Superior mechanical properties of a selective-laser-melted AlZnMgCuScZr alloy enabled by a tunable hierarchical microstructure and dual-nanoprecipitation

Achieving high mechanical strength and ductility in age-hardenable Al7000 series (Al-Zn-Mg) alloys fabricated by selective laser melting (SLM) remains challenging. Here, we show that crack-free AlZnMgCuScZr alloys with an unprecedented strength-ductility synergy can be fabricated via SLM and heat treatment. The as-built samples had an architectured microstructure consisting of a multimodal grain structure and a hierarchical phase morphology. It consisted of primary Al-3(Sc-x,Zr1-x) particles which act as inoculants for ultrafine grains, preventing crack formation. The metastable Mg-, Zn-, and Cu-rich icosahedral quasicrystals (I-phase) ubiquitously dispersed inside the grains and aligned as a filigree skeleton along the grain boundaries. The heat treated SLM-produced AlZnMgCuScZr alloy exhibited tunable mechanical behaviors through trade-off among the hierarchical features, including the dual-nanoprecipitation, viz, eta' phase, and secondary (Al,Zn)(3)(Sc9Zr), and grain coarsening. Less coarsening of grains and (Al,Zn)(3)(Sc9Zr) particles, due to a reduced solution treatment temperature and time, could overwhelm the more complete dissolution of I-phase (triggering more eta' phase), resulting in higher yield strength. Optimal combination of the hierarchical features yields the highest yield strength (similar to 647 MPa) among all reported SLM-produced Al alloys to date with appreciable ductility (similar to 11.6%). The successful fabrication of high-strength Al7000 series alloys with an adjustable hierarchical microstructure paves the way for designing and fine-tuning SLM-produced aluminum engineering components exposed to high mechanical loads.

Automated summary

By utilizing selective laser melting and heat treatment, high-strength AlZnMgCuScZr alloys with an unprecedented strength-ductility synergy were successfully fabricated, paving the way for designing and fine-tuning SLM-produced aluminum engineering components exposed to high mechanical loads.