Solidification paths of Al-Cu-Sn alloys: comparison of thermodynamic analyses and solidification experiments using in situ X-radiography

The increasing importance of Al-Cu-Sn alloys as materials for producing self-lubricating bearing materials in automotive industries requires the development of uniform microstructures with improved performance, which could be achieved by a precise control of solidification processes. Adding Sn to Al-Cu binary alloy could dramatically alters the solidification path, generating liquid phase separation and monotectic reaction. In this paper, Al-10 wt.% Cu-X wt.% Sn (with X = 0; 5; 10 and 20) alloys have their solidification paths investigated by three different complementary approaches. Firstly, the solidification paths were calculated by using the CALPHAD method through Thermo-Calc software revealing the sequence of transformations that could occur during the solidification of these alloys, from the formation of the initial α-Al dendrites to the final eutectic reaction. Secondly, experimental thermal analysis was carried out by DSC (Differential Scanning Calorimetry), which reveals the successive events that occur during the controlled melting and cooling of these alloys. Thirdly, directional solidification was performed on all alloys, with in situ and real-time observations achieved through the utilization of X-radiography. The comparison between the various approaches showed a suitable correspondence between the history of the alloy solidifications computed by Thermo-Calc and those obtained experimentally (DSC and directional solidification experiments). Additional information about the dynamics of each reaction was obtained during the directional solidification experiments in terms of microstructures, segregation, and the genesis of the liquid phase separation that occurred for high Sn-content alloys.