Thermodynamic stability of AlSi11 alloy microconstituents

Aluminium alloys possess excellent mechanical, physically chemical and technological properties which have found an extensive application in the automotive industry. Alloy AlSi11 belongs to a group of eutectic alloys characterized by high fluidity, low pouring temperature and narrow solidification interval which comprehend to the uniformly distributed eutectic microstructure indicating superior mechanical and technological properties. Study of AlSi11 alloy solidification sequence has been accompanied by calculation of equilibrium phase diagram, and simultaneous thermal analysis, all in correlation with microstructure development. Thermodynamic calculation revealed solidification sequence with corresponding temperatures in equilibrium state. Differential scanning calorimetry enables determination of exact temperatures of phases’ transformations correlated at different cooling rates. Dilatometer thermal analysis defined dimensional changes of AlSi11 alloy. Microstructural examination revealed development of following constituents: primary aluminium (α Al ), high-temperature intermetallic phases on the iron base (Al 5 FeSi and/or Al 15 (Fe,Mn) 3 Si 2 ), binary eutectic (α Al + β Si ) and secondary eutectic (Mg 2 Si and Al 5 Mg 8 FeSi 6 ) as a last solidifying phases. Synergy of performed phase diagram calculation, thermodynamic and microstructural investigation enables determination of thermodynamic stability of AlSi11 alloy exposed to different cooling conditions, with respect to phase’s evolution.