Fig. 1 Schematic diagram of the repeated upsetting-extrusion die

Fig. 2 Effective strain distribution in the longitudinal section of the deformed billet: a 1/2 pass; b 1 pass; c distribution of effective strain in different directions

Fig. 3 Flow velocity distribution in the longitudinal section of the deformed billet: a, b 1/2 pass; c, d 1 pass

Fig. 4 Microstructural characteristics of the initial alloy: a grain boundaries map; b grain size distribution; c misorientation angle distribution

Fig. 5 Inverse pole figure maps a-c; twinning boundary and DRXed grains distribution maps d-f; distribution histogram of misorientation angle with axis distributions for the angles of 30 ± 5° and 86 ± 5° g-i and grain size distribution chart j-l. EBSD of RUEed alloy after different temperatures: a, d, g, j 250 ℃; b, e, h, k 300 ℃; c, f, i, l 350 ℃

Fig. 6 Details of {10-12} twinning behavior of coarse grains a, b G1 and c, d G2 are selected in Fig. 5c: a, c inverse pole figure maps; b, d KAM maps; e corresponding (0001) pole figure, f inverse pole figure

Fig. 7 Details of DRX behavior and corresponding effects on the grain orientation in the typical regions R1 selected in Fig. 5a: a inverse pole figure map; b misorientation angle developed along the black arrow AB indicated in a; c (0001) pole figures, d inverse pole figures along the ED

Fig. 8 Details of DRX behavior and corresponding effects on the grain orientation in the typical regions R2 selected in Fig. 5b: a inverse pole figure map; b (0001) pole figures; c misorientation angle developed along the black arrow CD, d Schmid factor distribution map

Fig. 9 Schematic illustration of grain refinement and corresponding mechanisms during RUE process: a initial state, b CDRX, c CDRX and DDRX, d CDRX and TDRX

Fig. 10 TEM images of the 250 ℃ sample: a dislocation, b dislocation wall, c dislocation cells, d dislocation array and sub-grain boundaries

Fig. 11 Two-beam bright-field TEM micrographs of 250 ℃ sample: a high density dislocation, b g = 01-11, c g = 01-10, d g = 0002

Fig. 12 Microhardness chart of the AQ80 alloy after different deformation temperatures

Fig. 13 KAM maps: a 250 ℃, b 300 ℃, c 350 ℃, d the corresponding KAM relative frequency and average KAM value