Non-equilibrium solute partitioning in a laser re-melted Al-Li-Cu alloy

Aluminum-lithium alloy AA2199 was rapidly solidified through the application of a laser re-melting process to determine the relationship between laser pulse energy and microsegregation during solidification. It was determined that laser pulse energies of the order of 0.125-0.5 J s resulted in a fine cellular solidification structure. Through comparison of the measured cell spacing with that predicted by the Kurz-Giovanola-Trivedi (KGT) model it was possible to estimate that solidification front velocities (SFV) of between 3 and 25 cm s−1 occurred during solidification. The SFV calculated from the KGT model was then input into the continuous growth model for solute trapping developed by Aziz to predict the deviation from equilibrium partitioning during solidification for all pulse energy levels employed. The chemical profile of lithium within the re-melted samples was measured using X-ray photoelectron spectroscopy and compared with that expected for equilibrium segregation. Measurement of the lattice parameter via X-ray diffraction revealed that the solute trapping phenomenon resulted in the formation of a super-saturated solid solution, as is evident through a reduction of the lattice parameter from 4.0485 Å for the starting material to 4.0399 Å in the material re-melted with a pulse energy of 0.125 J.