抄録
To clarify the growth process of string ghosts in ingots, Al-3.5%, 5.5%, 15%Cu, Al-6%, 14%Mg, and Al-6%Mg-1.2%Cu alloys were holizontally, unidirectionally solidified, and quenched during solidification.
At low solidification rates (R), many string ghosts appeared in Al-Cu and Al-Mg alloys, in which the density of the interdendritic liquid (ρLS) changes remarkably with an increase in fraction of solid. On the other hand, few string ghosts appeared in Al-6%Mg-1.2%Cu alloy, in which ρLS is almost unchanged during solidification. In the holizontal cross-section of the specimens, the area occupied by string ghosts increased linearly with an increase in 1⁄R. The effect of R was larger in Al-Cu alloys than in Al-Mg alloys.
Tiny string ghosts arising from the neighborhood of the solidification front grow up to large ones with the progress of solidification. Since their growth is accompanied by the fluid flow in themselves, they cannot grow in the region with the fraction of solid exceeding 0.8±0.05 for Al-5.5%Cu alloy, or 0.7±0.1 for Al-14%Mg alloy, in which interdendritic liquid scarcely flow.
