One of the questions buyers placing work in Turkey from abroad ask most often: "Do you do the plating as well?" The answer is the same for most Turkish shops: machining in-house, surface treatment at a specialist sub-supplier, responsibility and delivery at a single point. This article explains how that chain works and what the buyer needs to specify. For the material side, see our articles on aluminium, stainless steel and heat-treatable steels.
The Most Common Surface Treatments and Their Standards
| Process | Material | Purpose | Standard | Typical thickness |
|---|---|---|---|---|
| Anodising, natural/coloured | Aluminium | Corrosion, appearance, electrical insulation | ISO 7599, MIL-A-8625 Type II | 10–25 µm |
| Hard anodising | Aluminium | Wear resistance | ISO 10074, MIL-A-8625 Type III | 25–60 µm |
| Chromating / chemical conversion | Aluminium | Corrosion + conductivity | MIL-DTL-5541 (Cr³⁺ types) | <1 µm |
| Zinc plating (electrolytic) + passivation | Steel | Corrosion | ISO 2081, ISO 19598 | 5–12 µm |
| Zinc-nickel | Steel | High corrosion (automotive) | ISO 19598 | 8–15 µm |
| Electroless nickel (ENP) | Steel, aluminium | Uniform thickness, hardness | ISO 4527 | 10–30 µm |
| Hard chrome | Steel | Wear, low friction | ISO 6158 | 10–100 µm |
| Passivation | Stainless | Free-iron removal, corrosion | ASTM A967, ASTM A380 | — |
| Electropolishing | Stainless | Brightness, hygiene, deburring | ASTM B912 | −10 to −30 µm |
| Phosphating (zinc/manganese) | Steel | Oil retention, running-in | ISO 9717 | 2–15 µm |
| Black oxide | Steel | Appearance, light corrosion | ISO 11408 | ~1 µm |
| Gas nitriding / nitrocarburising | Steel | Surface hardness, wear | DIN 17022-4, EN 10052 | 0.1–0.6 mm diffusion |
| Induction hardening | C45, 42CrMo4 | Localised hardness | — | 1–5 mm |
Thickness, Tolerance and Dimensional Validity
A coating adds thickness to the part; if the dimensional tolerance is IT7 or tighter, this difference matters:
- Anodising: About half the thickness grows outward (15 µm anodising → ~+15 µm on diameter). In hard anodising a 50 µm layer enlarges the diameter by ~50 µm.
- Electrolytic coatings: The full thickness is added; thicker at edges and corners, thinner in holes (Faraday effect). Electroless nickel deposits uniformly.
- Electropolishing: Removes material; dimensions shrink.
- Nitriding: Slight growth (a few µm) and possible distortion; tight-tolerance surfaces can be ground afterwards.
The drawing must state "dimensions apply after coating" or "before coating". If it does not, the supplier machines to the pre-coating dimension and fit problems arise after coating. For details see our technical drawing checklist.
Masking and Thread Protection
Threads, mating surfaces and electrical contact points usually need to be kept free of coating. Masking (plugs, tape, lacquer) is extra labour and appears as a separate line in the quote; the surfaces to be masked must be shown clearly on the drawing. Alternatives: cutting the threads after coating (one-sided corrosion risk) or cutting the threads with a coating allowance (ISO 965 pre-coating tolerance classes, e.g. 6e instead of 6g).
How Does the Finishing Chain Work in Turkey?
- The industrial zones of Istanbul, Bursa and Ankara have numerous specialist plating, anodising and heat-treatment plants; machine shops have worked with them for years.
- The machine shop sends the part for coating, takes it back, performs final inspection and delivers; for the buyer the single responsible party is the machine shop.
- For automotive customers the plater may need to be IATF or customer-approved; this must be stated at the quotation stage.
- Time: standard plating adds 3–7 days, heat treatment 3–5 days, hard anodising and special processes 1–2 weeks.
Surface treatment is the item most often overlooked among the factors that determine the price; standard zinc plating can be 5–10% of the unit price on a small part, hard anodising or electroless nickel 15–30%.
Documentation and Traceability
A coating certificate (process, standard, measured thickness, date, bath/lot), a salt-spray test report (ISO 9227, if required), a hardness report (for nitriding/induction) and a RoHS declaration of conformity may be requested. Thickness is measured with a magnetic/eddy-current gauge or by cross-section microscopy; for critical parts ask the supplier to record the measured values in the report.
RoHS and REACH Restrictions
Yellow chromating and some passivations containing hexavalent chromium (Cr⁶⁺) are restricted under RoHS; trivalent (Cr³⁺) alternatives are standard. Cadmium plating is in practice used only in aerospace under exemption. Leaded brass (CuZn39Pb3) benefits from the lead exemption in RoHS, but exemption periods may change; the buyer must check the compliance of their own product. Write the requirement in the quote as "RoHS-compliant coating".
How to Define a Surface Treatment on the Drawing and in the RFQ
Most disputes about surface treatment arise from a missing or ambiguous definition. A good definition contains these components:
- Process and standard: "Electrolytic zinc, ISO 2081, Fe//Zn8//C" or "Anodising ISO 7599, AA15, black".
- Thickness: Minimum or range; measurement location (specific surface).
- Appearance: Colour reference (RAL, sample), gloss; marking of visible surfaces.
- Dimensional validity: Before or after coating?
- Masking: Surfaces and threads to be protected.
- Performance requirement (optional): Salt-spray test duration (ISO 9227, e.g. 96 h no white rust), adhesion test.
- Compliance: RoHS/REACH; Cr⁶⁺-free note.
- Documentation: Coating certificate, thickness measurement values, test report.
When this information is in the RFQ, the supplier gets the right price from the plater and your quotes become comparable. When it is left vague, suppliers price on different assumptions and the cheapest quote is often the least comprehensive. The same logic applies to heat treatment and hardening: target hardness, tolerance, measurement location and hardening zone must be written; details in our heat-treatable steels article.
Frequently Asked Questions
Should I have the plating done in Turkey or in my own country?
Having it done in Turkey lowers unit cost and delivers finished parts from a single point. If a customer-approved special plater is mandatory, bare parts can be shipped.
Does anodising colour vary from batch to batch?
Depending on alloy and bath conditions there may be tonal differences; for visible parts a colour reference (sample) and the same alloy lot are recommended.
How is coating thickness tolerance written?
By standard and minimum thickness (e.g. "Fe//Zn8//C" ISO 2081) or as a range (12–18 µm); the measurement location is also stated.
Can a hardened part be plated?
Yes; but because of the hydrogen embrittlement risk, high-strength steels (≥1000 MPa) require post-plating baking (ISO 9588).
How are thread and fit dimensions preserved after anodising?
Threads are usually masked or cut after coating; mating surfaces are machined with the coating thickness subtracted. If the drawing carries the note "dimensions apply after coating", the supplier makes this calculation.
What should a surface treatment certificate contain?
Process name and standard, measured thickness (with location), lot and date, declaration of conformity; if required, salt-spray or adhesion test results. This information is part of the traceability chain.
Conclusion
When defined with the right standard and dimensional validity, surface treatments can be sourced in Turkey through the machine shop from a single point, economically and with documentation. Send the drawings of your parts requiring coating or hardening via our quote form; we present machining and surface treatment in one quote, together with the certificate scope. For the process, see our how we work page.
