SOLID SOLUBILITY AND RESIDUAL RESISTIVITY OF SCANDIUM IN ALUMINUM

The solid solubility and the residual resistivity of Sc in Al were determined by means of the measurement of the electrical resistivity at 77 K of AlSc alloys air cooled after annealing at various temperatures for a time sufficient to complete the precipitation of the equilibrium phase (ScAl3). Moreover, the solidus line of the Al-rich alloys was determined by thermal analysis. The solid solubilities of Sc in Al were found to vary from 0.186 at.% at 913 K to 0.033 at.% at 743 K. From the temperature dependence of the solid solubility the excess entropy of mixing Δs and the heat of mixing Δh associated with the solid solution of Sc in Al were calculated to be 6.0 R and 59 kJ mol-1, respectively. The compound ScAl3 reacts eutectically with Al to form an Al-rich solid solution. The eutectic temperature is 823 ± 1 K. Using the values of Δs and Δh, the maximum solid solubility of Sc in Al was estimated as 0.21 at.% at the eutectic temperature. The resistivity increment caused by Sc atoms in solution is linearly proportional to the concentration of Sc. The residual resistivity for Sc in Al is (3.4 ±0.1) × 10-8 Ω m (at.%)-1. © 1979.