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 metal to modify its solidification behavior and microstructure. TiC nanoparticles were able to effectively modify both primary and secondary phases while suppressing the hot cracking susceptibility of AA7075 during solidification. Despite the low cooling rate, nano-treated AA7075 exhibits fine equiaxed grains with an average size of 47.1 μm, in contrast to the large dendritic grains measuring 714.8 μm in pure AA7075. 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 which were traditionally considered impossible to fabricate by this method.