Microstructure Observation of AM60 Magnesium Alloy Solidified by Rapidly Quench

In solidification theory, with a slow cooling rate such as sand mold casting, it is easy to segregate the solute aluminum near the grain boundary of primary α-Mg phase under the solidification in Mg-Al system alloys. Thus, volume fraction of none-equilibrium crystallized β-Mg17Al12 phase showed the higher value compared with metal mold casting with faster cooling rate. However, in our microstructure observation results, the volume fraction of β phase in permanent mold castings was larger than that of sand mold castings. In the present study, these contradictory behavior was investigated by observation of as-solidified microstructure obtained from rapid cooling castings at the just below the solidus temperature of 723, 773 and 823K.