Variation of strain rate sensitivity of an aluminum alloy in a wide strain rate range: Mechanism analysis and modeling

The significant variation of strain rate sensitivity (SRS), i.e. the non-linear characteristics of SRS, within wide strain and strain rate ranges in high strain rate forming (HSRF) leads to the complexity of constitutive behaviors of aluminum alloys. Therefore, in order to achieve accurate simulation of HSRF process, a panoramic description of the SRS variation and related mechanisms are required within wide ranges. To address this problem, taking 5A06 aluminum alloy as an example, three distinct SRS zones were determined at 0.001 s−1-5000 s−1 in the present work, including quasi-static negative SRS zone (Zone-I), positive SRS zone at dynamic strain rate (Zone-II) and negative SRS zone at high strain and strain rate (Zone-III). Then, the mechanism for that in Zone-II is attributed to the conversion from dislocation glide to viscous drag through thermal activation analysis. In Zone-III, the dominant mechanisms are the change of dislocation configuration from dislocation cells and dislocation bands to subgrains in adiabatic shear bands in compression and to the increasing volume fraction of voids in tension, respectively, which is proved by SEM and TEM observations. Consequently, the effect of dislocation evolution on the SRS was quantitatively characterized and the nonlinear rate dependent stress responses of the aluminum alloy in a wide strain rate range were captured.