Fig. 1. Schematics of the step-ladder radial forging experiment (a), experimental equipment (b), and macroscopic morphology of the step-ladder specimen after three passes (c), where RD, PD, and TD represent the radial, processing, and tangential directions in this study, respectively.

Fig. 2. Simulation model used for radial forging (a) and the compression true stress?strain curves of ZK60 alloy at different strain rates (b).

Fig. 3. Effective strain distributions in the RF samples at different reduction rates: (a) R1 = 64.5 mm, (b) R2 = 54.5 mm, and (c) R3 = 43.25 mm.

Fig. 4. Temperature distributions of the samples subjected to the RF process after (a) one pass, (b) two passes, and (c) three passes.

Fig. 5. (a) SEM, (b) EBSD, (c) EDS, and (d) XRD patterns of the as-homogenized ZK60 magnesium alloy.

Fig. 6. Microstructural evolutions of the ZK60 magnesium alloy in different areas after one, two, and three passes of the RF process.

Fig. 7. (a) Bright-field TEM image of the β-phase after three RF passes, (b) high-resolution TEM image of lattice fringes from one of the nano-sized precipitates in E3 specimen.

Fig. 8. EBSD observation results of the ZK60 magnesium alloy after one pass of the RF process: inverse pole maps of (a) C1, (b) M1, and (c) E1; (d) enlarged inverse pole map of the part selected in (a); and (e) the corresponding map boundary misorientations in the E1 region.

Fig. 9. Misorientation angle distribution after one pass of RF process in (a) C1, (b) M1, and (c) E1.

Fig. 10. EBSD observation results of the ZK60 magnesium alloy after two passes of the RF process: inverse pole maps of (a) C1, (b) M1, (c) E1; (d) the enlarged IPF maps selected in (a) showing the orientation of DRX and matrix; (e) the point-to-origin misorientation curve along the straight line in grains G1 and G2; and (f) the microtextures of un-DRX and DRX, and statistical analysis of the deflection angle between the c-axis and the RD direction.

Fig. 11. Evolution of the {0001} pole figures of the ZK60 magnesium alloys in the center (left), mid-range (center), and edge (right) regions after different RF passes.

Fig. 12. Mechanical properties of the ZK60 magnesium alloys: (a) tensile stress-strain curves of the as-homogenized, E1, E2, and E3 samples; (b) tensile properties of the external regions after different numbers of passes; (c) tensile stress-strain curves after the final pass in the E3, M3, and C3 samples; and (d) ultimate tensile strength vs. total elongation for RFed ZK60 alloys in comparison with available literature data (Upsetting and extrusion [32]; Rolling [[33], [34], [35]]; Extrusion + heat treatment [36]; Extrusion + ECAP [37]; Forged [17]).