oSIST prEN 4473:2026

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

This document specifies the performance requirements of 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 or 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 - Aluminiumpigmentierte 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 oder 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.

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

Ta dokument določa zahteve glede zmogljivosti organskih premazov s pigmentom iz aluminija, ki se nanašajo na titan, titanove zlitine, zlitine na osnovi niklja ali kobalta ter korozijsko odporna jekla.
Ta specifikacija ne zajema električnega povezovanja ali uporabe teh premazov za zaščito pred udarom strele. Dodatni kvalifikacijski testi bodo dogovorjeni z OEM (izvirni proizvajalec opreme) ob kvalifikaciji.
OPOMBA Ti premazi niso priporočljivi za uporabo na pritrdilnih elementih iz jekla, ki ni odporno proti koroziji.

General Information

• Status: Not Published
• Public Enquiry End Date: 24-Jun-2026
• 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: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 20-Apr-2026
• Due Date: 07-Sep-2026
• Ref Project: prEN 4473 - Aerospace series - Aluminium pigmented organic coatings for fasteners - Technical specification

Relations

• Revises: SIST EN 4473:2025 - Aerospace series - Aluminium pigmented organic coatings for fasteners - Technical specification
• Effective Date: 04-Feb-2026

Overview

oSIST prEN 4473:2026 is a technical specification developed by CEN for the aerospace series, defining the performance requirements of aluminium pigmented organic coatings for fasteners. This standard applies specifically to coatings used on titanium, titanium alloys, nickel or cobalt-based alloys, and corrosion-resistant steels. The document is essential for ensuring coated fasteners deliver optimal corrosion protection and mechanical performance in aerospace applications.

It is important to note that this standard:

• Does not cover electrical bonding or lightning strike applications.
• Requires additional qualification tests as agreed with the original equipment manufacturer (OEM).
• Advises against the use of such coatings on non-corrosion resistant steel fasteners.

Key Topics

Performance Requirements

oSIST prEN 4473:2026 specifies key characteristics and test methods for qualifying and approving aluminium pigmented coatings:

• Appearance: Coatings must be uniform and defect-free.
• Thickness: Determined using recognized methods (e.g., ISO 2808, NASM 1312-12), with strict criteria for functional surfaces.
• Adhesion: Tested according to EN ISO 2409 to ensure long-term bond integrity.
• Heat resistance: Must withstand elevated temperatures without degradation.
• Chemical resistance: Coatings are tested against fuel, hydraulic fluid, paint strippers, and cleaning solvents.

Corrosion Protection

• Ensures galvanic compatibility between fasteners and structural materials, notably aluminium alloys.
• Laboratory corrosion tests (ISO 9227, ASTM B117) confirm that coatings provide protection comparable to or better than traditional cadmium or anodized finishes.

Types and Classification

Coatings are classified by:

• Presence or absence of hexavalent chromium.
• Whether lubrication (cetyl alcohol, per EN 6117) is used.
• Four types ensure alignment with environmental and performance requirements.

Test Procedures

• Defined protocols for coating qualification, fastener testing, and lot acceptance.
• Includes specific guidance on sample preparation, test coupon machining, and performance evaluation for adhesion, corrosion resistance, electrical conductivity, and mechanical properties like interference fit assembly.

Applications

The aluminium pigmented organic coating systems specified in oSIST prEN 4473:2026 are widely used in:

• Aerospace fasteners: For bolts, pins, screws, nuts, and collars installed in airframes, engines, and critical assemblies.
• Protection of fasteners exposed to aggressive environments, including chemical de-icing fluids, solvents, and fuels typical in aerospace operation and maintenance.
• Preventing galvanic corrosion where different metals interface, particularly when combining fasteners of steels or alloys with aluminium structure components.
• Reducing thread friction and facilitating assembly of interference fit fasteners with predictable installation forces.

Note: The standard ensures compatibility with aerospace manufacturing and quality management systems.

Related Standards

oSIST prEN 4473:2026 references and complements several key standards relevant to aerospace coatings and fastener performance:

• EN 4474: Details coating methods for aluminium pigmented systems.
• EN ISO 2409 and ISO 2808: Define adhesion and thickness measurement methods for paints and coatings.
• EN 2101, EN 4827: Specifications for anodizing aluminium and alloys.
• EN 6117: Fastener lubrication with cetyl alcohol.
• EN ISO 9227 / ASTM B117: Salt spray testing for corrosion resistance.
• NASM 1312: Fastener test methods for mechanical properties and durability.

Further reference is made to technical reports and aerospace product qualification procedures, such as EN 9133 and TR 4676.

oSIST prEN 4473:2026 establishes a robust technical foundation for aerospace manufacturers, suppliers, and quality assurance teams, promoting safer and more reliable assembly of critical fasteners in demanding environments.

Standards Content (Sample)

SLOVENSKI STANDARD
01-junij-2026
Aeronavtika - Organski premazi, pigmentirani z aluminijem, za vezne elemente -
Tehnična specifikacija
Aerospace series - Aluminium pigmented organic coatings for fasteners - Technical
specification
Luft- und Raumfahrt - Aluminiumpigmentierte organische Beschichtungen für
Verbindungselemente - Technische Lieferbedingungen
Ta slovenski standard je istoveten z: prEN 4473
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.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2026
ICS 49.040 Will supersede EN 4473:2024
English Version
Aerospace series - Aluminium pigmented organic coatings
for fasteners - Technical specification
Luft- und Raumfahrt ¿ Aluminiumpigmentierte
organische Beschichtungen für Verbindungselemente ¿
Technische Lieferbedingungen
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee ASD-
STAN.
If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 4473:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 5
4 Technical requirements . 6
4.1 General. 6
4.2 Classification. 6
4.3 Product composition and application . 7
4.4 Coating performance . 7
Annex A (normative) Performance requirements . 8
Annex B (normative) Test coupons for galvanic compatibility . 13
Annex C (normative) Test coupons for paint adhesion . 14
Annex D (normative) Test coupons for electrical conductivity tests . 15
Bibliography . 16

European foreword
This document (prEN 4473:2026) 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 document is currently submitted to the CEN Enquiry.
This document will supersede EN 4473:2024.
— addition of ISO 2808 as an alternative to NASM 1312-1 in Table A.1;
— editorial changes.
1 Scope
This document specifies the performance requirements of 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 or 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 2409, Paints and varnishes — Cross-cut test (ISO 2409)
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 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
ISO 2808, Paints and varnishes — Determination of film thickness

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/.
Published by International Organization for standardization (ISO), available at: https://www.iso.org/.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology 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/
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 coating surface
3.6
porosity
fine holes or pores within the coating surface
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: bearing surfaces, internal diameter;
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 customer).
If not otherwise specified:
— Types I and II shall be delivered with cetyl lubrication per EN 6117;
— Types III and IV shall be delivered without lubricant.
4.3 Product composition and application
The manufacturing method and product composition are defined by the product manufacturer. The
users shall be notified 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, nickel-and cobalt-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 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 parts coated with a qualified coating product.
Each lot of coated fasteners (or other parts) manufactured shall be subject to the acceptance tests and
sampling detailed in EN 4474 by the supplier before delivery. The results of these
...