Aerospace series - Micro-arc oxidation of aluminium and aluminium alloys

This document defines the requirements for micro-arc oxidation of aluminium and aluminium alloys for corrosion protection, wear, erosion, dielectric and thermal properties.
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 processors detailed process instructions.
This document relates only to micro-arc oxidation. It does not relate to finishing techniques, such as mechanical post treatment.

Luft- und Raumfahrt - Mikrolichtbogenoxidation von Aluminium und Aluminiumlegierungen

Série aérospatiale - Oxydation micro-arc de l'aluminium et des alliages d'aluminium

Le présent document définit les exigences relatives à l’oxydation micro-arc de l'aluminium et des alliages d'aluminium, et ses propriétés diélectriques, thermiques, de protection contre la corrosion, l’usure et l’érosion.
L’objet du présent document est d’indiquer les exigences de conception, de qualité et de fabrication. Il ne donne pas de gamme de production complète ; ces informations sont données dans les instructions détaillées de l’applicateur relatives au procédé.
Le présent document se rapporte uniquement à l’oxydation micro-arc. Il ne concerne pas les techniques de finition comme le traitement post-opératoire mécanique.

Aeronavtika - Mikroobločna oksidacija aluminija in aluminijevih zlitin

General Information

Status
Not Published
Current Stage
4060 - Closure of enquiry - Enquiry
Due Date
12-Aug-2021
Completion Date
12-Aug-2021

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SLOVENSKI STANDARD
oSIST prEN 4881:2021
01-julij-2021
Aeronavtika - Mikroobločna oksidacija aluminija in aluminijevih zlitin
Aerospace series - Micro-arc oxidation of aluminium and aluminium alloys
Luft- und Raumfahrt - Mikrolichtbogenoxidation von Aluminium und
Aluminiumlegierungen

Série aérospatiale - Oxydation micro-arc de l'aluminium et des alliages d'aluminium

Ta slovenski standard je istoveten z: prEN 4881
ICS:
25.160.10 Varilni postopki in varjenje Welding processes
49.025.20 Aluminij Aluminium
oSIST prEN 4881:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 4881:2021
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oSIST prEN 4881:2021
DRAFT
EUROPEAN STANDARD
prEN 4881
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2021
ICS 25.160.10; 49.025.20
English Version
Aerospace series - Micro-arc oxidation of aluminium and
aluminium alloys

Série aérospatiale - Oxydation micro-arc de Luft- und Raumfahrt - Mikrolichtbogenoxidation von

l'aluminium et des alliages d'aluminium Aluminium und Aluminiumlegierungen

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, Turkey 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

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 4881:2021 E

worldwide for CEN national Members.
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oSIST prEN 4881:2021
prEN 4881:2021 (E)
Contents Page

European foreword ...................................................................................................................................................... 4

1 Scope .................................................................................................................................................................... 5

2 Normative references .................................................................................................................................... 5

3 Terms and definitions ................................................................................................................................... 5

3.1 General terms ................................................................................................................................................... 5

3.2 Technical terms ............................................................................................................................................... 6

4 General principles of the process ............................................................................................................. 7

4.1 Purpose of the process .................................................................................................................................. 7

4.2 Applicability ...................................................................................................................................................... 7

4.2.1 Type A: As processed ..................................................................................................................................... 7

4.2.2 Type B: After blasting operation ............................................................................................................... 7

4.2.3 Type C: After machining operation........................................................................................................... 8

4.3 Limitations ........................................................................................................................................................ 8

4.4 Classifications .................................................................................................................................................. 8

4.4.1 System Types .................................................................................................................................................... 8

4.4.2 Layer thicknesses............................................................................................................................................ 8

5 Process requirements ................................................................................................................................... 9

5.1 Information for the processor .................................................................................................................... 9

5.2 Process schedule (information) ................................................................................................................ 9

5.3 Process conditions .......................................................................................................................................... 9

5.3.1 Tooling ................................................................................................................................................................ 9

5.3.2 Masking ............................................................................................................................................................ 10

5.3.3 Surface pre-treatment ................................................................................................................................. 10

5.3.4 Micro-arc oxidation ...................................................................................................................................... 10

5.3.5 Micro-arc oxidation post-treatments .................................................................................................... 11

5.3.6 Water quality .................................................................................................................................................. 12

5.4 Periodic bath chemical analysis .............................................................................................................. 12

5.5 Re-processing ................................................................................................................................................. 12

5.6 Glass bead blasting of the friable/porous layer................................................................................. 13

5.7 Machining ........................................................................................................................................................ 13

6 Test specimens requirements .................................................................................................................. 13

6.1 General.............................................................................................................................................................. 13

6.2 Materials .......................................................................................................................................................... 13

6.3 Tests for the qualification .......................................................................................................................... 13

6.4 Periodic tests .................................................................................................................................................. 13

7 Past requirements ........................................................................................................................................ 13

7.1 Conditions of parts prior to the treatment .......................................................................................... 13

7.2 Inspections before the processing .......................................................................................................... 14

7.3 Inspections after micro-arc oxidation ................................................................................................... 14

8 Quality assurance ......................................................................................................................................... 14

8.1 Process approval ........................................................................................................................................... 14

8.2 General.............................................................................................................................................................. 14

Annex A (normative) Tests on test specimens for the qualification ......................................................... 15

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Annex B (normative) Periodic tests on test specimens ................................................................................. 19

Annex C (normative) Tests on parts ..................................................................................................................... 22

Annex D (normative) Wear resistance test ........................................................................................................ 23

D.1 General ............................................................................................................................................................. 23

Bibliography ................................................................................................................................................................. 24

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oSIST prEN 4881:2021
prEN 4881:2021 (E)
European foreword

This document (prEN 4881:2021) 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 document is currently submitted to the CEN Enquiry.
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oSIST prEN 4881:2021
prEN 4881:2021 (E)
1 Scope

This document defines the requirements for micro-arc oxidation of aluminium and aluminium alloys for

corrosion protection, wear, erosion, dielectric and thermal properties.

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 processors detailed process

instructions.

This document relates only to micro-arc oxidation. It does not relate to finishing techniques, such as

mechanical post treatment.
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 6072, Aerospace series - Metallic materials - Test methods - Constant amplitude fatigue testing

EN ISO 2409, Paints and varnishes - Cross-cut test (ISO 2409)

EN ISO 4516, Metallic and other inorganic coatings - Vickers and Knoop microhardness tests (ISO 4516)

EN ISO 9227, Corrosion tests in artificial atmospheres - Salt spray tests (ISO 9227)

ASTM D4060, Standard Test Method for Abrasion Resistance of Organic Coatings by the Taber Abraser

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/
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 manufacturer can also apply the process.
3.1.2
manufacturer
company or person who makes, manufactures, assembles components
3.1.3
processor
company or person who applies the process
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prEN 4881:2021 (E)
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

parts of the same type (i.e. shape, size, material), processed at the same time in the same bath

Note 1 to entry: Unless otherwise specified.
3.2 Technical terms
3.2.1
mechanically disturbed layer
MDL

layer that is present at the surface resulting from the heat treatment and rolling process of the material

3.2.2
pit

surface corrosion defect at which the oxide layer 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 must exhibit at least two of the above characteristics.

3.2.3
MAO layer
layer which is constituted of a friable/porous layer and a functional layer
Note 1 to entry: See Figure 1.
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oSIST prEN 4881:2021
prEN 4881:2021 (E)
Key
1 Friable/porous layer
Hard ceramic (mainly α-Al O )
2 3
3 Aluminium
4 Functional layer
5 Initial surface
Figure 1 — MAO layer
3.2.4
functional layer

functional and hard part of the coating useful for wear application and paint adhesion (porous)

4 General principles of the process
4.1 Purpose of the process

Plasma electrolytic oxidation (PEO) or micro arc oxidation (MAO) is an electrochemical process of

anodization that is performed thanks to micro-discharges created on the surface of components

immersed in an electrolyte. The process is applied to aluminium, titanium, and magnesium to grow a

dense ceramic oxide layer that improves mechanical, wear, thermal, dielectric, and corrosion

properties.

A controlled high alternating current is applied to a metal part immersed in an electrolytic bath. Due to

this current and significant voltage resulting, micro-discharges as well as the development of an intense

plasma are created on the surface of the metal. This plasma oxidizes the surface of the part and a

ceramic oxide layer grows from the substrate material. The oxide layer is produced by subsurface

oxidation. As a result, the process can produce very thick coatings of varying porosity.

This specification applies to aluminium and aluminium alloys.
4.2 Applicability
4.2.1 Type A: As processed
This type of coating can be painted.
4.2.2 Type B: After blasting operation
It is intended for wear applications.
This type of coating can be painted.
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4.2.3 Type C: After machining operation

It is intended for either wear or erosion applications when tightened geometrical tolerances may be

achieved.
4.3 Limitations

All processes that can compromise the oxide layer such as forming, or heat-treatment shall be

performed prior to surface preparation of the parts to be oxidized.
Oxidizing should not be applied:
• in zones/areas ensuring electric conductivity;

• for tubes, pipes and open holes with a length to diameter ratio higher than 5:1 (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, except components that can be adequately masked.

The formation of oxide layer influences the dimensions of the part and is to be considered for close

tolerance parts (growth of 1/3 of thickness).
4.4 Classifications
4.4.1 System Types
Micro-arc oxidation layer is classified by the three following types:
• type A: as processed;
• type B: after blasting operation;
• type C: after machining operation.
4.4.2 Layer thicknesses
See Table 1.
Table 1 — Layer thicknesses corresponding to the class type
Class MAO typical Type Typical final Recommended application
type thickness correspondence thickness
For paint application
Class
30 μm to 60 μm Type A 30 μm to 60 µm
High roughness
For corrosion application
Type A 60 μm to 120 µm
Class 60 μm to
No specific surface condition
2 120 µm
Type B 50 μm to 90 µm
required
For corrosion application
Low friction coefficient
Class 100 μm to
Type C 60 μm to 100 µm
3 200 μm
Close tolerances
Optimized surface condition
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5 Process requirements
5.1 Information for the processor
Type and class designation;
• substrate standard reference and heat treatment;
• areas to be protected;
• oxidation thickness measuring points;
• electrical contact points or areas where these are inadmissible;
• specification for testing on parts and/or test specimens.
5.2 Process schedule (information)

1) only for type C: initial grinding of the area to be coated (to the required end-dimensions);

2) alkaline degreasing or degreasing with solvent;
3) fitting of the part on the masking and treatment tooling;
4) micro-arc oxidation;
5) rinsing;
6) only for type B: glass bead blasting: removal of the friable/porous layer;
7) only for type C: final grinding.
5.3 Process conditions
5.3.1 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 in such a manner as to:
• avoid any retention of air or treatment solution in the parts;
• facilitate neutralization and removal of solutions during rinsing operations;

• the electrical contacts shall be kept in good condition for the correct passage of the current;

• 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;

• electrical contact points should be agreed between purchaser and processor; use of screws,

fixturing on threaded areas or mechanical fixtures as electrical contact area is recommended to

ensure a firm contact;

• the fixturing tools (e.g. in aluminium alloy or titanium) shall provide effective electrical contact with

the parts;
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• the contact is preferably achieved at several points in order to ensure better current distribution.

Use of conforming electrodes is necessary to ensure better thickness distribution. These electrodes

should be made of corrosion resistant steel (other conductive material can be used provided that

innocuity with electrolyte is demonstrated).
5.3.2
...

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