Synergistic enhancement the strength and ductility of crossover Al–Cu–Zn–Mg alloys via Zr(Sc or/and Hf) microalloying to create heterogeneous lamellar structure

Abstract

A crossover Al–Cu–Zn–Mg alloy with a heterogeneous lamellar structure (HLS) was obtained by microalloying Zr(Sc or/and Hf) to form a multiscale second phase, and the microstructure and mechanical properties of the alloy were investigated. The Sc-containing alloys produce a large number of micron and submicron W phase particles and nano-sized Al3(Sc,Zr)/Al3(Sc,Hf,Zr) dispersions with core-shell structures. The Hf-containing alloys have a micron-sized second phase particles and nano-sized Al3(Hf,Zr) dispersions. The multiscale second phase formed by microalloying of Sc or/and Hf promotes recrystallization via particle-stimulated nucleation (PSN), whereas the nanoscale Al3M dispersions pinning sub-structures to inhibit grain growth, and these two mechanisms influence the recrystallization process to form a heterogeneous lamellar structure. The microalloying produces a large number of Al3M dispersions and the refinement grain by hindering recrystallization, which enhances the strength through precipitates strengthening and grain refinement strengthening. The Hf added alloy with typical HLS microstructure improve the ductility of the alloys due to the delamination toughening effect and the avoidance of the formation of coarse brittle phases.