Why alloy selection matters more than you might think
All three alloys - 6061, 7075 and 2024 - are heat-treatable aluminium alloys with broadly similar density (~2.7 g/cm³) and good machinability. But their mechanical properties, corrosion resistance, weldability and surface treatment compatibility differ significantly. A part designed around 6061-T6 and then switched to 7075-T6 mid-project may require a complete re-analysis of stress concentrations, fastener torque values and surface treatment specifications.
6061-T6 - the general-purpose workhorse
6061-T6 is the most widely used structural aluminium alloy in CNC machining. Its combination of strength, corrosion resistance, weldability and machinability makes it the default choice for a broad range of applications.
Tensile strength ~310 MPa, yield strength ~276 MPa, elongation ~12%. Machines cleanly with good chip formation. Anodises well - both standard anodising (15-25 µm) and hard anodising (25-75 µm) adhere uniformly and give consistent colour. Can be welded with standard techniques.
Use 6061-T6 when: you need a reliable, well-characterised alloy for structural or semi-structural parts; when anodising or hard anodising is required; or when weldability is important.
7075-T6 - maximum strength
7075-T6 offers the highest strength of the three alloys - tensile strength ~570 MPa, yield strength ~503 MPa - making it the choice for aerospace, motorsport and high-load structural applications where weight must be minimised.
7075 is significantly less corrosion-resistant than 6061. It should be protected with anodising or chromate conversion coating in most applications. It cannot be fusion welded reliably. Standard anodising is possible, but colour consistency and coating uniformity are inferior to 6061. It is also more expensive - typically 2-3x the material cost of 6061.
7075-T6 is worth the cost and complexity when strength-to-weight ratio is genuinely the design driver. For most structural parts where 6061 is adequate, the extra cost and corrosion management overhead of 7075 is hard to justify.
2024-T3 - fatigue resistance
2024-T3 is the preferred alloy when fatigue life is the primary design criterion. Tensile strength ~483 MPa with elongation ~18% - meaning it deforms significantly before fracturing, which is a valuable property in cyclic-load applications.
2024 is the standard alloy for aircraft fuselage skins and structural airframe members precisely because of its fatigue performance. However, it has poor corrosion resistance and must always be protected - clad sheet (Alclad) or anodising is standard in aerospace applications. It machines well, though slightly less freely than 6061.
Comparison table
| Property | 6061-T6 | 7075-T6 | 2024-T3 |
|---|---|---|---|
| Tensile strength | ~310 MPa |
~570 MPa |
~483 MPa |
| Yield strength | ~276 MPa |
~503 MPa |
~345 MPa |
| Corrosion resistance | Good | Poor | Poor |
| Weldability | Good | Poor | Poor |
| Anodising quality | Excellent | Moderate | Moderate |
| Relative cost | Low | High | Medium |
| Best for | General structural, anodised parts | High-load, weight-critical | Fatigue-critical, aerospace |
A note on temper designations
The temper suffix matters as much as the alloy number. T6 means solution heat-treated and artificially aged - the standard high-strength condition. T3 means solution heat-treated and cold-worked. T4 is solution heat-treated and naturally aged. Ordering 6061 without specifying the temper may result in receiving T4 material with significantly lower strength than T6.
Always specify both alloy and temper on your drawing: "Aluminium alloy 6061-T6 to BS EN 573" or equivalent.
Summary
- Default to 6061-T6 for most CNC machined structural parts. It offers a well-balanced combination of strength, machinability, corrosion resistance and anodising quality.
- Choose 7075-T6 only when strength-to-weight ratio is the primary driver and you can manage the corrosion protection requirement.
- Use 2024-T3 for fatigue-critical applications, particularly in aerospace and defence contexts.
- Always specify both alloy number and temper designation on the drawing.
- Discuss material selection with your manufacturer early - lead time and material cost can vary significantly between grades.