Why Aluminum Grade Selection Changes Everything
Aluminum is the most widely machined metal in the world — approximately 60% of all CNC-machined non-ferrous metal parts are aluminum, according to the International Aluminium Institute. But aluminum is not a single material. There are over 400 registered aluminum alloy designations, and selecting the wrong grade for aluminum CNC machining means either over-engineering (and overpaying), or under-engineering (and failing) your component.
The three grades that account for more than 80% of all custom CNC aluminum machining are 6061-T6, 7075-T6, and 2024-T4. Each has a distinct performance and cost profile that makes it correct for some applications and wrong for others.
| Property | 6061-T6 | 7075-T6 | 2024-T4 | 5083-H116 |
| Tensile Strength | 310 MPa | 572 MPa | 469 MPa | 317 MPa |
| Yield Strength | 276 MPa | 503 MPa | 324 MPa | 228 MPa |
| Machinability Rating | Excellent (10/10) | Very Good (8/10) | Good (7/10) | Good (7/10) |
| Corrosion Resistance | Very Good | Moderate | Poor (bare) | Excellent |
| Weldability | Excellent | Poor | Poor | Excellent |
| Relative Material Cost | 1.0x (baseline) | 1.8-2.2x | 1.5-1.8x | 1.2-1.4x |
Mechanical property data per ASM Aerospace Specification Metals database and Aluminum Association Alloy Composition Standards.
When to Use Each Grade
• Aluminum 6061-T6 — the best default for most CNC applications: At 310 MPa tensile strength with excellent machinability and corrosion resistance, 6061-T6 is the correct choice for structural brackets, enclosures, housings, fixtures, and any general mechanical component that does not operate under extreme stress. It machines cleanly, holds tight tolerances well, and accepts anodizing with excellent cosmetic results. For best aluminum grade for machining in general manufacturing, 6061-T6 is the answer 70% of the time.
• Aluminum 7075-T6 — when strength is the priority: At 572 MPa tensile strength, 7075 is the strongest commonly available aluminum alloy. It is the standard for aerospace structural parts, high-load bicycle and sports equipment frames, and any application where the lightest possible weight must carry the highest possible load. The tradeoff: 7075 has poor weldability and moderate corrosion resistance, making it unsuitable for welded assemblies or marine environments without protective coating.
• Aluminum 2024-T4 — for fatigue-critical aerospace applications: 2024 is selected specifically when fatigue life is the primary design driver, as it has superior fatigue performance compared to 6061 at similar stress levels. It is used extensively in aircraft fuselage skins and wing structures. Its poor natural corrosion resistance means bare 2024 requires cladding or alodine treatment in most applications.
• Aluminum 5083-H116 — for marine and weld-critical applications: Where the part will be welded or exposed to seawater, 5083 offers the best combination of weldability, strength retention after welding, and marine corrosion resistance of any common aluminum alloy. It is the standard for marine vessels, pressure vessels, and offshore equipment.
Tolerance Capability by Aluminum Grade
| Aluminum Grade | Achievable Positional Tolerance | Surface Finish Ra (achievable) | Best Surface Treatment |
| 6061-T6 | ±0.025 mm with standard tooling | Ra 0.4 µm with finishing passes | Type II anodize, clear or hard coat |
| 7075-T6 | ±0.025 mm with sharp tooling | Ra 0.4 µm achievable | Alodine (chromate conversion) |
| 2024-T4 | ±0.038 mm (slight gumminess) | Ra 0.6 µm typical | Alodine + paint system |
| 5083-H116 | ±0.05 mm typical | Ra 0.8 µm typical | Anodize or bare (marine grade) |
The Grade Selection Decision: A Practical Framework
Ask four questions before selecting an aluminum grade for CNC machining: (1) What is the maximum stress the part will experience in service? If yield strength requirements are below 250 MPa, 6061-T6 is sufficient. (2) Will the part be welded? If yes, use 6061 or 5083. (3) Will it be exposed to saltwater or high humidity without coating? Use 5083 or coated 6061. (4) Is this an aerospace structural part with fatigue requirements? Use 7075 or 2024 per the design specification. Matching these four criteria to the material data table above will yield the correct grade selection for more than 95% of custom CNC machining applications.
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