Al-Ca-Sr (Aluminum-Calcium-Strontium)
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Phase Diagram Evaluations: Section II
Al-Ca-Sr (Aluminum-Calcium-Strontium) V. Raghavan
The combined effect of the chemically similar additives Ca and Sr to Al- and Mg-based alloys cannot be described adequately by clubbing them together as (Ca + Sr) [2009Jan]. A thermodynamic treatment of this system using the modified quasi-chemical model was carried out by [2008Alj], without considering the ternary solubilities in the binary phases. Supported by new results from a limited number of key experiments and taking into account the solubility data of [2001Zha] along the Al2Ca-Al2Sr join, [2009Jan] presented a revised thermodynamic assessment of this system.
phases: Al4Sr (D13, Al4Ba-type tetragonal), Al2Sr (CeCu2type orthorhombic), Al7Sr8 (Al7Sr8-type cubic) and Al3Sr8 (Ca8In3-type triclinic). The Ca-Sr system [2003Zho] shows complete liquid and solid solubility. The isomorphous pairs bCa-bSr (bcc) and aCa-aSr (fcc) form continuous solid solutions.
Ternary Phase Equilibria To identify key experiments, [2009Jan] used preliminary calculations based on binary extrapolations. With starting metals of 99.998% Al, 99.99% Ca and 99.99% Sr, three alloy samples with Al contents ranging between 50 and 79 mass% were prepared and sealed in Ta capsules. Differential thermal analysis was performed at heating/cooling rates of 1 and 5 C per min. The phases were identified with scanning electron microscopy and electron probe microanalysis. The sample containing 60 mass% Al had not attained equilibrium. In their thermodynamic calculations, [2009Jan] used the binary descriptions of [2001Kev2] (Al-Ca), [2004Zho]
Binary Systems The Al-Ca system was experimentally reinvestigated by [2001Kev1] and assessed thermodynamically by [2001Kev2]. There are four intermediate phases in this system: Al4Ca (D13, Al4Ba-type tetragonal), Al2Ca (C15, MgCu2-type cubic), AlCa (or Al14Ca13; monoclinic, space group C2/m) and Al3Ca8 (Ca8In3-type triclinic). The Al-Sr phase diagram [2004Zho] depicts the following intermediate
um nti tro
Ma ss
S nt
Pe rce
rce Pe
nt A
ss
Ma
lum
inu
m
Sr
Ca
Al
Mass Percent Calcium
Fig. 1
Al-Ca-Sr computed liquidus projection [2009Jan]
Journal of Phase Equilibria and Diffusion Vol. 30 No. 6 2009
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Section II: Phase Diagram Evaluations
ss
tA lum
Ma
inu
m
Sr
m tiu
Ma
ss
n tro tS
Pe rc
en
en
rc Pe
Al
Ca
Mass Percent Calcium
Temperature, °C
Fig. 2 Al-Ca-Sr computed isothermal section at 500 C [2009Jan]
Al
Mass Percent Aluminum
46Al 16.9Ca 37.1Sr
Fig. 3 Al-Ca-Sr computed vertical section along the Al100-Al46Ca16.9Sr37.1 join [2009Jan]
(Al-Sr) and [2003Zho] (Ca-Sr). Liquid, fcc (Al, aCa, aSr), and bcc (bCa, bSr) phases were described by the substitutional solution model. No ternary interaction parameters
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were found necessary to describe these phases. The ternary solubility of Sr or Ca at constant Al content in the binary compounds Al4Ca, Al2Ca, Al4Sr, Al2Sr and Al7Sr8 was
Journal of Phase Equilibria and Diffusion Vol. 30 No. 6 2009
Phase Diagram Evaluations: Section II taken into a
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