Overview
ISO 8079:2025 - Aerospace process: Anodic treatment of aluminium alloys - Sulfuric acid process, dyed coating - specifies requirements for producing and testing dyed sulfuric‑acid anodic coatings on aluminium alloys used in aerospace manufacture. The standard defines process controls, bath and water quality, anodizing/dyeing/sealing procedures and inspection methods to improve paint adhesion, corrosion resistance and to produce specified colours per drawing requirements.
Key topics and technical requirements
- Materials and preparation
- Alloys must be compatible with sulfuric acid anodizing and free of surface defects, grease or heavy etching.
- Manufacturing processes should normally be completed prior to anodizing; masking is allowed when necessary.
- Water and bath quality
- Anodizing and final rinse: conductivity ≤ 20 µS/cm (resistivity ≥ 50 000 Ω·cm), total dissolved solids ≤ 10 mg/l, pH 5.5–8.0.
- Sealing bath: similar conductivity/resistivity limits; TDS ≤ 10 mg/kg (max 3 mg/kg SiO2); pH 5.5–8.0.
- Anodizing process
- Reference electrolyte: sulfuric acid solution ≈ 15 % (nominal), allowable 150–240 g H2SO4 per litre; dissolved aluminium ≤ 15 g/l; chloride as NaCl ≤ 0.2 g/l; bath temperature 14 °C–20 °C.
- Applied voltage: 16–22 V for 20–40 minutes; corresponding anode current density specified in the standard.
- Agitation of electrolyte and correct racking (aluminium or titanium racks) to ensure uniform current distribution.
- Dyeing, sealing and drying
- Immersion dyeing with agitation to achieve specified colour; thorough rinsing after dyeing.
- Sealing options include conventional methods and a hexavalent‑chromium‑free sealing solution (added in this edition).
- Drying and rework procedures are specified to maintain coating integrity.
- Quality assurance and testing
- Lot acceptance, process control and process qualification tests.
- Inspection and testing include visual examination, mass per unit area (gravimetric), coating thickness measurement, corrosion resistance (e.g., salt spray per ISO 9227) and sealing effectiveness.
- Packaging and delivery
- Requirements to prevent damage or contamination during transport.
Applications and users
- Primary users: aerospace manufacturers, surface treatment subcontractors, materials and process engineers, procurement/specification writers and quality/inspection personnel.
- Practical uses: producing dyed anodic coatings for aircraft parts to improve adhesion for subsequent paint systems, extend corrosion protection, and meet color/appearance requirements on structural and non‑structural aluminium components.
Related standards
Keywords: ISO 8079:2025, anodic treatment, aluminium alloys, sulfuric acid anodizing, dyed coating, aerospace anodizing, corrosion resistance, coating thickness, water quality, sealing.