In situ tension-tension strain path changes of cold-rolled Mg AZ31B

The widespread use of magnesium and its alloys in lightweight structural elements has been limited because of their poor formability at room temperature as compared to other ductile metals. Modern cold-forming processes subject the material to multiaxial stress states and complex strain paths that may additionally affect plastic deformation due to the anisotropic deformation behavior of Mg alloys. Here, for the first time, the mechanical behavior of cold-rolled Mg AZ31B is studied during in-plane multiaxial loading and tension-tension strain path changes using in situ neutron diffraction and EBSD. The effect of the different strain paths on the activity of slip and twinning mechanisms and the active twin variants are evaluated. It is shown that initial strains of 4-5% cause a strengthened yield stress during reload for strain path change angles of 90 and 135 degrees. The strengthening is due to a combination of dislocation-based work hardening and complex multivariant secondary twinning in the reload.