ISO 3079:2022

Two-electrode method using acetic acid to measure pitting potential of aluminium and aluminium alloys in chloride solutions

This document specifies a test method for the measurement of the pitting potential of aluminium and aluminium alloys in sodium chloride solution of a mass fraction of 5 %, with a fixed concentration of acetic acid as the oxidant, using a two-electrode system. This document provides a simple method for ranking aluminium alloys and is especially useful for evaluating galvanic protection performance of thin clad materials because the test method causes little specimen damage.

Méthode à deux électrodes utilisant l'acide acétique pour mesurer le potentiel de piqûre de l'aluminium et des alliages d'aluminium dans des solutions de chlorure

General Information

• Status: Published
• Publication Date: 13-Nov-2022
• ICS: 77.060 - Corrosion of metals
• Technical Committee: ISO/TC 156 - Corrosion of metals and alloys
• Drafting Committee: ISO/TC 156/WG 11 - Electrochemical test methods
• Current Stage: 6060 - International Standard published
• Start Date: 14-Nov-2022
• Due Date: 07-Dec-2022
• Completion Date: 14-Nov-2022

Overview

ISO 3079:2022 specifies a two-electrode test method using acetic acid to measure the pitting potential of aluminium and aluminium alloys in chloride environments. The method uses a 5 % sodium chloride solution with a controlled acetic acid concentration as the oxidant and provides a simple, low-damage approach for ranking alloys and assessing galvanic protection performance, especially for thin clad materials.

Key topics and requirements

• Test solution: sodium chloride mass fraction of 5 %; acetic acid added as oxidant. The acetic acid concentration is chosen so the corrosion potential stabilizes; 1 ml/L glacial acetic acid is adequate for most alloys (except very high-purity aluminium).
• Electrochemical system: simple two-electrode arrangement (working electrode and reference electrode) connected to a potentiometer with internal resistance > 10 Ω.
• Electrodes:
  • Working electrode: specimen area 1 cm², other areas masked or embedded in inert material (resin).
  • Reference electrode: saturated silver/silver chloride electrode (SSE) recommended (SCE permitted).
• Specimen preparation: pre-treat with NaOH (50 g/L, 60 °C, 30 s), rinse, then HNO3 (30 % mass fraction, 25 °C ±5 °C, 60 s), rinse and immediately immerse while wet.
• Test conditions:
  • Temperature 25 °C ± 1 °C.
  • Stirring at least 60 rpm; solution volume to test area ≥ 100 mL/cm².
  • Measurement interval 1 min, test duration 60 min.
• Evaluation: corrosion potential averaged over 30–60 min; at least two repeated tests. Inspect pits and check for crevice attack under resin.
• Advantages: less specimen damage than anodic polarization curves, shorter time, smaller area, repeatable measurements (useful for depth profiling of clad layers).

Applications and users

• Corrosion engineers and materials scientists evaluating pitting resistance of aluminium alloys.
• Quality control and testing laboratories performing alloy ranking or routine pitting-potential screening.
• Manufacturers of aluminium-clad components, notably heat exchangers in automotive and HVAC/R industries, assessing galvanic protection performance of thin clads.
• R&D teams developing new alloys or coatings where minimal specimen damage and repeated measurements are needed.

Related standards

• ASTM G69 - two-electrode pitting/corrosion potential method using H2O2 (historical comparator mentioned in ISO 3079).
• ISO 17474 - reference for electrode potentials relative to the standard hydrogen electrode.

ISO 3079:2022 is a practical, low-damage electrochemical test standard for reliable pitting-potential measurement of aluminium alloys in chloride solutions, optimized for ranking materials and assessing galvanic protection performance.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 3079
First edition
2022-11
Two-electrode method using acetic
acid to measure pitting potential of
aluminium and aluminium alloys in
chloride solutions
Méthode à deux électrodes utilisant l'acide acétique pour mesurer le
potentiel de piqûre de l'aluminium et des alliages d'aluminium dans
des solutions de chlorure
Reference number
© ISO 2022
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Field of application . 1
5 Comparison with conventional methods . 1
5.1 Anodic polarization curve measurement . 1
5.2 Corrosion potential. 2
6 General principles . 2
7 Apparatus . 3
7.1 Potentiometer . 3
7.2 Working electrode . 3
7.3 Reference electrode . 3
7.4 Stirrer . 3
8 Specimen . 4
9 Test procedure .4
9.1 Solution . 4
9.2 Test set-up . 5
9.3 Evaluation . 6
10 Test report . 6
Bibliography . 8
iii
Foreword
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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
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iv
Introduction
Aluminium and aluminium alloys show excellent corrosion resistance in near-neutral environments as
a result of the formation of an oxide or hydroxide film on their surface, thereby achieving passivation.
However, if the environment contains the chloride ion, the passive film will be broken, and localized
corrosion, such as pitting corrosion, can occur. Aluminium-clad material is used to prevent localized
corrosion by galvanic protection. In this method, the underlying core aluminium is protected by a
sacrificial layer whose pitting potential is lower than that of the core aluminium. Therefore, in order to
estimate the performance of galvanic protection, it is important to obtain the pitting potential.
Although anodic polarization curve measurement is one method for obtaining the pitting potential, the
method described in the test method in this document has several advantages in that it causes less
specimen damage, has a shorter measurement time and smaller specimen area, multiple measurements
are possible, and a two-electrode system is used. In an anodic polarization curve measurement, the
specimen is severely corroded due to excessive polarization. The method described in this document
causes less specimen corrosion, as the degree of polarization is small because the potential is maintained
near the pitting potential. This makes it possible to conduct repeated etching and measurements with
the same specimen, which is particularly useful for measurement of the depth profile of the pitting
potential in thin clad materials. As a method for measuring the corrosion potential of aluminium
alloys, ASTM G69 was established in 1997. ASTM G69 is widely used, substantially to obtain the pitting
potential without the anodic polarization curve measurement. In ASTM G69, 1 M (a mass fraction of
5,85 %) of sodium chloride is used as the solution and hydrogen peroxide is used as the oxidant. The
test method in this document, where a sodium chloride mass fraction of 5 % is used as the solution
and acetic acid is used as the oxidant, also has advantages over ASTM G69. In particular, it causes less
specimen damage and has a more stable oxidant with a buffer action.
v
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