Effect of melt superheating treatment on solidification structures of Al75Bi9Sn16 immiscible alloy

Abstract

In this paper, the liquid-liquid phase separation (L-LPS) and solidification process of the Al75Bi9Sn16 immiscible alloy were studied with calorimetric and resistivity methods to ascertain the melt superheated treatment process. The impact of melt superheating treatment (MST) on the phase constitution and solidification microstructures were investigated using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) to determine the structural sensitivity to the melt superheated degree, and find a new strategy for improving the forming ability of the core-shell structure of the Al75Bi9Sn16 alloy. The results show that: resistivity method is a more sensitive, intuitive, and effective method to investigate the liquid-liquid phase separation, and the liquid-liquid phase separation and precipitation of primary (Sn) phase occur in 1039K–880K and 460K–403K respectively. In addition, the core-shell structure with Sn-Bi-rich core and Al-rich shell can be formed under conventional casting conditions; the melt superheating treatment (MST) can promote the formation of core-shell structure by increasing solidification time t0 and decreasing the average solidification rate v and viscosity η.