Aluminum is one of the most versatile metals used in aerospace, automotive, construction, and manufacturing due to its lightweight strength, corrosion resistance, and workability. But not all aluminum is the same—its properties vary depending on its temper designation.
You may have seen aluminum marked as T6, T5, or O and wondered, what do these numbers mean? These temper designations describe how the aluminum was heat-treated or mechanically processed to achieve specific strength and hardness levels.
In this blog, we’ll break down what aluminum temper designations mean, how they affect performance, and how to choose the right one for your application.
What Are Aluminum Temper Designations?
📌 Temper designations indicate how aluminum has been treated to modify its mechanical properties, such as strength, hardness, and ductility.
The temper designation consists of:
A letter (e.g., T, H, O) indicating the type of processing.
A number (e.g., T6, H32) specifying the exact treatment.
💡 Example: 6061-T6 Aluminum
6061 = The alloy type (contains magnesium and silicon).
T6 = The temper designation (solution heat-treated and artificially aged for maximum strength).
Types of Aluminum Temper Designations
Aluminum tempers are categorized into five main groups:
TemperMeaningKey CharacteristicsExample Applications
F (As-Fabricated)No special treatmentSoft, unprocessedCastings, general fabrication
O (Annealed)Fully softenedMaximum ductility, easy to formAerospace fuel tanks, cookware
H (Strain-Hardened)Cold worked to increase strengthHigher strength, reduced elongationRoofing, truck bodies
T (Heat-Treated)Heat-treated for strengthBest for structural applicationsAircraft frames, bicycle parts
W (Solution Heat-Treated)Unstable temperUsed before artificial agingAerospace, automotive
Now, let’s focus on the most common heat-treated tempers: T6 vs. T5.
What Is T6 Temper? (Maximum Strength Aluminum)
📌 T6 aluminum is solution heat-treated and artificially aged to achieve maximum strength.
🔎 Process:
1️⃣ Aluminum is heated to a high temperature (solution heat treatment).
2️⃣ It is rapidly cooled (quenched) to lock in a strong microstructure.
3️⃣ It is then artificially aged at a moderate temperature to harden it.
✔ Best for: High-strength structural parts that require durability and stiffness.
✔ Common in: 6061-T6, 7075-T6 aluminum alloys.
💡 Example Uses:
✅ Aircraft and aerospace parts
✅ Automotive frames
✅ Bike frames
✅ High-performance machine parts
What Is T5 Temper? (Partially Hardened Aluminum)
📌 T5 aluminum is cooled from an elevated temperature and artificially aged—but it skips the solution heat treatment step.
🔎 Process:
1️⃣ Aluminum is cooled naturally from extrusion temperature.
2️⃣ It is then artificially aged to increase strength.
✔ Best for: Medium-strength applications where some flexibility is needed.
✔ Common in: 6063-T5, 6463-T5 aluminum alloys.
💡 Example Uses:
✅ Window and door frames
✅ Automotive trim
✅ Extruded aluminum tubing
T6 vs. T5: What’s the Difference?
PropertyT6 TemperT5 Temper
StrengthHigherLower
Heat TreatmentSolution heat-treated & agedOnly artificially aged
HardnessHarderSofter
DuctilityLower (more brittle)Higher (more flexible)
Best ForStructural applicationsDecorative & extruded parts
💡 Key Takeaway: If you need maximum strength, go with T6. If you need easier machinability or forming, T5 is a better choice.
Other Common T-Tempers
T4 (Heat-Treated, Naturally Aged)
✔ Medium strength, more formable than T6.
✔ Used in automotive panels, aerospace parts.
T3 (Heat-Treated, Cold Worked, Naturally Aged)
✔ High fatigue resistance, used in aircraft skins and fuselage components.
T651 (Stress-Relieved T6)
✔ Same as T6, but stress-relieved to prevent warping.
✔ Common in precision machined parts.
How to Choose the Right Aluminum Temper
🔹 For maximum strength → T6 Temper
🔹 For easier forming and extrusion → T5 Temper
🔹 For moderate strength and better flexibility → T4 Temper
🔹 For aerospace and precision machining → T651 Temper
Quick Selection Guide:
✔ 6061-T6 → Best for high-stress structural applications
✔ 6063-T5 → Best for decorative and extruded applications
✔ 7075-T6 → Best for aerospace and extreme strength needs
Final Thoughts: Why Aluminum Temper Designations Matter
Aluminum’s strength, durability, and machinability depend on its temper designation. Understanding the differences between T6, T5, and other heat-treated tempers helps engineers and manufacturers choose the right aluminum for their applications.
💡 Key Takeaways:
✅ T6 = Maximum strength (best for aerospace, structural applications).
✅ T5 = Medium strength (best for extruded aluminum, automotive trim).
✅ Different tempers affect strength, flexibility, and machinability.
✅ Choosing the right temper ensures better performance and cost savings.
🚀 Need expert advice on selecting the right aluminum temper? Let’s talk!
