Abstract
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.
Highlights
The relationship between process conditions, microstructure and composition is an important consideration in the design of industrial processes
Chemical compositions across each processed sample were precisely measured and those compositions were located on the Al-Si-Fe, Al-Si-Mn and Al-Fe-Mn ternary diagrams
The depiction of the mushy zone shown in the 2D maps (Figures 8–12) results from chemical composition mostly solidified at 575 ◦ C and resulting from Si, Fe and Mn release by intensive stirring (RMF)
Summary
The relationship between process conditions, microstructure and composition is an important consideration in the design of industrial processes. Phase diagrams are an important tool correlating these factors in both simple and more complicated materials systems [1]. Aluminum alloys are widely used in a variety of engineering applications, the automotive and aerospace industries. These alloys are characterized by an excellent combination of properties such as low coefficient of thermal expansion, high strength to weight ratio, and in. In the microstructure of AlSi alloy, primary grains of α-Al are visible, with interdendritic regions of AlSi eutectic and often minor intermetallic phases resulting from the presence of various impurity elements. The presence of iron most commonly results in β-Al5 FeSi, Metals 2017, 7, 506; doi:10.3390/met7110506 www.mdpi.com/journal/metals
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