SOLUTE TRAPPING IN ALUMINUM-ALLOYS

We report the first measurements of solute trapping in metallic alloys. The nonequilibrium solute partition coefficient k was measured in several dilute aluminum alloys (Al Cu, Al Ge, Al In, Al Sn). Pulsed laser melting was used to bring about rapid plane-front solidification at velocities of 0.6 5.1 m/s. Time-resolved melt depths and solidification velocities were determined using the transient electrical conductance and optical reflectance techniques. The solute trapping model with the fewest free parameters that accounts for the measured velocity dependence of k is the Continuous Growth Model of Aziz and Kaplan. We have also identified an inverse correlation between the diffusive speed (the only free parameter in that model) and the equilibrium partition coefficient; this correlation might be used to estimate diffusive speeds for systems in which it has not been measured. A possible origin of such a correlation is discussed.