Microstructures and mechanical behavior of magnesium processed by ECAP at ice-water temperature

Magnesium of high purity is processed by equal channel angular pressing (ECAP) up to eight passes at the ice-water temperature, in which a core-shell-like structure is used. The core-shell-like structure consists of pure iron (Fe) of 1.5 mm in thickness as the shell and magnesium (Mg) as the core. The microstructure, texture and mechanical behavior of the ECAP-processed Mg are studied. The ECAP processing leads to the formation of fine and equiaxed grains of ∼1.1 μm. The basal planes initially parallel to the extrusion direction evolve to slanted basal planes with the tilting angle in a range of 25°-45° to the extrusion direction. Increasing the number of the extrusion passes leads to the decreasing of twins and dislocation density in grains, while individual grains after eight passes still have high dislocation density. The large decreases of twins and the dislocation density make dynamic recrystallization (DRX) difficult, resulting in the decrease of the degree of DRX. Tension test reveals that the mechanical behavior of the ECAP-processed Mg is dependent on grain refinement and textures. The yield strength of the ECAP-extruded Mg first increases with the decrease of the grain size, and then decreases with further decrease of the grain size.