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Thermodynamic stability of microconstituents in AlSi11 alloy

An AlSi11 alloy (EN AC 44000) belong to the group of “eutectic alloys” and is characterized with relatively low melting point and narrow solidification interval which both brought to the uniformly distributed eutectic microstructure indicating superior mechanical and technological properties [1]. Silicon is one of the most important alloying elements which comprehend to good castability of aluminum alloys. Addition of silicon improves resistance to hot cracks and feeding capability [1, 2]. Synergy of influenced alloying and trace elements effect comprehend to different intermetallic phase evolution. The content of secondary alloying elements (Mg, Cu) and trace elements (Fe, Mn, Cr, Zn) significantly influence on solidification manner of an AlSi11 alloy [3-5]. Investigation of an AlSi11 alloy comprehends modelling of equilibrium phase diagram, simultaneous phase analysis and microstructural investigations. Polythermal section of phase diagram of AlSi11 alloy indicates solidification sequence as follows: dendrite evaluation αAl beside precipitation of high temperature intermetallic phases on iron base, silicon (primary and eutectic) evaluation, and precipitation of complex secondary eutectic intermetallic phases Al8FeMg3Si6 and Mg2Si. Since liquid is stable till 566 °C, and secondary eutectic phases evaluation is occurring below this temperature which indicate limited sources and positions for its precipitation. Equilibrium thermodynamic modelling also indicates precipitation of other intermetallic phases such as Al13Cr4Si4, Al5Cu2Mg8Si6 and Al3Ni, all below 400 °C as a result of solid state reactions. Metallographic analysis resulted in following microstructural constituents: primary aluminium αAl, main eutectic αAl + βSi, high temperature iron phase Al5FeSi, intermetallic phases in form of secondary eutectic Mg2Si and Al8FeMg3Si6. Correlation of established microstructural constituents with thermodynamic modelling and differential scanning calorimetry indicates thermodynamic stability of particular microstructural components as well as exact solidification sequence for this particular chemical composition.

AlSi11 ; thermodynamic modelling ; thermal stability ; microconstituents ; solidification sequence

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