6061-T6 and 7075-T6 are both heat-treatable aluminum alloys, and the choice between them comes down to three questions: how much stress the part carries, what environment it works in, and how it will be joined and finished. 6061-T6 is the general-purpose structural alloy. 7075-T6 is roughly 80% stronger, harder, more expensive and much less forgiving. This guide gives the numbers first, then the selection rules.
6061 vs 7075 at a glance
Choose 6061-T6 for welded frames, marine hardware, fixtures, enclosures and parts that need uniform anodized color at moderate cost. Choose 7075-T6 or 7075-T651 when yield strength above roughly 500 MPa (72 ksi) is mandatory, weight is critical, or threads take repeated load, and the part can be bolted instead of welded.
The alloys are not interchangeable at the drawing level. A straight swap changes strength margin, corrosion behavior, finishing yield and machining time, so decide in design review, not purchasing. The table below maps common part types to a default alloy.
| Application | Default choice | Reason |
|---|---|---|
| Welded frames, carts, machine guards | 6061-T6 | Welds with 4043 or 5356 filler |
| Marine and washdown parts | 6061-T6 | Good chloride resistance |
| High-stress aerospace fittings | 7075-T651 | Yield above 500 MPa in stress-relieved plate |
| Mold plates, jigs and tooling | 7075-T651 | 150 HB resists wear and clamp marks |
| Decorative anodized trim | 6061-T6 | Even dye pickup, repeatable color |
| Thin-wall housings with tight flatness | 6061-T651 | Lower quench stress holds flatness |
| Fatigue-critical levers and links | 7075-T73 | Higher endurance limit, better SCC resistance |
Chemistry: why the two alloy systems behave differently
6061 is an Al-Mg-Si alloy with a small copper addition, hardened by Mg2Si precipitates. 7075 is an Al-Zn-Mg-Cu alloy hardened mainly by MgZn2 and related phases. The zinc and higher copper in 7075 buy strength and hardness, and give up corrosion resistance, weldability and anodizing consistency.
Certified limits (ASTM B209 for sheet and plate, ASTM B221 for extrusions, EN 573-3 in Europe) put 6061 at 0.8 to 1.2% Mg, 0.4 to 0.8% Si, 0.15 to 0.4% Cu and 0.04 to 0.35% Cr. 7075 runs 5.1 to 6.1% Zn, 2.1 to 2.9% Mg, 1.2 to 2.0% Cu and 0.18 to 0.28% Cr. That copper level is why 7075 anodizes darker and corrodes sooner. The same trade-off drives the brass vs copper comparison.
Temper designations: T6, T651, T73 and T7351
T6 means solution heat-treated and artificially aged. T651 adds a controlled stretch after aging to relieve residual stress, which matters on thick plate. T73 is an overaged 7075 temper that trades roughly 12% of its strength for much better stress-corrosion resistance; T7351 is the stress-relieved plate version.
6061 is stocked as O, T4, T6, T651 and T6511. 7075 comes as T6, T651, T73, T7351, T76 and T74. Plate over about 50 mm (2 in) is usually supplied as T651 because the stretch is the reliable way to keep thick sections flat. If a drawing calls for 7075-T6 plate, ask whether T651 or T7351 meets the load case with less movement.
Mechanical properties compared
At room temperature 7075-T6 is about 80% stronger than 6061-T6 in tension and yield, roughly 60% harder, and its endurance limit is about 65% higher. 6061-T6 gives up strength but keeps more elongation, toughness and weldability, which is why structural weldments default to it.
| Property (room temperature, typical) | 6061-T6 | 7075-T6 / T651 |
|---|---|---|
| Ultimate tensile strength | 310 MPa (45 ksi) | 572 MPa (83 ksi) |
| Tensile yield strength | 276 MPa (40 ksi) | 503 MPa (73 ksi) |
| Shear strength | 207 MPa (30 ksi) | 331 MPa (48 ksi) |
| Elongation in 50 mm (2 in) | 12% | 11% (10 to 11% in T651 plate) |
| Hardness, Brinell | 95 HB | 150 HB |
| Fatigue endurance limit (5 x 10^8 cycles) | 96.5 MPa (14 ksi) | 159 MPa (23 ksi) |
| Modulus of elasticity | 68.9 GPa (10.0 Msi) | 71.7 GPa (10.4 Msi) |
| Density | 2.70 g/cm3 | 2.81 g/cm3 |
| Corrosion resistance | Good; suitable for marine service | Fair; stress-corrosion risk in T6 |
| Machinability (2011-T3 = 100) | About 50 | About 70 |
| Anodizing response | Type II and III, uniform color | Type II and III possible; darker, less consistent |
| Weldability | Good with 4043 or 5356 filler | Not recommended for fusion welding |
| Relative cost per kg | 1.0 | 1.5 to 3.0 |
| Typical stock forms | Sheet, plate, bar, tube, extrusions, angle | Sheet, plate, round bar; limited extrusion |
Values are typical for wrought product. ASTM B209 minimums sit lower, and plate varies with thickness and test direction, so check the mill certificate. Chemistry and temper data for both alloys sits in the materials selection guide. 7075 loses strength faster above about 120 C (250 F), while 6061 holds useful strength to roughly 150 C. 7075 also has lower fracture toughness, so impact-loaded parts need a damage-tolerance check, not just a yield comparison.
Fatigue and notch sensitivity
7075-T6 has the higher endurance limit, about 159 MPa (23 ksi) at 5 x 10^8 cycles against 96.5 MPa (14 ksi) for 6061-T6. It is also more notch-sensitive: a sharp corner, a machining mark or a corrosion pit costs 7075 a larger share of its fatigue life, so radii, finish and peening matter more.
A 6061 part with generous radii can outlast a poorly detailed 7075 part. Anodizing reduces fatigue strength on both alloys, more so on high-strength 7075, so keep coatings thin over peened surfaces on fatigue-critical parts.
Corrosion resistance: where 7075 needs help
6061-T6 resists atmospheric and marine corrosion well and suits boat fittings, dock hardware and washdown equipment. 7075-T6 is only fair: copper lowers its resistance, and sustained tensile stress in the short-transverse direction can trigger stress-corrosion cracking in chlorides. Where salt is unavoidable, use 7075-T73 or a coating system.
For 7075 in wet or salt service, specify T73 or T7351, keep short-transverse stress low, and add anodizing, chromate conversion coating or paint. Isolate it from steel fasteners to avoid galvanic attack. Salt spray testing to ASTM B117 rates the coating, not the uncoated alloy.
Anodizing response: color, hardness and consistency
6061 anodizes cleanly in Type II sulfuric and Type III hardcoat. It takes dye evenly, holds color across batches and reaches typical hardcoat hardness of 400 to 500 HV. 7075 anodizes as well, but zinc and copper push the coating darker and warmer, and lot-to-lot color matching gets hard.
Type II coatings per MIL-A-8625 are commonly 5 to 25 micrometers; Type III runs 25 to 50 micrometers. Growth is roughly half into the surface and half outward, so a 50 micrometer coating closes a thread flank about 25 micrometers per side: mask threads and bores. For 7075 cosmetic parts, expect color drift and consider chromate or paint. The surface finishing options page covers the full stack.
Welding and joining
6061-T6 is routinely TIG and MIG welded with ER4043 or ER5356 filler. The heat-affected zone falls toward T4 strength, roughly 40 to 50% below T6, and full strength needs post-weld solution treatment and aging. 7075 is not recommended for fusion welding: it hot-cracks and welded joints are prone to stress corrosion.
Put 6061 welds in low-stress regions. Use 5356 filler when the part will be anodized and 4043 when crack resistance matters more. Plan bolted, riveted or bonded joints for 7075; friction stir welding is a specialist process.
Machining behavior on the shop floor
7075-T6 machines faster and cleaner. It breaks chips, holds a sharp edge and tolerates higher feeds, rating around 70 on the common machinability scale where free-cutting 2011-T3 is 100. 6061-T6 sits near 50; in soft O and T4 tempers it smears, builds up on the cutter and needs sharp high-rake tooling plus coolant.
The 1.8 strength ratio shows up as more spindle load and wall deflection at the same removal rate. Five-axis and trochoidal paths help both, but 7075 rewards rigid setups and can run with less coolant because the chip carries heat away. 6061-T6 needs flood coolant to control built-up edge. Deburr either alloy: 7075 edges chip, 6061 edges roll. The CNC machining services used for both hold plus or minus 0.005 mm.
Cost and availability
7075 typically costs 1.5 to 3 times more than 6061 per kilogram, depending on form and temper, and the premium is largest for thick plate and small quantities. 6061 is stocked in far more forms: sheet, plate, bar, tube, extrusions and angle. 7075 is mainly sheet, plate and round bar.
On a complex part, 7075’s faster cycle can recover part of the premium; on welded assemblies and color-critical anodized parts, 6061 wins. Mill certificates and ultrasonic inspection add cost on both, and 7075 plate often carries a longer lead time. Compare at the part level with the CNC machining cost breakdown.
Distortion, residual stress and stress relief
Both alloys move after machining when residual stress releases, but 7075-T6 thick plate is the bigger risk because quench stresses and strength are higher. Specify T651 or T7351 for tight flatness, remove material symmetrically from both faces, and rough, stress-relieve, then finish.
Mechanical stretching in T651 and T7351 is the most reliable relief method. Thermal relief of rough-machined parts follows AMS 2770 cycles and costs a furnace cycle plus a re-fixture. For thin-wall parts, leave stock on non-critical surfaces, machine webs last and use fixture support. Flatness tighter than about 0.1 mm over 300 mm needs that sequence, not a single pass.
Decision checklist
Start with strength, then filter by joining, environment, finishing and flatness. Yield above 400 MPa (58 ksi) points to 7075, any fusion weld points to 6061, and a decorative anodized finish points to 6061. Cost and lead time break ties after those three questions.
- Yield above 400 MPa (58 ksi)? Yes means 7075-T6 or T651; no means 6061-T6 covers most structural work.
- Any fusion weld? Use 6061-T6; 7075 is a bolted or bonded design.
- Salt water or permanent wet service? 6061-T6, or 7075-T73/T7351 with a coating.
- Decorative anodized color? 6061-T6 dyes evenly; 7075 drifts darker between lots.
- Weight critical at fixed load? 7075 wins on specific strength if geometry is not notch-limited.
- Threads repeatedly assembled? 7075 holds them better; in 6061 use inserts or deeper engagement.
- Tight flatness on thick plate? 6061-T651 or 7075-T7351, rough, relieve, finish.
- Does volume justify the premium? 7075 pays back only on the right part.
DFM notes for each alloy
Design rules differ because 7075 is notch-sensitive and 6061 is more ductile. Give 7075 larger radii, thicker walls and a smoother finish; give 6061 support against distortion and settle the finish before anodizing. Call out threads, radii and flatness explicitly, because the shop cannot infer them from a nominal model.
- Thin walls. 6061-T6 holds 0.8 mm (0.030 in) walls with support; 7075 is safer at 1.0 to 1.5 mm (0.040 to 0.060 in) because it transmits chatter.
- Internal radii. At least half the wall thickness in 6061, and the full wall thickness in 7075.
- Edge margins. Keep 2x the hole diameter from an edge in both alloys, 2.5x in fatigue-loaded 7075.
- Threads. Plan 1.5x diameter in 6061 and 1.0 to 1.5x in 7075; add inserts where joints open repeatedly.
- Anodize allowance. Mask threads and bores and state coating thickness so the machinist leaves stock.
- Inspection. Call flatness or profile on plate parts and position on hole patterns, using standard GD&T symbol definitions so the CMM report matches the drawing.
Getting parts made in either alloy
Once the alloy and temper are fixed, the quote depends on stock form, finish and inspection, not the alloy name. A shop that machines both alloys will price the part from the drawing, the tolerance stack and the finish callout, and will flag a 7075 design that should be 6061.
YC Prime Precision is an ISO 9001 contract manufacturer in Qingdao with 3- and 5-axis CNC milling and turning to plus or minus 0.005 mm. Send your drawing to get an instant quote; most CNC parts ship in 3 to 10 business days after drawing approval.
FAQ
Is 7075 aluminum stronger than 6061?
Yes. 7075-T6 reaches about 572 MPa (83 ksi) tensile and 503 MPa (73 ksi) yield, against 310 MPa (45 ksi) and 276 MPa (40 ksi) for 6061-T6. That is roughly 80% more strength at about 4% more weight, so 7075 wins on specific strength, at the cost of corrosion resistance, weldability and price.
Can 7075 aluminum be welded?
No, not by fusion welding. The alloy hot-cracks, and welded joints are prone to stress-corrosion cracking. Use bolts, rivets or structural adhesive, or move the welded assembly to 6061-T6. Friction stir welding exists in aerospace but is not a general shop process.
Does 7075 corrode more than 6061?
Yes. 6061-T6 resists atmosphere and salt water well. 7075-T6 is rated only fair: copper lowers resistance, and sustained tensile stress can cause stress-corrosion cracking in the short-transverse direction. T73 or T7351 temper, a coating and low short-transverse stress reduce the risk.
Which aluminum alloy anodizes better, 6061 or 7075?
6061 anodizes more predictably. It takes Type II dye evenly and hardcoats to consistent color, which is why decorative parts are usually 6061. 7075 anodizes but tends to come out darker and shifts between lots, so it suits functional coatings better than color-matched cosmetic work.
Is 7075 worth the extra cost?
Only when the design needs the strength. If yield above roughly 400 MPa (58 ksi), minimum weight or thread durability drives the part, 7075’s faster machining can offset part of its 1.5 to 3 times material premium. For frames, brackets, enclosures and marine hardware, 6061-T6 does the job for less.
