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.
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