Effect of welding speed on microstructural evolution and strengthening mechanism of friction-stir welded 7075 aluminum

In present study, we aimed to analyze the microstructural characteristics and strengthening mechanism of AA7075-T6 alloy after the friction-stir welding speeds from 150 to 350 mm min⁻¹. The continuous dynamic recrystallization underwent actively with higher welding speed, leading to equiaxial and fine grains, as evidenced by misorientation distribution, grain orientation spread, and aspect ratio. Regarding the textural evolution of the stir zone, the weld at lower welding speed retained the deformation texture (e.g., Brass), while the higher welding speed showed the development of recrystallization texture (e.g., Goss). The weld at 250 mm min⁻¹ revealed superior weldability for strength of over ∼80 % owing to both grain refinement and accumulated dislocations despite the dissolution of precipitate such as ηˊ.