Mohammad Mezbahul-Islam

Essential Magnesium Alloys Binary Phase Diagrams and Their Thermochemical Data

Magnesium-based alloys are becoming a major industrial material for structural applications because of their potential weight saving characteristics. All the commercial Mg alloys like AZ, AM, AE, EZ, ZK, and so forth series are multicomponent and hence it is important to understand the phase relations of the alloying elements with Mg. In this work, eleven essential Mg-based binary systems including Mg-Al/Zn/Mn/Ca/Sr/Y/Ni/Ce/Nd/Cu/Sn have been reviewed. Each of these systems has been discussed critically on the aspects of phase diagram and thermodynamic properties. All the available experimental data has been summarized and critically assessed to provide detailed understanding of the systems. The phase diagrams are calculated based on the most up-to-date optimized parameters. The thermodynamic model parameters for all the systems except Mg-Nd have been summarized in tables. The crystallographic information of the intermetallic compounds of different binary systems is provided. Also, the heat of formation of the intermetallic compounds obtained from experimental, first principle calculations and CALPHAD optimizations are provided. In addition, reoptimization of the Mg-Y system has been done in this work since new experimental data showed wider solubility of the intermetallic compounds.

Thermodynamic Modeling of Hydrogen Storage Capacity in Mg-Na Alloys

Thermodynamic modeling of the H-Mg-Na system is performed for the first time in this work in order to understand the phase relationships in this system. A new thermodynamic description of the stable NaMgH3 hydride is performed and the thermodynamic models for the H-Mg, Mg-Na, and H-Na systems are reassessed using the modified quasichemical model for the liquid phase. The thermodynamic properties of the ternary system are estimated from the models of the binary systems and the ternary compound using CALPHAD technique. The constructed database is successfully used to reproduce the pressure-composition isotherms for MgH2 + 10 wt.% NaH mixtures. Also, the pressure-temperature equilibrium diagram and reaction paths for the same composition are predicted at different temperatures and pressures. Even though it is proved that H-Mg-Na does not meet the DOE hydrogen storage requirements for onboard applications, the best working temperatures and pressures to benefit from its full catalytic role are given. Also, the present database can be used for thermodynamic assessments of higher order systems.

Phase equilibrium in Mg-Cu-Y

Magnesium-based bulk metallic glasses (BMG) have potential in applications ranging from biomedical to sports equipment and the Mg-Cu-Y system offers some of the most promising alloys. Phase relations and ternary solubility of the binary and ternary compounds of this system have been experimentally investigated. The Isothermal section of Mg-Cu-Y system at 673 K for the entire composition range has been constructed. Phase relations in the Cu-rich (>66 at.% Cu) region of the Mg-Cu-Y system has been determined for the first time. The homogeneity range of three ternary compounds has been determined. Solidifications behavior of several key alloys have been discussed based on the differential scanning calorimetry (DSC) experiments and thermodynamic calculations. Extensive analysis of the DSC curves has been carried out to relate them to the corresponding phase transformation reactions and temperatures. Some of the most promising metallic glass forming regions have been analyzed using thermodynamic calculations.

Ternary Intermetallic Compounds across the Mg-NiY Line at 673 K

The phase relationship of the Mg-Ni-Y system along the Mg-NiY line has been investigated using electron probe micro analysis (EPMA) at 673 K. Three two phase regions (Mg2Y+τ6, Mg2Y+ MgNiY(τ3), MgY+Mg3Ni2Y4(τ1)) and two three phase regions (Mg2Y+Mg3Ni2Y4(τ1)+ MgNi2Y2(τ2) and NiY+Mg3Ni2Y4(τ1)+MgNi2Y2(τ2)) have been identified. One new ternary compound Mg5NiY(τ5) was found and reported for the first time. Ternary solubility of the Mg8-13NiY(τ6) compound has been established which extends from 77.10 at.% Mg until 86.77 at.% Mg along the Mg-NiY section. Solubility of the third element in the binary compounds, NiY, Mg2Y and MgY has also been determined. Keywords: Mg alloy, phase identification, phase equilibrium, isothermal section.

A Differential Scanning Calorimetric Study of the Mg-Cu-Y System

The Mg-Cu-Y system has been experimentally investigated using differential scanning calorimetry (DSC). Vertical sections and phase assemblage diagrams are calculated using thermodynamic modeling. Solidification behavior of the key alloys was discussed in light of the thermodynamic calculation. Melting temperatures of two of the ternary compounds; Mg18CuY and Mg4CuY, are predicted using the modified thermodynamic database of this system. Key words: Mg alloys, Bulk metallic glass, Differential scanning calorimetry, Thermodynamic modeling.