Experimental investigation and thermodynamic calculation of the Mg-Mn-Sr system

Both experimental investigation and thermodynamic modeling were performed for the Mg-Mn-Sr system. Four decisive alloys were selected and prepared using a powder metallurgy method to measure the isothermal section at 500 °C via a combination of X-ray diffraction (XRD) and electron probe microanalysis (EPMA). No ternary compound has been observed for this ternary system. Four three-phase regions, (Mg)+(αMn)+Mg17Sr2, Mg17Sr2+(αMn)+Mg38Sr9, Mg38Sr9+(αMn)+Mg23Sr6, and Mg23Sr6+(αMn)+Mg2Sr, have been identified at 500 °C. No appreciable ternary solubility has been detected in the binary Mg-Sr compounds. Phase transition temperatures of the Mg-Mn-Sr alloys were measured by means of differential scanning calorimetry (DSC) measurements. In the present modeling, the substitutional solution model was used to describe the liquid phase. Due to the high evaporability of Mg, Mn and Sr, the gas phase can affect higher temperature equilibria in the Mg-Mn-Sr system and thus was included and modeled as an ideal gas mixture. The thermodynamic calculations match well with the experimental data, indicating that no ternary thermodynamic parameters are needed for the thermodynamic description. In order to verify the reliability of the current thermodynamic modeling of the Mg-Mn-Sr system, five as-cast alloys in Mg-rich corner were prepared. The calculated liquidus projection is consistent with the observed primary phase regions. The present thermodynamic modeling is reliable and can be used in the development of the Mg alloys.