Effect of residual tensile stress and crystallographic structure on corrosion behavior of AZ31 Mg alloy rolled sheets

To investigate the effect of residual tensile stress on the corrosion behavior of AZ31 Mg alloy rolled sheets, various strain levels tensile pre-deformations (1%, 3%, 6%, 9%, 12%, 15%, and fracture) are conducted. After unloading, the immersion and electrochemical tests are performed on pre-tension samples to measure the corrosion properties. Microstructures are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the deformation is divided into two stages with 12% strain as the critical point due to the change of corrosion rate determinants. Before reaching 12% strain, the corrosion rate increases at first then decreases. In the range of 0 - 12% strain, the maximum value of corrosion rate is 4.42 mm/y at 3% strain. In this stage, the antagonistic effect of basal structure and dislocation aggregation plays a dominate role in corrosion resistance. After reaching 12% strain, the number of twins in samples increases as strain increasing. The galvanic corrosion effects caused by these twins destroy the surface oxide film, resulting in the corrosion resistance continuing to decrease. The maximum corrosion rate is 4.75 mm/y (Tf sample) throughout the study.