📋 Case Study

Aluminum for Aerospace Components

Intergranular corrosion (IGC) and exfoliation in 7075-T6 due to improper anodizing and fastener selection

🏗️ Project Overview

Fuselage skin panels for next-gen narrow-body aircraft (exposed to deicing salts, humidity cycling, galvanic coupling with Ti fasteners)

🎯 Challenge

Intergranular corrosion (IGC) and exfoliation in 7075-T6 due to improper anodizing and fastener selection

🔧 Design Approach

Switched to 2024-T351 with chromic acid anodize (CAA), titanium alloy fasteners (Ti-6Al-4V), and insulating washers; validated per ASTM B117 + ASTM G34

📐 Design Diagram

• Improper anodizing & fastenersSolution• 2024-T351 + CAA
• Ti-6Al-4V fasteners
• Insulating washersValidationASTM B117 (salt spray)
ASTM G34 (EXCO test)Key Metrics• Galv. current: 0.8 µA/cm²
• EXCO rating: ≤ EA2IGCExfoliationCAATi fasteners

AI-generated project design illustration

📐 Key Calculations

Galvanic Current Density

I = ΔE / R_total

Result: 0.8 µA/cm² (acceptable)

Below threshold for detectable IGC growth rate

Exfoliation Rating

ASTM G34 EXCO Test

Result: EA rating ≤2

Meets OEM airframe durability spec

📊 Results

Eliminated field-reported exfoliation incidents; extended panel service life from 12k to 28k flight hours

💡 Lessons Learned

• •Anodize thickness tolerance ±0.5 µm directly impacts galvanic current
• •Fastener coating (e.g., Alodine 1200S) must match substrate electrochemistry

✅ Key Takeaways

• 1Anodize thickness tolerance ±0.5 µm directly impacts galvanic current
• 2Fastener coating (e.g., Alodine 1200S) must match substrate electrochemistry