Numerical Investigation of the Origin of Anomalous Tensile Twinning in Magnesium Alloys

It has been observed that tension twins (TTs) are triggered in rolled polycrystalline magnesium alloys under tensile loading applied along the rolling direction (RD) or the transverse direction. This is surprising because these alloys have a near-basal texture, and TTs would therefore cause extension (instead of contraction) along the normal direction. In this work, the origin of these anomalous TTs is first examined by performing crystal plasticity-based finite element simulations using model textures, wherein the c-axis in one grain is systematically tilted toward the loading direction (RD), with the other grains maintained in ideal basal orientation. It is shown that strong basal slip is triggered in the former, which through its effect on the local stress distribution plays a catalytic role in activating TTs. The above behavior is also observed in a simulation performed with an actual texture pertaining to a rolled AZ31 Mg alloy. Most importantly, when basal slip is suppressed, evolution of TTs is found to be very much retarded. The present results corroborate well with experimental observations.