Fig. 1. EBSD orientation maps of different zones across the joint cross-section: (a) AA2024 BM; (b) AA2024 TMAZ; (c) AA2024 SZ; (d) AA7075 BM; (e) AA7075 TMAZ; (f) AA7075 SZ.

Fig. 2. Local misorientation or KAM (Kernel Average Misorientation) maps across the joint cross-section: (a) AA2024 BM; (b) AA2024 TMAZ; (c) AA2024 SZ; (d) AA7075 BM; (e) AA7075 TMAZ; (f) AA7075 SZ.

Fig. 3. Cyclic deformation response of the FSWed joint: (a) stress amplitude vs. the number of cycles; (b) plastic strain amplitude vs. the number of cycles.

Fig. 4. Cyclic deformation response of the FSWed joint at a total strain amplitude of 0.5 %: (a) stress amplitude vs. number of cycles; (b) plastic strain amplitude vs. number of cycles.

Fig. 5. Tensile results of the FSWed joints after pre-cyclic deformation and base materials: (a) engineering stress-engineering strain curves; (b) tensile strength and percent elongation.

Fig. 6. Strain hardening rate vs. net flow stress of the FSWed joints in different states and base materials.

Fig. 7. Experimental DIC contour maps of Mises strain across the cross section of the FSWed joint at different stress levels.

Fig. 8. Cross-sectional fracture location of joints in different states: (a) as-welded joint; (b) pre-cyclically deformed joint with 100 cycles; (c) pre-cyclically deformed joint with 500 cycles.

Fig. 9. Square of the average absolute value of cyclic hardening increment (Δσ)2 vs. cumulative plastic strain at various strain rates at the total strain amplitudes of (a) 0.4 % and (b) 0.5 %, and Bauschinger stress at a total strain amplitude of 0.5 % at the strain rates of (c) 1 × 10-2 s-1 and (d) 3 × 10-3 s-1.

Fig. 10. Cross-sectional Vickers microhardness maps (a, b) of the joint and TEM bright-field images of the LHZ (c, d): (a) as-welded joint, (b) cyclically-deformed joint, (c) TEM image of the LHZ of AA2024 side, and (d) TEM image of the LHZ of AA7075 side.

Fig. 11. TEM images of the AA2024 HAZ after 500 cycles cyclic deformation: (a) dislocation structures; (b) dark field image of S phase; (c) HRTEM image of the dislocations and S phases; (d) HRTEM image of S phase.

Fig. 12. The evolution of experimental (a) and calculated stresses (b, c, d) of each cycle during cyclic deformation: (a) cyclic hardening stress, (b) internal stress, (c) decrease of internal stress, and (d) stress increment due to slip irreversibility.