Investigation of the Coherent Strain Evolution of the η′ phase in Al-Zn-Mg-Cu alloys via scanning transmission electron microscopy

The coherent strain caused by the different sizes of the nanoscale eta' phases in Al-Zn-Mg-Cu alloys was investigated via scanning transmission electron microscopy and geometric phase analysis. It is found that after the eta' phase precipitates, a coherent strain field is generated in the matrix and inside the precipitated phase. Such coherent strain field changes with the thickness of the eta' phase. The tensile strain is mainly distributed in the 7-layers-thick eta' phase, whereas the compressive strain mainly exists in the 11-layers-thick eta' phase. The asymmetrically coherent compressive strains are present in the matrices around the 7-layers-thick and 11-layers-thick eta' phases, and the corresponding maximum values of the compressive strains are 11.2% and 14.4%, respectively. The quantitative characterization of the coherent strain field induced by the nanoscale eta' phase provides a valuable reference for the optimization of the mechanical properties of the Al-Zn-Mg-Cu alloy. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study investigated the coherent strain caused by different sizes of the nanoscale eta' phases in Al-Zn-Mg-Cu alloys using scanning transmission electron microscopy and geometric phase analysis. It was found that a coherent strain field is generated in both the matrix and the precipitated phase after eta' phase precipitation, and the strain changes with the thickness of the eta' phase. The tensile strain mainly exists in the 7-layers-thick eta' phase, while the compressive strain is predominant in the 11-layers-thick eta' phase.