*3.3. Residual Stress*

Residual stress curves of the top surface before and after DryLP treatment of the laser-welded specimens are shown in Figure 5a. The residual stress in the WM and HAZ areas of the as-welded specimen were tensile, while other areas had compressive stresses, which is a typical residual stress distribution for welded joints. This tensile residual surface stress in the WM and HAZ areas changed to compressive stress after DryLP treatment, while the magnitude of the compressive residual stresses outside these areas increased. The depth profiles of the residual stress in the WM, below the weld toe, and in the HAZ before and after DryLP treatment are shown in Figure 5b–d. The tensile residual stresses in the WM, below the weld toe, and in the HAZ were observed to a depth of ~300 μm from the weld center in the as-welded specimen. These tensile residual stresses inside the material between the surface and a depth of ~100 μm changed to compressive stresses after DryLP, which is comparable to the thickness of the compressive layer in the DryLPed BM [9].

**Figure 5.** (**a**) Residual stress distributions along the surface (up to 50-μm depth). Depth profiles of the residual stress in the (**b**) WM, (**c**) below the weld toe, and (**d**) in the HAZ of laser-welded specimens before and after DryLP.
