Overview
ISO 15329:2006 - "Corrosion of metals and alloys - Anodic test for evaluation of intergranular corrosion susceptibility of heat‑treatable aluminium alloys" - specifies an electrochemical (anodic polarisation) method to assess susceptibility to intergranular corrosion of solution‑heat‑treatable aluminium alloys (2XXX, 6XXX, 7XXX, 8XXX). The standard applies to cast and wrought alloys in castings, forgings, plates, sheets, extrusions and finished parts. Results provide a comparative measure of intergranular corrosion resistance and the quality of solution heat treatment, but are intended for relative assessment and must be correlated with service performance.
Key topics and technical requirements
- Test principle: anodic polarisation in chloride solution to identify pitting‑initiation potential (Epi) and an impressed potential (Eic = Epi + 50 mV) to provoke intergranular attack.
- Test medium & conditions:
- Sodium chloride solution, 0.1% mass fraction.
- Test temperature: 18–25 °C.
- Use distilled/deionized water (conductivity ≤ 10 µS/cm).
- Electrochemical setup:
- Potentiostat for controlled scans (scan rate 50 mV/min).
- Auxiliary electrode: platinum; reference: calomel or Ag/AgCl.
- Initial scan from a cathodic potential (reported example E = −2.00 V vs hydrogen) to determine Epi.
- Specimens & preparation:
- Representative sampling; at least three specimens per test.
- Mechanical grinding, degreasing (hydrocarbon solvent, bp 60–120 °C), rinsing and drying.
- Minimum exposed surface area: ≥ 1 cm²; surface roughness Ra ≈ 1 µm.
- Solution volume ≥ 50 ml per cm² of specimen area.
- Exposure:
- After finding Epi, expose at Eic for:
- Copper‑containing alloys (0.25–6.5% Cu): 10 min ±1 min.
- Copper‑free alloys (≤ 0.25% Cu): 40 min ±5 min.
- Examination & assessment:
- Metallographic sectioning and microscopy (×5–×20 to locate zones, ×200 for details).
- Rating by maximum corrosion depth (rating 1–5 from excellent to very poor).
- Required reporting items include alloy designation/composition, pitting potential, exposure time, corrosion type, current at Epi, and rating.
Applications and who uses it
- Quality control of solution heat treatment and quench practices for heat‑treatable aluminium alloys.
- Comparative alloy screening during material selection for aerospace, automotive, marine and structural applications.
- Corrosion testing laboratories, materials engineers, heat‑treatment suppliers, and OEM quality assurance teams.
Related standards
- ISO 11846 - intergranular corrosion determination (related procedures).
- ISO 3696 - water for analytical laboratory use.
- ISO 8044 - corrosion terms and definitions.
Keywords: ISO 15329, anodic test, intergranular corrosion, aluminium alloys, electrochemical method, pitting potential, metallographic examination, solution heat treatment.