Use of Nano-Structured Silanols on the Solidification of Aluminum-Silicon Based Casting Alloys

Minor alloying elements had been used to modify the solidification process leading to improve mechanical performance of Aluminum casting alloys. However, difficulties in balancing strength, ductility and the subsequent precipitation strengthening heat treatment remain. In this study, use of nano-structured silanols based on partially-condensed polyhedral oligomeric silsequioxanes (POSS-silanol) was examined. The silanols react with active aluminum surface to form stable Si-O-Al bonds, while cage-like POSS core enables control of subsequent solidification process leading desired mechanical performance. Specifically, trisilanol phenyl POSS modifier was added to the casting alloy A4047. Using standard casting approach, a highly refined fine fibrous of eutectic Al-Si formed instead of the irregular flakes, which lead to a significant improvement in its ductility while improve the tensile strength as compared to the unmodified A4047. This newly developed approach was expanded to other heat-treatable casting aluminum alloys with specific interest on changes in the eutectic Al-Si microstructure.