Iron is the most common and detrimental impurity in casting alloys and has been associated with many defects. The main consequence of the presence or adding of iron to AlSi alloys is the formation Fe-rich intermetallics with especially deleterious β-Al5FeSi. β-Al5FeSi phases are most often called needles on 2D micro sections, whilst platelets in 3D geometry. The x-ray tomography results have demonstrated Ferich phases with shapes different from simple forms such as needles or platelets and presented bent and branched phases. β grown as complicated structure of bent and branched intermetallics can decrease feeding ability, strengthen pores nucleation and eutectic colonies nucleation leading to lower permeability of mushy zone and porosity in the castings.
Directional solidification technique is an important research instrument to study solidification of metals and alloys. In the paper the model [6,7,8] of directional solidification in special Artemis-3 facility was presented. The current work aimed to propose the ease and efficient way in calibrating the facility. The introduced M coefficient allowed effective calibration and implementation of defined thermal conditions. The specimens of AlSi alloys with Fe-rich intermetallics and especially deleterious β-Al5FeSi were processed by controlled solidification velocity, temperature gradient and cooling rate.
Solidification of AlSiFe alloys was studied using a directional solidification facility and the CALPHAD technique was applied to calculate phase diagrams and to predict occurring phases. The specimens solidified by electromagnetic stirring showed segregation across, and the measured chemical compositions were transferred into phase diagrams. The ternary phase diagrams presented different solidification paths caused by segregation in each selected specimen. The property diagrams showed modification in the sequence and precipitation temperature of the phases. It is proposed in the study to use thermodynamic calculations with Thermo-Calc which enables us to visualize the mushy zone in directional solidification. 2D maps based on property diagrams show a mushy zone with a liquid channel in the AlSi7Fe1.0 specimen center, where significant mass fraction (33%) of β-Al5FeSi phases may precipitate before α-Al dendrites form. Otherwise liquid channel occurred almost empty of β in AlSi7Fe0.5 specimen and completely without β in AlSi9Fe0.2. The property diagrams revealed also possible formation of α–Al8Fe2Si phases.