Achieving superior strength-ductility balance in novel heterogeneous lamella structures of Al-Zn-Mg-Cu alloys

Abstract

Heterogeneous structures (HS) materials have the potential to exhibit simultaneous improvement in strength and plasticity due to hetero-deformation-induced hardening (HDI) between multiple grain structures. However, achieving HS in aluminum alloy can be quite challenging. In this study, 7000 series aluminum alloys are investigated by incorporating rare earth element Y to develop a dual-phase structure containing Al8Cu4Y and Al3(Y, Zr) phases. And a heterogeneous lamella structure (HLS) is formed through the synergistic effect of Al8Cu4Y which includes dynamic recrystallization nucleation during deformation, and Al3(Y, Zr) which hinders the growth of recrystallized grain by means of pinning dislocations and subgrain boundaries. Substructures such as precipitates and nanocrystals are incorporated during the fabrication of HS, allowing for precise control over the volume fraction of fine grains by adjusting the ratio of two-scale second phases. When Y content reaches 0.3%, the 7Y55-2/heterogeneous lamella structure (HLS) samples exhibit a fine grain volume fraction of 76.5 vol.%, a tensile strength of 695 MPa, and an elongation of 16.6%. The alloy contains a large number of dislocations that preferentially induce the growth of η' phases along specific directions, thereby promoting their development. The multi-coupling effect and composite strengthening mechanisms in the “heterostructure-dislocation-precipitate” microstructure contribute to the intrinsic excellent strength and plasticity of the alloy. This study tackles the challenge of inverted strength and plasticity observed in Al-Zn-Mg-Cu-Zr alloys, offering novel insights that pave the way for further applications of heterogeneous materials.