Understanding Aluminum Temper Designations

Aluminum alloys derive their mechanical properties not just from their chemical composition, but critically from their temper — the thermal and mechanical treatment applied to achieve specific strength, hardness, and formability characteristics.

The Aluminum Association (AA) temper designation system uses a letter suffix appended to the alloy number (e.g., 6061-T6, 5052-H32) to indicate the temper condition. Understanding this system is essential for engineers, procurement specialists, and fabricators working with aluminum products.

The Temper Designation System Structure

The system follows a straightforward format: Alloy Number + Temper Letter + Digit(s)

• Alloy Number: 4-digit designation (e.g., 1060, 5052, 6061)
• Temper Letter: Indicates the basic treatment category (O, H, T, W)
• Digit(s): Specify the exact temper condition within the category

O Temper: Annealed

Definition

The O temper designates annealed aluminum — the softest condition, achieved by heating the material to a specific temperature and holding it long enough to relieve internal stresses and recrystallize the grain structure.

Key Characteristics

• Strength: Lowest tensile strength in the alloy series
• Formability: Maximum ductility and formability
• Applications: Deep drawing, spinning, complex forming operations
• Typical Alloys: 1060-O, 1100-O, 3003-O, 5052-O

Processing

Annealing is typically performed at 343–413°C (650–775°F) for 1–3 hours, followed by controlled cooling. The result is a fully recrystallized, stress-free microstructure.

H Temper: Strain-Hardened

Definition

H tempers indicate aluminum that has been strain-hardened (cold worked) to increase strength. The H designation is followed by additional digits that specify the degree of strain hardening and any subsequent thermal treatment.

Digit Breakdown

The H designation uses a two or three-digit system:

• H1X: Strain-hardened only (no thermal treatment after hardening)
• H2X: Strain-hardened and partially annealed
• H3X: Strain-hardened and stabilized (low-temperature thermal treatment)
• H4X: Strain-hardened and lacquered/painted

The second digit indicates the degree of hardening:

• X = 2: Quarter-hard (approximately 25% of full hard)
• X = 4: Half-hard
• X = 6: Three-quarter-hard
• X = 8: Full-hard
• X = 9: Extra-hard (exceeds full-hard)

Common H Tempers

T Temper: Thermally Treated

Definition

T tempers indicate aluminum that has been thermally treated to produce stable tempers other than O, H, or F. The T designation encompasses solution heat treatment, aging, and various combinations.

Common T Tempers

T6 in Detail

T6 is arguably the most important temper in the aluminum system. The process involves:

1. Solution Heat Treatment: Heating to 515–540°C (for 6061), holding until alloying elements dissolve into the aluminum matrix
2. Quenching: Rapid cooling (water quench) to lock alloying elements in solid solution
3. Artificial Aging: Heating to 160–180°C for 6–18 hours to precipitate strengthening phases

Result: 6061-T6 achieves tensile strength of 310 MPa (45 ksi), yield strength of 276 MPa (40 ksi), and 12% elongation.

W Temper: Solution Heat Treated (Unstable)

Definition

W temper designates aluminum that has been solution heat treated but not yet aged. This is an unstable condition — the alloy will naturally age at room temperature over hours to days.

Practical Significance

• Material in W temper is in the most formable condition after solution treatment
• Forming operations must be completed before natural aging begins
• W temper is typically a transient condition — material will progress to T4 (natural aging) or be artificially aged to T6
• Some specifications allow W temper with a specified time limit (e.g., “W: 1 hour”)

F Temper: As-Fabricated

Definition

F temper designates aluminum in the as-fabricated condition — no special control has been exercised over thermal treatment or strain hardening. Mechanical properties are not guaranteed.

When F Temper Is Used

• Casting alloys where properties are determined by subsequent treatment
• Intermediate processing stages
• Applications where specific mechanical properties are not required

Comparative Properties: Common Alloys and Tempers

Procurement and Specification Guidance

Selecting the Right Temper

1. Identify the primary requirement: Formability (O or H2x) vs. strength (T6 or H1x) vs. stress-corrosion resistance (T7x)
2. Consider fabrication sequence: If extensive forming is required, specify a softer temper and heat treat after forming
3. Evaluate environmental exposure: Marine environments favor H3x (stabilized) or T7x tempers for improved corrosion resistance
4. Confirm availability: Not all alloys are available in all tempers — verify mill capability before specifying

Quality Verification

Always require Mill Test Certificates (MTC) specifying the exact alloy and temper. Verify mechanical properties match the applicable specification (ASTM B209 for sheet/plate, ASTM B221 for extrusions, ASTM B241 for pipe/tube).

Conclusion

Aluminum temper designations provide a standardized language for specifying the exact mechanical and physical condition of aluminum products. The O, H, T, and W designations — along with their subcategories — give engineers and procurement professionals precise control over material properties.

For aluminum sheet, plate, coil, extrusions, and tube supply in any temper condition, Xi’an Coremetal Steel Co., Ltd. offers comprehensive inventory and technical support. Contact us for alloy and temper selection guidance for your next project.