High strain rate Bauschinger response of 6061-T6 Aluminum alloy

This research aims to explore the Bauschinger effect (BE) of 6061-T6 aluminum alloy under different loading rates and pre-strains. Compression-tension experiments were conducted using a modified electromagnetic Hopkinson bar system (ESHB) within the strain rate of 800 s^-1 and pre-strain range of 1%-9%. High-speed photography and Digital Image Correlation (DIC) technology were employed to measure the strain. The experimental results show that under quasi-static loading, the BE intensifies with the increase of pre-strain until it reaches 3%, at which the BE parameter reaches saturation gradually. Under dynamic loading, the BE parameter goes up rapidly before 2% pre-strain and then reduces continuously as pre-strain increases. The differences of BE between quasi-static and dynamic loading were investigated by microstructural analysis. The non-monotonic back stress under dynamic loading arises from competition between dynamic strain aging (DSA) enhanced solute pinning at low pre-strains and irreversible dislocation cutting precipitates at high pre-strains. The suppressed thermal activation stabilizes these substructures through inhibited cross-slip/climb. Based on the experimental results, a strain-rate dependent Armstrong-Frederick (SAF) model and a physical based (PB) model are proposed. Compared with the traditional Johnson-Cook (JC) model, these two models can describe more accurately the behavior of the material under dynamic cyclic loading, providing effective tools for material performance optimization and engineering applications.