Thermodynamic evaluation of hypereutectic Al–Si (A390) alloy with addition of Mg

This paper presents the thermodynamic evaluation of A390 hypereutectic Al–Si alloy (Al–17% Si–4.5% Cu–0.5% Mg) and alloys up to 10% Mg, using the Factsage® software. Two critical compositions were detected at 4.2% and 7.2% Mg where the temperatures of the liquidus, the start of the binary and of the ternary eutectic reaction are changed. These critical compositions show differences in the formation of Mg₂Si intermetallic particles during the solidification interval. For compositions up to 4.2% Mg, the Mg₂Si intermetallic phase first appears in the ternary eutectic zone. With Mg contents between 4.2% and 7.2%, Mg₂Si particle appears in both the binary and ternary eutectic reactions. Above 7.2% Mg, it solidifies as a primary phase and also during the binary and ternary reactions. The calculated liquid fraction vs. temperature curves also showed a decrease of the eutectic formation temperature (knee point temperature) with the addition of Mg content up to 4.2% Mg. This temperature becomes almost constant up to 10% Mg. The calculation of eutectic formation temperature shows a good agreement with differential scanning calorimetry (DSC) tests.     

The system Ce–Ag–Sn: phase equilibria and magnetic properties

Phase relations in the ternary system Ce–Ag–Sn have been established for an isothermal section at 750°C. Experimental techniques used were optical microscopy, EPMA and X-ray powder analysis of arc-melted samples which had been annealed at 750°C for 10 days and quenched to room temperature. Phases equilibria are characterized by the formation of three ternary compounds: CeAgSn (CaIn₂-type), Ce₅AgSn₃ (Hf₅CuSn₃-type), and Ce₃Ag₄Sn₄ (Gd₃Cu₄Ge₄-type). CeAg₂Sn₂, earlier reported to form and crystallize in the CaBe₂Ge₂-type, was not observed in the present study. All these ternary phases order magnetically at low temperature; our measurements reveal that Ce₅AgSn₃ is ferromagnetic below T_C=5 K, and Ce₃Ag₄Sn₄ is antiferromagnetic below T_N=9 K.     

Thermodynamic modeling of the Nb–Si system

Optimized coefficients of the Gibbs free energy expression for each stable phase of the binary Nb–Si have been obtained, using the Thermo-Calc program for this purpose. The Nb₃Si, αNb₅Si₃, NbSi₂ and Diamond (Si) have been modeled as stoichiometric phases and the liquid L, BCC (Nb) and the βNb₅Si₃ phases as solutions, with the excess term described using the Redlich–Kister formalism. The Si solubility in the βNb₅Si₃ phase has been modeled according to two possibilities: (i) Si substituting for Nb and (ii) vacancies in the Nb positions. The calculated diagrams compare well with the experimental information taken from the literature.     

Phase equilibria of the long-period stacking ordered phase in the Mg–Ni–Y system

Phase equilibria in the Mg-rich Mg–Ni–Y system at 300, 400 and 500 °C have been experimentally investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), electron probe micro-analyzer (EPMA) and transmission electron microscopy (TEM). The results show that a long-period stacking ordered (LPSO) phase with 14H structure is thermodynamically stable in the Mg–Ni–Y system in a wide temperature range, but it dissolves varying from 492 to 559 °C depending on the alloy composition. The equilibrium 14H phase has a very limited solid solution range, and can be nearly regarded as a ternary stoichiometric compound with a formulae as Mg₉₁Ni₄Y₅. The isothermal sections of the Mg-rich Mg–Ni–Y system at 300, 400 and 500 °C have been finally established, and a eutectic reaction, Liquid ↔ α-Mg + 14H + Mg₂Ni, has been determined occurring at 492 °C with a liquid composition about Mg_84.8Ni_12.0Y_3.2.     

Thermodynamic modeling of the germanium–manganese system

Based on a careful review of the literature, the Ge–Mn system is modeled using the Calphad method. The liquid is described using an associate model regarding to physicochemical observations. The phases cub_a13, fcc_a1 and bcc_a2 are modeled as substitution solutions using the Redlich–Kister formalism. The Mn₁₁Ge₈, Mn₅Ge₃, LT_Mn₅Ge₂ and LT_Mn₃Ge are treated as stoichiometric compounds and the non-stoichiometry of Mn₃Ge, Mn₅Ge₂ and Mn₂Ge are respectively described as (Mn)_0.75(Ge,Mn)_0.25, (Ge,Mn)_0.714 (Ge,Mn)_0.286 and (Ge,Mn)_0.667 (Ge,Mn)_0.333. The results are in good agreement with the set of experimental data which is carefully selected. Finally, a few experimental data which could be checked are indicated.     

Liquid–solid equilibria in the quasicrystalline regions of the Al–Pd–Mn phase diagram

Phase equilibria were investigated in the Al–Pd–Mn phase diagram in the region where quasicrystals and approximant phases form. With respect to previous thermodynamic studies, the extents of the liquidus phase fields of several approximant phases are either established or precisely determined. In particular, compositional profiles across interfaces show the ternary character of the T(AlPdMn) and ξ′ phases which are close to the binary Al–Mn and Al–Pd limits respectively. It is pointed out that the relative stability of some of the phases involves very small energy differences leading to very long transformation times and the solidification of metastable phases.     

Experimental investigation of phase equilibria and thermodynamic modeling of the CaO–Al2O3–CaS and the CaO–SiO2–CaS oxysulfide systems

Phase equilibria of the CaO–Al₂O₃–CaS and the CaO–SiO₂–CaS systems were experimentally investigated using equilibration and quenching techniques. Equilibrium phases were analyzed by means of electron probe X-ray microanalysis, X-ray diffraction analysis and differential thermal analysis. Solubility limits of all solid phases in these liquid oxysulfide phases were successfully constructed in the temperature range investigated in the present study (1500–1600 °C). In order to supplement understanding the phase equilibria, a thermodynamic modeling of these liquid oxysulfides was conducted by taking into account strong chemical short-range ordering (SRO) in the framework of the modified quasichemical model in the quadruplet approximation. As for the solubility of CaS in the liquid oxysulfides, the solubility increases with increase in CaO in the case of the CaO–Al₂O₃–CaS system, whereas it decreases with increase in CaO in the case of the CaO–SiO₂–CaS system. Such opposite behavior is explained by differences in the effect of the SRO in different liquid phases. It is shown that consideration for the SRO in the thermodynamic modeling is essential in order to properly describe the Gibbs energy of the liquid oxysulfide phase. Using the thermodynamic model and the database developed in the present study, liquidus projections of these oxysulfide systems are proposed for the first time.     

HREM study and structure modeling of the η′ phase,the hardening precipitates in commercial Al–Zn–Mg alloys

The structure of the η′ phase, one of the most important age-hardening precipitates in commercial Al–Zn–Mg alloys, has been studied at the atomic level by means of high-resolution electron microscopy (HREM). A structural model of the η′ phase has been constructed on the basis of the structural characteristics in the observed images and the structure of the η-MgZn₂ phase. Image simulation of this model shows a good agreement between calculated and experimental images. Comparison of this model with the early existing model on the basis of the X-ray diffraction is also given.     

Dislocation-Induced Precipitation and Its Strengthening of Al–Cu–Li–Mg Alloys with High Mg

Generally, the good combination of pre-deformation and aging can improve the mechanical strength of the Al–Cu–Li–Mg alloys. However, the effects of pre-deformation on competitive precipitation relationship and precipitation strengthening have not been clarified in detail in Al–Cu–Li–Mg alloys with high Mg. In the present study, the effects of pre-deformation level on the microstructure and mechanical properties of an Al–2.95 Cu–1.55 Li–0.57 Mg–0.18 Zr alloy have been investigated. It is found that the introduction of dislocation by 5% pre-deformation can facilitate the precipitation of new successive composite precipitates and T _1 precipitates along the sub-grain boundaries or dislocations and inhibit the precipitation of dispersive GPB zones which is the main precipitates of the alloys without pre-deformation. The introduction of 5% pre-deformation can enhance the mechanical properties considerably. When the pre-deformation level increases from 5 to 15%, the number density of the successive composite precipitates and T _1 precipitates increases, and the aspect ratio of T _1 precipitates decreases. The decrease in T _1 precipitate aspect ratio and the increment of the successive composite precipitates result in the reduction in precipitation strengthening. Therefore, the increase in pre-deformation level from 5 to 15% does not further improve the mechanical properties of the alloys, although the dislocation strengthening increases continuously.     

Phase equilibria of Al–Fe–Sn ternary system

The isothermal sections of Al–Fe–Sn ternary system at 973 and 593 K were determined experimentally by the equilibriated alloy method using scanning electron microscopy coupled with energy-dispersive spectrometry and X-ray diffractometry. Experimental results show that no ternary compound is found on these two sections. The maximum solubility of Fe in the liquid phase is 1.6% (mole fraction) at 973 K and those of Fe and Al in the liquid phase are 0.6% and 5.1% (mole fraction) at 593 K, respectively. The maximum solubility of Sn in the Fe–Al compounds is 4.2% (mole fraction) at 973 K and 2.3% (mole fraction) at 593 K. All the Fe–Al compounds can be in equilibrium with the liquid phase.     

Microstructures and phase equilibria of the transition metal corner in the Rh–Al–C and Ir–Al–C ternary systems

The isotherms of the Rh–Al–C and Ir–Al–C ternary systems were determined at 1373 K for the transition metal rich corner. It has been revealed that the three-phase field consisting of primary solid solution of a transition metal, B2 type intermetallic compound and graphite extends over a very wide compositional range in these two alloy systems. There exists no carbide in related transition metal rich regions. The phase constitution in the Rh–Al–C and Ir–Al–C ternary alloys prepared by arc melting is basically the same as that by spark plasma sintering (SPS) except the presence of Al₂O₃ particles. The reaction scheme and liquidus surface projection in the transition metal corner of the Rh–Al–C and Ir–Al–C ternary systems were estimated by deliberating on the solidification sequence, as-cast microstructures and invariant reactions on the binary edges.     

Structure,phase composition,and strengthening of cast Al–Ca–Mg–Sc alloys

The structure and phase composition of Al–Ca–Mg–Sc alloys containing 0.3 wt % Sc, up to 10 wt % Ca, and up to 10 wt % Mg have been investigated in the cast state and state after heat treatment. It has been shown that only binary phases Al₄Ca, Al₃Sc, and Al₃Mg₂ can be in equilibrium with the aluminum solid solution. It has been found that the maximum strengthening effect caused by the precipitation of Al₃Sc nanoparticles for all investigated alloys is attained after annealing at 300–350°C.     

Experimental investigation of phase equilibria in the Ru–Fe–Al system at 1473 K

The low-Al part of the ternary Ru–Fe–Al phase diagram at 1473 K is established in this work. Due to the very promising properties of B2 ruthenium aluminide, the investigation of the B2 region of this system is of special interest. The experimental work includes diffusion methods, as well as quenching of annealed single-phase and two-phase alloys. The results of the different methods are in good agreement. Optical and scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction are used to investigate the samples. It is shown in this work that a three-component B2 phase exists over a wide composition range.     

Constitutive modeling for dynamic recrystallization kinetics of Mg–4Zn–2Al–2Sn alloy

In order to have a better understanding of the hot deformation behavior of the as-solution-treated Mg–4Zn–2Sn–2Al (ZAT422) alloy, a series of compression experiments with a height reduction of 60% were performed in the temperature range of 498–648 K and the strain rate range of 0.01–5 s^?1 on a Gleeble 3800 thermo-mechanical simulator. Based on the regression analysis by Arrhenius type equation and Avrami type equation of flow behavior, the activation energy of deformation of ZAT422 alloy was determined as 155.652 kJ/mol, and the constitutive equations for flow behavior and the dynamic recrystallization (DRX) kinetic model of ZAT422 alloy were established. Microstructure observation shows that when the temperature is as low as 498 K, the DRX is not completed as the true strain reaches 0.9163. However, with the temperature increasing to 648 K, the lower strain rate is more likely to result in some grains' abnormal growth.     

Thermodynamic modeling of lead blast furnace

A thermodynamic model was developed to predict the distribution behavior of Cu, Fe, S, O, Pb, Zn,As, and the heat balance in a lead blast furnace. The modeling results are validated by the plant data of a lead smelter in Kazakhstan. The model can be used to predict any set of controllable process parameters such as feed composition, smelting temperature, degree of oxygen enrichment and volume of oxygen-enriched air. The effects of the blast air, industrial oxygen, and coke charge on the distribution of Cu, Fe, S, O, Ph, Zn, As, the heat balance, and the lead loss in slag, were presented and discussed.