(V) Rapid solidification map for cellular structure in Al–Ni eutectic system

The Al–4 wt.%Ni hypoeutectic alloy, Al–6.1 wt.%Ni eutectic alloy and Al–8wt.%Ni hypereutectic alloy under rapid solidification condition were prepared by wedge-shaped copper mold casting, and the microstructure evolutions occurred with the increase of the cooling rate in the three Al–Ni alloys. The boundary of the eutectic coupled zone of Al–Ni system was determined by combining the experiments with the TMK model, and the formation zone of cellular structure was labeled in the phase diagram of Al–Ni system based on the KGT model. Discontinuous Al₃Ni-rich eutectic networks and spherical Al₃Ni phases were observed at the tip of the Al–4Ni sample, and fine primary α-Al cells and continuous Al₃Ni-rich eutectic networks were clearly visible at the tip of the Al–6.1Ni sample, while at the tip of the Al–8Ni sample, continuous and finer Al₃Ni networks as divorced eutectic were formed. The formation of network structures and spherical Al₃Ni phases is explained by combining α-Al growth and the eutectic coupled zone and metastable phase diagram of Al-Ni system. Finally, the effects of alloy composition and undercooling on the morphologies of eutectic networks are discussed. This study provides new insight into composition design of binary and multicomponent eutectic Al alloys and process selection for additive manufacturing.