The two most-specified machining aluminums differ in ways that matter. 7075 has almost double the yield strength of 6061, but costs 40–60% more, corrodes faster, and is nearly un-weldable. This page gives the specific numbers, the decision criteria that actually govern the choice in production, and the common specification mistakes that waste money or cause field failures.
Specify 6061-T6 unless you have a concrete reason to pay more. 6061 machines well, welds well, corrodes slowly, anodizes beautifully, and delivers 276 MPa yield strength — enough for most brackets, housings, plates, and enclosures. It's what every aluminum fabricator stocks in every section size.
Specify 7075-T6 when you need 503 MPa yield strength (1.8× higher than 6061) and the part is structurally critical enough to justify: higher material cost, worse corrosion resistance, essentially unweldable material, and faster tool wear in machining. This is the domain of aerospace structural components, high-performance bicycle frames, and firearms receivers.
| Property | 6061-T6 | 7075-T6 |
|---|---|---|
| Ultimate tensile strength | 310 MPa (45 ksi) | 572 MPa (83 ksi) |
| Yield strength (0.2%) | 276 MPa (40 ksi) | 503 MPa (73 ksi) |
| Elongation at break | 12–17% | 11% |
| Hardness (Brinell) | 95 HB | 150 HB |
| Density | 2.70 g/cm³ | 2.81 g/cm³ |
| Fatigue strength (5×10⁸ cycles) | 97 MPa | 159 MPa |
| Modulus of elasticity | 68.9 GPa | 71.7 GPa |
| Machinability | Excellent (good chip control) | Very good (harder, shorter tool life) |
| Corrosion resistance | Good | Poor (pits in saltwater) |
| Weldability | Excellent (TIG/MIG 4043/5356) | Poor — crack-prone HAZ |
| Anodizing response | Clean clear/colored anodize | Darker, more variable color |
| Relative cost (per kg) | 1.0× (baseline) | 1.4–1.6× higher |
Values per ASM Handbook Vol. 2 and ASTM B221. Test direction: longitudinal.
Most parts never see loads close to 6061's yield. Using 7075 "just to be safe" is almost always a waste — you're paying for strength that isn't needed and accepting disadvantages (corrosion, weld-prohibition, higher cost) that are real. Size the part for the load case, calculate the actual stress, and pick the alloy accordingly.
7075 cannot be arc-welded without cracking the heat-affected zone. If your bracket will be TIG-welded to an aluminum chassis, the entire welded assembly must be 5xxx or 6xxx series (typically 6061). Discovering this after drawings are released means expensive rework — always ask the fabrication engineer whether the part will be welded before releasing a 7075 drawing.
7075 has very poor corrosion resistance; it pits rapidly in marine or humid environments. If the part will see outdoor service, either coat it (hard anodize type III, or paint), use Alclad 7075 (pure aluminum-clad on surfaces), or step back to 6061. Never ship bare 7075 to a coastal customer — they will see surface pitting within months.
T7351 is an over-aged temper of 7075 that trades ~10% strength for dramatically better stress-corrosion-cracking (SCC) resistance. For parts that see sustained load in corrosive environment, T7351 is the correct temper. T6 is specified out of habit, not because it's the right choice.
6061-T6 yield is 276 MPa. If actual analysis shows sustained 250 MPa with safety factor of 1.0, you have 10% margin — insufficient for most engineering applications. Either increase the section (adding weight and cost), or move to 7075-T6 (yielding 503 MPa, margin 2×+). 6061 is not a magic low-cost answer; below ~200 MPa working stress, yes; above, probably not.
7075 is harder (150 HB vs 95 HB for 6061) and more abrasive. Carbide tool life drops ~30% in 7075 vs 6061 under identical conditions. For production runs, this shifts the cutting-parameter window: lower speeds, better coolant, more frequent tool changes. Estimators who quote 7075 at 6061 cycle times lose money on every part.
7075's larger grain structure and precipitation particles make sub-0.8 μm finishes difficult to achieve consistently in standard machining. If the surface finish requirement is Ra 0.4 μm or better, either plan on post-machining polishing, or consider whether 6061 would meet the application — it reaches Ra 0.4 μm reliably with a properly-tuned finish pass.
For a representative machined aluminum bracket (0.5 kg finished weight, requiring 1.2 kg bar stock):
| Cost element | 6061-T6 | 7075-T6 |
|---|---|---|
| Bar stock (1.2 kg) | $4.80 | $7.20 |
| Machining time (18 min) | $9.00 | $11.50 |
| Tooling amortized | $0.40 | $0.65 |
| Anodize (Type II clear) | $2.50 | $2.80 |
| Total cost per part | $16.70 | $22.15 |
| Delta vs 6061 | — | +33% |
Representative figures for quantities of 100–500. Actual pricing varies with geometry complexity and finish spec.
The ~33% cost premium for 7075 is real money on a 1000-unit production run. It's worth paying when the application needs the strength. It's a waste when 6061 would do the job.
Both alloys come in multiple tempers. The defaults (T6) are the most common but not always the best choice:
Every quote includes a DFM review by a mechanical engineer. If 7075 is overkill for your part, we'll tell you — and quote 6061 instead.