Investigating the Microstructural Impact of Tensile Stretching on Al-Zn-Mg-Cu Alloys: Dislocation-Precipitate Interactions

The study investigates the effects of tensile stretching on the microstructural evolution and mechanical properties of a high Zn-content Al-Zn-Mg-Cu alloy, emphasizing dislocation dynamics and precipitate behavior. The alloy, with a composition of Al-9.01 Zn-2.45 Cu-2.25 Mg-0.13 Zr (wt.%), prepared through casting subjected to peak-aged (T6) at 743 K for 1 h followed by 393 K for 24 h. Tensile stretching at room temperature (~ 298 K) and a strain rate of 1.0 × 10⁻³ s⁻¹ resulted in a 20% increase in yield strength from to 300 to ~ 360 MPa, with ductility decreasing to ~ 1% elongation to fracture. Microstructural analysis using scanning electron microscope (SEM), electron backscattering diffraction (EBSD), transmission electron microscope (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed significant changes, including an increase in low-angle grain boundaries (LAGBs) from 48.8 to 55% due to sub-grain formation and dislocation activity. TEM and HAADF-STEM imaging identified refined η′ precipitates (~ 5 nm) and solute clusters, indicating that tensile stretching enhanced the nucleation and growth of precipitates, transforming Guinier–Preston (GP) zones into η′ phases. The interaction between dislocations and precipitates facilitated solute drag and heterogeneous distribution, improving yield strength but reducing ductility. These findings provide new insights into optimizing the mechanical properties of Al-Zn-Mg-Cu alloys through controlled tensile stretching, highlighting the critical role of Zn in microstructural stability and alloy performance.