Microstructure of under-cooled Sn–Bi and Al–Si alloys

Rapid Solidification Processing (RSP), of metals and alloys, is established by increasing the under-cooling by applying high cooling rates (102 to 106 K/s) or by reducing the nucleation sites using low cooling rates (1 K/s). Melt under-cooling opens new solidification pathways for new non-equilibrium phases and unusual microstructures. Several techniques have been developed to reduce the nucleation sites and produce increased under-cooling in metals and alloys including the fluxing technique. The aim of this paper is to study the influence of the under-cooling level on microstructures of Sn–Bi and Al–Si alloys by using the fluxing technique. Increasing the under-cooling of the molten Sn–Bi alloys in the range of 11 K, lead to a refinement of the primary phase and eutectic constituent. However, for the molten Al–Si alloys, the increase of under-cooling, in the range of 25 K, led to no microstructure change. This is probably because sufficient under-cooling values were not obtained to produce rapid solidification in Al–Si alloys.