Aluminum is an element.
Pure aluminum is a very soft metal with a lower metal point, but of course all aluminum (even alloys) have the same modulus or stiffness, just different strengths.
An alloy is simply a mixture of mostly metals with a few special additives that can produce great results. Some of these alloys can strain harden better than others, some are more resistant to corrosion, etc. All aluminum alloys are mostly aluminum, only some can be heat treated and only some can be safely welded.
There are many ways to strengthen metal, and the trick is to do so without making it brittle. One method is to cold work or deform the metal, such as a foil or wire formed from a larger thickness, based on strain hardening, the yield will increase. This means that the load you need to apply to further deform the metal is at the final level without returning to the yield load! Yes, metal is usually "strongest" (aka most productive) before it breaks!
