Fig. 1 a Physical and schematic drawings of as deposited; b physical and schematic drawings of FSP-ed sample and physical drawing of the stirring tool; c schematic illustration of preparation process; d sample preparation methods for microstructural characterization and properties testing. Note the normal direction, transverse direction and welding direction are defined as ND, TD and WD, respectively. The transverse tensile sample and longitudinal tensile sample are defined as TS-T and TS-L

Fig. 2 Microstructure and composition analysis of the BM: a low magnification SEM; b high magnification SEM; c, d EDS maps of (b) showing the distribution of Al and Cu elements, respectively

Fig. 3 Grain structure of the BM: a EBSD IPF map; b grain size distribution; c grain boundary map and d misorientation angle distribution. For the boundary misorientation, red lines: between 2° and 15°, black lines: > 15°

Fig. 4 Optical micrographs of a BM; b AFSP; c SFSP

Fig. 5 Microstructure and composition analysis of the AFSP-ed samples: a low magnification SEM; b high magnification SEM; c and d EDS maps of (b) showing the distribution of Al and Cu elements, respectively. The microstructure and composition analysis of the SFSP-ed samples: e low magnification SEM; f high magnification SEM; g and h EDS maps of (f) showing the distribution of Al and Cu elements, respectively

Fig. 6 IPF and the corresponding grain size distribution of the SZ subjected to FSP: a, b AFSP c, d SFSP

Fig. 7 Corresponding grain boundary maps and misorientation angle distribution of the IPFs shown in Fig. 6: a, b AFSP c, d SFSP

Fig. 8 Hardness distribution of BM and FSP-ed

Fig. 9 KAM maps of a BM, b AFSP, c SFSP

Fig. 10 a XRD patterns of BM, AFSW-ed sample and SFSW-ed sample, b Williamson-Hall plots and linear fits for Al phases based on various reflections obtained from XRD results. Note the residual stress level is reflected by the value of slope e

Fig. 11 Tensile properties of the BM and FSP-ed samples: a engineering stress-strain curves; b histograms of average tensile strength and elongation

Fig. 12 Observation of the upper surface of the fractured samples near the fracture region of a BM and b SFSP-ed sample

Fig. 13 SEM micrographs showing fractographic surfaces of BM nanocomposite a-c, SFSPed sample d-f

Fig. 14 Schematic diagram of the deformation processes for both samples. For the BM: a the initial state; b the formation and increase of pores in the early stage of plastic deformation; c the enlargement and interconnection of pore in the later stage of plastic deformation; d the occurrence of intercrystalline fracture in the final stage. For the FSP-ed samples: e the initial state; f the formation of microvoids around the θ particles in the stage of plastic deformation; g the occurrence of necking and the rapid propagation of crack in the stage of yielding stage; h the occurrence of transcrystalline fracture in the final stage