Cast Plate
The most common type of aluminum is 3004, used primarily for beverage can bodies, followed closely by 5182, which is used for the caps of those cans.
However, 6061 aluminum is likely the next most common and is the type that engineers, machinists, fabricators, and welders are most familiar with.
Along with aluminum 6063, 6061 is a standard for structural aluminum, used in applications ranging from automotive superchargers to architectural panels. Due to its substantially stronger tensile and yield strength compared to 6063, 6061 is more commonly used.
While 6061 aluminum has significant strength, it is not the strongest aluminum available. Its widespread use is due to the combination of its star physical properties, such as tensile strength and easy workability.
Aluminum 6061 is easily cut to order, fairly forgiving, and offers good structural strength, allowing for consistent and reliable results with minimal difficulty.
Different Tempers of 6061 Aluminum Alloys
6061 aluminum is available in two tempers: aluminum 6061 T4 and 6061 T6.
The difference between the two is that T4 is naturally aged and T6 is artificially aged by heating it between 350 to 500°F for 12 to 24 hours.
This aging process gives the two tempers distinctly different properties, including fatigue strength. A comparative list of these mechanical properties can be seen below.
| Property | T4 Aluminum 6061 | T6 Aluminum 6061 |
| Tensile Strength | 35,000 psi | 45,000 psi |
| Yield Strength | 21,000 psi | 40,000 psi |
| Modulus of Elasticity | 10,000 ksi | |
| Thermal Conductivity | 1070 BTU-in/hr-ft²-°F | 1160 BTU-in/hr-ft²-°F |
| Thermal Expansion Coefficient | 13.1 µin/in-°F | |
Considering the mechanical properties and chemical composition, it can be challenging to see the need for 6061 T4 aluminum. However, T4 has a significant advantage in cold-forming processes, such as bending tubes or sheets, without applying heat.
This type of cold forming is limited for 6061 T6 due to its higher strength, which makes it more difficult to achieve satisfactory results without damaging the metal. The softer nature of T4 allows for easier manipulation and forming without compromising the integrity of the material.
However, of the two different tempers, 6061 T6 is the more widely used. The result of its heat treatment is an aluminum that has the ultimate tensile strength for most purposes.
If heated to higher temperatures or for longer periods, 6061 aluminum would achieve greater dimensional stability. However, this increase in thermal properties would come at the expense of reduced strength and hardness.
The balance between enhancing thermal stability and maintaining mechanical properties is crucial in applications requiring both features.
As it is, 6061 aluminum’s properties, specifically its high tensile and yield strengths have widespread applicability to a range of roles. This is enhanced by the fact that the alloy is among the most workable of the different aluminum alloys with good weldability, machining, and brazing.
This combination of high strength and good workability has seen aluminum alloys used in a dizzying array of applications.
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Why 6061 Aluminum Physical Properties Stand Out for Most Applications
Homebuilt aircraft is a niche hobby, but enthusiasts often use 6061 aluminum for building struts, ribs, and the skin of their planes.
The strength and versatility of these heat treatable, wrought alloys are evident in their widespread use across various industries, from aircraft construction to structural towers and shipbuilding.
Whether you’re crafting bike frames or a custom intake manifold for a sports car, 6061 aluminum alloys are typically the materials with the best chemical composition due to their lightweight, strength, and performance.
Below is a non-exhaustive list of vehicles, structures, and devices commonly made from aluminum 6061 alloys:
- Stairs, mezzanines, and railings
- Rail coaches
- Ambulance bodies
- Truck frames
- Electrical fittings
- Ships and watercraft
- Bridges, Pylons, and other Structures
- Fasteners
- Heat exchangers
- Bicycle frames
- Heat sinks
Workability of the 6061 Aluminum Alloy
This strength of the 6061 alloy would be meaningless if it wasn’t paired with a high degree of workability. One of the most compelling of the 6061 aluminum properties is how easily it can be machined, welded, and soldered.
This is partly due to its chemical composition, which includes significant amounts of magnesium, silicon, copper, and chromium. The relatively low proportion of silicon in 6061 aluminum properties (under one percent) makes it more manageable for welding compared to cast aluminum, which often has higher silicon content.
6061 aluminum’s lack of zinc, commonly found in 7000 series aluminum alloys, further enhances its suitability for hot work such as welding, brazing, and soldering.
Weldability of 6061 Aluminum
However, this hot workability isn’t without issues, as the 6061 aluminum alloy can be prone to heat cracking in heat-affected areas.
This problem can be mitigated by using appropriate filler metals. For instance, aluminum alloy 5356 filler metal, with a high magnesium content (5%), produces a strong weld but can suffer from stress corrosion cracking if the final product is heat-treated.
For projects that will be heat-treated or exposed to temperatures above 150°F, a high-silicon (5%), heat treatable, 4043 welding wire is recommended to enhance the weld’s durability and ease of welding.
The silicon will help the weld deal with heat over time better, and as a bonus, the actual welding should be easier to perform than with the 5356 aluminum alloy.
Welding without filler metal, as in the case of GTAW fusion, while technically possible is inadvisable due to a tendency for 6061 aluminum alloy to crack.
That particular use case is somewhat limited though. GTAW is not the most widely mastered welding process and most fabrications using 6061 aluminum alloy will require filler materials, as these will tend to be robust structural projects.
When it comes to machining, 6061 aluminum’s properties combined with its price and availability make it the baseline aluminum for CNC machining with alternatives mostly explored due to highly specific needs.
Overall, 6061 aluminum alloy is an aluminum that is difficult to go wrong with.