Deformation mechanism of ZK60 magnesium bars during radial forging: Mathematical modeling and experimental investigation

Abstract Radial forging (RF) is a multidirectional, simultaneous forging process in which four dies perform pressing operations through high-frequency radial movements. This paper proposes a regionalized, multiscale strain field model to analyze the microstructural characterization of ZK60 Mg alloys during RF. ZK60 magnesium alloy bars were processed under different accumulated strains using RF at 300 °C. Based on the theoretical calculation results, the microstructures, texture evolution and mechanical responses of the bars were systematically investigated. The results indicate that twinning dominated the early stages of deformation, while dynamic recrystallization occurred subsequently and dominated further deformation process. At the early deformation stage, a gradient structure was formed owing to the uniform distribution of strain along the radial direction (RD). The grains in various radial parts were gradually refined by increasing the number of RF passes, eventually evolving into a bimodal grained structure including coarse (~16.2 μm) and fine (~2.1 μm) grains. Meanwhile, a precipitation difference is formed between coarse grain and DRX grain. The texture of the RFed bars changed as the RF strain increased, and the c-axis of most of the deformed grains rotated in the RD. Furthermore, the basal pole intensity exhibited a decreasing trend, followed by the large-scale nucleation of the dynamic recrystallization. Additionally, superior mechanical properties including higher values of tensile strength (341 MPa) and ductility (27.1%), were achieved after the three passes.