Determination of Er and Yb solvuses and trialuminide nucleation in Al–Er and Al–Yb alloys

• The solvuses of Er and Yb in Al were evaluated from thermodynamic analysis of solubilities.
• The largest volume fractions of Al3Er and Al3Yb were 0.16% and 0.1%, respectively.
• The evaluation of nucleation rates implied a much denser fine precipitates in Al–Er or Al–Yb alloys.

The solubilities of Er and Yb in Al at high temperature were evaluated from the electrical resistivity measurement, from which the ΔS and ΔH were estimated to be 3.0 ± 0.1k and −0.86 ± 0.01 eV for Al–Er alloys, 3.7 ± 1.0k and −0.93 ± 0.07 eV for Al–Yb alloys, respectively. The solubility curves of Er and Yb therefore could be obtained. According to the solubility curves of Er and Yb, on the one hand, the largest volume fractions of Al3Er, Al3Yb at room temperature were calculated to be 0.18%, 0.10%, respectively, which were obviously less than that of Al3Sc, i.e., 0.92%. On the other hand, the free energy per unit volume for the nucleation of trialuminides was evaluated with the consideration of Gibbs–Thomson effect. According to the obtained chemical driving force, the corresponding critical radius, critical nucleation energy and the steady state nucleation rate could be further calculated. The results indicated that in the binary alloys with the same concentration at the same temperature, comparing with Al3Sc, Al3Yb and Al3Er showed smaller critical radius and larger steady state nucleation rate, which implied that in Al–Yb and Al–Er alloys, higher number density of fine precipitates would be possibly existed.