An improved thermo-mechanical treatment of high-strength Al-Zn-Mg-Cu alloy for effective grain refinement and ductility modification

A simple thermo-mechanical treatment (W-TMT) based on the idea of deformation-enhanced precipitation (DEP) and particle-stimulated nucleation (PSN) of recrystallization was proposed for Al-Zn-Mg-Cu alloy. The AA 7075 alloys were subjected to the proposed W-TMT, conventional hot rolling or a traditional thermo-mechanical treatment (RI-ITMT). During W-TMT, the coarse MgZn2 particles induced by DEP create preferential nucleation sites for recrystallization, and tailoring the sizes of these particles can effectively regulate or control the final grain sizes. Under the same total reduction of 85%, the grain size of W-TMT processed sheet can be decreased to ≤ 10 μm, similar to that of RI-ITMT processed sheet while relatively coarse grains (grain size > 25 μm) were obtained by hot rolling. After peak-aging (T6) treatment, the strength of all processed sheets were identical to each other, yet the fracture elongation of W-TMT processed fine-grained sheet was notably increased to 18.5%, compared to 13.1% for hot rolled sheet with coarse grains. Resultantly, this proposed short-cycled W-TMT processing possesses the synergetic capacity of grain refinement, ductility modification, as well as strength retention for Al-Zn-Mg-Cu alloy.