Structure of Al–Cu Alloy Ingots Solidified Unidirectionally from the Bottom

抄録

Aluminum and Al–Cu alloy ingots which were made from pure or commercial pure aluminum (99.99 mass%Al and 99.8 mass%Al) and electrolytic copper, were solidified unidirectionally with cooling only from the bottom. From the observation of the ingot structures and the analysis of the crystallographic orientations of the crystals in the ingots, it was proved that solidification of the ingots proceeded not only with growth of columnar crystals but also with production of free crystals, which became columnar free crystals or enclosed free crystals, and the columnar to equiaxed transition in the ingots had a transitional zone which began with the production of these free crystals and finished with the sufIicient supply of such free crystals on the freezing front to stop the competitive growth between such free crystals and the columnar crystals from the below.
It was also estimated that the most probable mechanism of the free crystals production in this kind of ingots is the “heterogeneous nucleation in the constitutionally supercooled liquid”.