| Morphological characteristics of Al-4.3wt.%Cu and Al-15wt.%Cu ribbons spun by planar flow casting were analyzed using an optical microscope, SEM and TEM. The local solidification velocity within the Al-4.3wt.% Cu ribbon was found to be a function of ribbon thickness as V = 34.78 S-1. The absolute stability velocity of an Al-4.3wt.%Cu alloy was estimated as 2,460mm/s. Segregation free zone with the planar interface was developed from the bottom layer of the ribbon, where relevant solidification velocity was higher than the critical value of 2, 460mm/s. Following this zone, cellular/dendritic transitions occurred as the velocity decreased across the ribbon thickness. In the Al-15wt.%Cu ribbon, however, no segregation free zone was found and only cellular/dendritic region was developed due to its lower velocity compared to the absolute velocity for an Al-15wt.%Cu alloy throughout the entire ribbon thickness. Solidification sequences during ribbon formation were proposed for Al-Cu hypoeutetic alloy systems. |
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