Bending-deformation-induced inhomogeneous aging behavior and accelerated precipitation kinetics of extruded AZ80 alloy

In this study, the effects of bending deformation on the precipitation behavior of an extruded AZ80 alloy are investigated by subjecting a plate of the alloy to three-point bending and subsequent aging at 200 °C. In the upper region of the bent specimen (denoted as CZ), numerous {10−12} extension twins are formed. In the lower region of the bent specimen (denoted as TZ), small quantities of {10−12} extension twins, {10−11} contraction twins, and {10−11}–{10−12} double twins are formed, and most of the bending deformation is accommodated by dislocation slip. In the central region of the bent specimen (denoted as NZ), few twins are formed, and the microstructural characteristics of this region are almost identical to those of the initial material. When the bent specimen is aged, the peak-aging time of the CZ and TZ (8 h) is 60% shorter than that of the NZ (20 h), which is attributed to the accelerated precipitation caused by the abundant twins in and high internal strain energy of the CZ and TZ. In the CZ, nucleation and growth of continuous Mg₁₇Al₁₂ precipitates (CPs) occur rapidly, especially inside the {10−12} twins, and this accelerated CP formation inhibits the formation of discontinuous Mg₁₇Al₁₂ precipitates (DPs). Because of the high internal strain energy of the TZ, promoted formation of CPs occurs in the early stage of aging, which, in turn, suppresses the formation of DPs. In contrast, the NZ, because of its low internal strain energy and insufficient twins, exhibits slower CP formation behavior and has a considerably larger amount of DPs than the CZ and TZ. Although the bending deformation before aging induces inhomogeneous precipitation behaviors, the prebending deformation shortens the overall peak-aging time of the material and increases its peak hardness.