Microstructural and mechanical response of ZK60 magnesium alloy subjected to radial forging

Abstract

Radial forging (RF) is an economical manufacturing forging process, in which four dies arranged radially around the workpiece simultaneously act on the workpiece with high-frequency radial movement. In this study, a ZK60 magnesium alloy step-shaft bar was processed under different accumulated strains by RF at 350 °C. The deformation behavior, microstructure evolution, and mechanical responses of this bar were systematically investigated via numerical simulations and experiments. At the early deformation stage of forging, the material undergoes pronounced grain refinement but an inhomogeneous grain structure is formed due to the strain gradient along the radial direction. The grains in different radial parts were gradually refined by increasing the RF pass, resulting in a bimodal grained structure comprising coarse (∼14.1 μm) and fine (∼2.3 μm) grains. With the RF pass increased, the initial micro-size β-phases were gradually crushed and dissolved into the matrix mostly, eventually evolving to form a higher area fraction of nano-sized Zn2Zr spheroidal particles uniformly distributed through the grain interior. The texture changed as the RF strain increased, with the c-axes of most of the deformed grains rotating in the RD. Additionally, excellent mechanical properties including higher values of tensile strengths and ductility were attained after the three RFed passes, compared to the as-received sample.