Aluminum Alloys
Aluminum is the most machined metal in our shop. But picking the wrong grade is a common mistake — 7075 ordered when 6061 suffices (overpaying 40%), or 2024 specified for a welded assembly (it's not weldable). This page helps you get it right the first time.
Which Alloy Do You Actually Need?
Stop here. Answer this question first — it determines everything else.
| Your Situation | Use This | Why |
|---|
| Don't know / general purpose | 6061-T6 | Covers 80% of cases. Machinable, weldable, anodizable, cheap. |
| Need maximum strength | 7075-T6 | 572 MPa tensile — stronger than mild steel. But not weldable, harder to machine. |
| Marine / saltwater exposure | 5052-H32 | Best saltwater corrosion resistance of any common aluminum. |
| Fatigue-critical (cyclic loading) | 2024-T4 | Best fatigue endurance. Used in aircraft skins, wing structures. |
| European structural projects | 6082-T6 | European equivalent of 6061, slightly stronger. EN 755 certified. |
| Need to weld after machining | 6061 or 5052 | 7075 and 2024 are NOT weldable. Period. |
| Electrical / thermal conductor | 1100 or 6061 | Pure aluminum (1100) has best conductivity, 6061 is a good compromise. |
| Budget is the primary concern | 6061-T6 | Cheapest to buy, fastest to machine, widest availability. |
Alloy Data at a Glance
| Property | 6061-T6 | 7075-T6 | 5052-H32 | 2024-T4 | 6082-T6 |
|---|
| Tensile (MPa) | 310 | 572 | 193 | 469 | 340 |
| Yield (MPa) | 275 | 503 | 145 | 324 | 290 |
| Elongation | 12% | 11% | 12% | 20% | 10% |
| Density (g/cm³) | 2.70 | 2.81 | 2.68 | 2.78 | 2.71 |
| Hardness (HB) | 95 | 150 | 60 | 120 | 100 |
| Thermal cond. (W/mK) | 167 | 130 | 138 | 121 | 180 |
| Machinability | Excellent | Good | Excellent | Fair | Excellent |
| Weldable | Yes | No | Yes | No | Yes |
| Anodize quality | Best | Fair (dark) | Good | Poor | Good |
| Relative cost | 1.0x | 1.8–2.5x | 0.9x | 1.5–2.0x | 1.1x |
T6 vs T651 — This Matters for CNC
When you order aluminum plate, you'll see both T6 and T651 offered. The difference matters a lot for machining.
T6 = solution treated + quenched + artificially aged. The quenching step locks in residual stresses. When you machine material off one side of a T6 plate, the stress imbalance causes warping.
T651 = same as T6, but with a controlled stretching operation (1–3% permanent elongation) between quenching and aging. This relieves the residual stress. The result: same mechanical properties, but the plate stays flat after machining.
Rule of thumb
Always specify T651 when ordering plate for CNC machining. The cost premium is minimal (5–10%), but it prevents warping — especially on thin-walled parts or when removing significant material from one side. T6 is fine for bar stock and tube where the cross-section is uniform.
Common mistake
Ordering 7075-T6 plate for a large flat bracket, then finding it warped after machining the pocket. This is the #1 aluminum machining problem. Solution: use T651, or add a stress-relief anneal before final machining.
7075 Stress Corrosion Cracking (SCC)
7075-T6 is susceptible to stress corrosion cracking in humid or marine environments. If your part will see sustained tensile stress in a corrosive environment, this is a real failure risk.
| Temper | Tensile (MPa) | Strength loss vs T6 | SCC resistance |
|---|
| T6 | 572 | Baseline | Poor |
| T73 | 503 | −12% | Excellent (10x improvement) |
| T7351 | 503 | −12% | Excellent + stress relieved |
SCC failure mode
Stress corrosion cracking is insidious — the part looks fine, then fails suddenly under load. No visible warning. If you're using 7075 for structural parts in any environment with moisture or salt, specify T73 or T7351.
Real Machining Parameters
These are starting parameters from our shop. Adjust based on your setup, tool condition, and part geometry.
6061-T6 (carbide tools)
| Operation | Speed (m/min) | Feed | Doc | Notes |
|---|
| Roughing (end mill) | 300–500 | 0.10–0.20 mm/tooth | 1–5mm | Aggressive — 6061 cuts easy |
| Finishing (end mill) | 500–800 | 0.05–0.10 mm/tooth | 0.2–0.5mm | High speed for good finish |
| Drilling (φ6–12mm) | 100–150 | 0.08–0.15 mm/rev | — | Peck cycle for deep holes |
| Tapping | 30–60 | — | — | Use spiral flute taps for blind holes |
| Face milling | 400–600 | 0.15–0.25 mm/tooth | 1–3mm | 45° lead angle preferred |
7075-T6 (carbide tools) — reduce speed vs 6061
| Operation | Speed (m/min) | Feed | Doc | Notes |
|---|
| Roughing (end mill) | 200–350 | 0.08–0.15 mm/tooth | 0.5–3mm | 20–30% slower than 6061 |
| Finishing (end mill) | 350–550 | 0.04–0.08 mm/tooth | 0.1–0.3mm | Harder material, lighter cuts |
| Drilling | 80–120 | 0.06–0.12 mm/rev | — | More abrasive — check tool wear |
| Tapping | 20–40 | — | — | Use thread-forming taps if possible |
Tool wear note
7075 and 2024 contain copper, which makes them more abrasive on carbide tools. You'll see faster flank wear. If you're running a large batch of 7075, budget for more frequent tool changes. Diamond-coated end mills last significantly longer on aluminum — worth the cost for production runs.
Surface Treatment Compatibility
| Treatment | 6061 | 7075 | 5052 | 2024 | 6082 | Key Point |
|---|
| Type II anodize | Best color | Dark, uneven | Good | Poor | Good | 6061 gives the most consistent color |
| Hard anodize (III) | Excellent | Good | Good | Not recommended | Good | 7075 hard coat is less wear-resistant |
| Chromate conv. | Yes | Yes | Yes | Yes | Yes | Thin film, paint primer only |
| Powder coat | Yes | Yes | Yes | Yes | Yes | Needs chromate primer first |
| Electropolish | Good | Fair | Good | Fair | Good | Not common for aluminum |
Procurement Tips
| Tip | Detail |
|---|
| Always specify temper | "6061 aluminum" is incomplete. Always say "6061-T6" or "6061-T651". Different tempers have vastly different properties. |
| Request mill cert | For critical parts, request the material test report (MTR). Verify the alloy and temper match what you ordered. |
| Watch for counterfeit 7075 | Some suppliers sell 7A04 as "7075 equivalent" — it's not the same. Insist on ASTM B209 certified material for aerospace parts. |
| Plate vs extrusion | Plate has more uniform properties across the cross-section. Extrusions can have grain structure variations at the surface. |
| Storage | Aluminum forms a natural oxide layer — this is normal and protective. No special storage needed. Just keep it dry. |
| Cost negotiation | Aluminum prices follow the LME (London Metal Exchange). Large orders (>500kg) can negotiate 5–15% off list price. |
Common Mistakes
| Mistake | What happens | Correct approach |
|---|
| Specifying 7075 "for strength" when 6061 suffices | Paying 2x material cost + slower machining = 3x total cost for no benefit | Do the stress calculation first. 6061 at 310 MPa handles most loads. |
| Ordering T6 plate for thin-wall parts | Warps after machining, scrap rate goes up | Use T651. Always. |
| Welding 7075 or 2024 | HAZ loses most strength, cracks form | Design for mechanical fastening or adhesive bonding |
| Anodizing 7075 and expecting bright colors | Gets dark brown/gray, color varies across the part | Use 6061 if cosmetic anodizing is needed |
| Using 7075-T6 in marine environment under load | Stress corrosion cracking — sudden failure | Use T73 temper, or switch to 5052/6061 |
| Not accounting for anodize thickness on tight features | Part goes oversize after anodize (adds 10–25μm per surface) | Machine undersize by half the anodize thickness before coating |