--- title: "MIL-A-8625 Anodising India:…" description: >- Explore the comprehensive guide on MIL-A-8625 anodising in India, covering types, compliance, and industry applications. canonical: "https://www.saravanaconsultancy.in/blog/mil-a-8625-anodising-india" source_url: html: "https://www.saravanaconsultancy.in/blog/mil-a-8625-anodising-india" md: "https://www.saravanaconsultancy.in/blog/mil-a-8625-anodising-india.md" last_modified: 2026-05-24 --- Compliance # MIL-A-8625 Anodising India:… Balasubramanian Iyer · April 2026 · 5 min read MIL-A-8625 anodising India represents a critical capability for manufacturers supplying defence, aerospace, and precision engineering sectors. As of 2026, Indian anodising facilities increasingly pursue compliance with this US military specification to access global supply chains. The specification MIL-A-8625F defines three anodising types and two classes, establishing coating thickness, hardness, and corrosion resistance requirements that exceed standard commercial grades. Understanding these requirements is essential for any facility planning to serve military or aerospace customers. ## Understanding MIL-A-8625 ### What is MIL-A-8625? MIL-A-8625 is the US Department of Defense specification governing anodic coatings on aluminium and aluminium alloys. The current revision, MIL-A-8625F, defines processing requirements, coating characteristics, and acceptance testing procedures for military-grade anodised finishes. The specification covers three distinct anodising chemistries (Types I, II, and III) and two finish classes (Class 1 and Class 2), providing a complete framework for coating qualification. The specification mandates specific coating weight requirements: Type I coatings must achieve minimum 2.8 mg/cm² (0.0004 oz/in²), while Type III hard anodic coatings require thickness ranges from 25–75 μm depending on application. These parameters ensure consistent performance across different manufacturing facilities worldwide. ### Common Industries Utilizing MIL-A-8625 In India, MIL-A-8625 compliance serves several critical sectors. Defence manufacturing—including components for Hindustan Aeronautics Limited (HAL) and ordnance factories—requires anodising to military specification India standards. Aerospace tier suppliers producing landing gear components, hydraulic fittings, and structural elements mandate Type III hard anodising with thickness ranges of 50–75 μm. For comprehensive guidance on aluminium surface treatment, consult an [Aluminium Anodizing Consultant India](https://www.saravanaconsultancy.in/) with military specification experience. Additional sectors include medical device manufacturing (surgical instruments requiring biocompatible coatings), precision electronics (EMI shielding housings), and automotive racing components where weight reduction meets durability requirements. ## Types of MIL-A-8625 Anodising ### MIL-A-8625 Type I Chromic Acid Anodising MIL-A-8625 Type I chromic acid anodising produces thin oxide layers (2.5–7.5 μm) using chromic acid electrolyte at concentrations of 30–100 g/L and temperatures of 32–38°C . This process offers superior fatigue resistance—critical for aerospace structural components where coating-induced stress concentration must be minimised. The thin coating provides excellent paint adhesion while maintaining dimensional tolerances within ±2.5 μm. Type I finds application in aircraft structural components, particularly those subjected to cyclic loading. However, environmental regulations under REACH restrict chromic acid use, pushing facilities toward alternative processes where specifications permit. ### MIL-A-8625 Type II Sulphuric Acid Anodising MIL-A-8625 Type II sulphuric acid anodising represents the most widely used process, producing coatings of 5–25 μm thickness. Process parameters include sulphuric acid concentration of 150–200 g/L, temperature of 18–22°C, and current density of 1.2–1.8 A/dm² . The resulting porous oxide structure accepts dyes readily, enabling coloured finishes under Class 2 designation. For deeper understanding of process differences, review our comparison of [Hard Anodizing vs Sulphuric Anodizing](https://www.saravanaconsultancy.in/blog/hard-anodizing-vs-sulphuric-anodizing). Type II coatings provide moderate wear resistance with excellent corrosion protection—suitable for general aerospace hardware, electronic enclosures, and architectural applications. ### MIL-A-8625 Type III Hard Anodising MIL-A-8625 Type III hard anodising creates dense oxide layers of 25–75 μm with hardness values of 60–70 HRC equivalent . The process operates at lower temperatures (0–5°C) with higher current densities (2.4–3.6 A/dm²) than conventional sulphuric anodising. These parameters produce coatings with abrasion resistance exceeding 3.5 mg loss per 10,000 cycles under Taber testing. Applications include hydraulic cylinder bores, valve components, firearm receivers, and wear-critical mechanical parts. Dimensional growth of approximately 50% of coating thickness must be factored into part design—a 50 μm coating adds roughly 25 μm per surface. ## MIL-A-8625 Class 1 vs Class 2 ### Definitions and Differences MIL-A-8625 class 1 vs class 2 distinction addresses post-anodising treatment rather than base process chemistry. Class 1 coatings remain undyed—presenting natural grey to dark grey appearance depending on alloy and coating thickness. Class 2 coatings incorporate organic or inorganic dyes before sealing, enabling black, blue, red, gold, and custom colours. Both classes require identical sealing—typically in deionised water at 96–100°C for 15–30 minutes or nickel acetate solution at 82–88°C. Sealing closes the porous oxide structure, locking in dye and maximising corrosion resistance. ### Applications of Class 1 and Class 2 Class 1 (non-dyed) serves applications where coating integrity trumps aesthetics: hydraulic components, electrical housings requiring EMI conductivity, and parts subjected to high temperatures where dye degradation concerns exist. Class 2 (dyed) addresses identification marking, decorative requirements, and optical applications requiring specific light absorption characteristics. For broader industry knowledge, explore our [Aluminium Anodizing Blog](https://www.saravanaconsultancy.in/blog.html) covering various finishing techniques and applications. ## Compliance and Certification ### Understanding MIL-A-8625 Compliance MIL-A-8625 compliance india requires documented process controls, calibrated equipment, and qualified testing capabilities. Mandatory verification tests include: 1. Coating thickness measurement via eddy current or microscopic cross-section (minimum per type specification) 2. Corrosion resistance via 336-hour salt spray testing per ASTM B117 3. Coating weight determination through strip-and-weigh method 4. Seal quality verification via dye-stain or admittance testing 5. Abrasion resistance testing for Type III coatings per Taber method ### Certification Process in India Indian anodising facilities can achieve MIL-A-8625 certification through NADCAP (National Aerospace and Defence Contractors Accreditation Programme) or customer-specific qualification. The certification process follows these stages: 1. Gap analysis against MIL-A-8625F requirements and facility capabilities 2. Process documentation development including work instructions and control plans 3. Equipment calibration to NABL or equivalent traceable standards 4. Trial processing with customer-witnessed testing 5. First Article Inspection Report (FAIR) submission per AS9102 6. Ongoing compliance audits (typically annual for NADCAP) Facilities planning MIL-A-8625 capability should reference guidance on [Anodizing Plant Setup India](https://www.saravanaconsultancy.in/blog/anodizing-plant-setup-india) covering infrastructure requirements. Investment costs for a compliant facility range from ₹1.5–4 crore depending on capacity and type coverage, plus GST at 18% on equipment procurement. ## FAQs ### What is the 7 20 rule for anodizing? The 7-20 rule refers to racking density guidelines: maintain minimum 7 cm spacing between parts and limit load to 20 dm² per 100 amperes of rectifier capacity. This ensures uniform current distribution and consistent coating thickness across all surfaces, particularly critical for MIL-A-8625 compliance where thickness tolerances are tightly controlled. ### What is MIL-A-8625 material? MIL-A-8625 applies to aluminium and aluminium alloys from the 1xxx through 7xxx series. The specification does not define a "material" but rather coating requirements for these substrates. Alloys with copper content exceeding 5% (certain 2xxx series) require Type I chromic acid anodising due to corrosion sensitivity in sulphuric acid processes. ### What is the difference between MIL-A-8625 and MIL PRF 8625? MIL-A-8625 and MIL-PRF-8625 refer to the same specification—the "PRF" (Performance) designation replaced "A" (Aerospace) in modern US military nomenclature. Current procurement documents may reference either designation interchangeably. The active specification remains MIL-A-8625F with Amendment 1. ### What is the difference between Class 1 and Class 2 MIL-A-8625? Class 1 designates non-dyed anodic coatings retaining natural oxide colour (grey to charcoal depending on alloy). Class 2 designates dyed coatings sealed after colour application. Both classes must meet identical thickness, corrosion resistance, and seal quality requirements per MIL-A-8625F. ### What does class 1 vs class 2 mean in MIL-A-8625? Class designation indicates dyeing status only—not coating quality or performance tier. Class 1 (non-dyed) suits functional applications; Class 2 (dyed) enables colour coding, identification marking, or aesthetic requirements. An MIL-A-8625 anodising consultant india can advise on class selection based on end-use specifications. ### What is the difference between MIL-A-8625 Type I, II, and III? Type I uses chromic acid electrolyte producing thin coatings (2.5–7.5 μm) with minimal fatigue impact. Type II uses sulphuric acid for moderate thickness (5–25 μm) general-purpose coatings. Type III (hard anodise) creates thick, dense coatings (25–75 μm) with superior wear resistance through low-temperature, high-current-density processing . Working on this in your plant? 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