Effects of loading conditions on twin characteristics in an extruded Mg-Zr alloy

In the present study, compression and compression-tension tests of different strain levels (maximum 4%) were carried out on an extruded Mg-Zr alloy rod along the extrusion direction. The effects of loading conditions (strain level and strain path) on twin characteristics (twin aspect ratio and twin incidence) in the alloy were quantitatively investigated from a statistical viewpoint, with focus on seeking for an appropriate loading condition where dense and fine twin lamellae can be obtained. The results show that the twin aspect ratio strongly depends on the strain path when the accumulated compressive strain levels are relatively small (≤ 2%) and that compression-tension deformation can obtain finer twin lamellae than simple compression deformation. In addition, under compression-tension deformation with the same accumulated compression strain (0%, 1% and 2%), the higher the initial compression strain is, the finer the residual twins become. The twin incidence, which shows an upward tendency with the increase of the initial compression strain (from 0.09 at the initial compression strain of 2% to 0.57 at that of 6%), is found to be sensitive to the strain path only when the accumulated compression strain is 0%. When the accumulated compression strain is larger (4%), the strain path has little effect on both the twin aspect ratio and the twin incidence.