How Heat Treatment (T4, T5, T6) Affects Extrusion Strength
Published: August 2026 | Reading Time: 5 mins
In heat-treatable aluminum alloys like the popular 6000-series (such as 6061 and 6063), chemical composition is only half the strength equation. The post-extrusion heat treatment—designated by temper codes like T4, T5, and T6—fundamentally alters the metal's internal crystalline structure, determining its ultimate tensile strength, ductility, and hardness.
Understanding these temper designations ensures engineers and buyers select extrusions that match structural safety requirements without over-specifying processing costs.
| Temper | Process Method | Tensile Strength | Formability | Best Used For |
|---|---|---|---|---|
| T4 | Solution heat-treated & naturally aged | Moderate (~180 MPa) | Highest / Excellent | Bending, forming, post-shaping |
| T5 | Cooled from extrusion & artificially aged | Medium-High (~200 MPa) | Moderate | Architectural profiles, window frames |
| T6 | Solution heat-treated & artificially aged | Maximum (~310 MPa) | Lower / Rigid | Heavy structural load applications |
T4 Temper: Maximum Formability
In the T4 temper process, aluminum extrusions are solution heat-treated at elevated temperatures (~520°C) to dissolve alloying elements evenly, rapidly quenched in water or air, and then allowed to age naturally at room temperature.
- Ductility: Retains high elongation, allowing severe bending, flanging, or cold-forming without cracking.
- Trade-off: Lower yield strength compared to artificially aged tempers.
T5 Temper: Precision & Architectural Balance
T5 temper bypasses separate high-temperature solution heating. Instead, profiles are rapidly air-cooled directly as they exit the extrusion press die and then placed into aging ovens for artificial aging (precipitation hardening).
- Dimensional Control: Minimizes thermal distortion, making it ideal for delicate wall thicknesses.
- Surface Quality: Delivers crisp extrusions ideal for anodizing and powder coating.
T6 Temper: Maximum Mechanical Strength
T6 temper combines high-temperature solution heat treating, rapid water quenching, and extended artificial aging in specialized precipitation ovens. This forces alloying elements to form microscopic precipitate structures that block dislocation movement inside the metal grid.
- Peak Performance: Boosts tensile yield strength up to 50–70% higher than T4/T5 conditions.
- Machinability: Provides clean chip formation during CNC milling and cutting operations.
Choosing the Right Temper for Your Project
- Select T4: If you plan to perform secondary bending, stamping, or cold forming after extrusion.
- Select T5: For architectural trims, window channels, louvers, and decorative profiles requiring tight tolerances.
- Select T6: For load-bearing frameworks, structural beams, solar mounting structures, and heavy machinery parts.