1. What are the standard accelerated corrosion test methods for aluminum alloys?
Common Test Standards:
Salt Spray (Fog) Testing (ASTM B117):
5% NaCl solution at 35°C
Evaluates pitting resistance (e.g., 3000hr for marine-grade 5083)
Galvanic Corrosion Testing (ASTM G71):
Couples aluminum with dissimilar metals (e.g., steel/copper)
Intergranular Corrosion (IGC) Testing (ASTM G110):
Immersion in acidified NaCl+H₂O₂ for 6-24hrs
Test Selection Guide:
| Aerospace | Automotive | Marine | |
|---|---|---|---|
| Preferred Test | EXCO* | SWAAT** | ASTM G85-A3 |
*EXCO: ASTM G34 (Exfoliation Corrosion)
**SWAAT: Acidified salt spray
2. How to interpret corrosion test results quantitatively?
Measurement Methods:
Weight Loss:
Formula: Corrosion rate (mpy) = (534×W)/(D×A×T)
W=weight loss (mg), D=density (g/cm³), A=area (in²), T=time (hr)
Pit Depth Analysis:
Optical profilometry for 3D mapping
Max depth ≤50μm for aircraft skins (AMS 2778)
Electrochemical Parameters:
| Parameter | Acceptable Range |
|---|---|
| Ecorr | >-0.8V vs SCE |
| Icorr | <1μA/cm² |
3. What are the key factors affecting aluminum's corrosion resistance?
Material & Environmental Factors:
| Factor | Effect | Example |
|---|---|---|
| Alloy Series | 5xxx > 6xxx > 2xxx | 5052 vs 2024 in seawater |
| Temper | T7 > T6 > T4 | 7075-T73 vs 7075-T6 |
| Chloride Concentration | 10x faster at 3.5% vs 0.5% | Coastal vs inland |
| pH | Severe at pH<4 or >9 | Acid rain (pH 4.5) damage |
Protection Methods:
Anodizing (20-25μm for MIL-A-8625)
Corrosion-inhibiting primers (e.g., strontium chromate)
4. How to perform field corrosion monitoring?
Industrial Techniques:
Electrical Resistance (ER) Probes:
Measures metal loss in real-time (0.1μm resolution)
Atmospheric Corrosion Coupons:
100×50×3mm samples exposed 1-12 months
Electrochemical Noise Monitoring:
Detects early pitting (<100μm)
Data Correlation:
ISO 9223 corrosivity categories (C1-C5) map to alloy performance
5. What advanced characterization techniques analyze corrosion mechanisms?
Laboratory Methods:
| Technique | Application | Resolution |
|---|---|---|
| SEM-EDS | Pit chemistry | 1μm |
| SKPFM | Volta potential mapping | 50nm |
| XPS | Oxide film composition | 5nm depth |
Case Study:
TEM reveals θ-phase (Al₂Cu) dissolution causing IGC in 2024-T3
