Thermodynamic Description Of Mg Research Articles

Thermodynamic description of Mg–Zn–Sb system supported by experimental work and extrapolation to the Mg–Zn–Al–Sb quaternary system

Magnesium-zinc-antimony (Mg–Zn–Sb) system is a promising cast Mg alloy system. Herein, the thermodynamic assessment of Mg–Zn–Sb ternary system was carried out using the CALculation of PHAse Diagram (CALPHAD) approach coupled with the experimental data in this work. The transformation temperatures and the isothermal section of the Mg-rich corner at 300 °C was investigated. Afterwards, a set of self-consistent parameters of Mg–Zn–Sb system were achieved combined with the thermodynamic descriptions of Mg–Sb and Mg–Zn systems as well as the updated description of Zn–Sb system in the present work. Meanwhile, the ternary Al–Zn–Sb system was re-assessed based on the available literature data. A set of reliable parameters describing the ternary Al–Zn–Sb system were obtained, and the present calculated results can reproduce most of the phase equilibria data. The thermodynamic description of Mg–Al–Zn–Sb systems was then developed using the extrapolation method from the descriptions of the constituent sub-ternary systems.

Assessment of the Mg–Al–Sb system supported by experiments and extrapolation to the Mg–Al–Sn–Sb quaternary system

The phase equilibria and transformation temperatures of the Mg–Al–Sb ternary system were investigated via thermodynamic modeling coupled with key experiments. The isothermal section of the Mg-rich corner at 400 °C and two vertical sections in the Mg–Al–Sb ternary system were constructed by the metallographic analysis and thermal analysis. No ternary compound was found in the Mg-rich corner. The thermodynamic modeling of Al–Sb and Mg–Al–Sb systems was carried out using the CALculation of PHAse Diagram (CALPHAD) approach. The associated solution model was used to describe the short-range ordering for the liquid phase. The calculated phase diagram and thermodynamic property of the Al–Sb system are consistent with most of the experimental data. A set of reliable and self-consistent thermodynamic parameters were obtained combining with Mg–Sb and Mg–Al systems as well as the updated Al–Sb system in the present work. The solidification paths in Sb-containing Mg alloys were analyzed using the present thermodynamic description of Mg–Al–Sn–Sb quaternary system extrapolated from that of the constituent sub-ternary systems.

Experimental investigation and thermodynamic description of Mg–Sc–Zn ternary system

The determination of the Mg-Sc-Zn phase diagram was motivated by the demand for alloying Mg–Sc shape memory alloy with Zn to enhance the phase stability of B2-structured phase at elevated temperatures. In the present work, the phase equilibria at 773 K and 873 K were experimentally investigated by analyzing chemical compositions and crystal structures of individual phases in the annealed alloy samples. MgSc_B2 and ScZn_B2 failed to form a continuous solid solution from the Mg–Sc binary boundary to the Sc–Zn binary boundary. Mg atoms were found to dissolve into the ScZn_B2 lattice that substitute Zn with a solid solubility up to 5 at.%. MgSc_B2 was proven not thermodynamically stable above 773 K. The solid solubility of Zn in bcc_A2 was measured to be around 1 at.%, giving rise to a narrow homogeneous range alongside the Mg–Sc binary vicinity. A thermodynamic database of Mg-Sc-Zn system was then successfully developed by optimizing parameters to reproduce phase present, phase equilibria, solidification paths, and transformation temperatures, etc. The assessed database together with the experimental findings can be utilized in the compositional design of multicomponent alloying in Mg–Sc based shape memory alloys.

Thermodynamic modeling and experimental investigation of the magnesium–zinc–samarium alloys

Magnesium (Mg)–Zinc (Zn)–Samarium (Sm) alloy system is being considered for the development of high-strength novel Mg alloys for structural applications. In this work, ternary phases in Mg–Zn–Sm system at Mg-rich corner were identified experimentally, based upon the investigation of five key alloys. Phase relationships at 350, 400 and 450°C of this system were also established. Furthermore, a self-consistent thermodynamic description of Mg–Zn–Sm system at Mg-rich corner was developed for the first time using the CALPHAD (CALculation of PHAse Diagram) method. Good agreement between the calculated phase diagrams and the experimentally measured data from both this study and literature validated the thermodynamic modeling approach used in this work.

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.

Microstructure investigations of directionally solidified Mg-rich alloys containing Al, Ca and Sn

The thermodynamic description of Mg–Al–Ca–Sn quaternary system in the Mg-rich region was developed on the basis of both our previous work and literature data on the key constituent ternaries, including Mg–Al–Ca, Mg–Al–Sn and Mg–Ca–Sn systems. Using this description coupled with the Scheil model, the solidification paths of Mg–Ca–Sn ternary alloys and Mg–Al–Ca–Sn quaternary alloys were calculated, which are in good accordance with the experimental results from directional solidification obtained by us.

Experimental study and phase diagram calculation in Al–Zn–Mg–Si quaternary system

The phase equilibrium of the Al–Zn–Mg–Si quaternary system containing (Al), (Si), MgZn 2 and Mg 2Si phases has been studied by means of scanning electron microscopy (SEM), electron dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential scanning calorimeter (DSC) as well as calculation of phase diagram based on PANDAT software. Two three-phase fields and one four-phase field among the 15 wt% Al–Zn–Mg–6 wt% Si alloys in the concentration of Zn ranging from 57 wt% to 67 wt% have been confirmed at 573 K. The result showed non-existence of quaternary compound in this region. Based on the experimental results, the appropriate thermodynamic description of Mg–Si system was chosen. The ternary interactions in the liquid phase of Al–Mg–Si and Mg–Zn–Si systems have been assessed and the calculated ternary phase diagrams agreed well with the experimental data. Combining with the related ternary systems, the thermodynamic description of the Al–Zn–Mg–Si system was presented, and the good agreement between the calculated results and the experimental results was obtained.