Comparison of room-temperature stretch formability of the as extruded Mg–Gd alloys with different double-peak pole spacing

This paper focused on the effect of angle α that the basal poles tilted from normal direction (ND) toward the extruded direction (ED) on the formability of as-extruded Mg-2Gd (wt.%) alloy sheets. The studied Mg-2Gd (wt%) alloy sheets with the angle α of 23°, 32° and 45°, respectively, were designed. The Erichsen test was carried out at the ambient temperature, in which the microstructure and texture evolution was characterized by the electron backscatter diffraction (EBSD) technique. The results showed that the strain coordination ability of the Mg-2Gd sheet along the thickness direction was enhanced with the increase of angle α, giving rise to a higher Index Erichsen (IE) value of 7.5 mm for the α of 45° due to a lower r-value. This superior high formability is not only closely associated with the lower r-value but also with the higher Schmid factors for basal slip (SF basal) in the large-angle α alloy sheets. Furthermore, the twinning induced a more random distribution along the transverse direction (TD) of basal texture in the early stage of the Erichsen test, which cancels out the SF basal reduction effect caused by the activation of basal slip. The TD-extended twinning texture provided a softer orientation for the TD strain during the Erichsen test, such that excellent formability was achieved in the alloy sheets with a larger angle α.