Relationship between formability and cast structures in end-chill directionally solidified Al–Cu alloys

End-chill unidirectional solidification experiments have been conducted on pure Al and Al–Cu alloys with 1, 3 and 4.5 wt.% Cu, using melt superheat varying between 50 and 200 K. The specimens produced were 50 mm in diameter and 150–200 mm long. Studying the solidification structure indicated that most of the specimens exhibited a columnar structure growing perpendicular to the chill surface, followed by equiaxed grains. The volume fraction of the columnar structure and the grain size of the equiaxed one are related to the Cu content, superheat and the cooling rate. The volume fraction of the eutectic phase varied, depending on the casting parameters. Compression testing has been performed, in order to study the formability of the columnar and equiaxed grain structures. Constant testing conditions of a specimen slenderness ratio (8: 8) and strain rate of 1 mm/s were used, as well as a lubricant. In the relationship σ=kεn, describing the true stress/true strain relationship for the region between the limits of initial yielding and necking in ductile materials, the strength coefficient (k) and strain hardening coefficient (n) are used as indices for formability. Hence, the difference in formability behaviour between the columnar and equiaxed grains is presented.