ISO 2106:2019

Overview

ISO 2106:2019 specifies a gravimetric method for determining the mass per unit area (surface density) of anodic oxidation coatings on aluminium and its alloys. The method is a destructive test: the anodic coating is dissolved chemically and the mass loss of a weighed specimen is used to calculate the coating mass in mg per dm². It applies to most cast and wrought aluminium alloys, except those with a copper mass fraction > 6%.

Keywords: ISO 2106:2019, anodizing, aluminium, surface density, gravimetric method, anodic oxidation coatings.

Key topics and technical requirements

• Principle: Dissolve the anodic coating with a specified reagent, reweigh the specimen, and compute mass loss per unit area.
• Test solutions:
  • Solution A: Phosphoric acid + chromium(VI) oxide - does not significantly attack aluminium substrate. (Handle chromium(VI) with care.)
  • Solution B: Phosphoric acid + sodium molybdate - can attack substrate slightly; take precautions to limit substrate dissolution.
• Specimen preparation:
  • Standard specimen size: 50 mm × 50 mm (acceptable area range 0.08–1.0 dm²); specimen mass ≤ 100 g.
  • Degrease and dry according to the standard procedure; protect non-tested surfaces mechanically or chemically.
• Test conditions:
  • Immersion typically 10 minutes at 95–100 °C with agitation; repeat until no further mass loss.
  • Use reagents of analytical grade and deionized or distilled water.
  • Laboratory balance resolution: 0.1 mg.
• Results calculation:
  • Surface density (mg/dm²) = mass loss / coated area.
  • Approximate thickness can be estimated if coating density is known; conventional densities for thin sulfuric-acid DC anodizing: ~2.6 g/cm³ (sealed), ~2.4 g/cm³ (unsealed). Density varies widely (≈1.5–>3 g/cm³).
• Safety and limits:
  • Chromium(VI) and molybdate(VI) are toxic; provide ventilation and environmental controls.
  • Not suitable for high-copper alloys (>6% Cu) due to substrate dissolution.

Applications

• Quality control and production monitoring of anodized aluminium components (architectural, automotive, aerospace, electronics).
• Verifying coating mass specifications when thickness measurement is impractical.
• Calculating apparent density or estimating average coating thickness when combined with thickness data (e.g., from ISO 2128).

Who should use this standard

• Metallurgical and surface-coating laboratories
• Quality engineers in anodizing plants
• Product designers specifying anodic coating requirements
• Certification bodies and inspectors verifying anodizing compliance

Related standards

• ISO 2128 - methods for measuring anodic coating thickness
• ISO 7583 - anodizing terms and definitions

ISO 2106:2019 is a practical, reproducible gravimetric procedure for assessing anodic coating mass and supporting coating specification, control and verification processes.