Friction Stir Welding（FSW） of 2024 aluminum alloy is carried out by selecting the optimized welding parameters. According to the microstructures and morphologies of the joints

the welded joints are divided into different regions

and the residual stresses in different parts of the joints are measured by the small hole method. MT type crack growth test specimens are selected to conduct crack growth tests at different parts of friction stir welded joints. The effects of residual stress on crack growth are studied by comparing crack growth rate between different regions and between welding state and rolling state. The experimental results show that the residual stress of friction stir welding is tensile stress

which promotes crack opening and propagation. In the crack growth test

the residual stress gradually releases with the crack growth

and the crack growth rate in the welded state is close to that in the rolling state. Rolling can eliminate the residual stress and make the residual stress in each area of welded joint tend to be the same

and the crack growth rate also tend to be the same.