Effects of duration of solution heat treatment on the evolution of 3D microstructure in AlSi7Cu3 alloy: A quantitative X-ray tomography study

The evolution of the microstructure of an AlSi7Cu3 alloy is investigated by optical microscopy and X-ray tomography in as-cast condition and with subsequent solution treatments for 2 h 30 min and 50 h at 495 °C, respectively. The analyzed microstructure contains pores and hard inclusions, i.e. eutectic Si, iron-intermetallics, and Al2Cu phases. 2D microscopic surface examination was performed to reveal the characteristics of eutectic Si phase while 3D characterization by X-ray tomography (Lab-CT) was performed for the pores, iron-intermetallics, and Al2Cu phases. The 3D quantitative characterization can provide new insight into the microstructures amount, size and morphology change mechanisms during heat treatment. The Al2Cu phase, which presents a 3D interconnected structure in the as-cast condition, undergoes significant morphological changes during the solution heat treatment. The incipient melting of Al2Cu phase was evidenced after 50 h of solution treatment at 495 °C, which leads to the formation of small pores (<60 μm). Statistical analyses of the Al2Cu particle distribution, their size and their local mean curvatures describe the disintegration of the interconnected network structure followed by the dissolving of the disconnected particles. The eutectic Si undergoes fragmentation, spheroidization, and coarsening during the solution treatment.