The age-hardened AA7075 in the friction stir welding (FSW) joints exhibits lower plasticity

posing challenges for further deformation processing. In this study

this paper employed a 3 mm thick AA7075–O plate for stir friction butt welding

investigating the impact of welding speed on the joint microstructure and strength-ductility

aiming to provide solutions for achieving highly ductile FSWed joints. The results reveal that the weld nugget zone (NZ) in the AA7075–O joint consists of fine equiaxed grains. With an increase in welding speed

the average grain size (AGS) in the weld NZ initially decreases and then gradually increases. At a welding speed of 40 mm/min

the smallest AGS in the weld NZ is approximately 1.96 μm. The microhardness distribution across the transverse section of the joint shows a convex shape at different welding speeds

indicating significant hardening in the joint region. The weld NZ exhibits the highest hardness

reaching approximately 145HV. The process window for FSW of AA7075–O is broad

with joint strength exceeding the base material (BM) strength at welding speeds within the range of 20–80 mm/min. The elongation of the welded specimen reaches 82% of the BM. The use of AA7075–O not only overcomes the softening issue in the agehardened AA7075 FSWed joints but also yields a higher elongation. Bending test results demonstrate that the FSWed joints of AA7075–O can withstand larger bending angles

with a maximum bending angle reaching 105°

indicating superior plastic deformation capabilities.