Fig. 1. Square specimen. (a) Specimen size and schematic of laser peening; (b) morphology after laser peening

Fig. 2. Experimental setup of CLP

Fig. 3. Dimension and laser peening area of specimen used for tensile test at room temperature

Fig. 4. SEM images and metallographic diagrams on top surface of 2024-T351 aluminum alloy specimen at different stages. (a) Untreated SEM image; (b) SEM image after RT-LP; (c) SEM image after CLP; (d) untreated metallographic diagram; (e) metallographic diagram after RT-LP; (f) metallographic diagram after CLP

Fig. 5. EDS analysis results of second phase

Fig. 6. TEM images on top surface of 2024-T351 aluminum alloy specimen at different stages. (a)(d) Untreated; (b)(e) after RT-LP; (c)(f) after CLP

Fig. 7. TEM images of different layers of 2024-T351 aluminum alloy specimen after CLP. (a) Sub-grain;(b) sub-structure; (c) dislocation cell; (d) dislocation wall; (e) high-density dislocation

Fig. 8. Images of CLP strengthening. (a) Schematic of microstructure evolution of specimen after CLP; (b) dislocation initiation around second phase; (c) dislocation pinning subjected to second phase and dislocation tangle