Overview
EN ISO 2128:2010 specifies a non‑destructive method for determining the thickness of anodic oxidation (anodizing) coatings on aluminium and its alloys using a split‑beam (split‑image) microscope. The procedure is widely used in industry for anodic coatings typically above 10 µm, or above 5 µm when the surface is smooth. The method requires that two luminous lines (reflections from the coating surface and the metal/coating interface) are visible and distinctly separated, so it is not suitable for opaque or dark‑coloured coatings.
Key topics and requirements
- Measurement principle: A parallel lamellar beam is incident (generally at 45°) on the anodized surface. Two reflected lines are produced in the ocular; the distance between them is proportional to the coating thickness and depends on the coating refractive index (n ≈ 1.59–1.62) and instrument geometry.
- Formula (approx): e ≈ 2.04 · e' (e = true thickness, e' = apparent thickness). Using e ≈ 2 · e' is stated as providing adequate accuracy for many instruments.
- Apparatus: A split‑beam microscope specially designed for transparent coating thickness measurement. Instruments may be calibrated to read true thickness directly; calibration must be checked against an anodized sample whose thickness was determined by the micrographic section (destructive) method.
- Procedure: Readings are taken using a graticule/vernier in the microscope ocular; follow manufacturer instructions and agree the inspection area between supplier and customer.
- Sampling and expression of results:
- Measure at not less than 10 points across the inspection area and report the arithmetic mean.
- Exclude anomalous values deviating more than ±10% from the mean; replace each anomalous value once by two further measurements. Anomalous values must not exceed 30% of total measurements.
- If anomalies persist, report the mean with the mean deviation.
- Test report must include reference to the Standard, product ID, results, mean deviation (if applicable), unusual observations, and date.
Applications and users
- Practical for quality control, incoming inspection, and production monitoring of anodized aluminium components in:
- Architectural aluminium and façades
- Automotive and transport components
- Consumer electronics and appliances
- Aerospace interiors and secondary structures
- Typical users: QC engineers, coating inspectors, material laboratories, anodizing suppliers, and procurement specialists specifying coating thickness requirements.
Related standards
- EN ISO 2128:2010 supersedes EN 12373‑3:1998 and cancels/replaces ISO 2128:1976 (first edition).
- Normative work developed by ISO/TC 79 (Light metals and their alloys), CEN/TC 132 (Aluminium and aluminium alloys).
Keywords: EN ISO 2128:2010, anodizing, anodic oxidation coatings, thickness measurement, split‑beam microscope, non‑destructive testing, aluminium.
