Benchmark Experiment to Evaluate Macrosegregation Generated by Bridging and Solidification Shrinkage Flow

Abstract

We developed an improved Satou mold that can intentionally generate macrosegregation via bridging of the solidification structure and solidification shrinkage flow. Herein, macrosegregation can be achieved in a relatively small mold with an inner dimension of 30 mm^T × 50 mm^W × 190 mm^H. Casting experiments were conducted on a Al–10mass%Cu alloy using this mold. The obtained samples were analyzed in detail by evaluating the 3D morphology of the macrosegregation by X-ray CT imaging, analyzing the microstructure and composition at the cross-section by SEM/EDX, observing the macrostructure, and visualizing the temperature and solid-fraction distributions at the cross-section using linear interpolation of the temperature measurement points. Channel-shaped positive segregation with a length of approximately 50 mm was generated along the sample’s center line in the height direction. X-ray CT imaging at a voxel size of 10 µm and microstructural and composition analyses by SEM/EDX helped clearly observe the 3D morphology of the channel-shaped positive segregation region. The average composition of this positive segregation region was 35.12 mass%Cu, corresponding to the eutectic composition of the Al–Cu alloy. From the observation of the macrostructure and the visualization of the temperature and solid-fraction distributions at the cross section, we could confirm the formation of bridging by the isosurface of the solid fraction. From these evaluation and analysis results, the formation mechanism of macrosegregation driven by bridging and solidification shrinkage flow was clarified. We confirmed that casting experiments using the improved Satou mold can serve as an effective benchmark for macrosegregation formation.