Fig. 1 Schematic of the experiment: a welding procedure; b EBSD measured positions

Fig. 2 Microstructural features of the base materials: a-c EBSD grain boundary maps; a pure aluminum; b pure copper; c Cu-30Zn

Fig. 3 Microstructural features at the deformation beginning position (P1): a1-c1 EBSD grain boundary maps; a2-c2 the corresponding KAM maps; a1,2 pure aluminum; b1,2 pure copper; c1,2 Cu-30Zn

Fig. 4 Microstructural features at the recrystallization beginning position (P2): a1-c1 EBSD grain boundary maps; a2-c2 the corresponding KAM maps; a1,2 pure aluminum; b1,2 pure copper; c1,2 Cu-30Zn

Fig. 5 Microstructural features at the high-speed flowing stage (P3): a1-c1 EBSD grain boundary maps; a2-c2 the corresponding KAM maps; a1,2 pure aluminum; b1,2 pure copper; c1,2 Cu-30Zn

Fig. 6 Dynamic equilibrium between the annealing twinning due to the thermally activated grain boundary migration and the twin destruction due to the continuous deformation during the material flow in the FSW of Cu-30Zn: a EBSD IQ map; b the corresponding misorientation angle distribution; c the IPF and KAM maps of the region c selected in a; d the IPF and KAM maps of the region d selected in a. Note: in the IQ and IPF maps, the black line donates HABs and the red line denotes ∑3 TBs

Fig. 7 Microstructural features at the material flow ending position (P4) before a12, c1,2, e1,2 and after a short-time annealing b1,2, d1,2, f1,2: a1-f1 EBSD grain boundary maps and KAM maps; a2-f2 the corresponding ODF maps; a1,2, b1,2 pure aluminum; c1,2, d1,2 pure copper; e1,2, f1,2 Cu-30Zn

Fig. 8 Schematic of grain structure evolution during the FSW of metals with different SFE