ISO 11881:1999

Overview

ISO 11881:1999 - "Corrosion of metals and alloys - Exfoliation corrosion testing of aluminium alloys" - specifies procedures for accelerated, constant-immersion exfoliation corrosion testing of aluminium alloys. Intended primarily for research, development and quality control, the standard describes required specimen preparation, exposure conditions, inspection and interpretation of results. It warns that hazardous materials and operations may be involved and that users must follow appropriate safety practices.

Key topics and technical requirements

• Scope and purpose: Accelerated, constant-immersion testing to assess relative susceptibility of wrought aluminium alloys (including powder metallurgy products and some cast/ingot materials with oriented structures) to exfoliation corrosion.
• Definition: Exfoliation corrosion is a stratified subsurface attack that detaches layers, often along grain boundaries, leading to blisters, flakes or layer-by-layer disintegration.
• Test principle: Continuous immersion of specimens in specified aqueous solutions at controlled temperature; qualitative assessment by visual examination against standard photographs or numerical ratings.
• Specimen preparation
  • Recommended flat specimen size at least 50 mm × 75 mm and full section thickness where practicable.
  • Final machining cut about 0.635 mm or less to avoid highly worked surfaces.
  • Surface roughness parameter R_a shall not exceed 2,5 (as given in the standard).
  • Special handling of alclad products (cladding removed from test surface) and weldments (weld centered and perpendicular to long side).
  • Degreasing and optional etching/desmuting procedures (example etch sequence referenced).
• Test solutions and exposure: Table 1 and Table 2 in the standard list recommended corrosive solutions and immersion conditions for specific alloy systems (e.g., Al–Mg, Al–Zn–Mg, Al–Cu types). Solutions must be prepared with reagent-grade chemicals and low-conductivity water; use fresh solution for each test.
• Testing procedure: Specimens may be vertical or horizontal depending on alloy and solution; do not expose dissimilar alloy systems together; inspect in-situ and consider extended duration for resistant materials.
• Rating and interpretation: Visual classifications (Procedure A) include No appreciable attack (N), Pitting (P), General corrosion (G) and Exfoliation (EA–ED). Control specimens from known high/low susceptibility materials are recommended to verify test validity.

Applications and users

• Useful for: materials researchers, alloy developers, metallurgists, corrosion engineers, QA/QC laboratories and manufacturers of aluminium mill products and components (aircraft, marine and industrial parts).
• Practical uses: screening alloy variants, trend studies in alloy development, comparative resistance evaluation, and production control when acceptance limits are agreed between parties.
• Service correlation: Test is intended to approximate severe marine/industrial outdoor environments; results are most valuable when compared with known service experience.

Related standards

• ISO 3696 - Water for analytical laboratory use
• ISO 8044 - Corrosion of metals and alloys - Basic terms and definitions
• ISO 11846 - Determination of resistance to intergranular corrosion of solution heat-treatable aluminium alloys

Keywords: ISO 11881, exfoliation corrosion, aluminium alloys, corrosion testing, accelerated immersion test, specimen preparation, visual rating, Al-Mg, Al-Zn-Mg, alclad.