Jingrui Zhao

Reassessment of the Al–Mn system and a thermodynamic description of the Al–Mg–Mn system

Abstract A thermodynamic optimization for the Al – Mn system is performed by considering reliable literature data and newly measured phase equilibria on the Al-rich side. Using X-ray diffraction, differential thermal analysis, and scanning electron microscopy with energy dispersive X-ray spectroscopy methods, the melting behavior of λ-Al4Mn was correctly elucidated, and two invariant reactions associated with λ-Al4Mn (L + μ-Al4Mn λ-Al4Mn at 721 ± 2 °C and L + λ-Al4Mn Al6Mn at 704 ± 2 °C) are observed. The model Al12Mn4(Al, Mn)10 previously used for Al8Mn5 was modified to be Al12Mn5(Al, Mn)9 based on crystal structure data. In addition, the high-temperature form of Al11Mn4 is included in the assessment. Employing fewer adjustable parameters than previous assessments, the present description of the Al – Mn system yields a better overall agreement with the experimental phase diagram and thermodynamic data. The obtained thermodynamic description for the Al – Mn system is then combined with those in the Al – Mg and Mg – Mn systems to form a basis for a ternary assessment. The thermodynamic parameters for ternary liquid and ternary compound Mn2Mg3Al18 (τ) are evaluated on the basis of critically assessed experimental data. The enthalpy of formation for τ resulting from CALPHAD (CALculation of PHAse Diagrams) approach agrees reasonably with that via first-principles methodology. Comparisons between the calculated and measured phase equilibria in the Al – Mg – Mn system show that the accurate experimental information is satisfactorily accounted for by the present description. A reaction scheme for the whole ternary system is presented for practical applications.

Experimental investigation and thermodynamic calculation of the Fe–Mg–Mn and Fe–Mg–Ni systems

Abstract Based on the thermodynamic calculations extrapolated from the corresponding binary sub-systems, four decisive alloys in the Fe–Mg–Mn system and three in the Fe–Mg–Ni system were selected and prepared using a powder metallurgy method to measure the isothermal sections at 500 8C in both systems. The prepared samples were annealed at 5008C, and then subjected to X-ray diffraction, optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectrometry as well as electron probe microanalysis. Taking into account the presently obtained experimental data and the experimental data available in the literature, thermodynamic modeling was performed for the above systems. It was found that a direct extrapolation from the corresponding three binary systems can well reproduce all the experimental data in the Fe–Mg–Mn system, while two thermodynamic parameters are needed in the Fe–Mg–Ni system to fit all the experimental data. The liquidus projections and reaction schemes for the Fe–Mg–Mn and Fe–Mg–Ni systems are also presented.

Thermodynamic Description of the Al–Mg–Y System

The Al–Mg–Y system was critically assessed by means of the CALPHAD technique. The solution phases of liquid, face-centered cubic (FCC), body-centered cubic (BCC) and hexagonal close-packed (HCP) were modeled with Redlich–Kister equation. The thermodynamic models of compounds Al12Mg17, Al30Mg23 and Al3Mg2 in the Al–Mg system, AlY2, Al2Y3, AlY and Al3Y in the Al–Y system, as well as Mg24Y5 in the Mg–Y system were kept consistent with that of the corresponding binary systems. In order to reproduce the ternary solid solubility of previously determined isothermal section at 400 °C, an identical formula of (Al,Mg,Y)2(Al,Mg,Y) was used to model Al2Y phase in the Al–Y system and Mg2Y in the Mg–Y system. The ordered part of BCC phase, i.e. the BCC_B2 phase, was treated with a thermodynamic model of (Al,Mg,Y)0.5(Al,Mg,Y)0.5(Va)3. The ternary phase of Al4MgY was described as linear compound with sub-lattice model. On the basis of the optimized thermodynamic parameters of Al–Mg, Al–Y and Mg–Y systems in literature, the Al–Mg–Y system was optimized in present work. The currently calculated isothermal sections at 400 and 800 °C, as well as the liquidus surface projection agree well with the previous experimental data.