Effect of rolling schedule on grain refinement and superplasticity of 7475 Al–Zn–Mg–Cu alloy sheet

Fine-grained superplastic 7475 Al-Zn-Mg-Cu alloy sheet was prepared by a simplified thermomechanical treatment involving warm rolling (following a single preheating operation) followed by cold rolling, thereby avoiding the complex repeated reheating steps of conventional routes. The effects of preheating temperature and warm/cold rolling reductions on grain refinement were systematically studied. The results show that raising the warm rolling preheating temperature from 200 °C to 320 °C slightly increases the average size and area fraction of coarse second-phase particles while markedly reducing the dislocation density. This leads to an increase in the critical particle size for PSN from 0.91 μm to 1.03 μm, causing grain coarsening and a decrease in superplastic elongation. Increasing the cold rolling reduction from 50% to 83% significantly promotes dislocation accumulation and stored energy, reducing the critical particle size from 1.36 μm to 0.99 μm. This achieves pronounced grain refinement and enhanced superplastic performance. Under the optimal conditions of 200 °C warm rolling preheating temperature with 53% warm rolling and 83% cold rolling reductions, sheets with a 4.3 μm average grain size and superplastic elongation up to 1500% were successfully obtained.