Periodically Changing Rod Distance in Unidirectional Solidified Al-Al3Ni Eutectic

The microstructure of eutectics is frequently lamellar or rod-like, depending on the phase fractions of the constituent phases. The effect of melt flow on eutectic microstructures has been investigated by several research groups, especially since the availability of solidification processing under microgravity conditions. This chapter discusses the periodically changing rod distance in unidirectional solidified Al - Al3Ni eutectic.

Eutectic Al-5.6 wt% Ni was directionally solidified with and without magnetic stirring, and the eutectic rod-like microstructures were characterised. The research aims to study the effect of a rotating magnetic field on the microstructure of the eutectic composition alloy. Rod-like eutectics are generally described by rod distance and the number of the nearest neighbours. More than the commonly used average values are required for complete characterisation of the microstructure because placing the rods is not homogenous. We measured the parameters above along straight lines and found a previously unknown phenomenon. In the case of intensive melt flow, the spacings between rods show a significant periodic inhomogeneity. This inhomogeneity can be explained by the formation of vortices in the melt at the solidification front. It is concluded that the rod spacing in the eutectic microstructure changed periodically.