6061 vs 7075 Aluminum: Which Alloy Should You Specify?
By NOX METALS
6061 and 7075 are the two most widely specified aluminum alloys in structural and aerospace applications. Both machine well and offer a favorable strength-to-weight ratio, but they differ substantially in strength ceiling, weldability, and corrosion behavior. Understanding where each alloy excels will prevent over-specification and help buyers avoid costly surprises during fabrication.
In Short
- →7075-T651 is much stronger: typically 83 ksi tensile and 73 ksi yield, versus 45 ksi and 40 ksi for 6061-T651.
- →6061 is the weldable, general-purpose choice. 7075 is generally unsuitable for conventional structural MIG/TIG welding.
- →7075-T7351 gives up some strength (73 ksi tensile, 63 ksi yield) for improved stress-corrosion resistance versus T651.
- →Densities are close: 0.0975 lb/in³ for 6061 and 0.1015 lb/in³ for 7075.
Tensile Strength
Typical 6061-T651 properties are 45 ksi tensile and 40 ksi yield - adequate for most brackets, fixtures, tooling plate, and medium-load structural members. 7075-T651 is typically 83 ksi tensile and 73 ksi yield, nearly double, which puts it in the same performance tier as many low-alloy steels at roughly one-third the density. If your analysis shows the load case is comfortably within 6061 limits, there is no structural justification for specifying 7075. Typical values are not design allowables; design to the minimums in your governing specification.
Weldability
Weldability is the sharpest practical dividing line between these two alloys. 6061 welds readily with 4043 or 5356 filler wire and produces joints with predictable mechanical properties - a post-weld anneal or re-age can partially restore strength. 7075 is generally unsuitable for conventional structural MIG/TIG welding: the high zinc content causes hot cracking in the weld pool, and the heat-affected zone suffers severe strength loss that cannot be recovered without a full solution heat treat. If your design includes weld joints, 6061 is the correct choice.
Corrosion Resistance
6061 has good natural corrosion resistance due to its magnesium-silicon alloy chemistry, and it anodizes easily to produce a durable oxide layer. 7075 has lower inherent corrosion resistance - the zinc and copper content make it susceptible to pitting and intergranular corrosion in humid or marine environments without protective coating. Where stress corrosion is the concern, 7075-T7351 offers improved stress-corrosion resistance versus T651. For outdoor or high-humidity applications where paint or anodize may be compromised, 6061 is the more conservative choice.
Machinability
Both alloys carry a machinability rating of B (on a scale of A through E, where A is best). In practice, 7075 is often considered slightly easier to machine because its higher hardness produces cleaner chip breaks and better surface finish in high-speed operations. 6061 is softer and can be slightly more prone to built-up edge on dull tooling. Either alloy runs well with sharp carbide tooling, proper feeds and speeds, and adequate lubrication.
Tempers: 6061-T651, 7075-T651 and 7075-T7351
6061 plate is supplied as T651: solution heat-treated, stress-relieved by stretching, and artificially aged, which limits warping as material is removed. 7075 plate comes in two common tempers. T651 has the higher typical strength (83 ksi tensile, 73 ksi yield, 150 HB). T7351 is typically 73 ksi tensile and 63 ksi yield with 13% elongation and 135 HB, and offers improved stress-corrosion resistance versus T651. Both 7075 tempers are stress-relieved by stretching. Order the exact temper your drawing calls for.
Density and Weight
The density difference between 6061 (0.0975 lb/in³) and 7075 (0.1015 lb/in³) is minor - roughly 4 percent. At the part level this difference is rarely the deciding factor. The more important weight consideration is design efficiency: 7075 allows a thinner or smaller cross section to carry the same load, which can reduce part weight even though the alloy itself is denser. This is the scenario where 7075's higher strength actually delivers a net weight advantage.
Cost and Buying
6061 and 7075 prices move daily with the metal market, and the gap between them varies with thickness. The quickest way to compare is to price the same size in both alloys in the instant quote: you get a delivered price and ship date for each in under 60 seconds. NOX METALS has a $90 order minimum and no minimum quantity, so a single piece of either alloy is fine.
Strength at a Glance
Typical Mechanical Properties (ksi)
Property Comparison
| Property | 6061-T651 | 7075-T651 | 7075-T7351 |
|---|---|---|---|
| Ultimate tensile strength (typical) | 45 ksi | 83 ksi | 73 ksi |
| Yield strength (typical) | 40 ksi | 73 ksi | 63 ksi |
| Elongation (typical) | 12% | 11% | 13% |
| Hardness (Brinell) | 95 HB | 150 HB | 135 HB |
| Density | 0.0975 lb/in³ | 0.1015 lb/in³ | 0.1015 lb/in³ |
| Machinability rating | B | B | B |
| Structural MIG/TIG welding | Good | Not recommended | Not recommended |
| Stress-corrosion resistance | Good | Lower than T7351 | Improved vs T651 |
| Plate specifications | ASTM B209, AMS 4027, AMS-QQ-A-250/11 | ASTM B209, AMS 4045, AMS-QQ-A-250/12 | ASTM B209, AMS 4078, AMS-QQ-A-250/12 |
| Max cut size at NOX METALS | 60.5 × 144.5 in | 60.5 × 144.5 in | 60.5 × 144.5 in |
When to Specify Each Alloy
Specify 6061 when the part includes weld joints, requires anodizing for corrosion protection, operates in a non-critical structural role, or when the budget favors the least expensive compliant material. Specify 7075 when the design analysis shows 6061 is insufficient, when weight reduction drives the design (enabling a thinner cross section), or when the application is aerospace-grade and the higher-strength alloy is already called out in the drawing or program spec. Never upgrade to 7075 for perceived quality reasons - the additional fabrication constraints are only justified when the load case demands it.
For the majority of machined structural parts, tooling, and fixtures, 6061-T651 is the correct starting point - it is weldable and provides adequate strength for most load cases. 7075-T651 is reserved for applications where the strength advantage justifies its fabrication constraints, particularly in aerospace primary structure and high-stress mechanical assemblies, with 7075-T7351 where stress-corrosion resistance matters. When in doubt, run the analysis before upgrading the alloy.
Frequently Asked Questions
Is 7075 aluminum stronger than 6061?
Yes. Typical 7075-T651 properties are 83 ksi tensile and 73 ksi yield, compared with 45 ksi tensile and 40 ksi yield for 6061-T651.
Can you weld 7075 aluminum?
7075 is generally unsuitable for conventional structural MIG/TIG welding: it is prone to hot cracking and loses strength in the heat-affected zone. Use mechanical fasteners for structural joints, or choose 6061, which welds with 4043 or 5356 filler.
Which is better for CNC machining, 6061 or 7075?
Both carry a B machinability rating and run well with sharp carbide tooling. 7075's higher hardness tends to give cleaner chip breaks and a better finish at high speed, while softer 6061 is more prone to built-up edge on dull tools.
When should I use 6061 instead of 7075?
Use 6061 when the part is welded, needs consistent anodizing, or does not need 7075's strength. It is the default for most general structural and machined parts.
What is the difference between 7075-T651 and 7075-T7351?
T651 has higher typical strength: 83 ksi tensile and 73 ksi yield. T7351 is typically 73 ksi tensile and 63 ksi yield, with improved stress-corrosion resistance versus T651. Both tempers are stress-relieved by stretching.
Is 7075 more expensive than 6061?
Prices for both alloys change daily with the metal market and vary by thickness, so price the same size in both alloys in the instant quote. You get a delivered price and ship date in under 60 seconds.
Can I buy a single piece of 6061 or 7075 plate?
$90 order minimum. No minimum quantity, so a single piece is fine.
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