Tailoring of the microstructure and mechanical properties of the flow formed aluminum alloy sheet

Tube flow forming followed by flattening is an effective way to make ultra-wide sheet for plastic forming of large thin-walled components. However, the work hardening and poor plasticity of flow formed sheet seriously restrict the subsequent plastic formability. To tailor the plastic formability, two types of heat treatments (recrystallization annealing and solution quenching) were conducted on the flow formed 2219 aluminum alloy sheet, and their microstructure evolution and mechanical properties were comparatively studied to obtain a suitable heat treatment scheme. It is found that the deformation in flow forming produces quantities of deformed substructures and the rotating cubic texture. In the recrystallization annealing, recrystallization occurs with the co-existence of two nucleation mechanisms, i.e., subgrain nucleation and particle stimulated nucleation, which produce a weak {100}//RD-CD texture and higher plasticity than that of the flow formed sheet. In addition, it is found that the annealing temperature and holding time have complex interactive effects on the average grain size, the uniformity of grain size and the resultant plasticity. In contrast, the solution quenching obtains weak {100}∥RD-CD texture at lower solution temperature and cube texture at higher solution temperature, respectively; meanwhile, it produces larger average grain size and better grain size uniformity than the recrystallization annealing. Because the uniform grain size can suppress the heterogeneous deformation and the dissolution of second phase particles can delay the generation of crack, the solution quenched sheet presents better plasticity than the recrystallization annealed sheet. Moreover, increasing the solution temperature can improve the plasticity. Therefore, it is suggested to take a solution quenching scheme with higher temperature (535 °C for 30 min) to tailor the flow formed sheet, which can get a similar elongation as that of the initial tube blank.