Arc mode selection for improved structural and tribological performance of wire arc additive manufactured low carbon steel walls

In this study, the mechanical and tribological behavior of ER70S-6 low-carbon structural steel multi-layer wall structures fabricated using two GMAW (gas metal arc welding)-WAAM (wire arc additive manufacturing) arc transfer modes, Control Weld (high-capacity spray transfer) and Speed Weld (voltage-controlled pulsed transfer), is investigated. Walls are fabricated using a CLOOS GMAW-WAAM system, and their properties are systematically evaluated through hardness, tensile, and Charpy impact toughness testing, complemented by microstructural characterization, X-ray diffraction (XRD), fractography, and wear analysis. Results show that Speed Weld produces finer, more equiaxed grains (11.80 µm) than Control Weld (13.75 µm), indicating 14% refinement and a more uniform phase distribution. Both modes predominantly exhibit α-ferrite; however, Speed Weld specimens show slightly broadened and less intense XRD peaks, higher average hardness (170.98 HV₅ vs. 165.52 HV₅) consistently along the build height, modestly improved tensile strength (509.33 MPa vs. 492.73 MPa), 11% greater uniform elongation, and over 8% higher impact energy. Fractography confirms ductile fracture in both conditions, with finer, more uniformly distributed dimples in the Speed Weld specimens. Additionally, Speed Weld specimens demonstrate superior tribological performance, reducing wear volume by 21.6% and wear rate by 21.5% compared to Control Weld specimens. These findings demonstrate that Speed Weld in GMAW-WAAM refines the microstructure while simultaneously enhancing mechanical and tribological properties, enabling more reliable, durable, and wear-resistant low-carbon steel components for structural and industrial applications.