Microstructure evolution, constitutive modeling and forming simulation of AA6063 aluminum alloy in hot deformation

Hot compression tests of the AA6063 aluminum alloy are conducted on a Gleeble-3500 thermo-mechanical system with different temperatures, strain rates and compression reduction ratios. The microstructure evolution mechanism is analyzed by observing the deformed samples using optical observation techniques. The results show that the microstructure evolution consists of dynamic recovery (DRV) and dynamic recrystallization (DRX). The primary microstructure evolution mechanism shifts from DRV to DRX at the temperature of 648 K. The recrystallized grains emerge firstly along the original grain boundaries, then within the grains, indicating that discontinuous dynamic recrystallization is prone to occur than continuous dynamic recrystallization. A lower strain rate (e.g., 0.01 s-1) promotes the occurrences of DRX and grain growth. Geometric dynamic recrystallization occurs only once the strain exceeds a critical value at certain temperature and strain rate. Based on the microstructure evolution mechanism, a set of unified viscoplastic constitutive model considering dislocation density, DRX fraction, and grain size evolution is established to describe the microstructure evolution during and after hot deformation. The established constitutive model is implemented into the finite element (FE) solver DEFORM-3D and uniaxial hot compression simulations are carried out to verify the prediction accuracy of the established model. Numerical procedure is developed to simulate microstructure evolution in a round bar hot extrusion process.

Automated summary

The AA6063 aluminum alloy was subjected to hot compression tests on a Gleeble-3500 thermo-mechanical system to investigate its microstructure evolution mechanism. The results indicated that the microstructure evolution involved dynamic recovery and dynamic recrystallization. The shift from dynamic recovery to dynamic recrystallization occurred at 648 K. Recrystallized grains appeared firstly along the original grain boundaries, then within the grains, suggesting that discontinuous dynamic recrystallization was more likely to occur. A lower strain rate promoted the occurrence of dynamic recrystallization and grain growth. A constitutive model considering dislocation density, dynamic recrystallization fraction, and grain size evolution was established to describe the microstructure evolution, and its accuracy was verified through simulations.