Effect of ECAP on microstructure and mechanical properties of Al–Zn–Mg–Cu alloys and coarsening behavior of SIMA

In this study, a combination of characterization techniques including optical microscopy, scanning electron microscopy, electron backscatter diffraction, X-ray diffraction, and room-temperature tensile testing was employed to investigate the effects of equal channel angular pressing on the microstructure and mechanical properties of an Al–Zn–Mg–Cu alloy, as well as the coarsening behavior during strain-induced melt activation semi-solid treatment. The results reveal that with increasing ECAP passes, the grain structure undergoes significant refinement accompanied by enhanced recrystallization. The dominant texture components gradually evolve into A and B shear deformation textures, as well as Q and R recrystallization textures. The second-phase particles are fragmented and more uniformly dispersed, with a notable transformation of the primary strengthening phase from the S phase to the θ phase. A reduction in dislocation density is observed after four ECAP passes, which coincides with a corresponding decrease in tensile strength. During semi-solid processing, the microstructure coarsens with increasing temperature and holding time, and a pinning effect caused by insoluble dispersed phases at grain boundaries is evident.