Investigation of the Microstructural Evolution of the As-Extruded Mg–6Zn–1Mn Alloy Sheets under High Strain Rate Tensile Loading

To study the microstructural evolution of the as-extruded Mg–6Zn–1Mn alloy sheets with different initial microstructures during high strain rate tensile deformation, the interruptible tensile tests were performed at the strain rate of 1000 s−1, with controlled strain of 2.5%, 7.5% and 12.5%. The microstructure of the samples was characterized by electron backscatter diffraction and transmission electrical microscopy. The results demonstrate that the microstructural evolution of alloys during high strain rate tensile deformation is strongly influenced by the grain size and texture. Twins are suppressed during deformation in the fine-grained samples with strong basal texture, and only a few tension twins are observed at the large strain. Conversely, tension twins are activated greatly in the coarse-grained samples with the weaker basal texture. Twins are firstly activated at a small strain, and then more twins form and grow up as the strain increases. Regardless of the degree of twinning activity, the plastic deformation of the samples with different initial microstructures under high strain rate tensile loading is mainly provided by dislocation slip, and the dislocation density increases with the increase of strain. Moreover, the large grain size and relatively weak basal texture promote the formation of more dislocations.