On the formation of intermetallics in rapidly solidifying Al–Fe–Si alloys

It is known from previous experimental observations that a rapid solidification of Al–Fe and Al–Fe–Si alloys results in the formation of various metastable phases. Despite attempts to explain why particular intermetallics form and to accurately predict a sequence of their precipitation, a fully satisfactory and prognostic explanation remains to be found. In this communication, it is conjectured that after the concept of the driving forces for the onset of precipitation is adapted to take into account important differences between the Al-rich FCC solution and all other solid phases, it can be used to identify intermetallics whose formation is thermodynamically permissible for a given supercooling. If the composition of some of the “possible phases” is close to the composition of the remaining liquid, then the precipitation of these particular phases is facilitated, because corresponding nucleation events do not require a long-range diffusion, which might be slow in supercooled melts.