Nanotechnology-Enabled Rapid Investment Casting of Aluminum Alloy 7075

Abstract

Rapid investment casting with additively produced molds can offer excellent surface finishes, tight dimensional tolerances, and complex geometries for high-performance metal parts in a rapid fashion. However, there is a long-standing challenge in the investment casting of high-strength aluminum alloy (AA) 7075 due to its hot cracking susceptibility and severe solidification shrinkage. Here, we show the unprecedented rapid investment casting of AA7075 by applying nano-treating technology, whereby a low-volume fraction of nanoparticles is dispersed into the metal to modify its solidification behavior and microstructure. TiC nanoparticles were able to effectively modify alloy's microstructure while suppressing its hot cracking susceptibility during solidification. Primary grain sizes were reduced by 95%, from 1000 µm to 50 µm. Secondary eutectic phases solidified as thin and dispersed fragments with disrupted lamellar morphologies. Nano-treated AA7075 parts produced by rapid investment casting exhibited exceptional tensile strength and ductility in both as-cast and heat-treated conditions. This study highlights the potential of investment casting high-performance alloys that were traditionally considered impossible to fabricate by this method.