Revealing the dynamic behavior and micromechanisms of enhancing the formability of AA1060 sheets under high strain rate deformation

Abstract

Developing high strain rate (HSR) forming technologies is significant for efficient and high-quality aerospace sheet metal parts manufacturing. Research on the deformation behaviors and micromechanism of materials under HSRs will contribute to the further application of HSR forming technologies. In this study, the mechanical behavior of AA1060 pure aluminum at low strain rates (LSRs, 0.001 s−1 and 0.1 s−1) and high strain rates (HSRs, 2400 s−1 and 3300 s−1) was tested utilizing quasistatic tensile tests and Hopkinson bar tests at room temperature. The results of the mechanical properties showed that the elongations were 30.01 %, 37.91 %, and 46.61 %, corresponding to strain rates of 0.1 s−1, 2400 s−1, and 3300 s−1, respectively, which were 29.86 % at a strain rate of 0.001 s−1. The maximum amplification of AA1060 elongation reached 56.10 % at the HSR. Microstructure characteristics, including the Schmid factor distribution, geometrically necessary dislocation (GND) distribution, slip band, and dislocation cell, were observed by electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM) under the condition of the same elongation with strain rates of 0.001 s−1 and 3300 s−1. In addition, the reasons for the plastic improvements during HSR loading were also investigated. The hard-oriented grains participate in plastic deformation at HSRs, providing additional space for dislocation multiplication and movement, increased dislocation density, and interaction between dislocations. In addition, the deformed hard-oriented grains also coordinated the strain gradient with soft-oriented grains. This improved the overall deformation uniformity, thus avoiding the premature occurrence of strain localization, namely, the elongation increase.