Materials
6061 vs 7075 Aluminum: Which to Spec
The short answer
Use 6061-T6 when the part needs to be welded, formed, or resist corrosion without a coating, and when its 276 MPa yield strength is enough. Use 7075-T6 when you need strength, at 503 MPa yield, and can accept that it is effectively unweldable, less corrosion resistant, and roughly two to three times the material cost.
Property comparison
| Property | 6061-T6 | 7075-T6 |
|---|---|---|
| Primary alloying elements | Magnesium and silicon | Zinc, magnesium, copper |
| Yield strength | 276 MPa (40 ksi) | 503 MPa (73 ksi) |
| Tensile strength | 310 MPa (45 ksi) | 572 MPa (83 ksi) |
| Elongation at break | About 12% | About 11% |
| Weldability | Good | Poor, not recommended |
| Corrosion resistance | Good | Fair, usually needs anodize or clad |
| Formability | Good | Poor |
| Relative material cost | Baseline | About 2 to 3x |
The three questions that decide it
Does it need to be welded? If yes, 6061. 7075 is prone to hot cracking in the weld zone and loses most of its strength advantage in the heat-affected zone anyway. There is no clever workaround worth the risk on a structural part.
Does it need to bend or form? If yes, 6061. 7075 has poor formability and will crack at radii 6061 handles comfortably.
Is it strength-limited? If yes, and neither of the above applies, 7075. You get nearly double the yield strength for a material cost premium that is often small relative to the machining cost of the part.
The corrosion catch
7075 in the T6 temper is susceptible to stress corrosion cracking, particularly in the short-transverse direction under sustained tensile load. This is a real failure mode, not a theoretical one, and it is why aerospace often specifies the T73 temper instead. T73 trades roughly 10 to 15 percent of the strength for substantially better stress corrosion resistance.
If a 7075 part is going to sit loaded in a humid or marine environment for years, specify T73 and anodize it. If it is a prototype bracket in a lab, T6 bare is fine.
What about machining cost?
Both machine well, and the difference is smaller than people expect. 7075 actually produces cleaner chips than 6061, which tends to be gummy and can build up on the cutting edge. On many parts the machining time is close to identical, meaning the total cost difference comes down to material, which is often a modest fraction of a machined part's price.
This is the argument for not defaulting to 6061 out of habit. If the part is strength-limited and never gets welded, the 7075 version may cost only slightly more.
Cost, availability and what it means for your quote
The material cost difference is real but often smaller in context than people expect, because on a machined part the material is frequently a minority of the price. Machining time dominates, and the two alloys machine similarly. 7075 actually chips more cleanly than 6061, which tends to be gummy and can build up on the cutting edge.
The practical consequence: if your part is strength-limited and never gets welded, the 7075 version may cost only modestly more than the 6061 one. That is the argument against defaulting to 6061 out of habit.
Where 7075 does cost you is availability. It is stocked in fewer forms and fewer sizes, particularly in larger plate and unusual extrusions, so an unusual size can add lead time even when the price is fine.
| Factor | 6061-T6 | 7075-T6 |
|---|---|---|
| Raw material cost | Baseline | About 2 to 3x |
| Machining time | Baseline | Similar, sometimes slightly better |
| Stock availability | Very wide, most forms and sizes | Narrower, especially large plate |
| Typical effect on a machined part price | Baseline | Modest increase on most geometries |
| Weldable | Yes | No, for structural purposes |
What to specify, and what to leave to the shop
Specify the temper, not just the alloy. 6061 and 6061-T6 are not the same thing to a buyer of material, and 7075-T6 versus T73 is a genuine engineering decision with a strength and corrosion trade-off attached.
Specify the finish if it matters. Both anodize, but 6061 gives more consistent Type II color and easier lot-to-lot matching. If your product has visible parts that must match across production runs, that is worth knowing before you commit to 7075.
Leave stock form to the shop unless you have a reason. Telling a shop to machine from plate when they have suitable extrusion, or vice versa, removes an option that might have saved you money. Say what the part must do, not how to buy the metal.
Forms, sizes and what that does to your lead time
Alloy choice is not only a strength decision. It is also an availability decision, and availability is where schedules quietly break.
6061 is stocked almost everywhere in almost every form: plate, sheet, round bar, square bar, hex, angle, channel, tube and a very wide range of standard extrusions. If your part can be machined from a common 6061 size, material is effectively never the constraint.
7075 is stocked in far fewer forms. Plate and round bar are usually available in common sizes; large plate, thick sections and unusual profiles frequently are not, and a mill order can add weeks. On a prototype run that can dominate your schedule.
The practical move is to ask about stock availability at quote time rather than after the purchase order. A shop that already has 7075 plate in the thickness you need will quote both a better price and a better date than one who has to buy it in, and you cannot tell which is which from the drawing.
| Form | 6061 availability | 7075 availability |
|---|---|---|
| Plate and sheet | Very wide | Common sizes only |
| Round bar | Very wide | Good in common diameters |
| Thick sections | Wide | Limited, often mill order |
| Standard extrusions | Extensive | Very limited |
| Tube | Wide | Limited |
When neither is the right answer
Two alloys cover most machined parts, but a handful of jobs are better served elsewhere, and knowing them saves a redesign.
5052 is the sheet metal alloy. If your part is being bent rather than machined, 6061 will crack at radii 5052 handles easily. This is the single most common misspecification we see on fabricated parts.
2024 sits between 6061 and 7075 on strength with better fatigue performance, which is why it persists in aerospace structure. It has poor corrosion resistance bare and is usually clad.
MIC6 and other cast tooling plate are the right call for large flat parts that must stay flat: fixture plates, base plates, optical benches. Cast plate is stress-relieved and stays stable after machining in a way rolled plate does not. If you have ever machined a large 6061 plate and watched it bow, this is the fix.
7050 and 7075-T7351 are worth knowing where stress corrosion cracking is a genuine concern in thick sections.