Overview
6061 is the most versatile and widely used heat-treatable aluminum alloy, with magnesium and silicon as principal alloying elements. The T6 temper (solution heat-treated and artificially aged) provides medium-to-high strength, excellent corrosion resistance, good machinability, and ready weldability. Aluminum 6061 is about one-third the weight of steel with roughly half the strength of mild steel.
Mechanical Properties (6061-T6)
| Property | Value |
|---|---|
| Density | 2,700 kg/m³ (0.0975 lb/in³) |
| Yield Strength | 276 MPa (40,000 psi) |
| Ultimate Tensile | 310 MPa (45,000 psi) |
| Elongation | 12% |
| Hardness | 95 BHN |
| Young's Modulus | 69 GPa (10 × 10⁶ psi — 1/3 of steel) |
| Shear Strength | 207 MPa |
| Fatigue Limit | 96 MPa (5×10⁸ cycles) |
Comparison to Steel
| Property | 6061-T6 Aluminum | A36 Steel | Ratio (Al/Steel) |
|---|---|---|---|
| Density | 2,700 kg/m³ | 7,850 kg/m³ | 0.34 |
| Yield Strength | 276 MPa | 250 MPa | 1.1 |
| Young's Modulus | 69 GPa | 200 GPa | 0.35 |
| Thermal Conductivity | 167 W/m·K | 50 W/m·K | 3.3 |
| Thermal Expansion | 23.6 × 10⁻⁶/°C | 11.7 × 10⁻⁶/°C | 2.0 |
| Relative Cost/Volume | Higher | Lower | ~2× |
Thermal Properties
| Property | Value |
|---|---|
| Melting Range | 582-652°C |
| Thermal Conductivity (20°C) | 167 W/m·K (3× steel!) |
| Specific Heat | 896 J/kg·K |
| Coefficient of Thermal Expansion | 23.6 × 10⁻⁶/°C |
| Electrical Conductivity | ~43% IACS |
Corrosion Resistance
Aluminum forms a thin, self-healing oxide layer (Al₂O₃) that provides excellent atmospheric corrosion resistance. It resists:
- Rural, urban, and mild industrial atmospheres
- Fresh water (pH 4.5-8.5)
- Many chemicals (nitric acid, organic acids)
- Marine environments (better than carbon steel; can pit in stagnant seawater)
Not resistant to:
- Strong acids (HCl, sulfuric above dilute concentrations)
- Strong alkalis (caustic soda dissolves aluminum)
- Mercury and mercury salts (catastrophic embrittlement)
- Prolonged contact with wet concrete/mortar (alkaline attack)
Common Tempers
| Temper | Process | Strength | Ductility |
|---|---|---|---|
| O | Annealed | Lowest | Highest |
| T4 | Solution heat-treated, naturally aged | Medium | Good |
| T6 | Solution + artificially aged | Highest | Moderate |
| T651 | T6 + stress relieved (stretched) | High | Moderate (flat plate) |
Applications
- Aircraft and aerospace structures (historically 2024/7075; 6061 for secondary structure)
- Truck and trailer bodies, rail cars
- Marine structures (boats, docks, gangways)
- Architectural — window frames, curtain walls, roofing
- Bicycle frames, ladders, scaffolding
- Heat exchangers (excellent thermal conductivity)
- Pressure vessels and piping for cryogenic service (down to -270°C)
- Machined parts, fixtures, tooling plates
Fabrication Notes
- Weldable with TIG or MIG using 4043 or 5356 filler (weld zone loses T6 strength — returns partially with age)
- Excellent machinability; chip-breaking alloys available
- Can be anodized for superior corrosion resistance and coloring
- Cold working increases strength (temper H116, H32 for sheet)
- T6 temper can be restored by re-heat-treatment after welding
Summary
6061-T6 aluminum (density 2700 kg/m³, yield 276 MPa) offers excellent strength-to-weight, corrosion resistance, and thermal conductivity. About 1/3 the weight of steel with comparable yield strength but 1/3 the stiffness (deflects more under load). Standard for lightweight structures, marine applications, heat exchangers, and architectural use. Watch for galvanic corrosion when dissimilar metals contact aluminum.