Aluminum extrusion suitable alloys for bending?

Many aluminum extrusions crack during bending. Others wrinkle or lose shape control. These problems waste material and time. Most failures come from choosing the wrong alloy or temper.

Aluminum extrusion alloys suitable for bending are those with balanced strength and ductility, allowing plastic deformation without cracking, such as specific 6xxx and 5xxx series alloys in appropriate tempers.

Bending is not just a forming step. It is a material behavior test. Understanding alloy limits before bending avoids costly redesign and scrap.

Which aluminum alloys offer the best bendability?

Poor bendability often surprises buyers. On paper, many alloys look similar. In practice, their bending behavior differs greatly.

Aluminum alloys with the best bendability are low to medium strength alloys with high ductility, especially 6xxx series like 6063 and 5xxx series like 5052.

Bendability depends on how much strain an alloy can absorb before cracking. This is closely linked to alloy chemistry and grain structure.

Why ductility matters more than strength

During bending, the outer radius stretches while the inner radius compresses. If the alloy cannot stretch enough, cracks form.

Alloys with high ductility allow:

• Larger bend radii
• Tighter bends
• Fewer surface cracks

High strength alloys resist deformation. This resistance increases cracking risk.

Best performing alloy families

6xxx series alloys are the most common choice for bent extrusions.

Reasons include:

• Balanced magnesium and silicon
• Stable grain structure
• Predictable response to forming

6063 is widely used for curved frames and architectural shapes. 6061 can also bend, but requires larger radii.

5xxx series alloys, such as 5052, offer even higher ductility. They bend very well but are less common in complex extrusions.

Bendability comparison by alloy

This table shows a clear trend. As strength rises, bendability falls.

Practical alloy selection advice

For designs that require bending:

• Choose the lowest strength alloy that meets load needs
• Avoid copper-rich alloys
• Specify bending early in design

From bending trials across many projects, alloy choice alone can reduce cracking risk by more than half.

How does temper affect bending performance?

Alloy selection is only half the decision. Temper often decides success or failure.

Aluminum temper strongly affects bending performance because harder tempers reduce ductility while softer tempers allow greater plastic deformation.

Temper describes the thermal and mechanical history of aluminum. It controls strength, hardness, and ductility.

Common tempers used in bending

Extruded aluminum is often supplied in these tempers:

• T4: solution treated and naturally aged
• T5: cooled from extrusion and artificially aged
• T6: solution treated and artificially aged

Each behaves differently during bending.

Softer tempers bend better

T4 temper offers the best bendability. It allows aluminum grains to slip and stretch.

Benefits of T4 for bending:

• Lower yield strength
• Higher elongation
• Reduced cracking risk

T5 and T6 tempers are stronger but less forgiving.

Tradeoff between strength and formability

Using a soft temper improves bending but reduces final strength. Many projects solve this by bending first, then aging.

Typical approach:

1. Extrude in T4
2. Perform bending
3. Heat treat to T6

This sequence improves both formability and final performance.

Temper influence comparison

Ignoring temper often leads to unexpected cracking even with the right alloy.

From production experience, switching from T6 to T4 before bending solves many failure cases without changing alloy.

Can thick-walled extrusions be bent cleanly?

Thickness adds another layer of difficulty. Many assume thick walls cannot bend well. This is not always true.

Thick-walled aluminum extrusions can be bent cleanly if alloy, temper, bend radius, and tooling are properly controlled.

Wall thickness affects strain distribution during bending. The thicker the wall, the higher the stress difference between inner and outer surfaces.

Challenges with thick sections

Common problems include:

• Outer radius cracking
• Inner radius wrinkling
• Cross-section distortion

These issues increase with thickness and tight bend radii.

Key factors that enable clean bending

Clean bending of thick extrusions requires:

• Large enough bend radius
• Soft temper before bending
• Internal support tooling
• Controlled bending speed

Mandrels or fillers can support hollow sections.

Bend radius rules for thick walls

A simple guideline is to increase bend radius as wall thickness increases.

Typical rule of thumb:

• Thin wall: radius equals 1 to 2 times wall thickness
• Thick wall: radius equals 3 to 5 times wall thickness

These are starting points, not guarantees.

Thick-wall bending performance factors

Thick-walled parts often succeed when bent in multiple stages rather than one pass.

From shop trials, most thick extrusion bending failures come from trying to use thin-wall rules.

Are certain alloys prone to cracking during bending?

Yes. Some alloys crack easily, even under mild bending. This risk must be understood early.

Certain aluminum alloys are prone to cracking during bending due to low ductility, coarse grain structure, or high levels of alloying elements like copper and zinc.

Cracking is a symptom of limited strain capacity. Alloy chemistry plays the main role.

High risk alloy groups

Alloys with higher cracking risk include:

• 2xxx series alloys
• 7xxx series alloys
• Over-aged 6xxx alloys

These alloys prioritize strength over formability.

Why copper and zinc increase cracking

Copper and zinc strengthen aluminum but reduce slip between grains. During bending, stress concentrates at grain boundaries.

This leads to:

• Microcrack initiation
• Crack propagation along bend line
• Sudden fracture

Surface cracks may appear small but often grow during service.

Grain structure influence

Coarse grains worsen bending performance. They reduce uniform deformation.

Grain size is influenced by:

• Extrusion temperature
• Cooling rate
• Alloy composition

Poor process control increases cracking risk even in normally bendable alloys.

Crack risk comparison

Designers should avoid high risk alloys when bending is required. If unavoidable, larger radii and softer tempers are mandatory.

From failure analysis, alloy cracking during bending is rarely random. It is predictable and preventable.

Conclusion

Successful aluminum extrusion bending depends on alloy ductility, temper choice, wall thickness control, and crack risk awareness. Selecting bend-friendly alloys and soft tempers early prevents failures and ensures clean, repeatable bending results.