Thermo-Calc Prediction of Mushy Zone in AlSiFeMn Alloys

Convection forces can cause significant segregation within the liquid during directional solidification, influencing the structure of the mushy zone and the type and distribution of phases present in the solidified alloy. The solidification behavior of AlSiFeMn alloys with strong convection was investigated via experimental results combined with thermodynamic calculations. Experimental specimens were processed in a directional solidification facility with forced melt flow, resulting in high levels of elemental segregation across samples. The resulting local compositions were located on phase diagrams Al-Si-Fe, Al-Si-Mn and Al-Fe-Mn for prediction of the variation in solidification behavior. Phase mass fraction diagrams created in Thermo-Calc showed the effect of segregation on the characteristic temperatures, mushy zone length and the order of occurring phases precipitating across specimens. These findings were used to create 2D maps for visualization of the mushy zone, mass fraction of α-Al dendrites, β-Al5FeSi, Al15Si2Mn4 and their spatial location. The specimen centers showed enrichment in AlSi-eutectic but for β-Al5FeSi and Al15Si2Mn4 results are ambiguous. Fe-phases start to grow mainly behind the dendrites tips and in general may flow between them. Mn-rich phases start to precipitate at higher temperatures than β and in many places before α-Al and in this way may flow in the melt above the mushy zone.