When picking materials for your next project, you want something strong, reliable, and easy to work with. Many people see 6061 aluminum as a top choice, but the T6 and T651 tempers can cause confusion. Both versions seem similar at first glance, but slight differences can have a significant impact on your results.
Both 6061-T6 and 6061-T651 offer high strength, good corrosion resistance, and excellent machinability. The main difference is stress relief. T651 is stretched after heat treatment, which reduces internal stresses. T6 is not. For most projects, either option can work, but T651 provides more stability when tight tolerances or large plates are required.
If you want to pick the right aluminum for your next job, keep reading. This guide breaks down the fundamental differences between these two tempers.
What is Aluminum 6061 and Its Tempers?
Aluminum 6061 is a heat-treatable alloy. It contains magnesium and silicon as its main alloying elements. This combination gives it a good balance of strength, weldability, and corrosion resistance.
6061 is available in different “tempers.” A temper refers to how the metal was treated to get specific mechanical properties. The most common tempers are T6 and T651. Both are solution heat-treated and artificially aged to increase strength. The key difference is that T651 is stress-relieved by stretching, while T6 is not.
Tempering changes how aluminum performs. It affects hardness, strength, and the degree to which the metal moves or warps when cut or machined. Without proper tempering, the material might have internal stresses. These can lead to deformation, especially in large parts.
Understanding the T6 Temper
T6 is one of the most widely recognized temper designs for aluminum 6061. It offers a potent combination of hardness and machinability, making it worthwhile across many industries.
Definition and Process of T6 Temper
T6 temper refers to the aluminum having undergone two primary steps: solution tratamiento térmico and artificial aging.
First, the metal is heated to a high temperature. This step dissolves alloying elements into a solid solution. Then, it is quickly cooled. After that, the metal is aged at a lower temperature for a set time. This boosts its strength and hardness.
This process improves the material’s performance without changing its shape. However, no stress-relief method—like stretching—is used in T6.
Key Properties of 6061-T6
Mechanical Strengths
6061-T6 offers high tensile strength and yield strength. For example, typical tensile strength is around 45,000 psi, while yield strength is about 40,000 psi.
It also has good hardness, corrosion resistance, and workability. However, because it’s not stress-relieved, internal tension may occur, especially in thick or wide pieces. This can cause slight movement during the machining process.
Aplicaciones comunes
6061-T6 is used in parts where strength matters more than tight dimensional control.
Common uses include:
- Accesorios para aviones
- Bicycle frames
- Hardware marino
- Componentes estructurales
- Truck bodies
Exploring the T651 Temper
T651 is a variation of T6 that includes an extra step. This step helps reduce internal stress and improves the material’s stability during machining.
Definition and Process of T651 Temper
6061-T651 goes through the same heat treatment and aging steps as T6. The difference is that after aging, the metal is stretched to relieve stress. This is called “stress-relief stretching.”
This added process makes the material more stable. It lowers the chance of warping or shifting during cutting, perforación, o fresado.
T651 is often used in thick plates or parts where precision is key.
Key Properties of 6061-T651
Enhanced Stress Relief
The main benefit of T651 is reduced internal stress. When large aluminum parts are machined, they can move slightly due to built-up tension. T651 minimizes that risk.
Tensile and yield strength in T651 are nearly the same as T6. However, T651 gives better flatness, fewer distortions, and tighter tolerances. That makes it ideal for Mecanizado CNC and structural applications.
Typical Use Cases
6061-T651 is used when stability is most critical.
Common applications include:
- Precision machined parts
- Componentes aeroespaciales
- Mold bases
- Plantillas y accesorios
- Large flat plates
Comparative Analysis of 6061-T6 and 6061-T651
T6 and T651 share a lot in common, but a few key differences affect how they perform in real-world use. This section will compare them side by side in terms of the following essential aspects.
Strength and Hardness Differences
Both tempers have similar strength levels. Tensile strength and yield strength are nearly equal—typically around 45,000 psi tensile and 40,000 psi yield.
Hardness is also similar. Both are strong and rigid, making them suitable for load-bearing parts. You won’t notice much difference here unless the part requires extreme flatness or tight tolerances. In that case, T651 has an edge because it’s more stable after machining.
Maquinabilidad y trabajabilidad
Machinability is where the difference becomes clearer.
T651 is easier to machine for precision parts. Since it’s stress-relieved, it holds shape better. You get fewer dimensional shifts, even after deep cuts or multiple passes.
T6 can still be machined, but it may move slightly during the process, especially in thick or wide sections. That’s not a problem for general parts, but it matters in high-precision work.
When it comes to formando o flexión, both have good workability. But once aged, both become less formable. Forming is usually done before the tempering step.
Comparación de la resistencia a la corrosión
Both T6 and T651 have the same base alloy, so they offer nearly identical corrosion resistance.
They hold up well in marine and outdoor settings. The choice between them doesn’t affect how the metal resists rust or environmental wear. If corrosion resistance is your primary concern, either option will perform similarly.
Conductividad térmica
6061-T6 and 6061-T651 have the same thermal conductivity. Both materials transfer heat well, making them useful for heat sinks, enclosures, or parts exposed to temperature fluctuations.
The typical thermal conductivity is around 167 W/m·K. Since they come from the same alloy and have the same heat treatment, there’s no significant difference in heat flow performance between the two.
Estabilidad dimensional
This is where T651 has a clear advantage.
Because it is stress-relieved by stretching, T651 stays flatter and more stable during machining. It resists warping when the material is removed. This makes it a better choice for large plates, precision components, or multi-step machining.
T6 can experience small shifts in shape due to internal stress. That’s why some fabricators avoid it for precision jobs or thick stock.
Soldabilidad
Both tempers are weldable, but there’s a small catch.
Welding can reduce the strength near the weld zone for both T6 and T651 aluminum alloys. That’s because heat from soldadura removes the temper in the affected area. After welding, a reheat treatment may be necessary to restore strength.
If welding is a significant part of the project, some may use 6061 in a softer temper (such as T4) first, weld it, and then heat-treat it to T6 or T651 afterward.
Costo y disponibilidad
In most markets, both T6 and T651 are widely available and affordable.
T651 is more common in thicker plates, and T6 is often used in bars, tubes, and smaller stock. The price difference is negligible. In some cases, T651 may cost a little more due to the added stress-relief process, but the difference is minor for most buyers.
| Propiedad | 6061-T6 | 6061-T651 |
|---|---|---|
| Strength & Hardness | High strength, similar to T651 | High strength, nearly identical to T6 |
| maquinabilidad | Good, but may shift due to internal stress | Better – stress-relieved, holds shape well |
| Resistencia a la corrosión | Excelente | Excelente |
| Conductividad térmica | Same – ~167 W/m·K | Same – ~167 W/m·K |
| Estabilidad dimensional | Moderate – can warp during machining | High – stays flat and stable |
| Soldabilidad | Weldable, may lose temper near weld | Weldable, same limits as T6 |
| Cost & Availability | Widely available, slightly cheaper | Widely available, slightly more expensive |
Choosing the Right Alloy for Your Project
Knowing when to use T6 or T651 can help you avoid part distortion, save machining time, and reduce waste. Here’s a simple breakdown to help you decide.
When to Choose 6061-T6？
Choose T6 if your part doesn’t need extreme dimensional accuracy.
It works well for general parts, welded assemblies, structural supports, or components with looser tolerances. It’s also a good choice for smaller pieces, thin sections, or projects that don’t involve heavy machining.
If you’re forming the part before the final heat treatment, T6 can keep costs lower without sacrificing performance.
When to Choose 6061-T651？
Choose T651 when dimensional stability is critical.
It’s the better option for thick plates, flat surfaces, or parts that require tight tolerances. Use it for CNC-machined components, molds, jigs, or fixtures where movement during machining would cause problems.
If you’re machining large or complex shapes, T651 helps maintain accuracy throughout the entire process.
Other Tempers of Al 6061
While T6 and T651 are the most common choices, 6061 aluminum also comes in other tempers. Each temper offers different strength, formability, and processing benefits. The table below provides a quick overview of other common temperatures and their typical applications.
| Temper | Process Description | Características principales | Typical Use Cases |
|---|---|---|---|
| O | Annealed (softened) | Very soft, excellent formability | Deep drawing, bending, forming before heat treatment |
| T1 | Cooled from hot working, naturally aged | Low strength, moderate hardness | Low-stress structural parts, decorative use |
| T4 | Solution heat-treated, naturally aged | Good ductility, moderate strength | Welded assemblies, parts to be heat-treated later |
| T42 | T4 condition after forming | Same as T4, often used after shaping | Formed shapes needing further aging |
| T5 | Cooled from hot working, then artificially aged | Higher strength than T1 | Structural profiles, extrusions |
| T52 | T5 with controlled cooling/aging | Balanced strength and formability | Architectural parts, marine hardware |
| T6511 | Stress-relieved by stretching (extruded only) | Similar to T651, for extrusions | Precision-extruded shapes needing stability |
Conclusión
6061-T6 and 6061-T651 are very similar in strength, corrosion resistance, and overall performance. The key difference lies in dimensional stability. T651 is stress-relieved, which makes it more stable during machining, especially for large or thick parts. T6 works well for general use, smaller parts, and projects where tight tolerances are not required. Choosing the proper temper depends on how precise your final part needs to be.
Need help selecting the right aluminum material for your project? Póngase en contacto hoy mismo con nuestro equipo de ingenieros—we’ll guide you to the best solution based on your design, budget, and lead time.
Hola, soy Kevin Lee
Durante los últimos 10 años, he estado inmerso en diversas formas de fabricación de chapa metálica, compartiendo aquí ideas interesantes de mis experiencias en diversos talleres.
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Kevin Lee
Tengo más de diez años de experiencia profesional en la fabricación de chapas metálicas, especializada en corte por láser, plegado, soldadura y técnicas de tratamiento de superficies. Como Director Técnico de Shengen, me comprometo a resolver complejos retos de fabricación y a impulsar la innovación y la calidad en cada proyecto.
