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

Diffusion coefficient decides the solute diffusion length and is a critical parameter in the selection of microstruc-ture 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.