Guides / Alloys

The Alloy You Choose When the Part Flexes Ten Million Times

September 21, 2026 by The Alu CNC Parts editorial desk / how this is checked

Most aluminum parts fail because someone loaded them past yield once. Some parts fail differently. They sit at a stress level well inside the safe range and crack anyway, after weeks or months, because they have been flexed several million times.

That is fatigue, and it is the reason 2024 exists.

What makes it different

2024 is aluminum with around 4.4 percent copper. The copper gives it a fatigue endurance that neither 6061 nor 7075 matches at the same stress, along with good damage tolerance, meaning a crack that does start propagates more slowly.

This is why it has been the standard aircraft skin and structure alloy for decades. Airframes are not loaded to yield. They are loaded gently, endlessly, every flight.

	2024-T351	6061-T6	7075-T6
Yield strength	~325 MPa	~276 MPa	~503 MPa
Fatigue behaviour	Best of the three	Moderate	Good but crack sensitive
Corrosion resistance bare	Poor	Good	Poor
Weldable	No	Yes	No
Relative cost	High	1x	High

When to specify it

• Linkage arms, levers and pivots that cycle continuously.
• Structural parts on aircraft, drones and anything that vibrates in service.
• Parts where a crack must grow slowly enough to be found at inspection rather than failing suddenly.
• Fixtures and tooling that get clamped and unclamped thousands of times.

When 7075 is the better answer

If the part is loaded heavily but rarely, 7075 gives you far more yield strength for a similar price. The comparison with 6061 applies here too: raising the yield point only helps if yielding is what threatens the part.

The honest question to ask is how the part will fail. Bent once under an overload points to 7075. Cracked after a long service life points to 2024.

Corrosion is the catch

Copper is what makes 2024 fatigue resistant and it is also what makes it corrode. Bare 2024 in a damp environment pits, and under sustained load it is susceptible to stress corrosion cracking.

A machined 2024 part is not optional to protect. It needs anodizing or chem film, and the coating has to cover everything including bores and tapped holes. Where an assembly cannot be fully coated, plan on sealant at the joints.

This is also why Alclad sheet is less useful once you machine it. The protective pure aluminum layer is on the surface, and machining cuts straight through it.

Machining notes worth putting on the RFQ

2024 cuts well. Chips break cleanly, surface finish is good and tool life is reasonable, better than the 5000 series by a wide margin.

The practical issues are availability and stress. 2024 is not on every shop’s rack in every size, so allow for a mill order if your stock size is unusual. It also carries meaningful internal stress in the T351 temper, so for large parts where flatness matters, expect the same rough, rest and finish sequence you would use on any stressed plate.

Say on the RFQ that the part is fatigue critical. It tells the shop that edge quality and surface finish are structural requirements rather than cosmetic ones, because fatigue cracks start at scratches and sharp corners. A part that has been correctly deburred with a proper edge break will outlast the same part with a machined-and-shipped finish.

Sources

Figures in this guide are checked against the following. Published values are typical ranges for test material, not a guarantee for your part.

• Aluminium alloy 2024
• Fatigue of materials
• Alclad

Frequently asked questions

Keep reading

• Giving Up 10 Percent of Strength to Stop a Crack That Starts Alone
• Why Thick Plate Is the Reason 7050 Exists