ISO 2128:2010

Overview

ISO 2128:2010 is an international standard developed by ISO that specifies a non-destructive method for determining the thickness of anodic oxidation coatings on aluminium and its alloys. The standard utilizes a split-beam microscope (also called an optical section microscope) to measure coating thickness reliably without damaging the sample. This method applies primarily to anodic coatings thicker than 10 µm, and for smooth surfaces, it can be used on coatings thicker than 5 µm.

The method is limited to coatings where two luminous lines, created by light reflection and refraction, are clearly visible and well-separated. It is not suitable for opaque or dark-colored anodic layers.

Key Topics

• Scope and Applicability

  • Measurement of anodic coating thickness on aluminium and aluminium alloys.
  • Applicable for industrial anodic coatings >10 µm, or >5 µm for smooth surfaces.
  • Not suitable for opaque or dark coatings where luminous lines are not distinguishable.

• Measurement Principle

  • A parallel, lamellar light beam is projected onto the anodized surface at an oblique angle (usually 45°).
  • One reflected beam comes from the outer anodic layer surface; another beam reflects off the metal/oxide interface, passing through the coating twice.
  • The split-beam microscope view shows two parallel luminous lines; the distance between them correlates with the coating’s real thickness.
  • Thickness calculation considers the refractive index of the anodic layer (around 1.59 to 1.62) and the microscope geometry.

• Equipment Requirements

  • Special split-beam microscope calibrated with anodized aluminium samples measured by micrographic cross-section methods.
  • Accurate micrometer reticle to read the distance between luminous lines.

• Measurement Procedure and Data Evaluation

  • Take at least 10 measurements across the designated surface area.
  • Compute the arithmetic mean thickness from these measurements.
  • Handle anomalous values (±10% deviation) by replacing with additional readings or excluding when exceeding 30% of total values.
  • Express results with mean thickness and, if needed, mean deviation for quality reporting.

• Reporting

  • Include reference to ISO 2128:2010 standard.
  • Identify the product and testing conditions.
  • Present measured thickness results and any anomalies.
  • Note date and details of the test.

Applications

ISO 2128:2010 serves a critical role in industries where aluminium anodizing quality and durability are vital. Common applications include:

• Quality Control in Anodizing Plants
  Ensures consistent anodic coating thickness which governs corrosion resistance and aesthetic finish.

• Aerospace and Automotive Components
  Confirms anodic layers meet safety and performance standards without physical sectioning damage.

• Architectural and Construction Materials
  Verifies anodic films protecting aluminium building panels, window frames, and claddings.

• Electrical and Electronics Housings
  Essential for measuring protective anodic coatings without compromising component integrity.

• Research and Development
  Useful in developing new anodizing techniques by measuring coating thickness precisely.

This non-destructive method allows manufacturers and quality inspectors to monitor anodizing processes in-line or post-production without wasting materials or causing damage.

Related Standards

ISO 2128:2010 complements and interacts with several other international standards on aluminium surface treatments and measurements, including:

• ISO 7599 - Specification for anodic oxidation coatings on aluminium for corrosion resistance and decorative finishes.

• ISO 4287 / ISO 4288 - Surface texture (roughness) measurements relevant to anodizing surface preparation.

• ISO 2234 - Test methods for measuring thickness of anodic oxidation coatings by cross-sectional microscopy (destructive test).

• ASTM B244 - American standard for anodic coatings thickness measurement techniques.

These standards collectively support comprehensive quality assurance in aluminium anodizing processes across multiple industries.

Keywords: ISO 2128, anodizing aluminium, anodic oxidation coating thickness, non-destructive measurement, split-beam microscope, aluminium coatings, anodic layer thickness, anodizing quality control, optical section microscope, aluminium surface treatment standards.