Evolution in hardness and microstructure of ZK60A magnesium alloy processed by high-pressure torsion

Severe plastic deformation is an attractive processing method for refining microstructures of metallic materials to have ultrafine grain sizes within the submicrometer or even the nanometer levels. Especially, it becomes generally known that processing of metals through the application of high-pressure torsion (HPT) provides the potential for achieving exceptional grain refinement in bulk disk metals. In the present study, a ZK60A magnesium alloy was processed by HPT at room temperature for a series of numbers of revolutions under a constant compressive pressure of 6.0 GPa. The change in texture was examined by X-ray diffraction (XRD) analysis and the evolution of hardness was evaluated using Vickers microhardness measurements to provide a comprehensive understanding of microstructural evolution. The XRD analysis showed the texture changed to weak and random in the early stage of HPT. The hardness results demonstrated that the hardness evolution with increasing equivalent strain follows the strain hardening model without microstructural recovery and the degree of hardenability was calculated as ∼0.07 which implies a high degree of strain hardening toward hardness homogeneity.