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Friction stir weld joints of 2024-T4 are strengthened by ultrasonic impact treatment (UIT). After ultrasonic impact treatment, the grains on the surface of the sample are refined to form a dense deformation layer, and residual compressive stress is applied on the surface of the sample. The corrosion rate and mass-loss rate of the UIT sample are significantly lower than those of the non-UIT sample, and uniform corrosion is exhibited. The average life of the UIT samples in the air is 1.74 times that of the non-UIT samples; meanwhile, the average life of the UIT samples in 3.5% NaCl solution is twice that of the non-UIT samples. The crack sources of the UIT sample in the air shift from the surface to the subsurface below the strengthening layer, whereas those of the sample in the 3.5% NaCl solution are located in the corroded area on the surface of the sample.

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Through investigating the effect of parameters on the fatigue properties and crack propagation behavior of friction stir crack repaired 2024 aluminum alloy, we demonstrated that the fatigue strength of friction stir repaired Al2024 was sensitive to the repairing parameters and had a “V” type discipline with the rotating speed or advancing velocity. The fatigue crack growth rates of the repaired specimens were higher than the base material counterpart, and the crack propagation mechanism in the repaired zone was mainly intergranular. When the improper repairing parameters were adopted, the delamination defect would form at the interfaces between the repaired layer and base material

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