Ahmad Mostafa

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.

Influence of cooling rate on microsegregation behavior of magnesium alloys

The effect of cooling rate on microstructure and microsegregation of three commercially important magnesium alloys was investigated using Wedge (V-shaped) castings of AZ91D, AM60B, and AE44 alloys. Thermocouples were distributed to measure the cooling rate at six different locations of the wedge casts. Solute redistribution profiles were drawn based on the chemical composition analysis obtained by EDS/WDS analysis. Microstructural and morphological features such as dendrite arm spacing and secondary phase particle size were analyzed using both optical and scanning electron microscopes. Dendritic arm spacing and secondary phase particle size showed an increasing trend with decreasing cooling rate for the three alloys. Area percentage of secondary phase particles decreased with decreasing cooling rate for AE44 alloy. The trend was different for AZ91D and AM60B alloys, for both alloys, area percentage of β-Mg17Al12 increased with decreasing cooling rate up to location 4 and then decreased slightly. The tendency for microsegregation was more severe at slower cooling rates, possibly due to prolonged back diffusion. At slower cooling rate, the minimum concentration of aluminum at the dendritic core was lower compared to faster cooled locations. The segregation deviation parameter and the partition coefficient were calculated from the experimentally obtained data.

Characterisation and thermodynamic calculations of biodegradable Mg–2.2Zn–3.7Ce and Mg–Ca–2.2Zn–3.7Ce alloys

ABSTRACT In the present study, the effect of Ca (0.5–6 wt-%) content on the microstructure, phase formation, and mechanical properties and in vitro degradation behaviour of Mg–2.2Zn–3.7Ce alloys were investigated. Microstructural analysis and thermodynamic calculations also showed that Mg–2.2Zn–3.7Ce alloy contain α-Mg, Mg12Ce and CeMgZn2, while after adding 0.5 wt-% Ca to Mg–2.2Zn–3.7Ce alloy, IM1 (Ca3MgxZn15−x) (4.6 ≤ x ≤ 12) phase was detected. Further addition of Ca to 6 wt-% resulted in forming Mg2Ca besides α-Mg, Mg12Ce and IM1 with the absence of CeMgZn2. The tensile strength and elongation of the Mg–Ca–2.2Zn–3.7Ce alloys increase with increasing Ca content up to 1.5 wt-%, while further addition of Ca to 6 wt-% has a reversed effect. Similarly, the degradation rate of the alloys increased first with increasing Ca content and then decreased.

Experimental Investigation of the Phase Equilibria in the Al-Mn-Zn System at 400°C

Al-Mn-Zn ternary system is experimentally investigated at 400°C using diffusion couples and key alloys. Phase relationships and homogeneity ranges are determined for binary and ternary compounds using EPMA, SEM/EDS, and XRD. Reported ternary compound T3 (Al11Mn3Zn2) is confirmed in this study and is denoted as τ2 in this paper. Two new ternary compounds (τ1 and τ3) are observed in this system at 400°C. τ1 is determined as a stoichiometric compound with the composition of Al31Mn8Zn11. τ3 has been found to have homogeneity range of AlxMnyZnz ( at%; at%; at%). The binary compounds Al4Mn and Al11Mn4 exhibit limited solid solubility of around 6 at% and 4 at% Zn, respectively. Terminal solid solution Al8Mn5 is found to have maximum ternary solubility of about 10 at% Zn. In addition, ternary solubility of Al-rich β-Mn′ at 400°C is determined as 4 at% Zn. Zn-rich β-Mn′′ has a ternary solubility of 3 at% Al. The solubility of Al in Mn5Zn21 is measured as 5 at%. Based on the current experimental results, the isothermal section of Al-Mn-Zn ternary system at 400°C has been constructed.

Binary Phase Diagrams and Thermodynamic Properties of Silicon and Essential Doping Elements (Al, As, B, Bi, Ga, In, N, P, Sb and Tl)

Fabrication of solar and electronic silicon wafers involves direct contact between solid, liquid and gas phases at near equilibrium conditions. Understanding of the phase diagrams and thermochemical properties of the Si-dopant binary systems is essential for providing processing conditions and for understanding the phase formation and transformation. In this work, ten Si-based binary phase diagrams, including Si with group IIIA elements (Al, B, Ga, In and Tl) and with group VA elements (As, Bi, N, P and Sb), have been reviewed. Each of these systems has been critically discussed on both aspects of phase diagram and thermodynamic properties. The available experimental data and thermodynamic parameters in the literature have been summarized and assessed thoroughly to provide consistent understanding of each system. Some systems were re-calculated to obtain a combination of the best evaluated phase diagram and a set of optimized thermodynamic parameters. As doping levels of solar and electronic silicon are of high technological importance, diffusion data has been presented to serve as a useful reference on the properties, behavior and quantities of metal impurities in silicon. This paper is meant to bridge the theoretical understanding of phase diagrams with the research and development of solar-grade silicon production, relying on the available information in the literature and our own analysis.

Conversion of Electric Arc Furnace Dust into Ceramics Using Thermodynamic Calculations and Experimental Work

Steelmaking is accompanied with releasing a large quantity of solid particle in the form of dust. Electric arc furnace dust (EAFD) is known to have high pH number and traces of heavy metals. The objective of this work was to find a suitable procedure for converting the dust waste into inert and useful byproducts using thermodynamic calculations and experimental investigation. The physical, chemical and mineralogical characteristics of initial EAFD were analyzed using different techniques, such as: X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), grain size analysis and metallography. The pH measurement procedure was carried out in accordance with the standard test method for pH of soils “ASTM 4972-95a”. The results of XRD, SEM and EDS analysis were consistent and showed that Fe2O3, CaO, Al2O3, SiO2, MgO, ZnO and traces of other oxides are in the main composition of the EAFD batches with different relative amounts. Furthermore, the particle size measurements revealed that the EAFD particles are in the 0.1 to 394 μm size range. The pH number was ranging between 11.15 and 12.21 for all measurements. The experimental results were used as input data for thermodynamic calculations and accordingly SiO2 and Al2O3 were among the candidates for making ceramic materials through forming glass regions that surround and encapsulate the iron oxide particles. SiO2 modified samples exhibited better apparent structural properties than other compositions. Whereas Al2O3-modified samples showed variation in the product color. Thus, it is concluded from this work that a mixture of EAFD can be modified by 5-20 wt.% of SiO2 and then fired at 1100°C to make inert ceramic materials with reasonable mechanical properties.