Phase formation in Mg–Sn–Si and Mg–Sn–Si–Ca alloys

Experimental work is done and combined with the Calphad method to generate a consistent thermodynamic description of the Mg–Ca–Si–Sn quaternary system, validated for Mg-rich alloys. The viability of a procedure for the selection of multicomponent key samples is demonstrated for this multicomponent system. Dedicated thermal analysis with DTA/DSC on sealed samples is performed and the microstructure of slowly solidified alloys is analyzed using SEM/EDX. The thermodynamic description and phase diagram of the ternary Mg–Si–Sn system, developed in detail also in this work, deviates significantly from a previous literature proposal. The phase formation in ternary and quaternary alloys is analyzed using the tool of thermodynamic equilibrium and Scheil calculations for the solidification paths and compared with present experimental data. The significant ternary/quaternary solid solubilities of pertinent intermetallic phases are quantitatively introduced in the quaternary Mg–Ca–Si–Sn phase diagram and validated by experimental data.

Research highlights▶ The solidification paths of ternary and quaternary alloys are analyzed in detail, using the tool of thermodynamic calculations. ▶ The precipitation sequence of phases and their amounts compare well with the microstructure of alloys. ▶ The most efficient comparison to the experimental thermal analysis data is done by calculation of the enthalpy variation with temperature. ▶ The viability of a procedure for the selection of multicomponent key samples is demonstrated for the development of the Mg–Ca–Si–Sn phase diagram.