6061 vs 7075 Aluminum: Which Grade for CNC Machined Parts

What each alloy actually is

Both grades are heat-treatable wrought aluminium, and both are used for machined parts every day. The difference starts in the alloying elements.

6061 is an aluminium–magnesium–silicon alloy. Magnesium and silicon form the strengthening precipitate; there is no copper in the mix. That absence is why 6061 resists corrosion well, anodizes to a clean and even finish, and welds without drama. It is the general-purpose structural aluminium, and it is what most machined brackets, housings, plates and fixtures are made from — the summary of grades and properties sits on our aluminum machined parts page.

7075 is an aluminium–zinc–magnesium–copper alloy. Zinc and magnesium carry the strength, and the copper addition is what lifts it into a different class — 7075 is roughly the strongest aluminium available as standard mill stock. The same copper that provides the strength is what degrades corrosion performance and discolours the anodized layer.

The practical consequence: 7075 is a high-strength alloy with strings attached, and 6061 is a moderate-strength alloy with almost none.

The numbers, side by side

Typical room-temperature properties for the two grades in their common tempers. Values are indicative and vary by product form and thickness.

Property	6061-T6	7075-T6
Yield strength (tension)	~276 MPa (40 ksi)	~503 MPa (73 ksi)
Ultimate tensile strength	~310 MPa (45 ksi)	~572 MPa (83 ksi)
Elongation	~12%	~11%
Density	~2.70 g/cm³	~2.81 g/cm³
Modulus of elasticity	~69 GPa	~72 GPa
Relative machinability	Very good	Good — more abrasive
Weldability	Good	Not a welding alloy
Corrosion resistance	Very good	Moderate
Anodized appearance	Clean and even	Darker, less uniform
Relative material cost	Baseline	Roughly 1.5–2×
Stress corrosion resistance	Not a concern	Limited in T6; T73 improves it

Two rows deserve more than a glance. The density row means 7075 gives up about 4% of its weight advantage before the strength comparison even starts. The modulus row is the one people miss: stiffness is nearly identical. Aluminium alloys do not differ much in elastic modulus, so a 7075 part does not deflect less than a 6061 part of the same geometry under the same load until it is close to yield. What 7075 buys is the ability to carry more load before it permanently deforms — not a stiffer part.

Strength, and where it actually matters

If the part is failing in service, 7075 is the answer. If it is not, 7075 is an expensive way to make a heavier chip pile.

The honest framing is this: 6061-T6 at 276 MPa yield is a strong material. It is stronger than mild steel. Most brackets, covers, plates, manifold bodies and housings never approach that limit, and specifying 7075 for them buys nothing except a larger invoice.

7075 earns its place when the part is genuinely strength-limited and weight is constrained:

• Aerospace and defence structural components where the strength-to-weight ratio is the design driver
• High-load brackets and fittings where a 6061 part would need to grow in section to survive
• Tooling, jigs and wear plates that see repeated load
• Racing and high-performance applications where mass is the enemy
• Applications where a thinner section is forced by packaging and 6061 would deflect too far

There is a second case that is easy to overlook: fatigue. Where a part cycles under load rather than sitting under a static one, the alloy and its condition matter in a different way, and 2024 — the third alloy in this family — is often the right answer rather than either of these two. If the loading is cyclic, say so at the quotation stage rather than after the parts crack.

Machinability and the finish off the tool

6061 is one of the most pleasant metals to machine. It produces clean, well-broken chips, tolerates aggressive feeds and speeds, holds fine detail and threads crisply, and leaves a good surface straight off the cutter. Cycle times are short and tool life is long. On a part that will be machined in quantity, this shows up in the unit price more than the material cost does.

7075 machines well, but it is a different experience. It is harder and more abrasive, so it runs hotter and wears tooling faster. It machines at lower surface speeds for the same tool life, and the chip is less forgiving. Deep pockets and thin walls — the two features that already test a setup — are harder to hold in 7075 than in 6061. And 7075 is more prone to leaving a slightly duller as-machined surface, which matters if the part is going anodized clear and finish is part of the product.

The practical result: a 7075 part usually costs more than the material premium alone suggests, because the cycle time is longer and the tooling wears sooner. When the two grades are compared on total part cost rather than on metal price, the gap widens.

Both grades cut cleanly at ±0.01 mm on precision features with ISO 2768-m as the general tolerance block, and both hold that equally well. Machinability affects cost, not achievable tolerance — the tolerances we hold are set by the machine and the setup, not by which of these two alloys is on the bar.

Anodizing: the difference people notice last

Anodizing is the most common finish for machined aluminium, and it is where 6061 and 7075 visibly diverge.

On 6061, the anodic layer grows evenly and takes dye predictably. Clear anodizing on 6061 is a clean, uniform result, which is why it is the default for dyed and clear anodized parts — the colour you approve on the sample is the colour you receive.

On 7075, the copper and zinc content changes the film. The result is darker and less uniform, and clear anodizing on 7075 does not match clear on 6061 side by side. This is not a defect in the process; it is the alloy. The usual responses are to specify a darker dye where the shift is masked, to accept the tone deliberately, or to use a conversion coating instead.

Two consequences worth planning for:

1. Do not approve a 7075 colour from a 6061 sample. If the programme mixes the two alloys, approve each separately.
2. Do not mix alloys within one visible assembly if the parts will be anodized and the appearance has to match. A 6061 cover on a 7075 body will not match in clear anodizing, and the mismatch is not correctable after the fact.

Type II (the everyday cosmetic and light-protective anodizing) and Type III (the thicker, harder layer for wear surfaces) are both available on either alloy, and hardened 7075 takes Type III well — which is one reason it appears on wear parts. Masking requirements, thread protection and any post-finish dimensional tolerance belong on the drawing, because anodizing builds a layer. Our anodizing page covers what each type suits and where the dimensional allowance has to be planned.

Corrosion, and the stress corrosion question

6061 resists atmospheric and marine corrosion well without any coating, and anodizing adds a further barrier. It is the safer choice outdoors, in washdown areas and anywhere the surface will be scratched in service.

7075 is a moderate performer. It is not fragile — plenty of 7075 parts live outdoors — but it needs a protective finish where the environment is aggressive, and it is more vulnerable once the surface is damaged. In marine or chemical exposure, 6061 with anodizing is the low-risk specification.

The subtler issue is stress corrosion cracking. 7075-T6 under a sustained tensile load — a bolt preloaded and left, a part held in permanent tension — can crack over time in a corrosive environment. The T73 temper exists specifically to address this: it sacrifices a modest amount of strength for a large improvement in stress corrosion resistance. For a highly stressed 7075 part that will sit under permanent load, T73 or T7351 is worth asking about rather than accepting T6 by default.

6061 does not pose the same concern in normal service.

Welding: the shortcut answer

7075 is not a welding alloy. Its weld zone loses strength and is prone to cracking, and no amount of process control fixes that — the alloy is simply not designed for it. If the part is welded, or will be welded later, or is part of a fabricated assembly, specify 6061 and stop there.

6061 welds well, which is why it dominates welded aluminium structures. If you are weighing the two grades and welding is anywhere in the process plan, the comparison is over.

Cost, and what it means over a production run

7075 typically costs roughly one and a half to two times 6061 per kilo, depending on the product form and the market at the time. On top of the material premium sit the longer cycle time and faster tool wear described above.

That premium is sometimes worth paying and sometimes is not:

• Prototype or small batch: the absolute difference is small. If the part is strength-limited, take 7075 and move on.
• Production run: the material premium is a permanent per-part cost. On a part that does not need the strength, that money buys a lighter wallet and nothing else.
• A part that could be redesigned: if a section change in 6061 would meet the requirement, redesigning is usually cheaper over the run than upgrading the alloy. Sending the loads rather than only the drawing is what makes that conversation possible.

There is a third option that gets skipped: material substitution by geometry. A 6061 part with a slightly thicker web often matches a 7075 part on stiffness at lower cost, because stiffness is driven by geometry far more than by alloy, as the modulus row above shows.

Availability and product form

6061 is the most widely stocked aluminium in the world. Plate, bar, tube and extrusion are available in a wide range of sizes in T6, and in T651 plate for parts that need stress-relieved stock.

7075 is well stocked in the common plate thicknesses and rounds, in T6 and T651, with T73 and T7351 available in fewer sizes. An unusual thickness or a temper nobody keeps locally adds lead time — not usually much on a common size, occasionally a great deal on an unusual one.

Material is bought against your drawing for your job, so the grade you name in the quote is the grade we buy. If a size or temper were to become a problem, you would hear about it before anything was cut, and the material certificate that ships with the batch is traceable to the mill heat it came from — see what ships with your order. The full list of grades we run is on the materials page.

Decision shortcuts by part type

Most grade arguments resolve the moment the part is named. This is the pattern that holds in practice.

The part	Specify	Why
Bracket, cover, plate, enclosure	6061-T6	Not strength-limited; welds, anodizes and machines cleanly
Fixture, jig, tooling plate	6061-T651	Stress-relieved plate holds flatness after heavy material removal
Heat sink	6061-T6	Thermal conductivity is close between the two, and 6061 costs far less
Marine or washdown hardware	6061-T6	Better corrosion resistance; anodizes evenly for added protection
Structural aerospace bracket	7075-T651	Strength-to-weight is the design driver
High-load fitting, thin section forced by packaging	7075-T651	6061 would have to grow in section to survive
Highly stressed part under permanent load	7075-T73 / T7351	Trades a little strength for stress corrosion resistance
Wear plate or hardened tooling	7075-T6, Type III anodized	Takes a hard anodic layer well
Part that will be welded	6061-T6	7075 is not a welding alloy; this ends the comparison
Part that cycles under load	Ask	Fatigue may point at 2024 rather than either of these

Two shortcuts on that table are worth stating plainly. Stiffness is not on it, because the modulus of the two alloys is nearly identical — if the requirement is “does not deflect”, the answer is geometry, not alloy. And “make it stronger” is rarely the real requirement; the real requirement is usually a specific load, a specific weight ceiling and a specific cost, and sending those three is more useful than sending an alloy name.

Changing grade mid-programme

Two situations come up often enough to plan for.

Scaling from prototype to production. A part proved in 7075 can sometimes move to 6061 for the production run if the margin allows, and the saving is real. That move should be a decision on the drawing, not a substitution in the shop. If the loads have margin, say so and we will quote both grades side by side so the comparison is on numbers.

A grade that will not arrive in time. Supply of an unusual size or temper can move. The rule we work to is that if a mill substitution ever became unavoidable you would be asked in writing before anything was cut. We do not downgrade a material quietly, and when the quote confirms a grade, that is the grade that gets bought.

Where the part is going straight into a production run and the alloy is still open, sending the load case along with the drawing is the fastest route to a decision — DFM feedback comes back within 24 hours, and a grade recommendation is part of it.

The callout that belongs on the drawing

The single most useful thing you can do is state alloy and temper, not just “aluminium”.

Instead of	Write
Aluminium	6061-T6, or 7075-T651
Alu, heat treated	6061-T6 (or the temper the drawing requires)
7075	7075-T651, stress-relieved plate if flatness matters
Anodize	Anodize Type II clear, 0.0004 in, mask the threads

And add these three, which cost nothing and prevent the most common rework:

1. Where the precision features are — a tolerance on a locating bore is not the same instruction as a tolerance on a decorative face.
2. Which faces must stay masked before anodizing — threaded holes, mating surfaces and electrical contact faces.
3. Whether the part is loaded statically or cyclically — it decides whether strength or fatigue governs the grade choice.

Send the drawing, the material callout and the quantity, and the quote comes back within 24 hours with DFM feedback on how the part will machine — including where a tolerance or a feature is adding cost without adding function.