Beryllium, molybdenum, chromium and manganese have been used to prevent the β phase by tying up the Fe in another phase such as α-Al(Mn, Fe)Si, which has a skeleton (or Chinese script) or granular morphology. The presence of iron most commonly results in β-Al 5FeSi, with a monoclinic crystal structure, which has a significant negative impact on ductility.
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. These alloys are characterized by an excellent combination of properties such as low coefficient of thermal expansion, high strength to weight ratio, and in Al-Si alloys good castability. For predicting the occurrence of phases and the interactions between them, modeling of thermodynamic properties using the numerical method CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) has emerged more recently as another valuable tool.Īluminum alloys are widely used in a variety of engineering applications, particularly the automotive and aerospace industries. Phase diagrams are an important tool correlating these factors in both simple and more complicated materials systems. The relationship between process conditions, microstructure and composition is an important consideration in the design of industrial processes. 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. Fe-phases start to grow mainly behind the dendrites tips and in general may flow between them. The specimen centers showed enrichment in AlSi-eutectic but for β-Al 5FeSi and Al 15Si 2Mn 4 results are ambiguous. These findings were used to create 2D maps for visualization of the mushy zone, mass fraction of α-Al dendrites, β-Al 5FeSi, Al 15Si 2Mn 4 and their spatial location. 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. 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. Experimental specimens were processed in a directional solidification facility with forced melt flow, resulting in high levels of elemental segregation across samples. The solidification behavior of AlSiFeMn alloys with strong convection was investigated via experimental results combined with thermodynamic calculations.
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Use the link given below and proceed to the developer's website in order to download Thermo-Calc free.Ĭonvection 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.
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