Thermal parameters and microstructure during transient directional solidification of a monotectic Al–Bi alloy

A directional unsteady-state solidification experiment was carried out with a monotectic Al–3.2 wt.%Bi alloy. The thermal parameters such as growth rates and thermal gradients rates were experimentally determined by cooling curves recorded along the casting length. The monotectic structure was characterized by metallography and the interphase spacing and Bi-rich particles diameter were correlated with growth rate and thermal gradient. It is shown that the λ2v=Cλ2v=C growth law can be expressed by a C-value of 1.7 × 10−12, which is about two orders of magnitude higher than those reported for the steady-state regime at any given growth rate.