Hot deformation behavior and microstructure evolution of hot-extruded 6A02 aluminum alloy

Abstract

The present work explored the impacts of temperature, strain rate, strain and initial orientation on hot-compression behavior and microstructural evolvement of hot-extruded 6A02 aluminum alloy. Initial samples were cut in two directions: parallel to the original extruding direction (D1) and perpendicular to the extruding direction (D2). Arrhenius and diffusion constitutive models of D1 samples were studied at 400 °C–560 °C under constant strain rate of 0.001 s−1–1 s−1. The predication accuracy of Arrhenius constitutive model was better than diffusion constitutive model considering lattice diffusion. The average activation energy of peak stress was 325.114 kJ/mol. Lattice diffusion was dominant diffusion mechanism and creep exponents n were larger than 5 in all strain ranges. Higher temperature and lower strain rate resulted in lower geometrically necessary dislocation (GND) density, lower stored strain energy E and higher dynamic recrystallization (DRX) degree. Stored strain energy ranged from 0.534 to 0.993 J/mol. The ultimate stress had linear relationship with dislocation density. The continuous dynamic recrystallization (CDRX) was gradually prior to discontinuous dynamic recrystallization (DDRX) with increase of strain rate. Hot deformation experiment of D1 samples with stepped strain rates showed that the large gaps between the two stages had more effective effect on improving DRX degree. Deformation mechanisms were in connection with grain types. For D2 sample, the fraction of DRX grains and texture types were less than D1 sample. Besides, CDRX mechanism was superior to DDRX mechanism at all constant strain rates.