Overview
EN ISO 4623-2:2016 - "Paints and varnishes - Determination of resistance to filiform corrosion - Part 2: Aluminium substrates" - is a standardized laboratory test method published by CEN/ISO for assessing the resistance of paint and varnish coatings on aluminium substrates to filiform corrosion originating from a deliberate defect (scribe) in the coating. The procedure uses controlled exposure to hydrochloric acid vapour and accelerated climate conditions to evaluate whether coatings inhibit the characteristic thread-like (filiform) corrosion growth.
Key topics and technical requirements
- Scope and limitation: The test assesses the protective action of a specific coating/substrate combination only; it is not intended to predict performance on different substrates or in every service environment.
- Test principle: A scribe mark is cut through the coating; hydrochloric acid vapour is introduced into the scribe; panels are exposed in a test cabinet at controlled conditions and inspected for filiform corrosion growth.
- Controlled exposure conditions: The standard specifies a test cabinet maintained at 40 °C and 82 % relative humidity (± tolerances) to promote filiform initiation and development.
- Scribe and panel preparation: Scribe geometry and width are defined in the standard (see Clause 9.2); test-panel material, coating application, drying/conditioning and film thickness follow referenced preparation methods.
- Reagent control: Use of analytical-grade 37 % hydrochloric acid (constant quality) for vapour generation is required.
- Reproducibility and sampling: The method calls for triplicate determinations (changed from duplicate in earlier editions) and references established sampling and preparation standards.
- Evaluation: Results are assessed using agreed criteria or by using ISO 4628-10 for the degree of filiform corrosion; test reports must document scribe tool, panel orientation, and other key parameters.
Applications and users
This standard is practical for:
- Coating manufacturers validating formulations on aluminium
- Independent test laboratories performing corrosion resistance testing
- Quality assurance and R&D teams in industries using aluminium components (e.g., transport, building, consumer goods)
- Specifications and procurement professionals who need objective corrosion-performance data
By providing reproducible, accelerated test data for a given coating/aluminium pairing, the standard helps compare products, support quality control and inform material selection.
Related standards
Keywords: EN ISO 4623-2:2016, filiform corrosion, aluminium substrates, paints and varnishes, corrosion testing, scribe mark, hydrochloric acid vapour, coating resistance.
