Improved thermo-mechanical processing for effective grain refinement of high-strength AA 7050 Al alloy

An improved thermo-mechanical processing (N-ITMT) was proposed for manufacturing fine-grained precipitation-hardening Al-Zn-Mg-Cu alloy based on cold rolling, short-period annealing and continuous rolling, and the corresponding microstructure evolution and mechanical properties were investigated. The N-ITMT processing can produce high-quality rolling sheets without edge cracks compared with the traditional RI-ITMT. The recrystallized fine-grained structures of N-ITMT samples are similar to those of RI-ITMT when the total reduction of N-ITMT reached 85% and exhibited high stability during long-period solution treatment. Moreover, the mechanical properties of N-ITMT samples are almost the same as those of RI-ITMT after peak aging (T6). It shows that cold deformation plus short-period annealing can acquire large quantities of MgZn2 particles with diameter ≥0.2 μm, which can perform as nucleation sites for new recrystallized grains during subsequent solution treatment. It is greatly indicated that the static long-period overaging used by RI-ITMT can be replaced by cold deformation plus shot-period annealing, and the continuous rolling after short-period annealing would benefit the crack-free rolling sheets. Thus, N-ITMT would be a good alternative to RI-ITMT for efficient commercial production of different heat-treatable Al alloys to acquire fine grains.