Microstructure vs properties correlation in Al-Si cast alloys

The paper presents an investigation on mechanical behaviour of cast Al alloys, as a function of microstructure and processing history. EN-AC 46000 and 46100 alloys have been gravity cast using a step-bar permanent mould. Microstructural investigations have been carried out, leading to the evaluation of various quantitative parameters, such as SDAS or cell size for α-Al phase, average area, length, roundness and aspect ratio for eutectic Si particles, and amount of primary α-Al phase and of eutectic. Results were obtained for steps of thickness 5, 10, 15 and 20 mm. Microstructural parameters have been correlated on one side, with the results coming from the numerical simulation of the casting process (cooling rate, local solidification time) and, on the other, with the mechanical behaviour of the cast alloys (YS, UTS, elongation). In general, porosity level, SDAS and length of eutectic silicon particles increased with section thickness, and consequently mechanical properties decreased.