Phase Contrast Imaging of Microsegregation of JIS ADCI2 Alloy and Damage Behavior

Abstract

  A single-distance phase retrieval technique was applied to the contrast-enhanced phase-sensitive imaging of micro segregation in die-cast aluminum alloy. Contrast between regions with and without micro segregation, spatial resolution and signal-to-noise ratio were evaluated to clearly differentiate micro segregations whose density difference from the matrix aluminum is small, making it difficult to visualize and differentiate them using ordinary absorption-contrast imaging. Since spatial resolution more or less drops during the phase retrieval process, a combination of the high-contrast phase-contrast imaging and the high-resolution absorption-contrast imaging was applied to reveal 3D microstructure/fracture relationship in an in-situ tensile test. Each phase-contrast image was registered with a corresponding absorption-contrast image to examine the positional relationship between the fracture path and micro segregation. A sectioning technique was also applied to identify the source of density difference. The results confirmed that three-dimensionally connected bands of micro segregations provide a preferential path for fracture in the die-cast aluminum alloy investigated. The observations suggest that the control of the 3D spatial distribution of micro segregation bands is of crucial importance for enhancing mechanical properties effectively even if its elimination is physically difficult.