Influence of Nano-Structured Silanols on the Microstructure and Mechanical Properties of A4047 and A359 Aluminum Casting Alloys

Abstract

Minor alloying elements present in aluminum silicon-based casting alloys, such as sodium, strontium, or boron–titanium, could eventually affect the alloy’s microstructure and hence its mechanical properties. However, difficulties in balancing strength, ductility, and the subsequent precipitation strengthening heat treatment remain. The effects of nano-structured silanols based on partially condensed polyhedral oligomeric silsequioxanes (POSS-silanol) on the microstructure and mechanical properties of A4047 and A359 aluminum alloys were studied using a “two-step” process technique. 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 to desired mechanical performance. Using standard casting approach, the increase of both ductility and the tensile strength of the A4047 and A359 alloys is due to a highly refined fine fibrous of eutectic Al–Si formed instead of the irregular flakes as well as a refined primary aluminum phase as compared to the unmodified alloys. It has been found that this newly developed approach can also be expanded to other heat-treatable casting aluminum alloys with specific interest on changes in the microstructure of both primary aluminum phase and eutectic constituent.