SIST EN 4827:2024

SLOVENSKI STANDARD
01-september-2024
Aeronavtika - Šestvalentni krom brez eloksacije aluminija in aluminijevih zlitin
Aerospace series - Hexavalent chromium free anodizing of aluminium and aluminium
alloys
Luft- und Raumfahrt - Anodisieren von Aluminium und Aluminiumlegierungen ohne
hexavalentem Chrom
Série aérospatiale - Anodisation sans chrome hexavalent de l'aluminium et des alliages
d'aluminium
Ta slovenski standard je istoveten z: EN 4827:2024
ICS:
49.025.99 Drugi materiali Other materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 4827
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2024
EUROPÄISCHE NORM
ICS 49.025.20; 49.040 Supersedes EN 4827:2019
English Version
Aerospace series - Hexavalent chromium free anodizing of
aluminium and aluminium alloys
Série aérospatiale - Anodisation sans chrome Luft- und Raumfahrt - Chrom(VI)-freies Anodisieren
hexavalent de l'aluminium et des alliages d'aluminium von Aluminium und Aluminiumlegierungen
This European Standard was approved by CEN on 5 May 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 4827:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
3.1 General terms . 7
3.2 Technical terms . 7
4 General principles of the process . 9
4.1 Purpose of the process . 9
4.2 Applicability . 9
4.2.1 Type A: unsealed anodizing . 9
4.2.2 Type B: sealed anodizing . 9
4.3 Limitations . 10
4.4 Classification. 10
4.4.1 System types . 10
4.4.2 Layer thickness . 11
5 Process requirements . 11
5.1 Information for the processor . 11
5.2 Process conditions . 11
5.2.1 Tooling . 11
5.2.2 Masking . 12
5.2.3 Surface preparation . 12
5.2.4 Anodizing . 12
5.2.5 Anodizing post-treatments . 12
5.3 Water quality . 13
5.3.1 General. 13
5.3.2 Anodizing bath . 13
5.3.3 Sealing and dyeing baths . 13
5.3.4 Final rinsing bath . 13
5.4 Periodic bath chemical analysis . 13
5.5 Re-anodizing . 14
6 Test specimen requirements . 14
6.1 Definition of test specimens. 14
6.1.1 General. 14
6.1.2 For the qualification . 14
6.1.3 For periodic tests . 14
6.2 Tests for the qualification. 18
6.3 Periodic tests . 18
7 Parts requirements . 18
7.1 Condition of parts prior to the treatment . 18
7.2 Inspections before the treatment . 19
7.3 Inspections during the treatment . 19
7.4 Inspections on parts after anodizing . 19
8 Quality assurance . 19
8.1 Process approval. 19
8.2 General points . 19
8.3 Qualification procedure . 20
Annex A (normative) Tests on test specimens for the qualification . 21
Annex B (normative) Periodic tests on test specimens . 25
Annex C (normative) Levels of requirements for corrosion resistance of thin film anodizing
on unpainted test specimens . 29
Annex D (normative) Tests on parts . 30
Annex E (normative) Dye-spot test . 31
E.1 Dye-spot . 31
E.2 Dye solution A . 31
E.3 Dye solution B . 31
Bibliography . 33

European foreword
This document (EN 4827:2024) has been prepared by the Aerospace and Defence Industries
Association of Europe — Standardization (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 January 2025, and conflicting national standards shall
be withdrawn at the latest by January 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 4827:2019.
This document includes the following significant technical changes with respect to EN 4827:2019:
— normative references have been updated;
— Figure 1 and Figure 2 were added to 3.2.4;
— Clause 6 “Engineering requirements” has been restructured into the new Clause 6 “Test specimens
requirements” and Clause 7 “Parts requirements”;
— requirements relating to the test specimens materials, numbers, dimensions and periodicity have
been included in Table 3 to Table 8;
— requirements for the definition of test specimens for the qualification have been changed and added
to Table 3 to Table 5;
— requirements for the definition of periodic tests have been changed and added to Table 6 to Table 8;
— Annex A has been renamed;
— in Table A.1, changes were made or added to the items: “visual appearance”, “anodic layer
thicknesses”, “corrosion resistance”, “paint adhesion” and “sealing quality”;
— Annex B has been renamed;
— in Table B.1, changes were made to the items “visual appearance”, “anodic layer thicknesses”,
“corrosion resistance” and “paint adhesion”;
— Table C.1 has been added concerning levels of requirements for corrosion resistance of thin film
anodizing on unpainted test specimens;
— in Table D.1, changes were made to the item “visual appearance”;
— document has been revised editorially.
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 requirements for hexavalent chromium free anodizing of aluminium and
aluminium alloys for corrosion protection, bonding and painting.
This document does not apply to hard anodizing and plasma electrolytic anodizing (micro-arc
oxidation).
The purpose of this document is to give design, quality and manufacturing requirements. It does not
give complete in-house process instructions; these are given in the processor's detailed process
instructions.
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 2284, Aerospace series — Sulphuric acid anodizing of aluminium and wrought aluminium alloys
EN 3665, Aerospace series — Test methods for paints and varnishes — Filiform corrosion resistance test
on aluminium alloys
EN 4704, Aerospace series — Tartaric-Sulphuric-Acid anodizing of aluminium and aluminium wrought
alloys for corrosion protection and paint pre-treatment (TSA)
EN 4707, Aerospace series — Acid pickling of aluminium and aluminium alloys without hexavalent
chromium
EN 6072, Aerospace series — Metallic materials — Test methods — Constant amplitude fatigue testing
EN ISO 1463, Metallic and oxide coatings — Measurement of coating thickness — Microscopical method
(ISO 1463)
EN ISO 2085, Anodizing of aluminium and its alloys — Check for continuity of thin anodic oxidation
coatings — Copper sulfate test (ISO 2085)
EN ISO 2360, Non-conductive coatings on non-magnetic electrically conductive base metals —
Measurement of coating thickness — Amplitude-sensitive eddy-current method (ISO 2360)
EN ISO 2376, Anodizing of aluminium and its alloys — Determination of breakdown voltage and
withstand voltage (ISO 2376)
EN ISO 2409, Paints and varnishes — Cross-cut test (ISO 2409)
EN ISO 2812-2, Paints and varnishes — Determination of resistance to liquids — Part 2: Water immersion
method (ISO 2812-2)
EN ISO 9220, Metallic coatings — Measurement of coating thickness — Scanning electron microscope
method (ISO 9220)
EN ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests (ISO 9227)
ASTM B 137, Standard Test Method for Measurement of Coating Mass Per Unit Area on Anodically Coated
Aluminum
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 General terms
3.1.1
OEM
producer who has the design authority and manufactures products or components that are purchased
by a company and retailed under that purchasing company’s brand name
Note 1 to entry: The OEM can also apply the process.
3.1.2
manufacturer
company or person who makes, manufactures, assembles components
Note 1 to entry: The manufacturer can also apply the process.
3.1.3
processor
company or person who applies the process
3.1.4
process instruction
document that describes the application scopes, detailed process (key parameters, detailed steps, etc.),
quality management, environmental and safety regulations, etc.
3.1.5
batch
unless otherwise specified, parts of the same type (shape, size, material), processed at the same time in
the same bath
3.2 Technical terms
3.2.1
de-anodizing
process, which removes the anodic oxide
3.2.2
smut
precipitations of alloying elements (e.g. Cu, Fe, Zn, Si) on the surface of parts after a process step
normally after alkaline etching step
3.2.3
Mechanically Disturbed Layer
MDL
layer that is present at the surface resulting from the rolling process of the material
3.2.4
pit
surface corrosion defect at which the anodic coating is penetrated and/or perforated
Note 1 to entry: Typical characteristics of corrosion pits are:
— rounded or irregular or elongated geometry;
— comet tail or line or halo that emerges from the cavity;
— some corrosion by-products inside pits (on aluminium the by-product may be granular, powdery or
amorphous and white, grey or black in colour).
To be considered as a corrosion pit, a surface cavity exhibits at least two of the above characteristics.
Note 2 to entry: See Figure 1 and Figure 2.

Key
1 pits with overflow
2 white spot without overflow
Figure 1 — Example of corrosion pits on an aluminium alloy after exposure to neutral salt spray
(NSS)
a) Corrosion pit with black corrosion by products

b) Corrosion pit with grey corrosion by products
c) Corrosion pit on machined 2024 T351

d) Corrosion pit on laminated 2024 T3
Figure 2 — Examples of analysis of corrosion pits on machined 2024 T351 and laminated
2024 T3 that have been SAA treated
3.2.5
re-anodizing
repetition of the anodizing process step after complete de-anodizing
3.2.6
sealing
chromate VI free sealing (of the anodized layers) which is applied to close the pores produced by the
acid anodizing process
Note 1 to entry: It is usually applied in a hot demineralized water bath with or without additives at different
temperatures. Sealing improves the corrosion resistance performance of the anodic film.
4 General principles of the process
4.1 Purpose of the process
The anodizing is a voltage controlled electrochemical process, allowing the transformation of the
aluminium surface (and its alloys) in a nanoporous and amorphous oxide layer made of a structure
close to alumina. The aim of this treatment is to ensure a protection against corrosion, and/or to be
used as an adhesion base before bonding or before painting. Anodizing is generally sealed for corrosion
protection applications (with or without painting or bonding) and can remain unsealed when the part is
bonded or painted.
4.2 Applicability
4.2.1 Type A: unsealed anodizing
It shall be used either as surface preparation before the application of painting/bonding as specified in
Table 1 or any other finishing.
4.2.2 Type B: sealed anodizing
It is intended for corrosion protection. It shall be with or without dyeing and used with or without
additional painting, as specified in Table 1.
Table 1 — Different application cases
Anodizing process Unsealed (type A) Sealed (type B)
Bonding
Unpainted Painted Unpainted Painted
(structural)
Sulphuric acid anodizing (SAA)
according to EN 2284
Thin film sulphuric acid
anodizing (TFSAA) Applicable
Not applicable Applicable
Tartaric sulphuric acid
anodizing (TSA) according to
EN 4704
Not applicable Applicable
Boric sulphuric acid anodizing
(BSAA)
Phosphoric acid anodizing
Not applicable
(PAA)
Applicable Not applicable
Sulphuric phosphoric acid
anodizing (PSA)
4.3 Limitations
All processes that can compromise the anodic film such as forming, or heat-treatment shall be
performed prior to surface preparation of the parts to be anodized.
Anodizing shall not be applied:
— in electric conductivity zones/areas;
— for tubes, pipes and open holes with a length to diameter ratio higher than 10 : 1 (unless using
specific cathode);
— for trapped holes with a length to a diameter ratio greater than 5 : 1;
— for parts or assemblies (e.g. spot-welded and riveted), which can permanently entrap treatment
solutions;
— for components which can permanently entrap treatment solutions, except components that can be
adequately masked.
NOTE The formation of oxide layer influences the dimensions of the part and is to be considered for close
tolerance parts.
4.4 Classification
4.4.1 System types
Anodizing layer is classified by the two following types:
— type A: unsealed anodizing: It shall be used as surface preparation before the application of
painting/bonding or any other finish;
— type B: sealed anodizing: It is intended for corrosion protection. It shall be with or without dyeing
and used with or without additional painting.
4.4.2 Layer thickness
The layer thickness shall be as specified in Table 2.
Table 2 — Layer thicknesses corresponding to the class type
Class type Typical thickness Anodizing process
Phosphoric acid anodizing (PAA)
Class 1 ≤ 1 µm
a
Sulphuric phosphoric acid anodizing (PSA)
Tartaric sulphuric acid anodizing (TSA)
b, c
Class 2 Boric sulphuric acid anodizing (BSAA)
2 µm to 8 µm
Thin film sulphuric acid anodizing (TFSAA)
Class 3 8 µm to 25 µm Sulphuric acid anodizing (SAA)
a
≤ 5 µm for some aluminium alloys under agreement between the processor and the OEM/manufacturer.
b
For wrought alloys.
c
12 µm maximum for castings.
5 Process requirements
5.1 Information for the processor
— type and class designation;
— substrate standard reference and heat treatment;
— areas to be anodized;
— anodizing thickness measuring points;
— electrical contact points or areas where these are inadmissible;
— specification for testing on parts and/or test specimens.
5.2 Process conditions
5.2.1 Tooling
The tools, bars, electrical contact systems, and metal masking tooling shall be free of
oxidation/corrosion or any other damage which may be detrimental to the treatment during use. The
part racks and tools shall be designed and set up to:
— avoid any retention of air or treatment solution in the parts;
— facilitate neutralization and removal of solutions during rinsing operations;
— avoid any accidental contact between the parts to be treated and the tank equipment or electrodes,
and between the different parts during all the process.
— In addition:
— the electrical contacts shall be kept in good condition for the correct passage of the current;
— electrical contact points should be specified between the processor and the OEM/manufacturer;
— the contact is preferably achieved at several points in order to ensure better current distribution;
— the fixturing tools (e.g. made of aluminium alloy or titanium) shall provide effective electrical
contact with the parts.
5.2.2 Masking
The parts shall be at least degreased prior to masking.
Component areas which shall not be coated shall be masked with suitable material.
5.2.3 Surface preparation
Surface preparation stands for any method to eliminate all surface contaminations.
In case of chemical pre-treatment, the final step prior to anodizing shall be acidic pickling, preferably
chromate-free.
Anodizing shall be performed immediately after pickling in accordance with aluminium and aluminium
alloys pickling standard EN 4707.
5.2.4 Anodizing
During the anodizing process:
— distance between electrode and part(s) and between parts shall be adapted to avoid damage of
parts by short-circuits and electric arc discharge;
— parts should be fully immersed;
— the parts shall not be subjected to any tensile, flexure, torsion or other stress;
— the process shall be performed in such a way that parts remain wet between each step of the
process;
— the anodizing parameters (temperature, voltage, time) shall be adapted to the material and to the
chemical composition of the bath;
— in case of re-anodizing, the former protection shall be removed (chemically or mechanically)
(see 5.5). The surface shall be free of any residue.
5.2.5 Anodizing post-treatments
After the anodizing procedure:
— parts shall be adequately rinsed with water according to 5.3.4;
— afterwards, the parts shall be either:
— dried immediately and painted within 16 h; this time can be extended in accordance with the
OEM/manufacturer requirements. In this case, it is recommended to handle the parts after
anodizing treatment with gloves;
— dried immediately and bonded within 8 h; this time can be extended in accordance with the
OEM/manufacturer requirements. In this case, it is recommended to handle the parts after
anodizing treatment with gloves;
— sealed with chromate VI free solution to achieve the desired corrosion resistance of the anodic
film.
5.3 Water quality
5.3.1 General
All water used for bath make-up and addition in the anodizing bath, for the final rinsing step as well as
for the sealing process shall be demineralized.
5.3.2 Anodizing bath
The water shall comply with the following requirements:
— pH value at 25 °C: 5,0 to 8,0
— total residue [mg/l]: ≤ 5
— conductivity [µS/cm]: ≤ 20
5.3.3 Sealing and dyeing baths
The water shall comply with the following requirements:
— pH value at 25 °C: 5,0 to 8,0
— total residue [mg/l]: ≤ 5
— conductivity [µS/cm]: ≤ 20
— silica content [mg/l]: ≤ 1
5.3.4 Final rinsing bath
The water shall comply with the following requirements:
— pH value at 25 °C: 5,0 to 8,0
— total residue [mg/l]: ≤ 5
— conductivity [µS/cm]: ≤ 20
5.4 Periodic bath chemical analysis
The baths composition shall be in the limits as specified in the processor's detailed process instruction.
The periodicity of the analysis shall be specified considering the ageing, contamination and the
efficiency of the baths, the production rate and the re-adjustment or refilling of the baths.
5.5 Re-anodizing
Any re-anodizing shall be agreed between the processor and the OEM/manufacturer.
6 Test specimen requirements
6.1 Definition of test specimens
6.1.1 General
Unless otherwise stipulated by the OEM/manufacturer, the qualification authorizes the treatment of all
types of aluminium alloy.
6.1.2 For the qualification
See Table 3 for class 1: PAA, PSA.
See Table 4 for class 2: TFSAA, TSA, BSAA.
See Table 5 for class 3: SAA.
6.1.3 For periodic tests
See Table 6 for class 1: PAA, PSA.
See Table 7 for class 2: TFSAA, TSA, BSAA.
See Table 8 for class 3: SAA.
Table 3 — Definition of test specimens for the qualification (class 1: PAA, PSA)
Test specimens
Characteristic
Material Number Dimension
Visual appearance X X X
Anodic layer thickness X X X
Sealing quality
Sealed with hot water
Sealed with hot water
and additives
NA NA NA
Sealed in 2 steps:
Corrosion
st
1 step sealed with
resistance
inhibitors
nd
2 step sealed with hot
water
Painted X X X
Paint adhesion X X X
Fatigue performance X X X
Bonding performance X X X
X  According to the OEM/manufacturer requirements.
NA  Not applicable.
Table 4 — Definition of test specimens for the qualification (class 2: TFSAA, TSA, BSAA)
Test specimens
Characteristic
Material Number Dimension
Visual appearance X X
All test specim
...