Fig. 1. Schematic illustration of the multi-directional impact forging process (a) and the observed position in hexagonal prisms sample (b).

Fig. 2. (a) Inverse pole figure map of solid solution treated E675 Mg alloy, (b) corresponding distribution of grain diameter, (c) {0001} pole figure map, (d) misorientation angle of grain boundaries, (e) SEM image and (f) EDX result of the cuboid-shaped phase.

Fig. 3. (a) Optical microstructure of MDIF30 sample of E675 alloy. (b-e) Quasi-in-situ OM images illustrating evolution of microstructure after different annealing time: (b) 10 min; (c) 10 + 5 min; (d) 10 + 5 + 2 min; (e) 10 + 5+2 + 2 min.

Fig. 4. (a) Enlarged image of interesting region A in Fig. 3(a). (b-e) Enlarged images of region A in microstructure after different annealing time: (b) 10 min; (c) 10 + 5 min; (d) 10 + 5 + 2 min; (e) 10 + 5+2 + 2 min.

Fig. 5. Quasi-in-situ EBSD results presenting the evolution of inverse pole figure maps and grain boundary maps for MDIF30 sample during annealing treatment at 450 °C.

Fig. 6. Evolution of the volume of pts for grain boundary and axis distribution of HAGBs in 80°-90° of MDIF30 sample during annealing treatment at 450 °C.

Fig. 7. Evolution of {0001} pole figure map and grain diameter distribution map of MDIF30 sample of E675 during annealing treatment at 450 °C.

Fig. 8. Typical untwinned grains (G1-G3) extracted from as-forged and final annealed microstructure of MDIF30 sample of E675 Mg alloy.

Fig. 9. Typical twinned grains (G7-G9) extracted from as-forged and final annealed microstructure of MDIF30 sample of E675 Mg alloy.

Fig. 10. Tilting angle range of 70°-90° favorable for the activation of extension twin based on SF analysis during uniaxial compression (a) and corresponding distribution of extension twin region for random orientation of solution treated alloy during forging along the N1 direction (b).

Fig. 11. Orientation dependence of basal slip and {10-12} extension twin activity in random orientation of solution treated E675 alloy during forging at different axis: (a) 2 axis; (b) 3 axis; (c) 4 axis; (d) 5 axis.

Fig. 12. The statistic result of twinned grain and untwined grain in microstructure of as-forged E675 alloy.Untwined grain and twinned grain were marked by a red circle and green triangle, respectively.

Fig. 13. Analysis of the transformation of twin boundaries into random HAGBs in typical grain G6 and grain G8.

Fig. 14. Effect of load direction change on SF of various slip systems in typical twinned grain GA (θ = 30°) and GB (θ = 0°). Various slip systems consist of basal slip <a>: {0001} <11-20>, prismatic <a>: {1-100} <11-20>, pyramidal slip <a>: {1-101} <11-20>, pyramidal slip <c+a>: {11-22} <11-2-3>.

Fig. 15. Evolution of local misorientation map of some typical grains in annealing treatment of MDIF30 sample of E675 at 450 °C: untwinned grain G1, twinned grain G6, and twinned grain G8.

Fig. 16. A schematic model for significant difference in recrystallization behavior between uniaxial compression and MDIF: (a) initial state, (b) twinning stage of uniaxial compression, (c) twinning and interaction in uniaxial compression, (d) SRX in uniaxial compression microstructure, (e) twinning process of MDIF, (f) twinning and interaction in MDIF, and (g) SRX in uniaxial compression microstructure.

Fig. 17. Typical twinned grains (G4-G6) extracted from as-forged and final annealed microstructure of MDIF30 sample of E675 Mg alloy.

Fig. 18. Evolution of inverse pole figure map and {0001} pole figure map for two typical twinned grains (G6 and G8) in microstructure of MDIF30 sample of E675 Mg alloy during annealing treatment at 450 °C.