Three-dimensional characterization of Fe-rich intermetallics in Al-Si-Mg (A6xxx) aluminium alloy DC cast billets with an increased scrap content by X-ray tomography

The characterization of Fe-rich intermetallic compounds (Fe-IMCs) in DC casting billets of aluminium alloys is critical for understanding their downstream processing and the properties of the final components. The use of recycled aluminium scrap in the formulation of these alloys results in the accumulation of Fe and other elements and modifies the volume fraction, the size and the shape of these Fe-IMCs. Standard techniques, like optical or electronic microscopy, allow for 2D visualization and quantitative comparison but do not provide enough information about the real 3D morphology of the intermetallics or the connectivity between them. In this study, we have used X-ray computed tomography to evaluate the 3D features of the intermetallics in DC billets for an Al-Si-Mg alloy with different levels of Fe in the as-cast and homogenized conditions. The 3D analysis shows that increasing Fe in the alloy results in thicker, more elongated and more interconnected particles, while during homogenization, the particles become thinner and more rounded and fragmented. We also provide a detailed comparison between the 2D and 3D results. The use of real 3D morphology characteristics of the secondary phases is more accurate and will allow a better understanding of the solidification process forDC billets in industry, as well as the subsequent microstructure and the properties of the extruded components.