Variation in bending deformation behavior and improvement in bendability of extruded pure Mg through Gd addition

Abstract

In this study, the twinning and slip behaviors of pure Mg and Mg–1Gd extrudates during bending deformation are investigated by subjecting the extrudates to three-point bending tests. The pure Mg extrudate has a coarse grain structure with a strong basal texture. The Mg–1Gd extrudate has a uniform and fine grain structure with a typical rare-earth (RE) texture because the added Gd causes the suppression of grain-boundary migration and the textural tilting during extrusion. When bending deformation is imposed, cracks are formed in the lower region (tension zone (TZ)) of the bending specimens of both extrudates. However, the bending yield strength and failure bending strain of the Mg–1Gd extrudate are 56% and 68% higher than those of the pure Mg extrudate, respectively. Both the extrudates exhibit similar deformation behaviors in the upper region of the bending specimens, in which {10–12} twinning is activated in most grains. However, because the activation stress for {10–12} twinning is lower in the pure Mg extrudate, its bending yield strength is lower than that of the Mg–1Gd extrudate. In the TZs of both the extrudates, a small amount of {10–12} twinning is caused by the minor tensile stress imposed along the width direction, and the dislocation slip is predominantly caused by the major tensile stress imposed along the longitudinal direction. In the TZ of the pure Mg extrudate, slip is activated to a limited extent during bending because of its strong basal texture, which is unfavorable for basal slip. In contrast, in the TZ of the Mg–1Gd extrudate, basal slip vigorously occurs owing to its RE texture. Furthermore, nonbasal slip also occurs because Gd addition reduces the difference between the critical resolved shear stresses of basal slip and nonbasal slip. Consequently, the bendability of the Mg–1Gd extrudate improves through the effective accommodation of the longitudinal tensile strain in the TZ during bending.