Correlation between stress state and crystal orientation distribution in alternating back extrusion of magnesium alloy

Deformation prediction and load evaluation were the keys to study the flow characteristics and microstructure evolution of magnesium alloy during alternating back extrusion (ABE). Firstly, the slip line field distribution at different downward loading depths of the split stem was determined by finite element simulation in this paper. After reasonably dividing into multiple rigid blocks, the extrusion load theoretical model was constructed based on the upper bound approach. On this basis, the stress state of the deformed billet was explored, which was related to the crystal preferred orientation of AZ31 magnesium alloy after ABE. The research results showed that the extrusion load model was consistent with the time-load curve trend of finite element simulation, and the predicted load in the initial stage of extrusion was about 8.14% higher than the finite element result. With the increase of downward loading depth of the split stem, the mean grain size of ABE in one loading cycle decreased to 6 μm, and the grain refinement reached 90%, which promoted the deep refinement of grain size. Affected by the maximum principal stress, the crystal orientation was segregated along with the stress distribution. The cooperative regulation law of deformation behavior and microstructure evolution for magnesium alloy during ABE was clarified, and the construction of the load theoretical model provided scientific guidance for the selection of deformation equipment and the formulation of research programs.