Aluminum 6061

6061 aluminum, known as “structural aluminum,” is a widely used alloy. It belongs to the 6000 series of aluminum alloys, which utilize magnesium and silicon to enhance strength and lower the melting point. This alloy exhibits excellent corrosion resistance, weldability, and tensile strength. Heat treatment can further enhance its strength through artificial aging. Its outstanding machinability and formability make it the preferred choice for extruded products.

Compared to specialized aluminum alloys, 6061 is versatile and cost-effective. While its physical properties are not exceptional, its versatility and ease of machining in metal forming processes remain unmatched.

Application Areas:

Transportation: Aircraft structures, automotive components, railway tank cars, ship hull structures, etc.

Building Structures: Heavy-duty structures, bridge components, etc.

Sports equipment: Bicycle frames, baseball bats, hockey sticks, etc.

Electronics: Smartphone cases, laptop cases, etc.

Other: Pipes, photography equipment accessories, military gear, etc.

Aluminum 6063

6063 aluminum, commonly referred to as “building aluminum,” is specifically designed for ease of extrusion and has a surface that is easily anodized. 66063 It has excellent corrosion resistance, especially after proper surface treatment. It is known for its good weldability, solderability, and machinability, as well as moderate tensile strength and good machinability. 6063 is widely used in extrusion applications and is highly favored in the construction, entertainment, and furniture industries, particularly in environments where exposure to weather or water is expected.

Application Areas:

Construction Industry: Window frames, door frames, curtain walls, architectural decorative profiles, railings, etc.

Furniture: Various furniture frames, tubing, etc.

Home Appliances: Radiators, appliance housings, etc.

Store Accessories: Display racks, shelves, etc.

Other: Irrigation pipes, lighting equipment, etc.

Chemical Composition of Aluminum 6061 vs 6063

Copper (Cu) content: 6061 contains a higher proportion of copper, which gives it superior strength and hardness but also slightly reduces its corrosion resistance (compared to 6063).

Silicon (Si) and magnesium (Mg) content: Although both contain silicon and magnesium, 6061 typically has a higher proportion of silicon and magnesium, further enhancing its strength. 6063 has relatively lower silicon and magnesium content, which gives it better extrusion performance and surface treatment properties.

Impurity elements: 6063 has stricter requirements for impurity elements such as iron, which helps improve its surface finish and anodizing results.

Weldability of Aluminum 6061 vs 6063

6061 aluminum alloy has excellent weldability and can be welded using the most common welding processes, such as TIG welding and MIG welding. Aluminum alloy welded joints can also withstand significant loads. 6063 aluminum alloy also has good weldability.

Machinability of Aluminum 6061 vs 6063

6063 aluminum alloy has excellent extrusion properties, good fluidity, and can be extruded into complex cross-sectional shapes. It is relatively soft, requiring less force and speed during cutting. Additionally, it has a high surface finish, making it ideal for producing various profiles, such as door and window frames, decorative strips, etc.

6061 aluminum alloy also has good machinability and can be welded and machined, but its extrusion performance is inferior to 6063. It is more suitable for manufacturing components requiring higher strength, such as mechanical parts and brackets. Machining 6061 produces sticky chips, and it is more difficult to machine than 6063. These chips are shorter and require lubrication for even the simplest cutting operations.

Heat Treatment of Aluminum 6061 vs 6063

The heat treatment for 6061 and 6063 is slightly different, resulting in different properties. 6061 and 6063 are typically in T4 and T6 conditions, respectively, after natural aging and artificial aging. The T6063 condition for 6063 involves three steps: solution heat treatment at 510°C, quenching at 175-190°C, and aging for 5-8 hours. 6061-T6 also undergoes three steps: solution treatment at 527°C, quenching, and artificial aging at 10-20°C for 160-180 hours. After artificial aging, both alloys exhibit reduced formability and ductility, while strength and corrosion resistance are enhanced. 6061 has a lower melting temperature and thermal conductivity, which is why its T6 temperature is slightly higher than that of 6063.

To eliminate artificial aging or mitigate the T6 effect to achieve optimal strength and toughness, 6061 and 6063 are annealed at 413°C for 2–3 hours (cooling rate of 10°C/hour) and at 415°C for 2 hours, respectively. The temperature and holding time can be adjusted based on the performance requirements of the specific application.

Which is better, 6061 or 6063?

Compared to 6063, 6061 forms smooth surfaces with complex shapes. Both 6061 and 6063 are structural materials used in furniture, recreational components, truck bodies, and window frames. Aircraft components, automotive bodies, fillers, hydraulic pistons, and brake structures are all manufactured using 6061 aluminum alloy. Additionally, compared to 6063, 6061 is suitable for ladders and bridge components due to its high strength and resistance to deformation.

As mentioned earlier, 6061 has excellent electrical conductivity, making it suitable for couplings, electrical fillers, and connectors. Its good corrosion resistance makes it an excellent choice for beverage cans.

Furthermore, 6063 can be used in general building products such as window frames, stair railings, and roofs, as it is easy to anodize and has good aesthetic appeal. Pipes, decorative components, structural supports, brackets, and conduits are also some applications of 6063. Due to its oxidation resistance, high corrosion resistance, and durability, household aluminum products such as cans can be recycled into more cans.

If thermal or electrical conductivity is critical in an application, aluminum alloys are a better choice than steel, and due to this property, they are used in power transmission lines. 6061 has better electrical conductivity than 6063.

Conclusion

Selecting the appropriate aluminum alloy (whether 6061 or 6063) depends on the specific requirements of your application. Both alloys can be formed using various aluminum forming techniques to achieve satisfactory product performance. The details of your project will play a key role in determining which alloy is more suitable for your intended application.

Aluminum 6061 is the second most popular aluminum alloy for extrusion, with a slightly higher strength-to-weight ratio compared to 6063. It offers excellent machinability and weldability, making it a versatile alloy suitable for a wide range of applications. If strength is a priority over corrosion resistance, opt for 6061.

On the other hand, 6063 alloy is the most popular aluminum alloy for extrusion. Notably, it offers slightly superior corrosion resistance and an aesthetically pleasing surface finish, making it ideal for anodizing. It is the preferred choice for applications requiring sufficient strength and enhanced corrosion resistance.

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In the aluminum alloy family, 6061 has become a common choice in structure, transportation and machinery manufacturing with its excellent comprehensive performance. However, many people are often confused by two different states 6061-T6 and 6061-T651 – when actually selecting materials. This article will give you an in-depth interpretation of the performance comparison, characteristics and applicable occasions between the two, to help you make the best decision for your design and project. Contact us

Common Temper Designation System for Aluminum Alloys

F (as fabricated): it’s used for wrought or cast aluminum products that have undergone a shaping process such as rolling, extrusion, forging, drawing, or casting. The F temper indicates that there was no special control over the thermal conditions or strain-hardening processes during the working of the material. Most F temper products are considered “semifinished” products.

O (annealed): the O temper is used for wrought or cast aluminum products that have been shaped through drawing, casting, rolling, extrusion, or forging, and at some point in the process have been annealed. Annealing is a heat treatment process that is used to achieve the lowest-strength condition in the material. This temper designation is chosen to maximize subsequent workability or to enhance ductility and toughness.

H (strain-hardened): it’s used for non-heat-treatable wrought alloys that have undergone a process called strain hardening or work hardening. Strain hardening is a method of increasing the strength of the alloy by subjecting it to plastic deformation, such as cold working.

W (solution heat-treated): the W temper is limited in its use and only applies to alloys that naturally and spontaneously age after undergoing solution heat treatment. Solution heat treatment involves heating the alloy to a specific temperature and then cooling it rapidly to achieve specific properties. It indicates that the material has been solution heat treated.

T (thermally treated): used for alloys that have been thermally treated to produce stable tempers other than F, O, or H. When a product is thermally treated, it’s designated with a “-T” temper. The digit after the T indicates the specific thermal treatment applied to the alloy. This can include supplementary treatments with or without strain hardening.

6061 T651 Aluminum Alloy

T651 aluminum represents an advancement in the T6 temper state in aluminum alloys, with excellent processing properties compared to traditional T6 tempered alloys. The T651 temper state is particularly suitable for machining tasks such as grinding, polishing and cutting, and is a very valuable choice. The process of achieving the T651 temper usually requires the formation of a solid solution, followed by stress relief through material stretching, and finally artificial aging to achieve this precise temper state. 6061 aluminum alloy is subjected to a tensile balance treatment based on the T6 temper. This process is called tensile balance treatment. Its purpose is to make the internal stress distribution of the aluminum alloy more uniform by adjusting it. Therefore, aluminum alloys in the T651 state have more excellent mechanical properties and deformation resistance.

Performance Characteristics of 6061 T651​

High dimensional stability: After stretching, internal stress is eliminated, deformation is small, and it is more suitable for large plates and precision structural parts.

Good flatness: The stretching process not only eliminates stress, but also significantly improves the surface flatness of the material.

Balance of high strength and good toughness: The T651 state improves the internal structure of the material through stretching while maintaining the high strength of T6, so that its toughness is also improved to a certain extent.

Slightly improved corrosion resistance: Due to the optimization of the organizational structure and the reduction of residual stress, it is suitable for use in humid and corrosive environments. ​

Good processing performance: T651 aluminum alloy retains the good processing performance of 6061 alloy and can perform various conventional machining operations.

Application Areas of 6061 T651​

Aerospace field: In the aerospace industry, the dimensional accuracy, weight and reliability of parts are extremely high.

High-end automobile manufacturing: Used to produce key parts of automobiles, such as engine blocks, suspension system components, body frames, etc.

Precision instruments and equipment: The high-precision dimensional control and good flatness of 6061 T651 aluminum alloy can ensure the precise installation and stable operation of internal parts of the instrument, and reduce equipment failures caused by material deformation. ​

Architectural decoration field: The good surface quality and corrosion resistance of 6061 T651 aluminum alloy enable it to maintain beauty and structural stability during long-term use, improving the overall quality and image of the building.

6061 T6 Aluminum Alloy

The T6 state is obtained by artificial aging after solution heat treatment. First, the 6061 aluminum alloy material is heated to a specific temperature range (about 495°C or 925°F) to fully dissolve the alloying elements in the aluminum matrix to form a uniform solid solution. Subsequently, the material is quickly cooled, i.e. quenched, to retain this supersaturated solid solution. Finally, the material is artificially aged at a lower temperature (about 120 – 180°C or 250 – 360°F) to cause the alloying elements to precipitate from the solid solution, thereby significantly improving the strength and hardness of the aluminum alloy.

Performance characteristics of 6061 T6

High strength: After T6 treatment, the strength of 6061 aluminum alloy is greatly improved. Its tensile strength can generally reach ≥310MPa, and its yield strength can reach ≥270MPa. It can withstand large loads and is suitable for the manufacture of structural parts with high strength requirements.

Good machinability: While maintaining high strength, 6061 T6 still has a certain plasticity and can be processed in a variety of operations, such as cutting, stamping, drilling, milling, etc., which can meet the processing of parts with different shapes and precision requirements.

Moderate corrosion resistance: Due to the characteristics of the alloy composition, 6061 T6 has good corrosion resistance. It can remain stable in general atmospheric environments and many industrial environments and is not prone to corrosion.

Good weldability: Aluminum alloys in this state can be welded by a variety of welding methods, such as argon arc welding, gas shielded welding, etc. The strength and sealing of the welded joints can meet the requirements of most engineering applications.​

Residual stress exists: The quenching step in the T6 treatment process will cause large residual stress inside the material. If the residual stress is released during subsequent processing or use, it may cause deformation of parts, affecting dimensional accuracy and product quality. ​

Application Areas of 6061 T6 ​

Industrial structural parts: widely used in the manufacture of structural components of various industrial equipment such as trucks, tower buildings, ships, trams, and railway vehicles.

Mechanical parts: used to manufacture various mechanical parts, such as shafts, gears, brackets, etc., which can meet the requirements of part strength and wear resistance during mechanical operation. ​

Precision machining: In some precision machining fields with high precision requirements, such as mold manufacturing, electronic equipment parts processing, etc., 6061 T6 also has certain applications.

Sports equipment: Some sports equipment uses 6061 T6 aluminum alloy to take into account the needs of strength and lightness, and improve the performance and use experience of the equipment.

Mechanical Properties : 6061 T651 vs. 6061 T6

6061 T651 : A key feature of 6061 T651 aluminum is its ability to maintain a high strength-to-weight ratio and hardness after tempering, making it ideal for a wide range of processing applications. However, during the manufacturing process, as external forces dissipate, internal stresses remain. These residual stresses induce a recovery effect that causes observable changes in the material’s dimensions—a dynamic interplay between external manipulation and internal response in the complex world of materials science.

T6 : When aluminum is treated with a T6 temper, such as 6061-T6 aluminum, the material’s mechanical properties improve dramatically. The yield strength of 6061-T6 aluminum increases significantly, almost four times, compared to 0 temper aluminum.

Machinability ：6061 T651 vs. 6061 T6

6061 T651: Has better machinability than T6 and is less prone to deformation during machining. T651 has slightly less stress than T6, so it is easier to machine than T6 material. There are also fewer deformation issues, which is especially important for applications with complex geometries.

6061 T6: Good machinability, but may require more careful processing to avoid deformation. In terms of machinability, aluminum alloys in the T6 state are well suited for many applications. However, during machining, more care needs to be taken to avoid part deformation; deformation can be common when designing complex parts or cutting thick materials.

Corrosion Resistance ：6061 T651 vs. 6061 T6

6061 T651: T6 is based on the addition of a stress relief step (usually by stretching), which greatly reduces the residual stresses within the material. Therefore, 6061 T651 is generally better than 6061 T6 in resisting stress corrosion cracking. In terms of other common corrosion forms (such as general corrosion, pitting), the two perform similarly.

6061 T6: This state of the alloy has good corrosion resistance and is suitable for outdoor and marine environments. However, due to residual stresses that may be generated during quenching, it may be sensitive to stress corrosion cracking (SCC) in certain corrosive environments (such as chloride-containing environments).

Cost ：6061 T651 vs. 6061 T6

Since 6061-T651 adds stretching to the T6 process, it needs more equipment and control, making it more costly.If you need extreme stability or precision, 6061-T651 is worth it for less deformation and waste.If cost is key and precision demands aren’t high, 6061-T6 is a more economical choice.

How to Choose 6061 T6 or 6061 T651

If the project is cost-sensitive, the processing is relatively simple, and the dimensional accuracy and deformation requirements of the final parts are not high, then 6061 T6 is usually a more economical and suitable choice.

If the project has strict requirements on the dimensional stability, flatness, surface finish and accuracy of complex shapes after processing, 6061 T651 is a better choice even if the cost is slightly higher. Especially when manufacturing large or thin-walled parts, the stress relief characteristics of T651 can effectively avoid warping and deformation caused by internal stress release during processing.

In short, both are excellent 6061 aluminum alloy heat treatment states, but T651 provides higher dimensional stability and better machinability through additional stress relief processes, making it more advantageous in precision and high-performance applications.

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