Alloy Comparison
Two very different alloys that rarely compete for the same application. 6061 is the default general-purpose structural choice. 7050 is the high-strength aerospace thick-section answer when stress corrosion cracking is a design requirement.
The Short Answer
If your part needs to be welded, needs moderate strength, or cost matters, specify 6061-T651. If your part is a thick-section aerospace or defense structural component where stress corrosion cracking is called out in the specification, or AMS 4050 is specified directly, specify 7050-T7451. There is very little gray area between the two.
| Property | 6061-T651 | 7050-T7451 |
|---|---|---|
| Alloy System | Mg-Si (6xxx series) | Zn-Cu-Mg-Zr (7xxx series) |
| Tensile Strength (T651 / T7451) | 42,000 psi min | 70,000 psi min |
| Yield Strength | 35,000 psi min | 60,000 psi min |
| Elongation | 8% min | 7% min |
| Weldability (MIG/TIG) | Excellent | Not recommended |
| Machinability Rating | B | B |
| SCC Resistance (thick section) | Good | Superior (formulated for it) |
| Corrosion Resistance (uncoated) | Good | Fair to Good |
| Primary Plate Temper | T651 | T7451 |
| Primary Plate Spec | AMS-QQ-A-250/11 | AMS 4050 |
| Typical Thickness Range | 0.25" to 10" | 0.25" to 6" |
| Relative Cost per Pound | Baseline | 2x to 3x of 6061 |
| DFARS Available | Yes | Yes |
| Primary Application | General structural, fixtures, marine | Aerospace thick-section structure |
6061 is the default North American structural aluminum for a reason. Its silicon-magnesium chemistry produces a balanced combination of properties: adequate strength for the overwhelming majority of structural jobs, excellent weldability using 4043 or 5356 filler, consistent machinability, and enough corrosion resistance to serve outdoor and marine applications without coating in many cases.
Specify 6061-T651 when the part will be welded or brazed, when corrosion resistance in uncoated service matters, when cost is a meaningful program constraint, or when the application does not require aerospace-grade strength. Machined fixtures, brackets, frames, jig plate, electronics housings, deck hardware, marine components, tool plate, and general industrial fabrication all fall cleanly into 6061 territory.
T651 is the plate temper for machining. The stress-relief stretch that happens after quench removes residual stress that would otherwise cause warping as material is removed. T4 is available for parts that will be formed before final heat treatment, but T651 is the default.
7050 exists because 7075 has a specific problem in thick plate: during quench, the interior cools more slowly than the surface, leaving reduced mechanical properties and greater susceptibility to stress corrosion cracking in the section core. 7050 solves this with a different alloy system (Zn-Cu-Mg-Zr) that is less sensitive to quench rate, maintaining consistent properties and superior SCC resistance across thick sections.
Specify 7050-T7451 when the program specification calls out AMS 4050, when the plate thickness exceeds 3 inches and the structure is loaded, when stress corrosion cracking is a formal design requirement, or when the part will be stressed in the short-transverse grain direction in a corrosive environment under sustained load. Aircraft wing center sections, fuselage frames, thick bulkheads, and large defense structural components are the primary applications.
7050 is not a substitute for 6061. It is more expensive, it cannot be welded, and its strength is only an advantage if the part geometry needs it. Specifying 7050 where 6061 would work wastes program budget without engineering benefit.
6061 is a silicon-magnesium general-purpose structural alloy with 42,000 psi tensile in T651, good machinability, good weldability, and good corrosion resistance. 7050 is a zinc-copper-magnesium-zirconium aerospace alloy with 70,000+ psi tensile in T7451, formulated specifically for thick-section aircraft structure with superior stress corrosion cracking resistance. The two alloys serve different application categories and are rarely interchangeable.
Yes. 7050-T7451 has a minimum tensile strength of 70,000 to 72,000 psi depending on thickness, compared to 42,000 psi for 6061-T651. 7050 is roughly 70 percent stronger. The strength advantage comes from the zinc-copper alloy system and careful heat treatment, at a substantially higher cost per pound than 6061.
No. 7050 is not recommended for structural arc welding. Like 7075, it is susceptible to hot cracking in the weld pool and significant strength loss in the heat-affected zone. 6061 welds cleanly with 4043 or 5356 filler using MIG or TIG. For applications that require welded assembly, 6061 is the correct alloy. For 7050, specify mechanical fasteners, adhesive bonding, or friction stir welding.
Specify 6061 when the application does not require aerospace-level strength, when the part will be welded, when corrosion resistance in coated or uncoated service matters, or when cost is a meaningful constraint. 6061 is the default choice for structural brackets, fixtures, machined tooling, marine hardware, and general industrial parts. Use 7050 only when thick-section aerospace strength and SCC resistance are specific design requirements.
Yes, substantially. 7050-T7451 plate typically runs two to three times the per-pound price of 6061-T651, reflecting the tighter chemistry control, more stringent heat treatment requirements, and smaller production volumes. For any application where 6061 meets the engineering requirements, specifying 7050 adds cost without benefit.
6061 plate is specified to AMS-QQ-A-250/11 and AMS 4027, and meets ASTM B209. 7050 plate is specified to AMS 4050 for T7451 temper, with AMS-QQ-A-250/14 as a general coverage. NOX METALS supplies plate certified to the applicable AMS specification with full mill certifications, heat numbers, and origin documentation on every order.
6061 Aluminum Plate
Full specs, T651 and T4
7050 Aluminum Plate
Full specs, AMS 4050
6061 vs 7075
Weldable vs high-strength
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