What are the main differences between aluminium alloys 7075 and 6061 and where are they best used for? While these are both extensively used in the manufacture of bicycle frames and components, there is a world of difference between the constitution and application of the two.
Where Lies the Difference?
The primary difference between aluminium alloys 6061 and 7075 starts with their main composition. Aluminium 6061 uses magnesium and silicon as its main alloying element while aluminium 7075 uses zinc. In general, aluminium grade 6061 is highly weldable using tungsten inert gas (TIG) or metal inert gas (MIG), highly resistant to corrosion and exhibits good mechanical properties. Alloy 7075, on the other hand, exhibits better tensile strength but is considerably less resistant to corrosion.
The mechanical properties of both alloys largely depend on the temper or heat treatment of the material. Annealed or pre-tempered grade 6061-O provides the least tensile strength (18,000 psi) and yield strength (8,000 psi) while tempered grade 6061-T6 provides the most tensile (42,000 psi) and yield strength (35,000 psi) among the 6061 alloys.
For the 7075 alloys, the un-heat treated 7075-O comes at the lower end of the tensile and yield strength spectrum (40,000 psi and 21,000 psi, respectively) while 7075-T6 provides the most tensile (74,000 to 78,000 psi) and yield strength (63,000 to 69,000 psi).
Since alloy 7075 is considerably more expensive as compared to other aluminium alloys, it is only used when cheaper alloys would not be enough to do the job. It is most commonly used in applications that require high strength-to-density ratio. As such, 7075 is the alloy of choice when it comes to transport (automotive, aviation and marine) applications.
Due to its lightweight nature, 7075 is also used in the production of hang glider airframes, rock climbing equipment, lacrosse stick shafts and bicycle components. Alloy 7075 is also used in the manufacture of M16 and precision rifles for the American Army, the Desert Tactical Arms and the French armament company.
Alloy 6061, on the other hand, is considered to be the aluminium alloy of choice for general purpose use. The alloy’s highly resistant nature makes it suitable for the production of heavy-duty structures such as truck and marine components, tank fittings, scuba tanks and other high pressure applications. It can likewise be used in the manufacture of homebuilt aircraft, small utility yacht and boats, bicycle components, fly fishing reels and aluminium cans for food packaging. In addition, 6065 is also the most suitable alloy for hot forging.
So, whether you simply want to know what material your bicycle frame was made with or you want to determine the most appropriate material to use for a particular project, knowing the difference between alloys 6061 and 7075 can come in quite handy.