It’s not an alloy in the usual sense of the word. In an alloy the two metals randomly fill spots in the crystal lattice, and no particular bond is favored so the rows of atoms can easily slide over each other. But this is an intermetallic compound, AuAl2, in which each gold atom is locked to two particular aluminum atoms, yielding a basic crystal unit that is not very strong but tends not to slide, so it just gives catastrophically. There isn’t much you can do about it. Maybe try reinforcing fiberglass fibers?