Numerical simulation of process and grain size for large-sized aluminum alloy 7050 forging

Elimination of metallurgical defects, such as voids, microcracks, loose structure and microstructural segregation in the core of forging ingots, is crucial to ensure a good quality of the finished product in the process of lager-sized forging manufacture. A numerical approach for process optimisation and microstructural evolution of lager-sized forging of aluminium alloy 7050 was proposed in this study, which combined a commercial FEM code Deform 3D with empirical models. To obtain the parameters of empirical constitutive equation and dynamical recrystallization models for aluminium alloy 7050, the isothermal compressive test of 7050 sample was performed on Gleeble-1500 thermo simulation machine in the temperature range of 250-450°C and strain rate of 0.01-10 s-1, and the metallograph analysis of the samples was carried out by a Leica DMIRM image analyzer. The simulation results showed that the forging processes proposed in this study are effective in eliminating the casting structures and optimising the forging structures; the effective strain rises significantly, while the average grain sizes reduces sharply with the increase of simulation steps; recrystallization behavior occurs when effective strain exceeds the critical value for studied temperature; recrystallized volume fractions in most parts of the final forging piece have reached 100% and the average grain size reduced to 10 μm from initial value of 90 μm. Also, temperature and effective strain are two important factors affecting the grain size.