6061 T6 vs T651: Which is Better?

When you see aluminum 6061 T6 and T651, it can be confusing. They’re both made from the same aluminum alloy, but they go through different treatments that affect how they perform.

In this blog, you’ll learn the key differences between 6061 T6 vs T651. This will help you decide which one is better for your project.

Overview of 6061 Aluminum Alloy

6061 aluminum alloy, first made in 1935 as “Alloy 61S,” is one of the most common aluminum types you can use. It’s strong, easy to weld, and resists rust well. It’s made mostly of aluminum (about 96–98%), with added magnesium and silicon to make it stronger and more flexible. It also includes small amounts of copper, iron, chromium, zinc, titanium, and manganese.

Aluminum 6061 T6

6061 T6 aluminum is a strong and lightweight material you can use for parts that need to handle stress and resist rust. It’s made by mixing aluminum with other elements and then heat-treating it through a process called T6 tempering. In this process, the metal is heated to boost its strength and then aged with heat to keep that strength over time.

6061 T6 Aluminum Heat Treatment Process

To heat treat 6061 T6 aluminum, you first heat it to 525°C for about an hour. This helps mix all the elements evenly in the metal.

Then, you quickly cool it down in water. This fast cooling, called quenching, stops the elements from forming separate particles. At this point, everything stays mixed together at room temperature, which helps increase the strength.

After quenching, you heat the metal again to a lower temperature between 162°C and 205°C. This step is called aging. It makes the elements come together in small, organized groups called GP zones. These zones are what give the aluminum its strength. You can heat it at 205°C for 1 hour or at 162°C for 8 hours, both give similar results.

Pros and Cons of 6061 T6 Aluminum

Here are the advantages of 6061 T6 aluminum:

• T6 aluminum gives you high strength while still being lightweight.
• It resists rust well and is easy to weld.
• It’s easier to shape and machine compared to other strong aluminum types.

Here are the disadvantages of 6061 T6 aluminum:

• To get these good properties, you need to follow a careful heat treatment process, checking the heating rate, time, and temperature.
• This process makes T6 more expensive than other options like T5.
• T6 aluminum is also less flexible, which means it can be more likely to crack if bent too much.
• If you’re working with thick pieces, T6 tempering may not work well because the metal doesn’t cool evenly. In that case, you’d need to adjust the process to save time and reduce waste.

6061 T651 Aluminum

6061 T651 aluminum is a type of T6 aluminum that’s easier for you to work with, especially when grinding, polishing, or cutting. You make it by heating the metal to mix the elements, stretching it to relieve stress, and then artificially aging it to lock in its strength.

T651 Aluminum Heat Treatment Process

The heat treatment for T651 is a bit different from T6. After quenching in water, there’s an extra step called stress relieving. This involves stretching the metal to remove internal stresses, and then aging it the same way as in T6.

During the heat treatment, internal stresses form in the metal. To get rid of them, you stretch the metal using a machine. This step helps the metal hold its shape better during the processes, which is why it is more stable.

Pros and Cons of 6061 T651 Aluminum

Below are some of the advantages of 6061 T651 aluminum:

• You still get all the great benefits of T6 aluminum; it’s strong, lightweight, resists rust, and is easy to weld.
• If you’re machining parts, T651 is a better choice because it helps the material stay in shape and not warp after cutting. This means your parts will stay the right size and shape.

And here are its disadvantages:

• Because there’s an extra step in the heat treatment process, T651 costs more than T6.
• It also takes more time to make, since it includes a controlled stretching step.

Mechanical Properties Comparison of Aluminum 6061 T6 vs T651

Below we discuss the main differences between aluminum 6061 T6 vs T651 when it comes to their mechanical properties:

Strength

Both 6061 T6 and T651 aluminum have nearly the same tensile strength of around 310 MPa. They also have the same density, giving them a high strength-to-weight ratio. This is because the heat treatment process only stretches the material, without changing anything else.

Heat Treatment

For both T6 and T651, you heat the aluminum to 980°F for an hour and then quickly cool it in water. After that, you do artificial aging. During T6, the cooling traps some internal stresses because the core and surface cool at different rates. In T651, after quenching, you stretch the aluminum by 1 to 3% to remove those stresses.

Dimensional Stability

6061 T651 aluminum stays more stable in shape than T6. Since T651 doesn’t have internal stresses, it’s easier for you to machine without warping the part. With T6, while it’s strong, you may notice it distorting during machining.

Physical Properties: Differences Between 6061 T6 and T651

Here’s a comparison table of the important physical properties of 6061 T6 and T651:

Cost Differences Between 6061 T6 and T651

T651 costs more because it goes through an extra stress-relieving step that makes it stronger and more stable. This is helpful for high-precision parts like aerospace or marine parts, where the extra cost is worth it.

But for general uses like bike frames or car parts, 6061 T6 is cheaper and usually good enough. T651 also machines better but can wear out tools faster, while T6 may save you on tool costs.

Applications for 6061 T6 VS T651

There are many uses of 6061 aluminum, such as the following:

6061 T6 Aluminum

• Used in aircrafts and watercrafts.
• Common in robotics and automation.
• Found in bicycle frames and sports industry products.
• Used for medical devices and precision instrument components.

6061 T651 Aluminum

• Used in automotive wheel hubs.
• Found in water pipes and tubes.
• Common in tooling and fixtures.
• Used in medical device components and die forging.

When to Choose: Aluminum 6061 T6 vs T651

When deciding between T6 and T651, think about the specific needs of your application:

6061 T6 Aluminum

• Choose T6 if you need a high strength-to-weight ratio. It provides enough hardness and strength for heavy load-bearing applications.
• Go for T6 if you don’t need complex machining processes. It’s ideal for simpler fabrication.
• T6 is cheaper than T651, so it’s a good choice if you’re on a budget.

6061 T651 Aluminum

• Choose T651 if you need improved machinability. T651 is treated with controlled stretching to make it easier to machine.
• T651 is better for applications that require high dimensional stability after machining. It reduces internal stresses and prevents distortions, making it great for automation and robotics.
• T651 also improves weldability, so it’s the best choice if superior welding is needed.

Conclusion

6061 T6 and 6061 T651 aluminum are both great for precision machining. However, T651 is better for high-precision jobs where tight tolerances and a smooth surface are needed. T6 is a good choice if you’re looking to save money or if the part doesn’t need the same level of precision or performance as one made from T651.

If you’re not sure which one to pick, ask a qualified precision machining manufacturer for advice. At DEK, we’re here to help you find the right materials and solutions for your machining needs. Contact us today to discuss your project!