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Fragmentation in an Al–7 wt-%Si alloy studied in real time by X-ray synchrotron techniques

Abstract One mechanism for the formation of equiaxed grains is the detachment of dendrite fragments which is believed to be at the origin of the central equiaxed core region in casting processes. Unfortunately, the dynamics of the fragmentation phenomena cannot be revealed by classical methods. Investigation of a unrefined Al–7 wt-%Si alloy using in situ and real time synchrotron X-radiography and X-ray topography at the European Synchrotron Radiation Facility, has allowed verification of the existence of dendrite fragmentation and of cascade fragmentation during directional solidification, and to study the evolution of the growth and sedimentation of the equiaxed grains formed from these fragments. An examination of the crystallographic misorientation of dendrites as fragmentation is ongoing. These results contribute to the understanding of the characteristics of the columnar to equiaxed transition and to knowledge of the origin of new equiaxed grains in unrefined alloys.