s seen in the phase diagram below, Aluminum has a huge solubitiy in Galium in the ambient temperature. What you mentioned as "eat Aluminum" is nothing more than the Aluminum being dissolved into the liquid Galium.
A cool experiment that you can make is dissolve a aluminum foil into liquid Gallium completely, than add water on top.
The oxigen on H2O will oxidize the dissolved Aluminum and release H2 (you can carefully set fire to prove it)... what remains later is liquid gallium and water with Al2O3 particles.