Initial crystallisation or nucleation in a liquid aluminium alloy containing spinel seeds

Step-by-step in situ near-atomic-resolution observations were presented for initial crystallization or nucleation in a liquid Al-10Mg (wt%) alloy containing spinel (MgAl 2 O 4 ) seeds. Ordering of Al atoms was observed in the alloy at the interface with spinel at the superheat of 73 °C or at the melt temperature of 680 °C, where three ordered layers of Al atoms formed and disappeared alternately. When cooled to the approximate liquidus of the alloy, 607 °C, three similar but more stable ordered layers of Al atoms formed. Subsequent crystallization occurred first through the formation of partially close-packed Al atoms on the solid-like outer ordered layer of Al atoms, followed by further crystallization into more close-packed Al atoms.