Achieving preeminent bendability in extruded Mg-Gd-Zr alloy sheets by introducing gradient texture and microstructure simultaneously

Abstract

In this work, preeminent bendability at room temperature is achieved by simultaneously introducing the gradient microstructure and texture along the normal direction (ND) of Mg-4.05Gd-0.57Zr alloy sheets prepared by turned bearing extrusion (TBE). The grain size of the VK-TBE sheet at the top, middle and bottom layers are 4.54 μm, 8.48 μm and 7.84 μm respectively. In addition, the fine-grained layer presents the highest texture deviation angle witch provides this layer with the highest Schmid factor (SF) for basal slip. When this layer is placed at the outer side, the bending angle is promoted by about 99.8% compared with the conventionally extruded sheet. The sample with a thickness of 3 mm is bent to 60° without cracking, revealing an excellent promotion in the bendability. During bending, the combination of high SF for basal slip and fine grains contributes to the elevated plasticity of the outer layer. Furthermore, at the inner region, a lot of twin bands appear in the relatively coarse grains with high SF for tensile twinning, which significantly regulates the strain distribution along the ND. Consequently, the VK-TBE-FG sample exhibits preeminent bendability owing to the cooperative effects of enhanced plasticity of the outer layer and regulated strain distribution.