Correlation between dendrite arm spacing and microhardness during unsteady-state directional solidification of Al-Ni alloys

Hypoeutectic Al-Ni alloys are characterised by the formation of as-cast structures composed by a dendritic aluminium-rich matrix surrounded by a eutectic mixture (alpha + beta), where alpha is the Al-rich phase and beta is the Al(3)Ni intermetallics. The morphology, size and distribution of the intermetallic particles decisively affect the mechanical properties of these alloys. This study aims to determine experimental laws relating the primary dendritic arm spacing (lambda(1)) and Vickers microhardness (HV) of hypoeutectic Al-Ni alloys. Upward unidirectional solidification experiments were performed in order to obtain castings with significant differences in the scale of microstructural parameters along the casting length. It was found that the microhardness values were directly influenced by both the amount of solute and lambda(1) and Hall-Petch-type equations relating the microindentation and lambda(1) are proposed.