SIST EN 4473:2025

Aerospace series - Aluminium pigmented organic coatings for fasteners - Technical specification

This document specifies the performance requirements for aluminium pigmented organic coatings to be applied on titanium, titanium alloys, nickel or cobalt based alloys and corrosion resistant steels.
This specification does not cover electrical bonding and lightning strike applications of these coatings. Additional qualification tests will be agreed with the OEM upon qualification.
NOTE   These coatings are not recommended for use on non-corrosion resistant steel fasteners.

Luft und Raumfahrt - Aluminium pigmenttete organische Beschichtungen für Verbindungselemente - Technische Lieferbedingungen

Dieses Dokument legt die Leistungsanforderungen an aluminiumpigmentierte organische Beschichtungen für Titan, Titanlegierungen, Nickel- oder Cobaltlegierungen und korrosionsbeständige Stähle fest.
In dieser Spezifikation werden keine auf die elektrische Kontaktierung und Blitzschlag bezogenen Anwendungen dieser Beschichtungen behandelt. Zusätzliche Qualifizierungsprüfungen werden bei Qualifizierung mit dem Originalgerätehersteller vereinbart.
ANMERKUNG   Diese Beschichtungen sind nicht für die Verwendung auf Verbindungselementen aus nicht korrosionsbeständigem Stahl empfohlen.

Série aérospatiale - Revêtements alumino-organiques pour éléments de fixation - Spécification technique

Le présent document spécifie les exigences de performances pour les revêtements alumino-organiques à appliquer sur le titane, les alliages de titane, les alliages base nickel ou cobalt et les aciers résistant à la corrosion.
Cette spécification ne couvre pas les applications de ces revêtements liées à la métallisation et à la foudre. Les essais de qualification supplémentaires seront convenus en accord avec l’OEM au moment de la qualification.
NOTE   Il n’est pas recommandé d’utiliser ces revêtements sur les éléments de fixation en acier non résistant à la corrosion.

Aeronavtika - Organski premazi, pigmentirani z aluminijem, za vezne elemente - Tehnična specifikacija

Ta dokument določa zahteve glede lastnosti za organske premaze, pigmentirane z aluminijem, ki se nanesejo na titan, titanove zlitine, zlitine na nikljevi ali kobaltovi osnovi in korozijsko odporna jekla.
Ta specifikacija ne zajema uporabe teh premazov v primeru električne povezave in udara strele. Dodatni kvalifikacijski preizkusi bodo dogovorjeni v posvetovanju s proizvajalcem originalne opreme (OEM) po kvalifikaciji.
OPOMBA: Ti premazi niso priporočljivi za uporabo na jeklenih veznih elementih, ki niso korozijsko odporni.

General Information

• Status: Published
• Public Enquiry End Date: 20-Jun-2023
• Publication Date: 11-Dec-2024
• ICS: 49.025.20 - Aluminium
• ICS: 49.030.01 - Fasteners in general
• ICS: 49.040 - Coatings and related processes used in aerospace industry
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 10-Dec-2024
• Due Date: 14-Feb-2025
• Completion Date: 12-Dec-2024
• Ref Project: EN 4473:2024 - Aerospace series - Aluminium pigmented organic coatings for fasteners - Technical specification

Relations

• Revises: SIST EN 4473:2010 - Aerospace series - Aluminium pigmented coatings for fasteners - Technical specification
• Effective Date: 20-Feb-2023

Overview

EN 4473:2024 - Aerospace series: Aluminium pigmented organic coatings for fasteners (CEN) specifies performance and qualification requirements for aluminium‑pigmented organic coatings applied to fasteners made from titanium and titanium alloys, nickel or cobalt based alloys, and corrosion‑resistant steels. The standard focuses on corrosion protection, friction reduction and chemical resistance for aerospace fasteners. It explicitly excludes electrical bonding and lightning‑strike applications and notes these coatings are not recommended for non‑corrosion‑resistant steel fasteners.

Key topics and technical requirements

• Scope and materials: Coatings for fasteners on Ti, Ni/Co alloys and corrosion‑resistant steels; limitations for non‑corrosion‑resistant steels and electrical bonding uses.
• Classification (Types I–IV):
  • Type I/III: contain hexavalent chromium (I with lubricant, III without).
  • Type II/IV: hexavalent chromium free (II with lubricant, IV without).
• Composition limits: Product must not contain lead or graphite; Types II and IV must be hexavalent chromium free. Manufacturers must notify users of formulation changes.
• Performance & qualification:
  • Coating thickness: typically 5–13 μm on external functional surfaces; up to 20 μm where internal functional surfaces apply (per NASM 1312‑12 methods).
  • Adhesion: EN ISO 2409 cross‑cut Class 0 (or equivalent cut/tape procedure on complex geometries).
  • Environmental / chemical resistance: specified immersion tests (EN ISO 2812‑1) for jet fuel, phosphate‑ester hydraulic fluids, paint strippers and aircraft solvents; salt spray galvanic compatibility (EN ISO 9227 / ASTM B117).
  • Heat resistance: exposure to ~315 °C for 4 h with no flaking, blistering or adhesion loss.
• Qualification & lot release:
  • New products qualified per Annex A (Table A.1) and tests performed per material/coating combination.
  • Lot acceptance testing and sampling per EN 4474 before delivery.

Practical applications

• Used to reduce thread friction in bolted and interference‑fit assemblies, improve galvanic corrosion protection between fasteners and structure, and protect fasteners from aggressive maintenance chemicals.
• Typical implementations: fasteners on airframe assemblies, engine components (compatible alloys), and MRO replacement parts where corrosion and chemical resistance are critical.

Who uses EN 4473:2024

• Aerospace OEMs and procurement teams specifying fastener coatings
• Fastener manufacturers and coating suppliers (product qualification)
• Quality, inspection and testing labs performing adhesion, thickness and environmental tests
• MRO organizations and design engineers assessing fastener compatibility

Related standards

• EN 4474 (coating methods / lot release)
• EN ISO 2409 (cross‑cut adhesion)
• EN ISO 2812‑1 (immersion tests)
• EN ISO 9227 / ASTM B117 (salt spray)
• NASM 1312‑12 (coating thickness), NASM 1312‑5 (stress durability)
• EN 2101 / EN 4827 (anodizing references)
• TR 4676 (industry product listing)

Keywords: EN 4473:2024, aluminium pigmented organic coatings, aerospace fasteners, corrosion protection, coating thickness, adhesion, hexavalent chromium free.

Standards Content (Sample)

SLOVENSKI STANDARD
01-februar-2025
Aeronavtika - Organski premazi, pigmentirani z aluminijem, za vezne elemente -
Tehnična specifikacija
Aerospace series - Aluminium pigmented organic coatings for fasteners - Technical
specification
Luft und Raumfahrt - Aluminium pigmenttete organische Beschichtungen für
Verbindungselemente - Technische Lieferbedingungen
Série aérospatiale - Revêtements alumino-organiques pour éléments de fixation -
Spécification technique
Ta slovenski standard je istoveten z: EN 4473:2024
ICS:
49.025.20 Aluminij Aluminium
49.030.01 Vezni elementi na splošno Fasteners in general
49.040 Prevleke in z njimi povezani Coatings and related
postopki, ki se uporabljajo v processes used in aerospace
letalski in vesoljski industriji industry
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 4473
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2024
EUROPÄISCHE NORM
ICS 49.040 Supersedes EN 4473:2010
English Version
Aerospace series - Aluminium pigmented organic coatings
for fasteners - Technical specification
Série aérospatiale - Revêtements alumino-organiques Luft- und Raumfahrt - Aluminiumpigmentierte
pour éléments de fixation - Spécification technique organische Beschichtungen für Verbindungselemente -
Technische Lieferbedingungen
This European Standard was approved by CEN on 30 September 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 4473:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Technical requirements . 6
4.1 General. 6
4.2 Classification. 6
4.3 Product composition and application . 6
4.4 Coating performance . 6
Annex A (normative) Performance requirements . 8
Annex B (normative) Test coupons for galvanic compatibility . 15
Annex C (normative) Test coupons for paint adhesion . 16
Annex D (normative) Test coupons for electrical conductivity tests . 17
Bibliography . 18

European foreword
This document (EN 4473:2024) has been prepared by ASD STAN.
After enquiries and votes carried out in accordance with the rules of this Association, this document has
received the approval of the National Associations and the Official Services of the member countries of
ASD-STAN, prior to its presentation to CEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by May 2025, and conflicting national standards shall be
withdrawn at the latest by May 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 4473:2010.
This document includes the following significant technical changes with respect to EN 4473:2010:
— editorial revision to comply with the updated layout in use;
— clarification of test requirements, e.g. coating adhesion on fasteners, measurement of coating
thickness.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
1 Scope
This document specifies the performance requirements for aluminium pigmented organic coatings to
be applied on titanium, titanium alloys, nickel or cobalt based alloys and corrosion resistant steels.
This specification does not cover electrical bonding and lightning strike applications of these coatings.
Additional qualification tests will be agreed with the OEM upon qualification.
NOTE These coatings are not recommended for use on non-corrosion resistant steel fasteners.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 2101, Aerospace series — chromic acid anodizing of aluminium and wrought aluminium alloys
EN 4474, Aerospace series — Aluminium pigmented coatings — Coating methods
EN 4827, Aerospace series — Hexavalent chromium free anodizing of aluminium and aluminium alloys
EN 6117, Aerospace series — Specification for lubrication of fasteners with cetyl alcohol
EN ISO 2812-1, Paints and varnishes — Determination of resistance to liquids — Part 1: Immersion in
liquids other than water (ISO 2812-1)
EN ISO 2409, Paints and varnishes — Cross-cut test (ISO 2409)
EN ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests (ISO 9227)
ASTM B117, Standard Practice for Operating Salt Spray (Fog) Apparatus
MIL-PRF-8625, Anodic Coatings for Aluminum and Aluminum alloy
NASM 1312-5, Fastener Test Methods, Method 5: Stress Durability
NASM 1312-12, Fastener Test Methods, Method 12: Thickness of Metallic Coatings
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/

Published as ASD-STAN prEN at the date of publication of this document, available at: https://www.asd-
stan.org/.
Published by American Society for Testing and Materials (ASTM International), available at:
https://www.astm.org/.
Published by Department of Defense (DoD), available at: https://assist.dla.mil/online/start/.
Published by Aerospace Industries Association (AIA), available at: https://www.aia aerospace.org/.
3.1
production lot
parts subjected to the same aluminium pigmented coating application at the same time under the same
condition
3.2
product
commercial chemical solution that constitutes the aluminium pigmented coating
3.3
blister
local convexity caused by a sub-surface inclusion of gas or liquid
3.4
nodule
localized build-up or unmixed solid particles
3.5
pit
void, hole in the surface
EXAMPLE Pits can be caused, for example, by corrosion.
3.6
porosity
fine holes or pores within the coating
3.7
functional surface
surface in contact with mating structure and threaded portion
EXAMPLE
— pins, bolts, lockbolts, screws: under head bearing surface, shank, lead-in radius and thread surface,
if applicable;
— nuts, threaded collars: bearing surfaces, thread surface;
— spherical washers: bearing surfaces;
— swaged collars: all surfaces.
3.8
generic part
family of similar fasteners
EXAMPLE
— pins, bolts, screws and lockbolts;
— nuts and threaded collars;
— swaged collars;
— solid rivets;
— blind bolts;
— bushes;
— washers.
4 Technical requirements
4.1 General
This document covers organic resin coatings pigmented with aluminium powder. Aluminium
pigmented coatings provide:
— friction reduction in threads and interference fit assemblies;
— galvanic corrosion protection between fasteners and the structure in which the fasteners are
installed;
— protection against aggressive chemicals used in operations and maintenance.
TR 4676 provides a list of commercial aluminium pigmented coating products widely used in the
aerospace industry. This list is non-exhaustive and the use of different products may vary for each OEM
and their specific applications.
4.2 Classification
Aluminium pigmented coatings are classified according to the following types:
Type I: Aluminium pigmented coatings containing hexavalent chromium, for use with cetyl
alcohol.
Type II: Hexavalent chromium free aluminium pigmented coatings, for use with cetyl alcohol.
Type III: Aluminium pigmented coatings containing hexavalent chromium, for use without
lubricant.
Type IV: Hexavalent chromium free aluminium pigmented coatings, for use without lubricant.
If no dedicated type is specified in the drawing, type II or IV shall be used depending on the need for
lubrication (to be confirmed with the OEM).
4.3 Product composition and application
The manufacturing method and product composition are defined by the product manufacturer. The
product manufacturer must notify its users of any changes.
The product shall not contain lead or graphite. Types II and IV shall not contain hexavalent chromium.
Unless otherwise specified, product application shall be carried out in accordance with EN 4474.
4.4 Coating performance
a) Qualification of a new coating product.
Qualification tests as per Table A.1 shall be performed for each combination of coating product and
material type (e.g. titanium alloys, corrosion resistant steels, Ni and Co-based alloys), unless
otherwise agreed with the mandated body.
b) Qualification of fasteners or other parts coated with a qualified coating product.
Unless otherwise specified, qualification tests shall be performed as per Annex A, Table A.1.
All the tests required by this paragraph shall be carried out on coated fasteners, unless otherwise
agreed with the mandated body.
c) Lot release of qualified fasteners or other pa
...