Overview
EN ISO 15329:2008 (ISO 15329:2006) specifies an electrochemical, anodic polarization test to evaluate the intergranular corrosion susceptibility of solution heat‑treatable aluminium alloys (notably 2XXX, 6XXX, 7XXX and 8XXX). The method applies to cast and wrought forms - castings, forgings, plates, sheets, extrusions and finished or semi‑finished parts - and is intended for comparative assessment of alloy grades, thicknesses and thermal‑processing quality. Results are relative indicators of intergranular corrosion resistance and quench/ageing performance, not absolute predictions of in‑service behaviour.
Key topics and technical requirements
- Test principle: anodic polarization in chloride solution to detect breakdown associated with intergranular attack; pitting‑initiation potential (Epi) is identified and an exposure is made at Eic = Epi + 50 mV.
- Applicable alloys: solution heat‑treatable aluminium 2XXX, 6XXX, 7XXX, 8XXX families.
- Specimens:
- Minimum three specimens of the same configuration for repeatable tests.
- Surface area for test electrode ≥ 1 cm²; surface roughness Ra ≈ 1 µm.
- Sampling should target representative zones (e.g., slowest cooling areas for quench checks).
- Surface preparation:
- Mechanical grinding, degreasing with an organic hydrocarbon solvent (boiling point 60–120 °C), rinsing and drying; optional ISO 11846 pre‑treatment.
- Electrochemical conditions:
- Test solution: sodium chloride, mass fraction 0.1%, prepared with water ≤ 10 µS/cm.
- Volume-to-specimen area ratio ≥ 50 ml/cm²; solution level 20 mm above specimens.
- Temperature: 18–25 °C; cell with working, platinum auxiliary and calomel or Ag/AgCl reference electrodes.
- Polarization scan: from E = −2.00 V (hydrogen electrode scale) at 50 mV/min to determine Epi.
- Exposure at Eic for copper‑containing alloys (0.25–6.5 % Cu): 10 ± 1 min; copper‑free alloys (≤ 0.25 % Cu): 40 ± 5 min.
- Examination and assessment:
- Metallographic analysis at ×5–×20 magnification; evaluate type (pitting vs intergranular), depth and extent of attack to interpret susceptibility and thermal‑processing quality.
Applications and users
- Who uses it: corrosion engineers, materials and metallurgical laboratories, heat‑treatment quality control, alloy suppliers, and OEM qualification teams.
- Practical uses:
- Comparative screening of heats and tempers for intergranular corrosion resistance.
- Verification of quench and ageing processes in production control.
- Supporting material selection and failure analysis for components made from heat‑treatable aluminium alloys.
- Note: test outcomes are best used comparatively and must be correlated with expected service environments.
Related standards
- ISO 11846 - determination of resistance to intergranular corrosion of solution heat‑treatable aluminium alloys
- ISO 3696 - water for analytical laboratory use
- ISO 8044 - corrosion of metals and alloys: basic terms and definitions
Keywords: ISO 15329, EN ISO 15329:2008, intergranular corrosion, anodic test, anodic polarization, heat‑treatable aluminium alloys, corrosion testing, pitting‑initiation potential.