Is aluminum or alloy lighter?

[aluhm]

It can be lighter, it can be heavier, depending on its alloy elements and their quantities. Density of Aluminum Check this link for a table of wrought alloys densities.

[lolitahe69]

depends on the alloy. usually aluminium is lighter (less dense), but duralumin (aluminium-lithium alloy) is lighter (less dense) than aluminium metal