Deformation behavior of two Mg alloys during ring hoop tension testing

Ring hoop tension testing (RHTT) was performed on circumferential samples taken from two Mg-based (+Al, Zn, Mn) alloy tubes. Two initial strain rates, 0.001 and 0.1 s−1, were used during these tests. The experiments were conducted at temperatures from ambient to 300 °C. The microstructural evolution during deformation was examined by optical microscopy and electron backscattered diffraction (EBSD) techniques. At moderate temperatures and/or high strain rates, the accompanying c-axis strains were mainly accommodated by twin formation. Contraction twins were formed in grains containing radial basal poles and extension twins in those with circumferential basal poles. At temperatures above 200 °C and the lower strain rate (0.001 s−1), the formation of voids in the partially dynamically recrystallized regions caused premature fracture. The unusual types of twinning behavior displayed under these conditions are responsible for the ductility and work hardening differences observed when the present results are compared with those of previous tension tests carried out along the longitudinal direction.