The coarsening of nanophases in Al–Zn–Mg–Cu alloy induced by cyclic stress

This study investigated the changes in the morphology and size of nanoscale precipitates in different defect-affected regions of Al-Zn-Mg-Cu alloys via high-cycle fatigue specimens. The results reveal that after 10 7 cycles of loading at a fatigue strength of 380 MPa, the average size of precipitates segregated at the Al 18 Cr 2 Mg 3 dispersoid interface increased by more than twofold, and the coarsened precipitates became the main sites for fatigue crack initiation. In regions with frequent dislocation motion, the average size of GPⅡ and η' precipitates increased by approximately 65%, and their shape transformed into a spherical morphology. However, in areas unaffected by dislocations, the lattice mismatch between the precipitates and the aluminum matrix decreased from 1.7%∼2.3% to 0.8%∼1.3%, while the average size of the precipitates increased by about 30%, maintaining a rod-like shape. The driving forces for precipitate coarsening were identified as interfacial energy, and the dislocations and vacancies generated by cyclic loading.