Wire Arc Additive Manufacturing using the Cold Metal Transfer process (WAAM-CMT) is a promising technique for producing medium- and large-scale stainless-steel components with high deposition efficiency and relatively low heat input. However, WAAM-fabricated 316L materials may still exhibit surface irregularities, thermal-cycle-induced microstructural heterogeneity, and anisotropic mechanical behavior. In this work, flat walls of 316L austenitic stainless steel were fabricated by WAAM-CMT. Tensile, microstructural, microhardness, SEM-based fractography and EDX analyses were conducted on specimens before and after shot peening. In the as-built condition, the bottom region showed the highest ultimate strength (UTS ≈ 480 MPa) but lower ductility (≈ 32%), while the middle and top exhibited lower strength (UTS ≈ 420 MPa) and higher elongation (≈ 40%). After shot peening, strength became more uniform across the wall (UTS ≈ 470–490 MPa) with reduced elongation (~ 25%). Microstructural observations revealed general grain refinement and surface strengthening, with ferrite and pearlite-like grains significantly refined at most positions. Microhardness increased in all regions due to plastic deformation, grain refinement, and compressive residual stresses introduced by shot peening. SEM fractography revealed ductile fracture behavior dominated by micro-void coalescence in both conditions. EDX analysis confirmed that shot peening did not significantly change the chemical composition of the WAAM-CMT 316L stainless steel. Overall, shot peening effectively enhanced surface hardness and strength uniformity in WAAM-CMT 316L stainless steel.

The effect of under water friction stir welding for 5 mm AA2017 aluminum alloy plaque on mechanical properties has been examined, nine different test were designed according to Taguchi orthogonal array (OA) without changing the welding tool. Three variable operating parameters (Welding velocity, rotational velocity and axial force) with three levels for each parameter have been used. The effects of each FSW parameters on the weld joint were discussed and analysed, the analysis of variance (ANOVA) is adopted to identify the contribution of each FSW underwater parameters. The statisticl Taguchi method (MT) was employed to pridect the optimal combination of welding parameters to improve the tensile properties such tensile strength (TS) of welded joints as retaining high production rates. The experimental tests show good agreement with the results estimated by the proposed mathematical model. Where the obtained validation results confirm the robustness of the optimization method as a tool for improving the quality responses of under water friction stir welding.