Aluminum 6061-T6, -T651, and -T6511 Explained
What is 6061-T6?
The T6 designation refers to a specific temper achieved through solution heat treatment followed by artificial aging. During solution heat treatment, the material is heated above the solvus temperature so the alloying elements form a uniform solid solution. Artificial aging then strengthens the material by forming fine precipitates. In general, 6061-T6 is available mainly in sheet or thin plate, typically in thicknesses under 0.25".
What is 6061-T651?
6061-T651 is a widely used structural aluminum grade primarily supplied in plate form. It undergoes the same solution heat treatment and artificial aging as T6, but with an additional stretching process to relieve internal stresses. This stress relief minimizes distortion and warping during machining. The "5" in T651 indicates an extra reduction in residual stress compared with T6. T651 plate is usually produced in thicknesses of 0.25" or greater.
What is 6061-T6511?
6061-T6511 is an extruded bar or rod that receives the same solution heat treatment and artificial aging as T6, plus a controlled stretching operation for stress relief and, if necessary, straightening. Many T6511 extrusions also carry dual certification to T6 on the mill test report. Compared with T651 plate, T6511 is typically more economical and available in a wide variety of extruded shapes.
Differences: 6061-T651 vs. 6061-T6 vs. 6061-T6511
6061-T651
Most commonly sold as a plate; cold-finished bars may also be designated as T651.
Offers the highest strength among the three tempers due to additional stretching during processing.
Less formable and workable because of this extra cold work.
Preferred for structural components requiring maximum strength and dimensional stability.
Low residual stress helps minimize warping in large, flat, or precision-machined components.
Features a consistent grain structure for a uniform appearance.
The broad availability of sizes makes it one of the most versatile 6061 options, though pricing is generally higher than other tempers.
6061-T6
Typically supplied as a sheet or thin plate under 0.25" thick.
Provides medium strength-stronger than annealed 6061 but slightly lower than T651.
More workable and formable than T651.
T6511 extrusions may often be dual-certified to meet T6 requirements.
Well-suited for general applications that require a balance of strength and formability, though size options are more limited than T651 plate.
6061-T6511
Supplied as an extruded bar or rod.
Offers the best formability and workability of the three temper types.
Ideal for turned components, general machining, and applications where full T651-grade stability is not required.
When thickness exceeds 1", width availability is limited-typically under 15".
Interchangeability of 6061-T6 and 6061-T6511
These two tempers may be dual-certified on mill test reports. Because T6511 meets or exceeds many T6 requirements for extruded products, 6061-T6 orders can often be fulfilled with 6061-T6511. However, 6061-T651 plate cannot be substituted for T6 in these cases.
