Microstructural characterization of rheo-cast billets prepared by variant pouring temperatures

The current article reports on the effect of pouring temperature on the morphology of primary α-Al particles and the rheological behaviour of the resulting microstructures for semi-solid Al–Si 356 alloy. Attempts have been made to explain the solidification mechanism of the primary α-Al particles in the as-cast semi-solid billets and to establish a correlation between the morphology of α-Al phase and viscosity of the billets, by employing quantitative metallography and parallel plate compression viscometry tests.The results have shown that the dendritic primary α-Al structures formed at the highest pouring temperatures of 675–695 °C used in this study, have the greatest viscosity numbers. They are almost two orders of magnitude greater than those for rosette structure formed at moderate pouring temperatures of 630–645 °C. The viscosity of the dendritic primary α-Al structures is three orders of magnitude greater than those for globular morphology formed at the lowest pouring temperature of 615 °C.