New Phases in Mg-Al-Ca System

Yu Zhong, Alan Luo, J. F. Nie, Jorge Osvaldo Sofo, Zi-kui Liu

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

Mg-Al-Ca alloys exhibit appealing creep strength at temperatures over 100°C. It is believed that it is due to the substitution of the γ-Al12Mg17 phase by laves phases of higher thermal stability. In the literature, the C15-Al2Ca phase in the Al-Ca binary system and the C14-Mg2Ca phase in the Ca-Mg binary system have been reported. Their relative stability in the ternary system may play an important role in the development of the Mg-Al-Ca alloys. Furthermore, recent experiments and firstprinciples calculations in the literature revealed the existence of a C36 laves phase in the Al2Ca-Mg2Ca pseudo-binary system in addition to the C14-Mg2Ca and C15-Al2Ca laves phases. In the present work, special quasirandom structures (SQS) for all three laves phases were constructed. The structures possess local pair and multisite correlation functions that mimic those of the corresponding random structures. First-principles calculations were carried out based on the SQS developed to predict the enthalpy of formation in the Al2Ca-Mg2Ca pseudo-binary system. It was observed that the enthalpy of formation of C36 is very close to that of C14 at the Mg2Ca end and decreases with the addition of small amount of Al, while the enthalpy of formation of C14 increases with the addition of Al. It is thus energetically plausible that C36 is stable in the Al2Ca-Mg2Ca pseudo-binary system. Experimental investigations were done using diffusion couple of Mg-Ca alloy and pure Al. EPMA analysis of the diffusion zone found the existence of two ternary phases (Mg,Al)2Ca and Al2(Mg,Ca).

Original languageEnglish (US)
Title of host publicationEssential Readings in Magnesium Technology
PublisherWiley-Blackwell
Pages427-432
Number of pages6
Volume9781118858943
ISBN (Electronic)9781118859803
ISBN (Print)9781118858943
DOIs
StatePublished - Mar 3 2014

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Enthalpy
Electron probe microanalysis
Ternary systems
Creep
Thermodynamic stability
Substitution reactions
Experiments
Temperature

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Materials Science(all)
  • Chemistry(all)

Cite this

Zhong, Y., Luo, A., Nie, J. F., Sofo, J. O., & Liu, Z. (2014). New Phases in Mg-Al-Ca System. In Essential Readings in Magnesium Technology (Vol. 9781118858943, pp. 427-432). Wiley-Blackwell. https://doi.org/10.1002/9781118859803.ch68
Zhong, Yu ; Luo, Alan ; Nie, J. F. ; Sofo, Jorge Osvaldo ; Liu, Zi-kui. / New Phases in Mg-Al-Ca System. Essential Readings in Magnesium Technology. Vol. 9781118858943 Wiley-Blackwell, 2014. pp. 427-432
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Zhong, Y, Luo, A, Nie, JF, Sofo, JO & Liu, Z 2014, New Phases in Mg-Al-Ca System. in Essential Readings in Magnesium Technology. vol. 9781118858943, Wiley-Blackwell, pp. 427-432. https://doi.org/10.1002/9781118859803.ch68

New Phases in Mg-Al-Ca System. / Zhong, Yu; Luo, Alan; Nie, J. F.; Sofo, Jorge Osvaldo; Liu, Zi-kui.

Essential Readings in Magnesium Technology. Vol. 9781118858943 Wiley-Blackwell, 2014. p. 427-432.

Research output: Chapter in Book/Report/Conference proceedingChapter

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AB - Mg-Al-Ca alloys exhibit appealing creep strength at temperatures over 100°C. It is believed that it is due to the substitution of the γ-Al12Mg17 phase by laves phases of higher thermal stability. In the literature, the C15-Al2Ca phase in the Al-Ca binary system and the C14-Mg2Ca phase in the Ca-Mg binary system have been reported. Their relative stability in the ternary system may play an important role in the development of the Mg-Al-Ca alloys. Furthermore, recent experiments and firstprinciples calculations in the literature revealed the existence of a C36 laves phase in the Al2Ca-Mg2Ca pseudo-binary system in addition to the C14-Mg2Ca and C15-Al2Ca laves phases. In the present work, special quasirandom structures (SQS) for all three laves phases were constructed. The structures possess local pair and multisite correlation functions that mimic those of the corresponding random structures. First-principles calculations were carried out based on the SQS developed to predict the enthalpy of formation in the Al2Ca-Mg2Ca pseudo-binary system. It was observed that the enthalpy of formation of C36 is very close to that of C14 at the Mg2Ca end and decreases with the addition of small amount of Al, while the enthalpy of formation of C14 increases with the addition of Al. It is thus energetically plausible that C36 is stable in the Al2Ca-Mg2Ca pseudo-binary system. Experimental investigations were done using diffusion couple of Mg-Ca alloy and pure Al. EPMA analysis of the diffusion zone found the existence of two ternary phases (Mg,Al)2Ca and Al2(Mg,Ca).

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Zhong Y, Luo A, Nie JF, Sofo JO, Liu Z. New Phases in Mg-Al-Ca System. In Essential Readings in Magnesium Technology. Vol. 9781118858943. Wiley-Blackwell. 2014. p. 427-432 https://doi.org/10.1002/9781118859803.ch68