Evaluation of Grain Density on the Surface of a Solidified Shell

Abstract

Refinement of the solidified structure is of importance for soundness of cast products. Formation of the grains on the surface is very important for the understanding of evolution of solidified structure. The evaluation method for grain density on the chill plate is proposed in this study.
Using an engineering model for grain selection, which has been separately developed, the number of grain decreases linearly in a first stage of solidification. Therefore, the solidified structure should be observed at least two cross sections. Extrapolating the data to the chill surface, the grain density on the surface can be evaluated.
Validity of the proposed method has been checked using Al-10mass%Cu alloy. A solidified shell, which was produced by dipping a chill plate in a molten alloy, has been closely observed. A grain is defined as a group of the dendrites that have the same orientation. Densities of grains were measured at two cross sections. Extrapolating these data to the surface, the grain density on the surface has been estimated. This estimated value agrees well with the density of grains, which was directly measured on the surface of the solidified shell.