Determination of Thermodynamic Properties of Ternary Al‐Cu‐Zn Alloys by Electromotive Force Method

The thermodynamic properties of ternary Al-Cu-Zn alloys containing 25-62 at.% Al have been determined by electromotive force (EMF) measurements between 420-920 deg C by an aluminum concentration cell of the type Al[AlCl sub 3 -LiCl-KCl] alloy. This concentration cell was evaluated via comparison with known partial free energy for Al measured in liquid Al-Cu alloys by Wilder, and several liquidus temperatures of Al-Cu phase diagram have been determined. From EMF values, activities of Al with respect to mole fraction of Al in ternary Al-Cu-Zn alloys for three quasi-binary sections (x sub Cu /X sub Zn )=7/3, 1, and 3/7) at 850 deg C were determined. The negative deviation from Raoultian behavior observed was more pronounced at high x sub Cu /x sub Zn ratios in agreement with binary Al-Zn and Al-Cu phase diagrams.