Eutectic channelling in a squeeze cast Al-4.5Wt%Cu alloy

Abstract

The purpose of this study was to investigate to what extent macrosegregation occurs during the squeeze casting of a simple cylindrical shape in an Al-4.5wt%Cu alloy. The application of 100 MPa pressure during solidification caused a sharp increase in the cooling rate, to an average value of about 14 Ks{sup {minus}1}. At this cooling rate the liquidus temperature was resolvable, however it was difficult to observe the eutective thermal arrest. The macrostructure was characterized by a V-shaped pattern that extended over a large fraction of the ingot cross-section. The V-shaped segregates were regions which consisted of a mixture of the {alpha}-Al phase, the {alpha}-Al + {theta}-Al{sub 2}Cu eutectic and pro-eutectic {theta}-Al{sub 2}Cu particles. The exact cause of the formation of the eutectic channels in squeeze cast alloys is unclear. A previous explanation was that the V-shaped channels in squeeze castings are produced along the liquid metal feeding path. However, as the segregated channels are very large, these regions should be relatively easily fed during solidification. Also, as the solidification process occurs under near hydrostatic pressure, it is unclear where the driving force for the filling of these channels could come from. A simpler explanation may be that the macrosegregation ismore » an effect of the different thermal conditions during solidification that exist between gravity and squeeze casting.« less