The effect of twinning on texture evolution during ECAP processing of an AM30 magnesium alloy

An AM30 magnesium alloy was processed through ECAP method at 200 °C. Optical and transmission electron microscopy as well as electron back scattered diffraction (EBSD) technique were employed to characterize the deformed microstructure. A partially recrystallized microstructure including ultrafine/nano structures was obtained. The area fraction of 49% was measured for the recrystallized regions, where grains of 95 nm to 1 micron were detected. X-ray diffraction pole figure measurements were conducted to assess the final texture. The processed material exhibited moderate randomized texture including three basal pole peaks denoting the effect of dynamic recrystallization on deformation texture. TEM analysis confirmed the contribution of nano twinning during deformation of AM30 alloy. EBSD characterization implied that extension twin may contribute to the nucleation of new grains and thereby to be related to texture evolution. The apparent crossing pattern of intersected extension twins provided fine domains with high angle grain boundaries, which act as DRX nuclei. The formation of intersection boundaries also plays a critical role in pileup of dislocations and provide a local high stored-energy for dynamic recrystallization nucleation site. The aforementioned recrystallization mechanisms generally adopt orientations which are different from those produced by conventional recrystallization mechanisms, and thus it offers a route to manipulate the texture.