[Kailhus]

This made me realise how little I know about alumiunium and made me summarise this from a quick wiki search:

- “2024 aluminium alloy is an aluminium alloy, with copper as the primary alloying element. It is used in applications requiring high strength to weight ratio, as well as good fatigue resistance. It is weldable only through friction welding, and has average machinability.

- “7075 aluminium alloy is an aluminium alloy with zinc as the primary alloying element. It has excellent mechanical properties and exhibits good ductility, high strength, toughness, and good resistance to fatigue. It is more susceptible to embrittlement than many other aluminium alloys because of microsegregation, but has significantly better corrosion resistance than the alloys from the 2000 series.”

- “6061 is a precipitation-hardened aluminium alloy, containing magnesium and silicon as its major alloying elements. It has good mechanical properties, exhibits good weldability, and is very commonly extruded. It is one of the most common alloys of aluminium for general-purpose us.”

[jacquesm]

There are 8 basic alloys of aluminum based on the alloying element(s) (or none for 1000, which is pure) with the 8000 serving as a sort of catch-all for various combinations that don't warrant a category all their own. The total number of formulations is quite large and the properties, machinability, weldability, various strengths, density, resistance to fatigue (and post processing options, such as hardening) vary considerably.

Materials science is a fascinating field.