Achieving high strength and low in-plane anisotropy in AZ31 magnesium alloy with RD-split bimodal non-basal texture through a novel pre-deformation-cryogenic composite treatment

AZ31 magnesium (Mg) alloy sheets with rolling direction (RD)-split bimodal non-basal texture have been extensively researched due to their excellent forming performance. However, their application potential has been greatly limited nowadays as this non-basal texture would lead to the low strength and strong in-plane anisotropy. To tackle the aforementioned issue, a novel pre-deformation-cryogenic composite treatment was developed in the present study. Afterwards, microstructural characteristics and mechanical properties of treated sheets during tensile deformation at room temperature had been analyzed using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) measurements. Results about mechanical experiments show that the conducted pre-deformation-cryogenic composite treatment leads to an obvious decreasing effect on fracture elongation (FE), and a notable strengthening effect on 0.2% proof yield stress (YS) and the ultimate tensile strength (UTS). The latter finally results in a rather close YS/UTS ratio (0.54 for RD sample and 0.59 for TD sample). Microstructure results demonstrate that the conducted pre-deformation-cryogenic composite treatment could introduce a high density of {10-12} extension twins (ETs), predominantly comprising para-position (PP) variant pairs with 7.4°<11-20>. Concurrently, it promoted the formation of extensive Al 8 Mn 5 and Mg 17 Al1 2 precipitates , exhibiting an average size of ∼181 nm. Moreover, dense dislocation tangles and substructures were observed not only within grain interiors but also in the vicinity of grain boundaries and twin lamellar interfaces. These microstructure characteristics collectively lead to the dislocation-dominated plastic deformation behavior of fabricated sheet, contributing to the realization of high strength and low in-plane anisotropy in AZ31 Mg alloy sheet.