Abstract
Recycling of aluminum alloy components plays a significant role in achieving sustainable society which requires superior performance of cast aluminum alloys containing high level of impurity elements such as iron. Since impurities of iron critically reduce both tensile strength and elongation of cast Al-Si alloys with iron content of over 1mass%, the morphological change in microstructure of Al-7mass%Si alloys with different iron contents was examined by applying ultrasonic vibration during the solidification, that is, the sono-solidification. The microstructure of conventionally solidified billets for thixocasting mainly composed of large plate-like β-Al5FeSi compound and dendritic primary a-aluminum solid solution is eminently modified into a fine and globular shape through the sono-solidification. After induction heating of the billet up to the semi-solid temperature of 583℃, it was immediately thixocast to observe their microstructure and mechanical properties. In addition to the refinement of β-Al5FeSi compound and primary α-aluminum in Al-Si-Fe alloy billets through the sono-solidification, eutectic silicon needles also become finer by thixocating, because of release of less latent heat compared with conventional castings solidified from their liquid state. This kind of characteristic microstructure generated by thixocasting with sono-solidified billets, exhibits not only high tensile strength, but also marked elongation even at high level of impurity iron. An increase in elongation of thixocast hypoeutectic Al-Si alloys with sono-solidified billets reflects major usage of recycled aluminum alloy ingots instead of virgin ones for the production of highly insured cast aluminum alloy components.
