Reassessment of Al-Cu System Considering Metastable Extensions of Solid/Liquid Phase Equilibria

The thermodynamic description of the Al-Cu system is reassessed considering metastable states of Al based alloys in rapid solidification. In previous work, only an improved thermodynamic description of the FCC phase was presented based on experimental results from electromagnetic levitation and simulation results for free dendritic growth to be in accordance with existing thermodynamic descriptions of the liquid phase. The phase diagram thus obtained enabled the correction of the artificial miscibility gap when calculating metastable extensions of the FCC/liquid phase equilibria, the unphysical change of the slope of the solidus line on the Al-rich side and the artificial maximum on the Cu-rich side. However, the description did not well align with the most recent experimental results on the Cu-rich side. The new description reassessing FCC, liquid and the α′-phase demonstrates high consistency with these recent experimental results, reproducing all invariant reactions (temperatures) with an accuracy of ± 4 K and the experimental liquidus line with an accuracy of ± 10 K, all well within the experimental error. The results provide a robust framework for predicting phase behavior under metastable conditions, as confirmed by our experimental data.