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Many buyers compare aluminum profiles only by price or shape. Later, they face bending, cracking, or early failure. In most cases, the real issue is not design, but misunderstanding tensile strength by alloy.

Aluminum extrusion tensile strength depends mainly on alloy system and temper. High tensile numbers come from the right alloy–temper combination, not from extrusion alone.

Tensile strength is one of the first values engineers look at, but it is also one of the most misused. The sections below explain which alloys are strongest, how tempering changes tensile values, whether surface treatment matters, and how tensile strength is confirmed in real profiles.

Which alloys offer the highest tensile strength?

Not all aluminum alloys are designed for the same job. Some focus on formability. Others focus on corrosion resistance. A smaller group focuses on strength. Knowing where each alloy sits helps avoid overdesign or underperformance.

Among common extrusion alloys, 7xxx series alloys offer the highest tensile strength, followed by selected 6xxx alloys like 6061 and 6082. However, higher tensile strength often comes with lower ductility and higher cost.

Understanding alloy series in simple terms

Aluminum alloys are grouped by main alloying elements:

• Řada 6xxx: Magnesium and silicon. Good balance of strength, corrosion resistance, and extrudability.
• Řada 7xxx: Zinc-based. Very high strength, harder to extrude, lower corrosion resistance.
• Řada 5xxx: Magnesium-based. Good corrosion resistance, medium strength, limited heat treatment response.

Most structural extrusions in industry use 6xxx alloys because they balance strength and production efficiency.

Tensile strength comparison by common extrusion alloys

The table below shows typical ultimate tensile strength ranges for popular alloys in common tempers. Values are approximate and depend on profile shape and process control.

Why the strongest alloy is not always the best

Very high tensile strength sounds attractive, but it introduces trade-offs:

• Lower elongation means less warning before fracture.
• Toughness often drops as tensile strength rises.
• Tooling wear and scrap rate increase with harder alloys.
• Availability and lead time may be longer.

For many frames, rails, and supports, 6061-T6 or 6082-T6 provides more than enough tensile strength without the risks of ultra-high-strength alloys.

Application-driven alloy selection

In practice, alloy choice follows application needs:

• General industrial frames: 6063-T5 or T6
• Nosné konstrukce: 6061-T6 or 6005A-T6
• Heavy-duty mechanical parts: 6082-T6
• Special high-strength needs: 7xxx series with careful design

How does tempering affect tensile values?

Alloy alone does not define tensile strength. Temper condition often makes an equal or larger difference. Two profiles of the same alloy can show very different tensile results because of tempering.

Tempering affects tensile strength by controlling precipitation hardening and internal stress state. Heat-treated tempers like T6 maximize tensile strength, while softer tempers trade strength for ductility and formability.

What temper really means

Temper describes the thermal and mechanical history of the aluminum after extrusion.

Common extrusion tempers include:

• T5: Cooled from extrusion temperature and artificially aged.
• T6: Solution heat treated, quenched, and artificially aged.
• T4: Solution heat treated and naturally aged.

Each step changes the size and distribution of strengthening precipitates inside the metal.

Tensile strength differences by temper

For most 6xxx alloys:

• T6 gives the highest tensile strength.
• T5 offers slightly lower strength but better dimensional stability.
• T4 provides lower strength but higher elongation.

The table below shows a simplified comparison using 6061 as an example.

Why T6 is not always chosen

Although T6 maximizes tensile strength, it is not always ideal:

• Thin or complex profiles may distort during solution treatment.
• Residual stresses may increase risk of warping during machining.
• Some applications need flexibility rather than maximum strength.

In these cases, T5 or even T4 can deliver better real-world performance.

Consistency and process control

Tempering quality depends on:

• Accurate furnace temperature control
• Proper quenching speed
• Uniform aging time

Poor temper control can lead to tensile values below specification, even if the alloy is correct.

Design tip for buyers

When specifying tensile strength:

• Always specify alloy + temper, not just alloy.
• Confirm whether values are minimum guaranteed or typical averages.
• Ask how tensile properties are verified for complex profiles.

Can surface treatment alter tensile performance?

Surface treatment is often discussed for corrosion or appearance. Many buyers ask whether anodizing or coating changes tensile strength. The short answer is subtle but important.

Surface treatments do not significantly change the bulk tensile strength of aluminum extrusions, but aggressive processes or high temperatures can slightly reduce effective strength or introduce surface-related failure risks.

Bulk strength versus surface condition

Tensile tests measure bulk material behavior. Most surface treatments affect only a thin outer layer.

Common treatments include:

• Eloxování
• Práškové lakování
• Elektroforetický nátěr
• Mechanical polishing

These processes do not change the alloy’s internal microstructure.

When surface treatment can matter

Although bulk tensile strength stays similar, surface treatment can influence performance indirectly.

Thick anodizing layers

Hard anodizing creates a brittle oxide layer. Under tensile loading:

• The oxide can crack.
• Cracks may act as initiation sites in fatigue or impact, not in static tensile tests.

High-temperature exposure

Some coatings require elevated cure temperatures. Excessive heat can:

• Over-age the alloy.
• Slightly reduce tensile strength, especially in T6 tempers.

Surface damage before coating

Improper pretreatment can introduce:

• Scratches
• Pits
• Chemical attack

These defects reduce effective cross-section and may lower measured tensile results in extreme cases.

What surface treatment does not do

Surface treatment does not:

• Increase tensile strength beyond alloy limits.
• Turn a low-strength alloy into a high-strength one.
• Replace proper alloy and temper selection.

Praktické pokyny

For tensile-critical parts:

• Confirm that coating temperatures stay within alloy limits.
• Avoid unnecessary thick or brittle surface layers.
• Focus tensile requirements on base material, not coating.

What tests confirm tensile strength in profiles?

Datasheet values are only meaningful if they are verified. Tensile strength must be measured using standardized tests that reflect real material behavior.

Tensile strength in aluminum extrusion profiles is confirmed through standardized tensile testing on samples taken from the profile, following defined procedures that control sample orientation, speed, and measurement accuracy.

Standard tensile testing basics

Tensile testing involves:

• Pulling a prepared specimen at a controlled rate.
• Measuring force and elongation.
• Calculating tensile strength, yield strength, and elongation.

The result represents the material behavior under uniaxial tension.

Sample location and orientation matter

For extrusions:

• Samples are usually taken along the extrusion direction.
• Properties across the section are generally uniform, but thin walls may vary slightly.

For hollow profiles, samples may come from:

• Outer walls
• Webs or ribs
• Flat sections with enough width

Typical test outputs

A standard tensile test provides:

• Mez pevnosti v tahu
• Pevnost v tahu
• Prodloužení při přetržení

These values together describe strength and ductility.

Batch testing versus per-profile testing

In production:

• Tensile tests are often done per alloy batch or heat.
• Not every profile is tested, but process consistency is monitored.

For critical applications, buyers may request:

• Additional tests on finished profiles
• Third-party verification
• Test reports linked to production lots

Limits of tensile testing

Tensile tests do not show:

• Odolnost proti nárazu
• Fatigue life
• Buckling behavior

They are one part of a complete mechanical evaluation.

Using test data correctly

When reviewing tensile reports:

• Check minimum guaranteed values, not just averages.
• Confirm test standard and sample location.
• Match reported temper to the delivered product.

Závěr

Aluminum extrusion tensile strength is driven by alloy choice, temper control, and verified testing. High numbers matter, but correct matching to application matters more. When tensile strength is understood in context, extrusions deliver reliable and predictable performance.