' * , sy Solidification Behavior and Structure of AI - Cu Alloy Welds

The microsegregation behavior of electron beam (EB, and gas tungsten arc (GTA) welds of Al-Cu alloys covering a range from 0.19 to 7.74 wt% Cu were characterized for dendrite core concentrations and fraction eutectic solidification. Although a single weld speed of 12.7 mm/sec was used, some differences were observed in the segregation behavior of the two weld types. The microsegregation behavior was also modeled using a finite differences technique considering dendrite tip and eutectic undercooling and solid state diffusion. Fairly good agreement was observed between measured and calculated segregation behavior although differences between the two weld types could not be completely accounted for. The concept of dendrite tip undercooling was used to explain the formation of a single through thickness centerline grain in the higher alloy content GTA welds.