Anomalous effect of grain size on the room-temperature bendability of Mg-Gd alloy sheet

In this work, grain size impacted on the bendability of the Mg-2Gd (wt. %) alloy sheets was investigated. The microstructures and textures evolution during the bending test were analyzed by the electron back-scattered diffraction (EBSD) and the scanning electron microscopy (SEM) technique. The results showed an anomalous grain size-dependent bendability in this alloy. The coarser grain size sample corresponded to a poorer bendability in the Mg-Gd alloys, which was dramatically different from the traditional Mg alloys (such as AZ31B alloys). This opposite mode between the Mg-Gd and traditional rare earth (RE) free Mg alloys was mainly attributed to the difference of microcracks nucleation mechanism during the bending test. The nucleation sites of microcracks were almost in the grain boundaries for the Mg-Gd alloys, while in the intragranular for the traditional Mg alloys. Furthermore, the larger size of initial microcracks and the more heterogeneous strain distributions in the coarser grain Mg-Gd samples led to a premature failure in the bending process and gave rise to this anomalous grain size-dependent bendability.