Thermodynamic properties and microstructure evolution of ternary Al-10%Cu-x%Sn immiscible alloys

The vertical phase diagram of ternary Al-10%Cu-x%Sn (x% from 3 to 75 wt.%) alloys is experimentally established with differential scanning calorimetry (DSC) method. The enthalpy of fusion during melting process is determined, which decreases linearly with the increase of Sn content. The undercoolability of those liquid alloys solidifying with the primary (Al) solid solution phase can be further enhanced by increasing the cooling rate. However, the increase of cooling rate has little influence on the other alloys with the preferential liquid phase separation. As Sn content rises, three kinds of liquid separation patterns are observed, which are the dispersed pattern of very fine L₂(Sn) droplets distributed within primary (Al) interdendritic areas, the segregated pattern of several large L₂ blocks enveloped by the Al-rich phase and the layered pattern consisting of top Al-rich zone and bottom Sn-rich zone.