6061-T651 vs T6 & T6511: What’s the Difference?

What’s 6061-T6?

The T6 refers to the temper or heat treatment applied. T6 temper involves solution heat treatment and artificial aging. Solution heat treatment involves heating the aluminum above the solvus temperature to form a homogeneous solid solution of alloying elements in the aluminum. Artificial aging completes the T6 process. For industry standards, 6061-T6 is typically only available in thicknesses under .25”.

What’s 6061-T651?

6061-T651 aluminum alloy is a frequently used structural aluminum in plate form. It has undergone the same heat treatment process as T6 to introduce strengthening precipitates within the material, making it harder and stronger than the bare alloy. In addition, the material is stretched after the solution heat treatment. This stress relieves the metal to mitigate warp and distortion during machining; the ‘5’ refers to an extra reduction in hardness compared to standard T6. Additionally, the T651 plate must have a thickness of at least .25”. 

What’s 6061-T6511?

6061-T6511 is an extruded bar or rod that undergoes the same heat treatment process as T6. It also receives a stress relief operation and may also be straightened. Typically, extrusions produced to T6511 temper will also be certed by the mill to T6 temper via a material certification or mill test report. T6511 is typically a less expensive stock compared to T651.

6061-T651 vs. 6061-T6 vs. 6061-T6511: What Are the Differences?

6061-T651:

• Plate stock is typical. Cold-finished bars are also classified as T651.
• Highest strength of the three due to additional cold working (stretching) during processing.
• Not as formable or workable as the others due to this extra cold working.
• Used for demanding structural applications where maximum strength is needed.
• The low residual stress provides dimensional stability and reduced warp risks over broad, flat, part designs.
• The uniform grain structure produces a uniform look, and finish.
• 6061-T651 is the most versatile 6061 alloy stock due to its wide availability of sizes and mechanical properties. The trade-off is higher costs compared to the other alloy tempers.

6061-T6:

• Sheet stock. Maximum thickness typically below .25”.
• Medium strength level – stronger than bare 6061 but not as strong as T651.
• More workable than T651.
• T6511 extruded bar can often be dual-certed to meet T6 temper.
• Good combination of strength and formability for many general applications but is limited in available stock sizes.

6061-T6511:

• Extruded bar or rod stock.
• Most formable/workable of the different 6061 alloy tempers.
• Useful for turned aluminum goods and general machining if the hardness, size availability, and stability of T651 are not necessary.
• Beyond 1 " thick, the available width of T6511 is more limited. The maximum width is typically less than 15”.

6061-T6 and T6511 Interchangeability

These tempers may be dual-certified, as indicated on material certifications. Due to the above differences, orders calling for 6061-T6 may be produced from 6061-T6511 but not 6061-T651.