6061-T651 vs 6061-T6 & 6061-T6511: What's the Difference?
6061 aluminum alloy is one of the most widely used aluminum materials in industrial manufacturing, valued for its excellent mechanical performance, corrosion resistance, and versatility. Within the 6061 alloy family, different temper designations-6061-T6, 6061-T651, and 6061-T6511-provide distinct advantages depending on part geometry, machining requirements, and structural demands.
Understanding the differences between these tempers is essential for engineers, designers, and buyers to select the most suitable material for specific applications. At GNEE, we help customers make informed material choices by clearly explaining alloy and temper distinctions.
Overview of 6061 Aluminum Alloy Tempers
All three tempers-6061-T6, 6061-T651, and 6061-T6511-are based on the same chemical composition of the 6061 aluminum alloy, which primarily contains magnesium and silicon. The key differences lie in heat treatment methods, stress-relief processes, available product forms, and mechanical behavior.
What Is 6061-T6 Aluminum?
6061-T6 aluminum refers to 6061 alloy that has undergone solution heat treatment followed by artificial aging.
During solution heat treatment, the aluminum is heated above the solvus temperature to dissolve alloying elements into a uniform solid solution. Artificial aging then allows fine precipitates to form, significantly increasing strength and hardness.
6061-T6 is commonly supplied as sheet material, and according to industry standards, it is typically available in thicknesses below 0.25 inches. This temper provides a good balance of strength and formability, making it suitable for many general-purpose structural and fabrication applications.
What Is 6061-T651 Aluminum?
6061-T651 aluminum is most commonly supplied in plate form and is widely used for structural and precision machining applications.
Like T6, 6061-T651 undergoes solution heat treatment and artificial aging. However, it includes an additional stress-relief step by stretching after solution heat treatment. This process significantly reduces internal residual stress, helping to minimize warping and distortion during machining.
The "51" designation indicates this stress-relief operation. Due to processing requirements, 6061-T651 plates must have a minimum thickness of 0.25 inches. The added stretching slightly reduces formability but improves dimensional stability, making T651 ideal for large, flat, or tight-tolerance parts.
What Is 6061-T6511 Aluminum?
6061-T6511 aluminum is typically supplied as extruded bars or rods. It undergoes the same heat treatment process as 6061-T6 and also receives a stress-relief operation. In many cases, the material is additionally straightened.
Extrusions produced in the T6511 temper are often dual-certified as 6061-T6 on mill test reports. Compared to T651 plate, 6061-T6511 is generally more cost-effective, making it a practical choice for many machined and turned components.
6061-T651 vs 6061-T6 vs 6061-T6511: Key Differences
6061-T651 Aluminum Characteristics
6061-T651 is most commonly available as plate, though some cold-finished bars may also fall under this designation. Due to additional cold working during stretching, it offers the highest strength among the three tempers.
This extra processing results in:
Reduced formability compared to T6 and T6511
Excellent dimensional stability and low residual stress
Minimal risk of warping in wide, flat part designs
Uniform grain structure and consistent surface appearance
Because of its wide size availability and strong mechanical properties, 6061-T651 is one of the most versatile 6061 tempers, though it typically comes at a higher cost.
6061-T6 Aluminum Characteristics
6061-T6 is commonly supplied as sheet, with thickness usually below 0.25 inches. It offers:
Moderate to high strength (lower than T651, higher than untreated 6061)
Better workability and formability than T651
A strong balance between mechanical performance and ease of fabrication
While stock size options are more limited, 6061-T6 remains a popular choice for applications requiring both strength and formability.
6061-T6511 Aluminum Characteristics
6061-T6511 is supplied as extruded bars or rods and is generally:
The most formable and workable of the three tempers
Well suited for turned parts and general machining
A good alternative when extreme flatness or dimensional stability is not required
However, for sizes exceeding 1 inch in thickness, the available width of T6511 is more limited, typically not exceeding 15 inches.
Interchangeability of 6061-T6 and 6061-T6511
In some cases, 6061-T6 and 6061-T6511 materials may be dual-certified, as indicated on mill certifications. This means that material ordered as 6061-T6 can sometimes be fulfilled using 6061-T6511 stock.
However, due to processing and form differences, 6061-T651 plate cannot be substituted for 6061-T6 unless explicitly approved.
Choosing the Right 6061 Aluminum Temper
Selecting between 6061-T6, 6061-T651, and 6061-T6511 depends on application requirements:
Choose 6061-T651 for large plates, precision machining, and applications requiring excellent flatness and dimensional stability
Choose 6061-T6 for thinner sections that need a balance of strength and formability
Choose 6061-T6511 for extruded bars and rods where machinability and cost efficiency are priorities
| Feature | 6061 T6 Aluminum | 6061 T651 Aluminum | Notes from Huawei Aluminum |
| Heat Treatment | Solution heat-treated & artificially aged. | Solution heat-treated, stress-relieved by stretching, & artificially aged. | The "51" signifies the stress-relief stretching. |
| Internal Stress | Higher | Significantly Lower | This is the key differentiator. |
| Dimensional Stability (Post-Machining) | Good | Excellent | T651 is far less prone to warping or distortion after material removal. Ideal for precision parts. |
| Machinability | Good | Excellent | While both machine well, the lower stress in T651 can lead to more predictable results and better surface finishes in complex machining. |
| Tensile Strength (Typical Ultimate) | ≥ 290 MPa (42 ksi) | ≥ 290 MPa (42 ksi) | Generally, no significant difference in ultimate tensile strength. Both meet the same minimum specification. |
| Yield Strength (Typical) | ≥ 241 MPa (35 ksi) | ≥ 241 MPa (35 ksi) | The stretching process in T651 can slightly reduce yield strength and elongation compared to a T6 part not straightened, but both usually meet the same spec. |
| Elongation | Good | Good | May be slightly lower in T651 due to cold work from stretching, but often within the same specification range as T6. |
| Hardness (Brinell) | ~95 HB | ~95 HB | Similar hardness levels. |
| Corrosion Resistance | Excellent | Excellent | No significant difference. |
| Weldability | Good | Good | Both can be welded effectively, though heat from welding will affect the temper in the heat-affected zone (HAZ). Post-weld heat treatment may be needed. |
| Typical Forms | Sheet, plate, extrusions, bar, rod, tube | Primarily plate, bar, rod (forms where stretching is feasible) | T651 is most commonly associated with plate and thicker sections. |
| Cost | Standard | Slightly Higher | The additional stress-relieving step adds to the processing cost of T651. |
GNEE: Your Trusted Supplier of 6061 Aluminum Alloys
At GNEE, we supply a full range of 6061 aluminum sheets, including 6061-T6, 6061-T651, and 6061-T6511, in plates, sheets, bars, and rods. Our team provides technical support to help you select the optimal temper for your project, ensuring performance, stability, and cost efficiency.
Whether your application demands precision machining, structural strength, or versatile fabrication, GNEE delivers reliable 6061 aluminum solutions tailored to your needs.
