Influence of HFMI Treatment Quality on Fatigue Performance of Hybrid WAAM Stiffeners

Kurzfassung

High-frequency mechanical impact (HFMI) treatment can significantly improve the fatigue performance of welded joints, although its effectiveness depends strongly on local treatment quality. This study investigates hybrid WAAM stiffeners produced from G4Si1 wire on ASTM A36 base plates, with particular focus on sub-optimal HFMI treatment at the fatigue-critical base plate–stiffener interface. As-welded, robot-assisted HFMI, and manually treated conditions are compared. Despite substantial scatter associated with locally imperfect HFMI execution, the treated specimens showed marked improvements in fatigue strength, meeting or exceeding current IIW guidance. Structured-light profilometry, hardness mapping, microstructural analysis, and fracture surface microscopy are used to relate HFMI-induced surface features, work hardening, and local weld-toe conditions to fatigue performance. The results indicate that beneficial HFMI effects can persist despite sub-optimal treatment quality, while also highlighting the need for improved quantitative quality-control criteria for complex WAAM geometries.