Flux-cored wires exist for arc welding specific materials, like carbon steel, stainless steel, and cast iron, but they don't exist for others, like titanium alloys, tungsten electrodes, or yes, aluminum alloys. So, why is this? There are several reasons. Aluminum is soft.

Why can't you weld aluminum with flux core?

The chemicals used in fluxes for carbon steels or stainless steels don't work for aluminum. The fluxes that have been developed for aluminum have several highly undesirable properties. First, they are very corrosive, so that every bit of them must be removed from each weld pass before proceeding.