The most common type of aluminum by far is the 3004 aluminum that beverage can bodies are made of. It is closely followed by 5182 which is the aluminum that makes up the caps of those beverage cans. It is fair to assume though that 6061 is the next most common aluminum, and the type of aluminum that engineers, machinists, fabricators, and welders are most familiar with. It alongside aluminum 6063 are effectively the standard for structural aluminum with everything from automotive superchargers to architectural panels made from them. Since two of 6061 aluminum’s physical properties are substantially stronger tensile and yield strengths than 6063 it is the more commonly used aluminum.

While tensile strength is one of 6061 aluminum’s properties it is not the strongest aluminum out there, and its strength alone is not the reason that it has found such widespread use. Instead its popularity lies in the combination of this tensile strength with easy workability. Aluminum 6061 is easily cut to order and is a fairly forgiving material with a good if not breathtaking structural strength that allows for consistent and reliable results without much difficulty.

Different Tempers of 6061 Aluminum

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 gives the two different tempers distinctly different properties, and a comparative list of these physical 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 ????in/in-°F

All things considered it can be a little difficult to see why aluminum 6061 T4 is even needed. T4 has an advantage when it comes to cold forming the metal bending tube or sheet without the use of heat. This type of cold forming is somewhat limited for 6061 T6 due to the temper’s higher strength making it more difficult to get a satisfactory result without damaging the metal.

However, of the two different tempers 6061 T6 is the more widely used. The results of its heat treatment is an aluminum that has the highest practical strength for most purposes. If heated to higher temperatures or for longer periods of time it would gain greater dimensional stability, but this would come at the cost of strength and hardness.

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 it is among the most workable of the different aluminum alloys with excellent response to machining, welding and brazing, and even bending sheets and tubes as needed. This combination of high strength and good workability has seen aluminum alloys used in a dizzying array of applications.

Why 6061 Aluminum Properties Make It the Preferred Aluminum for Most Jobs

Homebuilt aircraft is not a hobby that most will participate in. Those that do however build their aircraft out of kits where the struts, rib, and skin of the plane is made with 6061 aluminum. The strength and versatility of the aluminum alloy is hard to overstate as it is used in everything from aircraft to structural towers to ship building. Whether you’re building a bike frame or a custom intake manifold for a sport’s car, Aluminum 6061 is the most likely place to start when you’re looking in order to combine lightweight, strength and performance. A incomplete list of the sorts of vehicles, structures, and devices  made from 6061 aluminum can be read below:

• Stairs, mezzanines, and railings
• Rail coaches
• Ambulance bodies
• Truck frames
• Ships and watercraft
• Bridges, Pylons, and other Structures
• Fasteners
• Heat exchangers
• Heat sinks

This strength would be meaningless if it wasn’t paired with a high degree of workability. The most compelling of 6061 aluminum’s properties is how easily it is machined, welded, and soldered. This is in part due to its compositions which contain a significant amount of magnesium, silicon, copper, and chromium. When it comes to the weldability of cast aluminum the presence of silicon is what makes it hard to work. The proportion of silicon in 6061 aluminum is much lower, under a percentage point. In addition, 6061 aluminum lacks the zinc found in 7000 series aluminums using magnesium. The result is that 6061 aluminum properties usefully include being friendly to hot work like welding, brazing, and soldering in addition to machinability.

Now, this hot workability isn’t totally without issue. It can be prone to heat cracking in heat affected areas. This is, however, very easily addressed through the use of filler metals. Aluminum alloy 5356 filler metal with a high magnesium content (5%) produces a very high strength weld. Although, if the final product is going to be heat treated afterwards welds made from 5356 can suffer from stress corrosion cracking after heat treatment. If the final workpiece is going to be heat treated or will be serving in a work environment above 150°F high silicon (5%) 4043 welding wire should be used instead. 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.