Thermodynamics of Phase Formation in Mg–Al–C Alloys Applied to Grain Refinement

Deffrennes, Guillaume; Gardiola, B.; Lomello, M.; Andrieux, J.; Dezellus, Olivier; Schmid–Fetzer, Rainer

doi:10.1007/978-3-319-72332-7_49

Cited by 3 publications

(4 citation statements)

References 28 publications

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“…After a preliminary result recently published by Deffrennes et al [40], a reliable invariant decomposition temperature of Al2MgC2 is confirmed in the present study by the mean of Differential Thermal Analysis (DTA). In order to model the solubility of Mg in Al4C3, the standard enthalpy of formation of potential end-members phases is calculated by DFT.…”

Section: Introductionsupporting

confidence: 87%

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Thermal stability of Al2MgC2 and thermodynamic modeling of the Al–C–Mg system - Application to grain refinement of Mg–Al alloys

Deffrennes

Gardiola

Lomello-Tafin

et al. 2019

Calphad

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In the scope of supporting the development of Mg-Al alloys and related materials, an experimental study coupled with a CALPHAD thermodynamic modeling of the Al-C-Mg system was conducted. The peritectic decomposition of Al2MgC2 to form Al4C3, graphite and a liquid phase was measured at 1559±10 K by DTA. In order to model the Mg solubility in Al4C3, DFT calculations were performed on the end-member phases Mg4C3, Al2Mg2C3 and Mg2Al2C3 and it was shown that Mg substitutes on the Al2 crystallographic site of the carbide structure. Based on recent literature data and a revised Al-C binary, a model description of the Al-C-Mg ternary is proposed for the first time. More specifically, it is used to calculate the liquidus projection and the phase formation sequence during Scheil solidification of a 91Mg-9Al wt% alloy inoculated with carbon. This work provides a convincing argument that Al2MgC2 is the nucleant responsible for the grain refinement of Mg-Al alloys inoculated by C.

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Section: Introductionsupporting

confidence: 87%

“…The lack of reversibility is not surprising and commonly observed in the case of peritectic reactions. It is noteworthy that after DTA a few Al2MgC2 crystals could be found trapped in the middle of the biggest Al4C3 crystals [40]. Moreover, it is suggested that the films observed around the T2-Al2MgC2 phase in Fig.…”

Section: Resultsmentioning

confidence: 86%

Thermal stability of Al2MgC2 and thermodynamic modeling of the Al–C–Mg system - Application to grain refinement of Mg–Al alloys

Deffrennes

Gardiola

Lomello-Tafin

et al. 2019

Calphad

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“…The Ta crucibles were sealed inside vitreous silica containers under an absolute Ar pressure of 0.2 bar in order to avoid external oxidation and oxygen diffusion through the Ta crucibles during the heat treatment. The initial sample composition was not altered by magnesium evaporation as only a negligible fraction of Mg was needed to supply its equilibrium vapour pressure given the crucibles volume [22]. The samples were efficiently quenched by breaking the silica containers as soon as they were removed from the furnace.…”

Section: Synthesis Of T2-al2mgc2mentioning

confidence: 99%

Synthesis, crystallographic structure and thermodynamic properties of T2-Al2MgC2

Deffrennes

Gardiola

Jeanneau

et al. 2019

Journal of Solid State Chemistry

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T2-Al2MgC2 was synthesized from the elements in a Mg-Al melt at 1000°C using sealed Ta crucibles. Single crystals of T2-Al2MgC2 were extracted by evaporating the Mg-Al matrix. The crystal structure of T2-Al2MgC2 was refined for the first time on the basis of single-crystal X-ray diffraction. The crystal is trigonal (space group P-3m1, Z=1) with lattice parameters of a=3.3767(11) Å, c=5.807(2) Å and V=57.34(5) Å 3. Based on the refined crystal structure, DFT calculations were conducted to evaluate the thermodynamic properties and the electronic structure of the phase. The heat of formation of T2-Al2MgC2 was calculated to be-23.6 kJ/moles of atoms at 298K. The heat capacity of T2-Al2MgC2 was measured by DSC from 300 to 871K and calculated by DFT from 0 to 1000K. Based on the calculated heat capacity, the entropy of formation of the phase at 298K was determined to be 70.0 J/mol/K. The band structure and the electronic density of state of T2-Al2MgC2 was calculated leading to an indirect band gap value of 1.73 eV.

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“…However this hypothesis was not widely accepted; for example, Lu et al [21] pointed out that Al2CO is likely to be unstable in a Mg-rich melt based on thermodynamic calculations. In more recent studies [22,23], Al2MgC2 has been proposed to be the nucleant for grain refinement of Mg-Al alloys, although this phase was found [24] and synthesised [25] back in the 1990s. In the Al-C-Mg ternary system [13,25], Al4C3 and Al2MgC2 are both stable phases at 1000 K and Al4C3 is reported to be the equilibrium phase with Mg-Al liquid only when the Al content is more than 19 wt.%.…”

Section: Introductionmentioning

confidence: 99%

Al2MgC2 and AlFe3C formation in AZ91 Mg alloy melted in Fe-C crucibles

Peng

Zhang²,

Lin³

et al. 2021

Journal of Alloys and Compounds

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Magnesium alloys are commonly melted and held in steel or cast iron crucibles and small but important amounts of Fe and C can dissolve into Mg-rich melts. Here, carbide formation is studied during interface reactions between solid Fe-xC alloys (x= 0 -3.6 wt.%) and liquid Mg-9Al-0.7Zn-0.2Mn (wt.%, AZ91) at temperatures from 700 -800 C. Two ternary carbides, AlFe3C and Al2MgC2, formed in the reaction layers between the Fe-C and AZ91, and T2-Al2MgC2 additionally formed within the AZ91 alloy due to carbon pickup. T2-Al2MgC2 grew in liquid AZ91 as hexagonal plates that were commonly twinned. A reproducible orientation relationship was measured between T2-Al2MgC2 and -Mg, and the grain refinement of magnesium by heterogeneous nucleation on T2-Al2MgC2 is explored.

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Thermodynamics of Phase Formation in Mg–Al–C Alloys Applied to Grain Refinement

Cited by 3 publications

References 28 publications

Thermal stability of Al2MgC2 and thermodynamic modeling of the Al–C–Mg system - Application to grain refinement of Mg–Al alloys

Thermal stability of Al2MgC2 and thermodynamic modeling of the Al–C–Mg system - Application to grain refinement of Mg–Al alloys

Synthesis, crystallographic structure and thermodynamic properties of T2-Al2MgC2

Al2MgC2 and AlFe3C formation in AZ91 Mg alloy melted in Fe-C crucibles

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