Aluminium 7075 CNC Machining

What 7075 is, and what it costs

Aluminium 7075 is an aluminium-zinc-magnesium-copper alloy, and it is roughly the strongest aluminium available as standard mill stock. Yield strength in the T6 temper is around 503 MPa, against roughly 276 MPa for 6061 — about 80% higher.

That strength is real and it is the reason the grade exists. What comes with it is a set of trade-offs that a drawing should acknowledge before the grade is fixed:

• It is more abrasive to machine, so tooling wears faster
• It resists corrosion less well than 6061, because of the copper content
• It anodizes to a darker, less uniform tone, which matters on visible parts
• It is not a welding alloy
• It carries a stress corrosion risk in the T6 temper under sustained load
• It costs roughly one and a half to two times as much per kilo

None of those is a defect. They are the terms the grade works on, and a part that genuinely needs 7075 is a part where the strength is worth all of them. A part that does not need 7075 is a part that pays for the strength and uses none of it.

The tempers, and the one that matters most

7075 is heat treatable, so the temper is part of the specification rather than a detail.

Temper	Condition	Where it is used
T6	Solution heat treated and artificially aged	Highest strength; the default for machined parts
T651	T6 on plate, stress-relieved by stretching	Parts where flatness must survive heavy material removal
T73	Over-aged	Better stress corrosion resistance at slightly lower strength
T7351	T73 on stress-relieved plate	Highly stressed parts under permanent load
O	Annealed	Forming before aging

T6 is what most machined 7075 parts are quoted in, and it delivers the headline strength.

T651 is the same temper on plate that has been stress-relieved by stretching after the quench. On a part where a lot of material is removed and flatness has to survive, this matters: as-quenched material carries internal stress, and cutting metal from one face lets it redistribute, which can bow the part. For a thin, flat, heavily machined component, T651 is usually worth specifying.

T73 and T7351 are the tempers that exist to solve stress corrosion cracking. See the section below — this is the part of the 7075 specification most often left off a drawing, and it is the one that can matter in service.

Machining behaviour

7075 machines well, and it machines differently from 6061 in ways that show up in the price.

It is abrasive. The alloy is harder than 6061 and wears cutting edges faster. A cutter that runs a long life in 6061 will be changed sooner in 7075, and the tooling cost per part rises with it.

It runs hotter and cuts slower. For the same tool life, 7075 is machined at lower surface speeds. Cycle times are longer than the same part in 6061.

It is less forgiving on difficult geometry. Deep pockets and thin walls — the two features that already test a setup — are harder to hold in 7075 than in 6061, because the material is stiffer to cut and heat concentrates more.

The as-machined finish is slightly duller. Where the machined surface is the finished surface, 6061 leaves a better result straight off the tool. This matters most on a part that will be clear anodized, where the surface is visible and the finish is part of the product.

The practical consequence is that 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 hold ±0.01 mm on precision features with ISO 2768-m as the general block. Machinability affects cost, not achievable tolerance — see tolerances we hold.

The modulus point that gets missed

There is one property of 7075 that surprises people, and it is worth stating plainly because it changes design decisions.

The modulus of elasticity of 7075 is nearly identical to 6061 — around 72 GPa against 69 GPa. Aluminium alloys do not differ much in elastic modulus, and the modulus is what governs how far a part deflects under a given load.

The consequence: a 7075 part is not meaningfully stiffer than the same 6061 part. It will deflect almost the same amount under the same load. What it will do is carry far more load before it permanently deforms — the yield point is much higher.

That distinction matters for how a strength problem is solved:

• If the part must not deflect, the answer is geometry — a thicker web, a deeper rib, a shorter span. Changing to 7075 buys almost nothing.
• If the part is yielding or failing, 7075 buys a great deal, and it lets the geometry stay as designed.

A 6061 part with a slightly thicker web often matches a 7075 part on stiffness at a lower cost, because stiffness is driven by geometry far more than by alloy.

Stress corrosion, and when to specify T73

7075-T6 under a sustained tensile load — a preloaded bolt, a part held permanently in tension — can crack over time in a corrosive environment. This is stress corrosion cracking, and it is the reason the T73 temper exists.

Over-aging the alloy to T73 sacrifices a modest amount of strength for a large improvement in resistance to that failure mode. T7351 is the same treatment applied to stress-relieved plate.

The practical guidance:

• A part under static, low-stress load in a benign environment — T6 is fine.
• A highly stressed part held under permanent load — ask about T73 or T7351 rather than accepting T6 by default.
• A part in a corrosive environment under sustained load — T73 is the safer specification, and the strength it gives up is usually a small fraction of what it keeps.

This is the one place where specifying the highest-strength temper is actively the wrong instinct. T6 is not “better” than T73 — it is stronger and less resistant to one specific failure mode, and which matters depends on how the part is loaded.

Finishing 7075

7075 takes the same finishes as 6061, but not with the same results.

Finish	Behaviour on 7075
Anodize clear	Darker and less uniform than on 6061 — will not colour-match 6061
Anodize dyed	Works, but choose a darker colour where the tonal shift is masked
Anodize Type III (hardcoat)	Takes a hard layer well — one reason 7075 appears on wear parts
Alodine / conversion coating	Thin and conductive; a common choice where anodizing appearance is a problem
Powder coating	Full colour coverage; hides the substrate tone entirely
As machined	Acceptable indoors; the alloy has moderate corrosion resistance

Two rules follow, and both are about assemblies.

Do not approve a 7075 colour from a 6061 sample. If a programme mixes the two alloys, approve each separately on its own sample.

Do not mix the two alloys within one visible assembly that will be clear anodized. A 6061 cover on a 7075 body will not match, and the mismatch cannot be corrected afterwards.

Where appearance matters and the part has to be 7075, a powder coat or a conversion coating is usually a safer route than clear anodizing. The anodizing page covers the types and the dimensional allowance.

What 7075 is used for

The grade is chosen where strength-to-weight is the design driver and the geometry is constrained:

• Aerospace and defence structural components
• High-load brackets and fittings, where a 6061 part would need to grow in section
• Tooling, jigs and wear plates, particularly hardcoat anodized
• Racing and high-performance applications where mass is the enemy
• Components where packaging forces a thin section that 6061 could not carry
• Gears, shafts and drive components under high load in a dry environment

The common thread is a part that is genuinely strength-limited. Where it is not, 6061 does the job at lower cost on both the material and the machining line.

When 7075 is the wrong grade

Four situations where the premium buys nothing or the grade does not work.

The part is not strength-limited. This is the most common case. If a 6061 part would carry the load in the same envelope, 7075 is a per-part surcharge for a property the part will not use.

The part must be welded. 7075 is not a welding alloy. A fabricated assembly is built in 6061 or in a stainless grade.

The part has to be non-magnetic or highly corrosion resistant. Neither is 7075’s strength. Where corrosion is the requirement, the answer is a stainless grade — and where strength and corrosion are both required, a precipitation-hardening stainless such as 17-4PH rather than a harder aluminium.

The part must be clear anodized to match 6061. The two cannot be matched. Where an assembly has to read as one colour, both parts should be the same alloy.

What to put on the drawing

Instead of	Write
Aluminium	7075-T6, or 7075-T651 for flat plate work
7075	7075-T73 or T7351 where the part sits under sustained load
7075, anodized	7075 with a darker dye, or a conversion coating — not clear anodizing to match 6061
7075, welded	Wrong grade — 7075 is not a welding alloy
Aluminium, stiffer	Wrong lever — increase the section; the modulus is the same
7075, cost-sensitive	Confirm the part is strength-limited; 6061 may do the same job for less

The three lines that matter most are the temper, whether the part is welded, and whether it is load-limited or deflection-limited. Those three decide whether 7075 is the right grade at all, and they cost one sentence each.

Material is bought against your drawing for your job, and every batch ships with a material certificate (MTR) tracing the alloy to its mill heat plus pre-shipment photos of the actual parts. Orders start at 50 pieces per style and material, samples from a single piece in 5–10 days, and production runs in 25–35 days after sample approval. Send the drawing through the request a quote form and the reply comes back within 24 hours with DFM feedback, including a grade recommendation where the strength requirement is genuinely open.