oil; it is not a specification.
- Specifying manganese phosphate as a paint base. The crystal is coarse and heavy; a fine zinc phosphate is the normal paint pre-treatment.
- Leaving the oil undefined and then testing salt-spray hours. The oil is doing much of that work.
- Assuming phosphate replaces zinc plating for corrosion. Phosphate plus oil is a different, and generally shorter, corrosion system.
Defects this standard gets cited on
Steel grades where this decision is made
Frequently asked questions
ISO 9717 or DIN 50942 — are they the same?+
They are closely related but not identical documents, and drawings in Asia and Europe cite both. State which one governs your order and put the numeric requirement — coating mass and supplementary treatment — next to it, so nothing depends on which document a reader has on the shelf.
What coating mass should I ask for?+
It follows the function: a paint base sits at the light end, an oiled corrosion coating and a manganese run-in coating at the heavy end. If your drawing is silent, send the function and the mating condition and we will propose a range for your approval.
Can phosphate be applied to hardened fasteners?+
Yes. It is a low-temperature conversion process, so it does not temper the part. The point to watch on high-strength parts is the pickling step, not the phosphating temperature.
Values on this page are typical industry figures that depend on the part, the coating system and the governing specification. They are not guarantees. Always confirm against the edition in force and the customer drawing — this page does not replace either.
Related standards
Other standards in this reference
Send the drawing and let us check it against this standard
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