Fig. 1 EBSD, OM, SEM, XRD and hardness analysis of pre-extruded billets: a, b EBSD diagrams of pre-extruded billets in A and B alloys, c, d OM diagrams of pre-extruded billets in A and B alloys in ND; e, f SEM diagrams of pre-extruded billets in A and B alloys in ED, g XRD diffraction patterns of pre-extruded in A and B alloys, h hardness analysis diagrams of pre-extruded billets in A and B alloys

Fig. 2 EM analysis of the second phases for the pre-extrude billet in A alloy: a bright-field TEM diagram of the spherical phase in the pre-extrude billet, b SAED diagram of L zone in Fig. 2a (incidence along the [11 $\bar{2 }$ 0] axis), c SAED diagram of G zone in Fig. 2a (incidence along the [11 $\bar{2 }$ 0] axis), d the substructures and DRX grains distribution of pre-extruded billet, e labeling of the dislocation tangled zone (D1) in Fig. 2d, f the EDS analysis of the spherical phase in pre-extrude billet

Fig. 3 Substructure distribution for the pre-extruded billet in A alloy: a dislocation substructure distribution, b the plate substructure morphology, c grain boundary morphology of dynamically recrystallized grains, d second phases and dislocations distribution, e enlarged view of the Q-zone in Fig. 3d, f enlarged view of M-zone in Fig. 3e

Fig. 4 Second phases morphology of pre-extruded billet in B alloy: a bright-field TEM diagram of the equiaxial phases in pre-extruded billet in B alloy, b SAED diagram of R-zone in Fig. 4a (incidence along the [11 $\bar{2 }$ 0] axis), c EDS diagram of R-zone in Fig. 4a, d bright-field TEM diagram of the massive phases in pre-extruded billet in B alloy, e SAED diagram of P-zone in Fig. 4d (incidence along the [11 $\bar{2 }$ 0] axis), f EDS diagram of P-zone in Fig. 4d

Fig. 5 Substructure distribution diagrams of pre-extruded billet in B alloy: a, b the second phases morphology, dislocations, DRX grains, c analysis diagram of dislocation tangled zones

Fig. 6 Dynamic recrystallization and geometrically necessary dislocation density distribution of pre-extruded billets in A and B alloys: a, b the recrystallization distribution of pre-extruded billets in A and B alloys, c the recrystallized grain statistics, d, e the geometrically necessary dislocation density distribution of pre-extruded billets in A and B alloys, f, g the histograms of geometrically necessary dislocation density of pre-extruded billets in A and B alloys, h the quantitative comparison of geometrically necessary dislocation density of pre-extruded billets in A and B alloys

Fig. 7 The (0002), (11 $\bar{2 }$ 0) and (10 $\bar{1 }$ 0) pole maps of pre-extruded billets: a pre-extruded billet in A alloy, b pre-extruded billet in B alloy

Fig. 8 Schematic diagrams of the formation of the deformation substructure of pre-extruded billets in A and B alloys: a-c A alloy, d-f B alloy

Fig. 9 Model of LPSO phase formation mechanism and twin evolution

Fig. 10 Diagram of the c/a ratio of pre-extruded billets in A and B alloys

Fig. 11 Grain boundary diagrams and the schematic diagrams of difference in H-P slope (k-value) caused by the coexistence of different textures and dislocation piles-up of pre-extruded billets in A and B alloys: a, c low-angle grain boundary in A alloy, b, d low-angle grain boundary in B alloy, e effect of textures on H-P slope, f effect of dislocation piles-up on H-P slope