What is the difference between 6082 T6 and T651?

The main differences between T6 and T651 tempers of 6082 aluminum alloy lie in the heat treatment process, internal stress control, and applicable scenarios. T651 improves upon the residual stress issues of T6 through a stretching process, enhancing machining stability while retaining high strength characteristics. However, cost and specific application requirements must be considered.

T6: Solution heat treatment followed by artificial aging.
T651: Solution heat treatment, stress relief by stretching, then artificial aging.

6082 aluminum alloy belongs to the 6xxx series (Al-Mg-Si), known for its high strength, excellent corrosion resistance, and good machinability. Compared to the more common 6061 alloy, 6082 offers about 20% higher strength under the same tempering conditions.

6082 aluminum alloy is widely used in extruded profiles, rolled plates, and thin sheets. Typical applications include structural components, transport frames, bridges, trusses, beer barrels, and general-purpose machining blanks.

Aluminium 6082 T6 vs T651 Main Differences

6082-T6 and 6082-T651 are both solution heat-treated and precipitation-hardened tempers of the 6082 alloy, with nearly identical tensile and yield strengths. The difference lies in the addition of a stress-relief step in T651—controlled stretching after solution treatment and before artificial aging. This reduces residual stress, enhances dimensional stability, and minimizes distortion during machining or welding. Therefore, for thicker sections or precision-machined parts with tight tolerance requirements, T651 plates are preferred, while T6 is typically sufficient for thinner sections or less demanding applications.

Aluminium 6082 T6 vs T651 Definition and Process Differences

T6 Temper: Only undergoes solution heat treatment (high-temperature treatment followed by quenching) and artificial aging. The material reaches high strength directly after cooling, with no subsequent cold working.
T651 Temper: Builds on T6 by adding a stretching straightening process (typically 0.5% to 3% elongation) to relieve internal residual stress, improving machining stability.

6082 T651 vs T6 Residual Stress Comparison

T6 temper results in higher internal residual stress due to direct aging treatment, which can lead to deformation during machining, especially in thin-walled or complex structural components.
T651 uses a stretching process to reduce internal stress, significantly lowering the risk of post-machining deformation, making it suitable for high-precision machining scenarios.

6082 T651 vs T6 Material Properties and Suitability

Strength and Hardness: T6 and T651 have similar hardness and tensile strength, both falling under high-strength tempers. For example, 6082-T6 typically has a Brinell hardness (HBS) ≥ 80, and T651 maintains high mechanical performance even after stretching.
Machining Adaptability: Due to more thorough stress relief, T651 is more suitable for precision part machining (such as automotive components and optical instruments); T6 is often used for structural components with greater tolerance for deformation (like bridges and crane parts).
Cost and Efficiency: T651 involves an additional stretching step, making its production cost slightly higher than T6, but it reduces the scrap rate during subsequent machining.

Aluminium 6082 T6 vs T651 Typical Application Scenarios

T6: Shipbuilding components, building trusses, rail vehicles, and other areas where high strength is required but machining deformation has a lesser impact.
T651: Precision parts in aerospace, automotive chassis parts, high-precision molds, and other fields requiring strict dimensional control.

Practical Considerations When Choosing

Thickness and Section Size: As cross-sectional thickness increases, quenching stress also rises—T651 material is recommended for sections thicker than 6 mm.
Tolerance Requirements: For long spans with tolerances smaller than ±0.2 mm, T651 material ensures stability.
Post-Processing: If extensive machining or welding is expected, starting with T651 material can reduce the need for secondary straightening.

Both temper states have the same core strength and corrosion resistance as the 6082 alloy, but the pre-aging stretching step of T651 makes it the preferred choice for heavier, precision-demanding components, while T6 is adequate for lighter and less demanding applications.