Al-Mg-Sc (Aluminum-Magnesium-Scandium)
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Phase Diagram Evaluations: Section II
Al-Mg-Sc (Aluminum-Magnesium-Scandium) V. Raghavan
Ternary alloys having a four-phase monotectic reaction can possess interesting properties, with two different solidiļ¬ed liquids in the microstructure. [1999Gro] and [2005Gro] computed a liquidus surface of this ternary system. The other results of [1999Gro] on isothermal and vertical sections were reviewed by [2007Rag].
Binary Systems The Al-Mg phase diagram has the following intermediate phases: Mg2Al3 (cubic, labeled b), R or e (rhombohedral), and Mg17Al12 (A12, aMn-type cubic, denoted c). The Al-Sc phase diagram depicts the following intermediate compounds: ScAl3 (L12, AuCu3-type cubic), ScAl2 (C15, MgCu2-type cubic), ScAl (B2, CsCl-type cubic), and Sc2Al (B82, Ni2In-type hexagonal). The Mg-Sc phase diagram has one intermediate phase MgSc (B2, CsCl-type cubic). See [Massalski2] for the above phase diagrams.
Liquidus Projection In their thermodynamic calculation, [1999Gro] employed the binary interaction parameters from the pub-
lished literature. In addition, the ternary solubility of Mg in ScAl3, ScAl2 and ScAl was taken into account. There are no stable or metastable liquid miscibility gaps in the three binary systems. Yet, a miscibility gap occurs within the ternary region, Fig. 1. It is characterized by the presence of two four-phase ternary monotectic reactions M1 and M2. At M1, the solid phases in equilibrium with the two liquids are ScAl2 and ScAl. At M2, they are ScAl and Sc2Al.
References 1999Gro: J. Grobner, R. Schmid-Fetzer, A. Pisch, G. Cacciamani, P. Riani, N. Parodi, G. Borzone, A. Saccone, and R. Ferro, Experimental Investigations and Thermodynamic Calculation in the Al-Mg-Sc System, Z. Metallkd., 1999, 90(11), p 872-880 2005Gro: J. Grobner and R. Schmid-Fetzer, Phase Transformations in Ternary Monotectic Aluminum Alloys, JOM, 2005, 57(9), p 19-23 2007Rag: V. Raghavan, Al-Mg-Sc (Aluminum-Magnesium-Scandium), J. Phase Equilb. Diffus., 2007, 28(5), p 471-472
Fig. 1 Al-Mg-Sc computed liquidus projection. A schematic enlarged view of the Mg corner is shown [1999Gro]
Journal of Phase Equilibria and Diffusion Vol. 29 No. 2 2008
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