Guides / Materials

Picking Between 6061 and 7075 for a Loaded Part

September 23, 2026

Nearly every billet automotive part is cut from one of two aluminum alloys. Picking the wrong one is not usually catastrophic, but it costs money in one direction and reliability in the other.

Here is the honest comparison, including the cases where each one is a mistake.

The short version

6061-T6 is the default, and it deserves to be. It is available in every stock size, it welds, it anodizes evenly, it resists corrosion well and it costs the least. For brackets, spacers, covers, adapter plates and most mounts, it is the right answer.

7075-T6 roughly doubles the yield strength. It belongs on parts where weight and strength both matter and where the part will not be welded, will not sit in salt spray unprotected and will not be modified later.

Neither is a substitute for steel on a shock loaded part. Aluminum has no fatigue limit. Every cycle does damage, and a part that sees millions of load reversals eventually cracks whatever the alloy.

Strength and fatigue

Typical values for the common tempers. Treat them as the figures a designer starts from, not as guarantees for your specific stock.

Property	6061-T6	7075-T6
Yield strength	about 275 MPa, 40 ksi	about 500 MPa, 73 ksi
Tensile strength	about 310 MPa, 45 ksi	about 570 MPa, 83 ksi
Elongation	about 12 percent	about 11 percent
Density	2.70 g/cm3	2.81 g/cm3
Fatigue strength, 5 x 10^8 cycles	about 95 MPa	about 160 MPa

Read the last row carefully. Yield strength nearly doubles. Fatigue strength does not. That gap is the single most misunderstood thing about 7075 in automotive use, and it is why a bracket that vibrates is not automatically better in the stronger alloy.

7075 is also more notch sensitive. A sharp internal corner, a tool mark left in a fillet or a scratch from installation concentrates stress harder in 7075 than in 6061. If you specify it, specify generous radii with it and ask for the machined surface to be left clean rather than polished by hand.

For background on the alloy families, the 7075 aluminium alloy entry is a reasonable starting point.

Corrosion and finish

6061 handles weather and road spray well on its own, and it anodizes to an even, predictable finish.

7075 does not. Bare 7075 in a wheel arch or under a car in a salted climate corrodes faster, and in the T6 temper it is susceptible to stress corrosion cracking, which is a failure that happens under sustained tensile stress in a corrosive environment rather than under load alone. The T73 temper trades some strength for much better resistance, and it is worth asking for on a structural part that lives outside.

Both alloys anodize, but they do not anodize the same. 7075 tends to come out with a slightly different tone, and matching two parts made from different alloys in the same batch of dye rarely works. If the parts sit next to each other and the color has to match, make them from the same alloy.

Welding

6061 welds. The heat affected zone loses a good part of its strength, typically dropping toward the T4 condition locally unless the part is heat treated again after welding, so a welded joint should be designed with that loss in mind. It is still a normal, workable process.

7075 does not weld. It cracks. Parts in 7075 are bolted, riveted or bonded.

This matters more than the strength numbers on a project car. A bracket you might want to add a tab to in six months should be 6061, because the alternative is making a new part.

Cost and availability

Per kilo, 7075 runs roughly one and a half to two and a half times the price of 6061, and the spread widens on unusual sizes.

Availability matters more than the price per kilo. 6061 comes in a huge range of extruded and rolled sizes. 7075 is mostly plate and round bar. If your part needs a 90 mm tall section and the nearest 7075 plate is 100 mm, you pay for that extra material and you pay to cut it away. Sometimes the finished part in 7075 costs twice the 6061 version, not because of the alloy price but because of the stock size.

Both alloys machine well. 7075 actually chips a little more cleanly. Machine time is close enough to the same that it rarely decides the choice. What this means for a quote is covered in what a custom CNC auto part costs.

When to stop reaching for aluminum

Three cases come up repeatedly on automotive parts, and in all three the answer is steel or a steel insert rather than a better aluminum.

Bearing and pivot surfaces. A steel shaft turning directly in an aluminum bore wears the bore oval. Use a bushing or a bearing and let the aluminum carry the structure, not the sliding contact.

Threads that get removed and refitted often. Aluminum threads strip. A helicoil or a steel threaded insert costs very little at the machining stage and prevents the most common way a billet part gets thrown away.

Sustained shear and heat. Aluminum loses a significant fraction of its strength above roughly 150 C, and a T6 temper over ages if it is held hot. Parts near turbochargers, brakes and exhausts need that checked before the alloy is chosen.

What to tell a shop

Say the alloy and the temper together. “6061” on its own is ambiguous, because 6061-T6 and 6061-T651 are both common and only the second is stress relieved plate that stays flat after machining. For a plate part that has to stay true, ask for T651.

Then say what the part does. A shop that knows the bracket locates a suspension link rather than holding a wiring loom will tell you when the alloy choice looks wrong, and that conversation is worth more than any table.

Send the part details and we will match shops that cut both alloys routinely. If you are earlier in the process than this, start with the buyer’s guide or read billet or cast first.

Frequently asked questions

Keep reading

• 4130 or 4140 Chromoly: Which Steel for a Machined Car Part
• Choosing a Finish for a Billet Automotive Part