Refining detrimental intermetallic phases by niobium microalloying in recycled aluminium alloys

Coarse iron-containing intermetallic compounds (Fe-IMCs) degrade the mechanical performance of recycled aluminium alloys, restricting their high-performance applications. Here we investigate the impact of Nb on the formation of IMCs in recycled A356 alloys. We examine the microstructural evolution and elemental distribution, focusing on the modification mechanisms at the atomic scale. Atom Probe Tomography (APT) and electron microscopy show that while Nb is randomly distributed in solid solution within the Al matrix, it segregates at the interface between eutectic Si and Fe-IMCs. Nb enrichment peak does not coincide with the Fe-IMC/Si boundary but is offset toward the Si side, providing direct evidence that Nb enriches at the Si surface prior to Fe-IMC formation, creating potent heterogeneous nucleation sites. The kinetic restriction imposed by the slow diffusivity of Nb inhibits the coarsening of Fe-IMCs. The proposed mechanism of enhanced nucleation and restricted growth offers new insights to the refinement of detrimental IMCs.