Overview
ISO 26945:2011 - Metallic and other inorganic coatings - Electrodeposited coatings of tin‑cobalt alloy - specifies requirements for electrodeposited tin‑cobalt (Sn–Co) alloy coatings (approximately 75 %–80 % tin, remainder cobalt) as a decorative alternative to thin chromium finishes. The standard covers composition, designation, thickness ranges, basic process options and quality-control topics for coatings applied by rack or barrel plating. It clarifies that hardness and wear resistance are not equivalent to chromium but are similar to tin‑nickel alloys.
Key topics and requirements
- Composition: Tin‑cobalt alloy ≈ 75–80 % tin, balance cobalt.
- Intended use: Decorative substitute for chromium coatings of about 0.1 µm to 0.3 µm (surface lustre focus).
- Thickness: Specifies minimum coating thickness requirements and methods to indicate thickness in designations. Examples in the standard show typical values (e.g., 2–3 µm) used in practice.
- Application methods: Suitable for rack and barrel plating; high current efficiency (>70 %) makes it practical for complicated shapes (nuts, bolts, rivets).
- Undercoats & pretreatment: Undercoats (Cu, Ni) are recommended for certain base metals to ensure adhesion and corrosion resistance. Thicker undercoats (10–25 µm) may be required on Al, Mg or Zn alloys. The standard does not prescribe the basis‑metal surface condition - purchaser and processor must agree.
- Appearance & defects: Significant surfaces must be free of visible defects (blisters, pits, roughness, uncoated areas); finish samples can be specified.
- Heat treatments & embrittlement control: Designations allow stress‑relief (SR) before plating and hydrogen‑embrittlement‑relief (ER) after plating (e.g., SR(200)3, ER(190)12).
- Testing & measurement: Includes provisions for adhesion, quality‑evaluation tests and references methods for coating‑thickness measurement and sampling.
Practical applications
- Decorative finishing where chromium look is desired but a chromium process is unsuitable or restricted.
- Hardware and fasteners (nuts, bolts, rivets), small components produced in large batches via barrel plating.
- Industries requiring bright, corrosion‑resistant surface finishes with good processing efficiency: automotive small parts, consumer hardware, electrical contacts (subject to compatibility checks).
Who should use this standard
- Plating processors and surface‑finishing shops specifying tin‑cobalt deposits.
- OEMs and purchasers writing coating specifications or purchase orders.
- Materials, quality and corrosion engineers specifying tests, thicknesses and post‑treatments.
- Fastener and hardware manufacturers using rack or barrel plating lines.
Related standards
For procurement or process specification, include ISO 26945 in purchase orders and indicate basis metal, undercoat, finish, thickness, heat‑treatment and sampling/acceptance criteria to ensure compliant tin‑cobalt electrodeposited coatings.