- Practice · 5 marks
Aluminium alloys compared with steel
Short answer
Aluminium alloys have low density (2.7 g/cm³) and high specific strength, good corrosion resistance, but lower modulus (~70 GPa) and higher cost than steel. Advantges: light weight, extrudability, cryogenic toughnes. Limitations: lower stiffness, strength loss above ~200°C, galvanic corrosion with steel. Applications: aircraft frames (2024,7075), transmision lines, automotive panels.
Compare aluminium alloys with steel for structural use. State the advantages and limitations of aluminium alloys and give examples of applications.
Aluminium alloys are used where low weight, corrosion resistance and good conductivity matter more than the highest stiffness or lowest cost.
| Property | Aluminium alloys | Structural steel |
|---|---|---|
| Density | about 2.7 g/cm | about 7.85 g/cm |
| Young's modulus | about 70 GPa | about 200 GPa |
| Yield strength | 30-500 MPa | 250-1500 MPa |
| Specific strength (strength/density) | High (heat-treated alloys) | Moderate |
| Corrosion resistance | Good (oxide film) | Needs coating |
| Thermal/electrical conductivity | High | Low |
| Weldability | Needs special process (TIG/MIG) | Good (low-carbon steels) |
| Fatigue limit | None (no endurance limit) | Distinct endurance limit |
| Cost per kg | Higher | Lower |
Advantages of aluminium alloys
- Light weight and high strength-to-weight ratio.
- Good corrosion resistance, easy to extrude and cast in complex shapes.
- Recyclable using only about 5% of the energy needed for primary production.
- Non-magnetic and non-sparking; retains toughness at low temperature (FCC).
Limitations
- Low modulus gives larger deflection for same section.
- Loses strength above about 150-200 °C; low melting point (660 °C).
- Galvanic corrosion when in contact with steel or copper.
Applications
Aircraft skin and frames (2024, 7075), engine pistons and blocks (Al-Si), transmission lines (1350), beverage cans (3004, 5182), window frames (6063), and automotive body panels.
✓ Answer checked by Claude Opus 5.5 (high effort)
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