Influence of interlayer cooling strategies and contact tip to work distance on layer geometry, microstructure, hardness, and corrosion properties of WAAM ER70S-6 steel

Abstract Additive manufacturing (AM) enables the fabrication of complex geometries with reduced material waste and increasing relevance for sustainable production. Among AM technologies, wire arc additive manufacturing (WAAM) has attracted growing industrial interest due to its high deposition rate, scalability, and comparatively low cost for large metallic components. Despite the widespread industrial maturity of arc welding processes, their application to layer-by-layer component fabrication introduces distinct thermal and metallurgical challenges. Consequently, a clear understanding of how process parameters influence part quality remains essential for optimising deposition strategies. This work investigates the influence of interlayer cooling strategies and contact tip to workpiece distance (CTWD) on ER70S-6 steel wall structures manufactured using a 1-mm diameter wire feedstock. Two dwell time strategies and one fixed interlayer temperature condition are examined, while CTWD variation is employed to indirectly modify the thermal conditions during deposition. The effects on microstructure, mechanical behaviour, corrosion performance, and layer geometry are analysed. The results demonstrate that longer interpass dwell times (lower interpass temperature) enhanced wall height and geometric stability by promoting more effective heat dissipation and stable thermal conditions (at the cost of productivity), whereas increasing CTWD reduced layer height and penetration due to lower effective heat input, with negligible effects on bead width. Moreover, microstructural, mechanical, and corrosion responses were primarily governed by layer-dependent thermal cycling, with longer dwell times producing finer grains, higher hardness, and more active and poor corrosion behaviour, while CTWD variations within industrially realistic ranges had a secondary influence.