Superior mechanical properties of a selective-laser-melted AlZnMgCuScZr alloy enabled by a tunable hierarchical microstructure and dual-nanoprecipitation. (January 2022)

• Record Type: Journal Article
• Authors: Zhu, Zhiguang; Ng, Fern Lan; Seet, Hang Li; Lu, Wenjun; Liebscher, Christian H.; Rao, Ziyuan; Raabe, Dierk; Mui Ling Nai, Sharon
• Is Part Of: Materials today. Volume 52(2022)
• Page Start: 90
• Page End: 101
• Publication Date: 2022-01
• Subjects: Selective laser melting -- Al alloys -- Hierarchical microstructure -- Dual-nanoprecipitation -- Microstructure–mechanical properties relationship; Materials science -- Periodicals; Metallurgy -- Periodicals; Metal-work -- Periodicals; Biomedical and Dental Materials -- Periodicals; Manufactured Materials -- Periodicals; Metals -- Periodicals; 620.11
• DOI: 10.1016/j.mattod.2021.11.019
• Languages: English
• ISSNs: 1369-7021

Abstract

Graphical abstract: Abstract: 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 Al3 (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, η′ phase, and secondary (Al, Zn)3 (Sc9 Zr), and grain coarsening. Less coarsening of grains and (Al, Zn)3 (Sc9 Zr) particles, due to a reduced solution treatment temperature and time, could overwhelm the more complete dissolution of I -phase (triggering more η′ phase), resulting in higher yield strength. Optimal combination of the hierarchical features yields the highest yield strength (∼647 MPa) among all reported SLM-produced Al alloys to date with appreciable ductility (∼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.