SIST EN ISO 20728:2018

Corrosion of metal and alloys - Determination of resistance of magnesium alloys to stress corrosion cracking (ISO 20728:2018)

This document specifies a method for the determination of resistance to stress corrosion cracking (SCC) of magnesium alloys intended for use in structural applications (such as magnesium front end, gearbox and clutch housing units, steering column parts, shift actuators, valve covers and housings, brackets and intake manifold blades, electronic devices, power tools and medical equipment). The method allows determination of the resistance to SCC as a function of the chemical composition, the method of manufacture and heat treatment of magnesium alloys.
The document is applicable to cast and wrought magnesium alloys in the form of castings, semi-finished products, parts and weldments and covers the method of sampling, the types of specimens, the loading procedure, the type of environment and the interpretation of results.
The document allows assessment of the relative performance of materials and products in environments containing chlorides or sulphates, provided that the failure mechanism is not changed, but does not qualify a material or product for service application.

Korrosion von Metall und Legierungen - Bestimmung der Beständigkeit von Magnesiumlegierungen gegen Spannungsrisskorrosion (ISO 20728:2018)

Corrosion des métaux et alliages - Détermination de la résistance des alliages de magnésium à la fissuration par corrosion sous contrainte (ISO 20728:2018)

Le présent document spécifie une méthode pour la détermination de la résistance à la corrosion sous contrainte (CSC) d'alliages de magnésium destinés à être utilisés dans des applications structurales (tels les trains avant de véhicule en magnésium, les carters de boîte de vitesses et d'embrayage, les pièces de colonne de direction, les actionneurs de boîte de vitesses, les couvercles et logements de soupapes, les brides et lames de collecteur d'admission, les dispositifs électroniques, les outils électriques et les appareils médicaux). Cette méthode permet de déterminer la résistance à la corrosion sous contrainte en fonction de la composition chimique, du procédé de fabrication et du traitement thermique des alliages de magnésium.
Le présent document s'applique aux alliages de magnésium coulés et corroyés se présentant sous forme de produits moulés, produits semi-finis, pièces et assemblages soudés; il couvre la méthode d'échantillonnage, les types d'éprouvettes, le mode opératoire de mise en charge, le type de milieu et l'interprétation des résultats.
Le présent document permet d'évaluer la performance relative de matériaux et de produits dans des milieux contenant des chlorures ou des sulfates, à condition que le mécanisme de rupture ne soit pas modifié, mais il ne qualifie pas un matériau ou un produit pour son application en service.

Korozija kovin in zlitin - Ugotavljanje odpornosti magnezijevih zlitin proti pokanju zaradi napetostne korozije (ISO 20728:2018)

Ta mednarodni standard določa metodo za ugotavljanje odpornosti magnezijevih zlitin proti pokanju zaradi napetostne korozije (SCC). Ta mednarodni standard zajema metodo vzorčenja, vrste vzorcev, postopek nalaganja, vrsto okolja in razlago rezultatov. Ta mednarodni standard je namenjen ugotavljanju odpornosti proti pokanju zaradi napetostne korozije kot funkcije kemijske sestave, načina proizvodnje in toplotne obdelave magnezijevih zlitin. Ta mednarodni standard se uporablja za ulite in gnetene magnezijeve zlitine v obliki ulitkov, polizdelkov, delov in zvarov. Večina naravnih okolij in številna umetna okolja vsebujejo kloride, zato se lahko ta mednarodni standard uporablja za primerjavo zmogljivosti izdelkov, ki se uporabljajo v okoljih z vsebnostjo kloridov, pri čemer mora mehanizem okvare ostati enak. Vendar se rezultati tega preskusa naj ne bi upoštevali kot absolutno merilo za kakovost zlitin.

General Information

• Status: Published
• Public Enquiry End Date: 14-Jul-2017
• Publication Date: 11-Nov-2018
• ICS: 77.060 - Corrosion of metals
• ICS: 77.120.20 - Magnesium and magnesium alloys
• Technical Committee: IPKZ - Protection of metals against corrosion
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 22-Oct-2018
• Due Date: 27-Dec-2018
• Completion Date: 12-Nov-2018
• Ref Project: EN ISO 20728:2018 - Corrosion of metal and alloys - Determination of resistance of magnesium alloys to stress corrosion cracking (ISO 20728:2018)

Overview

EN ISO 20728:2018 - "Corrosion of metal and alloys - Determination of resistance of magnesium alloys to stress corrosion cracking" - is a test-method standard published by ISO and adopted by CEN. It specifies procedures to evaluate the stress corrosion cracking (SCC) resistance of magnesium alloys used in structural applications (cast and wrought forms, castings, semi‑finished products, parts and weldments). The method links SCC performance to chemical composition, manufacturing route and heat treatment, and covers sampling, specimen preparation, loading procedures, test environments and result interpretation.

Key topics and technical requirements

• Scope and applicability
  • Applicable to magnesium alloys intended for structural components (e.g., housings, brackets, electronic housings, medical devices).
  • Enables relative assessment in environments containing chlorides or sulphates, provided the failure mechanism remains the same; it does not qualify a material for service.
• Specimen and sampling
  • Defines specimen types, sizes, surface preparation and identification to account for microstructural orientation effects on SCC.
• Loading methods
  • Supports multiple loading approaches: constant load, constant strain, and slow strain rate testing (SSRT). Loading selection and evaluation criteria should be agreed between parties based on test purpose.
• Test environments and immersion
  • Allows continuous immersion and alternate immersion techniques; recommends stagnant conditions for continuous immersion to avoid secondary effects from stirring.
• Apparatus and materials
  • Specifies requirements for corrosion cells, specimen holders and materials (use of inert plastics/glass where feasible; isolation of metallic parts to prevent galvanic coupling).
• Assessment and reporting
  • Provides guidance for result interpretation, performance comparison and mandatory elements of the test report.

Applications and users

• Intended for:
  • Materials engineers, corrosion specialists and R&D teams evaluating magnesium alloy SCC resistance.
  • Manufacturers of automotive, aerospace, electronics, power tools and medical components that use magnesium alloys.
  • Test laboratories performing corrosion testing, supplier qualification and comparative material screening.
• Practical uses:
  • Comparative ranking of alloy variants, influence of heat treatment/process route on SCC, and screening of coating/processing options before component qualification.

Related standards

• ISO 7539 series (general SCC guidance, specimen preparation, SSRT methods)
• ISO 8044 (basic corrosion terms and definitions)

Keywords: EN ISO 20728:2018, magnesium alloys, stress corrosion cracking, SCC testing, corrosion testing, slow strain rate, alternate immersion, chlorides, sulphates.

Standards Content (Sample)

SLOVENSKI STANDARD
01-december-2018
Korozija kovin in zlitin - Ugotavljanje odpornosti magnezijevih zlitin proti pokanju
zaradi napetostne korozije (ISO 20728:2018)
Corrosion of metal and alloys - Determination of resistance of magnesium alloys to
stress corrosion cracking (ISO 20728:2018)
Korrosion von Metall und Legierungen - Bestimmung der Beständigkeit von
Magnesiumlegierungen gegen Spannungsrisskorrosion (ISO 20728:2018)
Corrosion des métaux et alliages - Détermination de la résistance des alliages de
magnésium à la fissuration par corrosion sous contrainte (ISO 20728:2018)
Ta slovenski standard je istoveten z: EN ISO 20728:2018
ICS:
77.060 Korozija kovin Corrosion of metals
77.120.20 Magnezij in magnezijeve Magnesium and magnesium
zlitine alloys
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 20728
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2018
EUROPÄISCHE NORM
ICS 77.060
English Version
Corrosion of metal and alloys - Determination of resistance
of magnesium alloys to stress corrosion cracking (ISO
20728:2018)
Corrosion des métaux et alliages - Détermination de la Korrosion von Metall und Legierungen - Bestimmung
résistance des alliages de magnésium à la fissuration der Beständigkeit von Magnesiumlegierungen gegen
par corrosion sous contrainte (ISO 20728:2018) Spannungsrisskorrosion (ISO 20728:2018)
This European Standard was approved by CEN on 6 September 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20728:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 20728:2018) has been prepared by Technical Committee ISO/TC 156
"Corrosion of metals and alloys" in collaboration with Technical Committee CEN/TC 262 “Metallic and
other inorganic coatings, including for corrosion protection and corrosion testing of metals and alloys”
the secretariat of which is held by BSI.
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 April 2019, and conflicting national standards shall be
withdrawn at the latest by April 2019.
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.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 20728:2018 has been approved by CEN as EN ISO 20728:2018 without any modification.

INTERNATIONAL ISO
STANDARD 20728
First edition
2018-09
Corrosion of metal and alloys —
Determination of resistance of
magnesium alloys to stress corrosion
cracking
Corrosion des métaux et alliages — Détermination de la résistance
des alliages de magnésium à la fissuration par corrosion sous
contrainte
Reference number
ISO 20728:2018(E)
©
ISO 2018
ISO 20728:2018(E)
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 20728:2018(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General principles . 2
5 Apparatus and materials. 2
5.1 Loading apparatus . 2
5.2 Construction materials for the test set-up . 2
5.3 Specimen holders . 2
5.4 Apparatus for alternate immersion in solutions . 3
6 Sampling . 3
7 Specimens . 5
7.1 Type and sizes. 5
7.2 Surface preparation . 5
7.3 Specimen identification . 6
7.4 Precautions . 6
8 Test environments . 6
9 Loading . 7
10 Procedure. 7
11 Assessment of results . 8
12 Expression of results . 9
13 Test report . 9
Annex A (informative) Assessment of grain size and orientation .11
Bibliography .12
ISO 20728:2018(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
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expressions related to conformity assessment, as well as information about ISO’s adherence to the
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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2018 – All rights reserved

INTERNATIONAL STANDARD ISO 20728:2018(E)
Corrosion of metal and alloys — Determination of
resistance of magnesium alloys to stress corrosion
cracking
WARNING — This document calls for the use of substances and/or procedures that can
be injurious to health if adequate safety measures are not taken. This document does not
address any health hazards, safety or environmental matters associated with its use. It is
the responsibility of the user of this document to establish appropriate health, safety and
environmentally acceptable practices.
1 Scope
This document specifies a method for the determination of resistance to stress corrosion cracking
(SCC) of magnesium alloys intended for use in structural applications (such as magnesium front end,
gearbox and clutch housing units, steering column parts, shift actuators, valve covers and housings,
brackets and intake manifold blades, electronic devices, power tools and medical equipment). The
method allows determination of the resistance to SCC as a function of the chemical composition, the
method of manufacture and heat treatment of magnesium alloys.
The document is applicable to cast and wrought magnesium alloys in the form of castings, semi-finished
products, parts and weldments and covers the method of sampling, the types of specimens, the loading
procedure, the type of environment and the interpretation of results.
The document allows assessment of the relative performance of materials and products in environments
containing chlorides or sulphates, provided that the failure mechanism is not changed, but does not
qualify a material or product for service application.
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.
ISO 7539-1, Corrosion of metals and alloys — Stress corrosion testing — Part 1: General guidance on testing
procedures
ISO 7539-4, Corrosion of metals and alloys — Stress corrosion testing — Part 4: Preparation and use of
uniaxially loaded tension specimens
ISO 7539-7:2005, Corrosion of metals and alloys — Stress corrosion testing — Part 7: Method for slow
strain rate testing
ISO 8044, Corrosion of metals and alloys — Basic terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8044 and ISO 7539-1 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 http: //www .electropedia .org/
ISO 20728:2018(E)
4 General principles
4.1 Stress corrosion cracking of magnesium alloys is sensitive to microstructural orientation with
respect to the stress axis. Accordingly, in testing SCC resistance, it is necessary to consider the manner
in which the specimens are prepared from cast or wrought alloy so that orientation dependent SCC
resistance can be assessed.
4.2 The corrosion of magnesium is associated with hydrogen evolution and generation of often very
soluble corrosion products. For that reason, testing in stagnant conditions is preferred during continuous
immersion as stirring can cause secondary effects, e.g. removal of corrosion product.
4.3 Two methods of immersion in the solution are proposed:
— alternate immersion;
— continuous immersion.
4.4 Tests may be conducted under constant load, constant strain or by the slow strain rate technique
with evaluation criteria for stress corrosion cracking resistance appropriate to the chosen loading method.
4.5 The method of loading, the value of stresses, corrosive environment and criteria of evaluation
should be agreed between the interested parties according to the purpose of the testing.
5 Apparatus and materials
5.1 Loading apparatus
Tensile stresses in the specimens are produced with yokes, stressing screws, springs, lever devices and
special testing machines.
5.2 Construction materials for the test set-up
5.2.1 If in contact with the corrosive environment, the construction materials for the test set-up shall
not be affected by the corrodent to such an extent that they can cause contamination of the solution and
change its corrosiveness.
5.2.2 Use of inert plastics or glass is recommended for the corrosion cell where feasible.
5.2.3 Metallic components in contact with the solution shall be made from an appropriate corrosion
resistant material, or protected with a suitable corrosion-resistant coating, sufficient to avoid galvanic
coupling.
5.3 Specimen holders
5.3.1 The specimen holders shall be designed to electrically insulate the specimens from each other
and from any bare metal parts. When this is not possible, as in the case of certain stressing bolts or
jigs, the bare metal contacting the specimen shall be isolated from the corrodent by a suitable coating.
Protective coatings shall be of a type that will not leach inhibiting or accelerating ions or protective oils or
leave any residue, e.g. vapour, on the non-coated portions of the specimen holder. In particular, coatings
containing chromates or releasing any other contaminants should be avoided. All samples holders should
be degrea
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