FprEN 4908

SLOVENSKI STANDARD
oSIST prEN 4908:2023
01-april-2023
Aeronavtika - Postopek kemične pretvorbe magnezija in magnezijevih zlitin brez
šestvalentnega kroma
Aerospace series - Hexavalent chromium free chemical conversion process of
magnesium and magnesium alloys
Luft- und Raumfahrt - Chrom(VI)-freies chemisches Umwandlungsverfahren von
Magnesium und Magnesiumlegierungen
Série aérospatiale - Procédé de conversion chimique sans chrome hexavalent du
magnésium et des alliages de magnésium
Ta slovenski standard je istoveten z: prEN 4908
ICS:
49.025.15 Neželezove zlitine na Non-ferrous alloys in general
splošno
77.120.20 Magnezij in magnezijeve Magnesium and magnesium
zlitine alloys
oSIST prEN 4908:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN 4908:2023
oSIST prEN 4908:2023
DRAFT
EUROPEAN STANDARD
prEN 4908
NORME EUROPÉENNE
EUROPÄISCHE NORM
February 2023
ICS
English Version
Aerospace series - Hexavalent chromium free chemical
conversion process of magnesium and magnesium alloys
Série aérospatiale - Procédé de conversion chimique Luft- und Raumfahrt - Chrom(VI)-freies chemisches
sans chrome hexavalent du magnésium et des alliages Umwandlungsverfahren von Magnesium und
de magnésium Magnesiumlegierungen
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
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 4908:2023 E
worldwide for CEN national Members.

oSIST prEN 4908:2023
prEN 4908:2023 (E)
Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 General principle of the process . 5
4.1 Purpose of the process . 5
4.2 Limitations . 5
5 Process requirements . 5
5.1 Information for the processor . 5
5.2 Process schedule . 5
5.3 Process conditions . 6
5.4 Reworks . 7
5.5 Removal . 7
6 Test specimens requirements . 8
6.1 Test specimens specification . 8
6.2 Qualification tests . 8
6.3 Periodic testing . 8
7 Parts requirements . 8
7.1 Sampling plan for serial inspections . 8
7.2 Inspection on parts after treatment . 9
8 Quality assurance . 9
8.1 Process approval . 9
8.2 General points . 9
Annex A (normative) Tests on test specimens for the qualification and for periodic testing . 11
Annex B (normative) Tests on parts . 13
Annex C (normative) Acceptance criteria after corrosion test . 14

oSIST prEN 4908:2023
prEN 4908:2023 (E)
European foreword
This document (prEN 4908:2023) 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.
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.
oSIST prEN 4908:2023
prEN 4908:2023 (E)
1 Scope
This document specifies the requirements for the hexavalent chromium free chemical conversion
process of magnesium and magnesium alloys to ensure an adhesion base before bonding and painting.
The purpose of this document is to specify design, quality and manufacturing requirements. It does not
specify complete in-house process instructions; these are specified in the processors 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.
prEN 4902, Aerospace series — Surface treatments — Definitions and test methods
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 9227, Corrosion tests in artificial atmospheres - Salt spray tests (ISO 9227)
ASTM B117, Standard Practice for Operating Salt Spray (Fog) Apparatus
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 4902 and the following 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
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.
3.2
manufacturer
company or person who makes, manufactures, assembles components
Note 1 to entry: The manufacturer can also apply the process.
3.3
processor
company or person who applies the process

In preparation at the date of publication of this standard.
Published by ASTM International, available at: https://www.astm.org/.
oSIST prEN 4908:2023
prEN 4908:2023 (E)
3.4
process instruction
document that describes the application scopes, detailed process (e.g. key parameters, detailed steps),
quality management, environmental and safety regulations
3.5
batch
unless otherwise specified, it comprises parts of the same type (i.e. shape, size, material), processed at
the same time in the same bath
4 General principle of the process
4.1 Purpose of the process
The treatment consists of a superficial chemical transformation of the magnesium alloy parts obtained
by hexavalent chromium free chemical conversion process.
It is used to ensure an adhesion base before bonding and painting.
It is used either for local application or by immersion.
4.2 Limitations
All the heat treatment, shaping, brazing, welding and machining operations shall be carried out before
chemical conversion of the parts.
Before applying the conversion process, the surfaces of the parts shall be free from etching and
corrosion pitting.
5 Process requirements
5.1 Information for the processor
— Part number;
— Quantity of parts to be processed;
— Alloy to be processed.
5.2 Process schedule
It shall, as a minimum, have the following steps:
— alkaline degreasing;
— pickling;
— phosphate and permanganate based chemical conversion;
— post-treatment (such as paint, as per the requirement of the drawing).
oSIST prEN 4908:2023
prEN 4908:2023 (E)
5.3 Process conditions
5.3.1 Tooling
The tools, bars, 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;
— remain inert and not contaminate solutions of the process.
5.3.2 Masking
The parts shall be at least degreased prior to masking.
Component areas which shall not be coated shall be masked with suitable material.
The areas of the assemblies containing parts made of materials other than magnesium and its alloys
shall be masked during the chemical conversion treatment.
5.3.3 Surface preparation
5.3.3.1 Degreasing
Before applying the conversion process, the surfaces of the parts shall be clean, perfectly wettable.
The key operating parameters (e.g. nature of the product, temperature, time, pH) shall be set in a
procedure that will be approved by the OEM.
5.3.3.2 Mechanical preparation
For local applications where parts are prepared by mechanical surface roughening, a rinsing with
deionized water shall be performed to remove contamination (abrasive residues) from the surface to be
processed.
The key operating parameters (nature of the product and operating method) shall be set in a procedure
that will be approved by the OEM.
5.3.3.3 Chemical pickling
For magnesium alloys with silver, a specific preparation is recommended depending on the process
applied.
The stripping should be carried out using a solution without hexavalent chromium.
The pickling carried out shall make it possible to remove the natural oxides in order to obtain a correct
chemical conversion. It shall not cause the appearance of intergranular corrosion or pits.
The roughness characteristics and the dimension after pickling shall comply with the technical
definition of the article.
The key operating parameters (e.g. nature of the product, time, temperature) shall be set in a procedure
that will be approved by the OEM. Also, the pickling(s) to be carried out shall be specified in a process
instruction per alloy.
The chemical pickling operation shall always be followed by rinsing with deionized water.
oSIST prEN 4908:2023
prEN 4908:2023 (E)
5.3.4 Conversion
Conversion by immersion or touching up shall immediately follow the surface preparation, with no
break in wettability between the chemical preparation and the conversion treatment.
The key operating parameters (e.g. composition of the conversion solution, temperature, time, pH) shall
be set in a procedure that will be approved by the OEM.
After the conversion treatment, rinsing with deionized water is required, followed by drying.
5.3.5 Drying
Th
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