Improvement of planar isotropy, mechanical properties and corrosion resistance of extruded Mg-3A1-1Zn alloy sheet by special grain re-orientation

摘要

The extruded Mg-3A1-1Zn (AZ31) wide sheet with 500 mm in width was possessed of a sub-strong c-axis parallel to transverse direction (TD) texture component in addition to owning primary typical strong c-axis parallel to normal direction (ND) basal texture. The asymmetric distribution of grain orientations around sheet normal gave rise to strong planar anisotropy in mechanical properties owing to different initial texture on slip and twinning during deformation along different directions, which further restricted the application of the wide sheet. Even more regrettably, the c-axis parallel to TD texture component arranged prismatic planes with high surface energy exposing to the sheet surface, which decreased the corrosion resistance of the sheet markedly. A special grain re-orientation process was carried out on the AZ31 sheet by consuming the c-axis parallel to TD textured matrix via special pre-twinning, and finally a symmetric weak basal texture was introduced. As a result, the anisotropic degree between tensile yield strengths along different directions of the sheet was minimized from 125 MPa to only similar to 10 MPa, and the average ultimate strength of the optimized sample increased 30 MPa compared with that of the as-extruded sheet. Meanwhile, texture modification based on re-orientating the initial c-axis parallel to TD textured matrix decreased the number fraction of prismatic planes exposing to the sheet surface, which "contributed to enhance the corrosion resistance of the sheet effectively. It seemed that special grain re-orientation through appropriate predeformation was an efficient way to deal with the unsatisfied comprehensive performances of magnesium alloy sheets. (C) 2017 Elsevier B.V. All rights reserved.