Effect of Low Diffusion Coefficient on Eutectic Instability of Al-25wt%Sm Alloy

Diffusion coefficient decides the solute diffusion length and is a critical parameter in the selection of microstructure scales and in governing microstructure transitions. Al-25wt%Sm alloy is selected to reveal the impact of low diffusion coefficient on the eutectic instability, and the results are compared with those of Al--Cu alloys. Laser remelting experiments are performed and the transition growth velocity from eutectic to α-Al dendrite is examined. Compared with Al--Cu alloys, the eutectic instability takes place at a velocity more than one order of magnitude smaller. The theoretical calculation by the Trivedi--Magnin--Kurz (TMK) model also predicts that the eutectic will become instable at smaller growth velocity for Al--Sm alloy than Al--Cu alloy, which is ascribed to the low diffusion coefficient.