Microstructural Evolution of Al-Zn-Mg-Cu Alloys in Accordance with Homogenization Time

The microstructural evolution of Al-Zn-Mg-Cu alloys has been investigated for the homogenization time effect on the texture, grain orientation and dislocation density. The Al-Zn-Mg-Cu alloys were casted and homogenized for 4, 8, 16 and 24 hours. Electron backscatter diffraction (EBSD) analysis was conducted to characterize the microstructural behavior. Micropillars were fabricated using focused ion beam (FIB) milling in grains of specific crystallographic orientations. Coarse precipitations in the grain boundaries are S (Al₂CuMg) and T (Al₂Mg₃Zn₃) phases verified by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) observation. With increasing homogenization time, equiaxed cell sizes increased. The volume fraction of S and T phases decreased with the diffusion of atomic elements into matrix. The Vickers hardness and tensile strength values decreased with homogenization temperature. The micropillar compression analysis was compared to macro tensile test results to understand the size effect and strain burst phenomenon on the mechanical properties of Al-Zn-Mg-Cu alloys.