Microstructure and mechanical properties of pure Mg after spiral equal-channel extrusion

One of the severe plastic deformation techniques, elliptical cross-sectioned spiral equal-channel extrusion (ECSEE) was successfully applied to the pure Mg processed at 200°C and the microstructure and properties were studied. The observation shows that the grains are refined to 2.1 µm after 2-pass deformation. The proportion of high-angle grain boundary increases to 49.4% after 6-pass. The minimum time of grain boundary rotating 30° is about 0.847 ms, and the maximum time is 2.34 ms. TEM observation illustrates the grain morphology evolves from shear bands to recrystallised grains. There was a significant increase in strength to ∼180 MPa but a decrease in the ductility (∼12%) of pure Mg after 6-pass ECSEE. The refinement mechanism is mainly divided into mechanical and physical refinement.