ISO 4623-2:2016

Overview

ISO 4623-2:2016 - Paints and varnishes: Determination of resistance to filiform corrosion - Part 2: Aluminium substrates - specifies a laboratory test procedure to assess how well a paint or varnish coating protects aluminium substrates from filiform corrosion originating at an intentional scribe (break) in the coating. The standard defines sample preparation, scribing, acid vapour initiation, exposure conditions and evaluation criteria. It is applicable only to the specific coating/substrate combination tested and is not a predictive method for other substrates or systems.

Key topics and technical requirements

• Scope and limitation: Evaluates the protective action of a given coating on aluminium only; not suitable for predicting performance on different substrates.
• Sample preparation: Test panels conforming to ISO 1514; minimum size 100 × 70 × 0.8 mm; back and edges normally coated. Conditioning per ISO 3270.
• Scribing details: Two perpendicular scribes per panel, each ≥ 30 mm long and 1–2 mm wide; debris removed and substrate visible (×10 magnification). If cladding exists, scribe depth 0.05–0.1 mm. Report scribe tool and orientation (rolling direction).
• Initiation method: Introduction of hydrochloric acid vapour (analytical grade HCl 37 %) into an acid-resistant container. Typical dosage: ~20 ± 2 ml HCl per litre of container volume. Note: CASS (ISO 9227) can be used to initiate filiform corrosion for some materials.
• Exposure conditions: Test cabinet at (40 ± 2) °C and (82 ± 5) % RH, panels positioned above the liquid at (100 ± 10) mm and at least 20 mm apart; panels usually held horizontally (orientation affects results).
• Replication and timing: Tests normally carried out in triplicate. Panels preconditioned and exposed for the agreed test period with periodic inspections.
• Evaluation metrics: Measure longest filament (L) and most frequent filament length (M) per ISO 4628-10; report results for each scribe separately and include coating thickness (ISO 2808).

Practical applications and users

ISO 4623-2:2016 is useful for:

• Coatings manufacturers verifying formulation resistance on aluminium.
• Corrosion engineers and test laboratories performing standardized durability testing.
• Quality assurance and specification writers who need objective test methods for procurement and acceptance criteria.
• R&D teams comparing coating systems or surface treatments for aluminium in marine/industrial environments.

This standard helps determine susceptibility to filiform corrosion-a common coating failure under humid, contaminated conditions-and supports product development, compliance testing and material selection.

Related standards

• ISO 4623-1 (steel substrates)
• ISO 4628-10 (assessment of filiform corrosion)
• ISO 4628-8 (delamination/corrosion around a scribe)
• ISO 1513, ISO 1514, ISO 15528 (sampling/preparation)
• ISO 2808 (film thickness)
• ISO 3270 (conditioning)

Keywords: ISO 4623-2:2016, filiform corrosion, aluminium substrates, paints and varnishes, scribe test, hydrochloric acid vapour, test cabinet, coating evaluation.