The microscopic-deformation mechanisms of an extruded magnesium alloy with and without precipitates [Guinier-Preston (GP) zones] subjected to cyclic deformation were investigated by in-situ neutron-diffraction (ND) measurements and crystal-plasticity modeling. The relationship between the macroscopic-cyclic-deformation behavior and the microscopic responses (particularly twinning and detwinning) at the grain level was established. The general deformation-mechanism evolution in the solution-state (ST) sample was similar to that in the peak-aged-state (PA) sample over fatigue cycles. Both samples plastically deformed by extension twinning during compression, and by a sequential process of detwinning and dislocation motion under reverse tension. The main difference is that in the PA sample, the presence of precipitating particles constrains the twinning/detwinning behaviors, which leads to an increase in the participation of dislocation slip in the plastic deformation and then induces a strengthening effect during cyclic loading. Based on the combination of the previous in-situ ND results and crystal-plasticity model, our work provides a comprehensive analysis of the interaction between the precipitation strengthening and twinning/detwinning mechanism under the whole multi-cycle cyclic loading and their effect on the macro- and micro-mechanical behavior of the precipitate-strengthened magnesium alloys.

The relatively insufficient knowledge of the deformation behavior has limited the wide application of the lightest structure material-Mg alloys. Among others, bending behavior is of great importance because it is unavoidably involved in various forming processes, such as folding, stamping, etc. The hexagonal close-packed structure makes it even a strong texture-dependent behavior and even hard to capture and predict. In this regard, the bending behaviors are investigated in terms of both experiments and simulations in the current work. Bending samples with longitudinal directions inclined from the transverse direction by different angles have been prepared from an extruded AZ31 plate, respectively. The moment-curvature curves and strain distribution have been recorded in the four-point bending tests assisted with an in-situ digital image correlation (DIC) system. A crystal-plasticity-based bending-specific approach named EVPSC-BEND was applied to bridge the mechanical response to the microstructure evolution and underlying deformation mechanisms. The flow stress, texture, twin volume fraction, stress distribution, and strain distribution evolve differently from sample to sample, manifesting strong texture-dependent bending behaviors. The underlying mechanisms associated with this texture dependency, especially the occurrence of both twinning and detwinning during the monotonic bending, are carefully discussed. Besides, the simulation has been conducted to reveal the moment-inclination angle relation of the investigated AZ31 extruded plate in terms of the polar coordinate, which intuitively shows the texture-dependent behaviors. Specifically, the samples with longitudinal directions parallel to the extruded direction bear the biggest initial yielding moment.