Three-dimensional observation of micro-pores in a 2024 aluminum alloy by synchrotron X-ray projection- and imaging-type microtomography techniques

Synchrotron X-ray microtomography has been utilized for the ex-situ observation of micro-pore growth/annihilation behaviors of a 2024 aluminum alloy at a high temperature. High-resolution experimental configurations have enabled the 3D reconstruction of micro-pore and intermetallic compound particle images with isotropic voxels with 0.088-0.474 μm edges. The variations in micro-pore shape, size and spatial distribution at the high temperature are readily observed, with the tomographic volumes then being provided for the quantitative image analysis of such quantities. It has been clarified that micro-pores, that appear to be nucleated heterogeneously on particles, exhibit the Ostwald growth behavior during the high temperature exposure. Three-dimensional finite element meshes have been generated to monitor distributions of local stress and strain in real materials with such micro-pores. Since micro-pores tend to lie along (former) grain boundary, there seems to be some anisotropic effect on the strain redistribution due to the existence of micro-pores. Since local strain elevation is predicted by 50-200% in the vicinity of micro-pores aligned along grain boundary, it can be inferred that ductile fracture would be promoted considerable by the growth of pre-existing micro-pores. (author)