The Influence of Dendritic Segregation Degree to the Recrystallization Nucleation in U4720LI

The effect of the dendritic segregation degree on volume fractions and nucleation sites of recrystallization was investigated through comparing three kinds of samples with heavy degree of dendritic segregation, with light degree of dendritic segregation and without the dendritic segregation. The degree of the dendritic segregation was controlled by altering homogenization time. Stress concentration was caused by uneven distributions of γ′ phases in dendrite arm and interdendritic areas. Meanwhile, recrystallization was retarded due to the pinning effect of γ′ phases in interdendritic areas. Thus, the recrystallization nucleation started along the grain boundary, then in the junction of dendrite arm and interdendritic areas but at the side of dendrite arm areas with the increase of the deformation degree. Finally, nucleation occurred in the interdendritic area. Moreover, strain concentration was released as γ′ phases were more evenly distributed with the increase of homogenization time which lead recrystallization volume fractions reduced with the decrease of dendritic segregation.